the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Feb 2025
Current-use and organochlorine pesticides' multi-annual trends in air in Central Europe: primary and unidentified secondary sources
Abstract. This study investigated 48 current-use pesticides (CUPs) and 30 organochlorine pesticides (OCPs) in ambient air at a rural-agricultural site in the Czech Republic, with biweekly sampling over three and 10 years, respectively. Despite being banned decades ago, OCPs persist in the atmosphere, with revolatilisation from soils apparent in summer. Temporal trend analysis revealed decreasing atmospheric concentrations for several OCPs, which indicate diminishing reservoirs in environmental compartments especially soil over the years. For β- and γ-HCH, o,p’- and p,p’-DDE, o,p’-DDD, o,p’- and p,p’-DDT, α-chlordane, and mirex levelling off is observed, which points to recently enhanced secondary sources in the region or beyond i.e., reversal of the direction of air-surface exchange or recent mobilisation from soils, water bodies, or the cryosphere. CUP concentrations peaked during application seasons, with multi-annual trends either insignificant or declining. For compounds like chlorpyrifos and fenpropimorph, declining trends aligned with regulatory bans, though their presence in the atmosphere was evident one-year post-ban, suggesting persistence.
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RC1: 'Comment on egusphere-2025-349', Anonymous Referee #1, 15 Mar 2025
Overall:
This manuscript reported multi-annual observations of CUPs and OCPs from a monitoring site in Czech Republic. Active air samples have been collected biweekly over 3 years (CUPs) and 10 years (OCPs) and temporal trends were analyzed. From the results, potential sources for the atmospheric presence of pesticides were indicated. Both OCPs and CUPs showed declining trends. The OCPs showed less decrease in the sampling period compared to the CUPs. Rcently banned CUPs showed the lowest half-lifes reflecting the immediate effects of legislation, but their presence may imply that they are persistent. While there are indications that the levels of OCPs are affected by secondary sources, CUP concentrations seem to correlate with application seasons.
Overall, this manuscript presents novel and important results, which has been sufficiently documented. The manuscript includes a great deal of information, and additional information is recorded in the SI. The approach and data help to advance the field of science. I would therefore suggest it can be accepted after some revision. In addition to the comments below, some parts need rephrasing/elaboration which is commented directly in the attached pdf of the preprint.
Specific comments:
Section 1 Introduction:
- The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
- Line 40: Levelling off air concentrations over time may imply that secondary sources are likely to influence to a larger extent, but how can conclusions regarding sources be made from time-trends by itself? I think this statement needs some moderation /elaboration or a reference.
Section 2 Methods:
For the OCPs, there were pointed at some methodological differences between the dataset in terms of recovery corrections. This gives rise to two different time trend curves. The half lifes for the two periods were then compared. This seems to be a reasonable way to account for the differences. The analytical methods are well-described with satisfactory measures to assure high quality of the data, but I have a few comments:
- The QFF and PUF/XAD samples have been analyzed separately, but the total concentration is used in further assessments. It should therefore be described how the results were combined. Furthermore, the recoveries given in SI (Table S7) should not only be indicated separately for QFF and PUF/XAD, but also for the two combined.
- For the OCPs, it seems like only 7 out of 30 have internal standards. This may give rise to higher uncertainty in data for the other OCPs and should be specified.
- Under section 2.5 it is not clear if the recoveries given account for both OCPs and CUPs, and for all samples/time periods, incl. 2013-2017. A reference to Table S7 is also missing. Furthermore, it is not clear if internal standards for all OCPs were introduced in 2018 (line 115). This part could be elaborated.
- Under 2.6 the term “timing” is not clear and a further explanation is needed.
Section 3 Results:
- Line 190-195: Why is 100 pg/m3 used as a limit for CUPs? For both CUPs and OCPs, it should be stated explicitly which compounds that were found in highest concentrations and their concentrations should be specified, e.g. the CUPs Metolachlor, Chlorpyrifos and Pendimethalin, and the OCPs HCB, ppDDE and gHCH. Methoxychlor should also be mentioned. It should explicitly be specified that the concentrations of OCPs are significantly lower than CUPs.
- For both OCPs and CUPs the comparison with other studies should be elaborated, i.e. how do the results align with previous findings, e.g passive air studies? Also, a reference to Table S9 and compliance with usage should be included.
- Line 200-205: The interpretation of DDT ratios is unprecise. Low ppDDT compared to ppDDE/ppDDD is due to degradation of DDT to DDE and indicate possible shift from primary to secondary sources, i.e past usage of technical DDT mixture. Pozo et al (2006) Environ. Sci. Technol. 2006, 40, 4867-4873 should be referenced. Also, the interpretation of HCH ratios should be elaborated. Note that Lindane contains >99% y-HCH (ref. Y.F. Li, R.W. Macdonald / Science of the Total Environment 342 (2005) 87–106). Furthermore, source indications of both DDTs and HCHs should be compared with other studies in Europe assessing sources (e.g Lunder Halvorsen et al 2023, PAS Europe 2016).
- Figure 1: The X-axis with months is not very consistent and it should be easier to see where the application/spring seasons are. Metolachlor and Chlorpyrifos should also be shown or mentioned in section 3.3 given their high concentrations.
- Temperature dependence (line 230): An overview of temperature during the sampling period is missing and should be included e.g. in Figure S6. How is the temperature dependence and can a peak be expected from volatilisation by itself?
- For the OCPs, the Clausius-Clapeyron equation is used to look into re-volatilisation. However, it is not clear to me how good correlation between partial pressure and the inverse ambient temperature implies that air concentrations and temperature are correlated, and this should therefore be elaborated. Correlation between air concentrations and temperature may be more intuitive and align better with Figure S6. In that case, R2 and p-values should be added to the figure.
- Line 270: How do the results of this study imply that the atmospheric concentrations of banned CUPs are dominated by resuspension and LRAT? This claim needs further explanation.
- Section 3.5: I question the assessment of time trends for OCPs/CUPs down to 20% detection frequency, as it is a possibility for bias due to MDLs. I would therefore suggest to use 80% as cut-off instead.
- The discussion of time trends for CUPs should highlight Chlorpyrifos given the decline in usage (Table S9) and high concentrations. The comparison with Fenpropiomorph (line 290) is interesting, given that the use of Chlorpyrifos has been more drastically reduced, while the half-life for Fenpropiomorph is lower. Time trends for Metolachlor and Pendimethalin should also be considered given their dominance in the atmosphere.
- Figure 2: Not easy to see purple line for the OCPs and I therefore suggest to change to a darker color.
- Line 300: The steepest slope is found for a-Endosulfan in accordance with regulation from 2013. Data for b-Endosulfan could have given valuable information regarding past/present usage. However, the number of compounds in the study is already extensive and it is understandable that not all isomers can be included in the instrumental analysis.
- Line 315: Time trends are compared with data extracted from EBAS, but it should be specified in SI how these trends have been developed. Also, HCB trends are specifically mentioned in EMEP status report 2/2022, which should be referenced.
- Line 300: Time trends of 12 OCPs indicate that the concentrations are levelling off, but to a less extent compared to the CUPs (i.e. higher half-life). This should be highlighted.
Section 4 Conclusion:
- While Kosetice is a regional background site, it is pointed out in section 2.2 that local sources exist for pesticides. Generalization and the impact of this study should therefore be moderated, given that these data are based on one rural site only and variations may exist within central Europe.
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AC1: 'Reply on RC1', Ludovic Mayer, 01 Apr 2025
We would like to thank the reviewers for the thoughtful reading and comments, which helped to improve this manuscript. We have addressed all comments below and have indicated the corresponding modifications to the manuscript.
Anonymous referee 1:
Overall:
This manuscript reported multi-annual observations of CUPs and OCPs from a monitoring site in Czech Republic. Active air samples have been collected biweekly over 3 years (CUPs) and 10 years (OCPs) and temporal trends were analysed. From the results, potential sources for the atmospheric presence of pesticides were indicated. Both OCPs and CUPs showed declining trends. The OCPs showed less decrease in the sampling period compared to the CUPs. Recently banned CUPs showed the lowest half-lives reflecting the immediate effects of legislation, but their presence may imply that they are persistent. While there are indications that the levels of OCPs are affected by secondary sources, CUP concentrations seem to correlate with application seasons.
Overall, this manuscript presents novel and important results, which has been sufficiently documented. The manuscript includes a great deal of information, and additional information is recorded in the SI. The approach and data help to advance the field of science. I would therefore suggest it can be accepted after some revision. In addition to the comments below, some parts need rephrasing/elaboration which is commented directly in the attached pdf of the preprint.
Specific comments:
Section 1 Introduction:
- 1. The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
Thank you for your comment. To clarify the reference, we will update the reference list to refer to the proper reference of the Stockholm Convention official website.
- 2. Line 40: Levelling off air concentrations over time may imply that secondary sources are likely to influence to a larger extent, but how can conclusions regarding sources be made from time-trends by itself? I think this statement needs some moderation /elaboration or a reference.
Thank you for your comment. The statement should have been more specific in mentioning that we consider seasonal patterns, and specifically the relationship between temperature peaks and pesticide concentration peaks to be an indication of either fresh application (primary sources) or revolatilization (secondary sources). So, to ensure that this idea is also expressed in the introduction, we will modify the sentence, to read as (lines 40-42):
“For both banned and authorised chemicals, it is generally possible to observe and distinguish between primary (e.g., application for pesticides) and secondary sources (e.g., re-volatilisation) by examining the seasonal variations of temperature, application and concentrations in air (Hoff et al., 1998; van den Berg et al., 1999).”
Section 2 Methods:
For the OCPs, there were pointed at some methodological differences between the dataset in terms of recovery corrections. This gives rise to two different time trend curves. The half lifes for the two periods were then compared. This seems to be a reasonable way to account for the differences. The analytical methods are well-described with satisfactory measures to assure high quality of the data, but I have a few comments:
- 3. The QFF and PUF/XAD samples have been analyzed separately, but the total concentration is used in further assessments. It should therefore be described how the results were combined. Furthermore, the recoveries given in SI (Table S7) should not only be indicated separately for QFF and PUF/XAD, but also for the two combined.
Thank you for your comment. To provide more clarity, we expanded the sentence (line 121), to describe how the results were combined. As QFF and PUF/XAD were extracted separately, no recoveries for QFF and PUF/XAD together were determined. An effective recovery could be derived based on the phase mass-weighted mean of the recoveries of the particulate (QFF) and gas (PUF/XAD) phases. The revised sentence will read (lines 121-123, in section 2.6):
“As relaxation to phase equilibrium is fast on the time scale addressed (weeks), and even so both phases were analysed separately, the data analysed was the total concentration i.e., sum of particulate and gaseous concentrations.”
- 4. For the OCPs, it seems like only 7 out of 30 have internal standards. This may give rise to higher uncertainty in data for the other OCPs and should be specified.
Thank you for your comment. It is true that we do not have C13-labelled structural analogues for all OCPs, but in most cases this should lead to limited uncertainty because the internal standard is an isomeric or structurally similar compound, e.g., γ-HCH is used as internal standard for 5 HCH isomers (Table S5). In the cases of the chlorobenzenes, HCHs and DDT compounds, we do not expect the internal standard to introduce uncertainty. However, the reviewer is correct in the case of the second set of pesticides (heptachlors, chlordanes, endosulfans, and drin pesticides); in this case 13C-α-endosulfan was used as an internal standard except for β-endosulfan, for which 13C β-endosulfan was used as internal standard. This may introduce additional uncertainty for a subset of these OCPs. We will add a sentence about uncertainties in the SI when different methods are described (SI, lines 61-64):
“As isotopically labelled internal standards were not available for all 17 additional OCPs analysed, 13C-α-endosulfan was used as an internal standard for all compounds (Table S5a and S5b; except for β-endosulfan for which 13C β-endosulfan was used), which may lead to additional uncertainties in expressed concentrations, which are expected to be minor.”
- 5. Under section 2.5 it is not clear if the recoveries given account for both OCPs and CUPs, and for all samples/time periods, incl. 2013-2017. A reference to Table S7 is also missing. Furthermore, it is not clear if internal standards for all OCPs were introduced in 2018 (line 115). This part could be elaborated.
Thank for pointing this out, we will add the reference to table S7 (line 114), as well as extra information to the sentence to fill this gap, to read (lines 111-114):
“For the 48 CUPs analysed using the HPLC-MS/MS, the method recoveries of individual analytes ranged from (68 ± 14)% (carbaryl) to (153 ± 22)% (iprovalicarb) for QFFs and from (61 ± 3)% (kresoxim-methyl) to (132 ± 10)% (iprovalicarb) for sandwiches (Table S7a), while for OCPs, recoveries ranged from (47 ± 8)% (PeCB) to (100 ± 9)% (p,p’-DDD) for QFFs and from (49 ± 6)% (PeCB) to (103 ± 10)% (p,p’-DDD) for all the samples from 2013 to 2022 (Table S7b).”
- 6. Under 2.6 the term “timing” is not clear and a further explanation is needed.
Thank you for comment. In order to clarify the sentence, we will remove the words “timing” and replace them with the more appropriate and precise terms “periodicity” and “period of application” (lines 135 and 139).
Section 3 Results:
- 7. Line 190-195: Why is 100 pg/m3 used as a limit for CUPs? For both CUPs and OCPs, it should be stated explicitly which compounds that were found in highest concentrations and their concentrations should be specified, e.g. the CUPs Metolachlor, Chlorpyrifos and Pendimethalin, and the OCPs HCB, ppDDE and gHCH. Methoxychlor should also be mentioned. It should explicitly be specified that the concentrations of OCPs are significantly lower than CUPs.
Thank you for the comment. We have added the additional information asked for CUPs, as well as explained why 100 pg m-3 matter in the context of our study in relation to the previous one done at this site. Will read (line 192-197):
“Previous observation at this site during the 2012-2013 period, showcased the observation of chlorpyrifos, metazachlor and s-metolachlor, in addition to acetochlor and isoproturon in concentration surpassing 100 pg m-3 (Degrendele et al., 2016). In this study, chlorpyrifos, s-metolachlor, and prosulfocarb were found most abundant (average concentrations of 116, 115, and 79.7 pg m-3, respectively; Table S10a). Similarly, high concentrations of these compounds had previously been reported from rural environments (Debler et al., 2024; Habran et al., 2024; Mayer et al., 2024; Ni et al., 2024).”
Similarly, the suggested statement comparing OCPs and CUPs concentration has been added. As well as, a clear statement about HCB, p,p’-DDE and γ-HCH being the OCPs found in the highest atmospheric concentrations (line 197-200):
“Overall, concentration of OCPs were found to be significantly lower than CUP concentrations. The average weekly concentration of Σ30OCPs was 44.3 pg m-3, with HCB, p,p’-DDE and γ-HCH accounting on average for 38, 29 and 8.1% of Σ30OCPs and found at highest concentrations (Figure 1c,d and Table S10).”
- 8. For both OCPs and CUPs the comparison with other studies should be elaborated, i.e. how do the results align with previous findings, e.g passive air studies? Also, a reference to Table S9 and compliance with usage should be included.
Thank you for your question. We believe the discussion covered other studies for CUPs completely in the original manuscript (lines 192-197), but indeed not so for OCPs (as there were way more). So, we will add references to recent OCPs studies where similar results were observed (lines 200-204), will read:
“These three OCPs have also been previously observed as the dominant atmospheric OCPs (Gevao et al., 2018; Wang et al., 2018; Wong et al., 2021; Mamontova et al., 2022; Khuman et al., 2023; Lunder-Halvorsen et al. 2023).”
Additional references:
Gevao, B., Porcelli, M., Rajagopalan, S., Krishnan, D., Martinez-Guijarro, K., Alshemmari, H., Bahloul, M., and Zafar, J.: Spatial and temporal variations in the atmospheric concentrations of “Stockholm Convention” organochlorine pesticides in Kuwait, Sci. Total Environ., 622–623, 1621–1629, 2018.
Khuman, S. N., Park, M. K., Kim, H. J., Hwang, S. M., Lee, C. H., and Choi, S. D.: Nationwide assessment of atmospheric organochlorine pesticides over a decade during 2008–2017 in South Korea, Sci. Total Environ., 877, 162927, 2023.
Lunder Halvorsen, H., Bohlin-Nizzetto, P., Eckhardt, S., Gusev, A., Moeckel, C., Shatalov, V., Skogeng, L. P., and Breivik, K.: Spatial variability and temporal changes of POPs in European background air, Atmos. Environ., 299, 2023.
Mamontova, E. A. and Mamontov, A. A.: Air monitoring of polychlorinated biphenyls and organochlorine pesticides in Eastern Siberia: Levels, temporal trends, and risk assessment, Atmosphere (Basel), 13, 1971, 2022.
Wang, C., Wang, X., Gong, P., and Yao, T.: Long-term trends of atmospheric organochlorine pollutants and polycyclic aromatic hydrocarbons over the southeastern Tibetan Plateau, Sci. Total Environ., 624, 241–249, 2018.
Wong, F., Hung, H., Dryfhout-Clark, H., Aas, W., Bohlin-Nizzetto, P., Breivik, K., Mastromonaco, M. N., Lundén, E. B., Ólafsdóttir, K., Sigurðsson, Á., Vorkamp, K., Bossi, R., Skov, H., Hakola, H., Barresi, E., Sverko, E., Fellin, P., Li, H., Vlasenko, A., Zapevalov, M., Samsonov, D., and Wilson, S.: Time trends of persistent organic pollutants (POPs) and chemicals of emerging Arctic concern (CEAC) in Arctic air from 25 years of monitoring, Sci. Total Environ., 775, 145109, 2021.
Comparison to passive sampler studies are discussed in relation to multi-annual variation in the corresponding. For concentrations however, only comparison to studies done with active samplers were discussed due to the uncertainties associated with recalculation of concentration from passive sampling. A reference to Table S9 will be added to section 3.2 to discuss high atmospheric concentration and national usage, will read: (lines 199-203):
“As mentioned previously, some of those compounds (i.e., chlorpyrifos, metazachlor, pendimethalin, spiroxamine, tebuconazole and terbuthylazine) were applied on the Czech territory in more than 50 t of active substance per year, which would influence their high atmospheric concentration, notably during application periods (Table S9).”
- 9. Line 200-205: The interpretation of DDT ratios is unprecise. Low ppDDT compared to ppDDE/ppDDD is due to degradation of DDT to DDE and indicate possible shift from primary to secondary sources, i.e past usage of technical DDT mixture. Pozo et al (2006) Environ. Sci. Technol. 2006, 40, 4867-4873 should be referenced. Also, the interpretation of HCH ratios should be elaborated. Note that Lindane contains >99% y-HCH (ref. Y.F. Li, R.W. Macdonald / Science of the Total Environment 342 (2005) 87–106). Furthermore, source indications of both DDTs and HCHs should be compared with other studies in Europe assessing sources (e.g Lunder Halvorsen et al 2023, PAS Europe 2016).
Thank you for the suggestion, we believe this idea was already expressed in the original manuscript. The indicator ppDDT/(pDDE+ppDDD), to our knowledge, was first used by Rapaport et al., 1985, and we will therefore add a reference to a review, Bidleman 1999, at the end of our original statement. In addition, the information regarding lindane and corresponding reference will be added (lines 207-208) and will read:
“Additionally, the ratio β-HCH/(α-HCH+γ-HCH) can be used to distinguish between technical HCH and lindane, generally composed of >99% of γ-HCH (Li and Macdonald, 2005), as …”
In addition, source indication of HCHs were elaborated upon based on the suggested references (lines 211-216), will read:
“Similarly, the ratio α-HCH/γ-HCH has been previously used to infer sources of HCHs. A recent study in Europe highlighted a distinction between the northern and southern regions: in the north, high α-HCH/γ-HCH values were observed, indicating the dominance of long-range atmospheric transport and re-suspension of α-HCH, whereas in the south, lower α-HCH/γ-HCH values suggested historical use of γ-HCH (lindane; Lunder-Halvorsen et al., 2023). In our study, the ratio α-HCH/γ-HCH ranged from 0.12 to 1.7, aligning with values reported in southern Europe.”
Additional references:
Bidleman, T. F.: Atmospheric transport and air-surface exchange of pesticides, in: Fate of Pesticides in the Atmosphere: Implications for Environmental Risk Assessment (van Dijk, H. F. G., van Pul, W. A. J., and de Voogt, P., eds.), Springer, Dordrecht, Netherlands, pp. 115–166, 1999.
Li, Y. F. and Macdonald, R. W.: Sources and pathways of selected organochlorine pesticides to the Arctic and the effect of pathway divergence on HCH trends in biota: a review, Sci. Total Environ. 342, 87-106, 2005.
- 10. Figure 1: The X-axis with months is not very consistent and it should be easier to see where the application/spring seasons are. Metolachlor and Chlorpyrifos should also be shown or mentioned in section 3.3 given their high concentrations.
Thank you for your suggestion. We will update the X-axis for Figure 1 to keep a consistent base for the month for CUPs and for OCPs. High concentrations of chlorpyrifos and s-metolachlor have been mentioned and discussed in section 3.2 total concentration, while seasonal variation and application period are discussed in section 3.3, where s-metolachlor, although not mentioned by name specifically, is part of the 16 compounds with peak application in spring (Table S12).
- 11. Temperature dependence (line 230): An overview of temperature during the sampling period is missing and should be included e.g. in Figure S6. How is the temperature dependence and can a peak be expected from volatilisation by itself?
Thank you for your suggestion, we will add a sentence at the beginning of section “3.4 Influence of temperature on pesticide revolatilisation” reading (lines 246-247):
“For the 2013-2022 OCPs collection period, the temperature ranged from -9.5 to 23.7 °C while for the 2019-2021 CUPs collection period, it ranged from -5.8 to 22.1°C.”
The conclusion regarding the temperature dependence and whether a peak can be expected from volatilisation alone is discussed and answered in section “3.4 Influence of temperature on pesticide revolatilisation”, as mentioned in lines 268-271 of the version published as preprint.
“For OCPs, temperature dependent volatilisation is the main influence on OCP atmospheric concentration. For authorised CUPs, atmospheric concentrations were mainly influenced by application, while temperature-dependent resuspension and LRAT determined CUPs atmospheric levels for banned compounds.”
This statement follows the discussion of the results from examining the Clausius-Clapeyron equation for OCPs and CUPs. It, indeed, concludes that atmospheric concentration for OCPs and some CUPs are temperature-dependent, and a seasonal peak can be due to elevated temperature, especially for OCPs.
- 12. For the OCPs, the Clausius-Clapeyron equation is used to look into re-volatilisation. However, it is not clear to me how good correlation between partial pressure and the inverse ambient temperature implies that air concentrations and temperature are correlated, and this should therefore be elaborated. Correlation between air concentrations and temperature may be more intuitive and align better with Figure S6. In that case, R2 and p-values should be added to the figure.
Thank you for the suggestion, we will add the R² and p-value from Spearman correlation to selected chemicals presented in Figure S6, and update the figure caption, to show the relationship between atmospheric concentration and temperature.
- 13. Line 270: How do the results of this study imply that the atmospheric concentrations of banned CUPs are dominated by resuspension and LRAT? This claim needs further explanation.
Thank you for your comment and question. Since for the Czech Republic, information about the amount of active substances applied yearly is available, it is possible to specify whether the level encountered in the atmosphere is due to primary emissions only. For banned pesticides, obviously this is not the case: Therefore, OCP levels encountered are due to resuspension from other media (e.g., soil) or long-range atmospheric transport and individual compound persistence. Whereas for authorized CUPs, levels are generally more influenced by seasonal applications. This is explicitly described in the version of the manuscript published as preprint (lines 268-270).
- 14. Section 3.5: I question the assessment of time trends for OCPs/CUPs down to 20% detection frequency, as it is a possibility for bias due to MDLs. I would therefore suggest to use 80% as cut-off instead.
Thank you for the comment and suggestion. We agree that 20% is a relatively low detection frequency threshold, but we have specifically selected this as relevant for pesticides, given their strong seasonality. Many pesticides are detected only in summer and/or around time of application and applying a threshold such as 80% would lead to the exclusion of substantial amounts of valuable data.
- 15. The discussion of time trends for CUPs should highlight Chlorpyrifos given the decline in usage (Table S9) and high concentrations. The comparison with Fenpropimorph (line 290) is interesting, given that the use of Chlorpyrifos has been more drastically reduced, while the half-life for Fenpropimorph is lower. Time trends for Metolachlor and Pendimethalin should also be considered given their dominance in the atmosphere.
Thank you for your suggestion, we will replace terbuthylazine by s-metolachlor in Figure 2 showcasing the significantly decreasing trends for selected CUPs. As pendimethalin trend was not significant, it has not been included in figure 2. However, results for all CUPs trends are presented in Tables S14 and S15.
- 16. Figure 2: Not easy to see purple line for the OCPs and I therefore suggest to change to a darker color.
Thank you for your suggestion, we will update the figure and caption accordingly. We decided to go with a brighter color (red) which adds to trend visibility.
- 17. Line 300: The steepest slope is found for a-Endosulfan in accordance with regulation from 2013. Data for b-Endosulfan could have given valuable information regarding past/present usage. However, the number of compounds in the study is already extensive and it is understandable that not all isomers can be included in the instrumental analysis.
Thank you for your comment. Indeed, it would have brought forth valuable information. β-endosulfan was included in the instrumental analysis, but only found in 6.3 % of the samples (Table S8), which we judge inconclusive with regard to time trends.
- 18. Line 315: Time trends are compared with data extracted from EBAS, but it should be specified in SI how these trends have been developed. Also, HCB trends are specifically mentioned in EMEP status report 2/2022, which should be referenced.
Thank you for the suggestion, we will add a reference to the EMEP status report 2/2022. The reference to the EBAS database will be dropped, as the data available on that website is the same as the one used in references already made (i.e., Ilyin et al., 2022; Lunder-Halvorsen et al., 2023; UNEP 2023).
- 19. Line 300: Time trends of 12 OCPs indicate that the concentrations are levelling off, but to a less extent compared to the CUPs (i.e. higher half-life). This should be highlighted.
Thank you for the suggestion, an additional sentence will be added (line 309-311):
“Compared to CUPs with insignificant trends, these 12 OCPs were levelling off on a slower time scale (i.e., higher half-life than for CUPs), highlighting the persistence of these compounds.”
Section 4 Conclusion:
- 20. While Kosetice is a regional background site, it is pointed out in section 2.2 that local sources exist for pesticides. Generalization and the impact of this study should therefore be moderated, given that these data are based on one rural site only and variations may exist within central Europe.
Thank you for your comment, indeed, NAOK is considered a regional background site in the context of air quality studies and research, which includes also some organic pollutants such as PAHs, but, as mentioned in section 2.2, NAOK is not (and never was) a background site in the context of pesticides studies and research. This article aims to bring forth data and interpretation of a time series of atmospheric CUPs from a site located in a source area. To make sure that we are showcasing the results from one central European agricultural site only, we will add a corresponding statement (line 344-346), which will read:
“As this study focuses on a single agricultural site, the findings cannot capture the variability across the entire CUP source area i.e., rural central Europe. However, the observations were consistent…”
Citation: https://doi.org/10.5194/egusphere-2025-349-AC1 - 1. The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
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RC2: 'Comment on egusphere-2025-349', Anonymous Referee #2, 05 Jun 2025
Overall comments
This study presents seasonal and multi-annual trends of organic pesticides at a rural agricultural site in Central Europe and investigates their primary and secondary sources. Over ten years of weekly air monitoring for a wide range of pesticides (48 CUPs and 30 OCPs) has produced a large dataset that enables a comprehensive assessment of atmospheric pesticide contamination in Central Europe and allows for the determination of seasonal and temporal trends with high confidence. The statistical analyses appear sound, and the resulting trends generally align with known usage patterns, regulatory restrictions, and dominant release pathways. However, some statements should be clarified, and the language could be improved for better readability. Detailed comments are provided below.
Detailed comments
The application of two separate equations for OCPs and CUPs is scientifically reasonable, but the manuscript would benefit from a clearer justification of why different models were chosen, especially for readers less familiar with OCP or CUP-specific seasonality patterns.
The authors employed HPLC, GC, and tandem mass spectrometry (MS/MS) to analyze the collected samples and identify OCPs and CUPs. However, both OCPs and CUPs can naturally degrade or transform under specific environmental conditions, potentially forming structurally similar degradation products. Therefore, the authors should discuss how they distinguish between parent compounds and their degradation/metabolic products. Is it possible that the parent compounds could be potentially interfered by their degradation/metabolic products during the analysis?
Title: I am not entirely sure if the modifier “unidentified” is necessary. I think the secondary sources primarily refer to volatilization from land and water surfaces; The “current-use and organochlorine pesticides” can be refined as “legacy and current-use pesticides”.
Consider a refined title of something like “Multi-annual trends of legacy and current-use pesticides in air in Central Europe: primary and secondary sources. “
Line 12, “with revolatilisation from soil apparent in summer.” For OCPs, they can not only be volatilized from soil but also from water bodies, in come cases, e.g. HCH, volatilization from water is more pronounced compared to direct volatilization from soil. (https://doi.org/10.1021/acs.est.4c05204; https://doi.org/10.1021/es034998k)
Line 16: “reversal of the direction of air-surface exchange or recent mobilisation from soils, water bodies, or the cryosphere” this is sentence is not clear. Reversal from what to what? Convert the direction from surface volatilization to atmospheric deposition? This statement repeatedly occurs in the manuscript that need to be well clarified. In addition, mobilisation from soil, water bodies, or the cryosphere share the same mechanism as air-surface exchange when regarding the emission to the atmosphere. Therefore, this sentence can be refined.
Line 22, rather than semivolatility, long-range transport ability is more precise accounting for the global cycling.
Section 2.4: To prevent potential breakthrough, PUF/XAD2/PUF sandwich was used for sampling gas-phase CUPs, while only two PUF plugs were used for sampling gaseous OCPs. Why did the author not apply PUF/XAD2/PUF sandwich to OCP sampling? Can the author assure that there is no breakthrough issue for hi-vol sampling of OCPs without XAD? If not, a limitation on this point should be included in the context.
Line 91-92, “100 μL of MilliQ water were then added to a 100μL aliquot of the respective extracts which were finally used for analysis.” This sentence is not clear. 100μL water was added to both OCP extracts and CUP extracts? Since n-nonane was previously added in the extracts, water and nonane are immiscible and extracts for OCPs analysis using GC-MS/MS should not contain any water. Please explain this.
Line 95, four different methods were used for CUP analysis. Why did not author combine these methods into one or two since they all are based on LC-MS/MS analysis?
Line 108-114, for the recoveries, were they calculated based on spiked native standards or isotopic standards? If based on the former, a series of recovery tests are required. Then, how many replicates were conducted? Otherwise, recoveries can be calculated for each real sample based on their ratio of labelled spike standards (surrogates) to the injection standards in samples relative to those in the calibration standards. Please clarify.
Line 115, “so was the internal standards for OCPs only.” does it mean that internal standards were changed as well” what dose the “only” refer to?
Line 147, what are the Non-parametric Mann-Whitney tests used for? Test for difference with previous measurements?
Line 160, I believe the Clausius-Clapeyron equation works for gaseous phase only. Please include a reference to support your statement of using total concentrations is more appropriate.
Line 201-202: Can you explain why the low and decreasing (o,p’-/(o,p’-+p,p’-) ratios ratio indicates that dicofol was not apparently a viable source for presence of DDT in the atmosphere. To make it understandable, additional information on dicofol and its relationship with DDT and DDT should be included in the context.
Line 207-208, please indicate how to use the ratio β-/(α-+γ-) HCH to distinguish between HCH isomers, and include a reference for it.
Line 228, how was application of pendimethalin in winter observed? In what cases people apply the pesticide in winter? It’s rare to apply pesticides in winter. In fact, it contradicts with the statements in lines 232-233.
Line 240-241: Were the maxima referred to the pre-ban period? If so, the maxima should be higher during the same period in the following years if the legislation works out.
Line 245 255: how did author determine whether the slope is steep or not? One approach is to use the slope of Clausius-Clapeyron plot can derive ΔHexp, and then the ΔHexp can be compared with theoretical ΔH, if derive ΔHexp is close to theoretical ΔH, we assume that local volatilization is dominant. If ΔHexp is much small than theoretical ΔH (shallow slope), the long-range transport is dominant (DOI:10.1016/j.ese.2022.100209; DOI: 10.1126/sciadv.adi808 ).
Line 255-258, how can the “narrow” or “wide” spread be linked to the sources, e.g., soil temperature or secondary sources” Please elaborate.
Line 266-267, a CUP metazachlor, peaked at summer, how can it be distinguished between application in summer and re-volatilization during the warmest period (summer)?
Line 300-301: is there a reason why pp-DDD increased during 2013-2017 while decreased during 2018-2022? Has a similar shift of the trend been reported?
Line 309-310: why this shift of ratio does not indicate any influence of fresh inputs of the pesticide? Because the ratios are both below 1?
Line 314-316, Industrial emissions could be more pronounced compared to the role of being a pesticide for HCB and PeCB. This point can be involved in the discussion in the context rather than being included at the end.
Line 331-332, could consider additionally include the evidence of net HCH volatilization from water to the atmosphere (https://doi.org/10.1021/acs.est.4c05204; https://doi.org/10.1021/es034998k).
Line 339-342: Despite that gas-particle partition calculation is not available, separate temporal trend analysis for gas- and particle phases is possible. Is there any difference between the two trends as well as compared with the trend for the total concentrations? It would be worthwhile to bring up this point or a short discussion.
Line 349, if the case for δ- and ε-HCH is the same, why was it separately mentioned rather than being included with other OCPs.
Small things:
Line 15, a comma should be inserted between “mirex” and “levelling off”.
Line 19 For clarity, consider changing “one-year post-ban” to “ one year after the bans”
Line 22-24, consider splitting into two sentences for clarity, rephrase like “Due to their severe health and environmental impacts, OCPs have been restricted in most countries (UNEP, 2001). For compounds like DDT and HCH, this has been consistently reflected in declining air concentrations.”
Line 32, and line 33: inserting a comma between “(CUPs)” and “have”, between “neonicotinoids” and “are”, could make the sentence clearer.
Line 33-34: consider rephrasing the sentence as “are chemically varied and subject to different environmental fates accordingly”
Line 36-39, consider splitting sentence into two for clarity. Something like “CUPs can enter the atmosphere during application, where up to 90% of the mass applied can be released
directly into the atmosphere (van den Berg et al., 1999). CUPs can be volatilised from surfaces such as soil, plants and surface water over longer periods of time following application (Bedos et al., 2002), and mobilised through wind erosion of soil particles containing CUPs “
Line 44: “ from a few European countries”
Line 46, “have become “
Line 50-53: consider rephrasing the sentence as: “In this study, biweekly samples of OCPs and CUPs were collected in both the gas and particulate phases at a rural site in an agricultural region of Central Europe, spanning 2013–2022 for OCPs and 2019–2021 for CUPs, allowing for the assessment of seasonal variations and time trends”
Line 82: change “on location until transported to the” to “on site until transport to the”
Line 110: “processed as per samples” sounds wired. It should be “which were then processed as samples” or in a clearer way like “which were processed in the same way as the samples”.
And “with a few exceptions, “
Line 114: “for QFFs and from 49 % ± 6 (PeCB) to 103 % ± 10 (p,p’-DDD) for PUFs”
Line 116, suggest use concise and sample expressions for “from 2018 onward” , e.g., “after 2018” , the word “for” in the “for both OCPs and CUPs” can be removed. The sentence can be rephrased as “the concentration of both OCPs and CUPs have been adjusted by the recoveries.”
Line 123, for clarity, here is a rephrased version, “For OCPs, with expected one annual amplitude, Equation (1) was used, which ..”
Line 168, The sentence can be rephrased in a clearer manner. “Eleven CUPs had detection frequencies (DF) greater than 80%, with two CUPs (pendimethalin and tebuconazole) being detected in all samples.”
Line 174, “these CUPs were all quantified in >65% of air samples”
Line 198, “38, 29 and 8 .1% of Σ30OCPs, respectively (Figure 1c,d Table S10).”
Line 214, suggest that a revised figure title of “ Time series of Σ CUP (a) and Σ OCP (c) concentrations and their relative abundances(b,d) in the atmosphere.
Line 222, change “pointing to” to “aligned with”
Line 239-240, The sentence can be refined as “High concentrations were due to clearly evident application.”
Line 242-243, can be improved as “… with spring being quite broad, ranging from …”
Line 255: “….suggest that soil temperatures play a significant role in influencing DDD levels at this site…”
Line 274, the sentence can be clarified as “Long-term annual variations in atmospheric concentrations were assessed for 22 CUPs with sufficient concentration data (DF > 20%) using Eq. (2) and Eq. (1) for CUPs and OCPs, respectively.”
Line 285: “one of them” can be removed.
Line 287: The sentence can refined as “Boscalid was the only in-use CUP in the Czech Republic that was decreasing.”
Line 289-291 , The sentences can be rephrased as “ ..was reported to approach zero or in a low amount in 2021. The observed decline was accelerated from 2020 to 2021 compared to the period during 2019-2020, reflecting the combination of these applications and the degradation in the total environment after ban”
Line 304-307, the sentence is not clear. Please clarify. Doubled period in the end of the sentence.
Line 325, equilibrium rather than equilibria?
Line 328, “which is global” seems not complete. Something like “ which impacts globally” or “which is a global concern”?
Line 329-330, the sentence is not clear. Please clarify.
Line 336, “ have been reported” rather than “have been reporting”
Line 340, the full name of SVOCs should be specified, Semivolatile Organic compounds (SVOCs)
Line 344, the sentence can be refined as “ Overall, this study provided long-term time series data for atmospheric OCPs and CUPs at a Central European site. Consistent with the perception of low degradation rate of many SVOCs in soils, Clausius-Clapeyron analysis results showed that….”
Line 356, “investigating” rather than “investigate” ; “ for the global OCP cycling”?
Line 367, The sentence can be rephrased as “ In addition, we observed that CUPs’ temporal trends are… They were generally negative or insignificant, during which CUPs national use …”
Line 359, “the decreasing trends were directly related to the revocation of their use authorization. “
Line 360, the sentence can be refined as “…in the atmosphere at detectable levels, suggesting a potential atmospheric persistence. “
Line 362-364, “…highlights… provide sufficient insights into .. and to further develop accurate models to predict key environmental processes such as.. “
Status: closed
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RC1: 'Comment on egusphere-2025-349', Anonymous Referee #1, 15 Mar 2025
Overall:
This manuscript reported multi-annual observations of CUPs and OCPs from a monitoring site in Czech Republic. Active air samples have been collected biweekly over 3 years (CUPs) and 10 years (OCPs) and temporal trends were analyzed. From the results, potential sources for the atmospheric presence of pesticides were indicated. Both OCPs and CUPs showed declining trends. The OCPs showed less decrease in the sampling period compared to the CUPs. Rcently banned CUPs showed the lowest half-lifes reflecting the immediate effects of legislation, but their presence may imply that they are persistent. While there are indications that the levels of OCPs are affected by secondary sources, CUP concentrations seem to correlate with application seasons.
Overall, this manuscript presents novel and important results, which has been sufficiently documented. The manuscript includes a great deal of information, and additional information is recorded in the SI. The approach and data help to advance the field of science. I would therefore suggest it can be accepted after some revision. In addition to the comments below, some parts need rephrasing/elaboration which is commented directly in the attached pdf of the preprint.
Specific comments:
Section 1 Introduction:
- The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
- Line 40: Levelling off air concentrations over time may imply that secondary sources are likely to influence to a larger extent, but how can conclusions regarding sources be made from time-trends by itself? I think this statement needs some moderation /elaboration or a reference.
Section 2 Methods:
For the OCPs, there were pointed at some methodological differences between the dataset in terms of recovery corrections. This gives rise to two different time trend curves. The half lifes for the two periods were then compared. This seems to be a reasonable way to account for the differences. The analytical methods are well-described with satisfactory measures to assure high quality of the data, but I have a few comments:
- The QFF and PUF/XAD samples have been analyzed separately, but the total concentration is used in further assessments. It should therefore be described how the results were combined. Furthermore, the recoveries given in SI (Table S7) should not only be indicated separately for QFF and PUF/XAD, but also for the two combined.
- For the OCPs, it seems like only 7 out of 30 have internal standards. This may give rise to higher uncertainty in data for the other OCPs and should be specified.
- Under section 2.5 it is not clear if the recoveries given account for both OCPs and CUPs, and for all samples/time periods, incl. 2013-2017. A reference to Table S7 is also missing. Furthermore, it is not clear if internal standards for all OCPs were introduced in 2018 (line 115). This part could be elaborated.
- Under 2.6 the term “timing” is not clear and a further explanation is needed.
Section 3 Results:
- Line 190-195: Why is 100 pg/m3 used as a limit for CUPs? For both CUPs and OCPs, it should be stated explicitly which compounds that were found in highest concentrations and their concentrations should be specified, e.g. the CUPs Metolachlor, Chlorpyrifos and Pendimethalin, and the OCPs HCB, ppDDE and gHCH. Methoxychlor should also be mentioned. It should explicitly be specified that the concentrations of OCPs are significantly lower than CUPs.
- For both OCPs and CUPs the comparison with other studies should be elaborated, i.e. how do the results align with previous findings, e.g passive air studies? Also, a reference to Table S9 and compliance with usage should be included.
- Line 200-205: The interpretation of DDT ratios is unprecise. Low ppDDT compared to ppDDE/ppDDD is due to degradation of DDT to DDE and indicate possible shift from primary to secondary sources, i.e past usage of technical DDT mixture. Pozo et al (2006) Environ. Sci. Technol. 2006, 40, 4867-4873 should be referenced. Also, the interpretation of HCH ratios should be elaborated. Note that Lindane contains >99% y-HCH (ref. Y.F. Li, R.W. Macdonald / Science of the Total Environment 342 (2005) 87–106). Furthermore, source indications of both DDTs and HCHs should be compared with other studies in Europe assessing sources (e.g Lunder Halvorsen et al 2023, PAS Europe 2016).
- Figure 1: The X-axis with months is not very consistent and it should be easier to see where the application/spring seasons are. Metolachlor and Chlorpyrifos should also be shown or mentioned in section 3.3 given their high concentrations.
- Temperature dependence (line 230): An overview of temperature during the sampling period is missing and should be included e.g. in Figure S6. How is the temperature dependence and can a peak be expected from volatilisation by itself?
- For the OCPs, the Clausius-Clapeyron equation is used to look into re-volatilisation. However, it is not clear to me how good correlation between partial pressure and the inverse ambient temperature implies that air concentrations and temperature are correlated, and this should therefore be elaborated. Correlation between air concentrations and temperature may be more intuitive and align better with Figure S6. In that case, R2 and p-values should be added to the figure.
- Line 270: How do the results of this study imply that the atmospheric concentrations of banned CUPs are dominated by resuspension and LRAT? This claim needs further explanation.
- Section 3.5: I question the assessment of time trends for OCPs/CUPs down to 20% detection frequency, as it is a possibility for bias due to MDLs. I would therefore suggest to use 80% as cut-off instead.
- The discussion of time trends for CUPs should highlight Chlorpyrifos given the decline in usage (Table S9) and high concentrations. The comparison with Fenpropiomorph (line 290) is interesting, given that the use of Chlorpyrifos has been more drastically reduced, while the half-life for Fenpropiomorph is lower. Time trends for Metolachlor and Pendimethalin should also be considered given their dominance in the atmosphere.
- Figure 2: Not easy to see purple line for the OCPs and I therefore suggest to change to a darker color.
- Line 300: The steepest slope is found for a-Endosulfan in accordance with regulation from 2013. Data for b-Endosulfan could have given valuable information regarding past/present usage. However, the number of compounds in the study is already extensive and it is understandable that not all isomers can be included in the instrumental analysis.
- Line 315: Time trends are compared with data extracted from EBAS, but it should be specified in SI how these trends have been developed. Also, HCB trends are specifically mentioned in EMEP status report 2/2022, which should be referenced.
- Line 300: Time trends of 12 OCPs indicate that the concentrations are levelling off, but to a less extent compared to the CUPs (i.e. higher half-life). This should be highlighted.
Section 4 Conclusion:
- While Kosetice is a regional background site, it is pointed out in section 2.2 that local sources exist for pesticides. Generalization and the impact of this study should therefore be moderated, given that these data are based on one rural site only and variations may exist within central Europe.
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AC1: 'Reply on RC1', Ludovic Mayer, 01 Apr 2025
We would like to thank the reviewers for the thoughtful reading and comments, which helped to improve this manuscript. We have addressed all comments below and have indicated the corresponding modifications to the manuscript.
Anonymous referee 1:
Overall:
This manuscript reported multi-annual observations of CUPs and OCPs from a monitoring site in Czech Republic. Active air samples have been collected biweekly over 3 years (CUPs) and 10 years (OCPs) and temporal trends were analysed. From the results, potential sources for the atmospheric presence of pesticides were indicated. Both OCPs and CUPs showed declining trends. The OCPs showed less decrease in the sampling period compared to the CUPs. Recently banned CUPs showed the lowest half-lives reflecting the immediate effects of legislation, but their presence may imply that they are persistent. While there are indications that the levels of OCPs are affected by secondary sources, CUP concentrations seem to correlate with application seasons.
Overall, this manuscript presents novel and important results, which has been sufficiently documented. The manuscript includes a great deal of information, and additional information is recorded in the SI. The approach and data help to advance the field of science. I would therefore suggest it can be accepted after some revision. In addition to the comments below, some parts need rephrasing/elaboration which is commented directly in the attached pdf of the preprint.
Specific comments:
Section 1 Introduction:
- 1. The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
Thank you for your comment. To clarify the reference, we will update the reference list to refer to the proper reference of the Stockholm Convention official website.
- 2. Line 40: Levelling off air concentrations over time may imply that secondary sources are likely to influence to a larger extent, but how can conclusions regarding sources be made from time-trends by itself? I think this statement needs some moderation /elaboration or a reference.
Thank you for your comment. The statement should have been more specific in mentioning that we consider seasonal patterns, and specifically the relationship between temperature peaks and pesticide concentration peaks to be an indication of either fresh application (primary sources) or revolatilization (secondary sources). So, to ensure that this idea is also expressed in the introduction, we will modify the sentence, to read as (lines 40-42):
“For both banned and authorised chemicals, it is generally possible to observe and distinguish between primary (e.g., application for pesticides) and secondary sources (e.g., re-volatilisation) by examining the seasonal variations of temperature, application and concentrations in air (Hoff et al., 1998; van den Berg et al., 1999).”
Section 2 Methods:
For the OCPs, there were pointed at some methodological differences between the dataset in terms of recovery corrections. This gives rise to two different time trend curves. The half lifes for the two periods were then compared. This seems to be a reasonable way to account for the differences. The analytical methods are well-described with satisfactory measures to assure high quality of the data, but I have a few comments:
- 3. The QFF and PUF/XAD samples have been analyzed separately, but the total concentration is used in further assessments. It should therefore be described how the results were combined. Furthermore, the recoveries given in SI (Table S7) should not only be indicated separately for QFF and PUF/XAD, but also for the two combined.
Thank you for your comment. To provide more clarity, we expanded the sentence (line 121), to describe how the results were combined. As QFF and PUF/XAD were extracted separately, no recoveries for QFF and PUF/XAD together were determined. An effective recovery could be derived based on the phase mass-weighted mean of the recoveries of the particulate (QFF) and gas (PUF/XAD) phases. The revised sentence will read (lines 121-123, in section 2.6):
“As relaxation to phase equilibrium is fast on the time scale addressed (weeks), and even so both phases were analysed separately, the data analysed was the total concentration i.e., sum of particulate and gaseous concentrations.”
- 4. For the OCPs, it seems like only 7 out of 30 have internal standards. This may give rise to higher uncertainty in data for the other OCPs and should be specified.
Thank you for your comment. It is true that we do not have C13-labelled structural analogues for all OCPs, but in most cases this should lead to limited uncertainty because the internal standard is an isomeric or structurally similar compound, e.g., γ-HCH is used as internal standard for 5 HCH isomers (Table S5). In the cases of the chlorobenzenes, HCHs and DDT compounds, we do not expect the internal standard to introduce uncertainty. However, the reviewer is correct in the case of the second set of pesticides (heptachlors, chlordanes, endosulfans, and drin pesticides); in this case 13C-α-endosulfan was used as an internal standard except for β-endosulfan, for which 13C β-endosulfan was used as internal standard. This may introduce additional uncertainty for a subset of these OCPs. We will add a sentence about uncertainties in the SI when different methods are described (SI, lines 61-64):
“As isotopically labelled internal standards were not available for all 17 additional OCPs analysed, 13C-α-endosulfan was used as an internal standard for all compounds (Table S5a and S5b; except for β-endosulfan for which 13C β-endosulfan was used), which may lead to additional uncertainties in expressed concentrations, which are expected to be minor.”
- 5. Under section 2.5 it is not clear if the recoveries given account for both OCPs and CUPs, and for all samples/time periods, incl. 2013-2017. A reference to Table S7 is also missing. Furthermore, it is not clear if internal standards for all OCPs were introduced in 2018 (line 115). This part could be elaborated.
Thank for pointing this out, we will add the reference to table S7 (line 114), as well as extra information to the sentence to fill this gap, to read (lines 111-114):
“For the 48 CUPs analysed using the HPLC-MS/MS, the method recoveries of individual analytes ranged from (68 ± 14)% (carbaryl) to (153 ± 22)% (iprovalicarb) for QFFs and from (61 ± 3)% (kresoxim-methyl) to (132 ± 10)% (iprovalicarb) for sandwiches (Table S7a), while for OCPs, recoveries ranged from (47 ± 8)% (PeCB) to (100 ± 9)% (p,p’-DDD) for QFFs and from (49 ± 6)% (PeCB) to (103 ± 10)% (p,p’-DDD) for all the samples from 2013 to 2022 (Table S7b).”
- 6. Under 2.6 the term “timing” is not clear and a further explanation is needed.
Thank you for comment. In order to clarify the sentence, we will remove the words “timing” and replace them with the more appropriate and precise terms “periodicity” and “period of application” (lines 135 and 139).
Section 3 Results:
- 7. Line 190-195: Why is 100 pg/m3 used as a limit for CUPs? For both CUPs and OCPs, it should be stated explicitly which compounds that were found in highest concentrations and their concentrations should be specified, e.g. the CUPs Metolachlor, Chlorpyrifos and Pendimethalin, and the OCPs HCB, ppDDE and gHCH. Methoxychlor should also be mentioned. It should explicitly be specified that the concentrations of OCPs are significantly lower than CUPs.
Thank you for the comment. We have added the additional information asked for CUPs, as well as explained why 100 pg m-3 matter in the context of our study in relation to the previous one done at this site. Will read (line 192-197):
“Previous observation at this site during the 2012-2013 period, showcased the observation of chlorpyrifos, metazachlor and s-metolachlor, in addition to acetochlor and isoproturon in concentration surpassing 100 pg m-3 (Degrendele et al., 2016). In this study, chlorpyrifos, s-metolachlor, and prosulfocarb were found most abundant (average concentrations of 116, 115, and 79.7 pg m-3, respectively; Table S10a). Similarly, high concentrations of these compounds had previously been reported from rural environments (Debler et al., 2024; Habran et al., 2024; Mayer et al., 2024; Ni et al., 2024).”
Similarly, the suggested statement comparing OCPs and CUPs concentration has been added. As well as, a clear statement about HCB, p,p’-DDE and γ-HCH being the OCPs found in the highest atmospheric concentrations (line 197-200):
“Overall, concentration of OCPs were found to be significantly lower than CUP concentrations. The average weekly concentration of Σ30OCPs was 44.3 pg m-3, with HCB, p,p’-DDE and γ-HCH accounting on average for 38, 29 and 8.1% of Σ30OCPs and found at highest concentrations (Figure 1c,d and Table S10).”
- 8. For both OCPs and CUPs the comparison with other studies should be elaborated, i.e. how do the results align with previous findings, e.g passive air studies? Also, a reference to Table S9 and compliance with usage should be included.
Thank you for your question. We believe the discussion covered other studies for CUPs completely in the original manuscript (lines 192-197), but indeed not so for OCPs (as there were way more). So, we will add references to recent OCPs studies where similar results were observed (lines 200-204), will read:
“These three OCPs have also been previously observed as the dominant atmospheric OCPs (Gevao et al., 2018; Wang et al., 2018; Wong et al., 2021; Mamontova et al., 2022; Khuman et al., 2023; Lunder-Halvorsen et al. 2023).”
Additional references:
Gevao, B., Porcelli, M., Rajagopalan, S., Krishnan, D., Martinez-Guijarro, K., Alshemmari, H., Bahloul, M., and Zafar, J.: Spatial and temporal variations in the atmospheric concentrations of “Stockholm Convention” organochlorine pesticides in Kuwait, Sci. Total Environ., 622–623, 1621–1629, 2018.
Khuman, S. N., Park, M. K., Kim, H. J., Hwang, S. M., Lee, C. H., and Choi, S. D.: Nationwide assessment of atmospheric organochlorine pesticides over a decade during 2008–2017 in South Korea, Sci. Total Environ., 877, 162927, 2023.
Lunder Halvorsen, H., Bohlin-Nizzetto, P., Eckhardt, S., Gusev, A., Moeckel, C., Shatalov, V., Skogeng, L. P., and Breivik, K.: Spatial variability and temporal changes of POPs in European background air, Atmos. Environ., 299, 2023.
Mamontova, E. A. and Mamontov, A. A.: Air monitoring of polychlorinated biphenyls and organochlorine pesticides in Eastern Siberia: Levels, temporal trends, and risk assessment, Atmosphere (Basel), 13, 1971, 2022.
Wang, C., Wang, X., Gong, P., and Yao, T.: Long-term trends of atmospheric organochlorine pollutants and polycyclic aromatic hydrocarbons over the southeastern Tibetan Plateau, Sci. Total Environ., 624, 241–249, 2018.
Wong, F., Hung, H., Dryfhout-Clark, H., Aas, W., Bohlin-Nizzetto, P., Breivik, K., Mastromonaco, M. N., Lundén, E. B., Ólafsdóttir, K., Sigurðsson, Á., Vorkamp, K., Bossi, R., Skov, H., Hakola, H., Barresi, E., Sverko, E., Fellin, P., Li, H., Vlasenko, A., Zapevalov, M., Samsonov, D., and Wilson, S.: Time trends of persistent organic pollutants (POPs) and chemicals of emerging Arctic concern (CEAC) in Arctic air from 25 years of monitoring, Sci. Total Environ., 775, 145109, 2021.
Comparison to passive sampler studies are discussed in relation to multi-annual variation in the corresponding. For concentrations however, only comparison to studies done with active samplers were discussed due to the uncertainties associated with recalculation of concentration from passive sampling. A reference to Table S9 will be added to section 3.2 to discuss high atmospheric concentration and national usage, will read: (lines 199-203):
“As mentioned previously, some of those compounds (i.e., chlorpyrifos, metazachlor, pendimethalin, spiroxamine, tebuconazole and terbuthylazine) were applied on the Czech territory in more than 50 t of active substance per year, which would influence their high atmospheric concentration, notably during application periods (Table S9).”
- 9. Line 200-205: The interpretation of DDT ratios is unprecise. Low ppDDT compared to ppDDE/ppDDD is due to degradation of DDT to DDE and indicate possible shift from primary to secondary sources, i.e past usage of technical DDT mixture. Pozo et al (2006) Environ. Sci. Technol. 2006, 40, 4867-4873 should be referenced. Also, the interpretation of HCH ratios should be elaborated. Note that Lindane contains >99% y-HCH (ref. Y.F. Li, R.W. Macdonald / Science of the Total Environment 342 (2005) 87–106). Furthermore, source indications of both DDTs and HCHs should be compared with other studies in Europe assessing sources (e.g Lunder Halvorsen et al 2023, PAS Europe 2016).
Thank you for the suggestion, we believe this idea was already expressed in the original manuscript. The indicator ppDDT/(pDDE+ppDDD), to our knowledge, was first used by Rapaport et al., 1985, and we will therefore add a reference to a review, Bidleman 1999, at the end of our original statement. In addition, the information regarding lindane and corresponding reference will be added (lines 207-208) and will read:
“Additionally, the ratio β-HCH/(α-HCH+γ-HCH) can be used to distinguish between technical HCH and lindane, generally composed of >99% of γ-HCH (Li and Macdonald, 2005), as …”
In addition, source indication of HCHs were elaborated upon based on the suggested references (lines 211-216), will read:
“Similarly, the ratio α-HCH/γ-HCH has been previously used to infer sources of HCHs. A recent study in Europe highlighted a distinction between the northern and southern regions: in the north, high α-HCH/γ-HCH values were observed, indicating the dominance of long-range atmospheric transport and re-suspension of α-HCH, whereas in the south, lower α-HCH/γ-HCH values suggested historical use of γ-HCH (lindane; Lunder-Halvorsen et al., 2023). In our study, the ratio α-HCH/γ-HCH ranged from 0.12 to 1.7, aligning with values reported in southern Europe.”
Additional references:
Bidleman, T. F.: Atmospheric transport and air-surface exchange of pesticides, in: Fate of Pesticides in the Atmosphere: Implications for Environmental Risk Assessment (van Dijk, H. F. G., van Pul, W. A. J., and de Voogt, P., eds.), Springer, Dordrecht, Netherlands, pp. 115–166, 1999.
Li, Y. F. and Macdonald, R. W.: Sources and pathways of selected organochlorine pesticides to the Arctic and the effect of pathway divergence on HCH trends in biota: a review, Sci. Total Environ. 342, 87-106, 2005.
- 10. Figure 1: The X-axis with months is not very consistent and it should be easier to see where the application/spring seasons are. Metolachlor and Chlorpyrifos should also be shown or mentioned in section 3.3 given their high concentrations.
Thank you for your suggestion. We will update the X-axis for Figure 1 to keep a consistent base for the month for CUPs and for OCPs. High concentrations of chlorpyrifos and s-metolachlor have been mentioned and discussed in section 3.2 total concentration, while seasonal variation and application period are discussed in section 3.3, where s-metolachlor, although not mentioned by name specifically, is part of the 16 compounds with peak application in spring (Table S12).
- 11. Temperature dependence (line 230): An overview of temperature during the sampling period is missing and should be included e.g. in Figure S6. How is the temperature dependence and can a peak be expected from volatilisation by itself?
Thank you for your suggestion, we will add a sentence at the beginning of section “3.4 Influence of temperature on pesticide revolatilisation” reading (lines 246-247):
“For the 2013-2022 OCPs collection period, the temperature ranged from -9.5 to 23.7 °C while for the 2019-2021 CUPs collection period, it ranged from -5.8 to 22.1°C.”
The conclusion regarding the temperature dependence and whether a peak can be expected from volatilisation alone is discussed and answered in section “3.4 Influence of temperature on pesticide revolatilisation”, as mentioned in lines 268-271 of the version published as preprint.
“For OCPs, temperature dependent volatilisation is the main influence on OCP atmospheric concentration. For authorised CUPs, atmospheric concentrations were mainly influenced by application, while temperature-dependent resuspension and LRAT determined CUPs atmospheric levels for banned compounds.”
This statement follows the discussion of the results from examining the Clausius-Clapeyron equation for OCPs and CUPs. It, indeed, concludes that atmospheric concentration for OCPs and some CUPs are temperature-dependent, and a seasonal peak can be due to elevated temperature, especially for OCPs.
- 12. For the OCPs, the Clausius-Clapeyron equation is used to look into re-volatilisation. However, it is not clear to me how good correlation between partial pressure and the inverse ambient temperature implies that air concentrations and temperature are correlated, and this should therefore be elaborated. Correlation between air concentrations and temperature may be more intuitive and align better with Figure S6. In that case, R2 and p-values should be added to the figure.
Thank you for the suggestion, we will add the R² and p-value from Spearman correlation to selected chemicals presented in Figure S6, and update the figure caption, to show the relationship between atmospheric concentration and temperature.
- 13. Line 270: How do the results of this study imply that the atmospheric concentrations of banned CUPs are dominated by resuspension and LRAT? This claim needs further explanation.
Thank you for your comment and question. Since for the Czech Republic, information about the amount of active substances applied yearly is available, it is possible to specify whether the level encountered in the atmosphere is due to primary emissions only. For banned pesticides, obviously this is not the case: Therefore, OCP levels encountered are due to resuspension from other media (e.g., soil) or long-range atmospheric transport and individual compound persistence. Whereas for authorized CUPs, levels are generally more influenced by seasonal applications. This is explicitly described in the version of the manuscript published as preprint (lines 268-270).
- 14. Section 3.5: I question the assessment of time trends for OCPs/CUPs down to 20% detection frequency, as it is a possibility for bias due to MDLs. I would therefore suggest to use 80% as cut-off instead.
Thank you for the comment and suggestion. We agree that 20% is a relatively low detection frequency threshold, but we have specifically selected this as relevant for pesticides, given their strong seasonality. Many pesticides are detected only in summer and/or around time of application and applying a threshold such as 80% would lead to the exclusion of substantial amounts of valuable data.
- 15. The discussion of time trends for CUPs should highlight Chlorpyrifos given the decline in usage (Table S9) and high concentrations. The comparison with Fenpropimorph (line 290) is interesting, given that the use of Chlorpyrifos has been more drastically reduced, while the half-life for Fenpropimorph is lower. Time trends for Metolachlor and Pendimethalin should also be considered given their dominance in the atmosphere.
Thank you for your suggestion, we will replace terbuthylazine by s-metolachlor in Figure 2 showcasing the significantly decreasing trends for selected CUPs. As pendimethalin trend was not significant, it has not been included in figure 2. However, results for all CUPs trends are presented in Tables S14 and S15.
- 16. Figure 2: Not easy to see purple line for the OCPs and I therefore suggest to change to a darker color.
Thank you for your suggestion, we will update the figure and caption accordingly. We decided to go with a brighter color (red) which adds to trend visibility.
- 17. Line 300: The steepest slope is found for a-Endosulfan in accordance with regulation from 2013. Data for b-Endosulfan could have given valuable information regarding past/present usage. However, the number of compounds in the study is already extensive and it is understandable that not all isomers can be included in the instrumental analysis.
Thank you for your comment. Indeed, it would have brought forth valuable information. β-endosulfan was included in the instrumental analysis, but only found in 6.3 % of the samples (Table S8), which we judge inconclusive with regard to time trends.
- 18. Line 315: Time trends are compared with data extracted from EBAS, but it should be specified in SI how these trends have been developed. Also, HCB trends are specifically mentioned in EMEP status report 2/2022, which should be referenced.
Thank you for the suggestion, we will add a reference to the EMEP status report 2/2022. The reference to the EBAS database will be dropped, as the data available on that website is the same as the one used in references already made (i.e., Ilyin et al., 2022; Lunder-Halvorsen et al., 2023; UNEP 2023).
- 19. Line 300: Time trends of 12 OCPs indicate that the concentrations are levelling off, but to a less extent compared to the CUPs (i.e. higher half-life). This should be highlighted.
Thank you for the suggestion, an additional sentence will be added (line 309-311):
“Compared to CUPs with insignificant trends, these 12 OCPs were levelling off on a slower time scale (i.e., higher half-life than for CUPs), highlighting the persistence of these compounds.”
Section 4 Conclusion:
- 20. While Kosetice is a regional background site, it is pointed out in section 2.2 that local sources exist for pesticides. Generalization and the impact of this study should therefore be moderated, given that these data are based on one rural site only and variations may exist within central Europe.
Thank you for your comment, indeed, NAOK is considered a regional background site in the context of air quality studies and research, which includes also some organic pollutants such as PAHs, but, as mentioned in section 2.2, NAOK is not (and never was) a background site in the context of pesticides studies and research. This article aims to bring forth data and interpretation of a time series of atmospheric CUPs from a site located in a source area. To make sure that we are showcasing the results from one central European agricultural site only, we will add a corresponding statement (line 344-346), which will read:
“As this study focuses on a single agricultural site, the findings cannot capture the variability across the entire CUP source area i.e., rural central Europe. However, the observations were consistent…”
Citation: https://doi.org/10.5194/egusphere-2025-349-AC1 - 1. The reference (UNEP, 2001) cannot be found in the list and a more precise reference to the Stockholm convention should be given.
-
RC2: 'Comment on egusphere-2025-349', Anonymous Referee #2, 05 Jun 2025
Overall comments
This study presents seasonal and multi-annual trends of organic pesticides at a rural agricultural site in Central Europe and investigates their primary and secondary sources. Over ten years of weekly air monitoring for a wide range of pesticides (48 CUPs and 30 OCPs) has produced a large dataset that enables a comprehensive assessment of atmospheric pesticide contamination in Central Europe and allows for the determination of seasonal and temporal trends with high confidence. The statistical analyses appear sound, and the resulting trends generally align with known usage patterns, regulatory restrictions, and dominant release pathways. However, some statements should be clarified, and the language could be improved for better readability. Detailed comments are provided below.
Detailed comments
The application of two separate equations for OCPs and CUPs is scientifically reasonable, but the manuscript would benefit from a clearer justification of why different models were chosen, especially for readers less familiar with OCP or CUP-specific seasonality patterns.
The authors employed HPLC, GC, and tandem mass spectrometry (MS/MS) to analyze the collected samples and identify OCPs and CUPs. However, both OCPs and CUPs can naturally degrade or transform under specific environmental conditions, potentially forming structurally similar degradation products. Therefore, the authors should discuss how they distinguish between parent compounds and their degradation/metabolic products. Is it possible that the parent compounds could be potentially interfered by their degradation/metabolic products during the analysis?
Title: I am not entirely sure if the modifier “unidentified” is necessary. I think the secondary sources primarily refer to volatilization from land and water surfaces; The “current-use and organochlorine pesticides” can be refined as “legacy and current-use pesticides”.
Consider a refined title of something like “Multi-annual trends of legacy and current-use pesticides in air in Central Europe: primary and secondary sources. “
Line 12, “with revolatilisation from soil apparent in summer.” For OCPs, they can not only be volatilized from soil but also from water bodies, in come cases, e.g. HCH, volatilization from water is more pronounced compared to direct volatilization from soil. (https://doi.org/10.1021/acs.est.4c05204; https://doi.org/10.1021/es034998k)
Line 16: “reversal of the direction of air-surface exchange or recent mobilisation from soils, water bodies, or the cryosphere” this is sentence is not clear. Reversal from what to what? Convert the direction from surface volatilization to atmospheric deposition? This statement repeatedly occurs in the manuscript that need to be well clarified. In addition, mobilisation from soil, water bodies, or the cryosphere share the same mechanism as air-surface exchange when regarding the emission to the atmosphere. Therefore, this sentence can be refined.
Line 22, rather than semivolatility, long-range transport ability is more precise accounting for the global cycling.
Section 2.4: To prevent potential breakthrough, PUF/XAD2/PUF sandwich was used for sampling gas-phase CUPs, while only two PUF plugs were used for sampling gaseous OCPs. Why did the author not apply PUF/XAD2/PUF sandwich to OCP sampling? Can the author assure that there is no breakthrough issue for hi-vol sampling of OCPs without XAD? If not, a limitation on this point should be included in the context.
Line 91-92, “100 μL of MilliQ water were then added to a 100μL aliquot of the respective extracts which were finally used for analysis.” This sentence is not clear. 100μL water was added to both OCP extracts and CUP extracts? Since n-nonane was previously added in the extracts, water and nonane are immiscible and extracts for OCPs analysis using GC-MS/MS should not contain any water. Please explain this.
Line 95, four different methods were used for CUP analysis. Why did not author combine these methods into one or two since they all are based on LC-MS/MS analysis?
Line 108-114, for the recoveries, were they calculated based on spiked native standards or isotopic standards? If based on the former, a series of recovery tests are required. Then, how many replicates were conducted? Otherwise, recoveries can be calculated for each real sample based on their ratio of labelled spike standards (surrogates) to the injection standards in samples relative to those in the calibration standards. Please clarify.
Line 115, “so was the internal standards for OCPs only.” does it mean that internal standards were changed as well” what dose the “only” refer to?
Line 147, what are the Non-parametric Mann-Whitney tests used for? Test for difference with previous measurements?
Line 160, I believe the Clausius-Clapeyron equation works for gaseous phase only. Please include a reference to support your statement of using total concentrations is more appropriate.
Line 201-202: Can you explain why the low and decreasing (o,p’-/(o,p’-+p,p’-) ratios ratio indicates that dicofol was not apparently a viable source for presence of DDT in the atmosphere. To make it understandable, additional information on dicofol and its relationship with DDT and DDT should be included in the context.
Line 207-208, please indicate how to use the ratio β-/(α-+γ-) HCH to distinguish between HCH isomers, and include a reference for it.
Line 228, how was application of pendimethalin in winter observed? In what cases people apply the pesticide in winter? It’s rare to apply pesticides in winter. In fact, it contradicts with the statements in lines 232-233.
Line 240-241: Were the maxima referred to the pre-ban period? If so, the maxima should be higher during the same period in the following years if the legislation works out.
Line 245 255: how did author determine whether the slope is steep or not? One approach is to use the slope of Clausius-Clapeyron plot can derive ΔHexp, and then the ΔHexp can be compared with theoretical ΔH, if derive ΔHexp is close to theoretical ΔH, we assume that local volatilization is dominant. If ΔHexp is much small than theoretical ΔH (shallow slope), the long-range transport is dominant (DOI:10.1016/j.ese.2022.100209; DOI: 10.1126/sciadv.adi808 ).
Line 255-258, how can the “narrow” or “wide” spread be linked to the sources, e.g., soil temperature or secondary sources” Please elaborate.
Line 266-267, a CUP metazachlor, peaked at summer, how can it be distinguished between application in summer and re-volatilization during the warmest period (summer)?
Line 300-301: is there a reason why pp-DDD increased during 2013-2017 while decreased during 2018-2022? Has a similar shift of the trend been reported?
Line 309-310: why this shift of ratio does not indicate any influence of fresh inputs of the pesticide? Because the ratios are both below 1?
Line 314-316, Industrial emissions could be more pronounced compared to the role of being a pesticide for HCB and PeCB. This point can be involved in the discussion in the context rather than being included at the end.
Line 331-332, could consider additionally include the evidence of net HCH volatilization from water to the atmosphere (https://doi.org/10.1021/acs.est.4c05204; https://doi.org/10.1021/es034998k).
Line 339-342: Despite that gas-particle partition calculation is not available, separate temporal trend analysis for gas- and particle phases is possible. Is there any difference between the two trends as well as compared with the trend for the total concentrations? It would be worthwhile to bring up this point or a short discussion.
Line 349, if the case for δ- and ε-HCH is the same, why was it separately mentioned rather than being included with other OCPs.
Small things:
Line 15, a comma should be inserted between “mirex” and “levelling off”.
Line 19 For clarity, consider changing “one-year post-ban” to “ one year after the bans”
Line 22-24, consider splitting into two sentences for clarity, rephrase like “Due to their severe health and environmental impacts, OCPs have been restricted in most countries (UNEP, 2001). For compounds like DDT and HCH, this has been consistently reflected in declining air concentrations.”
Line 32, and line 33: inserting a comma between “(CUPs)” and “have”, between “neonicotinoids” and “are”, could make the sentence clearer.
Line 33-34: consider rephrasing the sentence as “are chemically varied and subject to different environmental fates accordingly”
Line 36-39, consider splitting sentence into two for clarity. Something like “CUPs can enter the atmosphere during application, where up to 90% of the mass applied can be released
directly into the atmosphere (van den Berg et al., 1999). CUPs can be volatilised from surfaces such as soil, plants and surface water over longer periods of time following application (Bedos et al., 2002), and mobilised through wind erosion of soil particles containing CUPs “
Line 44: “ from a few European countries”
Line 46, “have become “
Line 50-53: consider rephrasing the sentence as: “In this study, biweekly samples of OCPs and CUPs were collected in both the gas and particulate phases at a rural site in an agricultural region of Central Europe, spanning 2013–2022 for OCPs and 2019–2021 for CUPs, allowing for the assessment of seasonal variations and time trends”
Line 82: change “on location until transported to the” to “on site until transport to the”
Line 110: “processed as per samples” sounds wired. It should be “which were then processed as samples” or in a clearer way like “which were processed in the same way as the samples”.
And “with a few exceptions, “
Line 114: “for QFFs and from 49 % ± 6 (PeCB) to 103 % ± 10 (p,p’-DDD) for PUFs”
Line 116, suggest use concise and sample expressions for “from 2018 onward” , e.g., “after 2018” , the word “for” in the “for both OCPs and CUPs” can be removed. The sentence can be rephrased as “the concentration of both OCPs and CUPs have been adjusted by the recoveries.”
Line 123, for clarity, here is a rephrased version, “For OCPs, with expected one annual amplitude, Equation (1) was used, which ..”
Line 168, The sentence can be rephrased in a clearer manner. “Eleven CUPs had detection frequencies (DF) greater than 80%, with two CUPs (pendimethalin and tebuconazole) being detected in all samples.”
Line 174, “these CUPs were all quantified in >65% of air samples”
Line 198, “38, 29 and 8 .1% of Σ30OCPs, respectively (Figure 1c,d Table S10).”
Line 214, suggest that a revised figure title of “ Time series of Σ CUP (a) and Σ OCP (c) concentrations and their relative abundances(b,d) in the atmosphere.
Line 222, change “pointing to” to “aligned with”
Line 239-240, The sentence can be refined as “High concentrations were due to clearly evident application.”
Line 242-243, can be improved as “… with spring being quite broad, ranging from …”
Line 255: “….suggest that soil temperatures play a significant role in influencing DDD levels at this site…”
Line 274, the sentence can be clarified as “Long-term annual variations in atmospheric concentrations were assessed for 22 CUPs with sufficient concentration data (DF > 20%) using Eq. (2) and Eq. (1) for CUPs and OCPs, respectively.”
Line 285: “one of them” can be removed.
Line 287: The sentence can refined as “Boscalid was the only in-use CUP in the Czech Republic that was decreasing.”
Line 289-291 , The sentences can be rephrased as “ ..was reported to approach zero or in a low amount in 2021. The observed decline was accelerated from 2020 to 2021 compared to the period during 2019-2020, reflecting the combination of these applications and the degradation in the total environment after ban”
Line 304-307, the sentence is not clear. Please clarify. Doubled period in the end of the sentence.
Line 325, equilibrium rather than equilibria?
Line 328, “which is global” seems not complete. Something like “ which impacts globally” or “which is a global concern”?
Line 329-330, the sentence is not clear. Please clarify.
Line 336, “ have been reported” rather than “have been reporting”
Line 340, the full name of SVOCs should be specified, Semivolatile Organic compounds (SVOCs)
Line 344, the sentence can be refined as “ Overall, this study provided long-term time series data for atmospheric OCPs and CUPs at a Central European site. Consistent with the perception of low degradation rate of many SVOCs in soils, Clausius-Clapeyron analysis results showed that….”
Line 356, “investigating” rather than “investigate” ; “ for the global OCP cycling”?
Line 367, The sentence can be rephrased as “ In addition, we observed that CUPs’ temporal trends are… They were generally negative or insignificant, during which CUPs national use …”
Line 359, “the decreasing trends were directly related to the revocation of their use authorization. “
Line 360, the sentence can be refined as “…in the atmosphere at detectable levels, suggesting a potential atmospheric persistence. “
Line 362-364, “…highlights… provide sufficient insights into .. and to further develop accurate models to predict key environmental processes such as.. “
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