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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Status: open (until 23 Apr 2025)
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RC1: 'Comment on egusphere-2025-349', Anonymous Referee #1, 15 Mar 2025
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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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