the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Pesticide transport through the vadose zone under sugarcane in the Wet Tropics, Australia
Rezaul Karim
Les Dawes
Ofer Dahan
Glynis Orr
Abstract. Photosystem II (PS II) pesticides, recognised as a threat to ecological health, were targeted for reduction in sugarcane farming in the Great Barrier Reef (GBR) catchments. Alternative herbicides, the non-PS II herbicides (including glyphosate, paraquat, 2,4-D, imazapic, isoxaflutole, metolachlor, and S-metolachlor), continue to be used in these catchments. However, the potential ecological fate, transport, and off-site environmental effects of non-PS II herbicides, with respect to their usage scheme, local rainfall patterns, and infiltration dynamics, has not been investigated previously. A vadose zone monitoring system, instrumented beneath a sugarcane land in a GBR catchment, was applied for real time tracing of pesticide migration across the unsaturated zone, past the root zone during 2017–2019.The monitoring of regularly applied pesticides (fluroxypyr and isoxaflutole), exhibited substantial migration through the unsaturated zone. Within one month after application of fluroxypyr, it leached to 2.87 m depth in the vadose zone, with declining concentrations with depth. Isoxaflutole, which was applied yearly, was found only once, in November 2018, at 3.28 m depth in the soil profile. Other pesticides (imazapic, metolachlor, glyphosate and haloxyfop), applied at the same period, were not detected through the vadose zone. However, imidacloprid, which was not applied at the site during the monitored period, was detected across the entire vadose zone, revealing substantial resistance to degradation. The results show no evidence of any regularly applied pesticides in the site bores at the end of the study, indicating their ultimate degradation within the vadose zone before reaching the groundwater.
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Rezaul Karim et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-691', Anonymous Referee #1, 19 Dec 2022
A timely, interesting, well-conceived, and planned study. The MS reports of the interesting results about pesticides transport through the vadose zone under sugarcane in the Wet Tropics, Australia and it will be of the interest to the readers and extend our knowledge about these processes. However, MS needs a little improvement for better reading. The analytical procedures (calibration, LOD, LOQ, recovery, matrix effect,… should be included in section 2.5. Chemical analysis. Therefore, minor revision is needed before being published.
Citation: https://doi.org/10.5194/egusphere-2022-691-RC1 -
AC1: 'Reply on RC1', Rezaul Karim, 29 Dec 2022
The reviewers’ comment are addressed in the revised manuscript. The issues (comments) with incorporated in the text are provided briefly below.
The analytical procedures (calibration, LOD, LOQ, recovery, matrix effect,… should be included in section 2.5. Chemical analysis.
Two subsections (2.5.1 Water analysis and 2.5.2 Soil Analysis) are added under 2.5 Chemical analysis (Below). The analytical methods and sample processing used in Queensland Health Forensic and Scientific Services are added. For the analytical procedures, the LOR and recovery are added in the text and subsequently in the Appendix Table A2 and Table A3 (attachment).
"2.5.1 Water Analysis
There were two analytical method groups (QIS 33963 for herbicides and pesticides and QIS 33917 for Glyphosate) for water analysis used in Queensland Health Laboratory. The analysis was performed by direct injection method by filtering 1mL of sample using 0.2 µm filter and analysed on LCMSMS. For water herbicide analysis for imidacloprid, imazapic, metolachlor, fluroxypyr, isoxaflutole and haloxyfop, the method details are provided in Table A2. During analysis, some matrix effects were experienced, and if this increased, the Limit of Reporting (LOR) was increased.
2.5.2 Soil Analysis
There were two analytical method groups (QIS 30814 for glyphosate and QIS 32456 for herbicides and pesticides) in soil / sediment. For QIS 30814: glyphosate and amino methyl phosphonic acid (AMPA) in soil/vegetation by LCMSMS, water was added to soil samples and shaken. The aqueous phase was filtered and analysed via direct injection on the LC-MSMS. On the other hand, QIS 32456: determination of herbicides in soil and sediment by LC-HRAM-Orbitrap, the soil/sediment sample was first shaken with acetone using a tabletop shaker for approximately 12 hours. The herbicides were then extracted using a QuEChERS method. The final extract was analysed by LC-HRAM-Orbitrap. The method details for pesticide and herbicides in soil and sediment are provided in Table A3. Imazapic showed low recovery (<40%) when it was analysed by QIS 33456 method."
As Queensland Health Forensic and Scientific Services takes up in-house methods, the other analytical details i.e., calibration and LOQ are not permitted to be released.
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RC2: 'Reply on AC1', Anonymous Referee #1, 09 Jan 2023
This paper may be accepted for publication.
Citation: https://doi.org/10.5194/egusphere-2022-691-RC2
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RC2: 'Reply on AC1', Anonymous Referee #1, 09 Jan 2023
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AC1: 'Reply on RC1', Rezaul Karim, 29 Dec 2022
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RC3: 'Comment on egusphere-2022-691', Anonymous Referee #2, 13 Mar 2023
The article shows interesting results about the transport and fate of pesticides through the vadose zone under sugarcane farming. Although locally assessed, findings are of interest to the global scientific community to understand about pesticides fate and know good experimental design to achieve this aim. However, some minor issues need to be addressed before acceptance for publication:
Include the name of abbreviations in all Tables and Figures used as Table foot or in the Figure caption to facilitate understanding.
L111. Can you please give the soil type classification according to a more international system to be understood by most readers? Such as Key to Soil Taxonomy of USDA or World Reference Base for Soil Resources of IUSS/FAO. Also include pH values besides organic matter, important to understand biochemical processes in soil.
L123-129. Can you also add mean annual T and potential evapotranspiration?
Table 3. Please, explain what you mean with X and √ and what the difference is. Not clear
Table 4. Please explain what you mean with “√” and “sampling regime”
Figure 4. Explain in the figure 4 what A, B and C represent with the circles
L326. It is written “As it was observed in the soil samples,…”, but where are the soil results? Not clear. Difficult to assess what is soil and what is water. I do not know where to find them. I only see results, but not explicitly indicated along the text, on Supplementary Tables S8 and S9. Clear information about results in soils should be provided. In addition, concentration in Tables S8 and S9 is in ug/L, what it is a unit for liquids. Give a concentration for the soil as ug/kg for example. Concentration of pesticides on soil should be in the manuscript, clearly described and referred.
Citation: https://doi.org/10.5194/egusphere-2022-691-RC3
Rezaul Karim et al.
Rezaul Karim et al.
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