28 Sep 2022
28 Sep 2022
Status: this preprint is open for discussion.

Pesticide transport through the vadose zone under sugarcane in the Wet Tropics, Australia

Rezaul Karim1,2, Lucy Reading1, Les Dawes3, Ofer Dahan4, and Glynis Orr5 Rezaul Karim et al.
  • 1School of Biology and Environmental Science, Queensland University of Technology, Brisbane, 4000, Australia
  • 2Department of Environmental Science and Technology, Jashore University of Science and Technology, Jashore, 7408, Bangladesh
  • 3School of Civil and Environmental Engineering, Queensland University of Technology, Brisbane, 4000, Australia
  • 4Department of Environmental Hydrology and Microbiology, Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990, Israel
  • 5Department Environment and Science, Queensland Government, Cairns, 4870, Australia

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.

Rezaul Karim et al.

Status: open (until 30 Dec 2022)

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Rezaul Karim et al.


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Short summary
The study was performed using continuous measurements of temporal variations in soil saturation plus measurements of the concentration of pesticides along the vadose zone profile and underlying alluvial aquifers at sugarcane fields in the Wet Tropical conditions in Australia. A vadose zone monitoring system was set up to enable the characterization of pesticide (non-PS II herbicides) migration with respect to pesticide application, sugarcane growing period and finally, rainwater infiltration.