Sorption-Desorption, Leaching, and Bioavailability of Aminocyclopyrachlor and Indaziflam in Minnesota Soils

Abstract

Accurate prediction of the environmental fate of pesticides is important for practical application and regulatory purposes, to enhance product efficacy and maintain environmental quality. Sorption-desorption of pesticides on soil influence their bioavailability and mobility and are important parameters in environmental fate and transport models. Limited information on the sorption-desorption of aminocyclopyrachlor and indaziflam is available in the scientific literature. Sorption coefficients (Kd and Koc) of these herbicides in surface and subsurface soils were determined for three locations in Minnesota, USA, and predictions for their off-site transport were established using Groundwater Ubiquity Scores. Indaziflam moderately sorbed to these soils with greater sorption in the surface soil, hysteretic desorption and moderate leaching potential. Aminocyclopyrachlor sorption was low for all soils, desorption was hysteretic and the leaching potential was classified as high to very high which prompted follow up research in attempt to reduce aminocyclopyrachlor bioavailability. Pseudo-steady state sorption studies with biochar, soil, and biochar-soil systems (<10% biochar by weight) were performed on the same soils as the initial experiments. Incorporating activated charcoal into the soil removed nearly all of the aminocyclopyrachlor in solution and would potentially limit the bioavailability of aminocyclopyrachlor to non-target flora. Biochar produced from olive mill waste feedstock was the most effective biochar that we assessed for reducing the aqueous herbicide concentration. We concluded that although these chars reduced the aminocyclopyrachlor concentration, implementing biochar for remediation would require extraordinarily high application rates in order to reduce the concentration by 50%; at least 0.92×105 kg ha-1. Our analyses emphasize the need for additional research to identify dominant sorption-desorption mechanisms of aminocyclopyrachlor and indaziflam in a wide variety of soils to improve model predictions of their environmental fate.