The impact of soil organic matter and soil sterilisation on the bioaccessibility of 14C-azoxystrobin determined by desorption kinetics

Abstract As soils represent a major sink for most pesticides, factors influencing pesticide degradation are essential in identifying their potential environmental risk. Desorption of 14 C-azoxystrobin was investigated over time in two soils under sterile and non-sterile conditions using exhaustive (solvent) and non-exhaustive (aqueous) methods. Desorption data were fitted to a two-compartment model, differentiating between fast and slow desorbing fractions. With increased ageing, rapid desorption ( F rap ) (bioaccessibility) decreased with corresponding increases in slowly desorbing fractions ( F slow ). The rapid desorption rate constant ( k fast ) was not affected by ageing, sterility or extraction solvent. The non-exhaustive extractions had similar desorption profiles; whereas exhaustive extractions in aged soils had the highest F rap . In non-sterile soil, F rap was lower resulting in higher F slow , while desorption rates remained unaffected. Organic matter (OM) reduces F rap ; but not desorption rates. Microorganisms and OM enhanced ageing effects, reducing the fraction of fast desorbing chemicals and potentially the bioaccessibility of pesticides in soil.