Pesticide residues remaining in soils from previous growing season(s) - Can they accumulate in non-target organisms and contaminate the food web?

Abstract

Epoxiconazole, tebuconazole, flusilazole, prochloraz, pendimethalin, and the atrazine transformation product (2-hydroxyatrazine) have been found in Czech arable soils at high detection frequencies and/or concentrations. As they have been shown to persist from one growing season to following ones, the question arises of whether they can be taken up by non-target soil organisms and by subsequently planted crops. To reveal this, soils field-contaminated with pesticide residues were subjected to laboratory microcosm studies to measure i) dissipation rates, ii) accumulation in earthworms and lettuce, and iii) exposure by means of solid-phase microextraction (SPME). In parallel, tests with a freshly laboratory-contaminated soil were performed and represented the worst case scenario to be compared with. It was observed that at the residual levels (≤0.1 mg/kg), the behavior of field aged and fresh residues was similar, except for bioaccumulation in earthworms that was significantly lower for aged residues than for fresh residues. Residues' potential for bioconcentration was generally low, i.e., below the maximum residue limits (MRLs) of lettuce. This is in line with SPME results showing low levels of exposure via soil porewater. It follows that these pesticide residues are not likely to pose significant threats to the soil environment, the food web and, consequently, human health if present in soils at levels of ≤0.1 mg/kg.