Plant protection products in agricultural fields – residues in earthworms and assessment of potentially toxic effects to the environment

The environmental risk assessment of plant protection products for soil organisms is mainly based on the results of laboratory and extended laboratory studies while the link from the laboratory to realistic field conditions over several seasons is not well established. The current environmental risk assessment is applied to a single active ingredient and does not consider that soil organisms are exposed to varying degrees to a mixture of active ingredients from different pesticides. In this study, earthworm samples were collected from eight fields in Croatia during two growing seasons and analyzed for 300 active ingredients. The concentrations of 26 analyzed active ingredients ranged between 0.000 and 0.247 mg/kg earthworm fresh weight with a mean of 0.005 mg/kg earthworm fresh weight. The percentage of samples with values below the limit of detection (LOD = ½ LOQ), values below the limit of quantification (LOQ = 0.001 mg/kg) and values above LOQ were 33, 44 and 23 %, respectively. Based on publicly available draft assessment reports from European Commission and European Food Safety Authority, degradation parameters (DT50, DT90) were used to calculate degradation curves and the current concentration in soil at the date of earthworm sampling. Subsequently, compound-specific bioconcentration factors in soil were determined by dividing the analyzed pesticide residues in earthworms by the calculated concentrations in soil. The results of the study showed that most active ingredients do not pose a risk to earthworms and have no secondary poisoning potential to birds and mammals that feed on them. The retrospective analysis method of analytically measured neonicotinoid residues in earthworm samples can be reliably used to calculate degradation and concentration curves in soil at the time of sampling.