Systematic Underestimation of Pesticide Burden for Invertebrates under Field Conditions: Comparing the Influence of Dietary Uptake and Aquatic Exposure Dynamics

Pesticides used inagriculture can end up in nearby streams andcan have a negative impact on nontarget organisms such as aquaticinvertebrates. During registration, bioaccumulation potential is ofteninvestigated using laboratory tests only. Recent studies showed thatthe magnitude of bioaccumulation in the field substantially differsfrom laboratory conditions. To investigate this discrepancy, we conducteda field bioaccumulation study in a stream known to receive pollutantloadings from agriculture. Our work incorporates measurements of streampesticide concentrations at high temporal resolution (every 20 min),as well as sediment, leaves, and caged gammarid analyses (every 2-24h) over several weeks. Of 49 investigated pesticides, 14 were detectedin gammarids with highly variable concentrations of up to 140 & PLUSMN;28 ng/g(ww). Toxicokinetic modeling using laboratory-deriveduptake and depuration rate constants for azoxystrobin, cyprodinil,and fluopyram showed that despite the highly resolved water concentrationsmeasured, the pesticide burden on gammarids remains underestimatedby a factor of 1.9 & PLUSMN; 0.1 to 31 & PLUSMN; 3.0, with the highest underestimationsoccurring after rain events. Including dietary uptake from polluteddetritus leaves and sediment in the model explained this underestimationonly to a minor proportion. However, suspended solids analyzed duringrain events had high pesticide concentrations, and uptake from themcould partially explain the underestimation after rain events. Additionalcomparison between the measured and modeled data showed that the pesticidedepuration in gammarids is slower in the field. This observation suggeststhat several unknown mechanisms may play a role, including loweredenzyme expression and mixture effects. Thus, it is important to conductsuch retrospective risk assessments based on field investigationsand adapt the registration accordingly.

Automated summary

Pesticides used in agriculture can negatively impact non-target organisms in nearby streams, with bioaccumulation levels differing significantly between field and laboratory conditions. A field study on pesticide bioaccumulation in a polluted stream revealed underestimations ranging from 1.9 to 31 times, especially pronounced after rain events, suggesting potential unknown mechanisms at play. Additional factors such as slower depuration rates in field conditions and uptake from suspended solids during rain events may contribute to the discrepancies observed.