Mechanistic approach for estimating bioconcentration of organic chemicals in earthworms (oligochaeta)

Abstract

AbstractEarthworms (Oligochaeta) represent an important food source for many vertebrates and as a result, predators may encounter toxic effects via the food chain (secondary poisoning) from consumption of contaminated worms. Therefore, including an assessment of secondary poisoning in risk assessment procedures is advisable. In this study, a mechanistic model is presented for estimating bioconcentration of organic chemicals in earthworms. It is assumed that bioconcentration can be described by a thermodynamic partitioning between soil solids, soil water, and the resident organism's tissues. For most chemicals, the lipid phase is the dominant site for sorption in the earthworm, but for more hydrophilic compounds, the water phase may also play a role. Model predictions are compared to literature data that were derived from experiments with earthworms in water, laboratory experiments with various soils, and from field experiments. Without calibration, the model was able to accurately predict bioconcentration factors (BCFs) from experiments in water, indicating the applicability of this theoretical approach. However, BCFs in soil were consistently overestimated by the model (on average a factor of 5.6), which may be due to the absence of true equilibrium conditions in the soil‐pore water‐earthworm system. The collected experimental data reveal no net influence of uptake via soil ingestion, growth dilution, or sorption to dissolved organic carbon. Field data were more variable, but were generally consistent with the model. Nevertheless, before field data can be accurately predicted, the influences of chemical sorption, sorption kinetics, and earthworm behavior must be quantified under field conditions.