Modelling the effects of the pyrethroid insecticide cypermethrin on the life cycle of the soil dwelling annelid Enchytraeus crypticus, an original experimental design to calibrate a DEB-TKTD model

The Dynamic Energy Budget theory (DEB) enables ecotoxicologists to model the effects of chemical stressors on organism life cycles through the coupling of toxicokinetic-toxicodynamic (TK-TD) models. While good progress has been made in the application of DEB-TKTD models for aquatic organisms, applications for soil fauna are scarce, due to the lack of dedicated experimental designs suitable for collecting the required time series effect data. Enchytraeids (Annelida: Clitellata) are model organisms in soil ecology and ecotoxicology. They are recognised as indicators of biological activity in soil, and chemical stress in terrestrial ecosystems. Despite this, the application of DEB-TKTD models to investigate the impact of chemicals has not yet been tested on this family. Here we assessed the impact of the pyrethroid insecticide cypermethrin on the life cycle of Enchytraeus crypticus. We developed an original experimental design to collect the data required for the calibration of a DEB-TKTD model for this species. E. crypticus presented a slow initial growth phase that has been successfully simulated with the addition of a size-dependent food limitation for juveniles in the DEB model. The DEB-TKTD model simulations successfully agreed with the data for all endpoints and treatments over time. The highlighted physiological mode of action (pMoA) for cypermethrin was an increase of the growth energy cost. The threshold for effects on survival was estimated at 73.14 mg kg(-1), and the threshold for effects on energy budget (i.e., sublethal effects) at 19.21 mg kg(-1). This study demonstrates that DEB-TKTD models can be successfully applied to E. crypticus as a representative soil species, and may improve the ecological risk assessment for terrestrial ecosystems, and our mechanistic understanding of chemical effects on non-target species.

Automated summary

The use of the Dynamic Energy Budget theory (DEB) and toxicokinetic-toxicodynamic (TK-TD) models allows ecotoxicologists to model the effects of chemical stressors on organism life cycles. However, the application of DEB-TKTD models for soil fauna has been limited due to a lack of appropriate experimental designs. In this study, the impact of the insecticide cypermethrin on the life cycle of Enchytraeus crypticus was assessed, and an original experimental design was developed to collect necessary data for the calibration of a DEB-TKTD model. The simulations of the DEB-TKTD model successfully agreed with the collected data, demonstrating its potential in ecological risk assessment for terrestrial ecosystems and understanding chemical effects on non-target species.