Toxicokinetics and toxicodynamics of lead in the soil invertebrate Enchytraeus crypticus

- Pb body concentration and toxicity were dependent on exposure concentration and time.
- Pb toxicity showed a delay compared to Pb bioaccumulation in E. crypticus.
- Pb uptake reached steady state in 7 days, Pb toxicity not even after 21 days.
- Internal concentration was a better measure of Pb toxicity than exposure concentration.
- Linking toxicokinetics to toxicodynamics may account for the effects of exposure time.

The aim of the present study was to link Pb toxicokinetics to toxicodynamics in Enchytraeus crypticus. The enchytraeids were exposed for 14 d to different Pb concentrations (uptake phase) in natural Lufa 2.2 soil, followed by a 14-d elimination phase in clean soil. Pb accumulation and enchytraeid mortality were determined at different time intervals. At each exposure concentration, internal Pb concentration increased with exposure time and achieved equilibrium in approximately 7 d. Median lethal concentration (LC50) based on total Pb concentration in soil decreased with exposure time, but did not reach a steady-state level. Pb toxicity, therefore, showed a delay compared to accumulation in E. crypticus. LC50s based on internal Pb concentrations in the surviving animals did reach steady state in approx.14 d, suggesting that linking toxicokinetics to toxicodynamics may reduce the effects of time. This study highlighted that exposure time, as an important factor in metal uptake and toxicity, should be taken into account in ecotoxicological tests for risk assessment.

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