Effect of soil properties on Pb bioavailability and toxicity to the soil invertebrate Enchytraeus crypticus

The present study investigated the bioavailability and toxicity of lead to the potworm Enchytraeus crypticus in six soils with different properties. Pb partitioning between the soil solution and solid phase was affected by soil organic matter (OM) content, cation exchange capacity (CEC) and water holding capacity (WHC). After 21 d exposure, Pb bioaccumulation in the enchytraeids was positively correlated with total soil Pb concentration. Bioaccumulation was best predicted by Pb availability (CaCl₂-extractable and porewater Pb concentrations), and by the Ca concentration in pore water and the CEC of the soils. Toxicity varied greatly among soils, with LC50s and EC50_reproductions based on total Pb concentrations ranging from 246 to >3092 and from 81 to 1008 mg Pb/kg dry soil, respectively. The variation in LC50s among soils was explained by differences in CaCl₂-extractable Pb concentrations in soil and internal Pb concentrations in the animals. The differences in EC50_reproductions could be explained from the CaCl₂-extractable Pb concentrations in the soils. Although it was also correlated with CEC and porewater Ca concentration, pH_CaCl2 was the dominating factor for predicting Pb toxicity based on total soil concentrations. This study demonstrates that soil properties, such as pH, CEC and Ca concentration in pore water, significantly affected the bioavailability and toxicity of Pb and therefore should be taken into account when assessing the ecological risk of metals in contaminated soils.