Effect of ageing and chemical form on the bioavailability and toxicity of Pb to the survival and reproduction of the soil invertebrate Enchytraeus crypticus.

This study investigated the effect of ageing on the bioavailability and toxicity of lead nitrate (Pb(NO)) and lead oxide (PbO) to Enchytraeus crypticus in LUFA 2.2 natural soil. The potworms were exposed after 2 weeks pre-incubation and after ageing the spiked soils for 3, 6, 12 and 18 months. Survival and reproduction after 21 d exposure were related to total, 0.01 M CaCl-extractable and porewater Pb concentrations in the soil and internal Pb concentrations in the surviving animals. Pb concentration in pore water showed little change during ageing for Pb(NO) but increased strongly for PbO-spiked soils. During ageing, toxicity of Pb(NO) did not change with LC50s and EC50s for the effect on enchytraeid survival and reproduction based on total soil Pb concentrations being constant at 523-619 and 89.8-99.4 mg Pb/kg dry soil, respectively. Toxicity of PbO, however, increased with LC50s and EC50s decreasing from 4830 to 1889 mg Pb/kg dry soil and from 151 to 97.5 mg Pb/kg dry soil, respectively. When related to internal Pb concentrations LC50s did not differ for both Pb forms at different ageing periods and were 73.4-78.7 mg Pb/kg dry body wt. Survival was better explained from internal Pb concentrations in the worms than from total or available Pb concentrations in the soil. Reproduction toxicity (EC50s) and Pb uptake in the worms however, were better explained from 0.01 M CaCl-extractable Pb concentrations in the soil. The latter finding could provide a scientific basis for the ecological risk assessment of contaminated soils and the derivation of soil quality standards based on extractable concentrations.