Effects of Soil Properties on the Toxicity and Bioaccumulation of Lead in Soil Invertebrates

The present study examined the effects of soil physical and chemical properties on the toxicity of lead (Pb) to earthworms (Eisenia fetida) and collembolans (Folsomia candida), and on bioaccumulation of Pb by earthworms, in soils amended with Pb salts. Toxicity tests were conducted in 7 soils varying in soil properties (pH 4.7-7.4, effective cation exchange capacity [eCEC] 4-42 cmol_c /kg, organic carbon 10-50 g C/kg) that were leached and pH corrected after spiking with PbCl₂ . The median effect concentrations (EC50s) based on total soil Pb concentrations ranged from 35 to 5080 mg Pb/kg for earthworms and 389 to >7190 mg/kg for Collembola. Significant positive correlations were observed between log (EC50) for earthworm reproduction and log (eCEC, total C, exchangeable Ca and Mg, or clay content), but no significant correlations were observed between Pb toxicity to Collembola and soil properties. Expressing Pb dose as either the free ion (Pb²⁺ ) activity in porewater or as the measured dissolved porewater concentration of Pb did not explain differences in toxicity among soils. The bioaccumulation factors (BAFs) for Pb in earthworms ranged up to >10-fold across 6 soil treatments, with a median of 0.16, and the BAF was significantly correlated with eCEC (p = 0.038, r = -0.84), but not with any other soil properties. Soil properties related to eCEC (total C, exchangeable Ca and Mg, clay content) had a significant effect on Pb toxicity and bioaccumulation in earthworms, but no relationship was found for Collembola. As a major soil property affecting the bioavailability of Pb, CEC should be incorporated into any soil hazard assessment of Pb as a modifying factor of toxicity and bioaccumulation for earthworms. Environ Toxicol Chem 2019;38:1486-1494. © 2019 SETAC.