Bioavailability and chronic toxicity of bismuth citrate to earthworm Eisenia andrei exposed to natural sandy soil

The present study describes bioavailability and chronic effects of bismuth to earthworms Eisenia andrei using OECD reproduction test. Adult earthworms were exposed to natural sandy soil contaminated artificially by bismuth citrate. Average total concentrations of bismuth in soil recovered by HNO3 digestion ranged from 75 to 289 mg/kg. Results indicate that bismuth decreased significantly all reproduction parameters of Eisenia andrei at concentrations >= 116 mg/kg. However, number of hatched cocoons and number of juveniles seem to be more sensitive than total number of cocoons, as determined by IC50; i.e., 182, 123 and > 289 mg/kg, respectively. Bismuth did not affect Eisenia andrei growth and survival, and had little effect on phagocytic efficiency of coelomocytes. The low immunotoxicity effect might be explained by the involvement of other mechanisms i.e. bismuth sequestered by metal-binding compounds. After 28 days of exposure bismuth concentrations in earthworms tissue increased with increasing bismuth concentrations in soil reaching a stationary state of 21.37 mg/kg dry tissue for 243 mg Bi/kg dry soil total content. Data indicate also that after 56 days of incubation the average fractions of bismuth available extracted by KNO3 aqueous solution in soil without earthworms varied from 0.0051 to 0.0229 mg/kg, while in soil with earthworms bismuth concentration ranged between 0.310-1.347 mg/kg dry soil. We presume that mucus and chelating agents produced by earthworms and by soil or/and earthworm gut microorganisms could explain this enhancement, as well as the role of dermal and ingestion routes of earthworms uptake to soil contaminant.