Arsenic accumulation and toxicity in the earthworm Eisenia fetida affected by chloride and phosphate

Chloride and phosphate (PO4) were added to field soils contaminated with arsenic and heavy metals, and Eisenia fetida were inoculated in these treated soils for 70 d. After 28 d, earthworm survival, body weight, and cocoon production were measured. During the exposure period, the accumulation of As and four metals (Cu, Zn, Cd, and Pb) in E. fetida was analyzed. Bulk soils and soil solutions were characterized for the contents of As, metals, organic matter, and major cations and anions; cation exchange capacity; and pH. Although addition of Cl to the soil did not impact As toxicity, it significantly reduced As uptake. The addition of PO4 induced changes in As toxicity and reduced As accumulation even though the As concentration in the soil pore water increased because of the substitution of As by P at soil sorption sites. These results imply that the addition of Cl induced the formation of an As-Cl complex, thereby resulting in decreased As bioavailability; they also imply that monovalent phosphate (H2PO4(-)) competes with As for uptake through transporter-mediated mechanisms in cells.