Responses of a non-target organism to metalliferous field soils amended by a phytoremediation-promoting chelator (EDTA): The earthworm, Eisenia fetida

The chelator EDTA is widely used to increase metal solubility and efficiency of phytoremediation. The main study aim was to assess EDTA (0.1 g/kg) effects on soil metal (Mn, Ni, Pb, Zn) solubility (0.01 M CaCl2-extractable), and tissue metal accumulation and toxic effects on demographic indicators in Eisenia fetida (Oligochaeta) exposed to four contrasting metal-contaminated soils: (i) an acidic, moderately Pb+Zn-contaminated mine soil (“Stream”); (ii) a circumneutral, heavily Pb+Zn-contaminated mine soil (“Draethen”); (iii) a heavily Mn-contaminated mine soil (“Barmouth”); (iv) a soil adjacent to a working Ni smelter (“Clydach”). Chelator treatment lowered soil pH (from 4.28 to 4.13), increased edaphic Pb solubility (101%), increased tissue Pb concentration and worm mortality in Stream soil; comparable effects were not found for Pb in Draethen soil, or for Zn in either of the two Pb/Zn-mine soils. EDTA addition to Barmouth soil did not alter Mn solubility or tissue accumulation, but suppressed cocoon production (35%) without increasing mortality. EDTA addition to Clydach soil did not alter Ni solubility, but resulted in a small increase in tissue Ni without altering demographic parameters. We conclude that the risk of chelator amendments causing unwelcome side effects on non-target, ecologically relevant, soil organisms is highest in acidic, base-poor, polluted soils.