Ecotoxicity of cyanide complexes in industrially contaminated soils

This study deals with acute and chronic ecotoxicity of leachates from industrially contaminated soils. Analyses focused on cyanides (complex and free forms) to study their possible involvement in leachates toxicity. No acute toxicity on the Microtox and 48 h-Daphnia magna tests was found in leachates collected over 18 months, but a high chronic toxicity was recorded on the reproduction of Ceriodaphnia dubia (EC50-7d=0.31±0.07%) and on the algal growth of Pseudokirchneriella subcapitata (EC50-72 h=0.27±0.09%). Ceriodaphnids were as sensitive to free cyanide as to complex forms (EC50-7d as CN(-)=98 μg/L, 194 μg/L and 216 μg/L for KCN, Fe(CN)(6)K(3) and Fe(CN)(6)K(4), respectively). The EC50-72 h of KCN to P. subcapitata (116 μg/L) as CN(-) was also of the same level as the EC50-72 h of potassium ferricyanide (127 μg/L) and ferrocyanide (267 μg/L). Complex cyanides explained a major part of the toxicity of leachates of the soil. On the other hand, cyanide complexes had no effect on survival of the earthworm Eisenia fetida up to 131 mg CN(-)/kg, while potassium cyanide was highly toxic [EC50-14 d as CN(-)=74 μg/kg soil]. Thermodesorption treatment eliminated a majority of cyanides from the soil and generated much less toxic leachates. Complex cyanides must be integrated into environmental studies to assess the impact of multi-contaminated soils.