USE OF METAL CHELATING-AGENTS TO DIFFERENTIATE AMONG SOURCES OF ACUTEAQUATIC TOXICITY

Metals are common toxicants found in effluents and other environmental samples. Within Toxicity Identification Evaluation methods proposed b y the U.S. Environmental Protection Agency and others, addition of eth ylenediaminetetraacetic acid (EDTA) is used as an indicator of metal t oxicity. Previous experiments showed that addition of sodium thiosulfa te, originally included to detect toxicity due to oxidants, was also e ffective at reducing toxicity from some common metals. In the present study, we characterized the effectiveness of both EDTA and thiosulfate in removing the toxicity of 16 different metal ions to Ceriodaphnia d ubia. Ethylenediaminetetraacetic acid addition removed toxicity associ ated with all cationic metals tested except for Cr3+, Fe2+, Al3+, and Ag+. Thiosulfate addition was less effective than EDTA for Zn2+, Mn2+, Pb2+, and Ni2+, but reduced toxicity of both Ag+ and selenite (Se[VI] ), which EDTA did not. Results of this research can be used to categor ize metal toxicity in unknown samples based on the response to additio ns of EDTA and thiosulfate.