ASSESSING THE IMPACT OF COMPLEXATION BY EDTA AND DTPA ON HEAVY-METAL TOXICITY USING MICROTOX BIOASSAY

The influence of complexation by ethylenediaminetetraacetic acid (EDTA ) and diethylenetriaminepentaacetic acid (DTPA) on the toxicity of iro n(III), cadmium, copper, mercury, lead and zinc was investigated. Micr otox bioassay, based on measuring the bioluminescence of Photobacteriu m phosphoreum, was used as an indication of toxicity. The reproducibil ity of data revealed correlation coefficients between 0.936-1.000. The results suggest that the complexation by these chelating agents incre ases the toxicity of iron, has very low or no influence on the toxicit y of Cu, Cd and Hg, and reduces noticeably the toxicity of Zn and Pb. The slopes of the dose-response curves were steeper for metal complexe s than for metals, suggesting that the mechanism of action of the toxi city changes during complexation. The inhibitory effect of EDTA and DT PA on metal toxicity is explained to be due to binding the reactive si tes of the heavy metal ions and thus preventing their normal action. ( C) 1996 Elsevier Science Ltd.