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 iron(III), cadmium, copper, mercury, lead and zinc was investigated. Microtox bioassay, based on measuring the bioluminescence of Photobacterium phosphoreum, was used as an indication of toxicity. The reproducibility of data revealed correlation coefficients between 0.936-1.000. The results suggest that the complexation by these chelating agents increases the toxicity of iron, has very low or no influence on the toxicity 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 complexes than for metals, suggesting that the mechanism of action of the toxicity changes during complexation. The inhibitory effect of EDTA and DTPA on metal toxicity is explained to be due to binding the reactive sites of the heavy metal ions and thus preventing their normal action.