The effect of EDTA and fulvic acid on Cd, Zn, and Cu toxicity to a bioluminescent construct (pUCD607) of Escherichia coli

The hypothesis, that metal toxicity is dominated by free ion activity, was tested by comparing calculated metal activities with measured toxic respons es to a genetically modified, luminescent bacterium, Escherichia coli. The toxicity of Cd, Cu, and Zn sulphate salts in the presence of EDTA and fulvi c acid in well-defined solutions was measured. Good agreement between free metal activity and toxicity was found for Cu but not for Zn and Cd. The tox icity relationships were altered by glucose addition to the organism. Stabl e chloride complexes may have contributed to the toxicity of Cd under the t est conditions. The results suggest that there is not always a simple relat ionship between toxicity and free-ion metal concentration and that further account should be taken of competitive interactions between living cells an d ligands and the physiological status of the organism. (C) 1999 Elsevier S cience Ltd. All rights reserved.