Interactions of chromium with nitrilotriacetic acid (NTA) in the induction of genetic effects in bacteria†

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Abstract
The genotoxic activity of NTA, which is a substitute for polyphosphates in household laundry detergents, as well as the interactions between NTA and soluble (potassium dichromate) and insoluble (lead chromate) Cr(VI) compounds in the induction of gene mutations and DNA damage in bacteria were investigated. NTA did not induce point mutations in S. typhimurium TA100 strain, independently of the presence of rat liver metabolic activation, nor did it modify the direct mutagenicity of potassium dichromate. Insoluble lead chromate was instead clearly mutagenic in the Salmonella/microsome assay only in the presence of NTA, and the levels of mutagenicity correlated very well with the amounts of Cr(VI) solubilized by NTA in the form of chromate ion, as determined by the colorimetric reaction with diphenylcarbazide. In a fluctuation test using E. coli WP2 uvrA, NTA was not mutagenic, but it significantly increased the mutagenicity of potassium dichromate besides that of lead chromate. Conversely, as assessed by means of three different procedures, NTA consistently yielded an increased lethality in repair‐deficient E. coli strains of the WP2 series, various genetic mechanisms being involved in repairing the specific DNA damage. Moreover, mixture of NTA with insoluble lead chromate resulted in the release of genotoxic Cr(VI) ion. Finally, NTA was negative in the SOS chromotest, evaluating the induction of SOS DNA repair mechanisms in E. coli PQ37. These results confirm the ability of NTA to elicit the genotoxicity of insoluble heavy metals in bacteria, indicate that also the interaction of NTA with soluble metals can result in a moderate increase of some genetic effects, and point to a possible direct genotoxicity of NTA itself, at least as far as the induction of DNA damage is concerned.