Solubilization by nitrilotriacetic acid (NTA) of genetically active Cr(VI) and Pb(II) from insoluble metal compounds

Abstract

Solubilization of heavy metals by chelating agents is well documented and is recognized as the major hazard deriving from the introduction of NTA in the environment, as a consequence of its use as a substitute for polyphosphates in household detergents. We already observed that solubilization of heavy metals by NTA is accompanied by an increase of their genotoxic effects in bacteria and mammalian cells. Here we determined the frequencies of sister chromatid exchanges (SCE) in Chinese hamster CHO cells, and found that they are significantly increased by insoluble salts of Cr(VI) (PbCrO 4: ≧ 10 −6 M) and Pb(II) (PbSO 4: 10 −6 to 10 −4 M). A further significant increase of this effect is produced when treatments with metal compounds are performed in the presence of equimolar concentrations of NTA. An interaction of NTA with the insoluble metal compounds is also inferrable from statistically significant increases in the frequencies of micronuclei and chromosomal aberrations in human lymphocytes treated in vitro with PbCrO 4 (10 −6 − 10 −4 M) and PbSO 4 (3×10 −5 − 3×10 −3 M) in the presence of NTA, compared to the frequencies induced by metals alone. These results were obtained by solubilizing metals with NTA at very high concentrations (300 mg/l for PbCrO 4/NTA; 3,000 mg/l for PbSO 4/NTA) and by treating the cells with very dilute solutions (0.003 – 0.3 mg/l for PbCrO 4/NTA and 0.03 – 3 mg/l for PbSO 4/NTA). We have also shown by the SCE test on CHO cells that even much lower concentrations of NTA (0.25 – 1 mg/l), such as those that are possibly found in highly contaminated environmental situations, are able to solubilize genetically active metals from dilute suspensions of PbCrO 4 (1 – 4 mg/l) and PbSO 4 (10 – 40 mg/l). NTA enhanced the induction of SCE by PbCrO 4 and PbSO 4 even in the presence, in the preincubation solution and in the medium used to treat CHO cells, of Na + and K + concentrations largely exceeding (e.g. 10 2 – 10 6 times) those of the genotoxic metals.