Oxidative stress, cytoxicity, and cell mortality induced by nano-sized lead in aqueous suspensions.

This paper reports on the effect of aqueous and nano-particulated Pb on oxidative stress (lipid peroxidation), cytoxicity, and cell mortality. As determined by the Thiobarbituric Acid Reactive Substances (TBARS) method, only 6h after incubation aqueous suspensions bearing nano-sized PbO(2), soluble Pb(II), and brain-homogenate only suspensions, were determined to contain as much as ca. 7, 5, and 1 nmol TBARS mg protein(-1), respectively. Exposure of human cells (central nervous system, prostate, leukemia, colon, breast, lung cells) to nano-PbO(2) led to cell-growth inhibition values (%) ca. ≤18.7%. Finally, as estimated by the Artemia salina test, cell mortality values were found to show high-survival larvae rates. Microscopic observations revealed that Pb particles were swallowed, but caused no mortality, however.

Arsenic(III) methylation in betaine-nontronite clay-water suspensions under environmental conditions.

This paper reports arsenic methylation in betaine-nontronite clay-water suspensions under environmental conditions. Two nontronites (<0.05 mm), NAu-1 (green color, Al-enriched) and NAu-2 (brown color, Al-poor, contains tetrahedral Fe) from Uley Mine - South Australia were selected for this study. Betaine (pK(a)=1.83) was selected as methyl donor. The reaction between 5 g L(-1) clay, 20 ppm As(III), and 0.4M betaine at 7< or =pH(0)< or =9 under anoxic conditions was studied. The presence of nontronite clays were found to favor As(III) conversion to monomethylarsenic (MMA). Arsenic conversion was found to be as high as 50.2 ng MMA/ng As(III)(0). Conversion of As was found to be more quantitative in the presence of NAu-2 ((Na(0.72)) [Si(7.55) Al(0.16)Fe(0.29)][Al(0.34) Fe(3.54) Mg(0.05)] O(20)(OH)(4)) than NAu-1 ((Na(1.05)) [Si(6.98) Al(0.95)Fe(0.07)][Al(0.36) Fe(3.61) Mg(0.04)] O(20)(OH)(4)). The inherent negative charge at the nontronite tetrahedral layer stabilizes positively charged organic intermediate-reaction species, thereby leading to decreases in the overall methylation activation energy. The outcome of this work shows that nontronite clays catalyze As methylation to MMA via non-enzymatic pathway(s) under environmental conditions.