Methylation of tin(II) by methyl iodide under simulated estuarine conditions in the absence and presence of fulvic acid

Abstract

This paper describes the methylation of tin(II) chloride and the formation of monomethyltin under conditions that model the estuarine environment. Two sets of factorial experimental designs clarified the significance of pH, salinity, and methyl iodide (MeI) concentration on monomethyltin formation in the absence and presence of fulvic acid (FA). The reactions gave percent yields for monomethyltin of 0.30 to 9.95 in the absence of FA and 0.18 to 4.90 in its presence. No other methyltin product occurred and several potential methylating agents failed to methylate tin(II). Analyses of variance (ANOVA) calculations at the 95% confidence level showed a high significance of MeI and FA concentrations in the methylation reactions. Increasing MeI concentration favors methylation while increasing FA concentration inhibits it. Calculations showed the distribution of tin(II) species was only slightly affected in the pH range of our experiments and was virtually unaffected by salinity and FA concentration. These results suggest that chemical processes can contribute to the formation of methyltin compounds in natural waters.