Simulate methylation reaction of arsenic(III) with methyl iodide in an aquatic system

Abstract

The methylation reaction of inorganic arsenic occurring in aquatic systems was studied by HPLC-HG-AFS as a method to separate and detect soluble methylarsenic species. Transformation from inorganic arsenic to methylarsenic was essential for major changes in toxicity to organisms. Monomethylarsenic [AsOCH 3 (OH) 2 ] was the only product in the methylation reaction of inorganic arsenic(III) with methyl iodide (MeI). This process can be described as an oxidative carbonium-ion transfer, with MeI acting as a methyl donor. From a thermodynamic point of view, the activity of the carbonium ion and pH were the two major influencing factors. The pH dependence of redox potential of As(III) was the reason for the effect of pH on methylation of arsenic. The influences of salinity and concentration of the methyl donor may be explained by their effects on the activity of carbonium. Moreover, kinetics experiments demonstrated that the methylation reaction was first-order for both As(III) and methyl iodide. First-order reaction rates were also calculated at different pH, salinity and MeI, and were found to be in the range 0.0026-0.0123 h −1 . The methylation rate varied largely under different reaction conditions.

Fumigant methyl iodide can methylate inorganic mercury species in natural waters

“…The net production rate of CH 3 Hg þ can be described as the difference of the photomethylation rate of inorganic mercury by CH 3 I (r  PAR) and the photodegradation rate of CH 3 Hg þ (k D ÂC CH3 Hg þ ÂPAR) at t time (equation (8)). Next, the function of C CH3Hg þ at t time could be obtained (equation (9)) by integrating equation (8). Degradation of CH 3 Hg þ can occur in natural waters and this process was deemed to be driven by sunlight 21,40 .…”

“…Compared with CH 3 Br, CH 3 I degrades more slowly in soil, hence increasing its chance of being transported to an aquatic environment via runoff 5,6 . CH 3 I is known to have the capability of methylating several metals and metalloids, including Sn 2 þ , As 3 þ , Pb 2 þ and Hg 0 , following an oxidative addition mechanism [7][8][9][10] . Among these metals/metalloids, mercury deserves special attention because its methylation product, methylmercury (CH 3 Hg þ ), is among the most widespread of all highly toxic contaminants.…”

Identification of mercury methylation product by tert-butyl compounds in aqueous solution under light irradiation

“…The pH and salinity are widely considered to be important factors influencing element methylation in aqueous solution (Chen et al, 2006(Chen et al, , 2007a(Chen et al, ,b, 2012Yin et al, 2012). Therefore, the influences of salinity and pH on the photo-methylation of inorganic Hg were also investigated in the present study, and the results are shown in Fig.…”

The Methylation of Metals and Metalloids in Aquatic Systems

“…(CH 3 ) 4 Pb + Hg II -> (CH 3 ) 3 Pb + + CH 3 Hg + ; and 2) methylation by other methyl-containing compounds such as methyliodide (CH 3 I). For example, experiments examining the potential for the abiotic methylation of As III by CH 3 I found that the reaction proceeded, but only at very high pH's (>10), above those typically found in the environment [100]. Monomethylarsenic was the only product formed.…”