New Method and Detection of High Concentrations of Monomethylarsonous Acid Detected in Contaminated Groundwater

Abstract

Monomethylarsonous acid (MMAIII) was detected in groundwater from a former herbicide production plant in the USA. The site has total arsenic concentrations up to thousands of mg/L, representing one of the most severe cases of arsenic contamination ever reported. Structure-specific detection of MMAIII, along with arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV), was achieved using liquid chromatography separation with electrospray ionization tandem mass spectrometry detection (HPLC-ESI-MS/MS). To enable the electrospray of MMAIII and AsIII, dimercaptosuccinic acid (DMSA) was used to derivatize these trivalent arsenicals online, so that their complexes with DMSA could be detected using negative ionization ESI-MS/MS. The presence of MMAIII was verified using high resolution mass spectrometry to measure accurate mass, tandem mass spectrometry to monitor fragmentation, and three different separation techniques to resolve arsenic species. The measured accurate mass of the suspected MMAIII compound in a groundwater sample was 122.9607+/-0.0003 amu, which was in good agreement with the theoretical value and that of the MMAIII standard. Simultaneous monitoring of AsO+ at m/z 91 and SO+ at m/z 48 using HPLC-ICPMS operating in dynamic reaction cell mode ruled out possible confounding from any sulfur-containing arsenic compound. The concentrations of MMAIII found in the groundwater samples from a contaminated site were as high as 3.9-274 mg/L, the highest ever observed in the environment.

Demethylation of methylarsonic acid by a microbial community

“…Considering that As(III) is less toxic than MAs(III), demethylation of MAs(III) to As(III) by Streptomyces might be a detoxification process. It is interesting to note that groundwater from a former herbicide production plant on the Menominee River in Wisconsin was shown to contain high concentrations of MAs(III) (McKnight-Whitford et al ., 2010), which suggests that first microbial reduction of MAs(V) may be widespread and second that MAs(III) is indeed a problem even with an oxidizing atmosphere. Following demethylation, some microorganisms can re-methylate As(III), but, again, the genome of the closely related Streptomyces ceolicolor does not have an arsM gene.…”

Impact of Microorganisms on Arsenic Biogeochemistry: A Review

“…Instead of aqueous methyl As, numerous studies showed the formation of gaseous methyl arsines such as Methanobacterium bryantii (McBride 1971), Methanobacterium formicium, Clostridium collagenovorans, Desulfovibrio gigas and Desulfovibrio vulgaris (Michalke et al 2000). Trivalent methyl As (monomethylarsonous acid and dimethylarsinous acid) were proposed to be the intermediates of As methylation according to Challenger's pathway, and have been detected in both environmental samples (Huang et al 2011b;McKnight-Whitford et al 2010) and human cells (Hippler et al 2011). However, both monomethylarsonous acid and dimethylarsinous acid have not yet been found during microbial As methylation.…”

The Methylation of Metals and Metalloids in Aquatic Systems

“…Arsenic speciation and methylation in freshwater ecosystems has also received attention and this has been driven mostly by studies in As contaminated environments. Methylation processes are similar to that found in the ocean with most of the methylated species being confined to the surface waters and levels in deeper waters depending on a variety of conditions [46][47][48][49][50]. Both seasonally and permanently stratified lakes have been examined and while high levels of the inorganic forms of As are found in anoxic waters, this is not the case for the methylated species.…”