Identification of dimethylarsinous and monomethylarsonous acids in human urine of the arsenic-affected areas in West Bengal, India

A speciation technique for arsenic has been developed using an anion-exchan ge highperformance liquid chromatography/inductively coupled argon plasma m ass spectrometer (HPLC/ICP MS). Under optimized conditions, eight arsenic s pecies [arsenocholine, arsenobetaine, dimethylarsinic acid (DMA(V)), dimeth ylarsinous acid (DMA(III)), monomethylarsonic acid (MMA(V)), monomethylarso nous acid (MMA(III)), arsenite (As-III), and arsenate (As-V)l can be separa ted with isocratic elution within 10 min. The detection limit of arsenic co mpounds was 0.14-0.33 mug/L. To validate the method, Standard Reference Mat erial in freeze-dried urine, SRM-2670, containing both normal and elevated levels of arsenic was analyzed. The method was applied to determine arsenic species in urine samples from three arsenic-affected districts of West Ben gal, India. Both DMA(III) and MMA(III) were detected directly (i.e., withou t any prechemical treatment) for the first time in the urine of some humans exposed to inorganic arsenic through their drinking water. Of 428 subjects , MMA(III) was found in 48% and DMA(III) in 72%. Our results indicate the f ollowing. (1) Since MMA(III) and DMA(III) are more toxic than inorganic ars enic, it is essential to re-evaluate the hypothesis that methylation is the detoxification pathway for inorganic arsenic. (2) Since MMA(V) reductase w ith glutathione (GSH) is responsible for conversion of MMA(V) to MMA(III) i n vivo, is DMA(V) reductase with GSH responsible for conversion of DMA(V) t o DMA(III) in vivo? (3) Since DMA(III) forms iron-dependent reactive oxygen species (ROS) which causes DNA damage in vivo, DMA(III) may be responsible for arsenic carcinogenesis in human.