“…Thus, it was likely that the formation of reactive methylated species containing As(III) should be considered as an activation process, which could increase the toxic potential of arsenic ingested as inorganic arsenic. Evidence that humans exposed to inorganic arsenic excrete MMA(III) and DMA(III) in urine (Le et al, 2000;Del Razo et al, 2001b) was consistent with the prediction of the Challenger scheme for methylation. Differences among individuals in the formation of reactive intermediates could be a determinant of the risk associated with exposure to inorganic arsenic.…”