Pure and Applied Chemistry

Abstract: Current knowledge indicates that total urinary arsenic is not a suitable biomarker of exposure to toxic, i.e., inorganic, arsenic (iAs), whereas measurement of iAs and its methylated metabolites in urine using speciation analysis provides much more reliable estimates of exposure. The relative proportions of urinary iAs, monomethylarsonate (MA), and dimethylarsinate (DMA) can be used as a measure of methylation capacity, provided that there are no confounding factors such as consumption of food rich in DMA or containing As compounds metabolized to DMA. We analyzed by gradient elution anion-exchange HPLC-ICP-MS (high-performance liquid chromatography-inductively coupled plasma-mass spectrometry) urine samples from 153 residents in Latium (central Italy) chronically exposed to iAs via water and food. Excluding 26 subjects that excreted high concentrations of arsenobetaine (AB) (≥50 μg As/L) due to seafood consumption, iAs and related metabolites summed up about 75 % of total urinary As as measured by ICP-MS. AB and other organoarsenic compounds were detected at low concentrations in all urine samples. Considering all subjects, the sum of iAs and metabolites ranged 2–72 μg/L and relative proportions were iAs 14 %, MA 13 %, and DMA 72 % (median values), with a wide individual variability. In addition to the above arsenocompounds, the analytical method used in this study enabled the detection of dimethylthioarsinic acid (DMTA), which was found to be present in 33 % of the samples at concentrations ranging mostly from trace amounts to ~6 μg As/L. We found that part of the certified DMA content of human urine reference material SRM 2669 was present as DMTA. Four unknown arsenicals were also detected as minor species in a small proportion of samples.