Metabolism of inorganic arsenic in children with chronic high arsenic exposure in northern Argentina

This study concerns the metabolism of inorganic arsenic (As) in children in three villages in northern Argentina: San Antonio de los Cobres and Taco Pozo, each with about 200 mu g As/l in the drinking water, and Rosario de Lerma, with 0.65 mu g As/l. Findings show that the concentrations of As in the blood and urine of the children in the two As-rich villages were on average 9 and 380 mu g/l, respectively, the highest ever recorded for children. The concentrations were about 10 and 30 times higher for blood and urine, respectively, than in Rosario de Lerma. Total As in urine was only slightly higher than the sum of metabolites of inorganic As (U-As-met) i.e., inorganic As, methylarsonic acid (MMA), and dimethylarsinic acid (DMA); this shows that inorganic As was the main form of As ingested. In contrast to previous studies on urinary metabolites of inorganic As in various population groups, the children and women in the present study excreted very little MMA. Thus, there seems to be a polymorphism for the enzymes (methyltransferases) involved in the methylation of As. Interestingly, the children had a significantly higher percentage of inorganic As in urine than the women, about 50% versus 32%. Also, the percentage of inorganic As in the children is considerably higher than in previous studies on children (about 13% in the two studies available) and adults (about 15-25%) in other population groups. This may indicate that children are more sensitive to As-induced toxicity than adults, as the methylated metabolites bind less to tissue constituents than inorganic As. In the children, the percentage inorganic arsenic in urine decreased, and the percentage of DMA increased with increasing U-As-met, indicating an induction of As methylation with increasing exposure.