Urinary excretion of inorganic arsenic and its metabolites after repeated ingestion of sodium metaarsenite by volunteers

Summary

Arsenic (125, 250, 500 or 1000 μg as NaAsO₂) was administered orally once a day for five consecutive days to 4 volunteers who refrained from eating marine organisms during the experiment. Urine was collected during 24-h periods starting one day before the first administration and up to 14 days later. The following determinations were performed: total arsenic, inorganic arsenic (As;), monomethyl arsenic (MMA) and dimethylarsinic (DMA) acids. In each case, the sum of As;, MMA and DMA approximated very closely the urinary concentration of total arsenic determined after mineralisation of the urine sample. It was concluded that these arsenicals are the only metabolic forms of arsenic following absorption of inorganic arsenic. Since a steady state in the urinary excretion of arsenic is reached within 5 days, our results demonstrated that at equilibrium, the total amount of arsenic excreted in urine per day amounts to 60% of the ingested dose. Speciation of the arsenic metabolites in urine indicated that the arsenic methylation capacity of the human body was not yet saturated, even with an oral daily dose of 1000 μg As for 5 days. However, when the administration of arsenic was stopped, the biological half life of arsenic in urine increased slightly with the dose (from 39 h at 125 μg to 59 h at 1000 μg). Determination of inorganic arsenic, MMA and DMA in urine appears to be the method of choice for the biological monitoring of workers exposed to inorganic arsenic since these measurements are not influenced by the presence of organoarsenicals from marine origin. From the linear relationship found in this study between arsenic administered and that excreted in urine, it was estimated that a time-weighted average exposure of 50 μg As/m³ would lead to an average urinary excretion of 220 μg As (sum of As_i, MMA and DMA) per gram creatinine.