Intra-individual variation in the metabolism of inorganic arsenic.
OBJECTIVE
Inorganic arsenic is metabolized to methylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are excreted in the urine. Previous studies have shown a marked inter-individual variation in the metabolism, but the within-person variation is unknown. Therefore, we determined the variation in the relative amount of urinary arsenic metabolites, i.e., inorganic arsenic, MMA and DMA, over time in women living in an Andean village with elevated arsenic levels in drinking water.


METHODS
For our investigation of the individual day-to-day variation, daily spot urine samples were collected (at the same time of the day) for 5 consecutive days by 15 women. For our investigation of the within-day variation, seven women collected all the urine voided over a 72-h period, each voided into a separate container.


RESULTS
Repeated measures analysis of variance (ANOVA) revealed no significant day-to-day variation, either in the relative distribution of inorganic arsenic metabolites (inorganic arsenic, MMA and DMA), or in the concentration of the metabolites. However, the percentage of DMA was slightly higher (on average 5.0%; P=0.003) and the percentage of inorganic arsenic lower (on average 5.8%; P=0.001) during the morning/day (03:00-15:00) compared with the evening/night (15:00-03:00). No within-day variation in the percentage of MMA was observed.


CONCLUSIONS
The arsenic methylation efficiency of an individual is remarkably stable over time.
Concha
Gabriela
G
Institute of Environmental Medicine, Karolinska Institute, Box 210, 171 77 Stockholm, Sweden.
Vogler
Gerardo
G
Nermell
Barbro
B
Vahter
Marie
M
D000328:Adult; D001152:Arsenicals / Q000378:metabolism* / Q000652:urine; D002101:Cacodylic Acid / Q000652:urine; D005260:Female; D006801:Humans; D008875:Middle Aged; D012015:Reference Standards; D013054:Spectrophotometry, Atomic; D013548:Sweden; D014881:Water Supply
D001152:Arsenicals; D002101:Cacodylic Acid; C020300:monomethylarsonic acid