Association between total ingested arsenic and toenail arsenic concentrations

The association between arsenic exposure from drinking water and toenail arsenic concentrations appears to be non-linear at low exposure levels. To investigate whether this observation is a result exposure misclassification, a dietary exposure assessment was conducted in a cohort of 47 women concurrently enrolled in a prospective longitudinal biomonitoring study in Pabna, Bangladesh. Arsenic intake was evaluated using a duplicate diet study design which collected food and water samples for a total of 6 days. Total inorganic arsenic was measured in 24-hour composite food samples (N = 282) using inductively coupled plasma-mass spectrometry coupled with a dynamic reaction cell (ICP-DRC-MS). Average annual tubewell arsenic concentrations and toenail arsenic concentrations were computed for each participant using biomonitoring data from the prospective study. Separate multivariate regression models evaluated the association between drinking water, total dietary intake, and total dietary dose with toenail arsenic, a biomarker of internal dose. In these models, dietary intakes were adjusted using the residual method to provide estimate that was independent of water arsenic concentrations. Median daily arsenic intake from food and drinking water was 48.3 μg/day and 4.2 μg/day. Taking into consideration participant's body weight, the median daily arsenic dose was 1.0 μg/kg-day from food and 0.1 μg/kg-day from drinking water although drinking water exposure was highly skewed and was the dominant exposure route for the upper 25th percentile of the distribution. The regression model that used total daily arsenic intake from food (β = 0.46; 95%CI: 0.18-0.73) and drinking water (95%CI: 0.26-0.38) explained the most variability in toenail arsenic concentrations (R2a = 0.71). The effect estimates for food and drinking water are similar suggesting that both sources have a similar contribution to internal dose.