Estimating perchlorate exposure from food and tap water based on US biomonitoring and occurrence data

Human biomonitoring data show that exposure to perchlorate is widespread in the United States. The predominant source of intake is food, whereas drinking water is a less frequent and far smaller contributor. We used spot urine samples for over 2700 subjects and estimated 24 h intake using new creatinine adjustment equations. Merging data from surveys of national health (NHANES) with drinking water monitoring (UCMR), we categorized survey participants according to their potential exposure through drinking water or food. By subtracting daily food doses of perchlorate from the oral reference dose (RfD), we derive an allowances for perchlorate in tap water for several populations. The calculated mean food perchlorate dose in the United States was 0.081 μg/kg/day compared to 0.101 μg/kg/day for those who also had a potential drinking water component. The calculated 95th percentile doses, typically falling between 0.2 and 0.4 μg/kg/day, were well below the RfD (0.7 μg/kg/day) in all populations analyzed. Children aged 6-11 years had the highest mean perchlorate doses in food (0.147 μg/kg/day), with an additional water contribution of only 0.003 μg/kg/day representing just 2% of exposure. Pregnant women had a mean food dose of 0.093 vs 0.071 μg/kg/day for all women of reproductive age. At the 95th percentile intake for both the total population and women of child-bearing age (15-44), the perchlorate contribution from food was 86% and from drinking water 14% (respectively, 30% and 5% of the RfD). At the mean for the same groups, the food to water contribution ratio is approximately 80:20. We calculate that an average 66 kg pregnant woman consuming a 90th percentile food dose (0.198 μg/kg/day) could also drink the 90th percentile of community water for pregnant women (0.033 l/kg/day) containing 15 μg/l perchlorate without exceeding the 0.7 μg/kg/day reference dose.