Trends in urinary arsenic among the US population by drinking water source: Results from the National Health and Nutritional Examinations Survey 2003-2014

Background: In 2001, the United States revised the arsenic maximum contaminant level for public drinking water systems from 50 mu g/L to 10 mu g/L. This study aimed to examine temporal trends in urinary arsenic concentrations in the U.S. population from 2003 to 2014 by drinking water source among individuals aged 12 years and older who had no detectable arsenobetaine - a biomarker of arsenic exposure from seafood intake. Methods: We examined data from 6 consecutive cycles of the National Health and Nutrition Examination Survey (2003-2014; N = 5848). Total urinary arsenic (TUA) was calculated by subtracting arsenobetaine's limit of detection and detectable arsenocholine from total arsenic. Additional sensitivity analyses were conducted using a second total urinary arsenic index (TUA2, calculated by adding arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid). We classified drinking water source using 24-h dietary questionnaire data as community supply (n = 3427), well or rain cistern (n = 506), and did not drink tap water (n = 1060). Results: Geometric means (GM) of survey cycles were calculated from multivariate regression models adjusting for age, gender, race/ethnicity, BMI, income, creatinine, water source, type of water consumed, recent smoking, and consumption of seafood, rice, poultry, and juice. Compared to 2003-2004, adjusted TUA was 353% lower in 2013-2014 among the general U.S. population. Stratified analysis by smoking status indicated that the trend in lower TUA was only consistent among non-smokers. Compared to 2003-2004, lower adjusted TUA was observed in 2013-2014 among non-smoking participants who used community water supplies (1.98 vs 1.16 mu g/L, p < 0.001), well or rain cistern users (1.54 vs 1.28 mu g/L, p < 0.001) and who did not drink tap water (2.24 vs 1.53 mu g/L, p < 0.001). Sensitivity analyses showed consistent results for participants who used a community water supplier and to a lesser extent those who did not drink tap water. However, the sensitivity analysis showed overall exposure stayed the same or was higher among well or rain cistern users. Finally, the greatest decrease in TUA was among participants within the highest exposure percentiles (e.g. 95th percentile had 34% lower TUA in 2013/2014 vs 2003/2004, p < 0.001). Conclusions: Overall, urinary arsenic levels in the U.S. population declined over a 12-year period that encompassed the adoption of the revised Arsenic Rule. The most consistent trends in declining exposure were observed among non-smoking individuals using public community water systems. These results suggest regulation and prevention strategies to reduce arsenic exposures in the U.S. may be succeeding.