Contribution of arsenic and uranium in private wells and community water systems to urinary biomarkers in US adults: The Strong Heart Study and the Multi-Ethnic Study of Atherosclerosis

Abstract

Background: Chronic exposure to inorganic arsenic (As) and uranium (U) in the United States (US) occurs from unregulated private wells and federally regulated community water systems (CWSs). The contribution of water to total exposure is assumed to be low when water As and U concentrations are low.

Objective: We examined the contribution of water As and U to urinary biomarkers in the Strong Heart Family Study (SHFS), a prospective study of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially/ethnically diverse urban U.S. communities.

Methods: We assigned residential zip code-level estimates in CWSs (µg/L) and private wells (90th percentile probability of As >10 µg/L) to up to 1485 and 6722 participants with dietary information and urinary biomarkers in the SHFS (2001-2003) and MESA (2000-2002; 2010-2011), respectively. Urine As was estimated as the sum of inorganic and methylated species, and urine U was total uranium. We used linear mixed-effects models to account for participant clustering and removed the effect of dietary sources via regression adjustment.

Results: The median (interquartile range) urine As was 5.32 (3.29, 8.53) and 6.32 (3.34, 12.48) µg/L for SHFS and MESA, respectively, and urine U was 0.037 (0.014, 0.071) and 0.007 (0.003, 0.018) µg/L. In a meta-analysis across both studies, urine As was 11% (95% CI: 3, 20%) higher and urine U was 35% (5, 73%) higher per twofold higher CWS As and U, respectively. In the SHFS, zip-code level factors such as private well and CWS As contributed 46% of variation in urine As, while in MESA, zip-code level factors, e.g., CWS As and U, contribute 30 and 49% of variation in urine As and U, respectively.

Impact statement: We found that water from unregulated private wells and regulated CWSs is a major contributor to urinary As and U (an estimated measure of internal dose) in both rural, American Indian populations and urban, racially/ethnically diverse populations nationwide, even at levels below the current regulatory standard. Our findings indicate that additional drinking water interventions, regulations, and policies can have a major impact on reducing total exposures to As and U, which are linked to adverse health effects even at low levels.

Keywords: Epidemiology; Exposure modeling; Metals.

Figure 1.. Percent change (95% confidence intervals, CIs) in urinary arsenic (As) or uranium (U) by 2-fold higher water As^1,2 or U^3,4 in the Strong Heart Family Study (SHFS) and the Multi-Ethnic Study of Atherosclerosis (MESA).

Estimates represent the adjusted percent change in urinary As per log µg/L increase in community water system (CWS) As, CWS U, or private well U, or the 25% increase in the probability of 90^th percentile private well water As > 10 µg/L. % change was calculated as (Geometric mean ratio −1) * 100%. Lines represent 95% CIs. iAs = inorganic As (arsenite and arsenate). SumAs =sum of iAs, monomethyl arsonate, and dimethylarsinate. ¹Arsenic model for SHFS includes random effects for zip code identifier and family identifier, and adjustment for natural log transformed creatinine, natural log transformed arsenobetaine, sex, age, smoking status, pack years, BMI, and natural log transformed dietary intake (g) of rice, organ meat, processed meat, and fish. ²Arsenic model for MESA includes random effects for zip code identifier and participant identifier, and adjustment for natural log transformed creatinine, natural log transformed arsenobetaine, sex, age, smoking status, pack years, body mass index (BMI), number of weekly servings of rice, and natural log transformed dietary intake (g) of red meat, and fish. ³Uranium model for SHFS includes random effects for zip code identifier and family identifier, and adjustment for natural log transformed creatinine, sex, age, smoking status, pack years, BMI, and natural log transformed dietary intake (g) of organ meat. ⁴Uranium model for MESA includes random effects for zip code identifier and participant identifier, and adjustment for natural log transformed creatinine, sex, age, smoking status, pack years, BMI, and natural log transformed dietary intake (g) of red meat.