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Introduction
The International Agency for Research on Cancer characterizes inorganic arsenic (iAs) as a Class 1 carcinogen (IARC 2004). Minimizing human iAs exposures has motivated guidance issued by the World Health Organization (WHO 1993) and the U.S. Environmental Protection Agency (EPA 2001). Among nonoccupationally exposed U.S. residents, drinking water and diet are considered primary exposure pathways for iAs. In drinking water, iAs is the primary form of arsenic (As), while in food matrices dietary As speciation techniques are used to differentiate iAs from less toxic arsenicals.
Table S1 summarizes published probabilistic models that estimate U.S. iAs exposures (Meacher et al. 2002; Schoof et al. 1999a; Tsuji et al. 2007; Xue et al. 2010; Yost et al. 1998; Yost et al. 2004). Predicted iAs exposures from drinking water intakes range from 1.75 to 2.5 μg/day, while dietary iAs estimates range from 3.1 to 3.6 μg/day. Each of these assessments uses iAs drinking water concentration data collected between 1980 and 1998. The age of these data, given changes in treatment and water sources, and the relatively small sample size [n=500] utilities in one study (Meacher et al. 2002)] limit their usefulness for estimating current exposures.
In each of these previous iAs intake assessments, information regarding the As concentrations and species present in foods was based on samples collected from two U.S. cities in 1997 (Schoof et al. 1999b). Xue et al. (2010) and Yost et al. (2004) estimated that rice consumption contributes approximately 20% of the total estimated iAs dietary intake in the United States, while Yost et al. (2004) estimated that, for children at the 95th percentile, rice consumption contributes 50% of the total iAs exposure. A study of adult Michigan residents also underscored the importance of rice consumption to total iAs exposures (Meliker et al. 2006).
Because rice consumption contributes to total dietary iAs exposure in the U.S. population, the authors of the studies in Table S1 highlighted the need for collecting speciated As data from dietary samples to address this source of uncertainty. In response, the U.S. Food and Drug Administration (FDA) measured speciated As levels in 1,300 samples of rice and rice-containing products (FDA 2013). Less stratified literature surveys of iAs species in rice suggest the ranges are 0.01–0.379 μg/g for iAS and...