Academic journal article Environmental Health Perspectives

Estimating Inorganic Arsenic Exposure from U.S. Rice and Total Water Intakes

Academic journal article Environmental Health Perspectives

Estimating Inorganic Arsenic Exposure from U.S. Rice and Total Water Intakes

Article excerpt

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 non-occupationally 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 pg/day, while dietary iAs estimates range from 3.1 to3.6 pg/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 [micro]g/g for iAs and 0.004-0.9 [micro]g/g for dimethylarsenic acid (DMA) (Ackerman et al. 2005; Heitkemper et al. 2009; Heitkemper et al. 2001; Lamont 2003; Laparra et al. 2005; Meharg et al. 2009; Torres-Escribano et al. 2008; Trenary et al. 2012; Williams et al. 2005; Zavala et al. 2008; Zhu et al. 2008), with some reports of monomethylarsonic acid near the detection limit. The European Food Safety Authority (EFSA 2014) recently developed an As exposure assessment based on 353 rice samples; the mean and standard deviation of the iAs concentration in brown, white, and parboiled rice were 0.152 [+ or -] 0.05,0.089 [+ or -] 0.03, and 0.105 [+ or -] 0.06 [micro]g/g, respectively.

The bioavailability of ingested As species in rice also contributes to uncertainty in exposure assessments. While bioavailability studies have been conducted in swine (Brattin and Casteel 2013; Juhasz et al. 2006, 2008; Rodriguez et al. 1999) and mice

(Bradham et al. 2011), the high cost of these studies has led to development of in vitro enzymatic gastrointestinal extraction (Ackerman et al. 2005; Alava et al. 2012; He et al. 2012; Laparra et al. 2005; Sun et al. 2012; Trenary et al. 2012) and human in vivo bioaccessibility (solubilized in the gastrointestinal tract but not necessarily absorbed) approaches (He and Zheng 2010) to estimate the physiological relevance of iAs intakes.

In this study, we used the Stochastic Human Exposure and Dose Simulation (SHEDS) model (Xue et al. 2012) to estimate iAs exposures from drinking water and rice consumption in the United States, addressing concerns identified previously (Meacher et al. …

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