Use of background inorganic arsenic exposures to provide perspective on risk assessment results☆
Introduction
Arsenic occurs naturally in the environment and is ubiquitous in water, food, and soil (ATSDR, 2000). Consequently, understanding how arsenic exposures from human activities compare to natural background exposures is important for communicating the relative magnitude of calculated risks in perspective with everyday exposures. Because risk assessments predict risks greater than one per million even for background exposures to arsenic, definition of de minimis risk at this level is less useful for indicating public health concern. Risk communication for arsenic will become even more critical if calculated risks for arsenic increase based on reanalyses (Morales et al., 2000, NRC, 2001; 66 CFR 6976–7066).
Recent attention has also been directed at children’s exposure to arsenic (CPSC, 2003, U.S. EPA, 2005a) and potential health risks (CPSC, 2003, Tsuji et al., 2004a, Tsuji et al., 2004b). In particular, concerns have been expressed regarding childhood exposure to inorganic arsenic from playsets and residential decks made of wood treated with chromated copper arsenate (CCA), because risk estimates exceed one per million (Patch and Maas, 2006). Although CCA-treated wood is no longer sold for residential uses, existing residential wood has not been recalled. Thus, context on how such exposures would compare to natural sources of inorganic arsenic from diet and typical water exposures would be helpful for risk communication and public health decision-making.
Background inorganic arsenic intake in the U.S. has been investigated recently for children exposed through diet (Yost et al., 2004), and previously for all ages exposed through diet (Schoof et al., 1999b), and for diet, water, soil, and air (Meacher et al., 2002). This paper builds on that earlier work to conduct probabilistic analyses of background inorganic arsenic intake for children (ages 1–6 years) and the general U.S. population (all ages) from the primary background sources, diet and water (Meacher et al., 2002). In comparison to the dietary intake modeling of Meacher et al. (2002), the more comprehensive dietary modeling reported by Yost et al. (2004) is used to estimate dietary and water intakes for the general U.S. population and for children ages 1–6 years. Our modeling also incorporated reduction in arsenic drinking water concentrations in the U.S. as a result of the compliance with the arsenic standard reduction from 50 to 10 μg/L.
As risk comparison examples, the results of this analysis are compared to arsenic intakes from soil exposure based on default EPA risk assessment assumptions and to estimated arsenic exposures from CCA-treated wood used for playsets and residential decks (U.S. EPA, 2005a, Zartarian et al., 2006).
Section snippets
Inorganic arsenic in food
Inorganic arsenic concentrations in food were as obtained from Yost et al. (2004) based on analysis of 40 types of food that were estimated to make up at least 90 percent of the inorganic arsenic intake for U.S. adults (Schoof et al., 1999a).
Background inorganic arsenic intake from diet and water
Background inorganic arsenic intake from diet and water for children ages 1–6 averaged 3.5–3.7 μg/day with a 90th percentile of 5.9–6.2 μg/day (range for water data truncated at 10 μg/L or untruncated) (Fig. 1). Intakes for the U.S. population were higher overall, and particularly at the upper percentiles (average of 5.6–6.1 μg/L and 90th percentile of 10.5–11.1 μg/day; Fig. 1). Variation in the higher percentiles of intake among regions of the U.S. was primarily a result of variation in upper-end
Comparison to arsenic intake from other studies
Probabilistic modeling of diet and water combined for all ages as well as for young children (ages 1–6 years) resulted in estimates of background inorganic arsenic intake that are more representative of the U.S. population than indicated by separate modeling of each source. Mean and 95th percentile intakes for diet and water in young children (Fig. 1) are not much higher than the mean (3.2 μg/day) and 95th percentile (6.2 μg/day) for diet alone reported by Yost et al. (2004) for children. Thus,
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Note. The authors received partial funding for this research from the American Chemistry Council. The views expressed in this paper are the scientific views of the authors and not those of their employer or sponsor.