In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment
Citation:
Bradham, K., G. Diamond, M. Burgess, A. Juhasz, J. Klotzbach, M. Maddaloni, C. Nelson, K. Scheckel, S. Serda, M. Stifelman, AND D. Thomas. In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH - PART B: CRITICAL REVIEWS. Taylor & Francis, Inc., Philadelphia, PA, 21(2):83-114, (2018).
Impact/Purpose:
Human exposure to arsenic (As) via ingestion of arsenic-contaminated drinking water can have serious health impacts including increased cancer risk and other adverse health effects (ATSDR 2007; IARC 2012; U.S. EPA 2016; WHO 2012). In addition to exposure from drinking water, people are exposed to arsenic in surface soils as a result of natural geological processes as well as anthropogenic sources (ATSDR 2007). The latter include production waste, application of arsenic-containing pesticides, and wastes from mining, milling, and smelting of arsenic-containing ores. Cancer risk for ingestion of arsenic-contaminated soils is estimated by applying a cancer slope factor, derived from epidemiological studies in populations chronically exposed to arsenic in drinking water, to estimated soil arsenic ingestion (Argos et al. 2014; Chung et al. 2013; Ferreccio et al. 2013; Saint-Jacques et al. 2014; U.S. EPA 2016; Yang et al. 2005). However, because oral bioavailability of arsenic in soil is less than that from water, cancer risk, as well as risks of other adverse health effects from ingestion of arsenic-contaminated soil may be overestimated (Bradham and Wentsel 2010; NRC 2003; U.S. EPA 2007a, 2007b). A recent compilation of data from a variety of arsenic-contaminated sites demonstrated that oral bioavailability of arsenic in soil tends to be lower than that of water soluble sodium arsenate (U.S. EPA 2012). Expressed as oral relative bioavailability (RBA, or the percent ratio of bioavailability of arsenic in soil to that of dissolved sodium arsenate), the median and 95th percentile RBA values for more than 100 soil samples were 30 and 60%, respectively (U.S. EPA 2012).
Description:
Arsenic (As) is the most frequently occurring contaminant on the priority list of hazardous substances, which lists substances of greatest public health concern to people living at or near U.S. National Priorities List site. Accurate assessment of human health risks from exposure to As-contaminated soils depends on estimating its bioavailability, defined as the fraction of ingested As absorbed across the gastrointestinal barrier and available for systemic distribution and metabolism. Arsenic bioavailability varies among soils and is influenced by site-specific soil physical and chemical characteristics and internal biological factors. This review describes the state-of-the science that supports our understanding of oral bioavailability of soil As, the methods that are currently being explored for estimating soil As relative bioavailability (RBA), and future research areas that could improve our prediction of the oral RBA of soil As in humans. The following topics are addressed: (1) As soil geochemistry; (2) As toxicology; (3) in vivo models for estimating As RBA; (4) in vitro bioaccessibility methods; and (5) conclusions and research needs.
