Arsenic relative bioavailability from diet and airborne exposures: Implications for risk assessment

Major human environmental health concern has been associated with inorganic arsenic (iAs) in drinking water in which dissolved iAs is highly bioavailable. More recently health concerns have been raised regarding the extent of iAs exposure via food and other potential sources. Arsenic relative bioavailability (RBA) in soil is known to be variable; the extent and role of iAs bioavailability in food are not well characterized. iAs in coal fly ash and bottom ash are other potential exposure media for which RBA has not been well characterized. A comprehensive literature search was conducted to support evaluation of the contribution of food and coal fly ash to iAs exposure. Few studies were found that investigated bioavailability associated with As-containing coal ash or airborne As-containing particles; estimated bioavailability in these studies ranged from 11% to 50%. The implications and potential usefulness of iAs bioavailability associated with inhalation exposure to human health risk assessment remain unknown at this time. Main sources of dietary iAs intake in the U.S. include rice and other grains, vegetables, and fruits. Due to low concentrations of iAs, seafood is not a primary contributor to dietary iAs intake. Three general kinds of food studies were identified: studies of As bioaccessibility in composites, As bioavailability and bioaccessibility in specific foods, and As consumption and urinary excretion in human volunteers. One in vivo study was identified that examined As bioavailability in food. A variety of experimental in vitro gastro-intestinal protocols have been used, however, few studies have included As speciation before and after the in vitro extraction. Current data suggest that the bioaccessibility of iAs in rice is quite high, typically 70% or more indicating that iAs in rice is highly bioavailable. Adjusting for RBA may not have a meaningful impact on iAs exposure estimates for rice-based foods.