A Multimedia, Multipathway Exposure Assessment for Arsenic on the Hopi Reservation

Abstract

Arsenic (As), a naturally occurring metalloid is associated with multiple diseases, including cardiovascular, diabetes, pulmonary disorders, and some cancers. Exceedances of the current U.S. Environmental Protection Agency (EPA) Reference Dose (RfD) of 0.30 µg/kg/day for As pose a disproportional health risk for rural and underserved communities across the United States including American Indian communities. The Hopi, an American Indian Tribe in Northeastern Arizona, struggle to meet the EPA regulatory limit of 10 µg/L for As in groundwater; actual As exposure data are limited for the Hopi. In the Hopi Environmental Health Project (HEHP), I measured As concentrations in multiple environmental media (air, water, and food) for each of the 76 Hopi participants and estimated average daily intake for each participant during the heating and non-heating seasons. To make the estimates specific for the Hopi, ultraviolet radiation exposure data from each participant were used to approximate the time spent indoors and outdoors. Separate exposure models revealed As intake via inhalation was significantly different (heating: p=0.002, non-heating: p=0.0001) when using exposure factors calculated specifically for Hopi versus exposure factors from the EPA Exposure Factor Handbook within seasons. Inhalation represented a small fraction of Hopi exposure and I found overall aggregate As exposure was not significantly different between heating and non-heating seasons (p=0.193). Although 30% of homes had piped water with As levels exceeding the EPA’s regulatory limit, dietary ingestion contributed the greatest proportion to the aggregate As exposure during both the heating and non-heating season. During the heating season, the average aggregate As exposure was 0.524±0.523 µg/kg/day (min: 0.0885 µg/kg/day, max: 3.72 µg/kg/day). During the non-heating season, the average aggregate As exposure was 0.548±0.452 µg/kg/day (min: 0.0921 µg/kg/day, max: 2.05 µg/kg/day). Both aggregate exposures exceeded the EPA’s reference dose (RfD) of 0.30 µg/kg/day. To reduce overall As exposure among the Hopi, the Tribe can increase education and awareness about the health hazards of using As contaminated water when cooking. Furthermore, teaching Tribal members about the variety of foods that contain higher concentrations of As will help reduce overall exposure.