Mercury Contamination in the Columbia River Basin: Health Risk Assessment of Tribal Exposure Through Subsistence Lifeways

Abstract

In the Northwest Pacific tribal areas of the Columbia River Basin, fish consumption is important to riverine tribal cultures, and represents deeply held beliefs that have roots in spiritual practices, subsistence lifestyles and community. Therefore, typical fish consumption may exceed levels usually reported for the general U.S. population. A principal exposure pathway of contaminants to riverine tribes is through fish consumption.

This study was designed to determine if mercury concentrations in fish in regions of the Columbia River Basin where tribal members fish were high enough to be a health concern. A large Columbia River Basin database on concentrations of mercury in fish, compiled mainly from state and federal monitoring programs, was used to evaluate trends for mercury contamination in fish from the Columbia River Basin waterways for a range of consumption rates. Trends were analyzed on data aggregated by site and by state, using samples of the same fish species. Site-based trends were evaluated from 1999 to 2010. There were significant and important differences in mercury levels among species, but the locational differences were relatively small. The highest mean mercury levels were in largemouth bass (577 ppm) and smallmouth bass (297 ppm). The concentrations of mercury in the anadromous fish were lower than in resident species. Eleven of the 105 rivers had fish samples over EPA human health guideline of 0.3 ppm, and five of 105 rivers had fish samples above 0.5 ppm. The findings from this study demonstrated few fish are low enough in mercury to be safe for tribal members eating resident fish at traditional historic rates or at a moderate rate.

The traditional methodology of a health risk assessment used by the federal government is based on the use of exposure assumptions that represent the entire American population. To limit human risk to mercury residues in locally caught species, fish consumption advisories have been established to protect local populations from health risk. For regions where mercury contaminant levels are elevated, elevated fish consumption by tribal members may lead to higher exposures to mercury. These exposures represent potentially disproportionate risks for many Northwest Pacific tribes. The state’s fish advisories suggest reducing fish consumption with the goal of lowering risk; in fact, this shifts the burden of avoiding risk to the tribal members who now carry the burdens of contaminant exposure, socio-economic impacts and heritage and cultural loss. Thus, tribal members are forced to choose between culture and health. Many tribal members would rather be exposed to risk than abandon their culture and religion. These issues represent the potential inadequacy of health risk assessments to reflect important cultural differences in environmental justice communities. This may warrant further mitigation to reduce mercury levels in surface waters that support commonly consumed or culturally important species.