Methylmercury risk and awareness among American Indian women of childbearing age living on an inland northwest reservation☆
Introduction
Exposure to methylmercury is recognized as a critical and emerging public health issue with fetuses and children at highest risk (Woodruff et al., 2003; US EPA, 2007a). This pervasive neurotoxin targets the brain in developing organisms, is linked to neurobehavioral testing disorders including deficits in attention span, fine motor function, language, visual–spatial ability and memory even at low exposure levels (Budtz-Jorgensen et al., 2002; Debes et al., 2006; Grandjean et al., 1997, Grandjean et al., 1998, Grandjean et al., 1999, Grandjean et al., 2001), and is also associated with increased blood pressure in exposed children (Sorensen et al., 1999).
According to the United Nations Environment Program (UNEP) and the United States Environmental Protection Agency (US EPA), the primary source of exposure to methylmercury occurs through the consumption of fish contaminated from a variety of anthropogenic sources but principally from atmospheric emissions from coal-fired power plants (UNEP, 2002; US EPA, 2007a). Inorganic mercury released into the atmosphere through combustion of fossil fuels can travel great distances before depositing in aquatic systems and bioaccumulating as methylmercury in the food chain (Clarkson, 2002; National Research Council (NRC), 2000; US EPA, 1997a, US EPA, 1997b).
Once this toxicant is in the food chain, balancing the public health risks and nutritional benefits of consuming fish presents a complex challenge (Burger and Gochfeld, 2009; Knuth et al., 2003). The primary method of protecting women of childbearing age from unknowingly exposing an unborn child to methylmercury is through education and the distribution of fish advisory messages based on the potential for local exposure (Mahaffey et al., 2008). This paper summarizes the results of a survey conducted with clients of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) on the Flathead Reservation (Confederated Salish and Kootenai Tribes [CSKT]) in northwest Montana. The goals of the study were to examine fish consumption, advisory awareness, and risk communication preferences among American Indian women of childbearing age.
The National Center for Health Statistics, a division of the Centers for Disease Control and Prevention (CDC), conducts the National Health and Nutrition Examination Survey (NHANES) to monitor the health and nutrition status of the US population (CDC, 2007). Body burden of mercury in women of childbearing age (16–49 years) is monitored annually through examination of dietary histories and analysis of blood mercury concentrations. Children born to women with blood mercury concentrations above 5.8 parts per billion are determined to be at increased risk. EPA's reference dose (RfD) for methylmercury maternal intake is set at 0.1 μg/kg/day which corresponds to 5.8 parts per billion mercury in blood (Rice, 2004; Rice et al., 2003; US EPA, 2001).
American Indian women and children may be the most overrepresented among the list of disparate populations exposed to methylmercury. An assessment of the 1999–2001 NHANES data focused on the racial/ethnic groups classified as “other” in the survey (Asians, Pacific Islanders, and Native Americans/Alaska Natives). Researchers found that this group was three times more likely to have elevated blood mercury levels than all other racial/ethnic participants of the survey (Hightower et al., 2006). Studies from coastal, Great Lakes, and Canadian indigenous populations have documented fish consumption patterns (Dellinger, 2004; Morrissette et al., 2004; Muckle et al., 2001a, Muckle et al., 2001b; Arquette et al., 2002; McKeown-Eyssen et al., 1983). In addition, Jewett and Duffy (2007) noted subsistence consumption rates of specific fish species among Alaskan Natives. As early as 1997, Harris and Harper identified fish consumption characteristics of indigenous subsistence lifestyle in the Lower Columbia River Basin on the Umatilla reservation and estimated a potential exposure scenario. More recently, the impact of fish contaminant burden coupled with the cultural and economic significance of fish for the Confederated Tribes (Cayuse, Umatilla, and Walla Walla) was examined to recommend risk-based action levels for the population with high consumption of contaminated fish species (Harper and Harris, 2008).
Fish advisories are critical to populations who eat certain species and amounts of commercial and sport-caught fish (Silver et al., 2007). Advisories are intended to alert consumers to potential risks and are based on fish sampling in specific water bodies (US EPA, 2004). The National Research Council (2000) scientific review of risk evidence summarized the toxicological effects of methylmercury on vulnerable populations and recommended improving the characterization of risk and regional differences of methylmercury exposure in the US population. The federal government through EPA's National Listing of Fish Advisories (NLFA), maintains a database of states, tribes, and territories issuing fish advisories and safe-eating guidelines. In 2006, 48 states (including Montana), the District of Columbia, two of four territories, and five of 562 federally recognized American Indian tribes (US Federal Register, 2002) issued fish consumption advisories (US EPA, 2007b).
Prior to 2003, Montana officials utilized site-specific fish consumption advisories by listing fish species with concentrations of methylmercury or polychlorinated biphenyls (PCBs) found in sampled fish in specific lakes and streams. In 2003 Montana adopted a statewide advisory system to alert anglers of potential hazards (US EPA, 2004). Fish advisory information is disseminated through fishing license brochures, fishing access postings, on websites sponsored by Montana Fish, Wildlife, and Parks (MT FWP) and Montana Department of Public Health and Human Services (MT DPHHS) Food and Consumer Safety. Locally, the CSKT follow the state advisories and publish fish consumption guidelines in the tribal license brochure. Fish advisory messages target the 220,000 resident and 50,000 non-resident anglers who purchase state or tribal fishing licenses (MT FWP, 2007). This population does not necessarily include American Indian anglers who often fish on home reservations where a state or tribal license is not required. It is assumed that tribes as sovereign nations take responsibility for informing tribal residents about potential dangers related to fish consumption (Anderson et al., 2004). There is, however, little evidence of tribal members receiving or acting on fish advisories on tribal lands.
Flathead Lake is the largest freshwater lake in the western US with a maximum length of 27 miles, a width of 15 miles, and depth of 386 feet. The lake is fed by two major rivers, the Flathead and Swan that flow from the Bob Marshall and Great Bear wilderness areas and Glacier National Park (University of Montana Biological Center, 2009).
The Flathead Lake and River System is uniquely important to people of the Confederated Salish and Kootenai Tribes (CSKT) by contributing ecological, cultural, spiritual, and economic benefits to the people. Native fish are significant to the survival of native people. The Salish, Pend O’reille, and Kootenai elders state that native people are merely the stewards of the land, while depending upon the fish, wildlife, water, plants, and air to remain in balance, which is significant to their cultural integrity (CSKT and MT FWP, 2001, p. 8).
Of the 25 species of fish commonly found in the Flathead River–Lake Ecosystem, 10 are native fish and 15 are non-native. Two species, lake trout and lake whitefish, have drastically increased in abundance since 1970 with the lake trout identified as directly responsible for a severe decline in native fish, primarily the bull trout. To rebalance the ecosystem, the predatory lake trout population management strategies include recreational angling incentives during a yearly spring and fall Mack Days fishing contest (CSKT and MT FWP, 2006). Creel surveys from 2000 to 2009 suggest a slow decline in lake trout even with annual harvest goals set at 60,000 fish and contest prizes worth approximately $40,000 per semi-annual event (CSKT and MT FWP, 2009).
Section snippets
Survey design
This study complied with requirements of the US human subject and research regulations and was reviewed and approved by the Montana State University Institutional Review Board for Protection of Human Subjects on March 4, 2006. A tribal council letter of approval to conduct research on the target reservation was received on December 20, 2005. Each participant received a letter from the investigators explaining the purpose of the study. Verbal informed consent was obtained from participants prior
Demographic characteristics of participants
Consistent with a population receiving WIC services, all participants were low-income (185% poverty), young (88% <36 years of age), and 57% were married or a member of an unmarried couple. Educational level was moderate with less than one-third indicating having less than a high school education. The majority of women were not currently working for pay. Among participants, one-fourth of the women were pregnant and those who were not pregnant were not planning on becoming pregnant in the next
Discussion
Three major findings emerged from this study related to fish consumption, fish advisory awareness/knowledge, and risk communication preferences among American Indian women of childbearing age living on the Flathead Reservation in the inland Northwest. First, most American Indian women of childbearing age who participated in this study included locally caught and/or commercial fish in their diet. Second, 80% (n=52) of study participants were unaware of local or statewide fish advisories. Those
Acknowledgments
Funded through NIH/NINR, 1P20NR07790-01 Center for Research on Chronic Health Conditions in Rural Dwellers, Montana State University, College of Nursing. The authors would like to thank Dr. Clarann Weinert for her mentorship and Dr. Donna Williams for her review and contributions to this manuscript.
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IRB Approval: This study complies with requirements of the US human subject and research regulations and was reviewed and approved by the Montana State University Institutional Review Board for Protection of Human Subjects on March 4, 2006. A tribal council letter of approval to conduct research on the target reservation was received on 20-12-05.