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Mercury concentrations in muscle, brain and bone of Western Alaskan waterfowl

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Abstract

Total mercury (THg), which includes both inorganic (Hg2+) and methylmercury (MeHg) species, has been reported for seabirds in the North Pacific and Alaska. For the Yup'ik and Aleut people of Alaska, waterfowl are a small but important seasonal component of the diet, but many Alaskan species have not been studied extensively for the presence of mercury. Birds are good subjects for examination of mercury concentrations because they feed at different trophic levels, they can be long-lived, and many are both abundant and widely distributed. In this study, we present the levels of mercury in muscle, brain, and bone tissue of 140 birds taken by subsistence food users across Western Alaska. THg wet weight mean concentrations in the 18 species of waterfowl surveyed ranged from 0.8 to 268.6 ng/g in muscle, from 0.4 to 197.7 ng/g in brain and from 0.7 to 422.9 ng/g in bone. The null hypothesis that there are no interspecific differences in the level of total mercury in the 18 species of Alaska birds surveyed was not supported. We found interspecific differences with the Lesser Scaup (Aythya affinis), and the Black Scoter (Melanitta nigra), having the highest muscle tissue levels of THg. In general, THg mean levels were higher in muscle than in brain with the exceptions of the Bar-tailed Godwit and Northern Shoveler. Bone THg were highest in the Black Scoter. The mean values for THg in the species studied are unlikely to cause adverse reproductive or behavioral effects in the birds.

Introduction

Natural levels of contaminants from geological, atmospheric, and oceanic processes are increased by anthropogenic sources. In recent years there has been a desire by both Alaskans and policy-makers to know the total mercury (THg) burdens on Alaskan subsistence food users as well as any health effects relating to the forms of mercury in Alaskans' diet. The subsistence lifestyle and diet provide not only for nutrition and fitness at reasonable costs but also maintain social and cultural values (Hild, 1998).

The potential health hazard to residents in rural coastal villages in the Arctic and sub-Arctic regions was recognized when relatively high concentrations of mercury were found in marine mammals (Galster, 1976). Many Yup'ik in Western Alaska live a traditional subsistence lifestyle, usually in small villages. In this lifestyle, food is obtained mainly from the near-shore and aquatic environments. Marine mammals, birds, salmon, and freshwater fish are the major sources of protein and fat in subsistence diets with intakes per individual of 375 to 600 lb/year (Nobmann et al., 1992, Egeland et al., 1998, Arnold and Middaugh, 2004). Birds account for 3% to 6% of the subsistence diets in Western Alaska.

The characterization of mercury exposure requires an understanding of all potential pathways through which mercury in the environment may result in exposure. This includes direct pathways such as through uptake in food sources, including lipid rich species (Morel et al., 1998). Recent studies in Alaska have focused on fish and marine mammals (Duffy et al., 1999, Beckmen et al., 2002, Arnold and Middaugh, 2004, Jewett et al., 2003), but little is known about the THg levels in many parts of the Alaskan food chain. Mercury, including MeHg, remains bound to muscle as methyl mercury cysteine (Harris et al., 2003), and in a study of Arctic Char, Salvelinus alpinus, an Inuit food, mercury concentrations increased four to six-fold during cooking and drying (Chan et al., 1995). The goal of this study was to expand the data base of Hg levels associated with birds commonly harvested by Yup'ik and Aleut subsistence users.

Birds are excellent bioindicators for the monitoring of mercury because they feed at different trophic levels, including the top-level piscivors (Burger and Gochfeld, 1997, Monteiro and Furness, 1995). They are abundant, widely distributed and, in some cases, long-lived. Not only can birds monitor local food webs, but also, if they are migratory they can be used to compare exposure in different regions (Rocque and Winker, 2004). As industrial growth in Asia continues, it is critical to have baseline information of temporal trends in Alaska for future comparison. Birds can also provide historical data since their skeletal remains are part of Alaskan archaeological sites with the most common western taxa being Anas, Aythya and Branta.

Section snippets

Sample collection

Samples were collected from Native subsistence hunters in villages across the Yukon-Kuskokwim Delta of Western Alaska. No effort was made to collect any particular species. The collection period was all of 2002 through summer of 2003. All samples (i.e. bird heads) were from the freezers of the families who agreed to participate in this study. A “sample” is a bird head with approximately 1–2 in. of neck attached. The samples were placed in Zip-Lock bags and immediately kept frozen for later

Results

Mercury was detected in all bird types analyzed, but not in every tissue (Table 2). The THg overall mean value for THg in the muscle was 55 ng/g wet weight (ww) while in brain, the mean was 44 ng/g (ww). THg in bone was more varied when compared to values of the other tissues and was very high in bone (422.9 ng/g) of the Black Scoter when compared with either brain (105.2 ng/g) or muscle (134.7 ng/g) of the Black Scoter. The median value for THg in bone is a better indicator of tissue exposure

Discussion

Birds comprise about 3% to 6% of the subsistence resources of Western Alaska (Arnold and Middaugh, 2004). For many years there has been a desire by both Alaskans and policy-makers to know the methylmercury (MeHg) and total mercury (THg) burdens on Alaskan subsistence food users as well as any health effects relating to both forms of mercury in people's diet (Egeland et al., 1998, Rothschild and Duffy, 2001, Weis, 2000). The subsistence lifestyle and diet provide not only for nutrition and

Conclusions

The results of this study indicate that there are differences in mercury levels for birds in Western Alaska. Mercury levels were highest in higher trophic level birds and the levels of mercury do not seem sufficiently high to cause adverse effects. In Alaska, there is a strong need to provide reference means and THg ranges in birds. More research on accumulation factors and pathways is necessary for this region of the north.

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