Methylmercury and the health of indigenous peoples: a risk management challenge for physical and social sciences and for public health policy

Abstract

Methylmercury in aquatic ecosystems and bio-accumulated in aquatic biota, especially fish, is a major public health concern internationally. Precautionary efforts are currently underway internationally to reduce the anthropogenic release of mercury, which in turn, over time, will reduce human exposure. However, at the present time, it is important to address the issue of management of the risks of exposure as they exist now. Of particular concern are the impacts of methylmercury on indigenous populations which depend on fish as a subsistence food source, both in remote areas of developed countries, such as Canada, and in developing countries such as Brazil. Research into these impacts over the past two or three decades has shown that, other than in very severe pollution situations such as occurred in Minamata, Japan, the direct impacts on human health are difficult to prove. On the other hand, the indirect negative effects of methylmercury on health, mediated through the disruption of lifestyle and eating patterns and the associated socio-cultural and socio-economic consequences among the affected native populations, have, in many cases, been significant. These social factors have raised serious challenges in determining practical public health policies on the issue. Policy development relating to environmental contaminants has been presented, with the problem of assessing the role of the various factors which contribute to the impact on health as a result of socio-cultural disruption. These factors include changes in diet and lifestyle due to methylmercury in the environment and its real or perceived risk. The standard physical sciences risk assessment process, based on the lowest observed adverse effects level (LOAEL) or no observed adverse effects level (NOAEL) used in defining health policies may be seen as over-simplistic theoretical extrapolations when viewed in the context of the concerns of the social sciences. Both approaches, however, have relevance to health policies that address the risks posed by environmental methylmercury. Therefore, the standard physical sciences approach of the past three decades now needs to be linked with the social sciences approach, with its focus on the indirect impacts of exposure to methylmercury, to provide a comprehensive approach to public health policy development. With this objective in mind, this paper reviews methylmercury-related data from both physical and social sciences. It attempts to draw on the findings in both disciplines to provide suggestions for an integrated approach in policy development relating to human health and human exposure to methylmercury, especially among indigenous peoples in remote areas and in developing countries. An integrated approach such as this may help to limit adverse health effects in the indigenous communities affected.

Introduction

Methylmercury bio-accumulated in aquatic biota, especially fish, is a public health concern internationally. Current international efforts aimed at reducing the anthropogenic release of mercury into the environment by lowering emissions from combustion and non-combustion sources, and consequently, lessening the accumulation of methylmercury in aquatic ecosystems (Iverfeldt et al., 1995, Environmental Protection Agency, 1997), are an essential component of mercury risk management and policy development. To not apply this precautionary approach would result in increased amounts of bio-available mercury in the environment. However, given the persistence of the methylmercury already present in aquatic ecosystems, this approach must be viewed as a long-term consideration in terms of reducing human exposure to methylmercury. In the meantime, risk management and public health policies must address the existing problems of exposure to methylmercury, especially among sub-population groups such as indigenous peoples. Of particular concern are the impacts on indigenous populations which depend on fish, or sea mammals, as a subsistence food source, in both remote areas of developed countries, such as Canada (Wheatley, 1979), and in developing countries such as Brazil (Cleary, 1990). Research into these impacts over the past three decades, in Canada and a number of other countries, has shown that, other than in very severe pollution situations such as occurred in Minamata, Japan (Katsuna, 1968), the direct impacts on human health are difficult to prove (Wheatley et al., 1979, Wheatley and Paradis, 1996). On the other hand, the indirect, negative effects of methylmercury on health, mediated through the disruption of lifestyle and eating patterns and the subsequent socio-cultural and socio-economic consequences among the affected indigenous populations, have, in many cases, been significant (Erikson, 1994, Wheatley, 1996, Wheatley, 1997). These factors pose serious challenges in determining practical public health policy on the issue. This paper attempts to illustrate these difficulties and suggest possible approaches to risk management and policy development using the Canadian experience as a case study.