The paper builds on existing literature, highlighting current understanding and identifying unresolved issues about MeHg exposure, health effects, and risk assessment, and concludes with a consensus statement. Methylmercury is a potent toxin, bioaccumulated and concentrated through the aquatic food chain, placing at risk people, throughout the globe and across the socioeconomic spectrum, who consume predatory fish or for whom fish is a dietary mainstay. Methylmercury developmental neurotoxicity has constituted the basis for risk assessments and public health policies. Despite gaps in our knowledge on new bioindicators of exposure, factors that influence MeHg uptake and toxicity, toxicokinetics, neurologic and cardiovascular effects in adult populations, and the nutritional benefits and risks from the large number of marine and freshwater fish and fish-eating species, the panel concluded that to preserve human health, all efforts need to be made to reduce and eliminate sources of exposure.

Methylmercury exposure and health effects in humans: a worldwide concern.

Low dose mercury toxicity and human health.

A review on heavy metal pollution, toxicity and remedial measures: Current trends and future perspectives

Although some areas of China are becoming more urban, more than 60% of the population is still rural, most of which still uses biomass (mainly wood and crop residues) and coal fuels that produce substantial pollution in simple stoves. In 2003 approximately 80% of the energy consumed by rural households was in the form of biomass and almost 10% as coal. Furthermore, although most Chinese cities have plans to eliminate coal for households, many urban communities continue to rely on coal. The combustion of biomass and coal (collectively called “solid fuels”) is the dominant source of indoor air pollution (IAP) in the country and contributes significantly to the total burden of ill health.

In the most recent global analysis of the health effects of major risk factors, the World Health Organization (WHO) estimated that solid fuels used in Chinese households cause approximately 420,000 premature deaths annually; this is 40% more than the approximately 300,000 premature deaths attributed to outdoor air pollution in Chinese cities with populations of more than 100,000 (Cohen et al. 2004; Smith et al. 2004). Household use of solid fuels is thus estimated to be the largest single environmental risk factor and ranks sixth among all risk factors examined for ill-health (Figure 1; Smith et al. 2005). These risk estimates, however, were based primarily on studies in other countries because, as discussed in this review, few epidemiologic studies have been conducted in China on biomass smoke compared with those conducted on coal smoke.



Figure 1

Rough estimates of the burden of disease in China: the top 10 risk factors plus other selected risk factors [adapted from Smith et al. (2005)]. Note: Indoor smoke from solid fuels does not include smoke from other fuels or tobacco. Burden of disease is ...



In the 1980s China conducted more IAP measurements focused on household combustion than all other developing countries combined. Indeed, by the early 1990s, the results of more than 100 published studies were combined into a WHO database (Sinton et al. 1996). In contrast, the Chinese environmental health community conducted few IAP measurements in the 1990s (Saksena et al. 2003), but epidemiologic studies of coal smoke, mainly on cancer end points, continued and have resulted in a large body of evidence. In particular, over 25 years a wide-ranging set of studies has been conducted on coal smoke exposures, toxicology, and health effects in one rural area—Xuanwei in Yunnan Province—with severe impacts.

In this review we address the following questions in order to put Chinese household IAP from solid fuel use into perspective, nationally and internationally, and highlight research gaps: a) What toxic constituents have been found in the emissions of solid fuel combustion? b) What are the reported human exposure characteristics? c) What health effects have been documented? and d) What technologies exist or are possible for reducing this IAP exposure?

Qu Liya

Papers

Total mercury, methylmercury and selenium in mercury polluted areas in the province Guizhou, China