Contaminant exposure to human health implications: environmental geochemistry of mercury and food consumption

Full text: The Pearl River Delta, South China, has become the world's manufacturer for electrical/electric equipment, textiles, footwear, furniture, etc., emitting a wide range of toxic chemicals into the environment. There is a high demand of electricity, to support rapid development of various industries. This paper attempts to illustrate the emission and transport of persistent toxic substances (PTS) which may eventually accumulated in our food production systems, imposing adverse health effects, through consumption of contaminated food. Among all PTS, it is commonly recognized that coal combustion and various industrial processes (such as metal mining and smelting) emit a large amount of mercury in the atmosphere. Upon their deposition, inorganic mercury will be transformed by bacteria under anaerobic conditions, to organic mercury (notably methyl mercury), which is highly toxic. Through bio-accumulation and bio-magnification, the concentrations of methyl mercury will be elevated in high trophic level fish (such as tuna, shark and swordfish). Most of the fish consumed in Hong Kong are farmed fish, including freshwater and marine fish, which are highly susceptible to various chemicals discharged from industrial sites nearby. The use of trash fish (small fish, without commercial value), and to certain extent, commercial feed pellets containing a high proportion of fish meal (very often made from trash fish), for feeding carnivorous fish (such as grouper), also resulted in higher concentrations of environmental contaminants, notably mercury in the cultured fish. In fact, "chemical food contaminants" is one of the 3 key global food safety concerns. Food safety is any action and policy which ensure food is safe, in the entire food chain, i.e. from production to consumption (WHO, 2013). More recently, there has been a concern on regular intake of food containing rather high levels of mercury, may affect certain more vulnerable members of our population, e.g., causing autism in children. This paper attempts to review environmental health issues related to mercury; from biogeochemistry, ecology, epidemiology, to policy and management, citing examples related to South China. Reduction of anthropogenic mercury emissions pays an important role for minimizing biotic exposure to methyl mercury and associated human health risks. The use of food wastes for producing safe and quality fish would be an attractive alternative, for replacing trash fish and fish meal used in commercial feed pellets. Furthermore, there seems to be an urgent need of developing a regional list of toxic chemicals for more efficient control, focusing on PTS commonly found in the region and local food items. (author)