Exposure to methylmercury via fish consumption in Ghana and an evaluation of methylmercury toxicity under a low food ration in Daphnia pulex

Abstract

For many people of the world, fish is a primary source of protein, especially in countries like Ghana, where about 60% of the protein consumed is derived from fish. Fish advisories have been established by some nations to protect the public from harmful health effects linked to eating contaminated fish. Methylmercury (MeHg) is one such contaminant that has resulted in fish advisories. Fish advisories have not been developed in Ghana, although MeHg contamination of aquatic ecosystems is likely due to the long history of mercury (Hg) use in artisanal gold mining. To address this gap in our knowledge, I compiled reported MeHg concentrations in fish from water bodies in Ghana, and estimated consumption patterns and potential health risk associated with consumption. The results of this study indicate that fish collected in Ghana have an estimated average level of MeHg at 0.1 mg/kg (± 0.15), although higher levels are seen in fish collected from rivers in the gold mining regions (0.25mg/kg ±0.23).

In humans, the most sensitive time period for MeHg exposure is in utero where maternal exposures are linked to neurodevelopmental deficiencies in offspring. Underlying nutritional status also affects the metabolism and ultimate toxicity of heavy metals. In low income countries, undernutrition during early childhood is common, yet studies informing the establishment of safe limits of exposure to a chemical rarely factor in nutrition. To address this knowledge gap, I evaluated the interaction between food and MeHg toxicity in Daphnia pulex. Daphniids that were fed a low ration exhibited no change in lifespan but a reduced reproductive output compared to those that were fed a standard ration. When daphniids were exposed to MeHg in early life and kept on either a low or standard food ration, an additive effect was seen such that lifespan was reduced by MeHg, and an additional reduction was seen in those fed a low ration. In summary, these studies in Daphnia suggest that early life MeHg exposure that occurs in combination with undernutrition may increase toxicity and should be examined in more detail in mammalian systems to determine the potential effect in humans.

Keywords: nutrition, methylmercury, early life exposures, Daphnia pulex, Ghana,