Mercury waste from artisanal and small-scale gold mining facilities: a risk to farm ecosystems-a case study of Obuasi, Ghana.

Frequent discharge of mercury waste from artisanal and small-scale gold mining (ASGM) facilities into nearby farms may contaminate foodstuffs and the entire farms. High contamination levels may result in ecological risks to the soil, plants, animals, humans, and the entire farm ecosystem. This original research is the first study within the catchment areas that describes the effects of mercury waste on the entire farm ecosystem. In this study, the contamination levels and the associated ecological risks of farmland soils, plantains, and cassavas from farms sited near ASGM facilities in four communities around Obuasi, Ghana, were evaluated using the Hakanson (1980) model. Results showed that all samples except for the edible parts of plantains from Tweapease, Nyamebekyere, and Ahansonyewodea and plantain peels from Nyamebekyere and Ahansonyewodea were contaminated and may pose moderate to very high ecological risks. All farms were also contaminated and may pose considerable to very high ecological risks. The farms at Odumase were the highest contaminated with degree of contamination (Cdeg) above 20, while those at Ahansonyewodea were the least contaminated with Cdeg = 8.1. This meant that farms at Odumase may pose the highest potential ecological risk (Per) to plants, animals, humans, and the entire farm ecosystem since Per > 600, while the farms at Ahansonyewodea may pose the least ecological risks with Per = 324. There is, therefore, the need for strict control of ASGM activities in these study areas to preserve the integrity of the ecosystem.

The human health risks assessment of mercury in soils and plantains from farms in selected artisanal and small-scale gold mining communities around Obuasi, Ghana.

Food consumption remains the commonest pathway through which humans ingest higher levels of mercury (Hg). Long-term exposure to Hg through Hg-contaminated food may result in acute or chronic Hg toxicity. Incessant discharge of Hg waste from ASGM facilities into nearby farms contaminates food crops. Ingestion of such food crops by residents may lead to detrimental human health effects. The human health risks upon exposure to total mercury (THg) and methylmercury (MeHg) in farmland soils and plantains from farms sited near ASGM facilities were studied in four communities around Obuasi, Ghana. The human health risk assessment was evaluated using hazard quotient (HQ), estimated average daily intake (e AvDI), hazard index (HI) and Hg elimination and retention kinetics. Tweapease, Nyamebekyere and Ahansonyewodea had HQ, e AvDI and HI for THg of plantains for both adults and children below the recommended USEPA limit of 1, 3 × 10-4 mg/kg/day and 1, respectively. Odumase had HQ, e AvDI and HI for THg of plantains for both adults and children, higher than the guideline values. This meant that only Odumase may cause non-carcinogenic human health effects upon repeated exposure. The HQ, e AvDI and HI values of MeHg for all the study areas were far below guideline values, hence may not pose any non-carcinogenic human health risks to residents even upon repeated exposure. Retention and elimination kinetics of Hg also showed that only plantains from Odumase may pose significant non-carcinogenic human health risks to residents because the final amount of inorganic mercury exceeded the extrapolated USEPA guideline value of 0.393 µg/kg/year.