A review of 45 scientific studies has found that toxic metals linked to illegal mining, popularly known as galamsey, are contaminating commonly consumed vegetables in Ghana and exposing consumers to increased health risks. Published in the journal Environmental Monitoring and Assessment, the study examined how five potentially toxic elements — lead, cadmium, chromium, mercury and arsenic — migrate from mining-affected soils and irrigation water into vegetables such as tomatoes, pepper, garden eggs and onions. The research was conducted by Mr Eric Osei Bonsu, a research assistant and scientist at the CSIR-Crops Research Institute in Kumasi, in collaboration with co-authors Michael Kwabena Osei, Harry Okyere and James Korang.
Cadmium found to be highest risk
The review, which examined studies conducted in 11 mining districts across Ghana, found that cadmium had the highest soil-to-plant transfer rates in tomatoes and garden eggs, with transfer factors exceeding 1.0. This indicates that cadmium concentrations in the vegetables could be equal to or higher than those in the soil in which they were grown.
The study also revealed that lead, arsenic and mercury levels in vegetables exceeded the limits set by the World Health Organisation (WHO) and the FAO Codex at several locations, particularly in the Ashanti and Western Regions. At the most contaminated sites identified, arsenic concentrations were as high as 200 times the permissible limit, while mercury levels reached up to 400 times the threshold.
The researchers further cautioned that the cumulative hazard index exceeded 1.0 in every mining-adjacent community where it could be calculated. This suggests that people who regularly consume vegetables grown in these areas face an increased risk of non-cancer-related health effects.
Chromium data incomplete
The study found that chromium uptake by plants remained low, even in soils where concentrations exceeded 300 milligrammes per kilogramme. However, it cautioned that almost none of the studies reviewed distinguished between trivalent chromium and the significantly more toxic hexavalent chromium. This means that low levels of total chromium transfer into plants could still mask a serious health risk.
The researchers proposed three key measures to address the issue. First, monitoring of vegetables, soil and irrigation water should focus on districts affected by mining rather than being distributed uniformly across the country. Second, proper washing and handling of produce after harvest can help reduce surface contamination before vegetables reach markets, although these measures cannot eliminate metals already absorbed into plant tissues. Third, buffer zones for agricultural activities around mining sites should be determined using local contamination data instead of applying a uniform distance across all areas.
The review also highlighted three major research priorities: measuring chromium and arsenic according to their chemical forms, improving models to assess the combined effects of multiple metals, and conducting long-term human biomonitoring in affected communities to establish links between contaminants detected in food and those found in people.
Mr Bonsu emphasised that the research was a collective effort, expressing appreciation to his co-authors and colleagues at the CSIR-Crops Research Institute and the CSIR College of Science and Technology.
