Mining induced heavy metal soil and crop contamination in Chililabombwe on the Copperbelt of Zambia

Abstract

Mining is considered to be the world’s most valued anthropogenic activity. For instance, in Zambia, mining is one of the most important economic sectors and contributes significantly to its Gross Domestic Product.On the other hand, it is recognised as being responsible for heavy metal soil and crop contamination. Mining induced heavy metal soil contamination is of concern because of its toxicity and accumulative power in soil and plants. These heavy metal contaminants eventually enter the food chain and endanger the health of human beings. Contamination of soils, water, air and food crops due to mining activities has been reported from other mining towns on the Copperbelt. Chililabombwe had hitherto been ignored by researchers due to the perception that heavy metal pollution was not a problem as the district did not have a smelter. This study makes an important contribution by showing that soil and food contamination can happen through other means. Therefore, this study investigated on heavy metal soil and food crop contamination in the mining district of Chililabombwe in the Copperbelt Province, Zambia. The aim of this study was achieved by collecting 96 triplicated soil samples from the surface layer (0 – 30 cm) and 80 samples of selected food crops (cassava, pumpkin, sweet potato leaves and white egg-plants) were collected. The levels of heavy metals such as copper, cobalt and iron were determined in each sample using the Atomic Absorption Spectrometer (AAS) PE 400. The study highlighted the actual levels of heavy metal contaminants in soil and food crops consumed in Chililabombwe. Simple regression analysis indicated that there is a strong significant relationship between distance and heavy metal soil concentration with p<0.05 at 0.95 confidence level (copper R² at 90 percent, cobalt 80 percent and iron 86 percent). Pearson’s Product moment correlation also displayed a moderate negative correlation between distance and levels of copper in soil with r above 0.3 (copper and distance r= - 0.5340212, cobalt with distance r = - 0.453402, iron and distance r = - 0.026407). The trends of heavy metal concentrations in soil revealed that Fe>Cu>Co and in food crops Fe>Cu>Co. It is also important to note that 80 percent of samples for copper and 100 percentfor iron in soil exceeded the World Health Organisation (WHO), Food and Agriculture Organisation (FAO) and Canadian thresholds with an exception of cobalt. Additionally, the study indicated 100 percent of heavy metal contamination in food crops in comparison with the FAO thresholds. These results indicate that the levels of heavy metals in soil and food crops are above thresholds. This entails that Chililabombwe suffers from heavy metal soil and food crop contamination. Therefore, it can be concluded that there is heavy metal contamination of soil and food crops in Chililabombwe on the Copperbelt of Zambia. The contamination of soil and food crops imply that heavy metals enter the food chain and pose potential risks to human life which leads to chronic illness and eventually death. It is therefore, recommended thatinformation from this study be used by the relevant authorities to develop appropriate measures for monitoring and control of heavy metal soil and food crop contamination in mining areas in Zambia. This study was conducted in March, 2013 towards the end of the rain season. Therefore, it is important that a comparative study on heavy metal soil and food crop contamination be conducted during thedry seasons.