Lead contamination and human health risk assessment through consumption of cow milk in Kabwe, Zambia.

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Zyambo, Golden
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The University of Zambia
Lead (Pb) contamination in the vicinity of lead mines and smelters affects both humans and animals. Chronic exposure to Pb via dietary intake of animal products such as milk from contaminated areas poses a health risk to consumers. Therefore, the aim of the current study was to evaluate the human health risk impact of Pb exposure through consumption of cow milk as well as to assess the seasonal variations of Pb concentrations in cow milk and blood of lactating cows in Kabwe, which has a long history of lead-zinc mine in Zambia. The cow milk and blood samples were collected from traditional smallholder, emerging smallholder and medium-sized dairy farms located in Kang’omba, Mukobeko, Mpima, Munga, and Kafulamase of Kabwe during the wet and dry seasons. The Pb metal concentrations were determined using Graphite Atomic Absorption Spectrophotometer (GFAAS) after samples were acid digested in a microwave-optimized system. Cow milk and blood lead levels (BLLs) showed seasonal significant differences at p = 0.05 using Dunn’s Multiple Comparison Test (DMCT, p < 0.05). The mean Pb metal level obtained in cow milk during the wet season ranged from 0.98 (± 0.30) to 2.32 (± 1.87) μg/kg while in the dry season the mean concentrations varied from 0.50 (± 0.24) to 4.24 (± 2.24) μg/kg. Similarly, the mean blood Pb concentrations ranged from 3.84 (± 3.22) to 21.8 (± 15.9) μg/kg in the wet season while in the dry season the mean ranged from 0.55 (± 0.24) to 23.8 (± 18.6) μg/kg. Of all the cow's blood samples analysed, 27% and 60% in Kang’omba and Munga respectively, exceeded the baseline value of 20 μg/kg. A higher concentration percentage of 37% in Kang’omba was recorded in the dry season while in Munga it remained unchanged at 60% in the wet season. Notably, the factors that influenced different Pb concentration patterns were the season, distance, and location of the farms from the Pb–Zn mine. The overall mean Pb concentration, chronic daily intake (CDIs), target hazard quotients (THQs), and incremental lifetime cancer risk (ILCR) results obtained were all below the maximum permissible limits of 20 g/kg, 3 and 12.5 g/kg-BW/day (for children and adults), 1 and 1.0 x 10-4 to 1.0 x 10-6, recommended by FAO/WHO, the joint FAO/WHO, FDA and USEPA respectively. In conclusion, although the study showed that Pb was present in all Kabwe studied regions, the health risk effects of Pb exposure associated with the consumption of milk in both adults and children were insignificant.
Thesis of Master of Science in Toxicology