Heavy Metals Levels in Forage Grasses, Leachate and Lactating Cows Reared around Lead Slag Dumpsites in Nigeria

A field study was conducted around Pb slag contaminated sites in Ibadan, Nigeria to assess the intake of trace metals by cows reared around the contaminated sites as indication of heavy metals contamination. Levels of Pb, Cd, Cu and Zn in blood, milk and faeces were determined in 20 cows exposed to the sites and 20 reference cows from uncontaminated areas. Chemical analysis of pasture grasses and leachate from the contaminated sites showed high levels of Pb. Range and mean levels of Pb, Cd, Cu and Zn in the forage grasses are: 209-899 (425 ± 79.0), ND-1.87 (0.94 ± 0.23), 4.01-8.78 (6.26 ± 0.62) and 17.4-202 (79.2 ± 23.5) mg/kg respectively. The mean values of 8.81±0.06, 0.041±0.003, 0.20±0.01 and 1.00±0.004 mg/L were obtained l for leachate Pb, Cd, Cu and Zn. Difference in blood and milk Pb was highly significant (p < 0.01) between the two groups of animals. Mean, median and range blood Pb concentration of 349±82.0, 312, < DL-1380µg/L, milk Pb concentrations of 347 ± 144, 313, < DL-630µg/L and faecal Pb concentrations of 2.08 ± 1.46, 2.00, 0.25-6.75 mg/kg were found in test animals whereas Pb was not detected in the tissues of the control animals. Analyses of blood, milk and faeces were found to be good indicators of environmental exposure to Pb. Test cows accumulated significantly higher levels of Zn in milk than in blood. Reverse is the case for Pb and Cu. The high concentration of Pb detected in both environmental and biological samples implies the need for sound management of hazardous waste.