Blood lead levels in lactating cows reared around polluted localities; transfer of lead into milk

Lead is pervasive environmental pollutant with potential public health hazard as a contaminant of food from animal origin. The present study examines the blood and milk lead level in animals reared in areas around different industrial activities and to find out correlation between blood and milk lead levels in lactating cows. Blood and milk samples (n = 149) were collected from animals reared around steel processing unit (n = 22), lead-zinc smelter (n = 21), aluminum processing plant (n = 25), rock phosphate mining area cum phosphate fertilizer plant (n = 21), coal mining areas (n = 46) and closed lead but functional zinc smelter (n = 14). Samples were also collected from randomly chosen 52 lactating cows reared in non-polluted areas to serve as controls. Significantly (P < 0.05) higher blood lead level was recorded in animals reared around lead-zinc smelting factories followed by closed lead but functional zinc smelter, aluminum processing unit and steel manufacturing plant, as compared to values recorded for control animals. The highest milk lead level (0.84 +/- 0.11 microg/ ml) was detected in animals reared in the vicinity of lead-zinc smelting unit followed by aluminum processing plant and steel processing unit. Analysis of correlation between blood lead levels and lead excretion in milk through sorting the blood lead values into 9 different ranges irrespective of site of collection of samples (n = 201) revealed significant correlation (r = 0.469 at P < 0.01) between blood and milk lead concentrations. The lactating cows with blood lead levels above 0.20 microg/ml (groups 5-9) had significantly (P < 0.05) higher milk lead excretion than those with blood lead levels from non detectable to 0.20 microg/ml (groups 1-4). Pearson correlation analysis between blood and milk lead concentrations in 122 animals with blood lead <0.20 microg/ml showed non-significant correlation (r = 0.030 at P < 0.05) but a significant correlation was observed between these two parameters with blood lead level above >0.02 microg/ml indicating that the excretion of lead through milk increases with the increased in blood lead level above 0.20 microg/ml.