Heavy metal toxicity is increasing due to increasing trends of urbanization and
industrialization. Lead poisoning has been recognized as a major public health risk,
particularly in developing countries. It is nephrotoxic, hepatotoxic, neurotoxic, carcinogenic
and mutagenic for animals and human. Sewerage water, fertilizers, leaded-gasoline and lead
based batteries are the sources of lead contamination in soil and forage. The lead particles are
taken up by animals from contaminated forages and excreted in animal products like milk and
meat.
The presence of Pb in drinking water, waste water, plant products and animal
products has been studied which is a serious risk for animal and public health. The
legislations for the disposal of household wastes and industrial effluents are very poor in
Pakistan. The calculation of safe Pb levels in different products is still to be needed.
Pathological effects of higher Pb levels have not been studied in Pakistan. The present study
was aimed to unveil the toxic effects at constant dose of Pb over a period of three months in a
local sheep breed of Pakistan. The status of Pb toxicity was also investigated in a polluted
area around sewage drain and mutton slaughter house at District Jhang, Pakistan.
The Pb concentration in soil, forage and irrigating water was found to be below the
permissible limits and was safe for agriculture but long-term ingestion of low Pb
concentration may have cumulative effect. The serum Pb concentration was found to be
above the recommended safe limits for producing Pb toxicity in animals. The different tissues
like kidney, liver and skeletal muscles also contained higher Pb level from the permissible
limits and found to be unsafe for public use. Kidney showed the highest Pb concentration and
the muscle contained the least Pb level in the present study.
Summary
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The erythrocyte count, hemoglobin concentration and packed cell volume showed
inverse correlation with Pb concentration and mean values were below the normal range in
Pb treated sheep but anemia was not developed. The erythrocyte sedimentation rate was also
influenced by given dose of lead acetate during third month of treatment. The white blood
cells also revealed no effect on given dose of lead acetate in Lohi sheep in this study.
The biochemical parameters of field and treatment group showed higher concentration
as compared to control group of Lohi sheep but their means were falling within the normal
range of reference values. The disturbed biochemical parameters in apparently healthy sheep
with higher serum Pb concentration were indicative for liver and kidney damage.
Lohi sheep exhibited less effect on given dose of lead acetate during first two months
but more pronounced changes of chronic Pb toxicity were observed during last month of trial.
The histological changes were not observed on early period in lead acetated treated sheep.
The characteristic histological changes were observed on last slaughtering at day 90 in kidney
and liver including degeneration and focal areas of necrosis, dilatation of blood vessels with
accumulation of red blood cells and fibrosis in some areas. The nuclear changes were more
typical with intranuclear inclusion bodies in renal tubular epithelial cells but less
distinguishable in hepatocytes.
It was concluded that soil, forage and water contained low Pb levels in the study area.
The ingestion of low Pb level for longer period had cumulative effect in animals. The animals
might be resistant to low Pb level but their products are a severe risk for public health. So the
necessary measures should be adopted to minimize the heavy metal contamination in animal
products.