Bone metabolism in occupational lead toxicity: Implications for polluted environments in developing countries

Abstract

Bone, the largest repository of lead (Pb) in the body, is not metabolically inert. Bone thus responds to
environmental toxins and pollution. Bone metabolism was examined in 86 all male lead workers drawn from various
lead-based occupations, and 51 apparently healthy subjects who had never been occupationally exposed to Pb. The
mean age of the Pb workers was 36.0 ± 0.03 years (± SEM) while that of the control population was 36.6 ± 1.2 years (±
SEM).
Blood lead concetration was significantly highe in the exposed than in unexposed subjects (p < 0.001). The
biomarker of environmental exposure, uric acid, was also significantly higher in Pb workers than in controls (p < 0.01).
Additionally, uric acid was positively correlated with blood lead (PbB) level (r=0.24; p< 0.026), serum zinc level was
also significantly higher in the exposed than unexposed subjects (p < 0.001).
In contrast, total and ionized levels of the major bone mineral, calcium, were lower in exposed than unexposed
subjects (p < 0.01 and p < 0.001) respectively. Calcium also appeared in the multiple regression analysis model,
indicating important association between lead and calcium. In addition, 19% of exposed subjects demonstrated
calcium level below 2 mmol/l (8 mg/dl) while only 4% of unexposed subjects demonstrated similar calcium levels.
Magnesium, inorganic phosphate, total protein and sub-fractions total and bone specific alkaline phosphatase (BAP)
were statistically similar in exposed and unexposed subjects (p > 0.05) in all cases.
Occupational lead toxicity and exposure to increasingly polluted environments impair bone mineralization which
may lead to increased incidence of bone disease (such as osteomyelitis and osteoporosis) in human and animal
populations. This is already a big health problem in the developed countries. This is frequently ignored in current
environmental health concern in developing countries.
Key Words: Lead toxicity; Bone metabolism; Bone mineralization; Blood lead; Rickets; Environmental pollution.