Objectives: To evaluate whether dimercaptosuccinic acid (DMSA) -chelatable lead, an estimate of current bioavailable lead stores, is a better predictor of lead-related symptoms than are other commonly used lead biomarkers.
Methods: A total of 95 male lead workers from three lead industries (one secondary lead smelting facility, one polyvinyl chloridestabilizer manufacturing plant, and one lead-acid storage battery factory), and 13 workers without occupational lead exposure recruited from an occupational health institute, were studied. Blood lead, blood zinc protoporphyrin (ZPP), 4 h DMSA-chelatable lead (after oral administration of 10 mg/kg DMSA), urine lead, and urinary delta-aminolevulinic acid levels were evaluated as predictors of 15 lead-related symptoms, assessed by self-administered questionnaire, with linear and logistic regression controlling for covariates. Total symptoms and symptoms in three categories (gastrointestinal, neuromuscular, and general) were evaluated.
Results: The mean (SD) 4 h DMSA-chelatable lead level was 288.7 (167.7) microg, with a range from 32.4 to 789 microg in the 95 lead workers. The mean (SD) in the non-exposed subjects was 23.7 (11.5) microg with a range from 10.5 to 43.5 microg. Blood lead, blood ZPP, and spot urine lead levels ranged from 21.4 to 78.4 microg/dl, 40 to 331 microg/l, and 7.5 to 153.0 micro/l, respectively, in the lead workers, and from 4.0 to 7.2 micro/dl, 27 to 52 microg/l, and 2.9 to 15.5 microg/l in the non-exposed controls, respectively. The overall mean symptom score (SD), derived as the sum of 0 or 1 point for absence or presence of 15 symptoms, of the lead workers was 3.7 (2.0), compared to 1.2 (1.5) for the non-exposed workers. DMSA-chelatable lead was the best predictor of symptom scores in both crude and adjusted analyses, compared with the other biomarkers. Lead workers with DMSA-chelatable lead values greater than the median (260.5 microg) were 6.2 times more likely to have frequent tingling or numbness of the arms or legs and 3.3 times more likely to have muscle pain than subjects with lower chelatable lead values. Three symptoms (tingling or numbness of arm or leg, muscle pain, and feeling irritation at the slightest disturbance) evidenced a dose-dependent relationship with DMSA-chelatable lead levels.
Conclusions: DMSA-chelatable lead was found to be the best predictor of lead-related symptoms, particularly of both total symptom scores and neuromuscular symptoms, than were the other other lead biomarkers.