Objective: To investigate the lead exposure, its effects, and the relationships between biomarkers of susceptibility in the workers with low-level occupational lead exposure, and to explore its sensitivity and practical value to evaluate the health hazard.
Methods: The concentrations of lead fume and lead dust in workplaces of a lead acid storage battery enterprise in Jiangsu Province, China, were measured by occupational health monitoring method. The blood samples of 233 workers with occupational lead exposure and 76 non-occupational lead exposure were collected to measure the blood lead (Pb-B) level using graphite furnace atomic absorption spectrometry (GFAAS), the zinc Protoporphyrin (ZPP) level with blood fluorescence assay, and the delta-aminolevulinic acid dehydratase (ALAD) concentration by a spectrophotometer, and to determine the gene polymorphism of ALAD with TaqMan real-time polymerase chain reaction. At the same time, their urine samples were collected to measure urine lead (Pb-U) concentration with GFAAS and delta-aminolevulinic acid (ALA-U) concentration with a spectrophotometer. The correlations between the above indices were analyzed by multiple linear regression method.
Results: The concentration of lead fume in 18 testing sites and the concentration of lead dust in 30 testing sites were 0.002-0.019 mg/m3 and 0.004-0.013 mg/m3, respectively. Pb-B level was positively correlated with Pb-U concentration (r=0.62, P<0.01) and ZPP level (r=0.47, P<0.01) and was negatively correlated with ALAD concentration (r=-0.77, P<0.01) in 233 workers with occupational lead exposure. Among 233 workers, 218 (93.6%) had ≤70 µg/L Pb-U, and 15 (6.9%) had ≥400≥g/L Pb-B. Pb-B level was not correlated with ZPP level as Pb-B level was <190 µg/L (r=0.18, P=0.068 ), while Pb-B level was positively correlated with ZPP level as Pb-B level was ≥190 µg/L (r=0.36, P<0.01). Pb-U concentration was positively correlated with ALA-U concentration (r=0.49, P<0.01) and ZPP level (r=0.47, P<0.01). ZPP level was negatively correlated with ALAD concentration (r=-0. 19, P<0.01), and was positively correlated with ALA-U concentration (r=0.27, P<0.01). ALAD concentration was not correlated with ALA-U concentration (r =-0. 11, P>0.05). And in 233 workers with occupational lead exposure, there were no significant differences in Pb-B level, ZPP level, and ALAD activity between the workers with ALAD1-2 genotype and the workers with ALAD1-1 genotype (P>0.05). In 76 workers with non-occupational lead exposure, there was no significant difference in Pb-B level between the workers with ALAD1-2 genotype and the workers with ALAD1-1 genotype (P >0.05). The workers with ALAD1-2 genotype had a significantly lower ALAD activity, and a significantly higher ZPP level compared with those ALAD1-1 genotype (P<0.01).
Conclusion: In the workers with low-level occupational lead exposure, ZPP level is positively correlated with Pb-B level when Pb-B level was ≥190 µ/L. ALAD could be used as an effect biomarker of low Pb-B level. ALAD gene polymorphism shows different effects on the Pb-B level and the toxic effects between the workers with occupational lead exposure and the workers with non-occupational lead exposure.