OBJECTIVETo 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.

METHODSThe 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.

RESULTSThe 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).

CONCLUSIONIn 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.