Objective To investigate the levels of blood lead and zinc protoporphyrin (ZPP), urine lead and δ-aminolevulinic acid (δ-ALA), and the fingerprint characteristics of stable lead isotopes among workers exposed to lead, and to analyze their correlations to provide a foundation for studies and applications of lead stable isotope tracing.

Methods Taking 40 lead-exposed workers in a lead-acid battery factory in a city as the research object, the relevant conditions such as working age, smoking, drinking, etc. were recorded by a questionnaire. The levels of blood lead, urine lead, and biomarkers associated with lead exposure were measured, as were the lead isotope ratio (LIR) (^207/206Pb, ^208/206Pb, ^204/206Pb) in blood, urine, environmental samples (workplace dustfall), and water, and statistical analysis was carried out.

Results The blood lead level of the subjects was 56.0-757.6 μg/L, with an average of (300.0 ± 159.8) μg/L, and the abnormality rate of 5.0%; the urine lead level was 2.5-235.3 μg/L, with an average of (40.1 ± 45.2) μg/L, and an abnormality rate of 7.5%; the blood ZPP level was 0.13-7.35 μmol/L, with an average of (1.78 ± 1.86) μmol/L, and an abnormality rate of 17.5%; the urine δ-ALA level was 0.71-7.46 mg/L, with an average of (2.78 ± 1.70) mg/L, and an abnormality rate of 7.5%. Pearson correlation analysis showed positive correlations between overall blood lead and blood ZPP, urine lead and urine δ-ALA, and blood lead and urine δ-ALA (r = 0.536, 0.728, 0.511, P < 0.01). Significant statistical differences were found in blood lead and blood ZPP levels among workers with different employment times (P < 0.05), with the higher levels observed in workers with employment times of 1-4 years; non-drinking workers had higher blood ZPP levels than drinking workers (P < 0.05). Workers exposed to lead had higher levels of ^208/206Pb and ^207/206Pb in their urine than in their blood (P < 0.01). The tap water from the plant showed lower levels of ^208/206Pb and ^207/206Pb compared to blood and urine (P < 0.01); the workplace dustfall had a lower level of ^208/206Pb compared to blood (P < 0.01), and both ^207/206Pb and ^208/206Pb were lower than those in urine (P < 0.01). There was a negative correlation between blood ^207/206Pb, ^208/206Pb and blood lead levels (r = -0.562, -0.673, P < 0.01) and between blood ^208/206Pb and urine δ-ALA levels (r = -0.416, P < 0.01). Urine ^207/206Pb and ^208/206Pb also showed a negative correlation with urine lead levels (r = -0.613, P < 0.01; r = -0.331, P < 0.05), and urine ^207/206Pb had a negative correlation with blood ZPP levels (r = -0.636, P < 0.01).

Conclusions Blood lead levels correlated well with blood ZPP and urine δ-ALA and were consistent with LIR in the environment. The difference in LIR in blood and urine indicated that lead may have "fractionation" after entering the human body.