δ-Aminolevulinic acid dehydratase activity, urinary δ-aminolevulinic acid concentration and zinc protoporphyrin level among people with low level of lead exposure

To evaluate the relationship of δ-aminolevulinic acid dehydratase (ALAD) activity, urinary δ-aminolevulinic acid (ALAU) level and blood zinc protoporphyrin (ZPP) concentration to low blood lead (PbB) levels, these biomarkers were determined for all subjects enrolled from a rural area of southeast China where people had low levels of exposure to lead. The mean values of PbB, ALAD, ALAU and ZPP were 67.11 μg/L (SD: 1.654, range: 10.90-514.04), 339.66 nmol ml−1 h−1 (1.419, 78.33-793.13), 20.64 μg/L (1.603, 2.00-326.00), and 0.14 μmol/L (3.437, 0.01-2.26), respectively. ALAD was inversely associated with low levels of PbB. ZPP was inversely related to low levels of PbB but positively related to relatively higher levels of PbB. Alcohol drinking contributed to low ALAD in men. Women had higher ZPP than men. ALAU had no significant association with PbB. In conclusion, ALAD possibly has a non-linear relation with low to moderate levels of PbB. At moderate levels of PbB, ZPP increases with increasing levels of PbB. ALAU is not suitable as an indicator for low levels of lead exposure.