Critical Dose of Lead Affecting δ-Aminolevulinic Acid Levels

Critical Dose of Lead Affecting δAminolevulinic Acid Levels: Katsuyuki MURATA, et al. Akita University School of Medicine—To estimate the critical dose of the association between the blood lead concentration (BPb) and δ-aminolevulinic acid (ALA) levels, ALA levels in plasma (ALA-P), blood (ALAB), and urine (ALA-U), and the activity of δaminolevulinic acid dehydratase (ALAD) were determined in 186 Japanese lead workers, aged 18– 62 yr, with BPb levels of 2.1–62.9 μg/dl. For this purpose, the benchmark dose (BMD) method, recently used in the environmental health field in place of the no-observed-adverse-effect level, was introduced into this study. The BMD was defined as the BPb level that resulted in an increased probability of abnormal change in ALA-related parameters by an excess risk (BMR) of 5% in exposed workers i.e., from P 0 (abnormal probability of 5% in unexposed workers) to P0+BMR for exposed workers at the BMD. ALA-related parameters were significantly correlated with BPb. The BMDs computed from the 186 workers, after controlling for age, were 15.3–20.9 μg/dl for ALA levels, and 2.9 μg/dl for ALAD; likewise, the BMDs from the 154 workers with BPb levels of less than 40 μg/dl were 3.3– 8.8 μg/dl for ALA levels, and 2.7 μg/dl for ALAD. Since the cutoff value of ALA-P, computed from the latter workers, seems to be closer to the upper normal limit in unexposed adults than does that from the former workers, it is suggested that the critical dose of BPb causing the increased levels of ALA is below 10 μg/dl. Such critical doses are necessary to promote preventive activities of adverse effects of lead. (J Occup Health 2003; 45: 209–214)