Reassessment of the threshold of the blood lead level to increase urinary δ-aminolevulinic acid based on their relationship in recent lead workers in Japan

Abstract

Objectives: The present study investigated the quantitative relationship between blood lead (Pb-B) and urinary δ⁻aminolevulinic acid (ALA-U) in lead workers, and examined the Pb-B level that induces increases in ALA-U and the corresponding ALA-U. Methods: We collected 10 562 data sets on Pb-B, ALA-U, age, and smoking habits from 808 workers (771 males and 37 females) who underwent multiple lead poisoning medical examinations at a lead-acid battery and lead smelting plant in Japan between 1995 and 2018. Females were excluded, and data collected in 169 subjects prior to engaging in lead work were used as the control. Pb-B and ALA-U levels were measured by graphite furnace atomic absorption spectrophotometry and high-performance liquid chromatography respectively. Results: A significant dose-response relationship was observed between Pb-B and ALA-U based on Pb-B-classified observations of increases in ALA-U values and the prevalence of over-reference ALA-U as well as regression analyses independent of smoking habits. The results obtained revealed that the threshold of Pb-B to increase ALA-U was 25.1-35.0 µg/dL based on the significant elevation point of the prevalence of over-reference ALA-U and 16.2-22.3 µg/dL from a 3rd degree regression equation. Conclusions: We proposed a threshold of Pb-B to increase ALA-U of 20 µg/dL and a biologically acceptable value of ALA-U of 1 mg/L, corresponding to the threshold.