Changes in urinary delta-aminolevulinic acid at low lead exposure level with special reference to production activity

A 7-year follow-up survey on 53 workers was carried out in a lead storage battery factory to evaluate the significance of urinary delta-aminolevulinic acid (ALA) and blood lead in a work environment where lead in the air was considered to be about or less than the current occupational exposure limit. While lead in the blood and ALA in the urine had a good correlation to each other cross-sectionally as well as longitudinally, geometric means of lead concentrations in the workroom air samples which were collected following grid sampling strategy, did not correlate with ALA in urine significantly. On the contrary, the semiannual production of batteries significantly correlated with changes in mean ALA in urine. The questionnaire survey proved that the prolongation in work hours, lead to an increase in the mean ALA in urine as well as a higher incidence of higher-than-normal urinary ALA. The results clearly demonstrated the importance of the biological indicators, such as lead in blood and urinary ALA, as well as the necessity of paying attention to non-industrial hygiene factors, such as the production rate of batteries and the length of the daily shift, for the protection of the workers' health when lead in the air is moderate.