Sister chromatid exchange in response to variations in occupational lead exposure.

Sister chromatid exchange (SCE) rates in 10 long-term lead-exposed men increased significantly with increasing zinc protoporphyrin concentration in blood. SCE rates were also related to blood lead levels, but this correlation was not statistically significant. These results were obtained before the summer vacation. Six men were examined again shortly after the vacation; both SCE rates and lead-exposure parameters had decreased significantly. An increase was seen in one worker; however, this result could be related to a serious disease for which he was undergoing treatment. Continued examinations showed a tendency of increasing SCE rates and exposure parameters, but the follow-up was too incomplete to allow a statistical analysis. Further studies of 18 newly employed workers failed to show any increase in SCE during the first 4 months of employment despite some increases in both zinc protoporphyrin and lead levels in the blood. The results obtained suggest that a genotoxic effect due to inorganic lead may occur in long-term lead-exposed workers.