Objective: To clarify the current and cumulative effects of hydrazine hydrate (HH) (N2H4 · H2O: CAS No. 7803-57-8) on workers' health. Methods: A cross-sectional survey was carried out on 172 male HH-exposed workers (age 18-60, mean 39.6; exposure duration 0.50-34.17) and 125 male referent workers (age 19-58, mean 40.9) at 5 factories making HH or hydrazine derivatives in Japan. Current exposure concentrations were assessed by determining hydrazine in the breathing zones and urinary hydrazine + acetylhydrazine. The cumulative exposure level was assessed by multiplying the individuals' working durations at the job sites and the estimated past environmental levels at the job sites. Clinical examinations were performed with particular focus on hepatic and renal function tests. N-acetyltransferase (NAT2) phenotypes were assessed. Acute and chronic subjective symptoms related to HH were examined by self-administered questionnaires. Results: No hydrazine was detected in either the breathing zones or the urine of the referent workers. The mean hydrazine concentration in the breathing zones, hydrazine + acetylhydrazine in urine, and cumulative exposure level were 0.0109 ppm (N.D.-0.2003), 0.8660 μmol/g · Cr (N.D.-14.20), and 2.80 ppm-years (0.003- 19) respectively. There was no difference and no dose-dependent change in either the means or the prevalence of abnormal findings in health examination items between the HH-exposed and the referent workers after adjusting confounding factors and by means of the differences of NAT2 phenotypes. Among 90 subjective symptoms, complaint of 'nightmares' was significantly related to HH exposure. Conclusion: In this study, no health effect regarding current and cumulative HH exposure was observed in the HH-exposed workers when compared to the referent workers.
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