Benzene exposure near the U.S. permissible limit is associated with sperm aneuploidy

Abstract

Background: Benzene is a common industrial chemical known to induce leukemia and other blood disorders, as well as aneuploidy, in both human blood cells and sperm at exposures > 10 ppm. Recent reports have identified health effects at exposure levels < 1 ppm, the permissible exposure limit (PEL; 8 hr) set by the U.S. Occupational Safety and Health Administration. Objective: We investigated whether occupational exposures to benzene near 1 ppm induce aneuploidy in sperm. Methods: We used multicolor fluorescence in situ hybridization to measure the incidence of sperm with numerical abnormalities of chromosomes X, Y, and 21 among 33 benzene-exposed men and 33 unexposed men from Chinese factories. Individual exposures were assessed using personal air monitoring and urinary concentrations of benzene and trans,trans-muconic acid (E,E-MA). Air benzene concentrations were not detectable in unexposed men; in exposed men, concentrations ranged from below the detection limit to 24 ppm (median, 2.9 ppm), with 27% of exposed men (n = 9) having concentrations of ≤ 1 ppm. Exposed men were categorized into low and high groups based on urinary E,E-MA (median concentrations of 1.9 and 14.4 mg/L, respectively; median air benzene of 1 and 7.7 ppm, respectively), and aneuploidy frequencies were compared with those of unexposed men. Results: Sperm aneuploidy increased across low- and high-exposed groups for disomy X [incidence rate ratio (IRR) = 2.0; 95% confidence interval (CI), 1.1-3.4; and IRR = 2.8; 95% CI, 1.5-4.9, respectively], and for overall hyperhaploidy for the three chromosomes investigated (IRR = 1.6; 95% CI, 1.0-2.4; and IRR = 2.3; 95% CI, 1.5-3.6, respectively). We also found elevated disomy X and hyperhaploidy in the nine men exposed to ≤ 1 ppm benzene compared with unexposed men (IRR = 1.8; 95% CI, 1.1-3.0; and IRR = 2.0; 95% CI, 1.1-3.9, respectively). Conclusions: Benzene appeared to increase the frequencies of aneuploid sperm for chromosomes associated with chromosomal abnormality syndromes in human offspring, even in men whose air benzene exposure was at or below the U.S. permissible exposure limit.