working on aircraft maintenance at an Air Force installation and eight nonexposed men at the same facility.

Semen quality was assessed at baseline, before entry into the exposed job, and at periods of 15 and 30 weeks post-baseline, during which the men were occupationally exposed to solvents or jet fuels (primarily JP4). Although those two periods were chosen to allow for two complete cycles of spermatogenesis, the distal regions of the epididymis contain sperm of different ages.

At baseline (before entry into the workplace) semen was collected but there was no exposure monitoring. For 15 and 30 weeks of occupational exposure, semen assays and exposure assessment—with industrial-hygiene monitoring and breath sampling—were conducted for the exposed group, and only semen assays were requested for the nonexposed office workers.

Overall, for most sperm measures, the mean values remained within normal range throughout the 30 weeks of exposure. The findings by cycle for all exposed subjects were compared with reference values, and all semen measures at all cycles were found to be similar to reference limits except for percent motile,1 which was consistently lower. The eight nonexposed subjects had sperm measures similar to the exposed group, and their percent motile was also lower at baseline than the reference. Thus, the findings indicate that exposure to jet fuel did not have an apparent effect on semen quality of aircraft-maintenance personnel. Two possible explanations for the findings are that the mixtures are not associated with spermatotoxic effects at low concentrations and that the exposure measured at one point may be inadequate for characterizing the true absorbed dose.

The strengths of the study were that analyses were adjusted for potential confounders, including alcohol, smoking, and caffeine. Limitations of the study include the appreciable differences in age among the men in the different job groups and the low statistical power.

Spontaneous Abortion

The most common cause of spontaneous abortion is a genetic abnormality of the embryo. Risk factors for spontaneous abortion include age, maternal illness, cigarette-smoking, alcohol use, use of some medications, and a previous spontaneous abortion. The risk of pregnancy loss is known to increase with maternal age, especially after the age of 30 or 35 years; and is also high in women under the age of 18 years. In a woman who has had one spontaneous abortion, the probability of a second is estimated to be 13–26%; and the probability of another increases with successive spontaneous abortions (Smith and Suess 1998). Several maternal occupational exposures have been associated with the risk of spontaneous abortion, including exposure to ethylene oxide, antineoplastic agents, and possibly anesthetic gases.

Spontaneous abortion was studied in women living near oil fields in the Amazon basin of Ecuador (San Sebastián et al. 2002). The water in the rivers and streams of that area is contaminated with oils and is used for drinking, cooking, and bathing. Women living in several communities downstream of oil fields (n=365) were compared with women living upstream and farther from the fields (n=283). The concentration of total petroleum hydrocarbons in drinking water were 0.02 to 2.88 ppm in exposed communities. After adjustment for confounders, women in exposed communities were more likely to report pregnancies ending in spontaneous abortion (OR 2.47, 95% CI 1.61–3.79, p<0.01). The multivariate analysis adjusted for age at interview, age at pregnancy, pregnancy order, year of pregnancy, and socioeconomic status (SES).


Percent motile depends on time from ejaculation until sample analysis.

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