Reproduction disruption: hydrocarbons may affect menstrual cycle. (Science Selections).

Studies have shown that exposure to hydrocarbons in fuels and solvents can adversely affect fertility in both men and women. In this month's issue, researchers from the University of Cincinnati and the National Institute for Occupational Safety and Health dig deeper into this issue with an investigation designed to examine the potential effects of low-dose hydrocarbon exposure on endocrine production of reproductive hormones in women [EHP 110:805-811]. Their analysis uncovers a disturbing association between low-level hydrocarbon exposure and reduced concentrations of an endocrine hormone that plays a role in whether a woman's menstrual cycle is capable of supporting conception.

The investigators examined female U.S. Air Force personnel who had been exposed to fuel (primarily jet fuel) and solvents to varying degrees in the course of their military duties. A sample of 170 women completed detailed questionnaires about their work, health, and reproductive and menstrual histories, along with other pertinent information. Of these women, 100 also kept daily diaries documenting two consecutive menstrual cycles, including chemical and physical exposures during that time, and urine sample collection data.

Daily first morning urine samples were analyzed for the presence of four key urinary endocrine markers that have been associated with nonconceptive menstrual cycles: lower preovulatory luteinizing hormone (LH), lower midluteal-phase pregnanediol 3-glucuronide and estrone 3-glucuronide, and higher follicle-phase pregnanediol 3-glucuronide. The researchers also collected exhaled breath samples from 63 of the participants, which allowed a more sensitive measurement of low-dose exposure to hydrocarbons than blood or urine sample analysis. This was a one-time sample collection performed during the initial interview, an average of 1.4 hours after the women had left their work sites. The researchers analyzed the breath samples to estimate internal doses of the two groups of hydrocarbons found in fuels and solvents: aliphatic hydrocarbons (such as hexane and octane) and aromatic hydrocarbons (such as benzene and toluene).

The major discovery was that preovulatory LH concentrations in urine were significantly lower in the women who had higher internal doses of aliphatic hydrocarbons. The investigators are careful to note that it is unclear whether those lowered LH concentrations were low enough to affect conception, and that their study was not designed to address that question. However, as they explain, LH controls the secretion of sex hormones in both sexes and is essential for ovulation and luteinization (a key step in the ovulatory process). As such, they write, "if [hydrocarbon] exposures chronically alter LH levels, this effect could impact LH-dependent processes and thereby compromise reproduction."

The researchers suggest that their findings need to be confirmed in future studies designed to detect the possible effects of aliphatic hydrocarbon exposure on the ability to conceive and maintain pregnancy. Although the study population in this case was at a greater risk of exposure to these compounds than the general population, most everyone comes into contact with them at one time or another in the course of activities as routine as refueling an automobile. As such, the implication that exposure to aliphatic hydrocarbons could adversely affect conception is of wide concern, and warrants further investigation.