Infertility and the Environment

by Michael S. Neal
Winter 2006

Although more than 80 percent of couples or individuals who experience difficulty conceiving have a diagnosis for their infertility, the underlying cause is rarely found. Increasing information suggests that some reproductive disorders, including both male and female infertility, are caused by environmental contaminants. Chemical exposure is a common daily occurrence. Industrial and technological advances have led to the production and use of many new compounds. Individuals may be exposed to these chemicals in the workplace and through soil, air, water and food. Furthermore, many chemicals are present in household products and exert their effects at very low concentrations. Exposure to environmental contaminants may affect reproductive processes depending on the dose, duration of exposure, timing of exposure (ie: in utero, during childhood, adolescence, or in adulthood) and in a certain genetic context. Genetic and environmental processes, however, are not necessarily independent, given that the effects of an environmental contaminant are believed to occur in a genetic framework, and may also cause genetic alterations that result in disease. These issues pose significant challenges in assessing the cause and effect of environmental chemicals on human health and, in particular, on reproductive health. This further challenges how health care professionals counsel patients for maximizing their fertility potential.

Endocrine Disruptors

Of all environmental contaminants, endocrine disruptors are perhaps the prototype for mechanisms underlying how environmental contaminants may result in disease. Endocrine-disrupting chemicals (EDCs) comprise a group of chemicals that cross-react with estrogen receptors and alter steroid hormone production or metabolism. These contaminants come from various sources including plastics, household cleaners, industrial by-products, pesticides, cosmetics and occupational solvents, and can infiltrate the endocrine system altering the reproductive ability of the individual. A wide range of hormone-dependant organs (pituitary gland, hypothalamus, and reproductive tract) are targets for EDCs. Upsetting routine physiological messages from cells and tissues by interfering with hormone production can have dramatic effects on reproduction. Although toxicants have the potential to cause damage in various ways, hormone disruption is a common mechanism by which adverse agents alter normal reproduction.

Cigarette Smoke

Another area of interest from the perspective of environmental exposure is focused on the association between cigarette smoking and infertility or sub-fertility. Arguably, tobacco smoke represents the largest worldwide chemical exposure in humans through both active and passive smoking. Smoking has a negative effect on the fertility of both men and women. Epidemiological studies show that smoking by men and passive and active smoking by women are associated with a longer time to pregnancy. Furthermore, the chances of being successful using assisted conception are reduced if the woman is exposed to mainstream or passive smoke. Tobacco smoking has been associated with a decrease in sperm concentration, motility, and sperm morphology and there is a correlation between cotinine (a metabolite of nicotine) levels in seminal plasma and fertilizing ability of sperm. Cigarette smoke constituents have also been detected in follicular fluid. Cotinine, benzo-[a]-pyrene, and cadmium (a heavy metal) have all been detected in the follicular fluid of women who smoke demonstrating that the chemicals present in cigarette smoke have access to the developing follicle. It has also been suggested that smoking has an adverse effect on gamete (sperm and egg) quality. Cigarette smoking has been associated with an increased incidence of chromosomally unbalanced oocytes and higher risk of aneuploidy in sperm. Taken together the use of compromised gametes either from the male or female may be one underlying cause of infertility among smokers.

Occupational Exposure

Although many studies of environmental exposure and infertility have focused on cigarette smoke, a few studies indicate that occupational exposures may also be associated with an increased risk for infertility. A number of studies show that exposure to a mixture of organic solvents in the workplace increases the risk of adverse reproductive outcomes. Solvents occur in relatively high concentrations in hairstyling products, paints, and mechanical grease. Studies have shown that women exposed to the solvent toluene (used in businesses that print coloured illustrations for magazines and catalogues) took longer to conceive. An increased risk for infertility may exist for women constantly exposed to ethylene oxide or nitrous oxide by working in medical or dental offices that use these chemicals. Radiant heat also can affect testicular function (eg. decreased or altered sperm production). Welders, ceramic and foundry workers, and food preparers potentially encounter this exposure. Heat can affect the seminiferous epithelium and subsequently the quality of sperm. Heavy metals used in a number of industries can affect both female and male fertility.

Summary

Exposure to environmental chemicals is an important consideration when one’s fertility is brought into question. Reproductive health professionals should counsel patients who are trying to achieve a successful pregnancy to limit their exposure to potentially harmful occupational and environmental toxicants, especially those from cigarette smoke. It is important to recognize, however, that many of the studies to date are limited to small sample size, poor exposure assessment, poor outcome measures or recall bias. Additional studies are necessary to clarify the magnitude of risk associated with fertility. However, precaution is advised, as well as increasing awareness among health care professionals with regard to estrogen-mimics, exposure windows, dose, mixtures and genetic context to better appreciate minor and major threats to reproductive health. Through better understanding it is hoped that prevention of infertility and miscarriage related to controllable factors in the environment can be accomplished.

About the author

Micheal S. Neal is Laboratory Manager at the Center for Reproductive Care, Hamilton Health Sciences.