Exposure to Hazardous Substances and Male Reproductive Health: A Research Framework

Article excerpt

The discovery in the mid-1970s that occupational exposures to pesticides could diminish or destroy the fertility of workers sparked concern about the effects of hazardous substances on male reproductive health. More recently, there is evidence that sperm quantity and quality may have declined worldwide, that the incidence of testicular cancer has progressively increased in many countries, and that other disorders of the male reproductive tract such as hypospadias and cryptorchidism may have also increased. There is growing concern that occupational factors and environmental chemical exposures, including in utero and childhood exposures to compounds with estrogenic activity, may be correlated with these observed changes in male reproductive health and fertility. We review the evidence and methodologies that have contributed to our current understanding of environmental effects on male reproductive health and fertility and discuss the methodologic issues which confront investigators in this area. One of the greatest challenges confronting researchers in this area is assessing and comparing results from existing studies. We elaborate recommendations for future research. Researchers in the field of male reproductive health should continue working to prioritize hazardous substances; elucidate the magnitude of male reproductive health effects, particularly in the areas of testicular cancer, hypospadias, and cryptorchidism; develop biomarkers of exposure to reproductive toxins and of reproductive health effects for research and clinical use; foster collaborative interdisciplinary research; and recognize the importance of standardized laboratory methods and sample archiving. Key words: hazardous substances, male reproductive health, research, semen quality. Environ Health Perspect 108:803-813 (2000). [Online 21 July 2000]


Paternal exposure to solvents, pesticides, and metals has been associated in animals and humans with the occurrence of spontaneous abortion, low birth weight, birth defects, childhood leukemia, brain cancer, change in the male:female sex ratio of offspring, and other end points related to growth and development. Certain paternal occupations--rubber worker, petroleum worker, agricultural chemical worker, painter, welder, and janitor--have been particularly implicated as detrimental to the reproductive health of men (1). The reproductive hazards of occupational exposure have been recognized by the National Institute for Occupational Safety and Health (NIOSH) as a priority area in need of further study. The National Occupational Research Agenda, coordinated by NIOSH, was established in 1996 to outline the research priorities that can lead to improved worker safety and health in 21 key areas of occupational health (2). One of the 21 priority research areas is fertility and pregnancy abnormalities, which includes male reproductive health.

However, exposure to environmental hazards is not limited to the workplace. Potential sources of exposure include food, air, water, soil, and hobbies. Individuals may have multiple exposures that in many cases occur chronically and at low doses. The reproductive health implications of chronic exposures to reproductive toxicants are not well documented and, in general, the mechanisms of toxicity are either poorly understood or unknown.

Reports of declining sperm counts over the past 50 years and other disturbing trends alerted scientists to the possibility that exposure to chemicals in the environment may damage male reproductive health. Testicular cancer, the most common malignancy in men 15-44 years of age (3), has increased markedly in incidence in this century in virtually all countries studied. The incidence of hypospadias, a developmental malformation of the male urethra, appears to be increasing worldwide. Cryptorchidism (undescended testicle), another developmental defect, may have increased in some human populations and appears to be increasing in wildlife (4,5). …