It has been a quarter of a century since the harmful effects of the nematocide dibromochloropropane (DBCP) on semen and sperm quality became known.
At the time, the discovery prompted a question: Was the DBCP incident an isolated phenomenon or just the tip of the iceberg? Jens Peter Bonde, MD, PhD, head of the department of occupational medicine, Aarhus University Hospital, Denmark, sank the iceberg theory during a presentation at the 8th International Congress of Andrology here.
“Several occupational risk factors to sperm and semen quality have been identified during the past 25 years, but effects, if any, often are weak,” Dr. Bonde said.
Dr. Bonde outlined various studies that were conducted in response to the DBCP incident. Investigators analyzed semen and reproductive hormones in workers in a wide range of occupations involving exposure to various chemicals.
“Although many studies showed positive associations between an occupational chemical exposure and one or more measures of semen quality, it is noteworthy that most associations were weak and, with a few remarkable exceptions, could not be considered causal,” he said.
In Europe, investigators looked for over-representation of men in specific occupations, with paradoxical results in at least one: men welding stainless steel, and thus exposed to hexavalent chromium, did not have increased risk of infertility.
However, mild-steel welders working on non-alloyed steel suffered a decreased fertility rate, higher infertility rate, and reduced semen quality.
Occupation and Semen Quality
Recently, the European Commission launched the Asclepios studies on three high-priority substances: pesticides, styrene, and inorganic lead.
“Most studies failed to demonstrate any consistent deleterious effect of occupational exposures on male fecundity,” Dr. Bonde reported. “Chemical workplace exposure in adulthood may not be an important risk for sperm and semen quality in Europe at present.”
Dr. Bonde emphasized several topics in need of rigorous research.
“To what extent does the moderate increase in scrotal temperature associated with sedentary work have a bearing on testicular function and infertility?” he asked.
In addition, examining effects of psycho-social stressors in the workplace has become a priority, Dr. Bonde said.
“Mental distress might be important from a biological point of view because of the links between reproductive hormones and stress hormones, and infertility itself may be a strong stress factor,” he said.
It is still an open question as to whether an adult male’s exposure plays a role in his child’s developmental abnormalities, Dr. Bonde noted. The converse is also true.
“There is a need for an entire new generation of studies linking prenatal exposure with sperm and semen quality in later life,” he said.