Oct. 12, 2005 -- A common type of pollutant widely found in the environment may damage sperm, according to a new report.
European researchers found rising levels of polychlorinated biphenyls (PCBs), a now-banned class of chemicals with about 200 toxic byproducts, in the blood was associated with rising levels of DNA damage to sperm. Among men with the highest levels of PCBs in their blood, up to 60% of their sperm displayed signs of damage.
According to the Agency for Toxic Substances and Disease Registry, PCBs are synthetic compounds that were used in the past as coolants and lubricants for a variety of equipment. In 1977, their manufacture was banned due to health concerns. However, items such as lighting and electrical devices made before 1977 may still harbor PCBs.
The use of PCBs has been banned by most countries, including the U.S., for many years, but they persist in the environment and can be found in water, soil, and air. Exposure can happen through ingestion of contaminated foods, such as fish that swim in polluted waters or contaminated well water. Also, air exposure can occur around older electrical equipment, such as televisions and refrigerators.
Researchers say it's too soon to tell if the sperm damage caused by PCBs might affect male fertility, but these findings suggest further research is warranted.
PCBs Linked to Sperm Damage
In the study, published in the journal Human Reproduction, researchers looked at the effect of two common pollutants, PCBs and DDE (a byproduct of DDT, a banned insecticide), on sperm quality in more than 700 adult men. The men included Inuits from Greenland, Swedish fishermen, and men from Warsaw, Poland, and Kharkiv, Ukraine.
Researchers measured levels of PCBs and DDE in the men's blood and examined sperm samples for DNA damage.
The results showed that among European men, the amount of damaged sperm rose along with rising levels of PCBs in the blood. But no such association was found among the Inuit men.
"The results from the Inuit cohort are surprising and reassuring. As usual, we wanted a simple answer and instead we found a lot of new questions," says researcher Marcello Spanò of the Italian National Agency for New Technologies, Energy, and the Environment in Rome, in a news release. "We can only speculate, at this stage, that genetic make-up and/or lifestyle factors seem to neutralize or counterbalance the pollutants in this group."
Affect on Male Fertility Unknown
Overall, the average level of damaged sperm associated with PCB exposure was 10%, and most of the men in the study were fertile.
Researchers say the probability of fathering a child begins to decrease when the percentage of damaged sperm reaches about 20% and becomes negligible at about 30%-40%.
"PCB exposure might negatively impact reproductive capabilities especially for men who, for other reasons, already have a higher fraction of defective sperm," says Spanò.
Researchers say the impact of pollutants on human fertility is still unknown and there have been many contradictory findings so far as to whether PCBs and DDT/DDE may damage male sperm.
In this study, the DDT derivative did not appear to affect sperm quality.
But Spanò says they only measured two major types of chemical pollutants, "so we are seeing only the tip of the iceberg."