Sperm (Credit: NASA)

Marcello Spanò, of the Italian National Agency for New Technologies, Energy and the Environment (ENEA) and members of an EU-funded international research team have demonstrated that polychlorinated biphenyls (PCBs), may damage sperm. However, despite this PCBs do not have dramatic effects on human fertility.

PCBs are synthetic organic compounds that have been used as dielectric fluids for electrical components, such as capacitors and transformers, heat transfer fluids, fluids for hydraulic equipment, as lubricants and cutting oils, and as additives in pesticides, paints, adhesives, sealants, and plastics.

However, their solubility in fat and potential for accumulation in the environment coupled with their toxic effects (for instance, chronic exposure in workers handling PCBs causes chloracne and potentially liver damage) means that they are little used now. Unfortunately their environmental persistence means that PCBs continue to enter the human food chain.

PCB Archetypal PCB (Structure by David Bradley)

Spanò and colleagues published their findings on PCBs online in the journal Human Reproduction on October 13, 2005. In the same report, they also considered the effects of dichlorodiphenyldichlorethylene (DDE), a breakdown product of the pesticide DDT and found that this compound did not damage sperm DNA.

The impact on human fertility of persistent organochlorine pollutants, of which PCBs and DDT are just two, remains a controversial area, particularly because research has been limited and contradictory findings have been obtained on the effects of such compounds on the integrity of chromatin, the DNA and associated proteins that make up a chromosome. They collated data from a general population of more than 700 men (193 Greenland Inuits, 178 Swedish fishermen, 141 men from Warsaw in Poland and 195 men from Kharkiv in Ukraine). A standard Sperm Chromatin Structure Assay (SCSA) tested chromatin integrity and profiled any DNA damage by the DNA fragmentation index (DFI).

The results produced an intriguing and puzzling finding: among the European men overall, the DFI rose in concert with rising levels of PCBs in the blood, with sperm DNA fragmentation reaching a 60% higher average level in the group exposed to the highest levels of persistent organic pollutants. But, the researchers saw no such significant association among the Inuit men.

"The results from the Inuit cohort are surprising and reassuring," says Spanò, "As usual, we wanted a simple answer and instead we found a lot of new questions." He adds that the researchers can only speculate, at this stage, that genetic make-up and/or lifestyle factors somehow counteract the effects of the pollutants in this group.

Spanò says that it is important to keep the results in perspective. The median level of damaged sperm DNA was 10% and most men in the study were fertile. The probability of fathering a child starts to decrease when the proportion of damaged sperm reaches about 20% and becomes negligible from 30-40% onwards. "PCB exposure might negatively impact reproductive capabilities especially for men who, for other reasons, already have a higher fraction of defective sperm," he adds.

Hum. Reprod. Advance Access published online on October 13, 2005, http://dx.doi.org/10.1093/humrep/dei297
 
Human Fertility at Risk from Biopersistent Organochlorines in the Environment? http://www.inuendo.dk
 
European Society of Human Reproduction and Embryology, http://www.eshre.com