Chemical exposure linked to sperm defects, says US study

29 December 2011

Exposure to certain organochloride chemicals was associated with chromosomal abnormalities in the sperm, results of a cross-sectional US study showed. There was a significant trend of increasing incidence rate ratios (IRR) for increasing quartiles of exposure to dichlorodiphenyldichloroethylene (p,p’-DDE) for XX (P<0.001 for trend), XY (P=0.001), and total sex chromosome disomy (P<0.001), according to Melissa Perry, ScD, MHS, from George Washington University in Washington, and colleagues.

For polychlorinated biphenyls (PCB), there was a significant trend of increasing IRRs for increasing quartiles of exposure for XY (P<0.001 for trend) and total chromosome disomy (P<0.001), they reported in Environmental Health Perspectives. However, there was an inverse relationship with the XX disomy (P<0.001).

“PCBs and p,p’-DDE are persistent, lipophilic, endocrine-disrupting organochlorines that readily penetrate the blood-testis barrier,” the authors stated.

A subset of 192 men was drawn from another study of environmental impacts on semen. The samples were collected from men ages 20 to 54 who underwent infertility evaluation at the Massachusetts General Hospital Fertility Center between January 2000 and May 2003. Subjects were eligible if they had a sperm sample for fluorescence in situ hybridization (FISH) analysis. Non-fasting blood samples were analyzed for 57 individual PCB congeners and p,p’-DDE.

A single investigator performed FISH, sperm imaging, and nuclei scoring. FISH was carried out for chromosomes X and Y. Chromosome 18 was also evaluated as an autosomal control.

The authors noted that although chromosomal abnormalities are major contributors to reproductive problems, few studies have looked at the role of environmental risk factors. They designed their study to look for linkages between the frequency of sperm sex chromosome aneuploidy and PCBs or p,p’-DDE exposures.

When the researchers evaluated p,p’-DDE exposure, the dose-response curve was non-linear with the most increase in disomy happening between the first and second quartiles. There were no substantial additional increases seen across the remaining quartiles.

There were similar findings when PCBs were evaluated. Again, the largest changes were between the first and second quartiles with some consistent increases across subsequent quartiles.
Men in this study were members of sub fertile couples seeking infertility evaluation and may differ from men in the general population, the authors cautioned.

However, the researchers pointed out that there is currently no evidence to indicate that men differ in ways that might alter their response to the chemicals being investigated, so the results may apply to general population samples.

The authors also pointed out that karotyping was not routinely performed, so the prevalence of other underlying reproductive conditions in their clinic sample was not known.

“The results of our study suggest that men with higher serum p,p’-DDE levels have significant increases in the rates of XX, XY, and total sex chromosome disomy,” they wrote. “Men with higher serum levels of PCBs had significant increases in the rates of YY, XY, and total sex chromosome disomy. In contrast, there was a significant decrease in the rate of XX disomy for higher serum levels of PCB.”

Source: M. McAuliffe, et al., “Environmental exposure to polychlorinated biphenyls and p,p’-DDE and sperm sex chromosome disomy,” Environmental Health Perspectives  2011; DOI: 10.1289/ehp.1104017.