Decreasing penis bone weight and other negative sexual side effects have been observed in English and Welsh otters -- and scientists warn it may spell bad news for humans.
Scientists from the Cardiff University Otter Project (CUOP) and the Chemicals, Health and Environment Monitoring Trust (Chem Trust) have been monitoring the effects of persistent organic pollutants (POPs) -- which include endocrine-disrupting chemicals (EDCs) -- in English and Welsh rivers.
While scientists could not draw an association between increasing levels of POPs and the otters' reproductive problems, they did find links between EDCs -- which affect hormones -- and lighter penis bones in some otters.
Dr. Elizabeth Chadwick, project manager at the Cardiff University Otter Project, told the BBC that the otter side effects "could be a warning for all mammals really, which include us humans".
The latest study examined 755 otters found dead between 1992 and 2009 for levels of certain POPs (Dieldrin, DDT, PCBs and HCBenz ) in their bodies and 17 other negative health indicators, including the otter's size and condition, parasite levels, reproductive issues, organ weights, presence of cysts and swelling, and abnormalities like kidney stones and fighting injuries .
The researchers found otter populations have increased as levels of POPs have decreased, but they have noticed that there are a number of reproductive problems that are becoming more prevalent.
The researchers discovered that over that time period, the otter's penis bone had decreased by half a gram. (Many animals still have a penis bone -- also known as an os penis or baculum -- but humans are able to maintain an erection through blood pressure and do not have one, according to the University of London.)
"We were surprised to see the reduction in the baculum weight," Chadwick said to the BBC. "(It's) certainly something that needs further investigation."
There was also an increase in other problems involving sexual organs, including cysts on the vas deferens and the number of undescended testicles. Since the last otter that was included in the report was found in 2009, 11 percent of more than 600 additional dead otters have been observed with cysts on the vas deferens, the authors reported.
In total, 11 out of 17 negative health indicators were associated with levels of at least one of the measured POPs. However, since the statistics varied between otter populations and the different pollutants, no associations could be made.
But, while POPs were not associated with reproductive problems, higher levels of the endocrine disruptors dieldrin and PCB 187 were linked with weight differences in the adrenal glands, kidney and heart. Levels of the endocrine disruptor PCB 138 were associated with the weight decrease of the penis bone in 282 otters, although bone length was not affected.
EDCs effects on reproduction in humans have been noted in other studies. Researchers behind a December 2012 Human Reproduction study that showed that sperm concentration of nearly 27,000 French men dropped 32 percent from 1989 to 2005 said that EDCs may be the culprit. Wired reported that male children who had been affected by the Yu-Cheng Incident of 1978 and 1979 pre-natally had smaller penis sizes compared to unaffected individuals. The Yu-Cheng Incident of 1978 and 1979 occurred when endocrine disruptors PCBs were accidentally included in a batch of rice bran oil, affecting 2,000 individuals.
Researchers fear that newer POPs that they did not look for in the study may be behind the reproductive problems.
"The pollutants analyzed in the current report do not appear to show any consistent negative associations with the selected reproductive indicators, suggesting that other factors (potentially including newer pollutants that are not measured here) are driving the observed changes," they wrote.
Overall, they said the study warrants more testing, especially for EDCs effects.
"These findings highlight that it is time to end the complacency about the effects of pollutants on male reproductive health, particularly as some of the effects reported in otters may be caused by the same EDCs that are suspected to contribute to the declining trends in men's reproductive health and cause testicular cancer, undescended testes and low sperm count," Gwynne Lyon, director of CHEM Trust, told the Telegraph. "This study has raised a warning flag. In reality humans and wildlife are exposed to a cocktail of many chemicals every day and some may be adding up to cause problems."