Abnormal Sperm: DDT Link
A new study has shown that men who were exposed to banned chemicals, even long-lasting ones as teens are more likely later on to develop defective sperm.
Researchers report today that organochlorine chemicals-specifically DDT and polychlorinated biphenyls (PCBs)-may affect how testicles mature and function. This is the first time that a study has been done to determine if men are exposed to organochlorine chemicals in their teenage years. It also examines abnormal sperm formation later on in life.
These chemicals are still present in the environment. While levels are declining in the last 30 year, we still have some chemicals in our bodies," Melissa Perry (lead author), a researcher and professor at George Washington University’s Milken Institute School of Public Health.
Perry and coworkers examined blood and sperm samples taken from ninety men who were from the Faroe Islands, North Atlantic Ocean. As adults, they examined organochlorine chemicals found in the blood and looked for abnormal chromosome numbers. They also took blood samples from 33 men at the age of 14.
At 14 years of age, abnormal sperm rates were higher in men who had high levels of DDE (a product of DDT's pesticide DDT) and polychlorinated biphenyls. According to a study in Environmental Health Perspectives, the same relationship was observed for the levels of chemicals found in adults and men.
Thomas Zoeller from the University of Massachusetts Amherst, who wasn't involved in the study, said that "It is another one of these studies that helps understand why male fertility declines in certain parts of the globe."
According to previous research, sperm with an abnormal number of chromosomes could lead to unsuccessful pregnancies as well as birth defects.
The study doesn't prove that the chemicals hamper sperm but both DDT and PCBs are known to disrupt the endocrine system. Perry stated that sperm production was a highly hormone-dependent process.
With many endocrine disrupting chemicals, the major risk is exposure as a fetus or young child. However, sperm production is a "continuous process" in men into adulthood, said Zoeller, who is a leading researcher on endocrine disrupting chemicals.
The United States was heavily using organochlorine insecticides from the 1940s until the 1960s. In the 1960s there was concern about their possible health effects. This is largely due to Rachel Carson’s 1962 book Silent Spring. It focused on DDT's harmful effect on birds and world food supplies.
In the United States, DDT and PCBs have been banned since 1973 and 1977 respectively. The International Stockholm Convention on Persistent Organic Pollutants also banned their production and use in 2001. 170 countries signed on to the Convention. Due to the increasing evidence about chemicals' harmful effects, bans were implemented in order to protect fertility, brain development, and immune systems.
But these chemicals won't disappear. These chemicals are very persistent and can persist in both the environment as well as the body. The majority of people get exposed by their diets, which include eating meat, fish, and certain dairy products.
Some countries continue to use DDT for the control of disease-spreading insect vectors. The Stockholm Convention's 2012 implementation was confirmed by a report that the "global usage of DDT has not significantly changed"
Perry stated that organochlorines can cause contamination in food imports from other countries.
Although the study is not able to pinpoint the source of exposure, the Faroe Islands' population eats a lot seafood (blubber and whale meat) which acts as a storage container for the persistent chemicals. Men in this study were exposed to much more DDE and PCBs that the average American.
Although organochlorines have been suspected by human health experts for years to affect male fertility, studies so far have not shown any significant impact. Researchers in the Netherlands found that PCBs in blood from adult men were associated with lower sperm counts in 2002. A 2004 Greenland study found that sperm quality could be affected by organochlorine.
Zoeller claimed Perry's studies are relevant to more than the banned chemicals. They should also inform today's chemical regulation.
"With PCBs...we know they're harmful, but it's already too late. "We're still being affected 40 years after their ban, and we still have a problem with them," he stated. "This knowledge seems to make it more prudent to produce chemicals similar to PCBs and DDT.