Many agricultural pesticides – including some previously untested and commonly found in food – disrupt male hormones, according to new tests conducted by British scientists.

The scientists strongly recommended that all pesticides in use today be screened to check if they block testosterone and other androgens, the hormones critical to a healthy reproductive system for men and boys.

“Our results indicate that systematic testing for anti-androgenic activity of currently used pesticides is urgently required,” wrote the scientists from University of London’s Centre for Toxicology, led by Professor Andreas Kortenkamp.

Thirty out of 37 widely used pesticides tested by the group blocked or mimicked male hormones. Sixteen of the 30 had no known hormonal activity until now, while there was some previous evidence for the other 14, according to the study, published online last Thursday in the scientific journal Environmental Health Perspectives.

Most of the newly discovered hormone disruptors are fungicides applied to fruit and vegetable crops, including strawberries and lettuce. Traces of the chemicals remain in foods.

“This study indicates that, not surprisingly, there are many other endocrine disruptors that we have not yet identified or know very little about,” said Emily Barrett, a University of Rochester assistant professor in obstetrics and gynecology who was not involved in the study.

“This underlines the glaring problem that many of the chemicals that are most widely used today, including pesticides, are simply not adequately tested and may have serious long-term impacts on health and development,” said Barrett, who studies how environmental chemicals affect human reproduction.

The findings come as the U.S. Environmental Protection Agency faces opposition from the pesticide industry after expanding its Endocrine Disruptor Screening Program, which requires testing of about 200 chemicals found in food and drinking water to see if they interfere with estrogen, androgens or thyroid hormones.

None of the 16 pesticides with the newly discovered hormonal activity is included in the EPA’s program, which means they are not currently screened and there are no plans to do so.

The EPA’s program has been slow to implement, largely due to a controversy over testing methods. Environmental groups criticize the EPA, which was granted the authority by Congress in 1996, for taking so long to order manufacturers to test only a small group of chemicals. But chemical industry officials say that the tests cost up to $1 million per chemical and the techniques have not been fully validated. They also stress that positive results don't necessarily mean that the pesticides are harming human reproduction.

The British researchers screened the chemicals using in-vitro assays, which use human cells to check whether the pesticides activate or inhibit hormone receptors in cells that turn genes on and off. They are a widely accepted lab techniques. Scientists, however, are uncertain what actually happens in the human body at the concentrations of chemicals that people encounter in fruits and vegetables.

Fetuses and infants may be particularly at risk when exposed in the womb or through breast milk because the hormones control masculinization of the reproductive tract.

Some research has linked pesticides to abnormal genitals in baby boys, such as cryptorchidism and hypospadias, and decreased sperm counts in men. Male fertility is thought to be declining in many countries, and testicular cancer is increasing. Some scientists have dubbed this compilation of male disorders “testicular dysgenesis syndrome,” and suggested that hormone-disrupting environmental contaminants play a role.

R. Thomas Zoeller, chair of the biology department at the University of Massachussetts, called it "a very important paper."

"It is telling us that the pesticides most prevalent in the human population have effects on the androgen receptor," said Zoeller, who directs the university's Laboratory of Molecular, Cellular and Developmental Endocrinology.

"Considering all the evidence that human male reproduction is exhibiting troubling secular trends (sperm count and quality, hypospadias, cryptorchidism, testis cancer), this is highly troubling," he said.

Funded by the European Commission, the University of London scientists selected the pesticides to test by identifying those found most often in European fruits and vegetables. They are approved for use in many countries, including the United States.

The researchers noted “a clear disparity” between today's most widely used pesticides and the current knowledge of their risks, “with the majority of the published literature focused on pesticides that are no longer registered for use in developed countries.”

Of the tested compounds, the most potent in terms of blocking androgens was the insecticide fenitrothion, an organophosphate insecticide used on orchard fruits, grains, rice, vegetables and other crops.

Others with hormonal activity include fludioxonil, fenhexamid, dimethomorph and imazalil, which are all fungicides. Fungicides are often applied close to harvest, so they are frequently found as residue in food. Some are new compounds which have been used for only a few years.

Fungicides “are typically applied as mixtures in order to increase effectiveness and prevent development of resistant strains and therefore, human exposure to mixtures of these in vitro anti-androgens may be considerable,” wrote Kortenkamp and the other study authors, Frances Orton, Erika Rosivatz and Martin Scholze.

For six of the pesticides that showed hormonal activity for the first time, the authors said they “strongly recommend” the next round of testing, using lab animals. “Due to estimated anti-androgenic potency, current use, estimated exposure, and lack of previous data, we strongly recommend that dimethomorph, fludioxonil, fenhexamid, imazalil, ortho-phenylphenol and pirimiphos-methyl be tested for anti-androgenic effects in vivo.”

For the first four pesticides, they called it “a matter of urgency.” They are used on strawberries, lettuce, grapes and other fruits and vegetables.

Mary Emma Young of CropLife America, which represents the pesticide industry, said the group is reviewing the new study and could not yet comment on it. She added that "we continue to work with EPA and others to understand the potential for a chemical to interact with the endocrine system as well as the potential consequences of that interaction on human health and the environment."

In 2009, the EPA ordered industry to use the in-vitro assays to screen 67 pesticides for their potential effect on hormones. The deadline is this October – 15 years after Congress granted the agency the authority to screen for such effects – but an extension is likely.

Last November, the EPA added another 134 pesticides and industrial chemicals found in water supplies. The testing is the first step toward including hormone data in the regulation of pesticides and industrial chemicals.

Pesticide companies, in a January letter to the EPA, asked the agency to refrain from listing more chemicals for testing "until the agency has had an opportunity to evaluate the performance" of the techniques used to test the initial 67 pesticides.

Sheela Sathyanarayana, a University of Washington pediatrician who studies effects of environmental chemicals on male development, said the new study provides strong evidence that the testing should be expanded to more chemicals.

“There are many chemicals that may possess endocrine disrupting properties and the only way to know is to screen,” she said.

“I definitely think all pesticides need endocrine disruption screening or a strong justification for not doing so. I’m sure most scientists would agree,” she said.