TORONTO - A researcher who studied factory workers in China is reporting an association between higher levels of bisphenol A in urine and decreased semen quality.
The study was done over a five-year period and involved analysis of samples from 218 participants -- including men who worked in factories where BPA is either manufactured or used in the manufacturing process, and a control group of men who worked in factories where bisphenol A was not involved.
"This study presents for the first time evidence of an association between a BPA biomarker (urine BPA level) and declining semen quality -- specifically reduced sperm concentration, total sperm count, vitality and motility -- in a human population," the authors wrote in the study, published Thursday in the journal Fertility and Sterility.
But a Canadian scientist who read the findings questioned whether another chemical or chemicals in the factories may in fact be involved.
The study was conducted by Dr. De-Kun Li and colleagues at the U.S. health care provider Kaiser Permanente in Oakland, Calif., and was funded by the U.S. National Institute of Occupational Safety and Health.
An earlier study by the same group found an association between exposure to high levels of BPA in the workplace and a higher risk of reduced sexual function in men.
"Our finding matches with whatever has been shown in animal studies, which has been there for years," Li also said in a telephone interview.
As a group, he said the Chinese factory workers with higher levels of BPA in their urine were not infertile.
"They didn't reach the level that it would reach infertility, so in other words, in our group, most of them still would be considered as fertile," he said.
Commenting on the study, Warren Foster, a professor in the department of obstetrics and gynecology at McMaster University, said it adds to our body of knowledge in an area that's been particularly weak, however it only adds a limited amount of information.
"You've got a population where you've got adverse outcome -- I don't debate that at all. They've got statistically significant effects, there's something going on here," Foster, an expert in reproductive endocrinology, said from Hamilton.
"But the question comes to me, is it bisphenol A, or is it something else?"
Chemical companies often have "tanker cars full of all kinds of different chemicals," he said, and some, such as solvents, are known to have effects on sperm and reproductive function.
"I would really need to know, to see, the entire menu, if you will," he said.
"For an occupational group, it's raising some questions, and the main question that I have is, 'What else is on the menu here?' It may not be BPA at all. It may be, but without knowing the other menu items, we don't know."
Li said that compared with men without detectable urine BPA, those with detectable urine BPA had more than three times the risk of lowered sperm concentration and lower sperm vitality, more than four times the risk of a lower sperm count, and more than twice the risk of lower sperm motility.
BPA is a chemical created in the production of polycarbonated plastics and epoxy resins. It's found in some hard plastic containers, some linings of cans and is used in dental sealants. Previous animals studies have linked it to adverse effects in reproductive systems of rodents.
Earlier this month, the Canadian government formally added bisphenol A to Canada's Toxic Substances List.
But Foster noted that Europe and other jurisdictions that have reviewed all the same data have not done so.
"What they're saying is that this is toxic under the Canadian Environmental Protection Act, which means that this chemical could induce toxicity in environment, so grass, wildlife, such as frogs, toads, salamanders, or potentially humans, and they don't make the distinction" he explained, adding that under CEPA, road salt is also considered toxic.
The government has also banned BPA in baby bottles.
Foster noted that when you look at absorption, metabolism, distribution and excretion related to bisphenol A, almost 98 per cent of what goes in orally goes back out in the urine.
"So it's dealt with very quickly, and so if that's the case, then one has to really wonder how much, if any, is really making it to the testes," he said.
"The issue is that in biology and in medicine, we've discovered that it defies simple explanations, and that these chemicals such as bisphenol A act through multiple mechanisms, one of which is this other receptor known as GPR30, whose relevance in reproductive biology and reproductive medicine has come under question of late."
He said that finding has raised questions about BPA relationships that have been observed.
