Hard-knock plastic: Terri Coles

By Terri Coles

TORONTO (Reuters) - A chemical found in plastics used for everything from water bottles to dental fillings poses a serious health risk, environmentalists and researchers say, although the jury has yet to deliver a final verdict.

Bisphenol A (BPA) is added to hard, clear polycarbonate plastics like those used in reusable water bottles and baby bottles, as well as the resins lining food cans and in some dental amalgams and sealants. Polycarbonate is identified by the number 7 inside the recycling symbol found on the plastic. About 95 percent of number 7 plastics contain BPA, according to Aaron Freeman, policy and campaign director at Environmental Defence, a Canadian health and environment group.

Research on lab animals has linked the chemical to changes to the genital tract, prostate enlargement, declined testosterone, pre-cancerous breast cells, prostate cancer, early puberty in females and hyperactivity.

Studies have suggested that BPA acts as an endocrine disrupter, which means that it can mimic or disrupt estrogen, interfering with the hormone system's normal functioning.

"These are the things that interfere with the natural development processes in our bodies," said Freeman, "the switches that tell our body when to develop certain types of systems."

Research done in the late 1990s at Cleveland's Case Western Reserve University found that polycarbonate plastic can leach low levels of BPA when washed with harsh chemicals, Freeman said, but newer research by Environmental Health Perspectives also found that while heating or harsh washing increased leaching, it also happens in new bottles.

BPA isn't biocumulative or persistent, so it doesn't last in the body longer than 24 hours, Freeman said. Environmental Defence has done four rounds of tests for chemical accumulation in the bodies of high profile Canadians, including politicians. The most recent round of testing found BPA in the subjects' bodies.

"What that means is there's chronic exposure," Freeman said, "and we found it at levels that were producing serious health risks in animal studies."

The effects of BPA on human health are examined in amounts as low as parts per trillion.

With chemicals like BPA, the length and timing of the dosage appears to be more important than the size, Freeman said. Exposure in utero and in infants and children is of particular concern, he said, because the chemical is thought to affect developmental processes.

The possible effect of very small doses of BPA was explained to him using the metaphor of a ship, he said: you can build the strongest hull you like, but if your navigation system is just slightly off, you won't get to your destination.

The current knowledge about how BPA acts on the body comes from animal studies, and no comparable human trials exist. There isn't yet a clear scientific consensus on the risks BPA may pose, but research suggests that the chemical affects lab animals at levels much lower than those currently considered safe.

Much of the research on BPA is very new, with several studies having come out in the past year. "I think this is a good time for people to sit up and take notice," said Adria Vasil, author of Ecoholic. "This isn't really just fringe groups doing research. It is really credible scientific journals coming out with this information."

The American Chemistry Council says that BPA doesn't pose a risk to human health at the typically low levels of exposure, although they support further research.

This past summer, the National Institutes of Health (NIH) in the United States conducted a review with 38 leading researchers, who concluded that BPA does pose some health risks, though they were mostly classified as minimal. The full NIH report is due this fall. The Canadian Cancer Society says that the relevance of laboratory animal studies to human health is unknown, and it's unclear if BPA poses a risk in cancer development.