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Medical researchers at the University of Alberta say that two chemicals leaking from plastic laboratory equipment were so biologically active they ruined a drug experiment.

The inadvertent discovery could have wide-ranging consequences because the chemicals causing the experiment to go awry were leaching from polypropylene, one of the most commonly used plastics in the world. Besides being found in scientific equipment, the plastic is used to make everything from yogurt tubs to clothing.

The findings were so alarming to the researchers, from the university's faculty of medicine, that they issued a warning yesterday in the journal Science, alerting others scientists to the possibility that contaminants from plastic ware in their laboratories could put experiments at risk.

Not enough is known about the two substances leaking from the plastic - quaternary ammonium biocides and oleamide - to know what hazard, if any, they might pose through exposure to consumer products made from polypropylene.

"It's very difficult to say whether we should be worried from a health point of view about this," said Andrew Holt, the paper's lead researcher and an assistant professor of pharmacology.

But Dr. Holt said that virtually all medical laboratories in the world routinely use materials, such as bottles and tubing, made from the polypropylene, putting their results at risk. "Scientists need to be aware of this," Dr. Holt said.

Other experts, though, said they were worried that plastics might be leading to human exposures, with unknown effects.

"We simply don't want these chemicals getting into our bodies," said Rebecca Sutton, senior scientist with Environmental Working Group, a U.S.-based advocacy organization.

The group wrote to the U.S. Environmental Protection Agency last month, objecting to an effort to loosen exposure standards for quaternary ammonium compounds.

The Alberta researchers aren't the first to be surprised that chemicals inadvertently leaking from some types of plastic can skew experimental results.

During the early 1990s, researchers at Stanford University School of Medicine in California found that bisphenol A leaking from a different type of plastic, polycarbonate, caused experiments investigating estrogen to run amok. Their discovery helped trigger a flurry of research into the chemical.

Last month, Health Canada said it would place bisphenol A, which is now considered a female hormone mimic, on the country's list of toxic substances.

At the U of A, a team lead by Dr. Holt made their discovery while conducting experiments on a human enzyme that is the target for drugs to treat Parkinson's disease.

The researchers were trying to inhibit the activity of the enzyme with ammonium chloride. They were surprised to find that even when they only added one part per million of the ammonium chloride, an amount that is so minute it was expected to have little effect, some mystery substance was still blocking the enzyme function.

The team initially suspected contaminants in the chemicals they were using, but eventually they determined that biologically active substances were leaking from the plastic tubes they used to transfer liquids in the experiment.

Using sophisticated testing equipment, they found that one of the mystery chemicals was oleamide, a compound used to improve the fluidity of molten plastic. Oleamide also occurs naturally in the human body, and is found in the brain and blood.

The chemical is also added to other types of plastic, such as polyvinyl chloride and low-density polyethylene.

Ms. Sutton expressed concern that exposing people to extra oleamide might alter brain function.

"If we end up dosing ourselves with higher levels, this could disrupt various processes."

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