Participants in a recent Harvard university study who drank only out of plastic bottles containing bisphenol A for a week showed an almost 70 per cent increase in concentrations of the chemical in their urine.

Bisphenol A (BPA) is a chemical used to make many everyday products such as water flasks, children's toys and food containers. Researchers, government bodies and the plastics industry have in recent months engaged in a much-publicized debate on the health effects of the chemical.

Previous studies have shown BPA can leach from a container to its contents. But the Harvard researchers say their study, published Thursday in online version of Environmental Health Perspectives, is the first to show an increase in urinary BPA after drinking solely from receptacles containing the chemical.

The researchers tested 77 students who were initially told to drink all their cold beverages out of stainless steel containers for a week. The aim of this "washout period" was to minimize the students' exposure to BPA, which was not found in the stainless steel containers.

The students had their urine tested in two of the final three days of this period.

They were then given hard polycarbonate bottles that contain BPA and told to drink cold beverages out of them for a week. Throughout the duration of the two weeks, the students did not change their routines in any other way.

Their urine was collected and tested towards the end of the trial period. Compared to the initial tests, the students' urinary BPA concentrations went up by 69 per cent to levels comparable to those found in the U.S. population.

Inconclusive evidence

While the study shows a significant increase in BPA among the participants, the evidence on the long-term effects of BPA on humans remains inconclusive.

Recent animal studies have linked BPA to early sexual maturation, decreased sperm production and altered development of mammary glands. Among humans, elevated levels of BPA has been linked to cardiovascular disease and diabetes, although causal relationships have not been firmly established.

The plastics industry has defended the chemical, noting it has been used widely for 50 years.

Nevertheless, in October 2008, Canada became the first country in the world to ban the import and sale of polycarbonate baby bottles containing BPA. The basis for the ban was a Health Canada review of studies that examined the health effects of BPA exposure.

The review showed the main source of exposure of BPA for newborns and infants is through the use of polycarbonate baby bottles when they are exposed to high temperatures, and the migration of bisphenol A from cans into infant formula.

But Health Canada has maintained that for most people, BPA does not pose a risk, as negative health effects only occur at levels of bisphenol A exposure much greater than those currently found.

The federal government has said it would devote $1.7 million over three years to study the chemical.

Meanwhile, the U.S. Food and Drug Administration (FDA) has said it does not consider normal exposure to BPA to be a hazard. However, on Apr. 14, 2008, the U.S. National Institutes of Health released a report that concludes that there is some concern that fetuses, infants and children exposed to BPA may be at increased risk for early-onset puberty and prostate and breast cancer.