perhaps another reason why ADD is on the rise in children?

The first comprehensive testing of bisphenol A (BPA) levels in canned soft drinks in Canada has found that most contain the controversial chemical.

While the levels are low, some environmentalists say the levels may very well be enough to cause harm to children, especially those who drink a lot of pop or energy drinks.

The study, the largest test of its kind, was conducted for Health Canada as it investigates Canadians' exposure to BPA, which has been linked to cancer and reproductive problems.

The study tested bisphenol A levels in 72 samples of canned drinks, including carbonated, non-carbonated, diet, non-diet, fruit-flavoured and energy drinks. The survey represented at least an 84 per cent market share of canned soft drinks sold in Canada.

The chemical was found in almost all of them, and was particularly high in the energy drinks sampled.

The only exceptions were two samples of tonic water. The researchers suggest the quinine in tonic may have interfered with BPA extraction.

BPA was detected at levels between 0.032 and 4.5ìg/l (micrograms per litre). The highest levels of BPA -- 4.2 and 4.5ìg/l -- were detected in two energy drinks - drinks that are popular with teens and university students who often used them to stay alert as they cram for exams.

The authors calculated that an adult weighing 60 kg consuming one canned soft drink per day would, at the average BPA level found, consume only 0.0034ìg/kg body weight per day and 0.027ìg/kg body weight per day at the highest BPA level.

The study was released quietly in the Journal of Agricultural and Food Chemistry in January and the Health Canada authors downplayed the findings, saying the levels detected are well below current recommendations from Health Canada of a tolerable daily intake (TDI) of 25ìg/kg body weight per day.

"The average concentration that was detected was about 0.5 parts per billion," Dr. Samuel Godefroy of Health Canada told CTV News. "Just to give you an idea, a part per billion is a billionth of a gram per gram. In this case, it would be one microgram per litre of a soft drink. So these are considered to be very low levels."

He said the average Canadian adult would have to consume more than 900 cans per day -- drinking the worst soft drink measured for BPA -- just to reach Health Canada's tolerable daily intake, "which is still considered to be a safe exposure."

But environmentalists, such as Aaron Freeman of Environmental Defence, say the levels are still worrisome, given that pop and energy drinks are most often consumed by teens and youngsters, whose body weight tends to be much lower.

"The people who are drinking these beverages are mostly young people and the health effects particularly affect young people. The younger you are, the more vulnerable you are to the effects of bisphenol A," he tells CTV News.

"If you take into account that a young person might drink one or two of these a day, the math is different."

Freeman says children are more vulnerable to BPA because they have smaller bodies that metabolize chemicals more quickly, "so the same level of bisphenol A going into a child's body results in higher concentrations."

Last year, Health Canada banned plastic baby bottles that contain BPA. Its own studies on cans of baby formula found BPA levels ranging from 2.3 parts per billion to 10.2 parts per billion - more than the levels found in soft drinks.

What are safe levels?

Frederick vom Saal, a biologist at the University of Missouri and an expert on BPA, suggest that Health Canada's TDI level is far too high, noting that a growing number of studies involving animals have found harmful BPA effects at concentrations far below Health Canada's limit.

Vom Saal calls Health Canada's belief that there is little danger in the small exposure "simple-minded."

BPA is thought to be a hormone disruptor that can interfere with the normal functioning of the reproductive system of both people and wildlife and lead to the growth of pre-cancerous cells.

Aluminum beverage cans contain BPA in their linings to prevent spoilage and protect beverages from direct contact with the aluminum. The Health Canada study authors say the variations in levels the study found might be due to differences in can coatings, can sterilization conditions, or exposure to heat during storage.

Refreshments Canada, the industry group for soft drink manufacturers in Canada, has said only a minute amount of BPA is used in can linings, and the presence of BPA is eliminated during the bottling process.

"No BPA has ever been detected in our beverage products in off-the-shelf testing by either the US Food and Drug Administration (USFDA) or the European Food Safety Authority (EFSA)," the group said in statement on its website. "Based on the extensive scientific research available, there is no need for concern about the safety of aluminum beverage cans."

These recent Health Canada tests suggest there are, in fact, small amounts of BPA in soft drink cans. Freeman believes any amount is too much and Canadians need to reduce the exposure to BPA wherever they can.

"We don't have a choice. Often, we don't know whether a container has it or not. so it's really about political leadership. We need to tell leaders to get BPA off the market; we need to get it out of food and beverage containers entirely," Freeman says.

Until then, Environmental Defence recommends that Canadians choose glass bottles over cans with BPA linings and use stainless steel for drinking water bottles.

In October 2008, the federal government designated BPA as "toxic" to human health and the environment and announced a ban on the sale of plastic baby bottles that contain bisphenol A. It also allocated an additional $1.7 million to fund further research projects on BPA.