OTTAWA -- Traces of medical drugs such as antibiotics, estrogen and antidepressants are being found in Canada's water system, Health Canada scientists say.

Federal officials announced yesterday that in response to studies that have found elements of drugs and foods in the water, they will develop a system to assess the environmental effect of the substances and will eventually require pharmaceutical companies to provide them with studies of drugs' potential environmental effects.

The studies found pharmaceutical compounds and chemicals from products such as cosmetics and shampoos, veterinary medicines, food additives and genetically modified foods in samples taken from sewage effluent.

The samples were taken across Ontario.

"It's an emerging area where we obviously have some growing concerns," Charles Ethier, director-general of the health department's general safety program, said yesterday.

Elizabeth Neilsen, the government's director-general of regulatory and international affairs, said research conducted on water systems in Europe has discovered compounds that make up such drugs as ASA, antidepressants and blood-pressure medications.

"Evidence from the scientific community, particularly from other countries, suggests that substances from products regulated under the [Canadian] Food and Drug Act are present in the environment, and further research is required to better understand what impact this might have on human health," Ms. Nielsen said.

"There's a lot here that needs to be further understood."

The chemicals enter the water system either through human excretion or are flushed down the toilet when no longer needed.

Ms. Nielsen said the government intends to set up regulations that will eventually require manufacturers of the potentially harmful drugs and other substances to provide the government with assessments of how their products will affect the environment. As of Sept. 13, however, companies that want to bring in or manufacture new drugs will be required to have them screened under the Canadian Environmental Protection Act. The new regulations are not expected for another two years. Ms. Nielsen also said Ottawa may regulate the disposal of the chemicals and educate consumers on how to dispose of leftover pharmaceuticals and cosmetics.

A government scientist said yesterday that although much work needs to be done to determine the potential effect on drinking water and on the environment, there is evidence of some damage.

John Carey, executive director of the national Water Research Institute in Burlington, Ont., said that elevated levels of estrogen found in fresh water have affected the ability of young salmon to adapt to salt water. Estrogen is one of the key components in birth-control pills.

Mr. Carey said that the detectable levels of the contaminants were first discovered in Germany, and that Canadian authorities invited the foreign scientists to Canada to do similar tests. He said that effluent from sewage plants in Toronto and other parts of Ontario were tested and showed chemical compounds from ibuprofin, beta blockers, blood-pressure drugs and several other medications.

Finished drinking water has not been tested for the compounds, Mr. Carey said, although Ms. Nielsen said it's possible that the chemicals are in the drinking water.

Mr. Carey also expressed concern about the detection of veterinary medications in the water system and whether the substances can impair resistance to disease.

Ms. Nielsen said the amounts are being found in "very, very low concentrations, and we really don't know what the impact of those concentrations is."

Still, Ms. Nielsen noted that such drugs are "not there for children. If children are getting them, or pregnant women are getting them through the water system, there is the potential that there could be a problem."