Pesticides Toronto homeowners use on lawns and gardens are polluting urban rivers such as the Don and Humber, says a joint study released this month by Environment Canada, the province and city hall.

"I think there's a message here for the homeowner that if you use chemicals like pesticides on your lawn, some of the active ingredients will go other places than the one [place] you apply," said John Struger, one of the primary authors of the study.

Taking samples from various points on both the Don and Humber from 1998 to 2000, Mr. Struger and his colleagues found evidence that chemicals from urban pesticides are washed from the city's lawns.

Diazinon, a chemical most often used to control lawn insects, was the most common pesticide found. In 20 per cent of the samples taken, diazinon concentration exceeded levels recommended by the province for the protection of aquatic life.

Specific effects of diazinon and other pesticides on river wildlife are still unknown; however, Health Canada has taken steps to reduce its use across the country. The amount of diazinon available for sale was to be reduced by 25 per cent this year and 50 per cent next year.

Eight other pesticides were detected, as were nutrients such as ammonia, large concentrations of which can cause fish to suffocate.

"This study supports the citizens in Toronto that have been calling for a ban on non-essential, cosmetic pesticides in the City of Toronto," said Shelley Petrie, executive director of the Toronto Environmental Alliance.

"Now that we have the proof in front of us that lawn pesticides are getting into our rivers and streams in Toronto, we have all the information we need to warrant taking action."

Ms. Petrie is calling on policymakers and city residents to move away from pesticides.

"Most of the use of pesticides on our lawns is purely for cosmetic reasons, to have greener grass," she said.

"We know that those same goals can be achieved using organic alternatives."

Mr. Struger said the results of the study will be used by Health Canada, the provincial and municipal governments and other decision-makers to determine what action needs to be taken to reduce or control the use of pesticides in Toronto and other cities.