The expanded line and air-rail link led by Metrolinx is expected to be ready in 2013, and would mean 250 to 450 diesel trains passing daily on the corridor, up from today's 50.
Diesel emissions have been linked to cancer, particularly of the lung, a fact that drew many people who live along the line to the board of health meeting.
"Why should kids be subjected to 10 years of this kind of pollution? No, it's not acceptable," resident Keith Brooks told the board.
Councillor Gord Perks called the expansion plans "the clearest case of the wrong way (to do) public transit I have ever seen.''
"It's quite disturbing this line would run right through – as a commuter line – right through the city, past all the schools, past all the people to drop (passengers) off in the 905. What the heck is going on here?'' said Councillor Paula Fletcher, another health board member.
She added it would be "unacceptable'' to have a line cutting through the city with that many diesel trains on it.
The health board's recommendations — which were endorsed this morning unanimously by the parks and environment committee – will be forwarded to the province and Ottawa.