By testing on humans, pesticide manufacturers could eliminate the additional safety margins required when using data collected from animal testing.
It is also concerned that the costs of the scheme (£450 million) are to be borne by consumers rather than the pesticide manufacturers and users.
It also extended the period of exclusive use for pesticide manufacturers.
Only one amendment won backing from CropLife America, a trade group that represents pesticide manufacturers.
The Port of Houston reached a $100 million settlement in a three-year-old suit regarding environmental damage by a pesticide manufacturer.
The move would benefit pesticide manufacturers, who have long opposed the law, known as the Delaney clause.
The Ontario legislation would also echo Massachusetts law requiring pesticide manufacturers to reduce the toxins they use in production.
The lobster fishermen allege that a pesticide manufacturer is responsible for destroying the fishery and their way of life.
The agriculture industry and pesticide manufacturers have complained that their views were ignored in the decision.
Representatives of the other pesticide manufacturers named in the suit could not be reached for comment.