I would first like to specify that the establishment of MRLs is the responsibility of the Pest Management Regulatory Agency. I think the key message here is that the establishment of a maximum residue limit is based on the latest science. As Dr. Butler-Jones said, this evolves and now we're able to detect traces of pesticides at levels that we could not even think about before.
On June 4th, 2007. See this statement in context.