Canada's food inspectors have issued border lookouts for vegetable proteins coming from China to prevent melamine — a chemical used to make plastics — from contaminating the human food chain, CBC News has learned.

Inspectors will seize wheat gluten, soy proteins, corn glutens and rice proteins from China — ingredients already found to contain melamine and other contaminants in hundreds of pet-food products. The proteins are destined for human food.

Melamine, also used to make fertilizer, was blamed for the deaths of a number of cats and dogs in North America and making hundreds of pets ill.

"That's why we have the border lookout for the ingredient, so that we can proactively assess any potential that the product is contaminated," said Paul Mayers of the Canadian Food Inspection Agency.

"We will subject the shipments to testing and the shipment will be held until the results of the test clear it in terms of the absence of the contaminant."

Vegetable proteins are impossible to avoid. They're found in everything from baby formula to pizza dough and wieners. Canadian manufacturers do not have to declare what country the ingredients come from.

The government doesn't know if ingredients contaminated with melamine have made it into human food before.

It says that last July, the same Chinese company that supplied melamine-contaminated wheat gluten for pet food also shipped wheat gluten to a British Columbia feed mill, which turned it into food for fish farms that has since been consumed by people.

But the CFIA said it believes the risk to people is low, even if the fish had been contaminated.

Food scientist Mansel Griffiths, with the Canadian Research Institute for Food Safety, said more inspections in the country won't solve the problem.

He said Canada needs to start the process back in China "and work with the Chinese government, work with the manufacturing industry in China to try to bring them up to the standards that we expect of Canadian companies."

It's unknown why melamine was ever in vegetable proteins, though American officials have speculated it was added deliberately. The presence of melamine makes it appear that the ingredient contains more protein than it actually does.