Originally published: Oct. 23, 2015

Updated with correction: Oct. 29, 2015

There are worries that the Trans-Pacific Partnership trade deal means milk from hormone-treated U.S. cows could end up in Canadian supermarkets.

Dr. Shiv Chopra is a former Health Canada scientist who lost his job after raising the alarm about dangers posed by bovine growth hormone (BGH). Partially because of his work, it is currently illegal to use the drug to boost milk production in Canada.

Chopra tells As It Happens host Carol Off, "We worked upon it so much and got [bovine growth hormone] rejected in Canada...Now, under the trade agreement, it's going to let the floodgates open."

In the agreement in principle reached in early October, Canada conceded an additional 3.25 per cent of its dairy market to imports from countries like the U.S., New Zealand and Australia.

TPP negotiators have told CBC that Canadian health and safety regulations will apply to all imported products. But that does not mean dairy producers in the U.S. have to follow the same rules Canadian farms do.

There are fewer restrictions on hormone use on U.S. cows.

According to Chopra, "The damage that occurs to the milk, to the cows, ultimately it translates into human health hazards."

Both in Canada and the European Union, however, restrictions on BGH are based on the hormone's effect on animal health, not humans.

An EU report found that cows which are given the hormone can experience "severe and unnecessary pain, suffering and distress...associated with serious mastitis, foot disorders and some reproductive problems."

The World Health Organization, Federal Drug Administration and other health bodies have stated that dairy and meat from these cows is safe for people to eat.

According to the American Cancer Society, "The evidence for potential harm to humans is inconclusive. More research is needed to help better address these concerns."

Chopra is currently an author and public speaker. He's also a controversial and outspoken critic of the use of vaccines in humans.

Even with new labelling, Chopra believes Canadian consumers won't fully know where their milk is sourced.

Yves Leduc from the Dairy Farmers of Canada told CBC he's concerned about a "double standard" between U.S. and Canadian farmers.

"It seems incoherent to restrict [its] use in Canada, when products made with the hormone can still enter the Canadian market," he wrote to CBC News.

Chopra is also worried about what the trade agreement could mean for Canadian dairy products that are sold abroad.

"The European Union actually banned BGH. That means our dairy products, if now mixed up with TPP, they cannot go to the European Union. That's going to harm our trade, our jobs, our agriculture.

"We should be listening to our dairy farmers. They know better."

Correction:

An earlier version of this article did not make clear that BGH restrictions in Canada and the EU are based on concerns over animal health. In fact, a number of leading health organizations state that milk from BGH-treated cows is safe for human consumption.

This earlier version also included a statement from Dr. Shiv Chopra about BGH and its connection to an "insulin growth-like hormone that causes cancer" in humans. We contacted Chopra about this claim. He stands by his statement but he could not provide scientific evidence.

As It Happens continues to request interviews with a representative from Health Canada. To date, no one has been made available.

Audio of this interview will reflect these changes in the coming days.