A University of Windsor professor has found that consumption advisories in Ontario may need to cast a wider net to completely protect against toxic contaminants.

Current fish consumption advisories by the Ministry of the Environment and Climate Change focus on one chemical at a time and are used to recommend the number of meals a person can safely consume in one month.

But a recent study into chemical mixtures and fish advisories, co-authored by Ken Drouillard, found that about half of the advisories currently issued are potentially “not adequately protective.”

“If you have chemicals that are part of the mixture and are impacting the same tissues or organs then their toxicity might be additive or even synergistic,” Dr. Drouillard said.

A professor at the Great Lakes Institute for Environmental Research and the biology department, he said the contaminants found in local fish are predominantly polychlorinated biphenyls (PCBs) and mercury.

“Both PCBs and mercury have neurotoxicity effects and therefore we felt it was appropriate to assume additive toxicity,” he said.

The study indicated that about 50 per cent of the current advisories would need to recommend eating half the number of fish meals per month if combined chemicals were taken into account.

The Detroit River currently has 10 species of fish with consumption advisories.

An angler pulling walleye from the waters of the Detroit River shouldn’t consume more than eight meals in one month if the fish measure 12 to 14 inches in length.

“If you catch a Canadian walleye in the Detroit River we know that they spend most of their time in western Lake Erie,” Drouillard said.

“So you’re catching a walleye that has collected most of its residues from Lake Erie and has high PCB concentrations and relatively low mercury concentrations.”

But Drouillard said focusing on the toxic contaminants can belie the health benefits of eating fish.

“We are now at the point where essentially all water bodies in Ontario will have some type of fish advisory associated with it,” Drouillard said. “Fish are an excellent source of dietary protein, essential fatty acids and have great health effects for the heart and immune function.”

The study recommends that agencies issuing advisories evaluate whether any measures currently in place would protect against the combined effects of multiple contaminants, and whether changes should be considered.

To view current advisories, visit the Ministry of Environment and Climate Change’s guide to eating fish in Ontario.