Chemicals foul Lake Ontario by air and wastewater

This synopsis was previously published by Environmental Health News

Different chemicals take different routes from cities to the Great Lakes, according to new research.

Scientists discovered that Toronto exports polychlorinated biphenyls, or PCBs, to Lake Ontario mostly through the air. But its flame retardants and combustion pollutants reach the lake through tributaries.

The routes are important to understand because they could help regulators determine where specific chemicals come from, and the tributary findings inform scientists searching for routes of emerging contaminants.

From 2006 to 2009, researchers from the University of Toronto and Environment Canada sampled Toronto’s air, tributaries, and treated wastewater for PCBs, flame retardants (including polybrominated diphenyl ethers, or PBDEs), polycyclic aromatic hydrocarbons (PAHs), and polycyclic musks (PCMs).

Toronto annually sends an estimated 2,260 kilograms of PAHs, 680 kilograms of PCMs, 24 kilograms of PCBs, and 18 kilograms of PBDEs to Lake Ontario’s “near shore”—about 25 miles out into the lake.

Toxins persist closer to shore

“The loadings are significant for the near shore lake as this area is both environmentally and economically important, yet typically suffers the most from pollution,” according to the study, which was published in Environmental Science and Technology on April 1.

PCBs, which were once widely used to insulate electrical equipment, were banned in Canada in the late 1970s. However, researchers estimate that Toronto still has about 400 tonnes of PCBs in use or in storage.

The findings indicate that “once a chemical has been designated for control, in-use inventories need to be aggressively reduced in order to stem ongoing emissions,” the authors wrote.

PCBs have been linked to many effects, including hormone disruption, cancer, reduced IQs in children, and asthma. The chemicals build up in fish and have spurred consumption advisories along Toronto’s Lake Ontario shore for decades.

Banned chemicals still showing up

Two of the three main polybrominated flame retardants are no longer produced in North America. Researchers estimate Toronto has about 1,800 tonnes of PBDEs in products or waste. PBDEs, linked to reduced IQ, behaviour problems, and hormone disruption in people, are showing up in Lake Ontario fish at levels similar to PCBs, according to the authors.

PAHs come from vehicles, industry, and coal-tar sealant. Polycyclic musks are in cosmetics and detergents, and they reached the lake through wastewater discharges. PAHs, which are carcinogens, are toxic to aquatic creatures. It is unclear what impact PCMs might have on aquatic life.

Invasive aquatic species store toxins

All of the chemicals are less likely to dilute in Lake Ontario because invasive mussels keep the contaminants near shore, the authors wrote.

“While this is ‘good news’ for offshore Lake Ontario, it implies that dilution can no longer be relied upon to reduce near shore pollution,” the authors wrote.