Breathe easy. Research suggests 3 toxic pesticides are finally eliminated from air around the Great Lakes

We can breathe a little easier around the Great Lakes, suggests new research, as several toxic insecticides have finally disappeared from the air over the region decades after they were banned in Canada and phased out in the United States.

Three toxic pesticides banned under the Stockholm Convention are now at such low concentrations that they are virtually undetectable at sampling stations around the Great Lakes, according to new research published last month in the journal Environmental Science and Technology.

Better yet, environmental specialists say the findings amount to good news across Canada.

"These results would probably apply to all locations where these chemicals were used [and then banned]," said Marta Venier, an environmental chemist at Indiana University and co-author of the study. "It's just that we are fortunate that we have this really long-term history of data for the Great Lakes."

Like DDT, these pesticides are part of a group called organochlorines. Known to cause serious environmental damage, prolonged exposure can lead to neurological damage and hormone dysregulation in wildlife. The International Agency for Research on Cancer lists most organochlorines as possible cancer-causing compounds. 

The most famous organochlorines are commonly known as the "dirty dozen." They are persistent pesticides, meaning they are highly stable and take a long time to break down in the environment — and inside wildlife. 

Effective pesticides, terrible effects

Using binational air sample data collected from around the Great Lakes basin since 1990, Venier and Indiana University colleague Ronald Hites looked at the concentrations of six different organochlorine compounds in the atmosphere.

The results were published in a paper titled, "Good news: Some insecticides have been virtually eliminated in air near the Great Lakes." The study was conducted under an agreement with the U.S. Environmental Protection Agency. 

The researchers found three of the pesticides — lindane, alpha-HCH and endosulfan — are now nearly undetectable.

Here are the locations of the testing sites across the region:

"This paper is a good example of showing that these sort of policy approaches to dealing with pollution work, but they might take a very long time," said James Longstaffe, an associate professor of environmental chemistry at Ontario's University of Guelph who was not associated with the study. 

"But if you can phase out or restrict the use of something harmful, you will see eventually a reduction in its occurrence in the environment." 

The stability and long-lasting properties of organochlorines made them potent insecticides. They were broadly used in agriculture and in cities for decades before the harm they were doing led to a ban on their use. 

"These chemicals were part of the dirty dozen for a reason," said Venier. "They have a significant impact on the environment — mostly they bioaccumulate."

Once ingested, breathed in or absorbed through the skin of an animal, the chemical can be passed up the food chain.

This causes a buildup that can be fatal or have effects on offspring, and has devastated populations of aquatic species and species at the top of the food chain across North America and around the planet for decades. 

For species like the bald eagle, whose eggs become brittle and beaks grow misaligned as a result of DDT buildup, recovery has been slow. But in the last several decades, these birds of prey have finally seen progress toward recovery. 

According to Health Canada, the effects of prolonged exposure to most organochlorides on the general public is still unknown, though associations with various diseases have been found.

DDT and other pesticides linger in the air

While three compounds may be gone from the air, some — like chlordane and DDT itself — are decreasing but are still found in significant concentrations. Others, like the carcinogen hexachlorobenzene (HCB), are not decreasing at all.

This is likely due to HCB being inadvertently emitted during manufacturing, especially of aluminum, Venier said

DDT has not been used in Canada or the U.S. in a half-century. Based on current trends, the researchers project DDT will reach virtual elimination within the next couple of decades. 

The authors suggest the differences between the other pesticides is likely due to where they were applied, whether in rural or urban settings. 

"When you think about chemicals that are used in agriculture, the soil is completely continuously moved, disturbed in a way every season or every year," she said. That allows the pesticides to enter the atmosphere and be eliminated from the area more rapidly. 

But in an urban setting, Venier said, the soil is disturbed much less often, meaning it can become a reservoir for pesticides that will be released over a much longer period. 

Longstaffe said it was a "very strong hypothesis" and he would likely propose a similar explanation for the different rates of elimination. He added that differences in soil composition may also play a role in how quickly the pesticides are released into the atmosphere. Still, further research will need to be done to test the hypothesis. 

Longstaffe said though organochlorines can be broken down by specific microbes deep in the soil, they are more commonly eliminated from an area once they enter the atmosphere, where reactions catalyzed by sunlight can destroy them. 

But all too often, they are not destroyed at all. 

"The Arctic is where a lot of these contaminants ultimately end up," he said. "They go into the air and they'll be blown away. That's where they go."

With the legacy of organochlorine pesticides finally fading, experts say this is yet another example of what can happen when we take collective action for our planet.