Climate change is fuelling mega-floods, awakening toxic zombie chemicals

National Observer

4 days ago

The moment Peter Ross saw floodwaters sweep across the Fraser Valley during BC's devastating 2021 floods, the ocean pollution expert and senior scientist at the Raincoast Conservation Foundation knew the water was becoming a toxic cesspool.
"I was talking to people on scene, and it smelled like death, it smelled like manure, it smelled like sewage, it smelled like diesel," he recalled. Rivers, streams and drainage ditches criss-crossing the region were swelling, spilling over fields, factories, homes and highways. As the waters flowed, they were picking up hundreds of pollutants that are typically stuck on dry land or in the soil.
When the floodwaters receded over the following weeks, Ross and his colleagues tested the waters for 379 chemicals, like cocaine and other pharmaceuticals, PFAS, hydrocarbons, pesticides and heavy metals. Their results showed the water was packed with enough toxins to "prompt significant concern," he said.
That nightmare scenario is poised to become more common — but worse — as the climate crisis worsens, a group of experts is warning. In a report published Thursday by the UN Environment Agency, a team of researchers warn that mega-floods, like the one that swept through BC in 2021, could contaminate huge areas of land with chemicals, including some banned decades ago because they're so toxic.
"In recent decades, we've come quite a long way globally in terms of chemical regulation to make sure that the chemicals we're producing, and that we're releasing into the environment, are safe," said Markus Brinkmann, a report co-author and University of Saskatchewan toxicologist.
There are hundreds of sites contaminated with banned chemicals like DDT or PFAS scattered around the globe. In many cases, the harmful chemicals don't threaten people or the environment because they're locked in the ground or in riverbed sediments. But when there's a flood, those chemicals get picked up and spread through floodwaters where they can harm human health, the environment, and come at a heavy cost to clean up.
"It's definitely an issue of importance that we often like to forget about, because they're buried in our rivers and streams," he said.
In a report published Thursday by the UN Environment Agency, a team of researchers warn that mega-floods could contaminate huge areas of land with chemicals, including some banned decades ago because they're so toxic.
Climate change, which is largely driven by burning fossil fuels, will make intense rainfall more common, increasing the severity of flooding worldwide. Poor land- and water-management practices could exacerbate the problem, and without adaptive measures, flood damage could be about 20 times more severe, the report notes.
Floods caused an average of $800 million annually in insured losses in Canada between 2019 and 2023. Insurers estimate that for every dollar of insured loss, people are shouldering about two dollars' worth of uninsured losses.
The presence of toxic chemicals could make those impacts even more severe, the authors note. Take the US: In 2021, a House committee estimated that nearly 60 per cent of the country's non-federal superfund sites (heavily contaminated waste sites) are in areas vulnerable to floods and other natural disasters. In 2017, flooding caused by Hurricane Harvey carried over three tonnes of mercury from legacy industrial deposits into Galveston Bay, Texas, harming marine ecosystems.
Tracking the places where toxic chemicals are buried in the soil or sediment before a flood, then trying to guide floodwaters to minimize their potential to contaminate the environment, can help reduce the risk. So can using bioremediation to get the chemicals out of the environment, or capping contaminated areas with concrete to reduce the risk of toxins getting into the water, said Brinkmann.
Building more green infrastructure and better buffer zones between water and land that can absorb floodwaters could also help, said Ross, the ocean pollution expert. He was "really struck" how the lack of riparian buffers in the Fraser Valley — a problem caused in part because farms are exempted from riparian buffer laws — exacerbated the impact of the 2021 floods.
"At the end of the day, all of this runoff from land and all of these pollutants from human activities end up in the water. They're going downstream. They're getting into food webs, and they're presenting a real risk," he said.