When Rivers Are Contaminated, Floods Are Only the First Problem

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As floods increase in frequency and intensity, chemicals buried in river sediments become “ticking time bombs” waiting to activate.

Hurricane Harvey flooded or damaged at least 13 Superfund sites in 2017, sending cancer-causing compounds into Texas waterways.

Dioxins—the category of chemicals that includes Agent Orange—have been banned in the United States since 1979. But that doesn’t mean they’re gone. Like in the plot of countless scary movies, dioxins and other banned chemicals are just buried beneath the surface waiting to be unearthed.

A new perspective paper in Journal of Hazardous Materials calls attention to an understudied area: the remobilization of pollutants buried in riverbeds. Chemicals have a knack for binding to sediments, meaning chemical spills in rivers frequently seep into sediments instead of flowing downstream. Future layers of silt bury the pollutants and hide the problem.

But persistent chemicals in riverbeds are “ticking time bombs,” warned Sarah Crawford, an environmental toxicologist at Goethe University Frankfurt and lead author of the paper. The buried chemicals can easily be remobilized. “It just takes one flood event,” she said.

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