Floods driven by climate change are raising the danger of long-banned toxic chemicals resurfacing in rivers, soil, and food chains, according to a new UN Environment Programme (UNEP) report.

The Frontiers 2025 report highlights floods as a growing threat that can stir up harmful substances buried in sediments and infrastructure over decades or centuries. These toxins risk spreading across agricultural lands, urban areas, and freshwater sources, endangering both human health and ecosystems.

“Floodwaters can remobilize chemicals thought safely buried,” the report said, warning that increasing extreme weather linked to global warming is amplifying this risk.

Experts note many of these persistent chemicals, banned under international agreements like the 2006 Stockholm Convention, remain trapped in riverbeds, landfills, and contaminated sites. Flooding events can release them back into the environment, allowing them to bioaccumulate in wildlife and humans.

Low-lying and coastal populations are particularly vulnerable, as more people worldwide settle in flood-prone areas. UNEP officials urge governments to strengthen water management, environmental monitoring, and emergency planning to address these risks.

Industrial toxins such as persistent bioaccumulative and toxic substances (PBTs), per- and polyfluoroalkyl substances (PFAS), and asbestos are among the dangerous chemicals that floods may release. Despite bans and restrictions, these compounds continue to appear in water systems globally, posing long-term health threats.

UNEP experts also highlight the urgent need to improve early warning systems and monitoring capabilities, especially in vulnerable regions, to better manage and mitigate the impact of chemical pollution linked to climate-driven flooding.

“Preventing contamination is far more cost-effective than dealing with its aftermath,” the report stresses, calling for greater policy attention to these emerging environmental challenges.

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