Why in news?
The United Nations Environment Programme (UNEP) released its 2025 Frontiers report titled “The Weight of Time”. It warns that increased flooding could remobilise toxic chemicals buried in sediments, threatening ecosystems and human health.
Key findings
- Legacy pollutants: Heavy metals like cadmium and lead and persistent organic pollutants (POPs) lie buried in river and coastal sediments. Floodwaters can stir them up, releasing toxins back into water bodies.
- Health risks: Cadmium levels in rivers such as the Ganga, Hindon and Vaigai exceed safe limits and are linked to cancer, kidney damage and reproductive disorders.
- Case studies: Hurricane Harvey (2017) remobilised mercury and carcinogens in Texas’ Galveston Bay. Niger Delta floods in 2012 released polycyclic aromatic hydrocarbons. Pakistan’s 2010 floods swept away large stores of obsolete pesticides.
- Persistent threat: Even banned chemicals remain for decades; current landfills hold millions of tonnes of POP wastes.
- Climate change effect: Intensifying rainfall and tropical cyclones amplify flood frequency, heightening the risk of pollutant release.
- Food chain contamination: Sediment‑bound pollutants can bioaccumulate in fish and crops, eventually entering human diets.
Challenges
- Lack of real‑time monitoring of sediment pollution; existing data is fragmented.
- Inadequate maintenance of waste storage sites and ageing infrastructure.
- Unplanned urbanisation and encroachment into floodplains increase exposure.
- Persistence of legacy chemicals despite bans.
Recommendations
- Adopt nature‑based solutions such as restoring wetlands and floodplains to slow floodwaters.
- Reinforce infrastructure—polders, dikes and retention basins—to manage sediment movement.
- Implement integrated river‑basin planning that considers hydrology, ecology and local communities.
- Create detailed maps of sediment‑bound pollutants and monitor pollutant pathways after floods.
- Safely dispose of obsolete pesticides and toxic industrial waste before disasters occur.
- Strengthen regulations and invest in research on chemicals’ long‑term effects.
Conclusion
The report underscores that climate change and pollution risks are interconnected. Managing floods now requires not only engineering solutions but also attention to buried toxic legacies. Countries must adopt holistic river‑basin management to protect people and ecosystems.