A sweeping investigation published in December 2025 has raised stark warnings about the risks posed by tens of thousands of historic landfill sites across the UK and Europe, many of which pre-date modern waste-management rules and sit dangerously close to watercourses, floodplains or coastlines.

Experts now fear that these so-called “hidden landfills” may be leaching toxic waste – including heavy metals, plastics and persistent “forever chemicals” such as PFAS and PCBs – into groundwater, rivers and ecosystems.

The mapping effort, undertaken by independent researchers working with media and environmental-watch organisations, estimates there are up to 500,000 abandoned landfill sites across Europe.

Roughly 90 per cent of those were created before the introduction of containment measures such as impermeable linings and waste-acceptance regulations.

In the UK alone, databases include more than 22,000 such historic sites.

The analysis identified more than 4,000 former landfills in England and Wales located within drinking-water protection zones.

Across Europe, 28 per cent of mapped landfills lie in flood-prone areas — a figure that a senior scientist warns may in reality be as high as 140,000 once private and unofficial dumps are included.

Many of these old landfill sites have already flooded at least once since 2000, or lie close to watercourses or low-lying coastal zones vulnerable to erosion or storm surges.

In dozens of documented cases, researchers found evidence of leachate — the toxic liquid produced as waste decomposes — containing dangerous levels of PFAS, heavy metals and other pollutants entering nearby streams or groundwater.

At one site in Cheshire, tests revealed PFAS concentrations twenty times higher than acceptable limits for drinking water.

At eroding coastal landfills, waste including hospital-grade materials was found partially exposed to tidal action, posing immediate contamination risks.

Experts warn that this mounting environmental threat is being driven by a dangerous mix of poor historical record-keeping, degraded protection measures, climate change and administrative neglect.

Many local authorities lack both the data and the funding needed to assess, monitor and remediate these sites.

For communities — often in deprived areas — the risks include contaminated drinking water, polluted rivers, degraded ecosystems, and heightened exposure to chemicals linked to long-term health hazards.

While modern, regulated landfills are generally considered safe thanks to protective liners, leachate management and monitoring, the absence of centralized records and inconsistent oversight mean that thousands of hazardous sites remain poorly understood.

Environmental scientists and campaigners are now urging government authorities to compile comprehensive national inventories, prioritise remediation of high-risk sites and allocate long-term funding to prevent further contamination.

As the climate warms and extreme weather events accelerate, old landfills once deemed closed could become new sources of environmental damage, threatening water security, public health and biodiversity across the UK and Europe — unless decisive action is taken soon.

The unfolding picture suggests a major challenge for regulators, water companies and communities alike: safeguarding water supplies and ecosystems while grappling with a legacy of decades-old waste — often hidden, poorly documented and dangerously overlooked.