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Toxic flame-retardant chemicals banned across Europe more than two decades ago are still present in soils, sediments, indoor spaces and food chains, raising concerns about continued human exposure, a new review of environmental research has found.

The chemicals, known as polybrominated diphenyl ethers, or PBDEs, were widely used in products including electronics, furniture, vehicles, aircraft, building materials and upholstery because of their ability to slow the spread of fire. A systematic review of 181 peer-reviewed studies found that the compounds remain detectable across Europe according to the study published in Environmental Research.

Concerns about PBDEs emerged in the 1990s as researchers discovered that the chemicals could persist in the environment and accumulate in living organisms. Studies detected PBDEs in human breast milk, with concentrations increasing sharply in Sweden between 1972 and 1997. Research in the United States later found substantial contamination there as well.

Those findings contributed to restrictions and bans on several PBDE compounds in Europe and other parts of the world during the early 2000s. Research has since associated exposure with potential effects involving the liver, thyroid and reproductive system, as well as possible links to certain cancers. However, much of the evidence comes from animal experiments and observational human studies, meaning the findings do not by themselves establish direct cause and effect.

The new review found that PBDE contamination remains widespread, ranging from heavily industrialized cities and landfills to remote alpine environments. Indoor concentrations were generally higher than outdoor levels, while areas with substantial industrial activity tended to show the greatest contamination.

Different PBDE compounds dominated different environments. BDE-209 was commonly detected in sediments and wastewater sludge, while BDE-47 and BDE-99 were more prominent in air and soil. Several studies indicated that concentrations in air and soil are declining, suggesting the bans have had an effect.

However, old products, recycled materials, landfills, sewage and contaminated industrial sites can continue releasing the chemicals. PBDEs can move between dust, wastewater, sludge, soil and aquatic ecosystems, allowing them to persist long after their original use has ended.

“Europe has made major progress in controlling PBDEs,” said lead author Khaled Abass, an environmental toxicologist at the University of Sharjah. But he warned that legacy contamination can continue affecting exposure patterns for years.

The findings also raise questions about recycling and reuse. As more materials enter circular supply chains, chemicals embedded in older products could potentially be redistributed unless they are identified and controlled.