A ‘Trojan Horse’ for Toxic Chemicals

Five years ago, an international team of scientists compiled the first global inventory of commercially available chemicals with sobering results: they identified three times as many chemicals on the market than previously estimated, driven by the explosive growth of petrochemical production over the past several decades. 

Less than 5 percent of the 350,000 chemicals and mixtures registered for production and use has been tested for safety. And with scant information about the environmental behavior or toxicity of most compounds, it takes academic scientists years to identify their potential risks. 

Now, a new peer-reviewed study adds to a growing body of evidence showing the failure of current regulatory approaches to protect environmental and human health.

The researchers focused on polymers, very large molecules made of long chains of smaller molecules, which scientists considered too big to leach from products or enter the body’s cells and cause harm. Polymers are exempt from U.S. and European toxics regulations to encourage production of alternatives to chemicals shown to cause harm. 

In the new study, published Monday in the journal Nature Sustainability, the team found that polymers can not only break down in the environment but also become “substantially more toxic” when they do.

The team focused on polymeric brominated flame retardants, or polyBFRs, which are widely used in electronics to reduce fire risk. They have been marketed as safer alternatives to flame retardants found to pose environmental and health risks.

“As one of the very few reports exploring the environmental impacts of polymeric BFRs, our work clearly shows that there are environmental risks associated with these polymers, and their use should be adequately assessed and regulated,” said Da Chen, an environmental chemist at Jinan University in China who led the study.

Chen likened polymers to a Trojan horse carrying harmful chemicals inside a seemingly innocuous shell.

More than 20 years ago, researchers raised concerns about “non-polymeric” brominated flame retardants, substances with simple chemical structures, which were widely used to reduce fire risk in numerous consumer and industrial products, from electronics and TVs to insulating foams and other building materials. At the time, there was little information about the toxicity of the scores of commercially available brominated flame retardants despite their increasing contamination of air, soil and waterways and buildup in people and wildlife species from bald eagles to endangered primates.

Since then, independent scientists discovered the non-polymeric brominated flame retardants cause diverse health problems, including reproductive, hormonal and neurodevelopmental damage, reduced IQ and increased risk of dying from cancer.

The polymeric versions emerged to replace brominated flame retardants that had been banned or phased out in the wake of a wealth of research on their ubiquity and toxicity. 

Noting that production of polyBRFs will likely continue to expand as the simpler versions are regulated, Chen and his colleague sought to test the claim that they are unlikely to pose risks.

The team collected environmental samples from electronic waste recycling facilities in South China, and from homes and outdoor environments within about a mile and at distances of more than 30 miles away. To determine whether the polyBFRs broke down into smaller molecules, they developed a new screening method to analyze the soil, dust and air samples they collected as well as what remained after they subjected the polymers to laboratory treatments designed to simulate real-world conditions that might cause them to degrade in the environment.

The screening detected 76 components of polyBRFs left behind when they break down that the team identified through structural analysis. It also identified more than 200 others that will require further analysis to identify. 

A battery of toxicology tests in zebrafish, a standard model organism for such tests, showed that the smaller molecules left by the breakdown of the polymers caused multiple developmental problems at low concentrations, including curved spines, smaller eye size, abnormal heartbeats and learning and memory problems. Additional analyses suggested that the smaller molecules likely mediated these developmental defects by disrupting a key metabolic pathway.

The results show that polyBFRs can no longer be assumed to be safe for environmental or human health, Chen said. But, he added, additional studies are needed from other regions of the world to provide sufficient scientific data to support chemical management and regulations.

No More Free Ride

The study shows that “big polymers, which we are told don’t break down, do!,” said toxicologist Linda Birnbaum, former director of the National Institute of Environmental Health Sciences. Birnbaum is not a co-author but was thanked for “invaluable comments” on the paper.

“I had gone through an earlier version of the paper more than a year ago and thought it was pretty amazing at the time,” she said. “I still do.”

Some molecules identified by the researchers are small enough to be absorbed by the body, Birnbaum said. “While the polymer may be ‘safer,’ it does break down and those products can clearly be toxic.”

A spokesperson for the North American Flame Retardant Alliance said the industry has made significant strides in developing safer and more environmentally friendly chemistries like polyBFRs.“The report fails to adequately recognize these advancements over legacy technologies and the industry’s commitment to continuous improvement,” he said.

He also noted that the industry adheres to U.S. and European guidelines for the use of flame retardants and updates its practices to align with the latest scientific findings and regulatory requirements. “The report’s implications that the industry is not adequately regulated are unfounded and misleading,” he said.

Small molecule flame retardants operate under a stringent regulatory framework, said co-author Arlene Blum, executive director of the Green Science Policy Institute. “However, larger molecules, such as those studied in the paper, are not regulated by the EPA or in the EU, and that is a problem because during their life cycle, production, use and end of life, the harmful small molecules can be present without any regulation.”

That’s why Chen, encouraged by Blum, undertook this daunting effort. They were concerned that polymers—which are exempt under the U.S. Toxic Substances Control Act and from the EU’s Registration, Evaluation, Authorization and Restriction of Chemicals, or REACH, framework—may not be as innocuous as assumed.

“This is really an in-depth study that took seven years from the idea to publication,” said Blum, who commended Chen and his team for following through with such a comprehensive suite of experiments and analyses. 

“We know that small molecules are harmful,” said Blum, who has long worked to reduce exposures to toxic chemicals. You can stick them together and say they’re not harmful, she said, but large molecules are very difficult to study. 

“Very few people do that work,” she said. But when they do, they discover that big molecules aren’t always safe because they can break down, yielding harmful small molecules.

The take-home of the paper is that polymers need to be regulated in the U.S. and EU, whether they’re polymeric flame retardants or polymeric PFAS, said Blum, referring to the “forever chemicals” that have been detected in the air and drinking water supplies around the world. “They should not be given a free ride, because that’s the direction the chemical industry is moving.”

When these chemicals enter the environment, Blum said, “they stick around and they’re harmful.”