Organophosphate esters (OPEs) have secured a substantial share of the flame retardant market, around 18%. They are an alternative to using brominated flame retardants, many of which have either been banned or are in line to be due to their toxicity. At least 600,000 tonnes of OPEs or more are produced each year, says the paper, produced by largely American experts and published in the journal Environmental Health Perspectives.
The chemicals are present in a wide variety of products, such as electronics, furniture, car seats and building materials. “As a result, organophosphate esters and their metabolites are routinely found in human urine, blood, placental tissue and breast milk across the globe,” it says.
But the paper demonstrates that such widespread use is another example of regrettable substitution, where one form of chemical replaces another, only for similar concerns to be discovered subsequently.
“Many scientific studies have shown that organophosphate ester flame retardants are developmental neurotoxicants, so are particularly concerning for the health of children and the public at large,” said Jamie Page, chief executive of UK charity the Cancer Prevention and Education Society, and a co-author of the paper. “In the UK, we have some of the highest exposures to flame retardants in the world,” he added, partly the result of the Furniture Regulations, which “have put toxic chemicals in our homes and may have made fires more dangerous by possibly increasing the amount of smoke and toxic gases”.
Some forms of OPE are used as insecticides and weaponised poisons – including the infamous nerve gas sarin and the Russian nerve agent novichok. They all work by disrupting the transmission of nerve signals via the neurotransmitter acetylcholine, by inhibiting the function of the enzyme acetylcholinesterase. Concerns about the human toxicity of pesticides of this type have led to some being banned in the EU, such as parathion and chlorpyrifos.
But potential harm from other OPEs has been more questionable. In 2019, the government's advisory Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) said that there was “a lack of biological plausibility” that OPE flame retardants substances are neurotoxic, as their structure meant that they would not interact strongly with acetylcholinesterase – the focus of scientific investigation into their effects.
But this conclusion was wrong, says the new paper, which finds “growing evidence from many studies” that OPEs are associated with developmental neurotoxicity through different modes of action. These included endocrine disruption and disrupting the action of two other neurotransmitters, dopamine and GABA.
There is therefore a “pressing need to acknowledge and manage the potential risks that OPEs pose to human neurodevelopment given their neurotoxic effects, rapidly increasing use, and environmental ubiquity”.
The paper suggests that exposure could lower IQ, attention span and memory in children – in ways not yet considered by regulators. It adds that many of these effects have been shown to occur during development and at environmentally-relevant doses, which “calls into question the assertion from the COT and others that OPEs are unlikely to cause neurotoxicity at human exposure levels”. The paper further raises the cocktail effect of exposure to complex mixtures of OPEs and that no routine testing for developmental neurotoxicity is conducted in the US, the EU, or elsewhere – which helps explain why so few chemicals have been categorised in that way.
“Organophosphate esters threaten the brain development of a whole generation,” said co-author and retired US National Institute of Environmental Health Sciences director Linda Birnbaum. “If we don’t stem their use now, the consequences will be grave and irreversible.”
“Organophosphate esters in many products serve no essential function while posing a serious risk, especially to our children,” said Carol Kwiatkowski, co-author and Science and Policy Senior Associate at the Green Science Policy Institute. “It’s urgent that product manufacturers critically reevaluate the uses of organophosphate ester flame retardants and plasticizers—many may be doing more harm than good.”
Dr Kerry Dinsmore, projects manager at UK environmental charity Fidra and who was not involved in the research, said: “This paper adds to the growing body of evidence that clearly demonstrates the devastating impacts that chemicals in our everyday products have on our health and our environment.
“The organophosphate esters considered here are just one group in a whole cocktail of chemicals we regularly, and unknowingly, bring into our homes, expose our families to and release into the environment. But importantly, with a number of policy activities currently underway, from the development of the UK Chemicals Strategy to the review of our outdated flammability standards, the UK is at a really pivotal moment where we have a genuine opportunity to address this growing health and environmental crisis.”
COT chair professor Alan Boobis, the chair of COT, told ENDS that the body had concluded that the available evidence indicted that phosphate-based flame retardants (PFRs), “do not pose a risk of developmental toxicity at anticipated exposure levels”, and that it had also concluded that they “were very unlikely to share the neurodevelopmental effects of other OPEs but could not exclude the possibility that PFRs could produce neurodevelopmental toxicity by some other mechanism”.