December 15, 2021

expert reaction to study of risks from atmospheric products of commercial chemicals

A study published in Nature looks to uncover global-scale risks from commercial chemicals in the air.

Prof Alastair Hay, Emeritus Professor of Environmental Toxicology at the University of Leeds, said:

“This is a superb paper. The work is original, very well conducted with good quality control, and it raises fundamental questions about the adequacy of risk assessments of chemicals in air and water.

“In the main risk assessments focus on the original parent compound; this paper suggests that this approach is missing a trick and that is that it ignores the toxicity of the (in many cases) multiple transformation products of these chemicals once they are in the air and enter aquatic systems?

“To make their point the authors look at one family of chemicals the organophosphate flame retardants (OPFRs), replacements for the older polybrominated diphenyl ether (PBDE) class of chemicals which have been phased out because of toxicity concerns. (Flame retardants do reduce the risk of fabrics catching fire).

“The authors use a model system to expose OPFRs to oxygen and assess the toxicity of the products using available software that has been used in OECD countries to perform hazard and risk assessments on thousands of chemicals and which takes account of their metabolism and toxicity. The authors also used their model outputs to help identify identical chemicals in the atmospheres of 18 global cities. 

“Atmospheric sampling carried out for between 42 and 92 days in the 18 cities (including London, New York, Buenos Aires and Delhi) indicates the presence of OPFR breakdown products in all, albeit at marginally different air concentrations. In other words the chemicals are ubiquitous.

“Some of the breakdown products are known to be more toxic than the parent chemical and, in some cases, much more persistent in the environment , but for others it may be the reverse. The important message is that we need to know what the real risks are.

“This work is a wake-up call for both the chemical industry and governments. For the industry the message is that we need to know far more about how your products behave in the environment and the implications for our health, and governments will have to assess whether the risks are acceptable or not.

“The task is hugely complex. Chemicals are not just exposed to oxygen in the air but to a multiplicity of other chemicals and this happens in water too. The range of possible chemical transformations is almost incalculable. But that should not deter us.

“The authors of this paper highlight tools that can help in the assessment and their evidence shows just why current reappraisals of the methodology used to assess risks from airborne and waterborne chemicals is needed.”

Dr Olwenn Martin, Lecturer in Global Challenges at Brunel University London, said:

“While air pollution is a well-known environmental risk factor for ill health, it is more widely monitored as the concentration for a few gases and particulate matter. The chemical composition of the atmosphere or particulate matter has received much less attention.

“This article points to a further complication and critical oversight that equally applies to other environmental media, such as water or soils; chemical risk assessments typically focus only on the parent compound. An underlying assumption in many past studies and risk assessments being that ultimate degradation products would be expected to be benign; if the parent compound disappears, the risk also supposedly disappears. It is clearly not necessarily the case but regulation lags behind science. 

“A good counterexample is that of the flame retardant c-decaBDE that was included in Annex A of the Stockholm convention on the basis of the toxicity of its degradation product and their contribution to mixture effects. Using a mixture of analytical chemistry and in silico predictive ecotoxicology, the authors demonstrate that degradation products of atmospheric pollutants can be more harmful that their parent compound. 

“The press release focuses on risk to urban (i.e. human) populations. The framework presented however relies on limited ecotoxicological modelled data (median lethal doses in rats and fathead minnows). It is a useful approach to prioritise the consideration of risks from various parent compounds but should not be interpreted as a health risk assessment for urban populations.

“A full assessment of the risks of the mixture of atmospheric pollutants on human health is most likely unfeasible at present due to the dearth of data and lack of knowledge about effects of these degradation products. It is entirely reasonable to assume that health outcomes of relevance for humans, specifically vulnerable populations such as children, the elderly and those with chronic conditions, may be more sensitive to these exposures. How much protection against potential health effects is afforded by existing regulatory limits using proxy measurements such as PM2.5 remains unclear.

“Chemical regulation does need to better account for degradation products and mixture effects, but it is unlikely that in the foreseeable future risks of such complex mixtures can be precisely predicted. Further research to better understand these risks is of critical interest but should not preclude pragmatic regulatory action, aiming to reduce exposures before a more detailed understanding of the risks is scientifically feasible.”

Stuart Harrad, Professor of Environmental Chemistry at the University of Birmingham, said:

“This is a valuable study that highlights a further concern about the extensive use of halogenated chemicals to meet furniture fire safety regulations. The study provides clear evidence that not only does London possess some of the highest concentrations globally of the parent compounds but that this also leads to similarly elevated levels of their degradation products – of which some may be more toxic than their parents. This is an important contributor to the debate on whether the use of halogenated chemicals to meet fire safety regulations is justified.”

‘Uncovering global-scale risks from commercial chemicals in air’ by Qifan Liu et al. was published in Nature at 4pm UK TIME on Wednesday 15 December.

DOI: https://doi.org/10.1038/s41586-021-04134-6

Declared interests

None received.