Uncovering new global risks from commercial chemicals in air

Abstract Commercial chemicals are used extensively across global urban centers, posing a potential exposure risk to 4.2 billion people, which accounts for 55% of the global population. Harmful chemicals are often assessed and regulated based on their environmental persistence, bioaccumulation, and toxic properties, under international and national initiatives such as the Stockholm Convention. However, current regulatory frameworks largely rely upon knowledge of the properties of the parent chemicals, with minimal consideration given to their atmospheric transformation products. This is mainly due to a significant lack of experimental data, as identifying transformation products in complex mixtures of airborne chemicals is an immense analytical challenge,hence making a comprehensive and reliable risk assessment for harmful chemicals currently unachievable. Here, we develop a novel framework, combining laboratory and field experiments, non-target analysis techniques, and in-silico modelling, to identify and assess the hazards of airborne chemicals, which takes into account atmospheric chemical reactions. By applying this framework to organophosphate flame retardants, as representative chemicals of emerging concern, we find that their transformation products are globally distributed across 18 megacities, representing a previously unrecognized exposure risk for the world’s urban populations. Furthermore, the transformation products can be up to an order of magnitude more persistent, environmentally mobile, and toxic than the parent chemicals. The results indicate that the overall human and environmental risks associated with flame retardants could be significantly underestimated, while highlighting a strong need to include atmospheric transformations in the development of regulations for all harmful chemicals moving forward.