Increasing concerns over PFAS in the environment, in the last ten years, have sparked a growing interest in emerging contaminants among regulators, environmental consultants, media and politicians. This interest seems to stem, at least in part, from an understandable desire to want to know what the next major chemical issue will be. Having experienced the scale of the impacts and response to PFAS, it is reasonable to develop strategies to prioritise the issues for other chemicals, based on available information on environmental behaviour (fate and transport) and toxicology. While this is certainly a useful exercise to prioritise current concerns for management, it is questionable as to whether such efforts will identify another issue on the scale of PFAS. To understand why this might be, it helps to look to the past and understand the development of the paradigms on which we now base our chemical prioritisation.
Over the 1960s and 1970s, several chemicals or groups of chemicals emerged with issues as great or greater than PFAS. These included organochlorine pesticides (OCPs; Rachel Carson’s Silent Spring) and chlorofluorocarbons (CFCs; ozone depletion). The OCPs, CFCs and PFAS have distinct similarities, all being synthetic halogenated organic chemicals with very limited routes for environmental degradation. In the case of OCPs and PFAS, they also share a tendency to bioaccumulate. So why did the issues with PFAS not emerge at the same time as the others?
Central to this understanding for both OCPs and PFAS is the PBT paradigm, which stands for Persistence, Bioaccumulation and Toxicity. These are characteristics that when present together result in sufficient environmental hazard to require management on a global scale, in the form of the Stockholm Convention on Persistent Organic Pollutants.
While the Stockholm Convention was initially set up to manage the so-called ‘dirty dozen’ OCPs, key PFAS and another group of halogenated synthetic organic chemicals, the polybrominated diphenyl ethers (PBDEs) have since been listed. Interestingly, both meet the criteria for PBT, and both have been extremely widely used in a wide array of products, yet the PBDEs have not received nearly the same attention as PFAS. The answer for this may lie in the other property considered by Stockholm but less frequently discussed – mobility. Environmental mobility, along with routes to environment, are key factors in hazard (the innate tendency to cause harm) manifesting as risk (probability of actually causing harm). The much higher water solubility of PFAS compared to PBDEs, along with the importance of firefighting foams as a direct route to environment, are key factors in this difference.
Consideration of mobility as a key property is however becoming more recognised. For example, in Europe, some jurisdictions are pushing for regulation of chemicals based on very persistent and very mobile properties (vPvM). This is a reflection of the importance of groundwater as a source of drinking water to large populations in some parts of the world, and contrasts with the PBT paradigm which is focused more on food-based exposures. The mobility of PFAS has cast a light on this issue in large parts of the US and parts of Sweden.
Paradigms such as PBT or vPvM are the means we have for prioritising chemicals for registration and approval schemes. Based on laboratory and modelled data we can screen chemicals to identify whether they have hazards that are likely to manifest as issues in the field. So given our understanding of the PBT paradigm predated the emergence of PFAS as an environmental issue, why was that issue not properly identified until some decades later? Will assessing chemicals against these properties be sufficient to ensure similar issues don’t emerge in the future? This presentation will look at emerging issues from the past to address these questions.
Turning the crystal ball to the future, other concerns will be discussed. For example, is adding mobility to the paradigm is enough, or should prioritisation also be issues based? Should we still be focusing on individual chemicals, or is the real concern the cumulative effects from diverse mixtures of chemicals being released to the environment? And how do we consider environmental effects from substances that cannot be captured using traditional properties, but may arise as the next major environmental issue?