Getting in control of persistent, mobile and toxic (PMT) and very persistent and very mobile (vPvM) substances to protect water resources: strategies from diverse perspectives

Abstract

Background Safe and clean drinking water is essential for human life. Persistent, mobile and toxic (PMT) substances and/or very persistent and very mobile (vPvM) substances are an important group of substances for which additional measures to protect water resources may be needed to avoid negative environmental and human health effects. PMT/vPvM substances do not sufficiently biodegrade in the environment, they can travel long distances with water and are toxic (those that are PMT substances) to the environment and/or human health. PMT/vPvM substance research and regulation is arguably in its infancy and in order to get in control of these substances the following (non-exhaustive list of) knowledge gaps should to be addressed: environmental occurrence; the suitability of currently available analytical methods; the effectiveness and availability of treatment technologies; the ability of regional governance and industrial stewardship to contribute to safe drinking water while supporting innovation; the ways in which policies and regulations can be used most effectively to govern these substances; and, the identification of safe and sustainable alternatives. Methods The work is the outcome of the third PMT workshop, held in March 2021, that brought together diverse scientists, regulators, NGOs, and representatives from the water sector and the chemical sector, all concerned with protecting the quality of our water resources. The online workshop was attended by over 700 people. The knowledge gaps above were discussed in the presentations given and the attendees were invited to provide their opinions about knowledge gaps related to PMT/vPvM substance research and regulation. Results Strategies to closing the knowledge, technical and practical gaps to get in control of PMT/vPvM substances can be rooted in the Chemicals Strategy for Sustainability Towards a Toxic Free Environment from the European Commission, as well as recent advances in the research and industrial stewardship. Key to closing these gaps are: (i) advancing remediation and removal strategies for PMT/vPvM substances that are already in the environment, however this is not an effective long-term strategy; (ii) clear and harmonized definitions of PMT/vPvM substances across diverse European and international legislations; (iii) ensuring wider availability of analytical methods and reference standards; (iv) addressing data gaps related to persistence, mobility and toxicity of chemical substances, particularly transformation products and those within complex substance mixtures; and (v) advancing monitoring and risk assessment tools for stewardship and regulatory compliance. The two most effective ways to get in control were identified to be source control through risk governance efforts, and enhancing market incentives for alternatives to PMT/vPvM substances by using safe and sustainable by design strategies.

Assessing the Persistence and Mobility of Organic Substances to Protect Freshwater Resources

“…Threshold values are currently under discussion in Europe for the PMT/vPvM substance hazard classes, related to the continuum where the longer the t 1/2 and lower the K OC sorption, the greater the hazard. As presented above, the combination of t 1/2 and K OC are fit-for-purpose to indicate an increased probability of a substance contaminating drinking water resources if emitted; further, they can also be used to indicate increased drinking water purification costs. , When certain combinations of t 1/2 and K OC thresholds are crossed, chemical regulations (like CLP and REACH) are needed to enable labeling or registration of this hazard to instigate risk management measures, or when necessary authorization or restriction steps, to prevent long-term threats to water resources of such substances. Other regulations, such as agrochemical regulations, industrial emission regulations (e.g., in Europe the Industrial Emissions Directive (2010/75/EU) and the Aarhus Convention), or water quality regulations (e.g., the Urban Waste Water Directive (91/271/EE), Water Framework Directive (2000/60/EC), Groundwater Directive (2006/118/EC) or Drinking Water Directive (2006/118/EC)) can also aim to prevent water resource contamination.…”

“…This approach demonstrated that substituting (expensive) 14 C-labeled compounds with nonradiolabeled aniline was suitable for benchmarking half-lives . This method was applied to a group of seven previously suspected PMT/vPvM substances that were all later confirmed to be persistent in water. , PMT/vPvM hazard assessments based on weight-of-evidence here could be further prioritized for persistency testing using this simplified method.…”

Persistent, mobile, and toxic plastic additives in Canada: properties and prioritization

“…32 Log K oc is generally considered a suitable measure for assessing the mobility of neutral organic compounds, as well as for some ionic compounds, because soil and sediment organic carbon (and its cation exchange properties) will rule the sorption for these compounds. [33][34][35] With that said, log K oc can be highly variable, especially for many ionic compounds, based on pH, ion exchange interactions with soil minerals, and weathering effects, to name a few. [36][37][38] While a log K oc value <4.0 over a pH range of 4-9 is the current metric for mobility assessment by UBA, discussions are underway to reassess the mobility criteria, namely reducing this log K oc value from <4 to <3, as a log K oc value <4 can include several substances which can be highly adsorbed, and thus unlikely to be mobile.…”

“…[36][37][38] While a log K oc value <4.0 over a pH range of 4-9 is the current metric for mobility assessment by UBA, discussions are underway to reassess the mobility criteria, namely reducing this log K oc value from <4 to <3, as a log K oc value <4 can include several substances which can be highly adsorbed, and thus unlikely to be mobile. 32,33 Nevertheless, log K oc serves as the best measure of mobility for a wide range of compounds. Given the variability and complexity in its measurement, experimental log K oc values are oen not available, and instead log K ow or log D ow (for ionizable substances), may be used as an analog to log K oc .…”

Screening and prioritising Persistent, Mobile and Toxic chemicals: development and application of a robust scoring system

“…These benchmarks were not applied in this work as these cutoff values might be considered to be too conservative. Particularly as the groundwater ubiquity score (GUS) indicates that chemicals with a log Koc of 4 (or higher) are considered only mobile enough to reach the groundwater if there is no (observable) degradation at all in the environment [25,26].…”