The Invisible Threat: How PMT/vPvM Substances Contaminate Our Water

Imagine a chemical so persistent that it doesn't break down in the environment, and so mobile that it travels freely through soil and rivers, slipping past water treatment systems to reappear in our drinking water. This isn't science fiction—it describes a growing class of emerging contaminants known as PMT (persistent, mobile, and toxic) and vPvM (very persistent and very mobile) substances.

This declaration signaled a critical shift in how we assess chemical threats, acknowledging that persistence and mobility in water resources can be just as dangerous as persistence and buildup in living organisms.

This article explores how these invisible water contaminants have emerged as a major environmental concern, how scientists detect and assess them, and what recent regulatory changes mean for protecting our most vital resource—clean water.

The Problematic Trio: Persistence, Mobility, and Toxicity

PMT and vPvM substances are defined by three key properties that make them particularly threatening to water resources:

The similar acronyms PBT (persistent, bioaccumulative, and toxic) and vPvB (very persistent and very bioaccumulative) are no coincidence. PMT/vPvM substances were deliberately named to highlight their equivalent level of concern to these already-regulated hazardous chemicals ¹ .

How PMT/vPvM and PBT/vPvB Substances Differ

While both categories pose serious long-term threats, they differ significantly in their environmental behavior and exposure pathways:

Both categories share the common problem that their long-term and long-range transport is difficult to predict with accuracy, making exposure and risk challenging to determine in advance ¹ .

The Scientific Journey

The scientific community first recognized the hazard posed by persistent, mobile chemicals as early as the 1990s, initially referring to them as "polar persistent pollutants (P3)," "polar-POPs," or "persistent, mobile organic contaminants (PMOC)" ¹ . The specific terms PMT and vPvM were first introduced by Neumann and colleagues in 2015, deliberately echoing the established PBT/vPvB terminology to emphasize their equivalent concern level ¹ .

This conceptual framing paved the way for the German Environment Agency (UBA) to lead efforts establishing formal criteria to identify PMT/vPvM substances under the EU's REACH chemical regulation ^{2 5} .

Breaking Through Water Treatment

A crucial concern with PMT/vPvM substances is their ability to bypass both natural and artificial water treatment barriers. Research has shown that these substances can break through wastewater treatment plants, including advanced systems like granular activated carbon (GAC) filtration, ultrafiltration, advanced oxidation processes, and even reverse osmosis ¹ .

One study by Stackelberg et al. demonstrated that even after multiple treatment stages—clarification, disinfection, and GAC filtration—many mobile substances were not effectively removed, with elimination rates varying between only 25-76% for compounds like DEET, nonylphenol, camphor, and bisphenol A ¹ . For the most persistent and mobile substances, this breakthrough occurs even more rapidly, allowing them to circulate continuously in water cycles and potentially reach irreversible contamination levels ¹ .

Methodology: Closing the Analytical Gap

A crucial series of European studies tackled one of the fundamental challenges in PMT/vPvM research: the "analytical gap" and "monitoring gap." Many highly mobile substances had previously gone undetected because standard analytical methods weren't designed to capture them ¹ .

Results and Implications: Revealing the Hidden Contaminants

The findings were startling: out of the 57 targeted substances, 43 persistent and mobile substances were detected in European waters, with 23 substances reported in the environment for the first time ¹ .

Among the newly discovered widespread contaminants were:

• Methyl sulfate
• 2-Acrylamino-2-methylpropane sulfonate
• Benzyltrimethylammonium
• Trifluoromethanesulfonic acid
• 1,3-di-o-tolylguanidine ¹

This research demonstrated conclusively that the "monitoring gap" was a genuine concern, with numerous persistent, mobile substances circulating undetected in water systems. The study provided critical evidence that a more holistic approach is necessary to protect water resources from these chemical threats ¹ .

Current estimates suggest that approximately 2% of identifiable unique chemicals registered under REACH (259 out of 13,405 substances) meet PMT/vPvM criteria ² . However, the true number is likely significantly higher—potentially affecting up to 28% of REACH-registered substances (3,677 out of 13,405)—due to substantial data gaps regarding persistence, mobility, and toxicity information ² .

This uncertainty highlights the challenge of managing chemical risks when critical property data is missing, and underscores why grouping strategies and predictive methods are becoming increasingly important for chemical assessment and management.

Formal Recognition in EU Regulation

The scientific consensus on the equivalent concern level of PMT/vPvM substances has recently translated into concrete regulatory action. The European Commission has published a Delegated Regulation amending the CLP (Classification, Labelling and Packaging) Regulation, establishing PMT and vPvM as formal hazard classes with corresponding hazard statements ⁸ :

The Grouping Strategy Approach

With thousands of potential PMT/vPvM substances requiring assessment, regulators and researchers are increasingly turning to grouping strategies to enable efficient identification and management. This approach allows substances with similar structures, properties, or breakdown pathways to be assessed collectively rather than individually ² .

Benefits of Grouping Strategies

• Facilitate early identification of lesser-known or new potential PMT/vPvM substances
• Prompt additional testing when needed
• Avoid regrettable substitution where a banned chemical is replaced by an equally problematic alternative
• Integrate effectively into existing risk management frameworks ²