If you run a municipal wastewater treatment plant and test your final effluent, you’ve probably run into a total head-scratcher: the water leaving your facility often has way higher concentrations of PFAS than the raw stuff coming in.

At a recent PFAS symposium hosted by Toronto Metropolitan University (TMU), Dr. Roxana Sühring, an Associate Professor in TMU’s Department of Chemistry and Biology, explained exactly why this happens. Looking at the data coming out of her Emerging Contaminants Lab, it turns out our standard wastewater infrastructure is accidentally acting like a chemical transformer.

“Wastewater treatment plants are PFAS receivers, not destruction technologies,” Dr. Sühring pointed out. Her research shows that standard biological and chemical treatment steps are actually just unmasking hidden “precursor” compounds, creating a massive analytical blind spot and a looming legal liability for Canadian utilities.

The chemistry behind the surge

To understand why treated effluent frequently finishes with double the PFAS concentration of the influent, Dr. Sühring walked us through the actual organic chemistry.

The real culprit here is a group called PFAS precursors—complex, often proprietary fluorinated molecules used everywhere from consumer products to pharmaceuticals and pesticides. Because these precursors aren’t on standard regulatory monitoring lists, they’re basically invisible when the influent first hits the plant.

But when these precursors enter the highly active microbial environment of aerobic activated sludge, things change. Bug cultures can’t break the ultra-strong carbon-fluorine bond, but they can readily eat away the surrounding organic structures of the precursor molecules. This partial breakdown trims those big, complex molecules down into the simple, highly stable terminal perfluoroalkyl acids (PFAAs) we all know—like PFOA and PFOS.

Because commercial labs only test for these final terminal compounds, it looks like PFAS is magically generated inside the plant. In reality, the treatment process is just stripping off the chemical camouflage.

Quantifying the blind spot

The most striking data from Dr. Sühring’s presentation showed just how massive this blind spot really is for Canadian operators. By using advanced, non-targeted high-resolution mass spectrometry alongside traditional standard testing, her lab evaluated final, fully treated effluent across multiple Canadian treatment plants.

The data revealed two massive gaps in how the industry currently tracks PFAS:

1. Short chains dominate the water

Traditional monitoring focuses heavily on legacy, long-chain PFAS (like C7 and C8 chains, including PFOA and PFOS). But Dr. Sühring’s data showed that these classic compounds make up only about 10 per cent of the PFAS detected in final Canadian effluent. Instead, over 70 per cent of what’s actually in the water are ultra-short and short-chain PFAS (C4 to C6).

2. The missing fluorine problem

To see how much total fluorine was actually being accounted for, Dr. Sühring’s lab ran a mass balance analysis comparing targeted PFAS against total extractable organic fluorine.

The results were eye-opening: in treated wastewater effluent, standard targeted testing explains under 10 per cent of the organic fluorine present. In biosolids, it only captures about half.

According to Dr. Sühring, a huge chunk of that remaining 90 per cent consists of mobile ultra-short chains like trifluoroacetic acid (TFA), which often comes from degrading pharmaceuticals and pesticides. These are slated for global regulatory scrutiny by 2030, but right now, we’re totally blind to them.

What this means for Canadian utilities

Dr. Sühring’s data shifts the conversation from a chemistry lesson to a real-world reality check for Canadian water managers:

Standard sorbents fail on ultra-short chains: Traditional end-of-pipe fixes, like granular activated carbon (GAC) or standard ion exchange resins, are notoriously terrible at catching highly mobile, ultra-short chain compounds like TFA.
Water and sludge have to be evaluated together: Because of how PFAS splits up, the highly soluble short chains stay in the water to contaminate effluent, while the longer chains prefer to stick to organic matter—directly threatening the beneficial reuse and land application of biosolids.
We need better testing metrics: Instead of relying on a rigid list of 20 or 30 targeted compounds, Dr. Sühring recommends the industry look at broader tools, like the Total Oxidizable Precursor (TOP) assay or total organic fluorine (TOF) tracking, to get an honest baseline of what is actually entering municipal systems.

Sitting back and waiting for perfect regulations isn’t an option anymore. As Canadian guidelines tighten—like Health Canada’s strict 30 ng/L drinking water objective for a sum of 25 PFAS, and the Canadian Food Inspection Agency’s (CFIA) 50 ppb interim limit for PFOS in biosolids—understanding the hidden chemistry of precursor transformation is no longer just for academics. It’s an operational necessity for protecting our infrastructure, managing our liabilities, and keeping our communities safe.