Wastewater is more than just a byproduct of modern society; it is an invaluable, real-time archive of chemical exposure, public health, and environmental contaminants. As regulatory scrutiny tightens around emerging threats, including microplastics and antimicrobial resistance, the analytical chemistry community is forced to adapt.
The field of environmental laboratory science is undergoing a significant transformation, according to Dr. Kevin Thomas, an environmental health scientist with the Queensland Alliance for Environmental Health Sciences (QAEHS) at The University of Queensland. His team is at the forefront of this change, driven by advancements in high-resolution mass spectrometry (HRMS) and the emergence of highly complex challenges such as nanoplastics. This shift marks a move away from guesswork and targeted analysis toward a more comprehensive, retrospective approach.
The Power of Retrospective Screening
Historically, standard environmental labs have relied on liquid or gas chromatography-mass spectrometry (LC–MS or GC–MS) workflows. These systems are frequently coupled to targeted single- or triple-quadrupole instruments. However, the integration of HRMS has shifted the paradigm, making these advanced instruments highly sought-after for broad screening applications.
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“Wastewater lets us look at what we don't know,” Dr. Thomas explains. While acknowledging that identifying true unknowns can be a lengthy process, he emphasizes, “One of the strong points of high-res mass spec is that you can go back into your data, look for something new, and see where it emerges.”
HRMS enables retrospective screening, allowing scientists to revisit old data to trace the emergence of newly identified contaminants. Dr. Thomas’s team utilizes a systematically collected wastewater archive from across Australia dating back to 2009. By mining these time-series samples, researchers can track downward trends in the disappearance of chemicals or identify the exact period when a new feature emerged.
A prime example of this workflow is the lab's effort to identify unknown transformation products and non-antibiotic pharmaceuticals that select for resistance in wastewater.
By leveraging these historical samples alongside advanced HRMS screening, researchers can build a much more comprehensive understanding of chemical exposure over time, shifting from reactive testing to proactive discovery.
The Nanoplastic Bottleneck: Sample Prep and Identification
While HRMS handles soluble chemicals effectively, analyzing nanoplastics introduces severe analytical and chromatographic bottlenecks. For standard contaminants, modern spectrometer sensitivity allows for minimal handling, with 90% of wastewater work relying on direct injection, centrifugation, and filtration.
“The nanoplastics are a different beast altogether because they're very difficult to extract and to work with,” explains Dr. Thomas. Extracting these ultra-trace particles from a complex colloidal matrix requires tedious techniques, such as specialized stir cell methods and thorough organic digestion to ensure measurement integrity.
Identification relies heavily on pyrolysis GC-MS (Py-GCMS), which captures a unique chemical fingerprint by breaking down the plastic. However, this indirect method can be prone to interference. In lipid-rich media with trace-level plastics, lipids can mimic these fingerprints—though in high-concentration matrices like biosolids, appropriate clean-up can reduce this signal to negligible levels. Similarly, even in simpler matrices such as beverages, incomplete polymerization fragments (PET oligomers) can be mistaken for actual nanoparticles.
Because of these complexities, Dr. Thomas stresses the necessity of orthogonal techniques. Coupling particle-size separation (such as asymmetric field-flow fractionation) with Py-GCMS, imaging, and nanoparticle tracking analysis drastically increases measurement confidence.
The Need for Real-World Standards and Strict QA/QC
A persistent roadblock in accurate nanoplastic quantification is the lack of authentic reference materials.
“We produce reference materials that are representative of pretty much pristine plastics, and we don't really know what the actual plastics in a wastewater stream at the nanoscale would look like,” Dr. Thomas states. “So we have standards that may not represent what we're actually looking for, and as an analytical chemist, that's quite challenging.” This disconnect between ideal laboratory standards and weathered environmental reality makes validating accurate quantification methods incredibly difficult.
Beyond the samples themselves, laboratories must also look inward to combat contamination. Commercial and academic labs are filled with plastic consumables that can easily skew ultra-trace results. To address this, Dr. Thomas’s team operates within a plastic-controlled stainless-steel environment equipped with airlocks and HEPA filters that turn over the room's air volume every three minutes.
Rather than relying on simple background subtraction—which is unreliable due to the unpredictable heterogeneity of lab contamination— laboratories must implement rigorous quality assurance. This involves running paired procedural controls and lab blanks alongside every sample from the point of collection straight through the analysis pipeline.
Data, Informatics, and the Future
Advances in wastewater monitoring analytics are creating a massive data footprint. To harness this, Dr. Thomas's team developed InSpectra, an informatics platform that serves as a repository for HRMS data from various labs. InSpectra was built to automatically and retrospectively screen archived data as soon as a new chemical is detected.
He anticipates a future in which routine use of quantum computing will enable the rapid, effective analysis of this extensive, structured collection of HRMS data. Dr. Thomas also points to the requirement for quicker physical testing. He observes that regulators in places such as California are beginning to regulate microplastics in drinking water, and he predicts this will soon extend to nanoplastics. This forthcoming legislation demands high-throughput methods characterized by precision and accuracy.
Looking ahead, while orthogonal screening is vital, it remains too intricate for high-throughput routine testing. To bridge this gap, the field must first expand its coverage of chemical space. As Dr. Thomas points out, “The industry is very much constrained at the moment by typically reversed-phase HPLC coupled to electrospray.” He hopes to see researchers break these constraints by using different separation techniques alongside more general ionization methods.
Sharing his wishes for the industry over the next five years, Dr. Thomas states: “I would really like a mass spectrometry vendor to come up with an ionization source that could ionize nanoplastics on the fly so that we could just directly measure them, for example, after our field flow fractionation step.” Doing so would finally open the door to the high-throughput environmental screening the industry desperately needs.
