Unregulated organic contaminants (UOCs) continue to enter the environment through everyday human activity, yet many remain largely invisible to routine monitoring programs. At the PFAS and Emerging Environmental Contaminants Symposium hosted by Separation Science, Youn Jeong Choi, Senior Analytical Chemist in the Department of Agronomy at Purdue University, examines how these compounds move through wastewater, biosolids, and agricultural soils—and what it takes analytically to measure them with confidence.
Choi frames her presentation around a central challenge: the number of synthetic chemicals in use far exceeds the scope of current regulatory frameworks. While some compounds remain unregulated because they pose low risk, others persist simply because analytical tools and monitoring strategies have not yet been developed to detect them. “Detection of unregulated organic contaminants in wastewater, biosolids, and agricultural soils is increasing,” she advises. “We need to understand their fate and behavior to properly assess environmental and human health risk.”
Why Unregulated Organic Contaminants Demand Attention
Choi explains that many UOCs originate in wastewater treatment systems, where they partition between liquid effluent and biosolids during processing. Biosolids, valued for their nitrogen and phosphorus content, are often applied to agricultural land as fertilizer. This practice creates a direct pathway for contaminants to move from human activity into soils, groundwater, and nearby surface waters. “Once these compounds enter environmental systems, they can accumulate in soil, impact biota, and move through multiple matrices,” she notes.
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Among the most concerning UOCs are endocrine-disrupting chemicals, which interfere with hormone systems in humans and wildlife. Choi highlights compounds such as bisphenols, hormones, and plasticizers, noting that research increasingly links them to developmental, reproductive, and transgenerational effects. “These compounds don’t just affect organisms that are directly exposed,” she adds. “They can impact future generations.”
From Biosolids to Soil: Following Contaminant Pathways
Choi emphasizes that understanding contaminant fate requires consideration of factors beyond water alone. According to Environmental Protection Agency (EPA) data, nearly 60% of biosolids generated in the United States are beneficially applied to land. “That high percentage means we need to understand what’s in these materials before application,” she reasons. “If biosolids contain organic contaminants, we may be introducing them directly into agricultural systems.”
Tracking these pathways raises analytical questions that traditional, single-class methods struggle to answer. The diversity of chemical structures, polarities, and behaviors among UOCs complicates extraction, separation, and detection—particularly in lipid- and protein-rich biosolid matrices.
Selecting Targets in a Sea of Chemicals
With millions of registered chemicals in commerce, Choi stresses the need for systematic prioritization. Her team compiles a comprehensive database from multiple sources, including in-house monitoring data, national sludge surveys, and suspect screening lists. From there, they filter candidates based on detection frequency, ecotoxicity, and the availability of analytical standards.
“We needed a strategy that balances environmental relevance with analytical feasibility,” Choi explains. This process yields a targeted list of more than 100 unregulated compounds across eight chemical families, including pharmaceuticals, personal care products, hormones, flame retardants, artificial sweeteners, opioids, and cannabinoids.
Addressing Multiclass and Isomeric Challenges
Analyzing such chemically diverse targets introduces further complexity. Choi points to isomeric compounds—chemicals with identical molecular formulas but different structures—as a major obstacle. “These compounds can share the same exact mass but behave very differently biologically and environmentally.”
To resolve these challenges, the workflow combines high-resolution mass spectrometry with carefully optimized chromatography. Retention time, fragmentation patterns, and column selection all play critical roles in differentiating closely related compounds. Choi also highlights the use of delay columns to separate background contamination originating from the LC system, thereby improving confidence at low concentrations.
Comparing Extraction Strategies for Complex Matrices
Choi compares two extraction approaches designed to improve on existing EPA methods. One employs a multi-step solid–liquid extraction (SLE) and solid-phase extraction (SPE) cleanup strategy to expand compound coverage, whereas the other uses a streamlined QuEChERS-style extraction coupled with enhanced lipid removal. “We needed methods that were comprehensive and practical for routine monitoring,” notes Choi.
The comparison reveals trade-offs between robustness and speed. While the more extensive extraction shows consistent recovery across compound classes, the faster approach significantly reduces solvent use and processing time—an important consideration for laboratories handling large sample volumes.
What this Means for Environmental Monitoring
Results from biosolid and soil samples show that UOCs are not theoretical concerns. Choi reports detections across a wide range of concentrations, with pharmaceuticals and personal care products dominating both matrices. Repeated biosolid application leads to accumulation in soils, reinforcing the need for long-term monitoring strategies.
Choi’s presentation underscores a broader message: effective environmental protection requires analytical methods that extend beyond regulated lists. “We hope this work enables more comprehensive monitoring of unregulated organic contaminants,” she shares. “That will support better risk assessment and more informed land management decisions.”
The on-demand presentation explores the data, method comparisons, and analytical considerations in greater detail. For laboratories interested in expanding beyond targeted regulatory methods and addressing complex environmental matrices, the whole session offers valuable insights into developing adaptable, forward-looking monitoring workflows.
