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Abstract Credit: ACS Environmental Au (2025). DOI: 10.1021/acsenvironau.5c00038

Scientific research can often resemble the work of detectives, as researchers embark on their quests with hypotheses and the anticipation of discovering particular results. However, sometimes unexpected findings lead to a deeper investigation into the data, revealing crucial insights that were not initially anticipated.

Such was the case for a team of researchers from the University of Colorado Boulder, who conducted a field campaign in an agricultural region located in Oklahoma. Utilizing a cutting-edge instrument designed to measure the formation and growth of aerosol particles in the atmosphere, they unexpectedly detected the first airborne measurements of medium-chain chlorinated paraffins (MCCPs) in the Western Hemisphere. The results of their groundbreaking study have been published today in ACS Environmental Au.

“It’s very exciting as a scientist to find something unexpected like this that we weren’t looking for,” expressed Daniel Katz, a Ph.D. student in chemistry at CU Boulder and the lead author of the study. “We’re starting to learn more about this toxic organic pollutant that we know exists, and we must understand it better.”

MCCPs are currently being considered for regulation under the Stockholm Convention, a significant global treaty aimed at safeguarding human health from hazardous and persistent chemicals. Previously, while these toxic pollutants have been detected in regions such as Antarctica and Asia, researchers had faced challenges in tracking their presence in the atmosphere of the Western Hemisphere until this pivotal discovery.

These chlorinated paraffins are commonly utilized in various applications, including metalworking fluids and the production of PVC and textiles. They often find their way into wastewater systems, leading to their subsequent presence in biosolid fertilizers—also referred to as sewage sludge. This sludge is a byproduct produced when liquid is extracted from wastewater during treatment processes. In the Oklahoma region studied, researchers suspect that the MCCPs they identified likely originated from biosolid fertilizers applied to agricultural fields nearby their measurement site.

“When sewage sludges are spread across the fields, those toxic compounds could be released into the air,” Katz noted. “While we can't definitively show that’s happening, it seems reasonable to consider that this is a pathway for their presence in the atmosphere. Studies have shown that these fertilizers can emit similar compounds.”

Interestingly, MCCPs are closely related to their shorter counterparts, short-chain chlorinated paraffins (SCCPs), which have been under regulation since 2009 by both the Stockholm Convention and the Environmental Protection Agency (EPA) in the United States. This regulatory action was prompted by studies highlighting the harmful impacts of these toxic pollutants, which can travel long distances and persist in the atmosphere, posing risks to human health. Researchers have begun to theorize that the regulation of SCCPs may have inadvertently led to an increase in the environmental prevalence of MCCPs.

“We often encounter unintended consequences of regulation, where one substance is controlled, yet there remains a demand for similar products, leading to their replacement,” stated Ellie Browne, a chemistry professor at CU Boulder and a CIRES Fellow, who also co-authored the study.

The measurement of aerosols at the agricultural site facilitated this surprising discovery. The research team employed a nitrate chemical ionization mass spectrometer, an advanced tool that enables scientists to identify airborne chemical compounds. Over the course of a month, the team continuously measured air quality at the site, documenting different isotopic patterns within the compounds detected.

Through meticulous data analysis, Katz observed unique isotopic patterns that deviated from previously recognized chemical compounds. Further research led him to identify these compounds as chlorinated paraffins associated with MCCPs.

Katz highlighted that the chemical structure of MCCPs is similar to PFAS (per- and polyfluoroalkyl substances), a class of long-lasting toxic chemicals notorious for their persistence in the environment and human body, earning them the moniker "forever chemicals." The proliferation of PFAS in soils recently prompted the Oklahoma Senate to place a ban on the use of biosolid fertilizers.

With the successful identification of MCCPs, the next step for researchers will be to measure these pollutants throughout different seasons to understand their varying concentrations over time. Many aspects of MCCPs remain shrouded in mystery, and there is a pressing need for further research to uncover their environmental effects.

“We’ve identified them, but we still do not have a comprehensive understanding of their behavior in the atmosphere, which necessitates further investigation,” Katz remarked. “It’s crucial that we have government agencies capable of evaluating the scientific findings and regulating these chemicals as needed to ensure public health and safety.”

For more information, refer to the publication: Daniel John Katz et al, Real-Time Measurements of Gas-Phase Medium-Chain Chlorinated Paraffins Reveal Daily Changes in Gas-Particle Partitioning Controlled by Ambient Temperature, ACS Environmental Au (2025). DOI: 10.1021/acsenvironau.5c00038