That is exactly what happened during a University of Colorado Boulder field study in an agricultural region of Oklahoma. The team was using advanced instruments to study how tiny airborne particles form and evolve. Instead, they uncovered something surprising: the first airborne detection of Medium Chain Chlorinated Paraffins (MCCPs), a type of toxic organic pollutant, in the Western Hemisphere. The findings were published in ACS Environmental Au.

"It's very exciting as a scientist to find something unexpected like this that we weren't looking for," said Daniel Katz, CU Boulder chemistry PhD student and lead author of the study. "We're starting to learn more about this toxic, organic pollutant that we know is out there, and which we need to understand better."

What Are MCCPs and Why They Matter

MCCPs are now being evaluated for possible regulation under the Stockholm Convention, an international agreement aimed at protecting human health from persistent and widespread chemicals. Although these pollutants have previously been detected in places like Antarctica and Asia, scientists had struggled to measure them in the air over the Western Hemisphere until this study.

These chemicals are commonly used in industrial processes, including metalworking fluids and the production of PVC and textiles. They frequently appear in wastewater and can end up in biosolid fertilizer, also called sewage sludge, which is produced during wastewater treatment. The researchers believe the MCCPs they detected in Oklahoma likely originated from nearby fields where this type of fertilizer had been applied.

"When sewage sludges are spread across the fields, those toxic compounds could be released into the air," Katz said. "We can't show directly that that's happening, but we think it's a reasonable way that they could be winding up in the air. Sewage sludge fertilizers have been shown to release similar compounds."

A Possible Side Effect of Regulation

MCCPs are closely related to Short Chain Chlorinated Paraffins (SCCPs), which are already regulated under the Stockholm Convention and by the U.S. Environmental Protection Agency since 2009. Those earlier regulations followed evidence that SCCPs can travel long distances, persist in the environment, and pose risks to human health.

However, researchers suspect that limiting SCCPs may have led industries to substitute them with MCCPs, increasing the presence of these related chemicals.

"We always have these unintended consequences of regulation, where you regulate something, and then there's still a need for the products that those were in," said Ellie Browne, CU Boulder chemistry professor, CIRES Fellow, and co-author of the study. "So they get replaced by something."

How Scientists Tracked the Chemicals

The discovery came from continuous air monitoring at the Oklahoma site. The team used a nitrate chemical ionization mass spectrometer, a sensitive instrument that can identify specific compounds in the air. Measurements were collected around the clock for a full month.

As Katz analyzed the data, he identified unusual isotopic patterns that did not match known compounds. After further investigation, those patterns were linked to chlorinated paraffins associated with MCCPs.

Links to "Forever Chemicals" and Future Research

Katz noted that MCCPs share similarities with PFAS, a group of chemicals often called "forever chemicals" because they break down very slowly in the environment. Concerns about PFAS contamination in soil recently led the Oklahoma Senate to ban biosolid fertilizer.

Now that scientists have confirmed how to detect MCCPs in the air, the next step is to track how their levels change over time. Researchers want to understand how concentrations vary across seasons and what effects these chemicals may have once they are airborne.

"We identified them, but we still don't know exactly what they do when they are in the atmosphere, and they need to be investigated further," Katz said. "I think it's important that we continue to have governmental agencies that are capable of evaluating the science and regulating these chemicals as necessary for public health and safety."