Toxic “Replacement” Chemicals Detected in U.S. Skies for the First Time

By Open Chronicle Staff with Agencies

BOULDER, CO — In a discovery that has blindsided environmental scientists, a new type of airborne toxin has been detected in the Western Hemisphere for the first time. Researchers from the University of Colorado Boulder, conducting field studies in rural Oklahoma, identified Medium-Chain Chlorinated Paraffins (MCCPs) drifting over agricultural lands, a find that suggests industrial pollutants are “hitching a ride” from the ground into the atmosphere via common farming practices.

Researchers from the University of Colorado conducted research that indicates the highly toxic medium chain chlorinated paraffins (MCCPs) they discovered in Oklahoma soil “came from biosolid fertilizer in the fields near where they set up their instrument.” What this article gets… pic.twitter.com/zuVykxDpVF

— Jim Shaw (@ShawForOK) June 9, 2025

An Accidental Discovery

The research team, led by PhD student Daniel Katz, was originally in Oklahoma to study the formation of tiny airborne particles. Instead, their high-sensitivity mass spectrometers picked up unusual chemical signatures that didn’t match any expected local pollutants.

“It’s very exciting as a scientist to find something unexpected like this,” Katz stated. “We’re starting to learn more about this toxic, organic pollutant that we know is out there, but which we need to understand better.”

The “Sewage Sludge” Connection

The study points to a likely, albeit indirect, source: biosolid fertilizers. Also known as sewage sludge, these fertilizers are products of wastewater treatment processes.

• The Process: Industrial chemicals used in metalworking and PVC production end up in wastewater.

• The Residue: These chemicals concentrate in the sludge during treatment.

• The Airborne Route: When the sludge is spread across farmland as fertilizer, the MCCPs appear to “off-gas” or evaporate, rising into the air to be carried by the wind.

The “Regretful Substitution” Trap

MCCPs are closely related to Short-Chain Chlorinated Paraffins (SCCPs), which were heavily regulated by the EPA in 2009 due to their toxicity and persistence. Experts believe that as industries were forced to move away from SCCPs, they simply switched to MCCPs to avoid regulation—a phenomenon known as “regretful substitution.”

“We always have these unintended consequences of regulation,” explained Ellie Browne, CU Boulder chemistry professor. “You regulate something, and then there’s still a need for the products… so they get replaced by something [similar].”

Health Risks and “Forever Chemical” Similarities

MCCPs are currently under evaluation by the Stockholm Convention, an international treaty managing persistent organic pollutants. These chemicals share troubling traits with PFAS (per-and polyfluoroalkyl substances), often called “forever chemicals”:

1. Persistence: They do not break down easily in the environment.

2. Bioaccumulation: They can build up in the bodies of animals and humans over time.

3. Long-Range Transport: They can travel vast distances through the atmosphere, having previously been detected as far away as Antarctica.

Looking Ahead

The discovery has already had political ripples; the Oklahoma Senate recently moved to ban biosolid fertilizers due to overlapping concerns regarding PFAS contamination.

The CU Boulder team plans to continue monitoring the site to determine how these levels change with the seasons and what long-term respiratory risks they might pose to rural populations. “We identified them, but we still don’t know exactly what they do when they are in the atmosphere,” Katz warned.

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