Here’s what you’ll learn when you read this story:

• Similar to the ‘forever chemical’ PFAS, medium-chain chlorinated paraffins (MCCPs)—often found in textiles and PVC products—are toxins that can take a long time to breakdown in the environment and negatively impact human health.
• In 2025, scientists at the University of Colorado Boulder detected these toxins in the North American air for the first time, while researching aerosol formation.
• These airborne MCCPs particles likely entered the atmosphere through biosolids—a fertilizer developed from treated wastewater.

One of the downsides of modern life is the proliferation of chemicals in the natural environment. Arguably the most well-known of these chemical culprits are per- and polyfluoroalkyl substances (PFAS), which are used for stuff like non-stick surfaces on frying pans. They are also known as “forever chemicals” for their tendency to linger in the environment.

But this environmental scourge is only one of many similar substances. Of the others, one of the most concerning is a type of toxin known as medium-chain chlorinated paraffins, or MCCPs. Like PFAS, these chemicals take a longtime to break down, and have been shown to be the driver behind health issues like liver and kidney toxicity, thyroid malfunction, and certain neurological issues. MCCPs have been detected in the atmosphere on other continents (including Asia and even Antarctica) but a 2025 study from the University of Colorado Boulder claims that North America has now joined that unlucky list.

In setting out to detect how aerosols form and grow in an agricultural region of Oklahoma, the team of scientists behind this recent study stumbled across trace amounts of MCCPs in the atmosphere. They detected these particles using a technique known as nitrate ion chemical ionization mass spectrometry, and the results were published in the journal ACS Environmental AU.

MCCPs start their lives within things like metalworking fluids, textiles, and PVC, which is why they can often find themselves in wastewater. That’s a problem, because a fertilizer known as biosolids (which is made from treated sewer sludge) is often spread across agricultural crops.

“When sewage sludges are spread across the fields, those toxic compounds could be released into the air,” Daniel Katz, lead author of the study, said in a press statement. “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.”

The creation of this synthetic chemical was in large part due to the regulation of its toxic cousin, Short Chain Chlorinated Paraffins (SCCPs), which have been regulated by the Environmental Protection Agency (EPA) and the Stockholm Convention (an international body formed in 2001 to protect human health against persistent organic pollutants).

In 2025, the Stockholm Convention also marked MCCPs for global elimination. Who knows if this will spawn the creation of another toxic chemical, but this regulatory game of whack-a-mole is similar in the truly Sisyphean task of trying to eliminate PFAS from the environment.

“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,” Ellie Browne, a co-author of the study, said in a press statement. “So they get replaced by something.”

Luckily, there is some good news. The Oklahoma Senate passed a bill in 2025 eliminating biosolids as a fertilizer, and a newly established environmental group called The Coalition for Sludge-Free Land aims to make the ban a national one (the EPA currently regulates, but doesn’t ban, the substance). Now that MCCPs have been found in the atmosphere, the UC Boulder team hopes that future efforts will be able to discern their airborne impact.

“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 in a press statement. “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.”