Medium-chain chlorinated paraffins (MCCPs) – a class of industrial chemicals considered potentially toxic and persistent – have been detected in ambient air for the first time in the Western Hemisphere. The study documents the first continuous, time-resolved measurements of MCCPs in the atmosphere.
The unexpected discovery came during a real-time atmospheric chemistry field study in rural Oklahoma using nitrate chemical ionization mass spectrometry (NO₃⁻ CIMS). Commonly used in PVC, textiles, and metalworking fluids, MCCPs are structurally similar to short-chain chlorinated paraffins (SCCPs), which are already regulated under the Stockholm Convention due to their persistence, bioaccumulation, and toxicity.
"It's very exciting as a scientist to find something unexpected like this that we weren't looking for," commented Daniel Katz, lead author of the study, in a recent press release. "We're starting to learn more about this toxic, organic pollutant that we know is out there, and which we need to understand better."
Using NO₃⁻ CIMS, the team measured gas-phase aerosol precursors continuously over a one-month period. When unexpected isotopic patterns appeared in the data, further analysis confirmed the presence of MCCPs. Real-time data from the study showed that MCCPs exhibited strong diurnal trends, with gas-phase concentrations peaking in the late afternoon and falling overnight – consistent with changes in temperature-driven gas-particle partitioning.
While MCCPs have previously been detected in Asia and Antarctica, the study represents the first time they have been measured in real-time air samples from North America. The researchers suggest the source may be linked to the use of biosolid fertilizer – treated sewage waste commonly spread on agricultural fields. “When sewage sludges are spread across the fields, those toxic compounds could be released into the air,” Katz suggested. “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.”
The team’s finding follows a broader trend of chemical substitution, where banned or regulated substances like SCCPs are replaced with less scrutinized alternatives – often with similar properties. “We always have these unintended consequences of regulation,” said Ellie Browne, CU Boulder chemistry professor and CIRES Fellow. “You regulate something, and then there’s still a need for the products that those were in. So they get replaced by something.”
MCCPs, the authors note, show similarities to PFAS in their environmental persistence and resistance to degradation, though their atmospheric behaviour and health effects remain poorly understood. “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.”
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