A coalition of 17 environmental organizations, led by Earthjustice, has submitted comments to the U.S. Environmental Protection Agency (EPA) urging it to not approve Opteon 2P50, an HFO made by Chemours that can be used as a liquid cooling agent for heat-generating servers in data centers.
The comments, posted publicly by the EPA on July 17, were in response to Chemours’ premanufacture notice (PMN) for Opteon 2P50 (flagged as p-26-0071), posted by the agency on June 15. The agency lists PMNs for new chemical substances whose safety it is reviewing under the Toxic Substances Control Act (TSCA). Other NGOs supporting Earthjustice’s comments include the Natural Resources Defense Council (NRDC), Food & Water Watch, Clean Water Action, the Center for Environmental Health and the Center for Public Environmental Oversight.
The critique of Opteon 2P50 comes at a time of considerable public opposition to data centers because of their demands on electricity, water and other resources. According to a recent Gallup survey, seven in 10 Americans oppose constructing data centers for artificial intelligence in their local area, including nearly half, 48%, who are strongly opposed.
Data center cooling has been traditionally handled by CRAC (computer room air-conditioning) units using f-gases and in some cases CO2 (R744), as well as chillers outside the computer room, including those employing CO2, propane (R290) and ammonia (R717). However, the growing demand for AI and other high-demand applications have led to higher server rack densities, creating a “thermal wall” where heat from chips cannot be effectively dissipated through traditional cooling. This has encouraged the development of liquid cooling technologies, such as direct-to-chip liquid and immersion cooling.
Chemours developed Opteon 2P50 – short for 3-Hexene, 1,1,1,2,2,5,5,6,6,6-decafluoro-, (3E)– as a dielectric (non-conducting) fluid for two-phase immersion cooling of data center servers. According to Chemours, it has a GWP of 10 and an ODP of zero, and it has a structure and properties similar to commercial HFOs like HFO-1234yf and HFO-1234ze. Chemours says that Opteon 2P50 can reduce cooling energy usage by more than 90% compared to air-cooled technology and nearly eliminates water use.
However, Opteon 2P50 falls under the category of PFAS (per- and poly-fluoroalkyl substances), industrial pollutants known as “forever chemicals.” In addition, when it escapes into the atmosphere Opteon 2P50 breaks down into trifluoroacetic acid (TFA) and perfluoropropanoic acid (PFPrA), according to Earthjustice’s comments. TFA and PFPrA, which are absorbed in rain and infiltrate the environment, are regarded as ultrashort-chain PFAS, though the EPA does not designate TFA as a PFAS.
Opteon 2P50 and its degradation products “present risks to human health and the environment that are not adequately disclosed in [Chemours’] PMN files.”
Earthjustice
Chemours has been the focus of concerns about its release of PFAS, notably PFOA, PFOS and GenX, into rivers that supply drinking water. Last year, tests commissioned by Cape Fear River Watch and the Southern Environmental Law Center showed “extremely high levels” of ultrashort-chain PFAS, including TFA and PFPrA, released by Chemours into the drinking water supply in North Carolina.
In June the EPA, the U.S. Department of Justice (DOJ) and the West Virginia Department of Environmental Protection (WV DEP) announced a $450 million [€380 million] settlement with Chemours, the first comprehensive federal settlement with a major PFAS manufacture, over releases of PFAS into rivers in North Carolina, New Jersey and West Virginia.
Chemours’ PMN ties the deployment of the Opteon 2P50 with current federal policy, such as the Trump administration’s executive order accelerating permitting of data center infrastructure. But Earthjustice urged the agency to make its determination regarding the chemical “based solely on risk-related factors.”
Chemours did not respond to a request for a comment on Earthjustice’s opposition to EPA approval of Opteon 2P50.
Risk assessment
Earthjustice argues in its comments that Opteon 2P50 and its degradation products “present risks to human health and the environment that are not adequately disclosed in [Chemours’] PMN files.”
Earthjustice pointed out that “substantial volumes of Opteon 2P50” are “likely to be used” in data centers, increasing the risk of release during use or maintenance. Lenny Siegel, Executive Director of the Center for Public Environmental Oversight (a signatory to Earthjustice’s EPA comments), urged in a blog that data centers should disclose the identity and quantities of substances used to cool computer systems and released into the environment, as well as what is being done to prevent releases and substitute environmentally friendly substances such as natural refrigerants as cooling agents.
Chemours has cited a Workplace Environmental Exposure Level (WEEL) of 200ppm for Opteon 2P50, Earthjustice noted. WEEL represents the airborne concentrations to which nearly all workers may be repeatedly exposed daily over a working lifetime without experiencing adverse health effects.
However, Earthjustice noted, this WEEL value was derived by a committee that was organized by Toxicology Excellence for Risk Assessment (TERA), which claims to be neutral but has been criticized for having links to the chemical industry. Moreover, the NGO said, “EPA cannot rely on the cited WEEL of 200ppm to characterize health harms given that its derivation is not transparent nor scientifically defensible since it provides no explanation for its uncertainty factors.”
Chemours’ PMN files “largely redact information related to assessing the environmental harms of Opteon 2P50,” Earthjustice said, adding that available public information finds that the substance is “hazardous to aquatic life and not readily biodegradable.” The NGO referred to the European Chemical Agency (ECHA) dossier for the chemical, which indicates that a 96-hour LC50 (the lethal concentration for 50% of a test population) for carp was calculated as 0.26mg/L, indicating “high acute toxicity.”
Breakdown in atmosphere
According to Chemours, Opteon 2P50 operates in “a closed system” whereby the vapor is “immediately condensed and returned to the fluid bath.” But Earthjustice argued that it is subject to evaporative losses and leaks as well as releases from end-of-life handling and disposal.
Upon release to the atmosphere, Opteon 2P50 reacts with the hydroxyl radical to form perfluorinated aldehyde in a molar yield of two, said Earthjustice; once the aldehyde is formed, it can degrade further to form PFPrA and TFA, with maximum molar yields 0.56 and 0.14, respectively, the NGO added.
Both PFPrA and TFA are known for their “high mobility in water and difficulty to contain and remediate, resulting in their ubiquitous presence, widespread contamination, and substantial risks to human health and the environment,” said Earthjustice.
The EPA said it has published a Human Health Toxicity Value for PFPrA based on “increased relative liver weight data from a single unpublished study in adult mice.”
TFA is the atmospheric byproduct of more common HFO refrigerants like HFO-1234yf. In the U.S., the only state that has formulated any drinking water guidance for TFA (the trifluoroacetate salt version) is Hawaii. At the federal level, the EPA announced in June a proposed rule to monitor 30 contaminants – including TFA – that are not currently regulated but may be present in drinking water.
Toxicity of TFA
While a universal consensus on the toxicity of TFA has not been reached, references to its potential toxicity are growing, particularly in the EU. The European Food Safety Authority (EFSA) recently lowered recommended values for the safe consumption of food, beverages and drinking water containing TFA, based on recent animal studies that showed TFA reducing levels of a thyroid hormone. The EFSA has also supported another study by Italian researchers, published in November 2025, that found that TFA reduced antibody production in human-relevant in vitro tests at levels similar to those caused by PFOS, which has well-documented immunotoxic effects.
The European Chemicals Agency (ECHA) concluded in June that TFA, based on animal studies, should be classified and labelled as toxic to reproduction, as persistent, mobile and toxic (PMT) and as very persistent and very mobile (vPvM); ECHA’s opinion still needs the approval of the European Commission before it becomes legally binding in the EU.
Under another regulation called REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals), ECHA is currently considering a sweeping restriction of PFAS that would ultimately ban certain f-gas refrigerants and TFA, with a possible enactment of regulations in 2028.
In defending the use of TFA-producing refrigerants, the fluorochemical Industry has pointed to the UN Environment Programme (UNEP) and its 2022 Environmental Effects Assessment Panel (EEAP) report. The report said that TFA is not bioaccumulative, is “not expected to pose significant risk to humans or the environment at the present time” and “is unlikely to cause adverse effects out to 2100.”
