The U.S. Environmental Protection Agency announced that it will formally designate five known or probable carcinogens as High-Priority Substances (HPS) that will undergo a risk evaluation under the nation’s chemical safety law, the Toxic Substances Control Act (TSCA). The substances include acetaldehyde, acrylonitrile, benzenamine, 4,4’-methylene bis(2-chloroaniline) (MBOCA), and vinyl chloride. EPA also announced the beginning of the 9- to 12-month statutory process to prioritize the next five chemicals under TSCA to determine whether to initiate risk evaluations on them. They include benzene, ethylbenzene, naphthalene, styrene, and 4-tert-octylphenol.

“Today we begin another five chemical risk evaluations under our nation’s strengthened chemical safety law and start the yearlong process to initiate five more,” said Assistant Administrator for the Office of Chemical Safety and Pollution Prevention Michal Freedhoff. “These risk evaluations will be used to determine how to protect people from harmful chemical exposures.”

Risk Evaluations

EPA began the prioritization process for acetaldehyde, acrylonitrile, benzenamine, 4,4’-methylene bis(2-chloroaniline) (MBOCA), and vinyl chloride in a December 2023 announcement. The final designation of each chemical for risk evaluation is the last step in the 9- to 12-monthlong statutory prioritization process.

Over the past year, EPA reports that the agency has continued to improve the prioritization process by investing in cutting-edge software to review more information earlier in prioritization. EPA has also implemented improvements to its systematic review approaches as recommended by the Scientific Advisory Committee on Chemicals (SACC) by incorporating additional data sources such as assessments published by other government agencies to identify potential hazards and exposures, clarifying terminology to increase transparency in the systematic review process, and presenting interactive literature inventory trees and evidence maps to better depict data sources containing potentially relevant information.

In a July 2024 announcement, EPA proposed to designate the five chemicals for risk evaluation. At that time, the agency made considerably more information about those chemicals publicly available a full year earlier in the process as compared to the first 30 chemicals to undergo risk evaluations under TSCA, giving the agency a head start on its work and giving the public earlier and better opportunities to provide input.  

The agency will now begin risk evaluations for these chemical substances to determine whether they present an unreasonable risk of injury to health or the environment, without consideration of costs or other non-risk factors, under the conditions of use. If at the end of the risk evaluation process EPA determines that a chemical presents an unreasonable risk of injury to health or the environment, the agency must immediately start the risk management process to address the unreasonable risk.  

EPA will begin risk evaluations on the following substances:

Vinyl chloride, which is primarily used in the manufacturing and processing of plastic materials like polyvinyl chloride (PVC), plastic resins, and other chemicals. Many of these materials are used for pipes, insulating materials and consumer goods. This chemical was also involved in the Norfolk Southern train derailment in East Palestine, Ohio. Exposure to vinyl chloride may result in a range of harmful health effects such as liver toxicity. Vinyl chloride is also a known human carcinogen. In the 1970s, the White House Council on Environmental Quality and EPA officials raised serious concerns about the health impacts of vinyl chloride. These concerns were the impetus for Congress to write the “original TSCA” law in 1976 to ensure chemicals were made and used safely.

Acetaldehyde, which is primarily used in the manufacturing and processing of adhesives, petrochemicals, and other chemicals, as well as intermediates for products like packaging and construction materials. Exposure to acetaldehyde may result in a range of harmful health effects such as irritation of the respiratory system. EPA reports that acetaldehyde is a probable human carcinogen. 

Acrylonitrile, which is primarily used in the manufacturing and processing of plastic materials, paints, petrochemicals, and other chemicals. Exposure to acrylonitrile may result in a range of harmful health effects such as irritation of the respiratory system. EPA reports that acrylonitrile is a probable human carcinogen. 

Benzenamine, which is used in the manufacturing and processing of dyes and pigments, petrochemicals, plastics, resins, and other chemicals. Exposure to benzenamine may result in a range of health effects such as adverse effects on the blood, fetal development, and reproduction. EPA reports that benzenamine is a probable human carcinogen. 

MBOCA, which is used in the manufacturing and processing of rubbers, plastics, resins, and other chemicals. EPA reports that MBOCA is a probable human carcinogen. There is also extensive data that demonstrate exposure to MBOCA may damage genetic material in cells, potentially leading to other adverse health effects, particularly when infants and children are exposed. 

In the coming weeks, EPA will also release for public comment preliminary lists of manufacturers (including importers) subject to fees for the five chemicals designated as HPS under TSCA. The preliminary lists will soon be available in the docket EPA-HQ-OPPT-2024-0501 at the Regulations.gov page. Additionally, EPA will host a webinar on the list of fee payers, including steps to self-identify, how to certify as meeting an exemption and how to report production volume, on Tuesday, Jan. 14, 2025, at 1:00 p.m. EST. Register at the U.S. EPA: TSCA Fees webinar page.

Next Five Chemicals

As EPA announced in December 2023, the agency expects to initiate prioritization on five chemicals every year to create a sustainable and effective pace for risk evaluations. EPA is now initiating the prioritization process for five additional chemical substances:

Benzene, which is primarily used in the manufacturing and processing of adhesives, cleaning chemicals, petrochemicals, as well as intermediates for petrochemicals, plastics, rubber products, resin, construction, transportation equipment and other chemicals. It is also used in the production of consumer products such as electrical and electronic products, fuel, paint, and automotive care products. Exposure to benzene may result in a range of harmful health effects such as adverse impacts to the immune system (e.g., decreased immune lymphocyte count) and developmental abnormalities (i.e., fetal malformations). Benzene is a known human carcinogen that causes leukemia.

Ethylbenzene, which is primarily used in the manufacturing and processing of petroleum, petrochemicals, paints and coatings, adhesives, plastic materials, products including transportation equipment, furniture, non-metallic minerals (e.g., clay), agricultural, construction, forestry, fishing and hunting products, electrical equipment, and appliances, as well as intermediate uses (e.g., plastics, resin, petroleum). It is also used in the production of consumer products such as adhesives and sealants, paints, plastic and rubber products, automotive care products, packaging and fuel. Exposure to ethylbenzene may result in a range of health effects such as adverse impacts to liver and kidney tissue, hearing loss, and developmental abnormalities (i.e., fetal malformations). Ethylbenzene is a probable human carcinogen, linked to lung and kidney tumors in animal studies.

Naphthalene, which is primarily used in the manufacturing and processing of paints and coatings, oil and gas, fabricated metal products and transportation equipment. It is also used in consumer products like paints and coatings, fuels, and related products. Exposure to naphthalene may result in a range of harmful health effects such as destruction of red blood cells resulting in lower blood oxygen levels, damage to eyesight, and damage to liver, lung and nasal tissue. Naphthalene is a probable human carcinogen, linked to lung and nasal tumors in animal studies.

Styrene, which is primarily used in the manufacturing and processing of adhesives and other chemicals, as well as intermediates for printing and related activities. It is also widely used in consumer products including adhesives, sealants, paints and coatings, petrochemicals, fuels, plastic and rubber products, construction materials, packaging, toys, printing products, electrical and electronic products, and mechanical appliances. Exposure to styrene may result in a range of harmful health effects such as hearing loss, memory loss, miscarriage and damage to the tissue in the lungs and nasal passages. Epidemiological data show that cancers of the lung, kidney, breast, blood, and esophagus in humans may be linked to exposure to styrene and, based on evidence of lung tumors in animal studies, styrene is a probable human carcinogen.

4-tert-Octylphenol, which is primarily used in the manufacturing and processing of plastic and rubber products, and other chemicals, as well as intermediates for plastic material and resin. It is also used in consumer products like automotive parts. Exposure to 4-tert-octylphenol may result in a range of harmful human health effects such as kidney inflammation and lowered sperm count and motility that may result in impaired fertility.

EPA is opening a 90-day public comment period and is requesting further information on how these chemicals are used, their potential hazards and exposures, and the availability of information on each, as well as any other information relevant to the potential risks of these chemicals that will inform the agency’s review of these chemicals. Learn more by visiting EPA’s Chemical Substances Undergoing Prioritization webpage.