The EPA recently announced a proposal to designate five chemicals as high-priority substances (HPSs) for risk evaluation under the Toxic Substances Control Act (TSCA), the nation’s chemical safety law.

If the designations are finalized as proposed, the Agency will immediately move forward with risk evaluations on the chemicals.

“Studying the safety of these harmful chemicals – all five of which have been linked to cancer and are used to make plastic – would help lead to critical public health and environmental protections in communities across the country and would ensure that the public has access to more data on these chemicals sooner,” said Assistant Administrator for the Office of Chemical Safety and Pollution Prevention Michal Freedhoff in an Agency news release.

The five chemical substances the EPA is proposing to designate as HPSs are:

• Vinyl chloride (Chemical Abstracts Service Registry Number (CASRN) 75-01-4)
• Acetaldehyde (CASRN 75-07-0)
• Acrylonitrile (CASRN 107-13-1)
• Benzenamine (CASRN 62-53-3)
• 4,4’-methylene bis(2-chloroaniline) (MBOCA) (CASRN 101-14-4)

“All five chemicals were selected from the 2014 TSCA Work Plan, which is a list of chemicals identified by EPA for further assessment based on their hazards and potential for exposure,” the Agency news release continues. “In proposing these five chemical substances as High-Priority Substances for risk evaluation, EPA had to consider the chemicals’ conditions of use and production volume or changes in conditions of use and production volume over time, impacts to potentially exposed or susceptible subpopulations including children and workers, and the chemicals’ potential hazards and exposures. EPA also considered more specific criteria such as the chemicals' bioaccumulation and environmental persistence and whether the chemical is stored near significant sources of drinking water.”

Vinyl chloride. Vinyl chloride is mainly used to manufacture and process plastic materials like polyvinyl chloride (PVC), plastic resins, and other chemicals. Recently the subject of media scrutiny due to the Norfolk Southern train derailment in East Palestine, Ohio, this chemical is a known human carcinogen and can cause liver, brain, and lung cancer. “Short-term exposure to vinyl chloride can also result in other health effects such as dizziness, nausea, and eye and skin irritation,” the news release adds. “In the 1970s, the White House Council on Environmental Quality and EPA officials raised serious concerns about the health impacts of vinyl chloride as an example when the Nixon Administration asked Congress to write a law to ensure chemicals were made and used safely, which led to passage of the ‘original’ TSCA in 1976.”

Acetaldehyde. Acetaldehyde is primarily used in the manufacturing and processing of adhesives, petrochemicals, plastic, and other chemicals, as well as intermediates for products like packaging and construction materials. “Acetaldehyde is a probable human carcinogen,” according to the EPA’s release. “Specifically, animal studies have shown that exposure to acetaldehyde can result in the formation of nasal and laryngeal tumors. Short-term exposure can also result in health effects such as irritation of the respiratory system and reduced heart function. Data further shows that acetaldehyde exposure can damage genetic material in cells, potentially leading to numerous adverse health effects.”

Acrylonitrile. Acrylonitrile is used in the manufacturing and processing of plastic materials, paints, petrochemicals, and other chemicals. Acrylonitrile is also categorized as a probable human carcinogen and can cause lung and brain cancer. Exposure effects include eye, skin, and respiratory irritation; reduced sperm count; and slowed fetal growth, according to the EPA.

Benzenamine. Benzenamine is used to manufacture and process dyes and pigments, petrochemicals, plastics, resins, and other chemicals, and it’s categorized as a probable human carcinogen. Exposure can result in pancreatic cancer, bladder tumors, difficulty breathing, tumor growth in the spleen, and possible reductions in fetal viability.

MBOCA. MBOCA is used in the manufacturing and processing of rubbers, plastics, resins, and other chemicals and is a probable human carcinogen. Animal studies have shown that exposure can cause liver and urinary bladder cancer, as well as eye and skin irritation in the short term. “Data further demonstrates that MBOCA exposure can damage genetic material in cells, potentially leading to numerous adverse health effects,” according to the Agency.

Process for regulating existing chemicals

The first step in regulating existing chemicals on the market and in use is called prioritization.

Just because the Agency proposes to designate a chemical as an HPS for risk evaluation doesn’t mean there has been a finding of risk. When an HPS designation is finalized, the EPA then initiates risk evaluations to determine whether the chemical presents an unreasonable risk to human health or the environment under the TSCA conditions of use (which cover the way the chemical is made and used).

Risk evaluations are required by law to be completed within a 3 ½-year period, although the Agency has been notoriously behind schedule in the past.

If the risk evaluation process results in a finding of unreasonable risk to health or the environment, the Agency begins the risk management process to determine the proper action(s) necessary to eliminate the unreasonable risks.

The prioritization process for these five chemicals began in December 2023.

The Agency also announced it expects to initiate prioritization on five new chemicals every year, believing this prioritization pace “will create a sustainable and effective pace for risk evaluations.”

Improvements made to the prioritization process by the Agency include:

• Investing in cutting-edge software to review more information earlier in prioritization;
• Improving 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.
• Completing a preliminary screening and technical review of large data sets to more efficiently identify relevant information for prioritization and risk evaluation and easily flag information that may be useful to retrieve later in the risk evaluation process.

“As a result, EPA now has a head start on risk evaluations. At this proposed designation stage, EPA has a much fuller understanding of how these chemicals behave in the environment and their potential hazards and exposures than it had at this point in the process in the previous prioritization cycle conducted in 2019,” according to the Agency’s release. “That has also enabled EPA to make considerably more information available to the public a year earlier than occurred for the first 30 chemicals designated for risk evaluation under TSCA. The public will be able to see which studies and what information EPA considered in its screening review for proposed designation and submit any additional information they would like EPA to consider via public comment.”

Comments on the proposed designations will be accepted until October 23, 2024, under docket #EPA-HQ-OPPT-2023-0601 on the Regulations.gov website.