California Proposition 65: Impact on TMPTA and Industry Response Strategies (Part 1)

Introduction: Regulatory Challenges and Responses 

As global awareness of chemical safety and environmental protection grows, California's Proposition 65, with its stringent enforcement mechanisms, continues to pose compliance challenges for products entering the California market. Recently, trimethylolpropane triacrylate (TMPTA, CAS# 15625-89-5), a key monomer widely used in the UV/EB curing industry, was added to the Proposition 65 list as a known carcinogen, attracting widespread attention within the industry. Due to its excellent performance and cost-effectiveness, TMPTA plays a vital role in coatings, inks, adhesives, and other applications, and its restriction undoubtedly brings new challenges to the related industry chain.

This article will analyze the specific impact of California Proposition 65 on TMPTA, outline the challenges faced by the UV/EB curing industry, and explore effective response strategies and feasible alternatives, providing decision-making references for industry practitioners.

Overview of California Proposition 65 

California Proposition 65, officially known as the "Safe Drinking Water and Toxic Enforcement Act of 1986," was approved by California voters in November 1986. Its core objectives include protecting California's drinking water sources from contamination by known carcinogens or reproductive toxicants, and requiring businesses to provide "clear and reasonable" warnings before product use or environmental releases that could expose consumers to such chemicals.

Implementation Mechanism and Chemical List 

The California Office of Environmental Health Hazard Assessment (OEHHA) is responsible for implementing the Act, with its core duty being to maintain and update the list of carcinogenic or reproductively toxic chemicals. As of now, this list contains nearly a thousand chemicals.

The mechanisms for chemicals to be listed include: 

• Identification by authoritative bodies such as the U.S. National Toxicology Program (NTP) and the International Agency for Research on Cancer (IARC) 
• Identification by the state's Scientific Advisory Panel 
• Federal or state government requirements for cancer or reproductive toxicity warning labels on chemicals 
• According to provisions of the California Labor Code 

Main Impact on Businesses 

California Proposition 65 imposes the following requirements on businesses operating in California (or selling products into California), typically those with 10 or more employees: 

1. Warning Obligation: If a product may expose individuals to chemicals on the list, a "clear and reasonable" warning must be provided.
2. Discharge Prohibition: Businesses are prohibited from discharging listed chemicals into waters that may enter drinking water sources.

Failure to comply with regulations can result in severe legal consequences, including civil penalties of up to $2,500 per day (calculated per exposure violation) and attorney's fees. The Act allows the California Attorney General and eligible private parties ("bounty hunters") to file lawsuits against non-compliant businesses.

Key Information of California Proposition 65 

• Goal: Protect drinking water sources, ensure consumer right to know 
• Managing Authority: OEHHA 
• Core Requirements: Provide warnings for exposure to listed chemicals, prohibit discharge into drinking water sources 
• Scope of Impact: Businesses operating in California or selling products into California 
• High Risk Points: High fines and private lawsuits 

TMPTA's Situation under California Proposition 65 

Trimethylolpropane triacrylate (TMPTA) is a foundational monomer in UV/EB curing technology, widely used in coatings, inks, adhesives, photoresists, and other fields. It is known for its high reactivity, excellent cross-linking performance, low viscosity, and good cost-effectiveness, imparting properties such as rapid curing, high hardness, abrasion resistance, and chemical resistance to products.

Key Information on TMPTA Listing under California Proposition 65 

OEHHA announced its intention to list "industrial grade TMPTA" as a known carcinogen on June 11, 2021, and it officially became effective on December 17, 2022.

The primary scientific basis for listing TMPTA as a carcinogen comes from the International Agency for Research on Cancer (IARC)'s 2018 evaluation, which classified TMPTA as "Group 2B: Possibly carcinogenic to humans," mainly based on animal experimental results.

Characteristics of California Proposition 65 Control over TMPTA: 

• Focus on Exposure Amount, Not Concentration Threshold: Unlike the EU CLP regulation (which requires special labeling when TMPTA content in mixtures is ≥0.1%), the core of California Proposition 65 is "exposure". Even if the TMPTA concentration in a product is below 0.1%, a warning may still be required if the exposure amount is sufficiently high.
• No Official No Significant Risk Level (NSRL) Yet: As of June 2025, OEHHA has not yet published an official "No Significant Risk Level" (NSRL) for TMPTA, which increases the difficulty for businesses to assess compliance.

Direct Challenges to the UV/EB Curing Industry 

• Mandatory Warning Labels: If the TMPTA exposure cannot be proven to be below an acceptable risk level, a warning label must be affixed to the product.
• Downstream Customer and Market Pressure: Consumers and brand owners are increasingly sensitive to "carcinogen" labels, which may lead customers to switch to TMPTA-free alternatives.
• Product Reformulation and Increased Costs: Finding suitable TMPTA alternatives requires significant R&D investment and performance validation, and the cost of alternatives is usually higher than TMPTA.
• Global Supply Chain Impact: Although it is a local regulation, due to the importance of the California market, it may affect global product standards.
• Legal Litigation Risk: Failure to provide necessary warnings may lead to lawsuits from "private prosecutors," resulting in high fines and reputational damage.