California Adds New Chemicals to Prop 65 List

The California Office of Environmental Health Hazard Assessment (OEHHA) has formally amended the California Proposition 65 (Prop 65) chemical list, added one new substance and expanded the hazard classification of another. The update introduces N-Methyl-N-Formylhydrazine as a carcinogen and completes the reproductive toxicity listing for Bisphenol S (BPS).

These regulatory changes activate Proposition 65 requirements for clear and reasonable warnings and may affect manufacturers, importers, distributors, retailers, and brand owners whose products could result in consumer exposure within California.

N-Methyl-N-Formylhydrazine Added as a Carcinogen

Listing Overview

• Chemical Name: N-Methyl-N-Formylhydrazine
• CAS Number: 758-17-8
• Hazard Classification: Carcinogen
• Effective Listing Date: December 8, 2025
• Listing Mechanism: State’s Qualified Experts process

OEHHA listed the substance following a determination by the Carcinogen Identification Committee (CIC) that it is clearly shown through scientifically valid testing to cause cancer.

Scientific and Public Review Process

• Hazard Identification Document Issued: August 29, 2025
• Public Comment Period: Through mid-October 2025
• CIC Review Meeting: November 18, 2025
• Committee Vote: Approved by an 8-to-1 majority

The listing reflects OEHHA’s formal evaluation and public consultation process under Proposition 65.

Compliance Timeline

• Warning Requirement Effective: December 8, 2026

Businesses have a 12-month grace period from the effective listing date to implement required warnings. After this date, warnings are mandatory for significant exposures unless an exemption applies.

Regulatory Impact

Companies must assess whether their products contain or result in exposure to N-Methyl-N-Formylhydrazine above applicable Prop 65 Safe Harbor Levels, where established. The listing may affect:

• Product testing strategies
• Chemical selection and reformulation
• Supplier declarations and due diligence
• Product labeling and risk communication

Bisphenol S (BPS): Full Reproductive Toxicity Listing Completed

Updated Hazard Classification

• Chemical Name: Bisphenol S (BPS)
• Classification: Reproductive Toxicant
• New Endpoint Added: Developmental toxicity
• Effective Date: December 8, 2025

The latest update completes the reproductive toxicity profile for BPS by adding developmental toxicity to previously listed male and female reproductive effects.

Phased Listing History

• December 29, 2023: Female reproductive toxicity
• January 3, 2025: Male reproductive toxicity
• December 8, 2025: Developmental toxicity

The chemical was evaluated through the Developmental and Reproductive Toxicant Identification Committee (DARTIC) under the State’s Qualified Experts process.

Compliance Considerations

Warning obligations for BPS exposures are tied to the effective dates of each listed endpoint. In many cases, businesses may already be subject to Prop 65 warning requirements due to earlier reproductive toxicity listings.

Use and Exposure Context

Bisphenol S is commonly used as a Bisphenol A (BPA) alternative in:

• Plastics and polymer formulations
• Thermal paper coatings
• Epoxy resins and industrial applications

Potential exposure sources include consumer goods, packaging materials, coatings, and treated surfaces.

Proposition 65 Compliance Implications

When is a warning required?

Under Proposition 65, a warning is required when:

• A listed chemical is present, and
• A significant exposure may occur under reasonably foreseeable use conditions

Warnings may be required on product labels, at points of sale, online listings, or in workplace environments.

Recommended Actions for Businesses

• Product Screening: Identify products and materials containing listed chemicals
• Exposure Assessment: Evaluate exposure levels against regulatory thresholds
• Labeling Strategy: Implement compliant “clear and reasonable” warnings
• Documentation: Maintain defensible compliance records
• Risk Mitigation: Consider reformulation or substitution where feasible

Industry Impact

Source: n-methyl-n-formylhydrazine-added-proposition-65-list-cancer