California Proposes Adding Microplastics to Candidate Chemicals List – Comment Period Open Through August 4, 2025

The California Department of Toxic Substances Control (DTSC) has proposed to amend its Safer Consumer Products (SCP) regulations by adding microplastics to the Candidate Chemicals List (Cal. Code Regs., tit. 22, § 69502.2). While this proposed action does not impose immediate compliance obligations, it has substantial implications because once microplastics are listed as Candidate Chemicals, DTSC may identify consumer products containing microplastics as Priority Products. The identification of a Priority Product triggers requirements under California law for manufacturers and entities throughout the supply chain, who must assess alternative product formulations and are subject to response measures prescribed by DTSC.

Background on SCP Regulations

DTSC adopted its SCP regulations in 2013 to identify and reduce hazardous chemicals in consumer products. The process consists of:

• Maintaining a Candidate Chemicals List — based on chemicals known to exhibit hazardous traits or endpoints and have exposure potential;
• Identifying Priority Products — specific product-chemical combinations that require action;
• Requiring action from manufacturers of Priority Products — to conduct an Alternatives Analysis and potentially implement a Regulatory Response.

A chemical must be on the Candidate Chemicals List to be part of a Priority Product. As such, adding microplastics would be a key regulatory step with potential for far-reaching consequences.

Notably, while microplastics are composed of chemical substances — typically synthetic polymers such as polyethylene, polypropylene, and polystyrene — they do not meet the SCP regulatory definition of a “chemical,” which is defined as “[a]n organic or inorganic substance of a particular molecular identity” or a combination of such substances that meets certain criteria. By contrast, microplastics lack a discrete molecular identity, varying in polymer type, size, shape, and additive content, i.e., they are not a singular substance.

This raises a threshold issue under California’s Green Chemistry approach, which underlies the SCP regulations and is intended to promote the use of safer chemical ingredients in consumer products through informed substitution. Without a “particular molecular identity,” it would be unclear what regulated entities are meant to analyze or substitute under the SCP’s Alternatives Analysis framework.

Targeting of Microplastics

DTSC’s proposed action lays the groundwork for impacts across supply chains, including manufacturers, importers, assemblers, and retailers of consumer products sold in California that contain microplastics. The proposal would define microplastics for purposes of the SCP regulations as “plastics that are less than 5 millimeters (mm) in their longest dimension, inclusive of those materials that are intentionally manufactured at those dimensions or are generated by the fragmentation of larger plastics.”

DTSC’s Initial Statement of Reasons for the proposed rulemaking evaluated microplastics using two principal factors — exposures and adverse impacts — that provide insight into DTSC’s targeting of microplastics-containing products.

First, DTSC determined that widespread human and ecological exposures to microplastics justify their inclusion on the Candidate Chemicals List (contained in Cal. Code Regs., tit. 22, § 69502.2). The agency identified several exposure-related concerns, including the ubiquity of microplastics in the environment, the release of microplastics during product use, and ecological exposure based on ingestion of microplastics by marine species and resulting food chain impacts.

Second, DTSC determined that microplastics demonstrate three hazard traits: their ability to persist in the environment, mobility in the environment, and potential to degrade into tiny particles that increase exposure pathways. This rationale shows DTSC’s potential intent to broadly target products that contain plastics and may degrade into the environment, for future listing as Priority Products.

What Should Manufacturers and Supply Chain Businesses Do Now

Adding a chemical to the Candidate Chemicals List does not itself impose requirements on businesses. However, manufacturers and others in supply chains for plastics-containing products should:

• Consider submitting public comments to inform DTSC’s rulemaking and the scope of the proposed listing,
• Evaluate whether products may intentionally contain, or unintentionally generate or release, microplastics during use or disposal, and
• Monitor DTSC’s regulatory activity for potential future Priority Products listings.

DTSC released its Notice of Proposed Action (Ref. No. R-2023-05R) for this action on June 20, 2025, and is accepting public comments through August 4, 2025.

This post is as of the posting date stated above. Sidley Austin LLP assumes no duty to update this post or post about any subsequent developments having a bearing on this post.