California’s Department of Toxic Substances (DTSC) is proposing a definition of microplastics, and the addition of microplastics to the candidate chemicals list under California’s Safer Consumer Products Program. The agency is accepting comments on the proposal through Aug. 4, 2025.

ACA will be submitting comments by the DTSC deadline.

Notably, a listing alone would not trigger regulatory requirements but would allow DTSC to select products containing microplastics for an alternatives analysis and/or regulatory action with possible phase out of the identified use.

Previously, DTSC announced that it is preparing a background document identifying products containing microplastics. It is expected to publish a draft this Fall, open to public comment.

The current proposal proffers the following revised definition of microplastics:

“Microplastics” are 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 states that the proposal is designed to provide greater flexibility in product identification by broadening the scope of the prior proposed definition:

“ ‘Microplastics’ are defined as solid polymeric materials to which chemical additives or other substances may have been added, which are particles having at least three dimensions that are less than 5,000 micrometers (μm). Polymers derived in nature that have not been chemically modified (other than by hydrolysis) are excluded.”

Notably, the new proposed definition replaces the term solid polymeric materials used in the prior proposal with plastic. DTSC does not directly address this change in its Initial Statement of Reasons. It also removed the prior exclusion of polymers found in nature to allow for greater flexibility in product identification. Additionally, DTSC included a reference to products that generate microplastics by fragmentation to allow for greater flexibility in product identification.

The Safer Consumer Products Statute defines a chemical, in part, as An organic or inorganic substance of a particular molecular identity . . . DTSC explains it is authorized to list mechanistically similar chemicals for which there is a known toxicity profile. (Initial Statement of Reasons, p. 3).

Assuming microplastics qualify as a defined chemical, DTSC focuses further justification in the Technical Document and Initial Statement of Reasons on persistence and mobility of microplastics and exposure potential. Exposure potential is marked by presence in household dust, air and drinking water and presence in human placenta, infant feces and adult organ tissue. DTSC also cites a study noting plant intake of microplastic particles.

DTSC identifies several products associated with release into homes, schools and workplaces and/or containing microplastics. Products include paint and industrial coatings, waxes, polishes, household and industrial detergents, textiles, etc. DTSC will publish a draft report regarding products containing microplastics this Fall.

The proposal and related materials are available on DTSC’s webpage.

Contact ACA’s Riaz Zaman for more information.