Microplastics Proposed Addition to California Department of Toxic Substances Control Candidate Chemicals List

News & Events

August 8, 2023

The California Department of Toxic Substances Control proposes to add microplastics to the Candidate Chemicals List. The proposal would enable the agency to evaluate products containing microplastics as potential Priority Products under California’s Safer Consumer Products Regulations.

In a recent proposal, the California Department of Toxic Substances Control (DTSC) is seeking to add microplastics to the Candidate Chemicals List.  Candidate Chemicals exhibit a “hazard trait and/or environmental or toxicological endpoint” that may contribute to adverse effects in humans, animals, or ecological communities.  The two hazard traits that are the basis of DTSC’s proposed listing of microplastics are environmental persistence and mobility.  DTSC uses the Candidate Chemicals List to identify potential Chemicals of Concern in Priority Products, as part of California’s Safer Consumer Products (SCP) Regulations.  If the proposal is adopted, DTSC would be able to evaluate and propose products as Priority Products based on whether they contain microplastics or will potentially release microplastics into the environment.  If the Priority Products are then adopted, after undergoing a formal comment and rulemaking process, manufacturers of those products would be required to assess safer alternative chemicals or product designs, as part of DTSC’s detailed Alternative Analysis process.

In its proposal, DTSC lists a range of products that may contain microplastics, including:


DTSC defines microplastics 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).” Notably, the DTSC proposed definition of microplastics does not set a lower size limit of 1 nanometer (nm), which is in contrast to the European Chemicals Agency (ECHA) and the Interstate Technology and Regulatory Council (ITRC), as well as the California State Water Resources Control Board, which identifies microplastics as “particles which have at least three dimensions that are greater than 1 nm and less than 5,000 micrometers (µm).” In addition, the DTSC definition does not differentiate between primary microplastics, those substances that are added deliberately during the manufacturing process, and secondary microplastics, which are derived from the degradation of larger plastic products. Thus, unless the proposed language is modified prior to adoption, both primary and secondary microplastics would be considered Candidate Chemicals under the DTSC proposal.

Though the addition of microplastics to the Candidate Chemicals List would not in itself result in new regulatory requirements, new obligations would emerge if DTSC proposes and adopts a new Priority Product, which could have a significant impact on manufacturers and businesses who sell their products in California. If you have any questions about how the DTSC proposal may impact your business, please contact:

Tom A. Lewandowski, Ph.D., DABT, ERT, ATS

Matthew P. Tymchak, M.S. 
Senior Hydrologist

Tim Verslycke, Ph.D.

Andrew Yeh, Ph.D., DABT
Senior Toxicologist