Proposed Priority Product: Motor Vehicle Tires Containing Zinc

DTSC proposes to list Motor Vehicle Tires Containing Zinc as a Priority Product under the Safer Consumer Products (SCP) regulations. DTSC’s Safer Consumer Products regulations allows stakeholders to petition the Department to adopt a product/chemical combination as a Priority Product. In May of 2018, the California Stormwater Quality Association (CASQA) petitioned DTSC’s Safer Consumer Products Program to list motor vehicle tires with tire tread containing zinc as a Priority Product. Per the petition, zinc is an aquatic toxicant that, when released from tires, causes or contributes to adverse impacts to aquatic organisms and potentially imposes high costs to California stormwater agencies responsible for meeting state and federal water quality objectives.   

Based on the criteria in the Safer Consumer Products regulations, DTSC has determined the petition is of sufficient comprehensiveness and quality to indicate the potential for exposure, adverse impacts, and adverse waste end-of-life effects.  

Zinc (typically as zinc oxide) is added to tire rubber to encourage the vulcanization process. This process strengthens the rubber and allows tire manufacturers to mold tire rubber into the precise shapes found in tire treads and other tire components. Small pieces of tires, commonly referred to as tire-wear particles (TWP), are generated as the tire rolls along the road. TWP can be deposited on roads and surrounding areas, where it can be carried by stormwater into surrounding waterways. Additionally, TWP can be transported through the air and deposited onto hard surfaces, such as roofs, where it is also subject to transport to the aquatic environment via stormwater.  

Once released into the environment, including local waterways, zinc can and does leach out of TWP. TWP represents a significant source of zinc to the aquatic environment. Aquatic organisms within California’s streams, rivers, and lakes may be adversely impacted by exposure to zinc. Because of this, the U.S. EPA and the State Water Resources Control Board (State Water Board) have developed water quality criteria for zinc that describe the point at which the amount of zinc in a water system becomes hazardous to aquatic organisms. Many California stormwater discharges and waterways, especially those in southern California, have been found to exceed zinc water quality criteria.  

Some California waterways have been classified as impaired under the provisions of section 303(d) of the Clean Water Act due to zinc contamination. In many instances, stormwater runoff, including the TWP contained therein, from nearby urban areas represents a major source of zinc contamination. California municipal agencies are responsible for adhering to permit requirements for stormwater discharges to protect local waterways. Many stormwater agencies report challenges staying in compliance with permits due to zinc exceedances. Stormwater treatment approaches to reduce zinc concentrations are prohibitively expensive and can be infeasible. 

Public Comment Period and Workshop 

DTSC will issue a technical document explaining the rationale for our decision and hold a public comment period and workshop prior to initiating the formal rulemaking process to list Motor Vehicle Tires containing Zinc as a Priority Product. DTSC anticipates issuing the technical document by the end of the first quarter of 2021. 

SCP Priority Products