Zinc and Tires

USTMA POSITIONS ON ZINC

There are many sources of zinc in the environment.

Zinc naturally occurs in soils and is found in numerous products, including galvanized metal, personal care products, batteries, paints and coatings, pharmaceuticals, fertilizer, brake wear, engine oil and tire wear.
Studies have found that zinc from agricultural and natural soils, as well as corrosion of galvanized metal and metal roofing, are significant sources of zinc not tires.

Without zinc, tires cannot be made.

Zinc plays a critical and irreplaceable role in manufacturing tires. 
Zinc serves as an “activator” in the vulcanization process that turns soft, sticky rubber into stable components that allow a tire to carry the weight of a vehicle and to stop safely.

There are no functional alternatives to the use of zinc in tires.

Without the use of zinc, tires cannot meet federal safety standards.   
Manufacturers have tested a variety of other metal oxides to replace or reduce the use of zinc but have not found a safer alternative.

Zinc loading from tire wear presents little if any risk to aquatic organisms.

Zinc in tires is not bioavailable as found in recent research.
There are no studies that specify that zinc from tires causes widespread and adverse harm in waterways.

Focus on zinc in tires is misplaced and on its own will not solve any one state’s water quality issues.

Even if it were possible to reduce zinc in tires, such reductions would not significantly reduce zinc in stormwater.
Potential regulatory response is unclear and so too is any implementation of that response that would meet near-term compliance dates established for Total Maximum Daily Loads (TMDLs) of concern.

The tire industry supports the use of the best available science to establish water quality criteria in addressing potential concerns related to zinc.

Water quality criteria for metals have evolved from simple hardness equations to sophisticated bioavailability models.
Some current methodologies used to establish water quality criteria for zinc – like those in California – fail to take into account the most robust science.
USTMA strongly recommends the biotic ligand model (BLM) to determine the most accurate and appropriate water quality objectives (WQOs).

A collaborative approach is needed to address zinc exceedances in waterways.

The logical and most productive regulatory course of action requires an assessment of all sources of zinc and their contributions to subject waterways.
Collaboration is needed to determine the extent to which potential zinc contributions can, from a technical, financial and legal standpoint, be effectively controlled.

FAQS ON ZINC

What is zinc and what is it used for?

Zinc is the 24th most abundant element in the Earth’s crust and has been present ever since the planet formed its surface. All life on earth has developed in the presence of zinc. Due to its unique properties, zinc is used in a wide range of consumer, infrastructure, agricultural, and industrial products, including tires.

Why is zinc used in tire manufacturing?

Zinc plays a crucial role as an activator in the chemical reaction process known as vulcanization, which transforms rubber from a soft gum into a solid article. Tire manufacturers utilize zinc or zinc oxide because it activates and promotes the highest number of crosslinks in the rubber chain imparting strength, stability and other useful properties in a finished tire. In short, zinc is the critical ingredient that allows a tire to perform safely. Without zinc, rubber tires cannot be manufactured.

How long has the tire industry been using zinc?

Zinc has been used by some tire manufacturers for decades because it is critical to tire safety. Zinc is a safer alternative to lead oxide, which was used to vulcanize tires decades ago.

Is zinc used in all tires?

Zinc is used by all USTMA members in manufacturing tires.

Can USTMA provide a list of chemicals used to manufacture tires?

The exact formulation of the materials in an individual tire company’s rubber compounds are proprietary, but quite a bit of public information is available about common materials used in tire manufacturing. The innovation section of USTMA’s website identifies broad categories of materials being used. Also, several publications contain additional information about the various chemistries used in tire manufacturing. The Vanderbilt Rubber Handbook has a helpful overview of common rubber compound formulations and materials used to manufacture tires.

Are there alternatives to zinc in tires?

Manufacturers have tested a variety of other metal oxides to replace or reduce the use of zinc but have not found a safer alternative. Without the use of zinc or zinc oxide, tires cannot meet federal safety standards.  

What is the tire industry’s reaction to the California Department of Toxic Substances (DTSC) decision to grant a petition to review zinc in automobile tires under the state’s Safer Consumer Products Regulations?

Zinc is found naturally in the environment and is contained in many products including galvanized metal, fertilizer, paint, batteries, brake pads and tires.  Research demonstrates that discharges of domestic wastewater and galvanized metal surfaces account for 75% of zinc in the environment, while tires typically account for less than 10%.

Because zinc is widely used in many products, zinc water quality issues can only effectively be mitigated through a collaborative, holistic approach.

Since 2016, USTMA has worked with the California State Water Resources Control Board, the International Zinc Association, and the California Stormwater Quality Association as part of a collaborative process to identify effective solutions to zinc water quality issues in the state. USTMA continues to believe that this effort is the most promising avenue to resolve California’s zinc water quality issues, and have asked that DTSC pause work related to zinc in tires under the Safer Consumer Product regulation to allow the state and Los Angeles Water Boards time to implement the biotic ligand model for zinc.

What is USTMA’s assessment of the current methodologies used to establish water quality criteria in California for zinc?

Currently methodologies in California fail to consider the most robust science. USTMA strongly recommends that the California Department of Toxic Substances Control (DTSC) pause work related to zinc in tires under the sager Consumer Products Regulations until the State Water Resources Board or the LA Water Board have implemented the most accurate model available, the biotic ligand model (BLM), for zinc. The BLM’s superior accuracy leads to appropriately protective water quality objectives (WQOs).

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