No law yet: EPA finalizes guidance for measuring 6ppd, 6ppd-q

WASHINGTON—The U.S. EPA has finalized water quality screening guidance for use in determining 6ppd and acute 6ppd-quinone levels in freshwater ecosystems, including stormwater runoff.

The threshold values and methodology, known as EPA Method 1634 and published in the Federal Register under the Clean Water Act June 10, is intended for measurement of short-term concentrations of 6ppd and 6ppd-q.

The guidance was fast-tracked for use by tribes, states and local governments, EPA said in a same-day release.

"Achieving clean water that protects aquatic life and supports commercial, recreational and cultural fishing practices takes partnership at all levels of government," said Bruno Pigott, acting EPA assistant administrator for water. "6ppd and 6ppd-q can be lethal to fish, so it's important we know where it's polluting waterways. The EPA's screening values provide important information that our partners can use to protect fish populations—especially coho salmon on the Pacific coast."

At the heart of the industry-wide scramble is the tire performance additive 6ppd, a small-molecule chemical designed to migrate to the surface of the tire to protect against wear and degradation.

However, 6ppd can morph into the salmon- and trout-killing chemical 6ppd-q during tire wear, as a tire's surface comes into contact with oxygen and ozone during abrasion.

6ppd, which comprises between 1 and 2 percent of a tire's mass, also is present as an anti-degradant in footwear, synthetic turf infill and playgrounds.

The chemical is at the foundation of at least one major lawsuit, a request for an immediate ban on 6ppd brought in October 2023 under the Endangered Species Act by two Pacific Northwest fisheries against 13 of the world's largest tire manufacturers.

Tire makers filed a motion to dismiss the lawsuit in March, a motion that was denied May 16 in U.S. District Court in San Francisco, plaintiff's attorney Earthjustice said.

"The science is now clear that 6ppd-q is killing highly imperiled salmon, and that it comes from their tires," Glen Spain, Northwest regional director for the Pacific Coast Federation of Fishermen's Associations and Institute for Fisheries Resources, told Rubber News June 11. "These companies have no right to pollute and are simply dragging their feet. It is time for them to focus on bringing non-toxic alternatives to market."

6ppd is, in fact, being studied for alternative replacement with urgency by the U.S Tire Manufacturers Association and within established partnerships between research firms and individual tire makers.

And the embattled chemical is under consideration for rulemaking by the EPA under both the CWA and the Toxic Substances Control Act, as petitioned in August 2023 by several Pacific Northwest Native American tribes.

EPA granted the tribe's petition in November 2023, effectively entering 6ppd in "consideration of" the rulemaking process.

The June 10 guidance on screening values and toxicity measuring methodology is independent from the rulemaking under consideration, which is expected in "advance notice" form by fall of this year and in final form by 2025.

The EPA and USTMA also are considering solutions like stormwater treatment and green infrastructure, mitigation efforts found to be effective at reducing concentrations of 6ppd and 6ppd-q.

The June 10 guidance issued by EPA is the latest in a series of actions "to better understand and reduce freshwater aquatic life exposure to these harmful chemicals," EPA states.

The method and screening values have been available for use since January, when the agency issued a draft of the testing method.

"The EPA derived the screening values for acute exposures to 6ppd (and 6ppd-q) in freshwaters using the best available data to reflect the latest scientific knowledge on the toxicological effects of 6ppd to aquatic life, following the general approach outlined in the guidelines, but with fewer studies and data than are typically used to develop national recommended aquatic life (Ambient Water Quality Criteria), resulting in greater uncertainty," EPA states in the final version of "Acute Aquatic Life Screening Value for 6ppd in Freshwater," signed by Pigott June 3.

According to the guidelines, the screening values for acute exposures to 6ppd and 6ppd-q in freshwater are 8,900 nanograms per liter (ng/L); and 11 ng/L, respectively.

EPA admits that major data gaps remain.

"Consistent with (the) CWA, the EPA expects to update these screening values from time-to-time as new information becomes available," EPA states. "Empirical data are very limited for 6ppd and 6ppd-q and do not fulfill the EPA's data requirements for deriving national recommended AWQC."

Further, much of the available data was developed using aquatic toxicity testing approaches that "do not fully conform" with other EPA ecological and ASTM testing guidelines, EPA states.

The recently released screening values "are not regulations and do not substitute for the CWA or the EPA's regulations."

"The EPA developed the 6ppd and 6ppd-q acute screening values to support protection of most freshwater aquatic communities," the federal agency states. "The EPA's acute screening values are the maximum concentrations of 6ppd and 6ppd-q, with associated frequency and duration specifications, that are expected to support protection of aquatic life from acute effects in freshwaters."  

As stated, in November 2023, EPA began consideration of rulemaking prohibiting the manufacturing, processing, use and distribution of 6ppd in tires and announced its intent to publish an advanced notice of proposed rulemaking under the TSCA.

Tire makers are trying to get out in front of the rulemaking process, as they already are involved in an alternatives analysis—spearheaded by the USTMA—for the tire additive under the guidelines of the California Department of Toxic Substances Control.

Five possible alternatives have been identified, following a comprehensive "preliminary" analysis completed by a consortium of 30 tire manufacturers March 25.

Results of the first stage of this alternatives study under California's rigorous Safety Consumer Product Regulations were released March 29 by the USTMA, which led the project along with Gradient L.L.C., a Boston- and Seattle-based environmental and health consultant and testing firm.

"The rigor, collaboration and transparency involved in this preliminary evaluation demonstrates our industry's commitment to this alternatives analysis process," Tracey Norberg, USTMA executive vice president and general counsel and project lead on the report, told Rubber News earlier this year. "Investigation of possible alternatives to 6ppd is a dynamic area of research."

The EPA in January also announced plans to finalize a rule requiring manufacturers (including importers) of 6ppd to report lists and copies of unpublished health and safety studies to the agency.

Separately, EPA in March announced a $12 million initiative in Washington state, a partnership between the Washington departments of ecology and commerce, to reduce untreated stormwater runoff entering Puget Sound and "impacting aquatic life including salmon, freshwater streams and exacerbating nutrient pollution that can cause harmful algal blooms."    

"The Biden-Harris Administration recognizes the unique significance of the Puget Sound and is committed to protecting treasured waters and vital species as part of our unprecedented investing in America agenda," Pigott said March 27. "This $12 million announcement is a perfect example of how federal dollars, interdisciplinary partnerships, and innovation can ensure clean and fishable waters for generations to come."