---
title: Federal Scientists Will Test Two Finalist Molecules to Replace the Tire Chemical Killing Salmon
description: Flexsys narrowed its 6PPD replacement to two molecules and sent them to USGS scientists for toxicity testing. A safe substitute is still years from tires.
author: Darie Nani (Editor-in-Chief)
date: 2026-08-28T13:30:00.000Z
updated: 2026-08-28T13:59:47.034Z
canonical: https://www.sovereignmagazine.com/article/6ppd-replacement-two-molecules-usgs-testing
image: https://cdn.nanimediahouse.com/tire-runoff-salmon-stream-215612.webp
categories: Green Tech
content_type: Analysis
region: United States
publication: Sovereign Magazine
access: members
schema_type: Article
---

Flexsys said on August 27 that it had narrowed its search for a replacement for 6PPD, the rubber chemical whose runoff byproduct kills Pacific salmon, to two final candidate molecules. Both were chosen from outside the PPD chemical family, so that neither breaks down into the toxic quinone blamed for the die-offs. The company says both molecules cleared its safety and performance benchmarks in internal and external testing. In the same announcement, Flexsys signed a Cooperative Research and Development Agreement with the U.S. Geological Survey, sending the two candidates to federal scientists at the agency's Western Fisheries Research Center for aquatic toxicity testing.

The agreement is a federal cost-share arrangement: the USGS toxicologists run the tests, and Flexsys funds the work. That makes it an outside check by government fisheries scientists, not a review the company runs on itself, but it is neither a blind third-party study nor regulatory approval. The agreement moves two candidate molecules into independent testing, one concrete step in a search that has run for years with no molecule yet ready for the market.

## The Chemical That Turns Lethal After It Rains

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