Derivation of Acute Aquatic Life Screening Values for 6PPD and 6PDD-quinone in Freshwaters by USEPA Office of Water.

In June 2024, the United States Environmental Protection Agency (USEPA) Office of Water published aquatic life screening values for acute freshwater exposures to two widely distributed rubber-tire compounds, 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylene diamine) and 6PPD-quinone (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylene diamine quinone). The purpose of this critical review is to outline the derivation of these protective values and provide a thorough summary of the toxicity data available at the time of screening value development to help identify current data gaps to inform future research needs. The detection of these compounds in U.S. waterways and toxicity data indicate short-term exposure to these compounds may present a risk to aquatic organisms. 6PPD-quinone, a transformation product of 6PPD, has been found to be highly toxic to certain adult salmonid species. As emerging contaminants for which scientific understanding of toxicity is rapidly evolving, the current 6PPD and 6PPD-quinone data did not fulfill the USEPA's requirements for deriving national recommended 304(a)(1) aquatic life ambient water quality criteria. Therefore, the USEPA developed screening values in accordance with Section 304(a)(2) of the Clean Water Act (CWA) to provide states, authorized Tribes, and other stakeholders with the best available information on the toxicity of 6PPD and 6PPD-quinone to aquatic organisms. The 2024 USEPA screening values for acute exposures to 6PPD and 6PPD-quinone in freshwaters are 8.9 µg/L (8,900 ng/L) and 11 ng/L, respectively, and are intended to support protection of freshwater aquatic communities from acute effects including coho salmon (Oncorhynchus kisutch), listed as threatened or endangered in several states, based on the best available data. The USEPA will continue to monitor newly reported toxicity data to evaluate the protectiveness of these values.