Poster Presentation
SOT 64th Annual Meeting and ToxExpo
Orlando - March 16-20 2025
Abstract:
Due to well publicised environmental and human health concerns, the State of Washington Department of Ecology has defined criteria for safer alternatives to N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD) and its ozonation transformation products. 6PPD is an antioxidant and antiozonant that prevents rubber from degrading and reacting with oxygen (O2) and ozone (O3). It is widely used in the motor vehicle tire and general rubber goods sector. Washington State Department of Ecology considers 6PPD as an environmental toxicant of high concern due to aquatic toxicity, reproductive toxicity, environmental persistence, and bioaccumulation potential. As a result of its function, when exposed to air, 6PPD reacts with ozone to form 6PPD-quinone (6PPD-Q). 6PPD-Q is highly toxic to aquatic organisms, and tire wear leading to environmental exposure from runoff has been directly linked to acute mortality in coho salmon, shown to be the most sensitive species.
Here we present a series of environmental studies conducted on N1,N4-dicyclohexylbenzene-1,4-diamine (CCPD, CAS No. 4175-38-6) and 2-(cyclohexylamino)-5-(phenylamino)-2,5-cyclohexadiene-1,4-dione (CCPD-Q, CAS No. 1653-85-6). CCPD is an innovation substance designed as a replacement for 6PPD using safe by design concepts. The study results are compared to the 6PPD Alternatives Assessment Hazard criteria (Washington State Department of Ecology, 2023) related to aquatic toxicity, persistence, and bioaccumulation.
The acute toxicity of CCPD and CCPD-Q to coho salmon was assessed in accordance with OECD TG 203 under GLP, using a flow-through design. The 96h LC50 of CCPD was determined to be 32 µg/L (measured) but CCPD-Q was determined not to be acutely toxic at the solubility limit of the test item in the test system of 149 µg/L (measured). The CCPD-Q results contrast with 6PPD-Q which has a 24h LC50 to coho salmon of 0.095 µg/L.
The ready biodegradability of CCPD was determined in accordance with OECD TG 301D under GLP. CCPD achieved 61 % degradation after 28-days although the “10-day window” OECD ready biodegradability criterion was not met. However, the results demonstrate that CCPD is not persistent in the environment in accordance with EU and US PBT criteria. Compared to other commercial members of the p-phenylenediamine group of compounds currently used as antioxidants/antiozonants, CCPD is the only substance known to exhibit such a high level of biodegradation. Similarly, in a GLP study conducted in accordance with OECD TG 111, CCPD was determined to by hydrolytically unstable (e.g. DT50 (20 ºC) = 2.5 h pH 7; 2.0 h pH 8.5), with a significant pH dependence.
The n-octanol/water partition coefficient was determined to be 4.8 at environmentally relevant pH and in a predominantly unionised form. Although (Q)SAR estimates indicate that the substance will not be bioaccumulative (BCF = 771, BAF = 773 (BCFBAF)), further investigation of potential bioaccumulation may be required.
Overall, the results indicate that CCPD may be a more environmentally friendly alternative to 6PPD, for use in tires and general rubber goods. The results meet critical Alternatives Assessment Hazard Criteria concerning persistence (CCPD) and the aquatic toxicity of the ozonation transformation product (CCPD-Q). For the parent compound CCPD, which does not meet the aquatic toxicity criteria, a risk-based approach is proposed to ensure that it does not present an unacceptable risk to the environment in accordance with the Washington State Department of Ecology (2022) special considerations. Future work will elucidate the aquatic toxicity of CCPD to other relevant environmental species, and performance of CCPD compared to other environmental and human health 6PPD Alternatives Assessment Hazard Criteria.
Presenter Bio: Dr. Damien Carson
Damien is a senior chemical regulatory expert with >20 years’ experience providing strategic, scientific and technical support to the chemical and biocide sectors. Damien is currently co-owner of the Blue Frog Scientific Group of Companies and sits on the Board of Directors of Blue Frog Scientific Limited, and Blue Frog Scientific EURL.
Damien is an expert chemical hazard and risk assessor in both the environmental (environmental fate and ecotoxicity) and human health (toxicology) disciplines, with a successful track record in the preparation, submission and defence of chemical registration dossiers.
Damien’s recent activities have focused on a combination of problem areas for Blue Frog clients, requiring advocacy representation, and supporting technical delivery of studies and associated expert reports dealing with both human health and environmental concerns. These activities include PBT assessment, endocrine disruption, and exposure assessment/risk characterisation.
