4,4'-cyclohexylidenedi-o-cresol

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

Persistence Assessment

A hydrolysis study performed according to OECD Guideline 111 (Hydrolysis as a function of pH) is available for DMBPC (Lockwood SH, 2001a). The initial concentration of DMBPC was 345 µg/L and the test was conducted at pH 4, 7, and 9 at 50 °C. There was no loss of DMBPC after 5 d; therefore, DMBPC is considered hydrolytically stable. There are no abiotic degradation data available for phototransformation in air, water or soil for DMBPC.
Three studies are available investigating the biodegradability of DMBPC in aquatic environments, all of which demonstrate that DMBPC is not readily biodegradable. In Lockwood SH (2001a), the aerobic biodegradability of DMBPC was examined according to OECD Guideline 301F, testing two types of domestic activated sludge for a contact period of 800 h (approximately 33.3 d). In these tests, a maximum of 38 % degradation (measured by O₂ consumption) was observed after 33.3 d. In the study conducted by the Institute of Ecotoxicology, Ltd. (2002), the ready biodegradability of DMBPC was investigated according to OECD Test Guideline 301C; after 28 d 0 % degradation was observed (measured by O₂ consumption) in all three replicate samples. In the Kurume Laboratory study (2001), the biodegradability of DMBPC was investigated by High Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) analysis; no biodegradation was observed using either analytical method. A key deficiency in this study is that a reference substance was not used.
Overall, the available data on ready biodegradability provide evidence of potential P or vP properties.

 

 

 

Bioaccumulation Assessment

 

The experimentally determined LogKow for DMBPC is 3.1. This is below the REACH screening criterion of 4.5 for a substance to be considered potentially bioaccumulative. The low bioaccumulation potential is confirmed by a study performed according to OECD Test Guideline 305C testing common carp (Cyprinus carpio); 28-d bioconcentration factors (BCFs) of 86 and 73 L/kg were reported when DMBPC was tested at initial aqueous concentrations of 0.01 and 0.001 mg/L, respectively (Institute of Ecotoxicology, Ltd., 2003). The REACH screening criterion is a BCF > 2000 L/kg; therefore, DMBPC is not bioaccumulative per REACH guidelines.

 

 

 

Toxicity Assessment

 

A substance is considered ‘toxic’ if it meets one of the following criteria:

• The long-term NOEC for marine or freshwater organisms is less than 0.01 mg/L. If only short term data are available, if the EC/LC50 is <0.01 mg/L then the T criterion is considered definitely fulfilled and if the EC/LC50 is <0.1 mg/L the T criterion is considered potentially fulfilled.

• The substance is classified as carcinogenic (category 1 or 2), mutagenic (category 1 or 2), or toxic for reproduction (category 1, 2, or 3); or

• There is other evidence of chronic toxicity, as identified by the substance meeting the criteria for classification: specific target organ toxicity after repeated exposure (STOT RE category 1 or 2) according to Regulation EC No 1272/2008.

 

No long-term ecotoxicological data are available for DMBPC in aquatic species; of the short term data available, the lowest LC/EC50 is 0.528 mg/L (in fish). This is above the threshold of 0.1 mg/L for the substance to be considered as T based on short term data.

 

Regarding the results of the toxicity studies:

• Germ cell mutagenicity: Data from in vitro and in vivo tests indicate DMBPC is not mutagenic.

• Carcinogenicity: Not classified based on mutagenicity data.

• Reproductive toxicity: Data indicate that DMBPC is not a reproductive/developmental toxicant.

These results do not support the characterisation of DMBPC as toxic. In addition, the available long term toxicity data on the substance do not indicate that the substance needs to be classified as a STOT RE Category 1 or 2 substance.

 

DMBPC therefore does not fulfil the REACH criteria to be considered T.

 

 

Overall conclusion:

 

Although there is evidence of P/vP properties, the substance is neither B/vB nor T and so cannot be considered either vPvB or PBT.

Likely routes of exposure:

DMBPC is neither PBT nor vPvB. Additionally, the substance is manufactured outside the EU, as does substance polymerisation. Consequently, there is no identified substance use within the EU and no emission characterisation needs to be addressed. Hence, an emission characterisation was not deemed necessary.