Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Assessment of the parent compound Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-,C7-9-branched alkyl esters (CAS: 125643 -61 -0)

Degradation:

The substance is not readily biodegradable as established in an OECD 301B test (CIBA 1989).

The degradation in an aerobic sediment/water system was tested according to OECD-guideline no. 308 (CIBA 2006, RCC study no. A10653), revealing that Benzenepropanoic acid, 3,5-bis(1,1 -dimethylethyl)-4-hydroxy-,C7-9-branched alkyl esters disappears rapidly mainly by microbial hydrolysis to Metilox acid (CAS: 20170-32-5). Metilox acid is then further eliminated mainly by adsorption to sediment (non-extractable residues) and degradation to several minor metabolites. OASIS results and the findings in the bioconcentration study support this transformation pathway. Therefore, it can be expeted that degradation will be higher in absence of sediment.

Bioaccumulation:

In an OECD 305 flow through test on Rainbow trout, a low bioaccumulation potential of Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-,C7-9-branched alkyl esters was established with a maximum BCF(whole fish) of 260.

Transport and distribution:

Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-,C7-9-branched alkyl esters exhibits a high potential for adsorption and negligible volatilization. Soil and sediment are expected to be the main target compartments for this substance.

Supporting assessment of the impurity Metilox (CAS 6386-38-5)

Degradation

The chemical structure of Metilox is indicative of primary degradability both abiotically and biotically leading to Metilox acid and methanol. Experimental data on hydrolysis is not available. However, a biodegradation study (1998) according to OECD guideline No. 301C was conducted on a product containing approximately 6% of free Metilox. It has been shown in this study by specific analysis, that Metilox was completely degraded to Metilox acid (CAS 20170-32-5) after 28 days. Therefore, only data on Metilox acid are considered to be relevant to assess the ecotoxicity and environmental fate of this impurity.

Supporting assessment of the impurity octan-1-ol (CAS 111 -87 -5)

Degradation

The substance is readily biodegradable (ECHA disseminated dossier August 5, 2015)

Bioaccumulation

The substance is not bioaccumulating (ECHA disseminated dossier August 5, 2015)

Transport and distribution

The KOC of the substance is < 1000 and the substance is moderately soluble in water (107 mg/L) (ECHA disseminated dossier August 5, 2015).

Therefore, if the substance is not degraded, limited adsorption to soil and sediment is expected.

Due to the environmental fate information this impurity is not considered as relevant for the chemical safety assessment.

Supporting assessment of the major degradation product Metilox acid (CAS: 20170-32-5)

Degradation 

Metilox acid is not readily biodegradable in the Modified Sturm test with 3-7% degradation at 10.3 and 20.3 mg/l.

Based on the results of the degradation study according to OECD 308 it could be expected that Metilox acid will either be further transformed or bound to the sediment as it disappears from the water phase and sediment (extractable part) of the river and pond systems.

The rate of transformation or ultimate degradation under environmental conditions are not yet known.

Bioaccumulation

The bioconcentration of Metilox acid was tested in a study on the uvcb substance CAS 179986 -09 -5. One constituent of this substance is Metilox (CAS 6386 -38 -5) and metilox acid was identified as relevant transformation product.

The study was conducted according to OECD guideline 305 C. At 50 ug/l, the bioconcentration factor was determined to be 60-223 and 121-532 at 5 ug/l, respectively, after 8 weeks of exposure. The exposure concentration is well below the solubility limit of Metilox acid in water.

The BCF values are clearly below 2000.

Furthermore, the PBT Expert Working Group of the Technical Committee of New and Existing Chemicals has agreed that Metilox should be deleted from the list of potential PBT / vPvB substances (see attachment IUCLID chapter 13).

Transport and distribution

In aquatox tests solubilities up to 100mg/l could be achieved (Elendt M4 Medium, short term toxicity test on Daphnia, 2011). Therefore, the substance is expected to end up in the soil and to a lesser degree in the water. Based on the results of the degradation study according to OECD 308 it could be expected that Metilox acid will either be further transformed or bound to the sediment as it disappears from the water phase and sediment (extractable) of the river and pond systems.