6-tert-butyl-2,4-xylenol

Endpoint summary

Additional information

The test substance is a viscous liquid under all environmental conditions and is of moderate solubility in water (120 mg/l) and is of low volatility (based on4.2 Pa at 25 °C).  The substance was evaluated using an appropriate QSAR technique to have a log Koc value of 3.1053, indicating a moderate affinity for soil. As such, any environmental release will result in virtually all of the substance compartmentalising into soil compartments, with little release directly to atmosphere or compartmentalising to water compartments.

Any potential exposure to the environment is predicted to result in redistribution to both water and soil; however due to its low volatility, low water solubility and partitioning values, these indicate that the majority of the substance would eventually partition to soil rather than the water compartment should it be released to the environment. 

A Level III fugacity model was conducted in the US EPA EPISUITE (Mackay,) which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of a range of components present in the substance between four environmental compartments (air, water, soil, sediment) at steady state in a unit world. The results obtained from modelling are as follows:

 

Air (%)	Water (%)	Soil (%)	Sediment (%)
0.589	14.3	82.3	2.82

It is proposed that the majority of the substance is modelled to distribute to the soil compartments within the constraints of the QSAR model. As such, and given the moderate solubility, the soil and water compartments are proposed to the areas to which partitioning would occur.

The substance displays a low ready biodegradability in that it achieved 4% biodegradation in a 28-day BOD ready biodegradation study, and 1% in a biodegradation assessment using GC. This indicates that the substance isunlikely to achieve a half-life of less than 40 or 60 days within fresh water attributed to ready biodegradation alone, but could potentially biodegrade over time. 

 

No data on hydrolysis is available. A study to determine this effect is ongoing, but will not be completed in time for the relevant deadline. Hence, the dossier will be subject to a spontaneous update once this data becomes available. To fulfil this endpoint, read across is utilised toC7-9-alkyl 3-(3,5-di-trans-butyl-4-hydroxyphenyl)propionate,CAS 125643-61-0. Experimental studies on hydrolytic effects demonstrated that the substance does undergo hydrolysis at environmentally relevant pH’s. At 25 deg C, the half life at various pH’s is as follows for the read across substance:

 

pH4: 10.7 d

pH7: 182.9 d

pH9: 14.1 d

 

This indicates that the read across substance is relatively stable to hydrolytic effects but is prone to hydrolysis at acid and alkali pH’s. The substance is relatively stable at environmentally relevant pH’s; however given the structure, some hydrolysis slowly over time under normal environmental conditions could be anticipated.  Studies on direct phototransformation in water are not available, but it is assumed on the basis of chemical structure and nature of use that the substance is not degraded by direct photolysis. It is concluded, therefore, that biotic and abiotic processes could contribute to the depletion of the substance within the environment, although this is likely to be a slow process.

 

The substance has been demonstrated to have a moderate partition coefficient value log Pow = 3.64 at 35°C which demonstrates the potential for this substance to accumulate biologically.  However, assessment of the substance using an OECD Guideline 305 C (Bioaccumulation: Test for the Degree of Bioconcentration in Fish) study indicated that the bioconcentration factor for the substance is low (BCF = 58 – 263). This value was confirmed with the use of the US EPA BCFBAF v3.01 programme, which gave a QSAR predicted value of 70.25 L/kg wet-wt. On the basis of the results, the substance is not considered to be bioaccumulative.

 

Adsorption to soil is deemed to be moderate, based on the derived QSAR value. Such potential indicates that the substance is likely to bind tightly to soils and sediments and not partition at high levels in water. As such, significant exposure related effects to water dwelling organisms are considered to be negligible. It is proposed that the substance is not hazardous to terrestrial organisms based onRead across to the structural analogue C7-9-alkyl 3-(3,5-di-trans-butyl-4-hydroxyphenyl)propionate,CAS 125643-61-0. Given that it is recommended as RMM that CAS1879-09-0 is not released to the environment, this use of read across is considered to be an appropriate way to address the terrestrial endpoint. As such, read across is applied for this substance to fulfil these relevant endpoints.

Based on its moderate water solubility and biodegradation rate it can be concluded that it is likely that the substance could potentially be persistent within the environment, however it is unlikely to bioaccumulate and enter the food chain. Abiotic effects within the environment could result in eventual removal from the relevant tropic levels. Given the low bioaccumulation potential, it is expected that effects on organisms in the food chain can considered to be minimised. 

Finally, the substance demonstrates toxicity in mammalian studies.  Howeverm as it is not anticipated to bioaccumulate, based on study data and hydrolysis effects, in the event of exposure to higher level organism via ingestion of environmental organisms, effects due to secondary poisoning can be excluded.

Reliability.

The studies have all been ranked reliability 1 or 2 according to the Klimish et al system. This ranking was deemed appropriate because the studies were all conducted to GLP in compliance with recognised guidelines, with the exception of the QSAR derived data which is allocated a Klimish rating of 2.

Justification for classification or non classification

On the basis of the results noted in the study, classification under the CLP Regulation (EC No 1272/2008 is as follows:

Chronic aquatic toxicity, Category 2; H411: Toxic to aquatic life with long lasting effects.