Hexadecyl acetate

Endpoint summary

Additional information

Abiotic degradation; Hydrolysis

 

The test item as a whole was expected to be essentially insoluble in water. Therefore the test solution concentration required to dissolve all the components (less than half the water solubility) would be impractically low and a sufficiently sensitive analytical method was not available. Furthermore, the main functional group within the components of the test item is an ester. Although esters usually hydrolyse readily, especially in alkaline solutions, the test item components may have a significantly reduced hydrolytic rate due to them being essentially insoluble in water. Overall, these issues make hydrolysis testing unfeasible and testing was not carried out using Method 111 of the OECD Guidelines for Testing of Chemicals (13 April 2004) and Method C.7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008.

 

Biodegradation

Low water solubility of the test item (< 1.14E-05 g/L of solution at 20.0 ± 0.5 °C) combined with low vapour pressure (4.8E-03 Pa at 25 °C) results in a high value for the Henry's Law constant. This was relevant with respect to air bubbles passed through the jars during investigation of ready biodegradation using OECD Guideline 301 B because the test item partitions to air even though vapour pressure is low. Expert advice was therefore accepted and investigation of ready biodegradation was undertaken in accordance with OECD Guideline 301 F and reported as the key study

The key study was performed to assess the ready biodegradability of the test item in an aerobic aqueous media. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No. 301 F "Ready Biodegradability; Manometric Respirometry Test" referenced as Method C.4 -D of Comission Regulation (EC) No. 440/2008 and US EPA Fate, Transport and Transformation Test Guidelines OCSPP 835.3110 (Paragraph (q)).

The test item at a concentration of 20 mg/L was exposed to sewage treatment microorganisms with mineral medium in sealed culture vessels in diffuse light at temperatures between 22 and 23 °C for 14 days. The study was terminated after 14 days with the sponsor's approval as degradation of the test item had reached a plateu for at least three determinations and hence the test item could be considered to be readily biodegradable.

Following the recommendations of the International Standards Organisation (ISO 1995), the test item was dissolved in an auxillary solvent prior to being absorbed onto a filter paper and subsequent dispersal in test media. High shear mixing was also applied to break up the filter paper containing the test item. Using this method the test item was evenly distributed throughout the test medium and the surface area of test item exposed to the test organisms was increased thereby increasing the potential for biodegradation.

Biodegradation of the test item was assessed by measurement of daily oxygen consumption values on Days 0 to 14. Control solutions with inoculum and reference item (aniline) together with a toxicity control were used for validation purposes.

The test item attained 73 % biodegradation after 14 days and satisfied the 10 -day window validation criterion whereby 60 % biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301 F.

A supporting study performed to assess the ready biodegradability of the test item in an aerobic aqueous medium was designed to be compatible with OECD Guidelines for Testing of Chemicals (1992) No 301B "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4 -C of Commission Regulation (EC) No 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OCSPP 835.3110 (Paragraph m).

The test item at a concentration of 10 mg carbon/L was exposed to activated sewage sludge micro-organisms with mineral medium in sealed culture vessels in the dark at 19 to 22 °C for 28 days. Biodegradation was assessed by determination of carbon dioxide produced. Control solutions with inoculum and the reference item, sodium benzoate, and a toxicity control were used for validation purposes. The test item attained 30 % biodegradation after 28 days and cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301 B.

 

Adsorption / desorption coefficient (Koc)

 

The determination of the adsorption coefficient was carried out using the HPLC screening method, designed to be compatible with Method C19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001.

 

The test utilised a high performance liquid chromatograph. A commercially available cyanopropyl reverse phase HPLC column containing lipophilic and polar moieties was used and the adsorption coefficient of the test item was determined to be greater than 4.27E05 with a log10 Koc > 5.63. The substance was therefore found to be highly absorbing to soil and will not be mobile in the terrestrial environment.