Phenol, heptyl derivs.

Endpoint summary

Additional information

Hydrolysis

The determination was carried out using a procedure designed to be compatible with Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004. 

The estimated half-life at 25°C for the test item is > 1 year at pH 4,7 and 9

Biodegradation

In the key study performed according to OECD 301D Closed Bottle Test Method inoculated test medium is dosed with a known amount of test substance as the nominal sole source of organic carbon. Degradation is followed by the analysis of dissolved oxygen over a 28-day test period. The dissolved oxygen uptake of the test solution (corrected for uptake of blank inoculum) is expressed as a percentage of the theoretical oxygen demand (ThOD) for the reference substance and chemical oxygen demand (COD) for the test substance. The test contained an inoculum control group, a reference group, treatment group, and a toxicity control group. The control, reference and treatment groups each contained twenty replicate test chambers. The toxicity control group contained four replicate test chambers. The inoculum control was used to measure the oxygen uptake of the inoculum and was not dosed with a carbon source. The reference chambers were dosed with sodium benzoate, a substance known to be biodegradable, at a nominal concentration of 2 mg/L. The treatment group test chambers were used to evaluate the test substance at a nominal concentration of 5 mg/L. The toxicity control group test chambers were used to evaluate toxicity of the test substance on the inoculum dosed at nominal concentrations of 2 mg/L (reference) and 5 mg/L (test substance). Measurements of dissolved oxygen were performed on two test chambers from the control, reference and treatment groups once a week and the toxicity control group on Days 0 and 14.

The results indicate that the inoculum was active by degrading the reference substance within the acceptable range. The results for the test substance were an average of 1.6% degradation over a 28-day test period.

The test substance is not readily biodegradable under the conditions of the study.

In a supplementary study determination of biodegradation was performed according to OECD 301B, US EPA 796.3260 and ASTM D 5864 -95.

The test material, at a concentration of 10 mg carbon/L was exposed to a preadapted mixed culture inoculum derived from activated sewage sludge/soil with culture medium at 20°C for 28 days (pH 7). CO2 released from the degradation chamber was was trapped and the amounts measured at the sample periods. Results are expressed as a percentage of the theoretical total amount of CO2 that could be produced by complete degradation.

The test material reached 25.4% biodegradation after 28 days.

The test material undergoes degradation with preadaptation of inoculum under the conditions of the study. As the substance does not reach 60% degradation after 28 days it cannot be considered to be readily biodegradable.

Bioaccumulation

In a study performed to a similar procedure to OECD Guideline 305 (Bioconcentration: Flow-through Fish Test), Atlantic cod were exposed to 4-hepthylphenol at a concentration of 15.5 nmol/L (as 4-[14C]heptylphenol) under flow-through conditions with a 192 hour exposure period and a 192 hour elimination period.

The steady state BCF was 555 and the kinetic BCF was 578. Rate constants for uptake and elimination were 29.94 and 0.052/h respectively. 

Elimination of 4-heptylphenol occurred rapidly following first order kinetics with an estimated biological half life of 13 hours. Substantial radioactivity was detected in seawater during the initial part of the elimination period but no radioactivity was detected in water after more than 96 hr recovery in clean seawater.

No radioactivity was detected in tissues of cod at the end of the elimination period, indicating a lack of retention in specific tissues. Radioactivity in autoradiograms extracted with nonpolar and polar solvents was not observed, giving additional support to the conclusion that 4-heptylphenol and metabolites do not bind to specific macromolecules or tissue structures in cod.

Adsorption/desorption

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

The method guideline states that the measurement of adsorption coefficient should be carried out on substances in their ionised and unionised forms. However, the dissociation constants of certain functional groups found in the test item made it impossible to satisfy this criteria. 

From structural information supplied by the Sponsor, estimations of the phenol functional group dissociation constants of 10.3 to 11.8 were generated using predictive computer modelling (SPARC version 4.6,October 2011, w4.6.1691-s4.6.1687).

Therefore, formation of the ionised form of the test item would only occur under basic conditions (pH >8). As such pH’s are not environmentally relevant, only a single determination was performed at an approximately neutral pH.

The adsorption coefficient (K_oc) of the test item has been determined to be within the range 91.8 to 5.79 x 10³, log₁₀K_oc 1.96 to 3.76. The dominant component of the test item (90.0% by percentage area normalisation) resulted in an adsorption coefficient value of 2.43 x 10³, log₁₀K_oc 3.39.

Henry's Law Constant

Henry's law constant was calculated to be 1.277E-06 Pa.m3/mol at 25 °C based on experimental water solubility vapour pressures . This value indicates a low rate of volatilisation from surface water is expected.