2,6,10-Trimethyldodecane (Farnesane)

Endpoint summary

Description of key information

Biodegradation Screening Assessment

Farnesane does not meet the criteria to be considered as readily biodegradable but clearly does degrade to an extent, as evidenced by 32.5% degradation in 28 days in a key OECD 301B study. In an additional supporting OECD 301b study there was 11.7% degradation after 28 days.

Biodegradation in freshwater sediment and water

This study showed that [14C]Farnesane did not remain in the water or sediment in either the high or low organic carbon aquatic sediment systems at 12°C; the majority of the applied radioactivity was captured in the volatile traps. Less than 2% of the applied radioactivity was present in the HOC overlying water by day 28, and in the LOC overlying water by day 7. The sediment extracts had a maximum of 2% and 4% of the applied radioactivity for the HOC and LOC sediment extracts, respectively. The mean sediment residue accounted for a maximum of 8% and 3% of the applied radioactivity for the HOC and LOC sediment extracts, respectively. The mean maximum % AR observed as a transformational product in the HOC and LOC overlying water samples were 3.4% and < 2%, respectively. No transformational products were observed in the Orbo™ tube extracts. 

The overlying water DT50 was calculated as 0.289 (DFOP kinetic analysis) and 0.302 (SFO kinetic analysis) days for the high and low organic carbon vessels, respectively.

Using double first-order in parallel (DFOP) kinetic analysis on the combined overlying water and sediment the DT50 was calculated as 1.45 days and 1.3 days for the high and low organic carbon vessels, respectively.

Biodegradation in soil

This study showed that the majority of [14C]Farnesane dissipated over time in all four soils (loam sand (Soil I), silt loam (Soil II and II), or silty clay loam (Soil IV)) at 12°C; the majority of the applied radioactivity was captured in the volatile traps.

Between 14.5% to 20.3% of applied radioactivity remained in the soils on Day 120 as bound radioactivity after all extractions had been carried out.  On day 120 the ‘harsh’ extractions removed 0.4, 0.5, 1.3 and 0.7% of the applied radioactivity for soil I, II, III, and IV respectively.  Therefore, these residues are not considered to be bioavailable and binding to soils was considered a pathway for disappearance.

Radio-TLC analysis of solvent extractions 1 and 2 showed the applied radioactivity was present as [14C]Farnesane, and no degradation products were detected.

On day 120 mineralisation accounted for 45.6, 38.8, 37.6 and 12.7% of the applied radioactivity in Soil I, II, III, and IV vessels, respectively, therefore Farnesane showed the potential to degrade.

For dissipation kinetic analysis the decline in [14C]Farnesane concentration was deemed to have occurred by degradation or transfer processes and was calculated using soil extracts only; bound residues were not considered to be bioavailable and were considered a method of disappearance.  The DT50 was calculated as 5.11, 5.01, 2.82 and 9.39 days for Soil I, II III, and IV vessels, respectively.

For degradation kinetic analysis the decline in [14C]Farnesane concentration was deemed to have occurred by degradation only, bound residues were considered to be 100% parent and not a mechanism for disappearance.  The DegT50 was calculated as 7.38, 7.68, 7.05 and 25.8 days for Soil I, II, III, and IV vessels, respectively.

Bioaccumulation: aquatic / sediment

An in silico study has been performed to evaluate the BIOCONCENTRATION FACTOR (LOG BCF) of the test item using several Quantitative Structure-Property Relationship (QSPR) models. These models have been checked to be compliant with the OECD recommendations for QSAR modeling. They all predict the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following the Guideline for Testing of Chemicals No. 305, "Bioaccumulation in Fish: Aqueous and Dietary Exposure". The criterion predicted was the bioconcentration factor (BCF) in L/kg expressed in his logarithm.

 

The BIOCONCENTRATION FACTOR (LOG BCF) values were determined using the following QSPR models:

•       iSafeRat® fishBCF v1.0;

•       BCFBAF model (BCF) v3.01 from EPI Suite v4.11 software;

•       BCF model from OPERA v2.6 software;

•       BCF model (Hierarchical Clustering) from TEST v5.1.1 software;

•       BCF model (Single Model) from TEST v5.1.1 software;

•       BCF model (Group Contribution) from TEST v5.1.1 software;

•       BCF model (Nearest Neighbor) from TEST v5.1.1 software;

•       BCF model (CAESAR) v2.1.14 from VEGA v1.1.5 software;

•       BCF model (kNN/Read-Across) v1.1.0 from VEGA v1.1.5 software;

•       BCF model (Meylan) v1.0.3 from VEGA v1.1.5 software.

For all of these models, the test item has been verified to be, at least partially, within the applicability domain.

The mean BCF was determined as 1000 with a min of 158 and a max of 2138. Only one model out of the 9 within the applicability domain predicted a BCF >2000. Using the consensus approach, the substance is considered to have a BCF of 1000 and to be below the B criterion used in PBT assessment of 2000 L/Kg.

Adsorption/desorption

The predicted log Koc was 4.279 and 6.5 using the MCI and Kow method, respectively, in the KOCWIN v 2.0 utlised in EPISuite v 4.11.