1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylindeno[5,6-c]pyran

Endpoint summary

Description of key information

DT50 aquatic compartment: 4.2 days

DT50 sediment compartment: 79 days

DT50 soil compartment: 35 days

All DT50's are considered relevant for 12oC

Additional information

Note: The whole WoE reasoning for water, sediment and soil is in the file attached. The information is based on the what is presented in the EU-RAR (2008) and literature data found thereafter. 

Modelled data and data available

According to (EPI) Suite v4.119 (EPA, 2011) BIOWIN models of the EPA do not indicate readily biodegradation for HHCB (BIOWIN models 1, 2, 5 and 6): all values are < 0.5. BIOWIN model 2 and 6 for non-linear biodegradability and BIOWIN 3 for ultimate biodegradation predict for HHCB: < 0.5 and < 0.5 and < 2.25 values, respectively. These values can be indicative for ‘persistency’ according to ECHA PBT guidance (R.11, page 62). BIOWIN 4 predicts primary biodegradation within days (value 4) to weeks (value 3) for HHCB which has the value of 3.08.

The removal of HHCB was simulated in EPISuite using the Sewage Treatment Plant model, BIOWIN output (as presented in the STP help-file) a. Based on the physio-chemical properties of HHCB, the model predicts total removal of HHCB at 96.6% in a aerobic waste water treatment plant with biodegradation accounting for 26% and sludge adsorption accounting for 70.6%. Loss via volatilization was modeled to be negligible.

Ready biodegradability: In a study according to OECD TG 301B, HHCB did not mineralise, hence, HHCB is not readily biodegradable.

Degradation in aquatic compartment: The degradation in water is based on a WoE using 3 key studies, which together cover the OECD TG 309. The overall DT50 value for the aquatic compartment was determined to be 4.2 days at 20°C (7 days at 12°C). The key metabolite formed is HHCB-lactone for which a DT50 of 27 days at 12oC was found. This HHCB-lactone is further degraded to HHCB-hydroxylated- carboxylic acid and other hydroxylated HHCB products for which a DT50 was not derived and is further assessed in the bioaccumulation section. 

Degradation in the sediment compartment: The degradation in sediment is based on a WoE, which does not completely cover the OECD TG 308, but the information is deemed sufficient also because of the available water and soil degradation information. The overall DT50 was determined to be 79 days at 12°C. The identity of the degradation products are anticipated to be similar to water.

Degradation in the soil compartment: The degradation in soil is based on a WoE using 3 key studies, which together cover sufficiently the OECD TG 307. The overall DT50 value was determined to be 35 days at 12°C. HHCB can be further degraded into HHCB-lactone and other more polar metabolites anticipated to be similar to metabolites in the water compartment.

Additional information on HHCB degradation pathway

The possibility of primary degradation is also found in literature. From the available degradation studies and literature HHCB will break down into HHCB-lactone and to HHCB-hydroxylated-carboxylic acid presented in the table below (Franke et al. 1999; Federle et al. 2002 and 2003; and Berset et al. 2004). The first metabolite is an oxidation next to the ether bond resulting in a lactone, which is an ester. This can be an abiotic or biotic process (Franke et al., 1999). This ester can subsequently be cleaved by carboxylesterases (a biotic process) which are ubiquitous present in the environment resulting in a carboxylic-acid and a primary alcohol (Wheelock et al., 2008): HHCB-hydroxylated-carboxylic acid, which is the 3rd structure in the table. 

The table presents a representative of HHCBs constituent and two of its metabolites. HHCB-lactone is the first oxidation product of HHCB and HHCB-hydroxylated-carboxylic acid is a subsequent metabolite as found in several studies.

 

Names	HHCB	HHCB-lactone	HHCB-hydroxylated-carboxylic acid
	Parent	First oxidized metabolite	Second oxidized metabolite
Chemical structure
Smiles	CC1(C)c2cc3COCC(C)c3cc2C(C)(C)C1C	CC1(C)c2cc3C(=O)OCC(C)c3cc2C(C)(C)C1C	O=C(O)c1cc2c(cc1C(C)CO)C(C)(C)C(C)C2(C)C
	C18H26O	C18H24O2	C18H26O3
MW	258	272	290

Reference list

Berset, Jean-Daniel, et al. “Considerations about the enantioselective transformation of polycyclic musks in wastewater, treated wastewater and sewage sludge and analysis of their fate in a sequencing batch reactor plant.” Chemosphere 8 (2004): 987-996.

Federle, T. W., N. R. Itrich 2003. Biodegradation of Galaxolide (HHCB) in Activated Sludge. Notebooks: ITS-257, ITL-417. Proctor and Gamble Central Product Safety Division/Product Safety and Regulatory Affairs Environmental Science Department, OH

Federle, T. W., N. R. Itrich, D. M. Lee, and D. Langworthy. 2002. Recent Advances in the Environmental Fate of Fragrance Ingredients. Presentation and poster of Proctor & Gamble presented at SETAC 23rd Annual Meeting, Salt Lake City, USA (as cited in EC, 2008).

Franke, Stephan, et al. “Enantiomeric composition of the polycyclic musks HHCB and AHTN in different aquatic species.” Chirality: The Pharmacological, Biological, and Chemical Consequences of Molecular Asymmetry 10 (1999): 795-801.

Jenkins, W. R., 1991. Abbalide: Assessment of its Biodegradability, Modified Sturm Test. Life Science Research Report 90/BAK003/1361. Bush Boake Allen, Inc. (as cited in EC, 2008).

Wheelock, C.E., Philips, B.M., Anderson, B.S., Miller, J.L., Miller, M.J., and Hammock, B.D., 2008, Application of carboxylesterase activity in environmental monitoring and toxicity identification evaluations, (TIEs), in Reviews of Environmental Contamination an Toxicology, ed. Whitacre, 117-178, D.M., Springer.