1,2,3,4,4a,7,8,8a-octahydro-2,4a,5,8a-tetramethyl-1-naphthyl formate

Endpoint summary

Description of key information

Assessment of hydrolytic stability was carried out according to OECD Guideline 111. Insignificant hydrolysis was observed at pH4 and pH7 at 25°C, although at higher temperatures or under conditions were residual dissolved oxygen may have been present a decrease in parent was observed. The data showed non-pseudo first order kinetics indicating that this loss was not due to hydrolysis alone. At pH9, the test item was found to be hydrolytically unstable (t1/2 = 368 hours at 25°C, calculated using the Arrhenius equation from data obtained at 40, 50 and 60°C). Degradation products were seen which were assumed to be the result of base catalysed hydrolysis of the ester functional group and the formation of corresponding alcohol and formic acid. Two new peaks were observed, which based on their relatively size, are attributed to 2,4a,5,8a-tetramethyl-1,2,3,4,4a,7,8,8a-octahydronaphalen-1-ol (major peak, hydrolysis product of the mono-constituent component) and to 2,5,5,8a-tetramethyl-1,2,3,5,6,7,8,8a--octahydronaphalen-1-ol (minor peak, hydrolysis product of the isomeric impurity).

The ready biodegradability of Oxyoctaline formate has been investigated in two independent OECD 301F ready biodegradability tests. Based on oxygen consumption, no biodegradation after 28 days was observed. Thus, the test substance should be regarded as not readily biodegradable according to these tests for the purposes of classification and labelling. The conclusion for the exposure assessment is that "under test conditions no biodegradation was observed". As such the biodegradation rate constant used for the environmental exposure assessment, performed using Chesar, is zero. For the purpose of the PBT assessment, chemical specific analysis was performed in one of the OECD 301F tests. This showed that Oxyoctaline formate is converted to the corresponding alcohol indicating that the parent substance is not persistent. Based on the parent remaining, the % of primary degradation is estimated to be approximately 55% after 42 days in a ready test performed at 30 mg/L. Given that the water solubility of the registered substance is only 2.2 mg/L, the rate of biodegradation in this test will be controlled by the dissolution rate. Another important consideration is potential toxicity to the inoculum, which could not be ruled out in either study. Biodegradation screening tests are performed under very stringent conditions compared to relevant environmental conditions. Thus the results from such tests are considered conservative and worst case. Therefore, it is expected that under realistic environmental exposure, more efficient and rapid biodegradation kinetics will be observed.

Bioaccumulation is not a specified endpoint below 100 t/y. However, given that Oxyoctaline formate is screened as potentially B based on the log Kow of 4.9, 5.0 and 5.3 (3 isomers) and that residual Oxyoctaline formate was detected at the end of the biodegradation study, it was considered appropriate to further assess the bioaccumulation potential of the substance. To this end, an in vitro metabolism assay using trout S9 fractions was performed. Due to the relatively low abundance of the minor two isomers, only the major isomer (79.7% abundance in test item) was quantified. In two independent experiments, a metabolic turnover of 57.8 and 57.9% of the starting concentration within a 60 minute exposure period was observed. The substrate depletion rates (0.84 and 0.85 ml/h/mg protein) were used as input into an “in vitro - in vivo” extrapolation model to give refined BCF estimates in the range of 191 L/kg (fu = 1, assuming no effect of differential binding to serum) and 1084 L/kg (fu calculated, assuming different binding to serum in vivo vs. in vitro). Given that both estimates are well below the B criterion of 2000, it is considered that the major isomer of Oxyloctaline formate is not bioaccumulative for the purpose of the PBT assessment. This is supported by QSAR estimates of 271-672 L/kg using the Arnot-Gobas BCF model.

The corresponding alcohol of the major isomer of Oxyoctaline Formate was detected as metabolite in the in vitro S9 study by GC-MS analysis and confirmed with synthesized material as reference. In addition, minor peaks corresponding to the alcohols of two minor isomers were detected indicating that these minor components in Oxyoctaline Formate are also not bioaccumulative. Importantly, two glucuronic acid conjugates were detected as Phase II metabolites by LC-MS analysis. This is a major elimination pathway in fish. Several peaks with similar m/z as the two glucuronides were found indicating the formation of these glucuronides with all isomers of Oxyoctaline Formate.

The same major metabolite was identified in the fish metabolism and biodegradation studies. Therefore, the environmental hazard of this transformation product has been assessed. This alcohol is also present as a minor impurity in Oxyoctaline formate itself. Based on the HPLC log Kow determination of the registered substance, this impurity was assigned a log Kow of 4.2 which is below the B screening criteria of > 4.5. Furthermore, the in vitro intrinsic clearance rate of the alcohol was determined in the aforementioned trout S9 assay. Enzymatic turnover was observed with 71.9% decrease of the starting concentration within a 60 minute exposure period. The in vitro intrinsic clearance rate was 1.27 ml/h/mg protein. The resulting predicted BCF was 115 L/kg (fu=1) and 382 L/kg (fu calculated), supporting the non-B conclusion for this transformation product. Moreover, the metabolite is more polar than the parent substance as indicated by the relative log Kow values of 4.2 versus 4.9-5.3. Thus it is expected to be less toxic to the aquatic environment. Thus no further assessment of the degradation product is warranted. It is also considered appropriate to base the environmental risk assessment on the properties of the parent substance, which represents a worst-case scenario.  

Information on phototransformation in air, water and soil is not available. It is not a standard information requirement under REACH and there is no indication from the CSA on the need to investigate further the fate and behaviour of the substance.

The Koc for the substance was determined to be 10400 (main isomer) according to an OECD 121 study. This value has been used for the purposes of environmental exposure assessment and derivation of PNECsoil and PNECsediment.