1,4-dioxacyclohexadecane-5,16-dione

Bioaccumulation: aquatic / sediment

Description of key information

The BCF is 156 l/kg based on read across from Verdox, which is tested in an OECD TG 305 (Klimisch 1).

Key value for chemical safety assessment

BCF (aquatic species):

156 L/kg ww

Additional information

The BCF of Zenolide is derived by using read across from Verdox which documentation is presented below. This section starts however with the executive summary of the BCF of Verdox followed by the conclusion on Zenolide.

Bioaccumulation of Verdox

The bioconcentration of the test substance in rainbow trout (Oncorhynchus mykiss) was determined in a GLP-compliant OECD guideline 305 study. In this flow-through test, groups of 85 fish were exposed for a 33-day uptake phase to nominal test concentrations of 0, 1.7 and 17 µg/L of the test substance followed by a 10 day depuration phase. Steady-state concentrations of 14C-labelled test substance were achieved in the tissues of rainbow trout (Oncorhynchus mykiss) after 33 days. The mean measured water concentrations based on total radioactivity were 2.3 and 29 μg/L. Steady-state BCF values for the 2.3 µg/L test concentration, based on total radioactivity of the test substance concentrations were 65, 335 and 179 in edible, non-edible and whole fish tissue, respectively. Steady-state BCF values for the 29 µg/L test concentration, based on total radioactivity of the test substance concentrations were 66, 402 and 203 in edible, non-edible and whole fish tissue, respectively. The test substance depurated quickly in fish tissue and ranged from 0.5 to 7 % of Day 33 steady-state values by Day 10 of depuration. Kinetic BCFK values derived by nonlinear regression for the 2.3 µg/L treatment group were 65, 312 and 167 for edible, non-edible and whole fish tissue, respectively. The time to reach 90 % steady state based on kinetics was 13.5, 5.3 and 6.6 days and time to reach 50 % clearance was 4.06, 1.61 and 2.00 days for edible, non-edible and whole fish tissue, respectively. The BCF whole fish of 203 will be converted to a lipid content of 5%, resulting in a BCF value of 156, which will be used for the CSA.

Bioaccumulation of Zenolide in an integrated testing strategy

Based solely on Zenolide’s characteristic the substance is not bioaccumulating:

1) It has a log Kow 3.65;

2) The substance is an ester which metabolises into Ethylene glycol and Dodecanedioic-acid , which are both non-bioaccumulating based on: a) low log Kow (-1.67 and 3.17, respectively); b) both being consumed in the Krebs-cycle (a glycol and a fatty acid); and 3) both are readily biodegradable. 

3) When calculating the BCF of Zenolide with the Veith relationship, the BCF is 254 l/kg ww (< 500). The Veith relationship is incorporated in EUSES and is applicable for substances with a log Kow up to 6: log BCF = 0.85 log Kow - 0.70.

4) When using the BCFBAF calculation, which includes metabolism, the BCF is estimated to be 283 and the DT50 is determined to be 3.24 minutes.

5) The BCFBAF calculation aligns with the BCF of the analogue Verdox, which has a BCF of 156 which is the key value also used for Zenolide and the read across justification is presented below.

Overall the BCF information presented support each other. Therefore, the information is sufficient for hazard assessment, C&L, PBT and risk characterization.

Bioaccumulation of Zenolide (CAS #54982-83-1) using read across from data available from Verdox (CAS #20298-69-5).

Introduction and hypothesis for the analogue approach

Zenolide is a cyclic aliphatic double ester. For this substance no experimental bioaccumulation test (OECD TG 305) is available. In view of its log Kow of 3.65, further BCF information is relevant because this value of 3.65 is higher than the cut off of 3 presented in Annex IX and therefore further information is needed. In addition to other information indicating absence of bioaccumulation such as QSAR information and ready biodegradability also information from an experimental BCF is used from the related analogue Verdox. In accordance with Article 13 of REACH, lacking information can be generated by i.e. applying alternative methods such as in vitro tests, QSARs, grouping and read-across. For assessing the bioaccumulation potential of Zenolide the analogue approach is selected because for the analogue Verdox in vivo experimental bioaccumulation information is available, which can be used for read across.

Hypothesis: Zenolide has a similar or lower bioaccumulation potential compared to Verdox.

Available information: For Verdox the BCF is 156 l/kg (including 5% lipid normalisation), based on an OECD TG 305 test (GLP and Klimisch 1).

Target chemical and source chemical

The information on Zenolide and Verdox supporting the read across are presented in the Data matrix.

Purity / Impurities

Zenolide is a mono-constituent with a high purity> 95% and therefore the impurities are not expected to influence the results.

Analogue approach justification

According to Annex XI 1.5 read across can be used to replace testing when the similarity can be based on a common backbone and a common functional group. When using read across the result derived should be applicable for C&L and/or risk assessment and it should be presented with adequate and reliable documentation, which is presented below.

Analogue justification: For Zenolide the substance Verdox is selected because of the structural similarity and for Verdox an experimental BCF information is available.

Structural similarities and differences: Zenolide has a Cyclic C13 backbone bridged with an Ethylene glycol group, while Verdox has a C11 backbone: a cyclohexyl ring to which a tert-butyl group is attached. Zenolide has a double ester within the ring while Verdox has a single ester outside its ring.

Bioavailability: Both substances are esters and present similar bioavailability based on their physico-chemical properties. Zenolide has slightly higher water solubility and a lower log Kow due to the double ester. The physico-chemical properties of both substances are in the range of being well bioavailable.

Metabolism: Zenolide and Verdox are both esters and therefore the first metabolisation step is the same and the basis for this read across. These esters will be readily cleaved by carboxyl-esterases (see metabolic scheme below) (Wheelock et al. 2008). It has been shown that Zenolide is instantaneously degraded in rat blood by carboxylesterases. As in fish tissue carboxyl esterases are present, Zenolide will also be metabolised in Ethylene Glycol and Dodecanedioic acid, while Verdox will be cleaved into its respective alcohol and acetic acid. 

Fig. 1. The anticipated metabolism of Zenolide and Verdox, respectively.

Uncertainty of the prediction: The BCF value derived from Verdox is considered conservative for Zenolide for three reasons. a) The metabolites of Zenolide are expected to be fully metabolised presenting absence of bioaccumulation, while the first metabolite of Verdox being its alcohol may be a bit more resistant to further metabolization. b) Zenolide is readily biodegradable while Verdox degrades up to 43%. c) QSAR-prediction using BCFBAF shows that Zenolide is expected to have a slightly lower BCF compared to Verdox.

Table 1: Comparison bioaccumulation and biodegradation

Substance	BCF experimental	BCF – EPISUITE	DT50
Zenolide CAS #54982-83-1	No data	283	0.05 days (1.3 hours)
Verdox CAS #20298-69-5	156 (lipid corrected)	384	0.44 days (10.6 hours)

Data matrix

The relevant information on physico-chemical properties and other environmental fate properties are presented in the Data Matrix below.

Conclusions on bioaccumulation

For Zenolide no experimental BCF is available. For the analogue Verdox such information is present, which can be used for read across. When using read across the result derived should be applicable for C&L and/or risk assessment and be presented with adequate and reliable documentation. This documentation is presented in the current document. Verdox has an experimental steady state BCF value of 156 l/kg (5% lipid normalised, OECD TG 305 test, Kl. 1), which can be directly applied to Zenolide in view of structure, bioavailability and metabolic features.

Final conclusion: Zenolide is not bioaccumulating and has a BCF of 156 l/kg.

Data matrix to support the read across to Zenolide from Verdox on bioaccumulation

Common names	Zenolide	Verdox
Chemical structures
CAS No.	54982-83-1	20298-69-5
EC no	259-423-6	243-718-1
REACH registered	Registered	Registered
Empirical formula	C14H24O4	C12H22O2
Molecular weight	256	198
Physico-chemical properties
Physical state	liquid	Liquid at 30°C
Water solubility, mg/L	75	10
Log Kow	3.65	4.75
Environmental fate
Biodegradation	Ready biodegradable	Not readily biodegradable (43% degradation)
BCF (L/kg)	156 Read across from Verdox	156 (OECD TG 305, Kl. 1)

References:

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 and Toxicology, ed. Whitacre, 117-178, D.M., Springer.