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Bioaccumulation: aquatic / sediment

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Description of key information

Cyclaprop has a BCF of 156 l/kg based on read across from Verdox, which are experimentally tested in OECD TG 305 (Klimisch 1).

Key value for chemical safety assessment

BCF (aquatic species):
156 L/kg ww

Additional information

The BCF of Cyclaprop is derived by using read across from Verdox which documentation is presented below. This section starts, however, with the executive summaries of the BCFs of Verdox.

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 used for the CSA.

Bioaccumulation of Cyclaprop (Cas no 68912-13-0) using read across from Verdox (CAS no. 20298-69-5).

Introduction and hypothesis for the analogue approach

Cyclaprop has a tricyclodecenyl type backbone to which a propionic ester is attached. For this substance no experimental bioaccumulation test (OECD TG 305) is available. In view of its log Kow of 4.4, further BCF information is relevant because this value of 4.4 is higher than the cut off of 3 presented in Annex IX and therefore further information is needed. 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 Cyclaprop 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: Cyclaprop has the same bioaccumulation potential as Verdox, because these share a similar hydrocarbon backbone, and both have an ester functionality on which bases these will have the same fish metabolism.

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

Target chemical and source chemical

Chemical structures of Cyclaprop and analogue Verdox is shown in the data matrix, including physico-chemical properties thought relevant for bioaccumulation and read across.

Purity / Impurities

Cyclaprop is a reaction mass containing a mixture of two very similar isomers differing only the site of the double bond which can be at the 5-yl or 6-yl position. All impurities are <1%.

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 Cyclaprop the substance Verdox is selected because of the structural similarity and for Verdox experimental BCF information is available.

Structural similarities and differences: Cyclaprop and Verdox have a hydrocarbon backbone to which the same ester functionality is attached. These backbones have the same number of carbons. The difference is that Cyclaprop has an additional hydrocarbon ring structure in which an unreactive double bond is present, while Verdox has a hydrocarbon tert-butyl group attached to its cyclohexyl ring. In addition, Verdox is an acetic ester while Cyclaprop is a propionic ester.

Bioavailability: Cyclaprop (target) and Verdox (source) have similar bioavailability based on the similarity in chemical structure, molecular weight and log Kow values.

Metabolism: Cyclaprop and Verdox have both an ester as functional group and therefore the propionic ester cleavage in fish is considered the same as the acetic ester cleavage because there is only one methyl group extra in Cyclaprop.

Other BCF parameters: Beside metabolism, the difference in log Kow may need to be used for adjusting the BCF as in view of Cyclaprop having the lower log Kow the BCF could be lower. However, the difference in log Kow between Cyclaprop and Verdox is below 0.5 (4.4 and 4.75, respectively) which may be due to experimental differences because the log Koc (also a log Kow depending parameter) is the same between these two substances. Therefore, a conversion is not needed. Acute fish toxicity can be related to BCF when using the Lethal Body Burden approach (LBB). The acute fish toxicity of both Cyclaprop and Verdox are similar: 6.7 and 5.6 mg/l, respectively, further supporting the BCF read across.

Uncertainty of the prediction: There or no remaining uncertainties other than those already addressed above.

Data matrix

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

Conclusions for Bioaccumulation

For Cyclaprop 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. The current document fulfils this documentation. Verdox has an experimental steady state BCF values of 156 l/kg (5% lipid normalised, OECD TG 305 test, Kl. 1), which can be directly applied to Cyclaprop because the molecular weight of both is almost the same: 206 for Cyclaprop and 198 for Verdox as well as the log Kow values (4.4 and 4.75).

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

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

Common names






Chemical structures

Cas no






REACH registration



Empirical formula



Molecular weight



Physico-chemical data


Physical state



Water solubility



Log Kow



Aquatic toxicity



Acute fish toxicity: LC50 (mg/L)



Environmental Fate


Log Koc



Bioaccumulation in l/kg


RA from Verdox


(OECD TG 305, Kl. 1)


Reference to support ester cleavage

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.