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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The DT50 of Cyclaprop is 17 days at 12°C, which is based on a compilation of data that resembles the outcome of the OECD TG 309 test sufficiently. This DT50 is derived from ready biodegradability curve (OECD TG 301F), showing maximum primary degradation after 6 days at 25°C, the identification of the degradation products in this test, correction to 12°C (using EUSES) and supporting QSAR model results from Arnot et al. (2005). The primary biodegradation product are Cycla-alcohol and Cycla-ketone (measured log Kow values are 2.4 and 3.3, respectively).

Key value for chemical safety assessment

Half-life in freshwater:
17 d
at the temperature of:
12 °C

Additional information

In this section it is outlined that Cyclaprop fulfils the Annex IX requirements. The derivation of the DT50 for the water compartment is presented in the Overall Endpoint summary because information from screening study in combination with other information is used.

Cyclaprop’s Annex IX requirements on derivation of half-lives in water without experimental testing (OECD TG 309) in these compartments.


Summary: Further biodegradation in water-simulation-systems for Cyclaprop is not needed because the substance is not PBT or vPvB, based on absence of bioaccumulation in fish, the substance is not T because it is not hazardous for human health and aquatic organisms (EC10/NOEC values are above 0.01 mg/L). In addition, a half-life of the parent substance can be estimated using information from its structure and propionic ester functionality, the ready biodegradability tests and the analysis and identification of the remaining parent substance and the metabolites, which is outlined in the DT50 derivation for water.



The present document outlines the available information showing the absence of need for further simulation testing based on

1) ECHA guidance

2) A DT50 for Cyclaprop that can sufficient accurately be predicted, because Cyclaprop is a propionic ester

3) The outcome of the OECD TG 309 versus the results obtained with other than experimental methods.

4) QSAR estimates support the primary biodegradation of Cyclaprop into its alcohol and acid.


Annex IX requirements

According to Annex IX further biotic degradation shall be proposed by the registrant if the chemical safety assessment, according to Annex I, indicate the need to investigate further the degradation of the substance and its degradation products. In the LRs view the CSA does not indicate the need for further testing based on the following:


1) ECHA’s further guidance: In one of ECHAs tip and tricks webinars (2014) on degradation it is presented that degradation is an important endpoint to fulfil the following regulatory needs:

1a) Persistency assessment, to identify whether a chemical has PBT or vPvB properties;

1b) Hazard assessment: To determine the potential to cause long-term adverse effects in environmental hazard classification;

1c) Risk assessment: To determine the Predicted Environment Concentration (PEC) of a chemical in environmental exposure assessment for use in risk characterisation.

Applying this to Cyclaprop

1a) In Cyclaprop’s PBT assessment the substance is not considered PBT. The substance is not P because the DT50 of Cyclaprop is 17 days. It is not T because the EC10/NOEC values are above 0.01 mg/L and Cyclaprop is not classified as CMR nor is there any other evidence of chronic toxicity. The substance is not B for aquatic organisms, because its BCF in fish is 156 l/kg based on read across from verdox. This means that Cyclaprop is not PBT in absence of P, B and T. The overall PBT/vPvB conclusion will not change and therefore further testing is not required.

1b) The substance needs to be classified as H411 according to EU CLP (EC 1272/2008/ and its amendments) because the lowest NOEC / EC10 from the chronic tests available is <1 mg/L and Cyclaprop is not rapidly biodegradable. By performing additional biodegradation tests, irrespective of the outcome, Cyclaprop will still have to be classified for Aquatic Chronic toxicity. Furthermore, the classification will not become more stringent as a result of additional testing, so further biodegradation studies do not fulfil a regulatory need.

1c) In the current chemical safety assessment, there is no risk for the environment as all Risk Characterisation Ratios (RCR) are below 1. Therefore, further biodegradation studies are not needed.


2) Cyclaprop, its half-life and its metabolites

The Cyclaprop’s half-life can be sufficient accurately be derived for fulfilling Annex IX, using existing biodegradation pattern in screening studies, measuring the metabolites therein.


3) Cyclaprop’s ready biodegradability tests versus expected outcomes of OECD TG 309: Relation between the half-lives and degradation products presented:

3a) Firstly, all the ready biodegradation tests are considered very stringent tests but the OECD TG 309 test is more stringent. In the latter test lower substance concentrations, lower bacteria concentrations and a lower temperature are applied at which the test should be performed (12° versus 20-25°C) have to be used. As a result, the pseudo half-life found in the ready test will need to be converted to 12°C. It has been experimentally shown that the tricyclodecanyl backbone is more stable in the ready biodegradation tests and that these are still present after 60 days in prolonged tests (Cyclabute information). From these data and the expectation that the OECD 309 test is more stringent than the biodegradation ready test the same degradation products can be found.

3b) Secondly, from the OECD TG 309 test, more information can be retrieved compared to a ready biodegradation tests, but this additional information will have limited influence on the final results of the different frameworks C&L, PBT and RCR.

3c) Thirdly, difference in experimental procedures will have limited influence on the results. There is no mass balance but considering volatility, the evaporation loss is limited based on the Henry law’s constant of 1.16 Pa.m3/mol at 12°C. Considering adsorption, Cyclaprop’s adsorption to suspended solids will also be limited due to a low log Koc of 3.1. This value indicates that Cyclaprop will mainly remain in the water phase (84% as is estimated in the Simple Treat model). There is no lag phase seen in the degradation studies and because Cyclaprop has a propionic ester group this group will be biodegraded first, which will also occur in the OECD TG 309 test.

In summary on Cyclaprop’s ready tests versus the OECD TG 309: the key elements of the OECD TG 309 can be deduced from the ready biodegradability tests based on the pattern of degradation, and the experimental determination of the parent and the key metabolites.

4) QSAR models as included in the discussion on simulation testing show that the predicted half-lives are 10-13 days which is in line with the derived values. The QSAR model predictions are included in the derivation of the DT50.