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Toxicity to microorganisms

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Description of key information

The toxicity to micro-organism EC10 of Cyclaprop is 48 mg/ after conversion.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
48 mg/L

Additional information

For Cyclaprop no experimental data on toxicity to micro-organisms is available. This information can be retrieved from Cyclacet using read across. First the experimental information of Cyclacet is presented and thereafter the read across justification to use this information for Cyclaprop.

Activated sludge respiration inhibition test for Cyclacet

An activated sludge respiration inhibition test with Cyclacet has been performed, according to ISO 8192, which is similar to OECD TG 209. The sludge concentration was 6g/l. The nominal test concentrations were, 100, 180, 320, 560 and 1000 mg/l. A dose related increase in inhibition was seen from 26 to 88 mg/l. An EC50 of 245 and an EC10 of 53 mg/L was derived.

Cyclaprop (Cas no 68912-13-0) and its toxicity to micro-organisms using read across from Cyclacet (Cas no 54830-99-8)

Introduction and hypothesis for the analogue approach

Cyclaprop has a tricyclodecenyl fused ring structure backbone to which a propionic ester is attached. For this substance, no data on toxicity to micro-organisms is available. In accordance with Article 13 of REACH, lacking information can be generated by means of applying alternative methods such as QSARs, grouping and read-across. For assessing the toxicity to micro-organisms of Cyclaprop the analogue approach is selected because for Cyclacet, a closely related analogue, reliable data is available.

Hypothesis: Cyclaprop has similar toxicity to micro-organisms compared to Cyclacet after conversion based on similarity in chemical structure and similarity in aquatic toxicity.

Available experimental information: For Cyclaprop, an activated sludge respiration inhibition test is available performed according to ISO 8192 following GLP receiving a Klimisch score of 2. In addition, Cyclaprop and Cyclacet have a full base set for aquatic toxicity (algae (acute and chronic), Daphnia, fish) all receiving Klimisch 1.

Target chemical and source chemical(s)

Chemical structures of the target chemical and the source chemical are shown in the data matrix.

Purity / Impurities

Cyclaprop is a reaction mass, containing two very similar isomers in which the double bond is at the 5-yl or 6 yl position. Impurities are all below 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 information from its nearest neighbour Cyclacet is used for which experimental information on micro-organism toxicity is available.

Structural similarities and differences: Cyclaprop (target) and Cyclacet (source) both have a tricyclodecenyl fused ring structure with an unsaturated bond in the outside ring. On the other side of the ring an ester bond is attached with a short alkyl chain. The alkyl chain of Cyclacet is an ethyl chain while the Cyclaprop has a propyl one and this shorter chain results in a slightly lower log Kow of Cyclacet compared to Cyclaprop.

Bioavailability: Cyclaprop has similar bioavailability based on the similarity in chemical structure and physico-chemical properties compared to Cyclacet as presented in the Data matrix.

Mode of Action (MoA): Cyclaprop has the same mode of action as Cyclacet based on their similar backbone and their similar functional ester group (see Data matrix). This same MoA of action has resulted in an incremental increase of acute LC50 and EC50 values for fish, algae, and Daphnia based on the decreased alkyl chain: Cyclacet is slightly less toxic compared to Cyclaprop.

Conversion: Cyclaprop’s toxicity to micro-organisms can be predicted from Cyclacet converting the Cyclacet values using molecular weight and log Kow differences. The used formula is: Log EC10 target (mmol) = Log EC10 source (mmol) x log Kow source/Log Kow target.

Uncertainty of the predictions: There are no other uncertainties than already addressed above.

Data matrix

The relevant information on physico-chemical properties and ecotoxicological characteristics are presented in the Data matrix.

Conclusions for long-term fish and Daphnia toxicity

For Cyclaprop no experimental toxicity to micro-organism test is available. For Cyclacet data is available, which can be used for read across. In case of using read across the result derived should be applicable for risk assessment and be presented with adequate and reliable documentation. This documentation is presented in the current document. For Cyclacet the EC10 for toxicity to micro-organisms is 54 mg/L. After conversion for differences in log Kow and MW, the EC10 is 48 mg/L.

Final conclusion on hazard: Cyclaprop has a 30-min EC10 to micro-organisms of 48 mg/l.


Data matrix to assess the toxicity to micro-organisms of Cyclaprop from Cyclacet

Common names






Chemical structures

Cas no of 5-yl

Cas no of the generic





Empirical formula



EC number



REACH registration



Molecular weight



Physico-chemical data



Physical state



Vapour pressure Pa



Water solubility mg/l



Log Kow



Acute Aquatic toxicity



LC50 Fish (mg/L)

6.7 (OECD TG 203)

15.8 (OECD TG 203)

EC50 Daphnia (mg/L)

>14 (OECD TG 202)

25 (OECD TG 202)

EC50 Algae (mg/L)

2.5 (OECD TG 201)

6.4 (OECD TG 201)

EC10 Algae(mg/L)

1.9 (OECD TG 201)

2 (OECD TG 201)

30-min EC10 Toxicity to Micro-organisms (mg/L)

48 (After conversion using difference in MW and log Kow)

RA to Cyclacet

53 (ISO 8192)