(Z)-cyclooctene

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The biodegradability of Z-cyclooctene was evaluated in tests on ready biodegradability and inherent biodegradability. Although both tests showed that this substance is not ready biodegradable, the study on inherent biodegradation (Hüls 1996) showed 28% degradation after 28 days and thus indicates that Z-cyclooctene can be metabolized and degraded by microorganisms.

Furthermore, QSAR calculations with Biowin indicate a biodegradation potential for the substance fulfilling the ECHA screening criteria for not persistent substances according to the Guidance on information requirements and chemical safety assessment PartC and chapter R.11 (European Chemicals Agency, 2008). The calculation with Biowin 2 indicates that the substance biodegrades fast (probability > 0.5 (0.81)) and Biowin 3 ultimate biodegradation timeframe is lower than months (weeks; value of 2.96), Moreover Biowin 6 also indicates that Z-cyclooctene biodegrades fast (probability is also > 0.5 (0.7)).

In addition to these results, it is highly improbable that Z-cyclooctene reaches the water, the soil or sediments in significant amounts since it is manufactured and used under dry conditions in closed systems. Even in case that the substance would be released to the environment, the Mackay level I calculations indicate that the substance would be distributed to the atmosphere at > 99%. Therefore the target compartment for Z-cyclooctene is the atmosphere. The half life in the atmosphere has been calculated to be approximately 2 h, meaning that this chemical will not be long distance transported and it will not persist in the environment.

Altogether the substance is considered to be not persistent, although the tests showed no ready biodegradability.

Information about the bioaccumulation of Z-cyclooctene in aquatic/sediment species was considered not necessary due to the lack of exposure. The substance is to be manufactured and used in dry processes and only in closed systems.Since the exposure to water and sediment compartment is negligible (please refer to point 9)no estimation of bioaccumulation will be required.

Calculations with QSAR (BCFBAF v3.00) resulted in a value of 924.7 L/kg wet weight, which is below the criterion for bioaccumulative behaviour. Since a measured BCF value is not available, experimentally derived or calculated log Kow values can be used as a screening criterion. The measured log Kow is 5, indicating a potential to bioaccumulate.

In contrast to this, a published study showed the formation of sulfur containing metabolites in female rabbits and rats. Animals received a single dose of 2 mmol (220mg) per kg bw, 24h urine was collected and analysed. More than 80% of the dose was recovered as sulfur containing metabolites of which 2-hydroxy and 3-hydroxy-mercapturic acids were identified. More than 80% of an oral dose of 2 mmol cyclooctene (220mg)/kg bw was excreted within 24h as sulfur containing metabolites indicating extensive absorption and extensive metabolism including hydroxylation as well as rapid excretion. Based on this study result no bioaccumulation potential can be observed.

Based on these data it can be concluded that the criterion for bioaccumulation (B) might be fulfilled, but the criterion for very persistent substances is not fulfilled

Cis-cyclooctene is not classified as carcinogenic, mutagenic or toxic for reproduction and it is not classified as T, R48 or Xn, R48 according to Directive 67/548/EEC. No chronic toxicity data are available due to the lack of exposure of the aquatic organisms (the substance is manufactured and used only in closed systems and sampling, filling and transport takes place only in closed systems). The lowest acute L/EC₅₀ value is > 0.1 mg/L, indicating that the substance is not considered to meet potentially the T-criterion. Therefore, cis-cyclooctene does not fulfil the T criterion.