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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB
Justification:

The registered substance is not readily biodegradable but a strong and consistent evidence of mineralisation was provided. Therefore, the registered substance is not persistent (P) in the environment. However, based on data lacking on degradation potential of the identified degradation products (DD-ma, which is the main degradation product, and two other larger metabolites: DD-mp and DD), these compounds are potentially persistent (P) or very persistent (vP) in the environment.

With a measured log Kow value at 9.5 and an experimental BCF result lower than 38, the registered substance is not bioaccumulable (B). This is supported by the fact that no mammalian or environmental toxicity was found in acute or longer term studies performed to date. For degradation products, the log Kow values were estimated using QSAR calculations, to be lower than 4.5 (3.1 for DD-ma, 3.3 for DD-mp and 3.6 for DD). Therefore, these compounds are not considered bioaccumulable (B) or very bioaccumulable (vB).

Finally, the registered substance is presumably not toxic (T) based on the absence of acute toxic effects on aquatic organisms up to and significantly higher than its solubility limit in test water. Based on the very low water solubility of the parent substance, it's technically not feasible to obtain relevant endpoints values. In addition, the degradation products are also presumably not toxic (T) based on the estimated L(E)C50 values greater than 0.1 mg/L for aquatic organisms.

In conclusion, the registered substance and the corresponding degradation products could not be considered as a PBT or vPvB substances.

Likely routes of exposure:

None

Environmental fate and pathways:

As described in the physical and chemical properties summary, the registered substance is a liquid of very low water solubility and very low volatility.

The registered substance is not readily biodegradable but a strong and consistent evidence of mineralisation was provided. Therefore, the registered substance is inherently biodegradable (not fulfilling specific criteria) and not persistent in the environment. Delta-Damascone mercapto acetic acid (DD-ma) was identified as the main degradation product. This compound is slowly degraded and in the absence of other biodegradation study on this metabolite, DD-ma is considered as potentially persistent (P) or very persistent (vP).All larget metabolites found can be considered as transient intermediates.

Regarding the bioaccumulation potential, with a measured log Kow value at 9.5, the registered substance would not be expected to bioaccumulate significantly. This statement was confirmed with an experimental bioaccumulation study, performed for a Japan notification on the registered substance, and showing a BCF value lower than 38. The registered substance is not considered as bioaccumulable. Also, the final degradation product of the registered substance, DD-ma, is not expected to bioaccumulate significantly in the environment with a log Kow at 3.1 (arithmetical mean value of QSAR results).

Finally, the adsorption coefficient (Koc) of the registered substance was estimated by the KOCWIN v2.00 model to be 1953500 L/kg (log Koc = 6.3), using an experimental log Kow value at 9.5, indicated that the registered substance is immobile in soil(according to P.J. McCall et al., 1981).

Aquatic toxicity:

Acute data, reliable with restrictions (Klimisch rating), based on international guidelines, are available to assess the toxicity of the registered substance to the three trophic levels: Algae, Invertebrates and Fish.

Based on the very low water solubility of the substance, it's technically not feasible to obtain a relevant endpoint value. The substance had no acute toxic effects on aquatic organisms up to and significantly higher than its solubility limit in test water.

In addition, according to the supporting acute toxicity study onDaphnia magna(Fraunhofer, 2013), the total lack of reproducibility within the various replicates and concentration levels demonstrates that it is not technically feasible to dissolved the substance in solution and to obtain reliable concentrations. Therefore, it is not possible to conduct a chronicDaphniatest and moreover aquatic toxicity tests in general are not likely to be technically feasible for this substance.

As a strong and consistent evidence of mineralisation of the registered substance was provided, the acute toxicities of the degradation products, which are the relevant species for the environmental risk assessment, were determined using the ECOSAR v1.11 QSAR model available from the U.S. EPA. The assessed degradation products were Delta-Damascone mercapto acetic acid (DD-ma) (which is the main degradation product) and two other larget metabolites (Delta-Damascone mercapto proprionic acid (DD-mp) and Delta-Damascone (DD)).

The degradation products are presumably not toxic (T) in a PBT assessment context.

The registered substance was considered as non-toxic to the microorganisms of a water treatment plant (3h-EC50 > 1000 mg/L).