Myrtus communis, ext.

Short-term toxicity to fish

Description of key information

Myrtle oil is a Natural Complex Substance (UVCB) with a well-defined composition for which the relative percentage and its reported variation of each constituent is known. The acute toxicity to fish property has been investigated using an in-house calculation method that mimics an OECD 203 study and guideline for Testing of Chemicals No. 23 (i.e. WAF conditions). The acute toxicity to fish was determined using a calculation method for Mode of Action 1 (non-polar narcotics) for each individual constituent present in the mixture. This algorithm is based on a QSAR model which has been validated to be compliant with the OECD recommendations for QSAR modeling (OECD, 2004). Further to this, the lethal loading rate of the WAF is determined by using a series of calculation steps using phase equilibrium thermodynamics first to determine the analysable fraction (the concentration which should be analysable in a WAF study) and then excluding the non-bioavailable fraction of the remaining constituents. The remaining, bioavailable fraction corresponds to the lethal loading value of the mixture. This approach has been validated using data derived from 96-hour LL50 tests on fish with similar complex substances (OECD 203 study and the OECD guidance document on toxicity testing for difficult substances and mixtures No. 23, i.e. WAF conditions). Two theoretical compositions have been investigated, the “typical” composition proposed by the Lead registrant and a theoretical worst case composition that maximizes the concentration of the most toxic constituents. The 96-h LL50 was 4.3 mg test material/L for the typical composition of Myrtle oil, and the 96-h LL50 was 3.5 mg test material/L for the theoretical worst case composition. LL50s were based on mortality. Conclusion: The 96-h LL50 for fish was calculated at 4.3 mg test material/L for the typical composition and at 3.5 mg test material/L for theoretical worst case composition.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

3.5 mg/L

Additional information

 

Short-term toxicity to fish is provided in the dataset even if the tonnage band (1 -10 tonnes/year) does not require that endpoint. Indeed that endpoint is fulfilled according to environmental classification rules. Classification should be derived from the most sensible species. Because toxicity data have demonstrated the lowest LC50 values for constituents, it has been decided to calculate fish L(E)C50, in order to ascertain the classification for environment of Myrtle oil.

 

Myrtle oil is a Natural Complex Substance (UVCB) with a well-defined composition for which the relative percentage of each constituent is known. Therefore, it has been decided that the ecotoxicity of Myrtle oil will be derived from knowledge of the constituents, constituent approach

The mixture ecotoxicity properties may be derived from the ecotoxicity of the individual constituents (table 1) using the CLP additivity calculation approach. However, CLP additivity approach is calculated on the basis that all the substances are at their maximum solubility and it has been observed that CLP additivity calculations for mode of action 1 compounds are unreasonably conservative when compared to classic WAF studies. This has been proved in a number of cases for natural complex substances. Indeed, natural extract compositions are a mixture of hydrophilic alcohol molecules and hydrophobic terpene molecules. Therefore, when a WAF is performed most of substances fully dissolved in the aqueous phase are the hydrophilic fraction while the hydrophobic fraction (the more toxic elements for MOA 1 substances) may be below their water solubility value.

 

The acute toxicity to fish property for Myrtle oil has been investigated using an in-house calculation method (iSafeRat WAF module for mixture Toxicity calculation) that mimics an OECD 203 study and guideline for Testing of Chemicals No. 23 (i.e. WAF conditions). Two theoretical compositions have been investigated, the “typical” composition proposed by the Lead registrant and a theoretical worst case composition that maximizes the concentration of the most toxic constituents.The acute toxicity to fish was determined using a calculation method for Mode of Action 1 (non-polar narcotics) for each individual constituent present in the mixture. This algorithm is based on a QSAR model which has been validated to be compliant with the OECD recommendations for QSAR modeling (OECD, 2004).

The first step of the iSafeRat mixture toxicity calculation employs phase equilibrium thermodynamics in order to determine the concentrations of each constituent within the WAF. This fraction equates to the analyzable fraction of a WAF study.

In the calculation the second step is to remove this non-bioavailable fraction. Within the WAF, the constituents also partition between themselves further reducing the bioavailable fraction and thus the toxicity of the mixture compared to the individual constituents. These two reasons explain why ecotoxicity values from WAF studies are always higher for non-polar narcotic mixtures than the calculated values from CLP additivity calculation.

 

The final step is to determine the truly bioavailable fraction of the WAF per constituent. The LC50s of each constituent are already known from literature or predicted using the iSafeRat QSAR model. Each value has been included as a supporting study in the IUCLID. An additivity approach (based on Chemical Activity of each constituent) is used in order to calculate the Lethal Loading of the WAF. Using this approach, the 96-h LL50 for fish was 4.3 mg test material/L for the typical composition of Myrtle oil, and the 96-h LL50 was 3.5 mg test material/L for the theoretical worst case composition. These LL50 were based on mortality. 

 

The in-house calculation has been designed to mimic the behavior of the mixture in a WAF test where the final toxicity is calculated by additivity of the residual bioavailable fraction of each constituent. This approach has been validated using a Natural Complex Substance similar to myrtle oil as presented in the position paper attached to the dossier.

 

Based on the results of this study, Myrtle oil would not be classified as acutely toxic to aquatic organisms in accordance with the classification of the CLP.

This toxicity prediction has been validated and is considered acceptable to fulfill the fish toxicity endpoint.

 

Table 1 Myrtle oil, constituents data used to derive Myrtle oil Ecotoxicity value.

constituent	typical composition (%)	worst case concentration (%)	96-fish LC50 (mg/L)	96-fish LC50 reference
α-pinene	26.00	35.00	0.280 [0.259 – 0.303]	experimental data
cineol 1,8	29.00	25.00	57 [32 – 100]	experimental data
myrtenyl acetate	13.00	20.00	7.61 [6.18 – 9.36]	iSafeRat® prediction
limonene	11.00	15.00	0.71 [618 – 839]	experimental data
linalool	4.60	2.20	55.13 [45.08 – 67.46]	iSafeRat® prediction
terpineol	3.50	2.00	60.93 [49.60 – 74.89]	iSafeRat® prediction
para-cymene	0.40	0.40	1.63 [1.21 – 2.20]	iSafeRat® prediction
β-pinene	0.40	0.40	0.44 [0.29 – 0.66]	iSafeRat® prediction