Reaction mass of 4-methylene-2-phenyltetrahydro-2H-pyran and 4-methyl-2-phenyl-3,6-dihydro-2H-pyran

Toxicity to aquatic algae and cyanobacteria

Description of key information

A closely structurally-related compound, Pelargene, was found in a guideline and GLP study to have an 72 hour ErC50 of 10.2 mg/L and ErC10 of 8.2 mg/L. It was considered justifiable to use this measured data for Pelargene to read-across to Rosyrane on the basis that both substances are expected to have similar ecotoxicological properties as a result of structural similarity, the same expected aquatic toxicity mode of action and similar physicochemical properties. In fact, based on the relative hydrophobicity (as modelled by log Kow), the strength of effect(s) in the target substance is expected to be slightly lower than that observed for the source substance. Hence the prediction constitutes a worst case. 

Key value for chemical safety assessment

EC50 for freshwater algae:

10.2 mg/L

EC10 or NOEC for freshwater algae:

8.2 mg/L

Additional information

A valid study is available for the analogue substance, Reaction mass of rel-(2R,6R)-2-methyl-4-methylene-6-phenyltetrahydro-2H-pyran and rel-(2R,6R)-4,6-dimethyl-2-phenyl-3,6-dihydro-2H-pyran and rel-(2R,6R)-2,4-dimethyl-6-phenyl-3,6-dihydro-2H-pyran (Trade Name: Pelargene). It is a GLP compliant study conducted in compliance with agreed protocols, with no deviations from the standard test. Important considerations for the use of read-across are:

 

i)  There are structural similarities between the two chemicals. Both substances are isomeric mixtures of phenyl substituted tetrahydropyrans and dihydropyrans. The only, structural difference is the presence of an extra methyl group in the source substance, Pelargene. This does not affect the mode of action but will lead to the source substance being slightly more hydrophobic and hence slightly more toxic to aquatic organisms than the target substance, Rosyrane (see also point v). Therefore the predicted strength of aquatic effects for Rosyrane is based on a worst case.

ii)  Both substances are expected to act via the same mode of action for aquatic toxicity. The major isomer in both substances is a tetrahydropyran and classed as a neutral organic molecule for which the mode of action is considered to be simple non-polar narcosis. The minor isomers in both substances are dihydropyrans and are assigned to the vinyl/allyl ether ECOSAR class. The ratio between the major isomer (neutral organic class) and minor isomers (vinyl/allyl ether class) is similar in both substances and hence both substances are considered to have similar overall mechanistic profiles.

iii) There are no impurities that are expected to affect the ecotoxicological properties of the source and target substance

iv) Both substances have similar physico-chemical properties relevant for fate and behaviour of the substance under aquatic toxicity test conditions (e.g. vapour pressure, water solubility and log Kow). Both substances are not readily biodegradable

v) Hydrophobicity (as modelled by log Kow) is a known determinant of the toxicity in aquatic organisms. The measured log Kow values for Rosyrane and Pelargene are 3.1, 3.3 (isomers) and 3.8 (two main peaks) respectively. As the source substance (Pelargene) has the higher logKow it is expected to exhibit the highest aquatic toxicity of the two substances and thus read-across of aquatic toxicity data from this source substance to Rosyrane will be conservative and worst-case

 

Based on the above, the read-across is justified and considered adequate for the purpose of classification and labelling and/or risk assessment