α-methylenebenzyl acetate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Toxicity to aquatic algae: 72 h EC50 3.0 mg/l, EC10 0.38 mg/l and NOEC 0.32 mg/l (nominal concentration), OECD 201

Key value for chemical safety assessment

EC50 for freshwater algae:

3 mg/L

EC10 or NOEC for freshwater algae:

0.32 mg/L

Additional information

A 72 hour ErC₅₀ value of 3.0 mg/l, an ErC₁₀ value of 0.38 mg/l and a NOEC value of 0.32 mg/l, based on nominal concentrations, have been reported for the effects of α-methylenebenzyl acetate on growth rate of Desmodesmus subspicatus. A 72 hour EyC₅₀ value of 0.73 mg/l, EyC₁₀ value of 0.29 mg/l and NOEC value of 0.32 mg/l, also based on nominal concentrations, have been reported for the effects of α-methylenebenzyl acetate on yield of Desmodesmus subspicatus.

Considerable loss of test material was experienced during the algae test. During validation of the analytical method, there was low recovery of the test item under the test conditions. Therefore the content of the test item in the test solutions was determined at the beginning and every 24 hours using gas chromatography. The measured concentrations were in the range of 89 - 95 % of the nominal concentration at the start of the test. At the end of the test, no test item was detectable.

The low recovery of test material is unexplained and is not thought to be due to volatilisation or hydrolysis reaction. Therefore it is likely that the test substance is not being lost from the test system, but may be adsorbing to the biomass or undergoing some sort of biological reaction with the algae. The decrease in concentration of the test substance in the course of the test was not accompanied by a decrease in growth inhibition.

For these reasons, the nominal test substance concentrations are used to calculate the EC₅₀, EC₁₀ and NOEC values, following Point 40 from the OECD 201 guidance:

"The algal growth inhibition test is a more dynamic test system than most other short-term aquatic toxicity tests. As a consequence, the actual exposure concentrations may be difficult to define, especially for adsorbing substances tested at low concentrations. In such cases, disappearance of the test substance from solution by adsorption to the increasing algal biomass does not mean that it is lost from the test system. When the result of the test is analysed, it should be checked whether a decrease in concentration of the test substance in the course of the test is accompanied by a decrease in growth inhibition. If this is the case, application of a suitable model describing the decline of the concentration of the test substance may be considered. If not, it may be appropriate to base the analysis of the results on the initial (nominal or measured) concentrations."