Cineole

Toxicity to aquatic algae and cyanobacteria

Description of key information

The toxicity of the test substance to the freshwater algae Pseudokirchneriella subcapitata was investigated according to OECD Guideline No. 201 and gave a 72-hour growth rate EC50 value of >74 mg/L/  The corresponding No Observed Effect Concentration was 37 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

74 mg/L

EC10 or NOEC for freshwater algae:

37 mg/L

Additional information

Following a preliminary range-fining test, Pseudokirchneriella subcapitata was exposed to solutions of the test item at nominal concentrations of 6.25, 12.5, 25, 50 and 100mg/l for 96 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. The test item was known to be volatile and hence testing was conducted in completely filled, stoppered test vessels in order to minimise possible losses due to volatility.

Analysis of the test preparations at 0 hours showed measured test concentrations to be near nominal with the exception of the 50 and 12.5 mg/l test samples which showed measured test concentrations of 76% and 77% of nominal were obtained. Given the extremely volatile nature of the test item (EPIWIN V3.20 predicted Henry's law constant = 96 Pa.m³/mol) it was considered that the failure to obtain near nominal test concentrations in all instances was due to losses through volatilisation despite every care and precaution having been made to minimise such losses. Analysis of the test preparations at 72 hours showed a decline in measured test concentrations in the range of 70% to 73% of nominal. A similar decline in measured test concentrations was observed at 96 hours in the range of 64% to 70% of nominal.

Due to the volatile nature of the test item, additional test replicates were prepared at 0 hours and incubated alongside the test to provide samples for unopened vessel analysis at 96 hours. Analysis of these preparations showed measured test concentrations to range from 65% to 76% of nominal thereby indicating that the decline observed was due to possible instability and/or adsorption of the test item to the algal cells present rather than losses due to volatility. Given this decline in measured test concentrations it was considered justifiable to base the results on the time-weighted mean measured test concentrations in order to give a "worst case" analysis of the data. The time-weighted mean measured test concentrations were determined to be 4.7, 9.1, 18, 37 and 74 mg/l.

A re-growth test was performed which showed the test item to be algistatic in effect.

A positive control test showed that the use of a modified test system to reduce losses of test item through volatility (completely filled and sealed test vessels) had a slightly lowering effect on the EC50 values obtained, and, a notable effect on the No Observed Effect Concentration (NOEC) compared with that obtained in a conventional test system. As such, it can be considered that the results obtained from the definitive test system give a worst case result for the test item.

The preferred observational endpoint in this study is algal growth rate inhibition because it is not dependent on the test design (ECHA guidance Chapter R.7b v1.1). Thus the ErC50 value of > 74mg/l has been used for the chemical safety assessment.