2-Methylpropene, trimers

Toxicity to aquatic algae and cyanobacteria

Description of key information

The 96 hr EC50 for algae was calculated to be 1.099 mg/L for a representative C8 structure. Experimental data are available for C12 and C16 streams in this category which show no effects at saturation.

Key value for chemical safety assessment

EC50 for freshwater algae:

1.099 mg/L

Additional information

Two studies were available for streams in this category (97280-83-6 dodecene, branched predominant carbon number of C12 and 9003-29-6 butene, homopolymer predominant carbon number of C16). 

Huntingdon Life Sciences (2009b) report that due to the low solubility of dodecene, branched a WAF method was used to prepare the stock solution. The WAF was prepared by adding 100 mg of the test item to the test media and stirring overnight. This solution was used as the single exposure concentration in a 72 hour static test. Results are reported based on the nominal loading rate. No effects were observed at this concentration. The 72 hour EC50 was therefore determined to be > 100 mg/L WAF and the NOEC was 100 mg/L WAF. 

Dr. U. Noack-Labortorien (2009) also used a WAF method was used to prepare the stock solution of butene, homopolymer due to the low solubility of the test substance. 100 mg of the test item was added to the test media and stirred for 24 hours. This solution was used as the single exposure concentration. Samples were taken to confirm the exposure concentrations at the start of test. The measured concentration at the highest loading rate was 19.2 mg/L. No effects were observed on growth rate or yield at this concentration. The 72 hour EC50 was therefore determined to be > 19.2 mg/L and the NOEC was 19.2 mg/L. This value have been used in the PBT assessment of this category.

QSAR estimates (ECOSAR, part of EPISuite V4.0) were used to predict toxicity based on representative members of the category. The 96 hour EC50 for algae was calculated to be 1.099 mg/L for a representative C8 structure. For C12, the 96 hour EC50 for algae was calculated to be 0.104 mg/L but as experimental data are available which shows no effects at saturation the QSAR estimate for the C12 structure will not be used further in the assessment. For C16 structures, the QSAR model predicted no effects at saturation which supports the experimental data for the C16 stream.