A mixture of: 3,3'-dicyclohexyl-1,1'-methylenebis(4,1-phenylene)diurea; 3-cyclohexyl-1-(4-(4-(3-octadecylureido)benzyl)phenyl)urea; 3,3'-dioctadecyl-1,1'-methylenebis(4,1-phenylene)diurea

Toxicity to aquatic algae and cyanobacteria

Description of key information

In freshwater green algae, the 72 -h ErC50 and 72 -h ErC10 values are determined to be >100 mg/L based on nominal concentrations (or > limit of solubility in test medium).

Additional information

The toxicity to algae was examined in a study according to OECD 201 and in compliance with GLP criteria. Cultures of freshwater green algae (P. subcapitata) at a starting cell concentration of ca. 1E+04 cells/mL were exposed to 100% and 10% of a filtrate prepared at a loading rate of 100 mg/L (after 96 hours stirring) for under static conditions for 72 hours. No analysis of the dissolved test item could be performed as no analytical method was available for the substance. Throughout the test cell densities were determined by spectrophotometric measurement of samples using a spectrophotometer with immersion probe. After 72 hours exposure to 100% of a filtrate prepared at a loading rate of 100 mg/L, a statistically significant reduction of growth rate of 9% was found. However, the percentage of growth rate reduction was < 10% and therefore considered to be biologically not relevant. Based on these findings, the 72 -h ErC50 and 72 -h ErC10 values were determined to be higher than the limit of solubility in test medium. The test is valid.

In a second algae toxicity study, also according to OECD TG 201 and in compliance with GLP criteria, cultures of green algae (S. subspicatus) at a starting cell concentration of ca. 1E+04 cells/mL were exposed to nominal concentrations of 0 (control) and 100 mg/L for 72 hours under static conditions and continuous illumination. No analytical determination of the concentrations of the dissolved test item could be performed due to the very low water solubility of the test item and the low sensitivity of the analytical method. For these reasons the test was not performed with filtrates of a stock suspension, but, in order to secure that the maximum bioavailable concentration is maintained during the test period, with a suspension of the test item above the water solubility limit. Therefore, the test medium was prepared with the emulsifier Tween 80. A solvent control was tested in parallel. For determination of the maintenance of the nominal test item concentration during the test period, quantification of the test medium was performed spectrophotometrically by VIS-detection at 250 nm at the start of the test and after 72 hours (in test solutions without algae). The mean recoveries found in the treatment samples were 102% at the start of the test, and 95% after 72 hours, exposure indicating that the test substance was nearly stable during the performance of the biological test. At the end of the test, algae in the test medium were partially aggregated with substance particle and therefore were treated ultrasonically before determining the algal cell densities. Possible 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. Therefore, it was concluded that the concentration of the substance tested was satisfactorily maintained within ± 20 % of the nominal concentration, and the results are expressed as nominal.

The mean algal cell densities in the test medium were identical to, or even slightly higher than in the parallel solvent control cultures. Thus, the test item had clearly no inhibitory effect on the growth of algae during the exposure period of 72 hours. Based on these findings, both the 72 -h ErC50 and the 72-h ErC10 are determined to be >100 mg/L based on nominal concentrations (or > limit of solubility in test medium).