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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Administrative data

Link to relevant study record(s)

Description of key information

Toxicity to aquatic algae has been assessed in two reliable studies conducted with substances that would fall within the MDI category definition. The studies used water accommodated fractions or saturated solutions as the test items are poorly soluble. Both studies demonstrated EC50 values above the highest concentration tested, and NOEC values at the highest test concentration.

Based on these results, members of the MDI category are not expected to be toxic to aquatic algae at the limit of solubility.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
100 mg/L

Additional information

Three studies were conducted on three different MDI category members in order to assess toxicity to aquatic algae. Two of the studies are considered to be reliable and one is unreliable, and has therefore been disregarded from the assessment.


A study was performed to assess the effects of Reaction product of 4,4’-methylenediphenyl diisocyanate and amines, coco alkyl on the growth of the green alga Pseudokirchneriella subcapitata (Vryenhoef 2018). The method followed was designed to be compatible with the OECD guideline 201, “Freshwater Alga and Cyanobacteria, Growth Inhibition Test”. Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to Water Accommodated Fractions (WAF) at a single nominal loading rate of 100 mg/L (six replicate flasks) for 96 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter.


EL50 values for growth rate and yield were determined to be greater than 100 mg/L WAF. Correspondingly the No Observed Effect Loading Rate was 100 mg/L WAF. It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/L. LC-MS/MS analysis of the test preparations was performed at 0 and 96 hours and measured concentrations of less than the limit of quantification (0.00046 mg/L) were obtained. Given that the toxicity cannot be attributed to a single component or a mixture of components but to the test item as a whole the results were based on nominal loading rates only.


A second study was performed to assess the effect of 3,3'-dicyclohexyl-1,1'-methylenebis(4,1-phenylene)diurea (EC 406-370-3) on the growth of the green alga Desmodesmus subspicatus. The method followed was designed to be compatible with the EC Method C3 and a nominal loading rate of 1 mg/L was used. The study determined EC50 and NOEC values for growth rate and biomass of greater than 1 mg/L, the limit of water solubility.

One study conducted with N,N''-(methylenedi-4,1-phenylene)bis[N'-octyl]urea (EC 445-760-8) did show effects below the highest concentration tested. This study was included in a NONS registration and permission to refer has been granted by ECHA under an Article 25(3) request. A limited summary was provided in the data received from ECHA. Reference to the same study on the ECHA dissemination portal indicates that the study has subsequently been disregarded by the registrants as the study used very high nominal loading rates (up to 4000 mg/L) and only analysed for one constituent of the substance, which was found to be in solution at <LOQ (0.5 mg/L). As the analysed constituent was present at <LOQ but a dose-response relationship was observed at the highest loading rates, toxicity appears to be attributed to an unknown impurity in the test item. As it is not possible to determine which constituent the observed toxicity is attributed to, the water solubility of the main constituent should not be used for the reporting of results, as this is not the constituent that is leading to the observed toxicity. This study has therefore been disregarded as the results are unreliable.