1,1'-methylenebis(4-isocyanatobenzene) and its oligomeric reaction products with butane-1,3-diol, 2,2'-oxydiethanol and propane-1,2-diol

Toxicity to microorganisms

Description of key information

The potential toxicity of the source substances of the category 4,4’-MDI and 4,4’-MDI/DPG/HMWP to activated sludge microorganisms was investigated, following the current OECD 209 guideline under GLP (Reliability 1). To determine the potential toxicity to microorganisms, the tested substances were directly added by initial weight into the test flasks. Activated sludge was exposed for a period of 3 hours to concentrations of 1,000; 500; 250; 125 and 62.5 mg/L (nominal). After the testing period, total oxygen consumption was measured, and the consumption rate determined. EC50 (3h) values of greater than 1,000 mg/L were obtained for both substances (Dammann et al., 2020). Since no effects on gross respiration were observed, the potential effects on nitrifying respiration was not investigated. Supporting evidence is provided by an OECD 209 study using pMDI, in which also no adverse effects have been observed (Caspers et al., 1986).
Based on the respiration rate using activated sludge, the 3h-EC50 was found to be >100 mg/L, since no hazard was identified up to the highest loading rate tested, no PNEC could be derived.

The available tests of ready biodegradability (OECD 301F) for the source substances included toxicity control reactions that did not provide evidence for inhibition of the dilute microbial inoculum by the 100 mg/L (nominal) concentrations of these test substances. The data confirm that MDI substances are not harmful to microorganisms. The available data are reliable and therefore adequate for risk assessment purposes. Additional testing is not suggested.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L