Bis(2,6-diisopropylphenyl)carbodiimide

Biodegradation in water: screening tests

Description of key information

Carbodiimide: The substance can be considered to be "not readily biodegradable".
Main hydrolytical degradation product (DIPA): The compound can be considered to be "not readily biodegradable".

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

Regarding biodegradation in water (screening tests) two experimental results (both key studies with reliability 1) are available for the substance bis(2,6-diisopropylphenyl)carbodiimide. Both studies were conducted in compliance with the Principles of Good Laboratory Practice (GLP) and all validity criteria of the corresponding guideline were met.

Weyers (2009) performed an experiment according to EU method C.4 -D, which is equivalent to OECD Guideline 301 F. A measured volume of inoculated mineral medium, containing the test item in a concentration of 100 mg/L, giving at least 50 - 100 mg ThOD/L as the nominal sole source of organic carbon, was stirred in a closed flask at a temperature of 22 +/- 1 °C for up to 28 days. A mixed population of aquatic organisms (activated sludge) was taken as inoculum, taken from an aeration tank of a wastewater plant treating predominantly domestic sewage (Wupper area water authority, STP Odenthal). The concentration of the inoculum was 30 mg/L. The mineral medium was prepared from stock solutions of mineral components; a mineral salt solution, magnesium sulphate solution, calcium chloride solution as well as an iron(III) chloride solution. Sodium benzoate (with a purity of 100.1 %) was used as reference compound. Also a toxicity control (test item and reference compound mixed) was run in parallel, to ensure, that the chosen test concentration was not inhibitory to microorganisms. The consumption of oxygen (BOD) was determined by measuring the quantity of oxygen (produced electrolytically) required to maintain a constant gas volume in the respirometer flask. Evolved carbon dioxide was absorbed in a solution of potassium hydroxide. The amount of oxygen taken up by the test item (corrected for uptake by blank inoculum, run in parallel) was expressed as a percentage of theoretical oxygen demand (ThOD) or chemical oxygen demand (COD). The test item is an N-containing compound; therefore, the increase in concentration of nitrite and nitrate over the test period was determined. The oxygen consumed by nitrification was calculated. This oxygen consumption by nitrification was subtracted from the respective measurements. Within 28 days, a degradation of 1 % was determined for the test compound. Therefore it can be considered to be "Not Readily Biodegradable". Due to the toxicity control it can be concluded, that the used concentration of the test item did not show toxic effects to the microorganisms. The reference compound reached the level for ready biodegradability within 14 days and after 28 days a degradation of 87.2 % was determined.

In another study, the test substance was investigated according to OECD Guideline 301B, EU method C.4 -C and US EPA Fate, Transport and Transformation Test Guidelines OPPTS 835.3110 Paragraph (m) (Mead, 2001). The study was conducted in compliance with the Principles of Good Laboratory Practice (GLP). A mixed population of activated sewage sludge micro-organisms collected from the aeration stage of the Severn Trent Water Plc (UK), which treats predominantly domestic sewage was used as inoculum. For the purpose of the definitive study the test material was dispersed directly in culture medium. It was used in a concentration of 10 mg carbon/L for the study. Sodium benzoate (C6H5COONa) was used as reference substance. The test material plus the reference substance in inoculated culture medium gave a final concentration of 20 mg carbon/L acting as toxicity control. A blank (inoculated culture medium) was run in parallel. Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids (ss)/L. The study was conducted under aerobic conditions in a temperature controlled room at 21 °C, in darkness. Each CO2 and DOC (Dissolved Organic Carbon) analysis was carried out in triplicate. The pH was measured at the end of the test. Sodium benzoate attained 83 % degradation after 28 days thereby confirming the suitability of the inoculum and test conditions. The toxicity control attained 38 % degradation at the end of the test which confirms that the test material was not toxic to the sewage treatment microorganisms used in this experiment. Inorganic carbon (IC) analysis of the samples form the second absorber vessel on Day 29 confirmed that no significant carry-over of CO2 into the absorber vessel occurred. The degradation rates calculated from the results of the DOC analysis were higher than those calculated from IC analysis. This was considered to be due to incorporation of sodium benzoate into the microbial biomass prior to degradation, and hence CO2 evolution occurring. The test material attained 3 % degradation after 28 days and therefore cannot be considered to be "readily biodegradable" under the strict terms and conditions of OECD Guideline 301B.

Additionally, as supporting data a QSAR calculation was performed to predict the biodegradability potential of the test substance due to its chemical structure. The prediction was determined by the computer program BIOWIN v4.10 (EPIWIN software) of US-EPA. The program calculates with seven different models: Linear Model (Biowin 1), Non-linear Model (Biowin 2), Ultimate Biodegradation Timeframe (Biowin 3), Primary Biodegradation Timeframe (Biowin 4), MITI Linear Model (Biowin 5), MITI Non-linear Model (Biowin 6) and Anaerobic Model (Biowin 7). The overall result gives the ready biodegradability prediction of the desired compound. According to Biowin 1 and 2 the substance is biodegrading fast. The Ultimate Biodegradation Timeframe is given in months, whereas the Primary Biodegradation Timeframe gives weeks as result. Both MITI Models predict that the substance is not readily biodegradable, which is also the overall prediction result. Also under anaerobic conditions the substance is not expected to be degraded fast.

For the main hydrolytical degradation product DIPA biodegradation potential was also modelled. The prediction for biodegradability of 2,6-diisopropylaniline, (CAS 24544 -04 -5) was determined by the computer program BIOWIN v4.10 (EPIWIN software) of US-EPA. The program calculates with seven different models: Linear Model (Biowin 1), Non-linear Model (Biowin 2), Ultimate Biodegradation Timeframe (Biowin 3), Primary Biodegradation Timeframe (Biowin 4), MITI Linear Model (Biowin 5), MITI Non-linear Model (Biowin 6) and Anaerobic Model (Biowin 7). The overall result gives the ready biodegradability prediction of the investigated compound. According to Biowin 1 the substance is biodegrading fast, whereas Biowin2 estimates that the compound does not biodegrade fast. The Ultimate Biodegradation Timeframe is given in weeks-months, whereas the Primary Biodegradation Timeframe gives days-weeks as result. Both MITI Models predict that the substance does not biodegrades fast. Also under anaerobic conditions the substance is not expected to be degraded fast. The overall Ready Biodegradability Predictions reveals: No.