Trisodium, bis [2-((E)-(4-hydroxy-2-oxido-3-((E)-(5-sulfonatonaphthalen-1-yl)diazenyl)phenyl)diazenyl)benzoate] chromate(3-)

Biodegradation in water: screening tests

Description of key information

The test item is not rapidly biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Type of water:

freshwater

Additional information

Ready biodegradability of the test item was evaluated in an experimental study on 1 g/l aqueous solution of the test item which measured the 5-day Biochemical Oxygen Demand (BOD5), the Total Organic Carbon (TOC) using a Beckham 915A instrument, the Chemical Oxygen Demand (COD) and the bacterial inhibition by the glucose/glutamic acid modification of the BOD5 method (same concentrations as BOD5 method). BOD5 and bacterial inhibition were measured at concentrations of 1, 3.2, 10 and 32 mg/l test item without a nitrification inhibitor. A reference substance, glucose/glutamic acid, was tested at approximately a 1:47 dilution of the standard strength solution (150 mg/l of each compound) without nitrification inhibitor.

The inherent biodegradability of the test item was evaluated in an experimental study according to the OECD Guideline 302 B (1981), the Modified Zahn-Wellens Test. 251 and 250 mg/l test item was exposed to microorganisms from the secondary effluent of a domestic waste water sewage plant in test medium for 28 days, and samples were taken in in order to monitor dissolved oxygen concentration (DOC) in triplicate at 0 and 3 hours, 7, 14, 21 and 28 days of the incubation period. A negative control (inoculum in test water without test item) and a reference substance (99.5 mg/l ANILINE) were tested in parallel. pH was maintained between pH 7.0 and pH 8.5.

A substance is considered to be rapidly degradable in the environment if:

- in a 28-day ready biodegradability study, 70 % biodegradation is achieved in a test based on dissolved organic carbon (DOC) within 10 days;

- in a 28-day ready biodegradability study, 60 % biodegradation is achieved in a test based on oxygen depletion or carbon dioxide generation within 10 days;

- the ratio of BOD5/COD is ≥ 0.5 in the case that only BOD and COD data are available; or

- other convincing scientific evidence is available to demonstrate that the substance can be degraded (biotically and/or abiotically) in the aquatic environment to a level > 70 % within a 28-day period.

The BOD5 of the test item was found to be less than 3 % of COD, which is less than a ratio of 0.5, therefore the test item is not readily biodegradable. Inherent biodegradation of the test item was found to be 23 % over 28 days, which is less than 70 %, the amount required for classification. Based on these findings, the test item is not considered to be rapidly biodegradable.