Dihydrogen (ethyl)[4-[4-[ethyl(3-sulphonatobenzyl)]amino]-2'-sulphonatobenzhydrylidene]cyclohexa-2,5-dien-1-ylidene](3-sulphonatobenzyl)ammonium, disodium salt

Biodegradation in water: screening tests

Description of key information

The test substance is not readily biodegradable (according to OECD criteria).

Additional information

A GLP guideline study according to OECD 301B has been conducted (BASF SE 2016). Activated sludge from a municipal sewage plant was exposed for 28 d and the CO2-Evolution was determined. After 28 d the biodegradation was determined to be < 10%. Therefore, the test substance is not readily biodegradable.

Additional, two literature studies are available: Pagga and Brown (1986) conducted a static test according to a modified OECD Guideline 302 B. 100 mg/l of the dye was added to 500 mg activated sludge (ds)/l and degradation based on the DOC content (initial concentration: 56 mg/L) was measured over a period of 42 days. For the test substance a degradation of 45 % was measured. Since an elimination of 14 % was measured in the first three hours of this test, the authors classified the substance, based on their own criteria, as being capable of only partial elimination from water, or potentially biodegradable.

Tonogai et al. (1978) performed aerobic and anaerobic tests on the degradation of dyes. In aerobic tests 750 ml activated sludge from the municipal sewage plant in Nakahama, Osaka, was acclimated for one week or more to a synthetic effluent solution (glucose-peptone-potassium dihydrogen phosphate solution) and then spiked with 250 ml 0.03 M (= 23.8 g/L) dye solution. The suspension was aerated at 20 °C and 5 ml samples were taken daily for DOC analysis. After a 10-day experimental period the test substance was degraded by about 5 %.

Anaerobic tests were performed by a similar method. Instead of air, nitrogen was injected into the suspension and the containers sealed. Degradation under anaerobic conditions was somewhat more rapid than under aerobic conditions, about 25 % having been degraded after a 6-day experimental period.

Furthermore, the BUA Report 242 (2002) cites the investigations of Borgerding and Hites (1994) and Jank et al. (1998) are summarized:

In investigations on the aerobic degradation of food and cosmetic dyes in a municipal sewage plant, containing effluent from a plant producing food and cosmetic dyes, Borgerding and Hites (1994) found that the test substance was not degraded. The measured values were 0.520 ± 0.066 mg/l in the sewage plant inlet and 0.530 ± 0.060 mg/l in the outlet (residence time not indicated).

The authors qualify their results, stating that they represent only daily values and that concentrations may vary greatly depending on the effiuent quantity of the emission source. The very acidic sulphonate groups (pKs of about 1.5), on each of the three aryl groups of the molecule, prevent sorption to sewage sludge and thus cause all of the substance to remain in the aqueous phase.

Jank et al. (1998) carried out various experiments on decolouration (combination of active carbon and H2O2) and on the abiotic degradation of wastewaters dyed with the test substance. They also found that the dye was not subject to biodegradation. They suggested pre-treatment with Fenton's reagent under the following reaction conditions.

- temperature: 10 °C (preferred, also 20 °C und 40 °C)

- pH setting: 3.0

- H2O2 concentration: 10 mI/l (35 %); 3.53 g/l

- Fe 2+ concentration: 0.5 g/l [1.36 g FeSO4/l; 2.489 FeSO4 x 7(H2O)/l]

- reaction time: 4 hours (up to 24 hours at a higher temperature)

After this pre-treatment and a two-day lag phase, the subsequent reaction products are degraded to 93-97 % within 14- 15 days. lt should be pointed out, however, that these were model experiments with an initial concentration of 2 g test substance/l, the residence times in typical sewage plants are less than 14- 15 days and pre-treatment with reagents is not prescribed in OECD guidelines.

Therefore, in overall conclusion, the test substance is not readily biodegradable according to OECD criteria. However, based on literature studies it can be assumed that the test substance is potentially biodegradable.