Tetrasodium 4-amino-5-hydroxy-6-[[2-methoxy-5-[[2-(sulphonatooxy)ethyl]sulphonyl]phenyl]azo]-3-[[4-[[2-(sulphonatooxy)ethyl]sulphonyl]phenyl]azo]naphthalene-2,7-disulphonate

Endpoint summary

Description of key information

Reactive Blue 250 has a very high water solubility. Screening tests for biodegradation of the structural analogue Reactive Black 5 in water or under environmental conditions showed that the test substance is not readily biodegradable. However, it is rapidly hydrolysed with a half-life of 1 to 2 days at pH 7. When Reactive Black 5 was applied to a sediment/water test system at a final concentration of 1 mg/kg in the test system, the test substance was rapidly degraded to Reactive Black 5 bis-vinyl and further to Reactive Black 5-OH. The DT50 of Reactive Black 5-ester was 2 days. After 3 to 6 days, only 10% of the applied Reactive Black 5 could be found. All metabolites decreased at the end of the test period to levels around the lower level of quantification. Consequently, an accumulation of metabolites could be excluded. The majority of the metabolites of Reactive Black 5 were deposited in form of non-extractable residues in sediment during test phase. After about 1 month, mineralization of the metabolites started.

A bioaccumulation study in the carp revealed bioconcentration factors < 11 for 0.2 mg/L and < 1.1 for 2 mg/L. Hence, Reactive Black 5 either as bis-ester, or as bis-vinyl does not bioaccumulate in the aquatic compartment. Based on data from kinetic and metabolism studies in rats (oral and intravenous administration), the test item Reactive Black 5 as well as its structural analogue Reactive Blue 250 does not have any bioaccumulation potential in animals. Due to the very low toxicity, rapid degradation and lack of bioaccumulative properties, secondary poisoning can be excluded for both items.

Additional information

The target substance Reactive Blue 250 is a mono-constituent consisting of tetrasodium 4-amino-5-hydroxy-6-[[2-methoxy-5-[[2-(sulphonatooxy) ethyl]sulphonyl]phenyl]azo]-3-[[4-[[2-(sulphonatooxy)ethyl]sulphonyl]phenyl]azo] naphthalene-2,7-disulphonate as the major constituent. In water it is rapidly hydrolysed to its vinylised forms trisodium 4-amino-6-{2-[5-(ethenesulfonyl)-2-methoxyphenyl]diazen-1-yl}-5-hydroxy-3-(2-{4-[2-(sulfonatooxy)ethanesulfonyl]phenyl}diazen-1-yl)naphthalene-2,7-disulfonate, trisodium 4-amino-3-{2-[4-(ethenesulfonyl)phenyl]diazen-1-yl}-5-hydroxy-6-(2-{2-methoxy-5-[2-(sulfonatooxy)ethanesulfonyl]phenyl}diazen-1-yl)naphthalene-2,7-disulfonate, and disodium 4-amino-6-{2-[5-(ethenesulfonyl)-2-methoxyphenyl]diazen-1-yl}-3-{2-[4-(ethenesulfonyl)phenyl]diazen-1-yl}-5-hydroxynaphthalene-2,7-disulfonate, which are the active forms during the dyeing process. The content of these vinyl-forms in the testing material can vary largely, as its development is dependent on temperature and humidity during synthesis, storage and/or transport (see section 1.2 in IUCLID). As these vinyl-components form rapidly in the presence of water and under testing conditions, they have therefore been tested together with the ester form.

The reactive forms of the dye, the mono- or bis-vinyl-sulfone forms, are generated in the dye bath by treatment with base. The dye-fibre adduct is formed in a subsequent reaction by Michael-type 1,4-nucleophilic addition (Weber, 1990). Competing with this reaction is hydrolysis to give the 2-hydroxyethylsulfone. This reaction is the same in each dye containing the 2-sulfatoethylsulfone moiety, independently of the remaining dye-structure, therefore it is a general mechanism as described in many literature sources (Zollinger, 2003).

A common dyeing process for reactive dyeing of cellulose fiber textiles consists of two phases. In the first phase, the dyeing process takes place at 60° C for 45 - 60 minutes at a neutral range of pH. During the second process step the dyebath is adjusted to a high alkalinity (pH approx. 10-11 for 60 minutes).

For home-dyeing in the washing machine, the dye is also formulated to a basic pH to assure the hydrolysis to the vinyl-forms, which are required to form the covalent bond to the fabric. The recommend washing program for dyeing in the washer is using an easy-care wash program (ca. 2 hours) with a temperature of 60°C. Hence, as in industrial/professional dyeing, the dyeing takes place with elevated pH and temperature over a time of 2 hours and only hydrolysed substance is released into the environment.

Hence, the substance not bound to the fiber in the dye-bath is completely hydrolysed to the hydroxyethylsulfone-form of Reactive Blue 250 at the end of the dyeing process as shown in the study for abiotic degradation and in surface water with the close structural analogue Reactive Black 5.