Reactive Orange 16

Endpoint summary

Additional information

Reactive orange 16 is a organic not readily biodegradable dye (OECD301E, biodegradation < 10%).  However, further studies on ultimate biodegradation in surface water performed on similar substance 2 following OECD309 showed that complete mineralisation is achieved by the end of the test and no metabolites are detected above the LOD. Based on the read across considerations same results apply to test item.

Abiotic reactions:

The reaction between reactive orange 16 and water shows a half life of 6 days at 25°C at pH 7.(Bartsch 1985). In agreemnet with the behaviour of the similar substance 2 , which reacts rapidly with water, with a Half life in water of 1.9 days (Appel M. 1989). The degradation steps are similar for both substances.

It was found that the sulfonated azo dyes can be destroyed by UV photooxidation process (Saliha 2004). The kinetics of the degradation depends on the azo,benzene and naphthalene groups of the dyes. We found that the first step of the degradation is related to cleavage of azo bond of the molecule and naphthalene ring which leads to further degradation until complete mineralization.

Degradation of RO16 by TiO2 photocatalysis also was evaluated (Chen 2009). The degradation followed first-order kinetics. The efficiency of decolorization is influenced by the initial concentration of RO16, photocatalyst amount, UV light intensity, and temperature.

Biotic reactions:

There are many studies that describes the interactions between azo dyes and microorganisms.

Anaerobic conditions:

Microbial decolorization of azo dyes in an anaerobic environment occurred as a result of reduction of azo bonds. This gave rise to the liberation of decolorization metabolites. No ready biodegradation of these metabolites was expected in the anaerobic system that gives rise to decolorization. However these metabolites could be further reduced by means of either biodegradation or autooxidation under subsequent aerobic treatment.The mixed bacterial cultures decolorized three structurally dissimilar azo dyes, suggesting that anaerobic decolorization was not a specific process (Supaka 2003). It was clear that the majority of the color removal occurred in the anaerobic stage.

Aerobic conditions:

Studies conducted with selected fungal strain and microbial strain from local textile effluent channel at 37°C, neutral pH, shows the high percentage of biodegradation (70 - 90 %) after 240 hrs of incubation in presence of oxygen.

The rate of decolorization of azo dyes is affected by their molecular weights, substitution groups of the dye molecules, and the intramolecular hydrogen bond between the azo and hydroxy groups.

 

Sorption:

Four types of waste sludge were collected from a drinking water treatment plant (waterworks sludge; WS), sewage treatment plant (sewage

sludge; SS), anaerobic digestion (digested sludge; DS) and landfill site (landfill sludge; LS). These sludges were evaluated as biosorbents for the removal of Reactive Orange 16 (RO 16). The maximum sorption capacities of the four waste sludges estimated using the Langmuir equation at pH 2 were in order LS (159.0±6.0 mg g−1) > SS (114.7±4.7 mg g−1) >DS (86.8±4.5 mg g−1) >WS (47.0±5.8 mg g−1). However, the desorption efficiency of LS was insufficient (43.2%) compared with that of SS (90.0%), indicating that the SS has the potential to be regenerated as a biosorbent. From the potentiometric titration and FTIR study, the binding sites present in the SS were considered to be protonated amine groups (–NH3+) , which play a role in the electrostatic interaction with the negatively charged sulfonate groups of RO 16.

In addition, a sorption study was performed using the HPLC method as described in the European Commission Regulation (EC) No. 440/2008 on similar substance 2. The adsorption coefficient (log Koc) determined in this test was < 1.25. The sorption effect of dyes is predominately governed by the protonated amine groups (–NH3 +) , which have an electrostatic interaction with the negatively charged sulfonate groups of Reactive Orange 16.