Azo dyes toxicity

Brown MA, DeVito SC (1993) Predicting azo dye toxicity. Crit Rev Environ Sci Technol 23 249-324... 

Three different mechanisms for azo dye toxicity have been identified and were reviewed by Brown and DeVito in 1993 In order of decreasing nnmber of pnblished papers, these mechanisms are ... 

Brown M A and DeVito S C, Predicting azo dye toxicity . Critical Reviews in Environmental Science and Technology, 1993,23(3), 249-324. 

Dinitrochlorobenzene is used primarily in the manufacture of azo dyes other areas include the manufacture of fungicides, mbber chemicals, and explosives. It is produced by Eastman Kodak Company and Sandoz Chemical Corporation and its bulk fob price is 2.73/kg. 2,4-Dinitrochlorobenzene is more toxic than nitrobenzene. It is an extremely powerful skin irritant and must be handled with great cate. 

Several comments about the toxicity of pharmaceutical, agrochemical and azo dye pyrazoles have been made previously in Section 4.04.4.1. Some LDso values from the literature are shown in Table 41 (B-76MI40404). 

Sulphonamides were introduced by Domagk in 1935. It had been shown that a red azo dye, prontosil (Fig. 5.16B), had a curative effect on mice infected with /3-haemolytic streptococci it was subsequently found that in vivo, prontosil was converted into sulphanilamide. Chemical modifications of the nucleus of sulphanilamide (see Fig. 5.16A) e compounds with higher antibacterial activity, although this was often accompanied by greater toxicity. In general, it may be stated that the sulphonamides... 

Aniline, which is used not only to synthesise drugs, pesticides and explosives but also as a building block for materials such as polyurethane foams, rubber, azo dyes, photographic chemicals and varnishes, is manufactured at a quantity of approximately three million tons each year [61]. The toxic effects of aniline include increased nitration of proteins in the spleen [62]. 

Hu TL (2001) Kinetics of azoreductase and assessment of toxicity of metabolic products from azo dyes by Pseudomonas luteola. Wat Sci Technol 43 261-269... 

Gottlieb A, Shaw C, Smith A et al (2003) The toxicity of textile reactive azo dyes after hydrolysis and decolourisation. J Biotechnol 101(l) 49-56... 

Sulfonated azo dyes are widely used in different industries [16]. Some structure of sulfonated and unsulfonated azo dyes is shown in Fig. 1. These water-soluble azo dyes will enter the environment generally with wastewater discharge. Also, these sulfonated and unsulfonated azo dyes have a negative aesthetic effect on the wastewater, and some of these compounds and biodegraded products are also toxic, carcinogenic, and mutagenic [17]. There exists clear evidence that sulfonated azo dyes show decreased or no mutagenic effect compared to unsulfonated azo dyes... 

The removal of dyes from industry effluents is desirable not only for aesthetic reasons but also because azo dyes and their breakdown products are toxic to aquatic life and mutagenic to humans [8,9]. Without adequate treatment these azo dyes are stable and can remain in the environment for an extended period of time. Consequently, azo dyes have to be removed from wastewaters before discharge. 

The ambient temperature and the possible use of solar UV are the advantages of photocatalysis moreover, Ti02 is not toxic. The reaction mechanisms of Ti02 photocatalytic oxidation of azo dyes was similar to the biodegradation process of oxidation of azo dyes with OH radical. 

IsiK M, Sponza DT (2004) Monitoring of toxicity and intermediates of C.I. Direct Black 38 azo dye through decolorization in an anaerobic-aerobic sequential reactor system. J Hazard Mater 114 29-39... 

An inverse relation between the efficiency of decolorization and the dye concentration has frequently been observed. This fact can be ascribed to several factors, the main of which can be considered the toxicity of the dyes at higher concentrations [41, 45, 51-53]. With Reactive Red 3B-A, concentrations from 100 to 2,000 ppm were tested with C. bifermentans [5]. At concentrations less than 200 ppm, 90% decolorization within 12 h was observed, while at very high dye concentration (>1,000 ppm), the decolorization rate decreased. Khalid et al. [54] observed an inverse relationship between the velocity of the decolorization reaction and the dye concentrations between 100 and 500 mg L 1 azo dye (Reactive Black 5, Direct Red 81, Acid Red 88, and Disperse Orange 3) by Shewanella putrefaciens. A decrease in decolorization percentage at a Acid Black 210 initial concentration growing from 100 to 400 ppm was also observed with V. harveyi, but the decrease was low [44]. 

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