Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 227

parent dye (Solis-Oba et al. 2009 ). Several azo dyes and the amines from their
degradation have shown mutagenic responses in Salmonella and mammalian assay
systems, and their toxicity depends on the nature and position of the substituents in
the molecule. For example, the dyes Acid Red 18 and Acid Red 27 are non-
mutagenic, whereas the structurally similar dye Acid Red 26 is carcinogenic
because of the presence of a methyl group and the difference in the position of the
sodium sulphonate. Similarly, 3-methoxy-4-aminoazobenzene is a potent hepato-
carcinogen in rats and a strong mutagen in bacteria, whereas 2-methoxy-4-amin-
oazobenzene is apparently non-carcinogenic and an extremely weak mutagen in
bacteria (Ferraz et al. 2011 ). Acid Violet 7 has a signi

cant ability to induce
chromosome aberrations, lipid peroxidation and the inhibition of acetylcholines-
terase and the toxicity of this dye increases signi cantly after static biodegradation

by Pseudomonas putida due to the corresponding azo reduction metabolites 4

-
aminoacetanilide and 5-acetamido-2-amino-1-hydroxy-3, 6-naphtalene disulphonic
acid (Mansour et al. 2010 ). Therefore, in general, it becomes very important for any
bioremediation technology to assess the toxicity of the pollutants and metabolites
formed after dye degradation in order to study the feasibility of the method (Jadhav
et al. 2011 ). Toxicity has been evaluated using various methodologies with respect
to phytotoxicity, ecotoxicity, genotoxicity, mutagenicity, acute toxicity, microbial
toxicity and toxicity on invertebrates (Fig. 11 ). Phytotoxicity methodologies have
become more prevalent, because they are less expensive and easier than other
methods. According to the inhibition of the germination of selected seeds, the most-
used species have been Sorghum vulgare (Parshetti et al. 2010 ; Jadhav et al. 2011 ;
Kurade et al. 2011 ; Waghmode et al. 2011 ); Phaseolus mungo (Parshetti et al.
2010 ; Jadhav et al. 2011 ; Waghmode et al. 2011 ; Kumar et al. 2012 ; Kurade et al.
2012); Triticum aestivum (Parshetti et al. 2010 ; Ayed et al. 2011 ; Kumar et al.
2012 ); Sorghum bicolor (Parshetti et al. 2010 ; Ayed et al. 2011 ); Oryza sativa
(Bohmer et al. 2010 ; Zhuo et al. 2011 ); Lepidium sativum (Jonstrup et al. 2011 );
Cucumis sativus (Anastasi et al. 2011 ); Cajanus cajan and Cicer arietinum
(Anjaneya et al. 2011 ). Ecotoxicity has been measured in the terms of number of

'

Fig. 11 Methods to evaluate the toxicity of azo dyes and their degradation products in treated
efuents