Bacterial Degradation of Azo Dye Containing Wastes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 76

Table 4 Methods for evaluation of toxicity of azo dyes
Methods Organisms

Microbial toxicity Bacteria (E. coli, Bacillus spp., Rhizobium spp.,

Vibrio scheri), Algae (Chlorella vulgaris,
Gloeocapsa minutus, Phormidium ceylanicum)

Phytotoxicity Sorghum vulgare, Phaseolus mungo,

Triticum aestivum, Oryza sativa, Cicer arietinum

Mutagenicity (Ames test) Salmonella typhimurium

Cytotoxicity A. cepa

Genotoxicity (Comet assay) A. cepa

Ecotoxicity Lemna minor

Acute Toxicity Artemia nauplii

Oxidative stress in plants A. cepa

Toxicity of azo dye is caused by more than one mechanism. Several methods,
used to determine toxicity of azo dyes or their metabolites, are listed in Table 4 .
Amongst these toxicity tests, phytotoxicity method has gained major attention
because of easiness to perform, less expensiveness and simple analysis of seed
germinations. However, determination of toxicity of dyes and their metabolites on
standard known microorganisms is a more sensitive method with high reproduc-
ibility of results. The Salmonella mutagenicity assay or Ames test is widely used to
detect chemical mutagenic and potential carcinogenic ability of azo dyes and their
metabolites produced. Ferraz et al. ( 2011 ) reported mutagenic effect of dye Disperse
Orange 1 on Salmonella typhimurium strains viz. TA98, YG1041, TA100 and
YG1042. Similarly, toxicity of Reactive Black 5, Acid Orange 7, Food Yellow was
studied using bioluminescent marine bacterium Vibrio scheri by Gottlieb et al.

( 2003 ). However, Agrawal et al. ( 2014 ) studied microbial toxicity using B. subtilis,
E. coli, Azotobacter and phosphate solubilizer and reported a decrease in toxicity of
trisazo Acid Black 210 after decolorization by Providencia sp. SRS82. However,
non toxic effect of azo dye Reactive Red BS and its metabolites on important soil
bacteria Bacillus cereus, Azotobacter and Rhizobium was reported by Sheth and
Dave ( 2009 ). Green unicellular alga Pseudokirchneriella subcapitata was also used
to evaluate toxicity of dyes. Apart from phytotoxicity and microbial toxicity,
cytotoxicity and genotoxicity using plant Allium cepa are now widely studied by
researchers. Higher Plants are recognized as an excellent genetic model to evaluate
mutagenicity of toxic chemicals and A. cepa species is having advantages of low
cost and easy to handle. Chromosome aberrations in root cells of A. cepa are used to
detect genotoxicity, while mitotic index and some nuclear abnormalities are eval-
uated for cytotoxicity of azo dyes. The oxidative stress response is recently studied
for the assessment of toxicity of azo dyes. Analysis of antioxidant enzymes, such as
ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase, glutathione
reductase and peroxiredoxins along with analysis of lipid peroxidation and protein
oxidation, was carried out to assess oxidative stress response by toxic azo dyes