Environmental Engineering Reference
In-Depth Information
have also been done by many others to relate the toxicity of dyes with their
structures (Mietzsch
1936
; Goldacre and Phillips
1949
; Fischer
1957
). Michaelis
and Granick (
1945
), Michaelis (
1947
,
1950
) attempted to explain the toxicity by
showing that basic dyes react irreversibly with nucleic acids. Similar studies have
been also carried out by other workers (Neuberg and Roberts
1949
; di Marco and
Boretti
1950
; Steiner and Beers
1958
). Basu and Whitaker (
1953
) found that acid
and basic dyes were inhibitory to the isolated cellulase of Mlyrothecium verrucaria.
Conn (
1935
) disclosed the use of Crystal violet and malachite green for the pres-
ervation of cotton
sh nets. Singh et al. (
2007
) also found an inhibition in the
growth of fungus Trichoderma harzianum during the degradation of some haz-
ardous dyes. In the same sequence, the toxicity of dyes and certain related com-
pounds was also tested with six species of wood-destroying fungi, because of their
economic importance to the wood-preserving industry (Weaver et al.
1959
). The
arylmethane basic dyes, particularly those containing three phenyl groups with two
p-dialkylamino substituents, appear to be effective fungicides when tested on
nutrient agar plates against six species of wood-destroying fungi. Brilliant green
and Malachite green, both available commercially, are the most toxic dyes of the
group, and it was concluded that alkyl substituents on the amino nitrogen atoms
increase their toxicity. Malachite green is more toxic than Doebner
'
s violet, while
crystal violet is more toxic than para magenta (Weaver et al.
1959
).
Most of the dyes are synthetic poly aromatic compounds and are difcult to be
degraded in the environment. They are also potential to form carcinogenic break-
down products in the environment (Chung et al.
1992
). Several amino-substituted
azo dyes, including 4-phenylazoaniline and N-methyl- and N,N-dimethyl-4-
phenylazoanilines, are mutagenic as well as carcinogenic (McCann and Ames
1975
).
The carcinogenicity of an azo dye may be due to the dye itself or to aryl amine
derivatives generated during the reductive biotransformation of the azo linkage.
10 Future Prospectives
The work on microbial degradation/decolorization of synthetic dyes and other
hazardous compounds or on the puri
cation of wastewaters by using some ideal
microbes is still not reached to development of a better alternate or superior
technology. Presently, many laboratories in India and from abroad are involved in
the same task and in the coming years, there would be a better option to use
microbes for biodegradation. The use of microbes including fungi, bacteria, acti-
nomycetes and algae in environmental biotechnology is still under investigation for
their proper implementation. One main fact is clear that if any microbe has been
shown ability to do work in vitro conditions, it doesn
'
t mean that same work would
be done in vivo conditions or vise versa. There is a need for further study on the
microbes regarding the role of fungal genes to promote the degradation capacity of
any microbe.
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