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Abstract

The emission of effluents from textile industries has been a major concern of the modern world, due to the great pollution that these effluents promote on the water resources. Among the synthetic dyes released in effluents from textile industries, azo dyes is one of the more detrimental classes because it is highly persistent in the aquatic environment, due to its chemical composition, involving aromatic rings, azoic linkages and amino groups. This review aimed to gather information on the importance of the production and industrial use of azo dyes, as well as present some studies that have been developed to evaluate the toxicity of such chemical compounds and their metabolites on different living organisms. This paper presents some considerations on the importance of the biological treatment of textile effluents, the discovery of microorganisms capable of degrading azo dyes efficiently in order to reduce potential risks of these dyes to organisms and environment.
Textiles and Light Industrial Science and Technology (TLIST) Volume 2 Issue 2, April 2013 www.tlist-journal.org
85
Azo Dyes: Characterization and Toxicity– A
Review
Bruna de Campos Ventura-Camargo1, Maria Aparecida Marin-Morales2
Department of Biology, Institute of Biosciences, São Paulo State University (UNESP),
Avenue 24A, 1515, 13506-900, Rio Claro, SP, Brazil
1brunabio@yahoo.com.br; 2mamm@rc.unesp.br
Abstract
The emission of effluents from textile industries has been a
major concern of the modern world, due to the great
pollution that these effluents promote on the water resources.
Among the synthetic dyes released in effluents from textile
industries, azo dyes is one of the more detrimental classes
because it is highly persistent in the aquatic environment,
due to its chemical composition, involving aromatic rings,
azoic linkages and amino groups. This review aimed to
gather information on the importance of the production and
industrial use of azo dyes, as well as present some studies
that have been developed to evaluate the toxicity of such
chemical compounds and their metabolites on different
living organisms. This paper presents some considerations
on the importance of the biological treatment of textile
effluents, the discovery of microorganisms capable of
degrading azo dyes efficiently in order to reduce potential
risks of these dyes to organisms and environment.
Keywords
Dyes; Textile Effluents; Cytotoxicity; Genotoxicity; Mutagenicity;
Carcinogenicity; Bioremediation
Introduction
The use of dyes is a very mature practice used to
modify the colour characteristics of different
substrates, such as fabric, paper, leather, among others
[1, 2]. Before the mid nineteenth century, substances
with colouring properties were extracted from natural
sources, mainly from animals or vegetables. However,
natural dyes were almost completely replaced by the
synthetic in the beginning of the twentieth century.
Today, virtually, all dyes and pigments commercially
available are synthetic substances, with exception of
some inorganic pigments. Every year, hundreds of
new coloured compounds flooded the market and
developed into a series of different applications [3].
Dyes and several organic compounds used for dyeing
which are chemical substances have been already
incorporated by the technology of our daily life. The
global consumption of dyes and pigments
approximates 7x105 tons/year and only in the textile
industry it consumes about two-thirds of all the world
production [4, 5]. According to Guaratini and Zanoni
[6], in Brazil, a decade ago, 26,500 tons of dyes were
consumed every year, which corresponded to 3.8% of
all the dye produced in the world.
During the textile process, inefficiency in the colouring
generates large amounts of dyes residues, which are
directly released into water bodies, consequently,
contaminating the environment. In the dyeing
processes, enormous quantities of pollutants are
discharged in aquatic bodies, resulting from
impurities of the removal of the crude material and
residual chemical reagents used in such processes [7].
Residues of dyes either are discharged in waters that
pass by treatment systems of the companies or are
released directly into the environment, causing a
severe contamination of water bodies, which is mainly
observed and aggravated next to areas with the
presence of many textile industries [8, 9].
Among the residues of dyes that pollute environment,
there are azo dyes that are discharged in large
quantities, directly in water bodies, characterizing an
important way of environmental contamination [10].
According to Nam and Renganathan [11] and Jarosz-
Wilkolazka et al. [12], about 10 to 15% of the total dye
used by the industries are lost during the dyeing
process and, thus, are being released into the
environment. According to O’Neill et al. [13], these
values can be even higher, reaching until 50%.
However, the exact data of the amount of dyes
released into the environment are not yet fully known
[14]. In Brazil, the textile industry is responsible for the
generation of great volumes of residues, with high
organic load and strong colouration, which represents
a major environmental problem generated by the
textile sector.
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According to Kirk-Othmer [15], dyes can be classified
into:
- acid dyes: anionic dyes, soluble in water, with one or
more sulphonic or carboxylic acid groups in their
molecules and, chemically, constituted by compounds
azo, anthraquinones and triarylmethanes,
iminoacetone, nitro, nitrous and quinoline, with
application in nylon, silk, modified acrylic, wool,
paper, food and cosmetics;
- basic dyes: cationic dyes, soluble in water, producers
of colouring cationic compounds in solution and
chemically constituted by compounds azo,
anthraquinone, triarylmethane, methane, thiazine,
oxazine, acridine and quinoline, with application in
modified acrylic, modified nylon, modified polyesters
and papers, and some of them having biological
activity are used in medicine as antiseptics;
- direct dyes: anionic compounds, soluble in water,
when in the presence of electrolytes (salts that increase
their affinity for the fibre). Chemically they are
constituted by azo compounds, with thiazoles,
phtalocyanines and oxazines, with application in the
dyeing of cotton and regenerated cellulose, paper,
leather and nylon;
- fluorescent dyes (group of the xanthenes): colourless
compounds that absorb incident ultraviolet light and
re-emit in the visible region (blue) of the spectrum. In
fact, they are not dyes, but due to the wide application
in fabrics and other materials, the Colour Index made
their classification within this group of chemicals;
- reactive dyes: compounds of very simple chemical
structure, with absorption spectrum presenting
narrow range of capitation and dyeing possessing
brilliant characteristics. Chemically they are
constituted by azo compounds, anthraquinones and
phtalocyanines, with high fixing property by simple
dyeing methods, making covalent bridges with the
fibre (cotton, wool or nylon), by the compatible
hydroxyl group of cellulose;
- sulphurous dyes: small group of dyes, however, with
low cost and good fixing properties. They are applied
to cotton, after alkaline reduction bath, with sodium
sulphite as reducing agent;
- vat dyes: insoluble compounds in water and applied,
mainly, to cellulosic fibres, such as leuco-soluble salts,
after reduction in alkaline bath, normally with sodium
hydrosulphite. After exhaustion of the fibre, they are
re-oxidized to the keto-insoluble form and after
treatment normally by soda, develop crystalline
structure. Chemically they are the anthraquinones and
indigo;
- dye precursors: dyes obtained from raw materials.
This group has simple chemical characteristic, such as
benzene and naphthalene, whose colour is given by a
variety of chemical reactions. Normally they are cyclic
aromatic compounds and derivatives, mainly of
petroleum and coal.
According to Guaratini and Zanoni [6], there are still
the dispersive dyes which are water insoluble
products, applied to cellulose fibres and other
hydrophobic fibres by suspension. During the dyeing
process, the dye suffers hydrolysis and the originally
insoluble formation is slowly precipitated in the
disperse form on the cellulose acetate. Generally, the
process occurs in the presence of dispersing agents of
long chains which stabilize the dye suspension, and
facilitate the contact with the hydrophobic fibre. This
class of dyes is mainly constituted by azo dyes, and
has been used in the dyeing of synthetic fibres, such as
cellulose acetate, nylon, polyester and polyamide.
According to Majcen-le Marechal et al. [3], there are
more than 3,000 different dyes available in the market
and half of them belong to the azo dyes compounds
class. These dyes are used in the textile industry for
the colouring of polyester, nylon, cellulose diacetate
and triacetate and acrylic fibres [9], and are also used
as additive in products derived from the petroleum
and in the dyeing of leather, paints, plastics, papers,
wood, oils, cosmetics, pharmaceuticals, metals and
food [8]. In addition to its versatility, due to the
diversity of applications, there are other advantages in
using azo dyes in industries. These chemical
compounds are easily synthesized, have excellent
fixative and permanency properties and present a
great variety of colours, when compared to natural
dyes [16, 17].
Azo dyes are compounds characterized with the
presence of one or more azo groups (-N=N-), usually
in number of one or four, linked to phenyl and
naphthyl radicals, which are usually replaced with
some combinations of functional groups including:
amino (-NH2), chlorine (-Cl), hydroxyl (-OH), methyl
(-CH3), nitro (-NO2), sulphonic acid and sodium salts (-
SO3Na) [18]. Azo dyes, synthesized from aromatic
compounds, are not basic in aqueous solution (due to
the presence of the linkage N=N, which reduces the
possibility of unpaired electron pairs in nitrogen
atoms), are readily reduced to hydrazines and primary
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amines, functioning as good oxidizing agents [19].
On the one hand, the azo dyes meet the needs of man,
on the other hand, they entail ecological and sanitary
changes in the hydric resources, soil and atmosphere.
The presence of dyes in the aquatic bodies leads to an
aesthetic problem and can have a negative impact on
public health [20]. However, several liquid and solid
effluents of textile industries are treated before being
released into the environment, which reduces the
impact of these agents on the aquatic environment.
Despite the difficulty in the treatment of the residues
generated and the adverse indications for their use,
azo dyes, especially sulphurous, are widely used for
dyeing fibres. This is mainly due to its affordable cost
and its good fixative characteristics [21].
Several countries have adopted environmental
legislation and requirements to restrict the use of
hazardous chemicals in the production of textiles and
clothing and one of the most known laws in this issue
is the Second Amendments to the Consumer
Protection Act, elaborated by the German government
in 1994, prohibiting the use of azo dyes. According to
the German legislation, some azo dyes are considered
allergenic (Disperse Yellow 1/3; Disperse Orange
3/37/76; Disperse Red 1; Disperse Blue 1/35/106/124)
and some are considered carcinogenic (Acid Red 26,
Basic Red 9, Basic Violet 14, Direct Black 38, Direct Red
28, Direct Blue 6, Disperse Yellow 3, Disperse Orange
11, Disperse Blue 1) [22]. In addition, other European
countries, such as Sweden, France and Denmark,
formulated their own legislation for azo dyes [22]. The
Portuguese government, for example, published the
Decree-Law nº 208/2003 [23], which states: Azo dyes
that, by reductive cleavage of one or more azo groups,
can release one or more aromatic amines in detectable
concentrations, i.e., higher than 30 ppm, cannot be
used in textile and leather articles susceptible to enter
in direct and prolonged contact with human skin or
with the oral cavity.
It was stated that azo dyes, after cleavage, present the
capacity to release aromatic amines considered as
carcinogenic, the European Union, by the Directive
2002/61/EC, reformulated by the Directive 2004/21/CE,
has banned the use of these dyes used in the
production of textile articles that enter in contact with
skin or mouth. These Directives also establish that the
referred textile articles cannot contain the 22 amines
listed in the legislation, in a concentration higher than
30 ppm and, if the articles are made of recycled fibres,
they cannot contain more than 70 ppm [22, 24].
According to Umbuzeiro et al. [25], the black
commercial dye (BDCP - Black Dye Commercial
Product), widely used in the dyeing industry of
synthetic fibres, is composed by 3 dyes belonging to
the group of nitro-aminobenzenes: C.I. Disperse Blue
373, C.I. Disperse Violet 93 and C.I. Disperse Orange
37. According to Oliveira (2005) [2] and USEPA (1994)
[17], BDCP is an organic compound that belongs to the
class of dispersive dyes with azo function, which has,
at least, one azo bond, besides presenting insolubility
in water and good fixing to natural and synthetic
fibres. Guaratini and Zanoni [6] cited that in the
dyeing process of fibres with azo dyes, there is
impregnation of the fibre with a compound soluble in
water (coupling agent), which presents high affinity
for cellulose. The addition of a diazonium salt (RN2+)
provokes a reaction with the coupling agent already
fixed to the fibre, producing a dye insoluble in water.
Thus, the dye is formed directly on the fibre, allowing
that this process provides good results, such as high
fixation pattern and high resistance to light and
humidity. Due to the fact that these compounds are
insoluble in water, dispersing agents are added to the
dye to produce finely divided particles. This mixture
results in a stable dispersion in the dye bath.
Toxicity of Azo Dyes
A great variety of substances derived from dyes have
been tested, in laboratorial animals, to determine the
real toxic effects of these compounds on living
organisms [26]. Studies that assess the toxicity of azo
dyes and metabolites related to their degradation are
important for the establishment of strategies to reduce
the harmful effects of these chemicals [27, 2].
The evaluation of the toxicity of textile dyes is very
important, mainly due to the different effects that they
cause in the environment and the organisms exposed
to them. The biological activities also differ greatly
between the dyes and, despite the similarities of the
structures, the toxicological properties cannot be
generalized according to the reference of only one
chemical group [3].
The uncontrolled discharge of azo dyes in water
bodies causes serious environmental problems, such
as: reduction of the light absorption due to the
organisms that inhabit the aquatic environments and
production of different amines under anaerobic
conditions [28-30].
The acute toxicity of azo dyes, according to the criteria
of the European Union for the classification of
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dangerous substances, is low and the values of LD50
are 250-2000 mg/Kg body weight [31]. Some azobasic,
acid and direct dyes are classified into very toxic or
toxic to fishes, crustaceans, algae and bacteria, while
reactive azo dyes are toxic only at very high
concentrations (Effective Concentration Levels >100
mg/L), therefore, excluded from considering toxic for
aquatic organisms. [32].
Acute toxicity of azo dyes, defined by the criteria of
the European Union for the classification of dangerous
substances, is very low, and only few of them have
values of LD50 below 250 mg/kg body weight [33].
However, the occupational sensitivity to azo dyes has
been shown in textile industries since 1930 [34], like,
for some disperse dyes (monoazo or anthraquinone)
that were involved with allergic reactions [35].
Studies showed the presence of some azo dyes in
certain algae and plants [36], and also have shown the
adverse effects for aquatic microbial populations
exposed to effluents containing dyes [37].
Several studies shows that the release of azo dyes into
the environment is alarming due to the toxic,
mutagenic and carcinogenic characteristics of these
dyes and of their biotransformation products [38],
which can cause different damages to the organisms
exposed.
Amin et al. [39] evaluated the toxic effects of two azo
dyes used as food additives, tartrazine and carmoisine,
by oral administration of two concentrations (one low
and other high), in albino male rats, for 30 days. It was
measured the quantities of ALT, AST, ALP, urea,
creatinine, total protein, albumin, lipid profile, blood
glucose in serum, and estimated the activities of GSH,
catalase, SOD and MDA in the hepatic tissue of the
animals. Data showed a significant increase in the
rates of ALT, AST, ALP, urea, creatinine, total protein
and albumin in the serum of rats treated with
tartrazine and carmoisine, especially in the higher
concentrations. The activities of GSH, SOD and
catalase decreased and MDA increased in the tissues
of rats fed with the high dose of tartrazine and
different doses of carmoisine. It is concluded, therefore,
that both azo dyes affected adversely and altered the
biochemical markers of vital organs such as liver and
kidney, not only in higher concentrations but also in
the lowers. Tartrazine and carmoisine not only cause
changes in the hepatic and renal parameters but their
effects become a risk to the organisms at higher doses,
since it can induce oxidative stress by means of the
formation of free radicals.
Studies have also shown the presence of azo dyes in
different samples of water and sediments. Studies
performed by Umbuzeiro et al. [40], in the
Salmonella/Microsome test, showed a low to moderate
mutagenic activity in Cristais River (Cajamar/SP), due
to the presence of azo dyes, nitroaromatic compounds
and aromatic amines. Another study carried out by
Umbuzeiro et al. [25] detected the presence of dyes in
all the samples collected (effluent of the dyeing
industry, raw water and water treatment station), and
associated the mutagenicity of these samples mainly of
the raw water with the presence of dyes and colourless
polycyclic nitroaromatic compounds, possibly
generated during the treatment of the effluent. Oliveira
[2] also showed the presence of components of the
black commercial dye (BDCP) and aromatic amines in
the raw and treated effluents discharged by a dyeing
industry, indicating that the industrial treatment was
not efficient for the removal of these compounds,
which corroborated some studies performed by some
authors [14, 28, 41] showing that activated sludge
systems were not efficient in the removal of azo dyes
present in industrial effluents.
Maguire and Tkacz [42] detected 15 different dyes in
samples of water, suspended solids and sediments of a
river of Canada, and 3 of which were identified as: C.I.
Disperse Blue 79, C.I. Disperse Blue 26 and C.I.
Disperse Red 60. Oliveira [2] showed that the
presence of about 1 µg of C.I. Disperse Blue 373 and 10
µg C.I. Disperse Orange 37, for each 1 g of the
sediment of two distinct environmental samples (one
located immediately below the discharge of the
effluent of a textile industry and the other from a
collection site situated at the entrance of the water
treatment station for public supply), which
characterizes high rates of mutagenic activity for these
two samples. These same dyes were detected in water
samples in the same area analyzed by Umbuzeiro et al.
[25].
Some azo dyes only exhibit mutagenic activity when
the azo bond is reduced. The aromatic amines formed
can be more or less carcinogenic and/or mutagenic, in
relation to the original compound, depending on their
chemical structure [25]. According to Plumb et al. [43]
and Yoo et al. [44], these aromatic amines are always
more dangerous than the original compounds and
may have toxic [45, 46]), mutagenic and carcinogenic
actions [47]. The reduction of these azo dyes can
generate DNA adducts [48, 49], which can lead to toxic
effects, even for the microorganisms that act in the
discolouration of azo dyes [29, 50-53].
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According to Biswas and Khuda-Bukhsh [54], the azo
dye p-dimethylaminobenzene (p-DAB) caused
cytotoxic and genotoxic effects in the chromosome
aberrations test, micronucleus test and mitotic index in
bone marrow cells and spermatozoids of rats. Rats fed
chronically with p-DAB resulted in an increase in the
number of chromosome aberrations and nuclear
abnormalities in germ cells, when compared to the
control group.
Al-Sabti [55] observed mutagenic effects for a textile
azo dye, the “chlorotriazine reactive azo red 120”, by
the induction of micronuclei in erythrocytes of fishes.
Some authors [56] concluded, according to studies
performed with mammalian cells, that some textile
dyes induce the formation of micronuclei by
mechanisms of clastogenicity.
Researchers [57] showed genotoxicity and
mutagenicity of the C.I. Disperse Blue 291dye, based
on the induction of fragmentation in the DNA,
formation of cell bearing micronuclei and increase in
the index of apoptosis in mammalian cells (HepG2).
Caritá and Marin-Morales [58] showed the mutagenic
potential o certain concentrations of industrial
effluents contaminated by azo dyes, by the means of
micronucleus and chromosome aberration tests with
the Allium cepa test-organism.
Matsuoka et al. [59] showed that the compounds of
PBTA1 and PBTA2 and their respective precursor azo
dyes are cytotoxic for the hamster cells CHL and V79-
MZ, inducing the formation of micronucleated cells,
multilobulated nuclei and highly condensed and
binucleated cells. The precursor azo dye of PBTA1 also
induced the endoreduplication in V79-MZ hamster
cells. Probably, these compounds affect not only the
DNA, but also structural and regulatory proteins
involved in the cell division process.
In a literature review [60], it was described the
mutagenic activity of several azo dyes by the Ames
test. C.I. Solvent Yellow 14, C.I. Pigment Solvent
Yellow 7, C.I. Pigment Orange 5, C.I. Pigment Red 4
and C.I. Pigment Red 23 were considered mutagenic,
while C.I. Pigment Red 3 was considered weakly
mutagenic. C.I. Pigment Red 53:1 C.I. Pigment Red
57:1 did not present mutagenic action and this must be
associated with the formation of sulphated aromatic
amines that are not genotoxic.
Chequer et al. [61] showed the mutagenicity of the azo
dyes C.I. Disperse Red 1 and C.I. Disperse Orange 1,
extensively used in several countries, by the increase
in the dose-response of the micronuclei frequency in
human lymphocytes and mammalian cells (HepG2),
when compared to the negative control group.
Some studies [62] performed with the assays of
Salmonella, micronuclei and comet, showed that 10
commercial products containing azo dyes presented
genotoxic action for bacteria and human keratinocytes.
Another study [63], also using the Salmonella assay,
besides the mouse lymphoma assay, showed that 15 of
53, i.e., approximately 28% of the samples of textile
dyes tested were positive for the Ames test and 60% of
the samples that presented positive responses to
Salmonella, also induced genotoxic effects in the mouse
lymphoma assay.
Sudan azo dyes induce genotoxic effects and the
monoazo Sudan 1 dye is considered a carcinogen of
liver and bladder for mammals and of mutagenic
potential for humans, while Sudan 2 is considered
genotoxic for hepatic cells of rats. Now, Sudan 4
requires reduction and microsomal activation to be
mutagenic [64].
Ventura-Camargo et al. [65] showed, through
chromosome aberration assay, chromosome banding
and FISH, that a commercial azo dye that confers black
colouration (BDCP Black Dye Commercial Product)
to textile products, in concentrations of 1, 10, 100 and
1000 µg/L, is cytotoxic, genotoxic and mutagenic to
meristematic cells of Allium cepa, by inducing cell
death, chromosome aberrations, variations in the
quantity of nucleoli and micronuclei. It was also
observed that the azo dye presents aneugenic and
clastogenic actions for the test organism studied,
which prevailed even after the recuperation
treatments. Moreover, the techniques of C-banding
CMA3/DAPI and FISH showed chromosome sites
more susceptible to breaks, which confirmed the
aneugenic action of the azo dye. Ventura [66] also
observed, by assays with A. cepa, that when the black
commercial dye pass through biodegradation
treatment with a pool of heterotrophic bacteria, yeast
of the species Candida viswanathii or by the
basiciomycete fungus Phanerochaete chrysosporium, its
toxic potential increases, which proves that the
biodegradation of this azo dye produces metabolites
potentially more toxic than that the original dye,
probably due to the cleavage of the azo bonds. The
genotoxic effects observed in the meristematic cells of
A. cepa before and after the biodegradation were
similar, however, higher frequencies of genotoxic
damages were observed after the microbial treatment.
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Recent toxicological studies with the azo dye Red
HE3B (Reactive Red 120), before and after bacterial
treatments, showed that the dye was able to induce
oxidative stress and a high frequency of chromosome
aberrations and micronuclei in root cells of A. cepa,
when compared to the effects caused by its
metabolites. Moreover, by the comet assay, performed
with the same test organism, it was possible to detect
that the rate of damages induced by the dye in the
DNA in a significantly higher form than that induced
by its metabolites, indicating that the microbial
treatments were favourable to the detoxification of
Red HE3B [67].
A recent study [68] assessed the efficiency of the
conventional chlorination treatment to remove the
genotoxicity and mutagenicity of the azo dyes
Disperse Red 1, Disperse Orange 1 and Disperse Red
13 in aqueous solutions, using the comet assay and the
micronucleus test with HepG2 cells, and the Salmonella
assay. The comet assay showed that the three dyes
studied induced damages in the DNA of HepG2 cells
in a dose-dependent form and that, even after
chlorination, these azo dyes remain genotoxic,
although they had induced a lower index of damage.
The micronucleus test showed that the mutagenic
activity of the azo dyes was completely removed after
chlorination, under the conditions tested. The
Salmonella assay showed that chlorination reduced the
mutagenicity of the three compounds tested with the
strain YG1041, but enhanced the mutagenicity of
Disperse Red 1 and Disperse Orange 1 with the strain
TA98. In general, it was concluded that the chemical
treatment used must be performed with caution for
the treatment of aqueous samples contaminated with
azo dyes.
Toxicity of the azo dye Direct Red 28 is mainly related
to its intermediate metabolites, benzidine and 4-
aminobiphenyl, since they are capable of inducing a
high frequency of damages in the DNA and apoptosis
in human cells from promyelocytic leukaemia cell line
(HL-60) [69]. It was also showed that culture of Bacillus
velezensis is able to degrade and detoxify completely
the toxicity presented by the metabolites of the azo
dye Direct Red 28.
Oral exposure of humans to azo dyes can lead to the
formation of aromatic amines, both by the intestinal
microflora and by liver azoreductases and some of
these amines have presented carcinogenic properties
[70].
Several azo dyes present genotoxic, mutagenic and
carcinogenic activity in tests with microorganisms and
mammalian cells [71-75]). The 3-methoxy-4-
aminobenzene, for example, is mutagenic for bacteria
and carcinogenic for rats, while 2-methoxy-4-
aminobenzene is weakly mutagenic for bacteria but
not carcinogenic for rats [76]. Thus, the genotoxicity,
mutagenicity and carcinogenicity of dyes are closely
related with the nature and position of the substituent
bond to the azo group [25].
Exposure to some azo dyes has been related to the
development of bladder cancer, splenic sarcomas,
hepatocellular carcinomas, cell anomalies and
chromosome aberrations [61, 77-80]. These effects can
be derived from the direct action of dyes on cells or
mainly from the formation of products of the
metabolism resulting from the reduction of the azo
bond [28], which are capable of interaction with the
molecule of DNA, damaging it [25, 81-82].
Studies performed by Alves de Lima et al. [83], in the
aberrant crypt test, showed that a sample of a certain
effluent containing azo compounds (C.I. Disperse Blue
373, C.I. Disperse Violet 93 and C.I. Disperse Orange
37) of the Black Dye Commercial Product (BDCP),
induced an increase of pre-neoplastic lesions in the
colon of rats exposed to concentrations of 1% and 10%
of this effluent.
Some authors [60] described carcinogenic activities for
the azo dye C.I. Pigment Red 53:1, through
observation of lung tumours in male rats. They also
reported that, according to IARC, o azo dye C.I.
Solvent Yellow 14 is also considered carcinogenic,
since it is able to induce hepatocellular carcinoma,
besides tumours in the urinary tract of rats.
It was proven the hepatocarcinogenic action of the azo
dye p-dimethylaminobenzene (p-DAB) for mice and
rats, when they were fed by long periods with low
doses of this compound. Chronic intake of these
animals with p-DAB resulted in a significant increase
in the mitotic activity of the liver parenchyma cells in
relation to the negative control [54].
Besides the carcinogenic and teratogenic effects, azo
dyes cause dysfunction in the reproductive organs of
rodents. For example, pre-natal exposure to Congo
Red permanently reduced the number of germ cells in
male and female rats and mice [84]. Another study
showed adverse effects of the exposure of the gonads
of young males and females of rats, but there was only
reduction of the fertility for young females [85].
Suryavathi et al. [86] studied the toxic effects in short
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91
term (15 days) of textile effluents on the male
reproductive system of adult rats and mice. The
effluents containing azo dyes caused the decrease of
the body weight (7-25%) and length of the
reproductive organ (testes, epididymis, prostate and
seminal vesicles) (2-48%) of the animals treated.
Histopathological analyses also showed alterations in
the spermatogenesis process with various
abnormalities in sperm, such as reduction in the
quantity of spermatozoids (10-59%) and altered
mobility (14-56%), which affected the fertility of the
animals.
Treatments of Textile Effluents
General Considerations
Aquatic environments are of extreme importance for
the world population, since they are used as source to
obtain water, agricultural activities and for animal
production, and are also associated to recreational
activities. The final destination of a large quantity of
pollutants, derived from industrial, agricultural and
domestic activities, are the rivers, lakes and oceans.
This water pollution puts at risk all the population that
lives near to hydric resources [87].
Dyestuff industries and textile industries are,
respectively, the largest producers and users of azo
dyes, producing tons of residues which are released
into the environment and cause serious problems, due
to the chemical and photolytic stability, which elapses
in its high persistence in natural environments [26, 88-
89]. Installation of efficient treatment of effluents in
textile industries that use azo dyes is a growing
concern due to the visible aesthetic impact caused by
the discharge of residues that reaches water bodies, as
well as the possible toxic effects that these compounds
can promote on the biota associated to these hydric
resources. As the environmental legislation becomes
more demanding, the effectiveness and reduction of
the cost of the treatment processes become more
important [1].
Environmental contamination resulted from the
emission of effluents of dyeing industries is a global
problem [9], therefore different methods of effluents
treatment have been used in an attempt to minimize
the problems resulted from this contamination [2]. The
textile dyes can be removed, physically by processes of
flocculation, adsorption, activated coal, wood chips,
silica gel, filtration by membranes, ion exchange, UV
radiation, electrokinetic coagulation and filtration, or
chemically by processes of oxidation, peroxidation of
salts of iron II (Fenton reaction), ozonization,
photochemical processes of electrochemical
destruction, UV-peroxide system, cucurbituril and by
sodium hypochlorite [5]. However, most of these
methods, which simply accumulate or concentrate the
dyes [5], present high cost and trigger secondary
pollution, caused by the excessive use of chemical
substances [90].
Azo dyes biodegradation
Bioremediation, i.e., biological degradation of these
dyes is a treatment process that has been highlighted,
since it degrades the pollutants and do not accumulate
these chemical compounds into the environment.
However, for the bioremediation constitutes an
efficient treatment, it is necessary to take into
considerations which are the enzymes able to degrade
certain azo dyes [29, 90, 91], since they are synthetic
compounds relatively resistant to biological
degradation processes, due to the complex chemical
structure [26, 92]. It should be also performed tests
that evaluate the toxic or inhibitory effects of these
pollutants in the microbial population [93]. Due to the
fact that most of the synthetic dyes are recalcitrant to
the microbial degradation, effluents of the textile
industries are normally resistant to the biological
treatment, both with microorganisms and plants [94-
97].
Mcmullan et al. [98] stated that the ability of the
microorganisms to discolour and metabolize dyes is
known for a long time, and the use of technologies
based on the bioremediation, for the treatment of
textile effluent, has aroused great interest. Researches
performed in the last decades have shown an increase
in the number of microorganisms that are able to
discolour and degrade artificial dyes [99].
Azo dyes are scarcely biodegradable organic
compounds due to their high stability to light and
resistance to microbial attack. These dyes are resistant
to conventional biodegradation [100, 101], however,
under anaerobic conditions, they have been associated
with the generation of metabolites. According to
Saratale et al. [102], there are some species of
microorganisms that, under certain environmental
conditions, are able to completely mineralize several
types of azo dyes. In the initial stage of anaerobic
degradation of azo dyes, a reductive cleavage of the
azo bonds begins to occur, originating from aromatic
amines, which are recalcitrant for anaerobic bacteria
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[103, 104], with exception of few aromatic amines
substituted by hydroxyl and carbon-hydroxyl groups,
which are degraded under methanogenic conditions
[105]. On the other hand, aromatic amines are readily
degraded anaerobically [106, 107].
Although azo dyes represent a potentially important
class of pollutants, little is known about their fate [108].
For about 30 years, several studies have been carried
out aiming to use microorganisms as agents in the
bioremediation treatment of aquatic bodies containing
textile dyes [109]. According to Saratale et al. [102], a
great variety of organisms are able to discolour dyes,
such as bacteria, basidiomycete fungi, yeasts, algae
and plants. Biological methods used in the treatment
of effluents that contain dyes use different organisms
[2], and some microorganisms have received great
attention, regarding their capacity and ability in the
process of discolouring effluents of textile industries
[29]. Discolouring of dyes by microorganisms is
commonly performed by bacteria and basidiomycete
fungi. However, there are other organisms able to
degrade azo dyes, such as some algae [110-112] and
plants [113, 114].
Contaminations by dyes of the azo type can
characterize a great danger to exposed organisms,
besides being toxic due to their own chemical
properties, they can be transformed into even more
toxic compounds by their metabolization of
microorganisms present in the environment. There is
an urgency to assess the effectiveness of biological
treatments of industrial effluents, since, normally, the
biodegradation products are even more detrimental to
the environment, due to the high toxicity of the
metabolites produced during the biodegradation
processes [66].
Due to the diversity, concentration and composition of
the dyes present in the effluents, there is a great
motivation for researchers to study the biodegradation
of hazardous compounds as well as to discover
microorganisms that are able to degrade efficiently a
great number of pollutants at a very low operational
cost [9].
Bacteria group used in the degradation of dyes is
considered, particularly, useful in the degradation of
azo dyes, since they have the capacity to perform the
reductive cleavage of the azo bonds, present in this
type of compound [9].
Metabolization of azo dyes by bacteria, under
anaerobic conditions, may occur in different ways: 1.
cleavage of the azo bond, catalyzed by azoreductases
(cytoplasmic enzymes with low specificity to the
substrate) [8, 9]; 2. non-specific reduction by electron
carriers (redox reaction), from cell metabolic pathways
(ex: release of flavins, quinines, hydroquinones) [115-
117]; 3. action of reduced inorganic compounds, such
as Fe2+, which are formed as final product of certain
metabolic reaction by strictly anaerobic bacteria [8,
117-119]; 4. chemical reduction by sulphil radicals,
generated in the reduction of sulphate salts [116, 117].
According to Brown and Hamburger [120], total
mineralization of non coloured aromatic amines,
formed from the bacterial degradation of azo dyes, is
not possible under anaerobic conditions and, therefore,
these amines are accumulated in the environment,
which may have toxic, mutagenic actions and,
possibly, carcinogenic actions to the exposed animals
[1]. It is important to consider that the bacterial
treatment, in aerobic conditions, is generally efficient
to mineralize totally these aromatic amines [121, 122].
In the State of São Paulo - Brazil, most industries of
dye processing, mainly use systems of activated
sludge to treat their effluents. However, some studies
showed that the activated sludge systems are not
efficient to remove all the dyes and aromatic amines
present in industrial effluents. According to the
studies of Van der Zee et al. [118], it was observed that
the application of activated sludge in ascending
laminar flow hood, in anaerobic conditions, caused the
significant reduction in the colouration in only 8 of the
20 types of azo dyes. Shaul et al. [101], studying 18
types of azo dyes, observed that 11 of them were not
altered by the activated sludge treatment, 4 (Acid Blue
113, Acid Red 151, Direct Violet 9 and Direct Violet 28)
were adsorbed into the activated sludge (composed by
different species of bacteria) and only 3 (Acid Orange
7, Acid Orange 8 and Acid Red 88) were biodegraded.
Studies [123] showed that 20% of the dye C.I. Disperse
Blue 79 remained in the final effluent after treatment
with activated sludge. Detection and quantification of
components of black commercial dye (BDCP Black
Dye Commercial Product), present in samples of raw
and treated effluents of Cristais River, showed that
this commercial product is recalcitrant even after
aerobic treatment [124].
Bacterial ability to biodegrade azo dyes has been
reported for many species, such as: Aeromonas sp.,
Bacillus sp., Pseudomonas sp., Rhodococcus sp., Shigella
sp., Klebsiella sp., Proteus mirabilis; Pseudomonas luteola
and Mycobacterium avium [125-128]. Studies performed
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by Wong and Yuen [46] showed that the bacteria
Klebsiella pneumoniae was efficient in the degradation
of an azo dye, the methyl red, inferring that it could be
used in the treatment of industrial effluents containing
other azo dyes. Zissi and Lyberatos [129] showed that
the bacteria Bacillus subtilis was able to degrade azo
dyes present in effluents of textile industries. Studies
performed by many researchers [98, 130-133] showed
that certain bacteria of the genus Streptomyces, known
to produce extracellular peroxidases that acted in the
degradation of lignin, were effective in the
degradation of dyes. However, in aerobic conditions,
azo dyes are more resistant to the bacterial attack [125].
The bacteria Kocuria rosea presents high potential of
discolouring and degrading the sulphonated azo dye
methyl orange, besides originating degradation
products (4-amino sulphonic acid and N,N’-dimethyl-
p-phenilenediamine) that were not toxic for plants
(Sorghum vulgare and Phaseolus mungo) and bacteria
(Kocuria rosea, Pseudomonas aeruginosa and Azotobacter
vinelandii) [134].
According to Kakuta et al. [135], some yeasts are able
to degrade synthetic dyes. Some studies [136-139]
showed that some species of yeasts, such as Candida
zeylanoides, Saccharomyces cerevisiae and Issatchenkia
occidentalis, have the ability to cleave the azo bonds of
azo dyes, originating aromatic amines, by reduction
mechanism similar to those of several bacteria. Vitor
[140] showed that the yeast Candida albicans has the
ability to degrade an azo dye, the “Direct Violet 51”,
indicating that the more vulnerable sites for disruption
of this compound are the bonds of nitrogen with
secondary amines. According to Meehan et al. [141],
colour removal of Remazol Black-B by the yeast
Kluyveromyces marxianus occurred due to the chemical
adsorption of these azo dyes by the cell biomass but
not due to any chemical enzymatic activities. Studies
[90] showed that the yeast Saccharomyces cerevisae
degraded efficiently, the azo dye methyl red,
considered toxic, may be used in the biodegradation
processes of dyes present in the environment.
According to Ramalho et al. [139], yeasts, mainly
Saccharomyces cerevisae, are good agents in the
bioremediation of azo dyes, since their growth and
viability are not affected by the presence of dyes and
their metabolites (potentially carcinogenic and
mutagenic), besides organisms being able to perform
the complete mineralization of azo compounds. The
yeast Saccharomyces cerevisae represents, besides a low
cost biological material, a promising organism in the
removal of a toxic azo dye, the methyl red, was found
in effluents from dyeing industries, since it was able to
rapidly and totally degrade the referred dye [142].
Kunz [143] confirmed that studies concerning the
biodegradation of toxic effluents have increased in the
last years, and there is a great highlight for the
basidiomycetes fungi. These fungi are used in the food
industry, in the production of enzymes, treatment of
effluents and other activities.
The degradation process of dyes by basidiomycete
fungi, mainly the white-rot fungi, which are
microorganisms with great ability to biodegrade dyes,
are linked to the action of exoenzymes that act on
lignin (structural polymer found in the cell wall of
plants), such as laccases, ligning peroxidases (LiP),
peroxidases dependent on manganese (MnP) [144,
145], as well as enzymes that produce H2O2 [5, 6, 146],
which has the ability to degrade several recalcitrant
pollutants, including the synthetic dyes [147-148].
Among the white-rot fungi that have the capacity to
degrade dioxins, polychlorinated biphenyls (PCBs),
other chlorinated organic compounds and azo dyes,
this capacity is directly related to the nature of the
substituent groups of the aromatic rings, we can
mention Phanerochaete chrysosporium [96, 146, 149-152],
Trametes versicolor [153-155], Coriolus versicolor [156,
157] and Bjerkandera adusta [153, 158]. Other groups of
fungi that have also shown to be efficient in
discolouring dyes are: Aspergillus niger [159],
Geotrichum candidum [92, 160], Pleurotus ostreatus [97];
[161, 162] and Cunninghamella elegans [163, 164],
among others.
Martins et al. [95, 96, 97] have carried out several
assays on the biodegradation of azo dyes of textile
applications by the filamentous fungus Phanerochaete
chrysosporium to assess its recalcitrance, mainly, until
at which point they would be recalcitrant. It was
verified that the concentrations of nutrients and the
azo dyes, as well as the structures of the azo dyes,
interfere in the processes of their biodegradation.
Studies [162] showed that white-rot fungi degrade the
azo dye Disperse Orange 3, originating aromatic
amines, by an oxidative mechanism, which is different
from the anaerobic bacterial way. Kirby et al. [146]
showed that the fungi Phlebia tremellosa were able to
degrade 8 synthetic textile dyes present in artificial
effluents, at the concentration of 200 mg/L, reducing
about 96% its colour. Studies [165] showed the
fragmentation of different azo dyes by the action of
the fungi Neurospora crassa, originating, at least, two
amino compounds, besides producing aniline in great
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quantities, which explains the increase of the toxicity
of azo dyes after degradation. According to these
studies, the dyes “Procion Red MX-5B” and “Acid Red
151” were considered the most toxic and the dyes
“Direct Red 23” and “Erythrosine B”, the least toxic.
Anastasi et al. [166] performed a study on the
degradation of industrial dyes, among which the azo
in 17 species of basiciomycete fungi belonging to
different ecophysiological groups, meanwhile he
demonstrated the efficiency of fungi in performing the
discolouration of simulated effluents composed by one
or several dyes together. According to the above, the
ecotoxicity test with Lemna minor showed a significant
reduction in the toxicity of dyes after treatment by the
fungi Bjerkandera adusta, indicating that the
discolouration induced by this fungus was followed
by detoxification events.
There are some algae species able to degrade azo dyes,
with the help of reduction mechanisms [167]. The ones
form the genus Chlorella [110, 112] and Oscillatoria [110]
and Spirogyra [111] are able to degrade these
compounds into aromatic amines, which, in turn, can
be further metabolized into organic compounds or
CO2 [112].
Among the organism that are able to degrade azo dyes,
some species of plants can be cited, such as Rheum
rabarbarum [113] Brassica juncea, Sorghum vulgare and
Phaseolus mungo [168] and several typical plants of
flooded environments [114]. Studies performed by
Kagalkar et al. [169] showed the efficiency of Blumea
malcommi (an herbal plant from the Asteraceae family)
in degrading a textile azo dye, the Reactive Red 5B.
Deniz and Saygideger [170] showed that princess tree
leaves (Paulownia tomentosa) can be used in the
removal of another textile azo dye, the Basic Red 46.
Although plant species are able to biodegrade dyes,
their large-scale application is still not absolutely
feasible, mainly due to the limited tolerance of the
plants to concentration of pollutants as well as the
need of large areas for implanting phytoremediation
[168].
Final Considerations
The major environmental problems in the textile
industry are related to the use of azo dyes, a large
family of synthetic dyes highly resistant to natural
degradation and proved toxic potential due to their
ability to induce various toxic, cytotoxic, genotoxic,
mutagenic and carcinogenic effects on different
organisms when exposed to such compounds.
In addition to the problems related to the release of
toxic substances or to the discharge of compounds
which can be converted into metabolites which are
most harmful to the environment, the effluents
derived from dye activities have strong staining.
Besides being a source of visual pollution, that feature
offers serious environmental risks; mainly due to the
interference in the natural photosynthetic processes
that causes incalculable losses in medium and long
term for all aquatic biota.
From the data presented here, it can be concluded that
the immediate development of dyes free from toxic
potential as well as dyes with low toxicity is urgently
required; so does the increased investment in the
research aiming at developing effective methods for
the biological treatment of effluent textiles, in order to
avoid or reduce the possibility of harmful effects of
these chemical compounds on the environment and
the exposed organisms, including human health.
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Bruna.Ventura-Camargo.Born in the city of Itapetininga,
São Paulo State, Brazil, in 1981. Bachelor of Biological
Sciences, São Paulo State University (UNESP), Rio Claro,
São Paulo, Brazil, in 2002. Licensed in Biological Sciences,
São Paulo State University (UNESP), Rio Claro, São Paulo,
Brazil, in 2003. Master in Biological Sciences (Molecular and
Cellular Biology), São Paulo State University (UNESP), Rio
Claro, São Paulo, Brazil, in 2004. PhD in Biological Sciences
(Molecular and Cellular Biology), São Paulo State University
(UNESP), Rio Claro, São Paulo, Brazil, in 2009. Since 2011 is
a postdoctoral researcher at São Paulo State University
(UNESP), Rio Claro, São Paulo, Brazil. Since 2000, Dr.
Ventura-Camargo acts in the Ecotoxicology and
Environmental Mutagenesis areas.
Maria Aparecida. Marin-Morales.Born in the city of
Limeira, São Paulo State, Brazil, in 1953.Degree in
BiologicalSciences, São Paulo StateUniversity (UNESP), Rio
Claro, São Paulo, Brazil, 1976. Master in BiologicalSciences
(PlantBiology), São Paulo StateUniversity (UNESP), Rio
Claro, São Paulo, Brazil, 1983. PhD in BiologicalSciences
(PlantBiology), São Paulo StateUniversity (UNESP), Rio
Claro, São Paulo, Brazil, 1992. Post-doctoral in Biological
Sciences, Superior Council for Scientific Research (CSIC),
Barcelona, Spain, 2011. Since 1992 is teacher of graduation
and post-graduation courses at São Paulo State University
(UNESP), São Paulo, Brazil. Dr. Marin-Morales has
experience in Genetics, and since 2000, she acts in the
Ecotoxicology and Environmental Mutagenesis areas.
... Because synthetic dyes are more affordable, offer a greater variety of vibrant shades, and have significantly better fastness properties than natural dyes, the textile dyeing industry currently uses an excessive amount of synthetic dyes to meet the required coloration of textiles for global consumption (El- Nagar et al., 2005;Iqbal et al., 2008) [11,17] . Such dyes have detrimental effects on the eco-balance of the environment and pose major health risks when applied (Bruna and Maria 2013; Goodarzian and Ekrami 2010;Jothi 2008) [8,13,18] . Because of this, natural dyes are one of the most viable possibilities for creating a more environmentally friendly textile dying process, and the growing number of recent publications reflects this enthusiasm. ...
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... Despite the essential role that food additives play in food supply, they can also have various harmful effects such as urticaria, hyperactivity, dermatitis, migraines, and anaphylaxis [7]. Sunset Yellow was previously associated with hyperactivity in children, suppression of the immune system's response, and was believed to be genotoxic to human lymphocytes even at permissible levels [8]. ...
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... The comprehensive analysis of this cell, which includes the Quinoline Yellow dye sensitizer, DOSS surfactant, cellobiose reductant, and fabrication parameters like Sodium Hydroxide (NaOH) in distilled water, has shown exceptional electrical performance, indicating potential for commercialization. Given the environmental risks associated with dyes [26] so the use of Quinoline yellow which is a food-grade dye [27] alongside the biodegradable cellobiose reductant, presents an eco-friendly and cost-effective photogalvanic system. Furthermore, the adoption of a smaller platinum electrode (0.2 × 0.15 cm 2 ) has not only enhanced electrical performance but also proven more economical compared to larger electrodes in previous designs. ...
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Solar energy is gradually becoming integrated into households, holding the potential to address energy requirements through technologies like PV cells. Ongoing research is actively exploring diverse methods of harnessing solar power, with Photogalvanic cells emerging as a particularly promising alternative to Photovoltaic cells. The advantage lies in the cost-effectiveness and simplified fabrication, coupled with the capability of power storage. The utilization of the economical Dioctyl sulfosuccinate sodium (DOSS) surfactant, widely employed in industry, has yielded impressive electrical performance. The present investigation presents a reliable photogalvanic system composed of the photosensitizer dye Quinoline Yellow, the reductant Cellobiose, and the surfactant Dioctyl sulfosuccinate sodium (DOSS), all in a highly alkaline solution with platinum and graphite electrodes. The platinum electrode employed is notably small, boasting a surface area of 0.03 cm2, which enhances the diffusion characteristics of the dye molecules, it is contributing to an enhanced electrical performance of the photogalvanic cell. The resulting photogalvanic cell demonstrates superior electrical performance, featuring a maximum potential of 870 mV, a maximum current of 8000 μA, power at PowerPoint of 695 μW, a fill factor of 0.11, and a conversion efficiency of 13.78 %. Spectrophotometric analysis has confirmed the stability of the dye within the electrolyte solution. Additionally, conductometric analysis has revealed that the surfactant Dioctyl sulfosuccinate sodium (DOSS) enhances the electrical conductivity of the electrolyte solution.
... Dyes and various organic compounds used for coloring are chemical entities; have been included by the technology in our regular life (De CamposVentura-Camargo & Marin-Morales, 2013). Among all synthetic dyes, azo dyes comprise the largest and the most substantial class of dyes for industrial utilization. ...
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The oxidation of acid orange 7, a mono azo dye by hexacyanoferrate abbreviated as HCF(III) ions in the aqueous basic medium using polyvinylpyrrolidone assisted Ir-Ni bimetallic nanoparticles abbreviated as (Ir-Ni/PVP BMNPs) as promoter has been examined by kinetic spectrophotometric technique at λ max 484 nm of the reaction mixture. The impact of different parameters on reaction rate such as dye concentration, (oxidant) HCF(III) ions concentration, and pH of the solution have been investigated under the same practical conditions. The outcome represents that the oxidation rate of the dye enhances linearly with the increment in [oxidant] and [dye] at optimum pH 8.5 and stable temperature 40±0.1 • C. Thermodynamic parameters such as activation energy (Ea), enthalpy (∆H #), free energy of activation (∆F #), and frequency factor (A) have been calculated by analyzing the rate of reaction at four different temperature, that is, 40-55 • C. Ultraviolet visible spectroscopy (UV-Vis), fourier transform infrared spectroscopy (FTIR), and liquid chromatography (LC) mass spectrometry (LCMS) analytical techniques were used to confirm the oxidation of dyes into some simpler and less perilous products. Thus, the present method is simpler, and cost effective due to the need of less amount of oxidant (about 10 times less) as compared to the reported methods. Thus, this study may be helpful for industrial purposes for improvement in quality of wastewater of textile industries and many others. K E Y W O R D S azo dye (Acid orange 7), degradation, hexacyanoferrate (III) ions, Ir-Ni bimetallic nanoparticles, polyvinylpyrrolidone
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Biological oxidation of azo-dyes is important for wastewater treatment. Azo-dyes are synthetic organic colorants that exhibit great structural variety. A large majority of these dyes are released into the environment. The textile industry and dyestuff manufacturing industry are two major sources of released azodyes. In the present study, we focus on the anoxic degradation of a disperse azo-dye, p-aminoazobenzene (pAAB), a simple azo-dye, by a pure culture of Bacillus subtilis, growing on a synthetic medium. Bacillus subtilis is a bacterium capable of using nitrate and/or nitrite as terminal electron acceptor under anoxic conditions. This bacterium lacks the capability for fermentation. The degradation of p-aminoazobenzene by Bacillus subtilis was examined through batch experiments in order to elucidate the mechanism of dye degradation. The results proved that Bacillus subtilis co-metabolizes p-aminoazobenzene under denitrifying conditions, in the presence of glucose as carbon source, producing aniline and p-phenylenediamine as the nitrogen-nitrogen double bond is broken.
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The biodegradability of seventeen N-substituted aromatic and six alkylphenol compounds were evaluated under methanogenic conditions. Biodegradation was assessed in batch assays inoculated with unacclimated and predigested anaerobic granular sludge at 30°C under agitated conditions over a 150 day period. The compounds were supplied at sub-toxic concentrations in the assays in order to prevent inhibition to the methanogens. The biodegradability test was performed by the measurement of the methane composition in the headspace of the serum flasks. The methanogenic consortia completely mineralized 2-, 3-aminobenzoate, 2-aminophenol and 4-cresol; whereas, 4-aminobenzoate was only partially degraded. The other N-substituted compounds and the alkylphenols tested were not biodegradable under the experimental conditions employed. An additional biodegradability assay was conducted with sludge from an upward-flow anaerobic sludge bed reactor adapted to the degradation of 2-nitrophenol. This sludge mineralized 2-aminophenol without any lag phase while the unadapted sludge required 110 days of acclimation. The three aminobenzoate isomers were fully mineralized by the adapted sludge after similar lag periods observed in the unadapted sludge. The 2-nitrophenol adapted sludge cross-acclimatized to the mineralization of 5-aminosalicylate and 4-aminophenol. This constitutes the first report demonstrating the anaerobic mineralization of 5-aminosalicylate, which indicates that at least some azo dye cleavage products can be degraded in methanogenic consortia.
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The present study describes the relationship between gonadal agenesis and fertility in male and female mice exposed in utero to the diazo dye Congo red (CR). Maternal CR treatment inhibited testicular and ovarian function in the offspring alter oral administration of I or 0.5 g/kg/day on Gestational Days 8–12. The testes of male offspring from CR-exposed dams were small in size and contained hypospermatogenic seminiferous tubules. However, despite the fact that testis weight was reduced by more than 70% in some males, they displayed normal levels of fertility when mated to untreated females for over 10 months. In contrast, female offspring from CR-exposed dams produced only about half as many litters and pups as the control pairs did under long- term mating conditions. Histological examination of the ovaries revealed that subfertility was correlated with ovarian atrophy. Females lacking maturing follicles were considerably less productive (1.3 litters and 11.5 pups) than treated females with histologically normal ovaries (7.1 litters and 78.1 pups). In sum mary, prenatal exposure to the dye CR affects the gonads of both male and female offspring, but only the female offspring display reduced fertility.
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The mechanism, technology and character of the anaerobic-aerobic treatment of dye wastewater by combination of fixed film with suspended growth after acclimatization are discussed in this paper. The results show that the COD decreased from 600-900mg/l of influent to about 150mg/l of effluent. The BOD and the dilution times of colourity decreased from 200-300mg/l and 200-500 times to less than 50mg/l and about 80 times respectively, when the HRT and COD RBC-area load of anaerobic and aerobic RBC were 7-8hrs and 4.5-5hrs and 40-50g/m2·d and 30-40g/m2 respectively. This treatment process has the advantage of very low waste sludge. Either anaerobic or aerobic RBC has better quality transmission and mixing ability, so that MLSS in the tank were about 1000-3000mg/l without any blockages of RBC. The efficiency of a 3 stage alone oblique cross passageways packing RBC with sludge return was also high, except in regard to colour under aerobic conditions only.
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Pseudomonas luteola grew well in media containing low glucose concentration (0.125%) and no nitrogen source. It had 95% color removability within 5 days through shaking-static incubation process. It was found that the azoreductase of P. luteola was an inducible enzyme; it reacted with RP2B in a first order reaction. The azo dye acted as an inducer without serving as a growth substrate. The metabolic product of the degradation of RP2B by P. luteola was onhanilic acid. P. luteola's high RP2B degradation ability, low nutritient requirement and shaking-static decolorization process enable it to be used in the treatment of industrial effluent containing azo dyes.
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Of the five species of white rot fungi evaluated for their ability to decolorize Amaranth, Remazol Black B, Remazol Orange, Remazol Brilliant Blue, Reactive Blue, and Tropaeolin O in agar plates, Bjerkandera sp. BOS55, Phanerochaete chrysosporium, and Trametes versicolor displayed the greatest extent of decoloration. In static aqueous culture, the three cultures formed fungal mats which did not decolorize any dye beyond some mycelial sorption. When agitated at 200 rpm, the biomass grew as mycelial pellets. Bjerkandera sp. BOS55 pellets decolorized only Amaranth, Remazol Black B, and Remazol Orange. P. chrysosporium and T. versicolor pellets were capable of decolorizing most dyes with decoloration by T. versicolor being several times more rapid. Batch cultures of Bjerkandera sp. BOS55 and P. chrysosporium had a limited ability to decolorize repeated dye additions; however, T. versicolor rapidly decolorized repeated additions of the different dyes and dye mixtures without any visual sorption of any dye to the pellets. The choice of buffer had a profound effect on pH stability upon dye addition, and consequently, decoloration. The use of 2,2′-dimethylsuccinic acid allowed for excellent pH control and resulted in high decoloration ability.