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Synthetic azo dyes are widely used in industries. Gerhardt Domagk discovered that the antimicrobial effect of red azo dye Prontosil was due to the reductively cleaved (azo reduction) product sulfanilamine. The significance of azo reduction is thus revealed. Azo reduction can be accomplished by human intestinal microflora, skin microflora, environmental microorganisms, to a lesser extent by human liver azoreductase, and by non-biological means. Some azo dyes can be carcinogenic without being cleaved into aromatic amines. However, the carcinogenicity of many azo dyes is due to their cleaved product such as benzidine. Benzidine induces various human and animal tumors. Another azo dye component p-phenylenediamine (p-PDA) is a contact allergen. Many many azo dyes and their reductively cleaved products as well as chemically related aromatic amines are reported to affect human health, causing allergies and other human maladies.
Azo Dyes and Human Health: A Review
King-Thom Chung, Department of Biological Sciences
The University of Memphis, Memphis, Tennessee 38152
Synthetic azo dyes are widely used in industries. Gerhardt Domagk discovered that the
antimicrobial effect of red azo dye Prontosil was due to the reductively cleaved (azo
reduction) product sulfanilamine. The significance of azo reduction is thus revealed. Azo
reduction can be accomplished by human intestinal microflora, skin microflora,
environmental microorganisms, to a lesser extent by human liver azoreductase, and by non-
biological means. Some azo dyes can be carcinogenic without being cleaved into aromatic
amines. However, the carcinogenicity of many azo dyes is due to their cleaved product such
as benzidine. Benzidine induces various human and animal tumors. Another azo dye
component p-phenylenediamine (p-PDA) is a contact allergen. Many many azo dyes and
their reductively cleaved products as well as chemically related aromatic amines are reported
to affect human health, causing allergies and other human maladies.
Azo compounds are chemically represented as R–N=N-R’, where –N=N- is the azo
group, and the R or R’ can be either aryl or alkyl compounds. The International Union of Pure
and Applied Chemistry (IUPAC) defines azo compounds as “derivative of diazene (diimide),
HN=NH, wherein both hydrogens are substituted by hydrocarbyl group, e.g. PhN=NPh
azobenzene or diphenyldiazene” (1). The word azo comes from azote, the French name for
nitrogen that is derived from the Greek a (not) zoe (to live). Historically, the emmergence of
azo dyes was an important step in the development of the chemical industry.
Azo dyes are compounds consisting of a diazotized amine coupled to an amine or a
phenol and contain one or more azo linkages. The essential precursors of azo dyes are
aromatic amines.
Azo compounds have vivid colors and comprise about two-thirds of all synthetic dyes
and are by far the most widely used and structurally diverse class of organic dyes in
commerce (2). At least 3,000 azo dyes available in the past and were used in
pharmaceutical and paper industries as well as printing inks, paints, varnish, lacquer, and
wood stains (3). The colorants of synthetic and natural textile fibers, plastics, leather, hair
dyes, waxes, and petroleum are also azo dyes (4). Azo dyes are the largest and most versatile
class of dyes and account for more than 50% of the dyes produced worldwide (5).
Presumably, more than 2,000 different azo dyes are currently used and over 7 x 105 tons of
these dyes are produced worldwide (6). More than 3,000 tons of azo dyes were certified in
1991 by the U.S. Food and Drug Administration (FDA) for use in foods, drugs, and
cosmetics. These dyes constitute the major group of FDA certified colorants (5).
Azo dyes are stable in light and resistant to microbial degradation or fading away due to
washing. Therefore, azo dyes are not readily removed from waste water by conventional
waste water treatment methods. It has been estimated that about 10% of the dyestuff in the
dyeing process of textiles do not bind to fibers and are, therefore, released to the environment
(5, 7).
Some azo dye components such as benzidine have been linked to cancers of human
bladder. Also, there is a higher incidence of bladder cancer in dye workers exposed to
azo dyes (5). Therefore, azo dyes pose lethal effects, genotoxicity, mutagenicity, and
carcinogenicity to humans as well as animals. Indiscriminate disposal of azo dyes into the
environment especially from the textile industry is a major threat to human health and
environment (8). This paper is to review the effects of azo dyes and their metabolites and
some chemically related compounds.
a. Story of Prontosil
The first azo dye used in medicine is Prontosil (sulfamidochrysoidine) (C12H13N5
O2S) (Figure 1), which is a red coal-tar dye with low toxicity and is used on leather dye. Other
names for this substance include Sulfoamidochrysoidine, Rubiazol, Prontosil, Aseptil Rojo,
Streptocide, and Sulfamidochrysoidine Hydrochloride. Later the name was abbreviated to
Prontosil. Prontosil was first synthesized by Bayer chemists Josel Klarer (1898-1953) and
Fritz Mietzsch (1896-1958) as part of a research program designed to find dyes that might act
as antibacterial drugs for the I. G. Farbeni Industrie directed by Gerhardt Domagk (1895-
Prontosil was found to be effective against Gram-positive cocci but not against enterobacteria.
in a murine model of Streptococcus pyogenes systemic infection that preliminary establishedT
the antibacterial efficacy of Prontosil in mice was established in the murine model of
Streptococcus pyogenes systemic infections. This was accomplished from late before
December of 19321. In the same year, I. G.
Farbenindustrie obtained a German patent for the medical utility of Prontosil.
on December of 1932. In the late autumn of 1932, it was found effective against some
important bacterial infections in mice led by Gerhardt Domagk (1895-1964).
Gerhardt Domagk was responsible for finding antibacterial agents, fir test tube, and then in
vivo or living using rats or rabbits
both in vitro and in vivo.such as mice and rabbits. Domagk tested thousands of compounds
related to azo dyes, and
brought the importance of Prontosil to the world’s attention shortly afterward in 1932.
Domagk conducted an experiment whereby he injected 26 mice with a hemolytic
streptococcal bacterial culture, then injected 12 mice with as single dose of Prontosil an hour
and a half later. The 14 control mice died. The 12 injected mice, on the other hand, survived.
Domagk discovered that Prontosil affected streptococci in vivo but not in vitro and was non-
toxic to mice. For reason unknown, A very dramatic but not published story) was that
Domagk tested this compound
on his four-year-old daughter, Hildegarde, who contracted a streptococcal infection in her
father’s laboratory when she wasaccidently pricked with a needle. After making 14 incisions,
the physiciansurgeon could find no other solution than to recommend to Domagk the parent
that they should
haveve herthe arm amputated. At this moment Domagk himselhimself fintervened in the
Domagk injectedinjected Hildegarde with a dose of Prontosil and she recovered. The results
finally published in a paper in the February, 1935 issue of the German journal Deutsche
Medizinische Wochenschrift (9). Eventually, the therapeutic effect of Prontosil it was well
spread, out,and many other researchers began to work with Prontosil. French scientist
Tréfouël (1892- 1978) and his group (the third Director of Pasteur Institute) in 1936
discovered that Prontosil was metabolized into
sulfanilamide (p-aminophenyl-sulfonamide) and identifiedy this group as the active
of Prontosil (10).
Sulfanilamide is a simple, colorless molecule and was a simple, colorless molecule,
which was first synthesized by Paul Geimo, a chemistry student working at the University of
Vienna in his 1909 thesis. Sulfanilamide was patented in Germany patent as in 1909 by and
later sold by Bayer as Prontalin. Prontosil was redefined as a prodrug then. Sulfanilamide
Prontalbin became the first oral version of sulfonamide drugs fanilamide but without realizing
its medical potential at this(10, 11). Following studies discovered that this compound was
bacteriostatic by blocking metabolism. The mode of action mechanism of sulfanilamide was
to act as an antimetabolite of para-aminobenzoic acid (PABA), which is a precursor of
nucleic acid biosynthesis. Sulfanilamide also interferes in different metabolic steps in protein
synthesis. Sulfanilamide and its derivatives were proved to be effective against pneumonia,
meningitis, blood poisoning, and gonorrhea. Sulfanilamide empowered medical doctors to
treat bacterial infections. Because the active gradient sulfanilamide contains sulfur in the
structure, sulfur drugs gained their names and became the major antibacterial agents in that
era. However, these sulfur drugs are basically aromatic amines. Examples of sulfur drugs are
shown in List 1. These aromatic amines also induce urinary tract disorders, hematopoietic
disorders, porphyria, hypersensitivity reactions as side effects. When used in large doses, they
can cause strong allergic reactions such as Stevens-Johnson syndrome and epidermal
necrolysis (Lyell syndrome). About 3% of the general population developed adverse reaction.
In adult immunodeficiency disease (AIDS) patients, the adverse response can reach 50%.
Most common manifestations of hypersensitivity reactions are rash and hives.
Although sulfanilamide (the breaking product from Prontosil) was first synthesized by
Paul Geimo, a chemistry student working at University of Vienna in his 1909 thesis who
however, did not realize its medical potential and cheap to produce. The sulfanilamide moiety
was easily linked to other molecules. Sulfanilamide was off patent in 1936. Sulfanilamide
was off patent in 1936. Prontosil has been replaced in clinical use by other newer
sulfonamide drugs including sulfathiazole, sulfamethoxazole, etc. and soon gave rise to
hundreds of second generation sulfonamide drugs.
Prontosil was investigated by many researchers including Leonard Colebrook (1883-
1967) in England who introduced Prontosil as a cure for puerperal fever (12, 13). Sulfur drugs
were quickly replaced by the newly developed antibiotics that proved to be more effective
against pathogens and diminished the importance of sulfur drugs in chemotherapy. However,
Although quickly eclipsed by these newer “sulfur drugs” and in the mid1940s and through
1950s and a string of newer antibiotics that proved more effective against more type of
bacteria. Prontosil remained as a major drug until the 1960s. Prontsoil is still in use
extensively for
opportunistic infections in patients of urinary infections and burn therapy. SSulfonamide in
combination with -trimethoprim and sulamethoxazole (TMP-SMZ) is an excellent example of
drug synergism. are still used extensively for opportunistic infections in patients with
AIDS, urinary infections and burn therapy. However, Prontosil’s discovery ushered in
the era of antibiotics and had a profound impact on the pharmaceutical industry, medical
history, and human welfare.. Prontosil was investigated by many investigators including
Leonard Colebrook (1883-1967) in England who introduced Prontosil as a cure for
puerperal fever (16, 17, 18, 19).
The metabolism of lipid soluble Prontosil to sulfanilamide is an azo reduction that can
be accomplished by the liver; water soluble azo dyes are mostly reduced by intestinal
and skin microflora. However, during Domagk’s (or Tréfouël’s) time, the role of intestinal
microflora in the metabolism of xenobiotics including azo dyes was not known.
b. Story of Methyl Yellow (Butter Yellow, DAB)
James A. Miller (1917-2000) and Elizabeth C. Miller (1920-1987) pioneered the study of
the carcinogenicity of a well-known azo dye, Methyl Yellow (p-dimethylaminoazobenzene,
DAB, Butter Yellow) (Fig. 2) and its metabolites. They discovered that only 4-monomethyl-
aminoazobenzene and its parent compound DAB were carcinogenic (14). All other
metabolites including 4-aminoazobenzene, 4’-hydroxy-4-monomethyl-
aminoazobenzene, 4’-hydroxy-4-aminoazobenzene, and the reductive cleaved products N-
methyl-p-phenylenediamine, p-phenylenediamine (p-PDA), aniline, p-aminophenol and
o-aminophenol wereas reported not carcinogenic (Fig 2). Nine other compounds, i.e,
4’-hydroxy-4-dimethylaminoazobenzene, 3’-hydroxy-4-dimethyl-amino-azobenzene,
2’-hydroxy-4-dimethylaminoazobenzene, 4-formylamino-azobenzene, 4-hydroxy-
azobenzene, 2, 4’-diamino-5-dimethylaminodiphenyl, 3-dimethyl-aminocarbazole, N, N-
dimethylphenylenediamine (DMPD), and p-hydroquinone may be metabolites, and were also
not carcinogenic. But DMPD was found to be mutagenic in Salmonella typhymurium tester
strain TA1538 in the presence of microsomal activation (15, 16). Azo-reduction of DAB has
been claimed to be a detoxicification (i.e. metabolic deactivation) pathway (17) .Miller and
Miller regarded that azo reduction is a metabolic deactivation (detoxicification).
Chung reviewed the significance of azo reduction in the mutagenesis and carcinogenesis
of several azo dyes and noticedstated that azo reduction is an important metabolic activation
for carcinogenesis of many of many azo dyes ((2318-20). and further postulated that azo
reduction is an initial step of metabolic activation for many azo dyes (24).LATER, P-
Human exposure to azo dyes may occur through ingestion, inhalation, or skin contact.
Azo dyes are biotransformed inside of the body into aromatic amines. Most notable
biotransformation is reductively cleaved into aromatic amines by azo reductases of intestinal
microflora (20). Examples of aromatic amines metabolically produced from azo dyes are
shown in Table 1. A substantial number of environmental microorganisms including
helminths capable of azo dye reduction has been reported (21). Examples of reported
intestinal microorganisms with azo reduction activity are shown in List 2. The azo reductase
activity in a variety of intestinal preparations was affected by various dietary factors such as
cellulose,proteins, fiber, antibiotics, or supplements with live cultures of lactobacilli (20).
Plazek, et al. (22) reported that carcinogenic amines were also produced from azo dye by
human skin bacteria in vitro. Stingley et al. (23) also showed that azo dyes such as Methyl
Red and Orange II were cleaved by human skin microbiota including many species in the
genera of Staphylococcus, Corynebacterium, Kytococcus, Micrococcus, Dermacoccus, and
Kocuria (23). Several hundred species are residents of the human skin and many of them
express azo reductase activity. These facts should be of significance to those who use tattoo
inks, textiles, and cosmetics (22, 23).
Only a few aerobic bacteria have been found to reduce azo dyes under aerobic conditions.
The enzyme responsible for azo dye reduction has been partially purified and
characterizedation. There are three distinct groups of azo-reductases that have been
describedfound. There are: flavin dependent NADH preferred azo reductase, flavin dependent
NADPH preferred azo reductase, and flavin free NADPH preferred azo reductase (24). Each
enzyme has been purified from specific microorganism and studied on the characterization
and crystal structure of azo
reductase in Bacillus subtilis, Escherichia coli, Enterococcus fecalis), Pseudomonas
aeruginosa , Streptomyces cereviceae, and Candida zeylanoides (25-31).
Other environmental microorganisms including (fungifungi yeast), protozoa, and
cestodenematode Ascarins lumbncoides and the nematodecestode Monimezia expansa have
also been reportedreported to reduce azo dyes (32, 33). Chemical reducing agents such as
sodium hydrosulfite, sodium dithionite, zero-valence iron (Feo) and electron sources for
biological reactions such as reduced flavin adenine nucleotides (FADH) as well as reduced
nicotinamide adenine dinucleotide (NADH) are also able to reduce azo dyes (34-36).
Recently, Hong and Gu (37) demonstrated that azo reduction by Shewanella strains was
coupled to the oxidation of electron donors and linked to the electron transport and energy
conservation in cell membranes. Anaerobic azo reduction by bacteria was shown to be capable
of coupling the transformation of toxic organic substances to the reduction of azo compounds
simultaneously. It would be ideal for bioremediation of environments contaminated with azo
dyes and other toxic organic chemicals (37).
Several studies have shown that oxidation of organic compounds using Fenton’s reagents
(H202, Fe++) is efficient to degrade organic compounds like azo dyes (38); Guivarch et al. (39)
also demonstrated the degradation of azo dyes in water by electron-Fenton processes. Tantak
and Chaudhari (40) also demonstrated degradation of azo dyes by sequential Fenton’s
oxidation and aerobic biological treatment of wastes. Konstantonow and Albanis (41)
reported that TiO2 assisted photocatalytic degradation of azo dyes in aqueous solution. These
processes were reported to achieve effective oxidative degradation and mineralization of azo
dyes. These processes produced some intermediates such as hydroxylated derivatives,
naphthoquinone, phenolic compounds, organic acids, and other toxic products. Small
quantities of aromatic amines are also detected in the residues. These toxic wastes including
aromatic amine remain to be an environmental problem.
Examples of aromatic amines would be released from azo dyes upon reduction are listed
in Table 1.
Some azo dyes can be carcinogenic directly without being cleaved into aromatic amines
(14). The following are examples (List 3).
1.4-Aminoazobenzene (Cas No-60-09-3)
4-Aminoazobenzene is also called Aniline Yellow or 4-phenylazoaniline and was first
produced in 1861 by C. Mene. Aniline Yellow is used in microscopy for vital staining, in
pyrotechnics for yellow colored smoke, in yellow pigments and in inks including inks for
inkjet printers. It is also used in insecticides, lacquers, varnishes, waxes, oil stains and styrene
resins. It is also an intermediate in the synthesis of other dyes such as Chrysoidine, Indulines,
Solid Yellow and Acid Yellow. It has high hepatocarinogenicity to male mice when given as a
single intraperitoneal injection as low as 0.027 to 0.15 μmole/g body weight but not in female
mice (42). This dye also induces liver tumors in rats by oral administration and epidermal
tumors by application to the skin (43).
2. o-Aminoazotoluene (Cas No. 97-56-3)
o-Aminoazotoluene is also known as C.I. Solvent Yellow 3 or Fast Garnet GBC base.
In hamsters, o-aminoazotoluene produced tumors in urinary bladder, gall bladder, lung, and
liver. It can also induce tumors in urinary bladder, gall bladder, and liver in dogs and rats (44).
3. Methyl Yellow (Cas No. 97-56-3)
MethyYellow (Butter Yellow) was used as a food additive in 1918 but was quickly
removed from the food additive list in the same year because it was discovered to be a strong
cancer agent (14, 45, 46).
4. Methyl Yellow Derivatives
Methyl Yellow derivatives were carcinogenic to rats. 3’-methyl-4-monomethylamino-
azobenezene and 3’-methyl-4-dimethylaminoazobenzene were nearly twice as active 4-DAB,
and 4-ethylmethylaminoazobenzene had the same activity as 4-DAB. Both 3’-nitro- and 3-
chloro-4-dimethylaminoazobenzene had about the same activity as 4-DAB. However, since
the 3’-nitro derivatives were incompletely absorbed, their real activity appears to be about one
and half that of 4-DAB. 2’-Nitro and 2-chloro-4-dimethylaminoazobenzenes were about one
half to one third as active, and 4’-chloro-4-dimethylaminoazobenzene was approximately one
fourth as active as the parent dye (14)
5. Sudan Azo Dyes
Sudan azo dyes such as Sudan 1 (1-phenylazo-2-naphthol) (Cas No. 842-07-9) is also
called CI Solvent Yellow 14 and Solvent Orange R. It is an intense orange-red solid that is to
colorize waxes, oils, petrol, solvents, and polishes. Sudan I has also been adopted for coloring
various foodstuffs, especially curry powder and chili powder, although the use of Sudan I in
foods is now banned in many countries because it is reported as a carcinogen (47). Sudan I is
still used in some orange-colored smoke formulations and as a coloring for cotton refuse
(cotton waste) used in chemistry experiments.
Sudan II (Cas No. 3118-97-6) {1-[(2, 4-dimethylphenyl)azo]-2-naphthalenol} or [1-(2, 4-
xylylazo)-2-naphthol], also known as Solvent Orange 7, is a member of the Sudan family of
hydrophobic fat-staining dye. Sudan dyes are a group of lipid soluble solvent dyes often called
lysochromes. They are diazo dyes. Sudan II is used for certain solvents and may also be used to
stain some proteins bound lipids in paraffin sections. By studying the cellular regions where
the dye is sequestered, Sudan II has been used to evaluate how certain toxins interact with
membranes. Sudan II is considered a hazardous substance according to Osaha 29 CFR
1920.1200, although it is not reported as a carcinogen.
Sudan III (Cas No 85-96-9) [1-(4-(phenyldiazenyl)phenyl]azonaphthalen-2-ol] is a
lysochrome diazo dye. Its other names are Sudan Red BK, Fat Ponceau G, Cerasin Red, C.I.
26100, Solvent Red 23, Sudan Red, Sudan Red III, Sudan V, Sudan Red B, Sudan G, Scarlet
B, and Tony Red. It is used to color nonpolar substances like oils, fats, waxes, greases,
various hydrocarbon products, and acrylic emulsions. Its main use is as a fuel dye in the
United States of America mandated by the IRS to distinguish low-taxed heating oil from
automotive diesel fuel and by the EPA to mark fuels with higher sulfur content. It is reported
as a carcinogen (48).
Sudan IV (C24H20N4O) (Cas No. 85-83-6) [1-{2-methyl-4-(2-methylphenyldiazenyl)
phenyl}azonapthalen-2-ol] is also called Sudan R, C.I. Solvent Red 24, C.I. 26105, Lipid
Crimson, Oil Red, Oil Red BB, Fat Red B, Oil Red IV, Scarlet Red, Scarlet Red N.F, and
Scarlet Red Scharlach. Sudan IV is a fat-soluble diazo dye used for the staining of lipids,
triglycerides and lipoproteins on frozen paraffin sections. Sudan IV is considered an illegal
dye, mainly because of its harmful effect over a long period of time. It is a carcinogen and
was ruled unsafe in the 1995 food safety regulations report. Susan dyes are often found as
food contaminants and are illegally used (49-51). Sudan I, Sudan III, and Sudan IV have been
classified as category 3 carcinogens by IARC (51).
6. Para Red (Cas No. 7410-10-2)
Para Red {1-[(E)-(4-nitrophenyl)diazenyl]-2-naphthol} is also called Paranitraniline
Red, Pigment Red 1, and C.I. 12070. It is used to dye cellulose fabrics. The dye can be
washed away easily cellulose fabrics if not dyed correctly. Acidic and basic stages both occur
during the standard formation of Para Red, and acidic or basic by products may be present in
the final product.
In the United Kingdom (UK), the Para Red is not permitted in food. The UK's Food
Standard Agency Standards (FSA) stated that, "The Agency’s independent scientific experts
have advised that, although there are very limited data available, it would be prudent to
assume that it could be a genotoxic carcinogen."
7. Other Azo Dyes
Many azo dyes of the organic colorants were listed as carcinogens in the safety review of
the use of certain azo dyes in cosmetic products adopted by the Opinion of the Scientific
Committee on Cosmetic and non-Food Products Intended for Consumer Concerning
(SCCNFP) during the 19th
plenary meeting of 27 February , 2002 (52). Azo dyes listed as
carcinogens are shown in List 4. Although the above named compounds were listed as
carcinogens, some of them are limited evidence in experimental animals, and inadequate
evidence in humans for their carcinogenicities (IARC category 3). Other carcinogenic azo
dyes might not be included in the SCCNFP list. For those listed as carcinogens, the author did
not know whether their carcinogenicity was due to the dye itself or due to the cleaved
products, aromatic amines. If the carcinogenicity is due to the cleaved aromatic amines, then t
hose dyes should be classified into the section of carcinogenicity of azo dye metabolites (VI).
Other azo dyes are not discussed above. Examples are: M-methyl-4-aminoazo-
benzene (MAB) is a hepatocarcinogen in mice (53), 6-dimethylphenylazobenthiazole (6BT) is
also a rat hepatocarcinogen (18, 54). Ponceau 3R is a human carcinogen (55). Orasol Navy
Blue 2R (Cas No. 61969-42-4) and thiodiphenyl-4, 4’-diazo-bis-salicyclic were both
mutagenic in the Salmonella/mammalian microsome system (18, 56) and were possible
Brown and De Vito predicted the carcinogenicity of azo dyes by pointing out that azo dyes
with structures containing free aromatic amine groups that could be metabolically oxidized
without azo reduction. These azo dyes that may be activated via direct oxidization of the azo
linkage to highly reactive electrophilic diazonium salts. Each mechanism may be compound
specific (57).
Carcinogenicity or the adverse effects of the majority of azo dyes were probably due
to the cleaved components, aromatic amines. Chung and Cerniglia in 1992 (19)
postulated that azo dyes contain benzidine or p-
phenylenediamine (p-PDA) as the mutagenic moieties. Therefore, this author will address
primarily the carcinogenicity of benzidine, p-PDA and some aromatic amines structurally
related to benzidine and p-PDA.
1. Carcinogenicity of benzidine and its congener
1. Benzidine has been
identified as a carcinogen that can cause human urinary bladder cancer (120, 12157-59)).
Benzidine has also been reported to induce cancer of genitourinary tract (58), pancreas, liver
(58), gallbladder (58), bile duct (58), lung (58), large intestine (58), stomach (58),
lymphopoies (58), and renal cell (58) as well as non-Hodgkin’s lymphoma (58, 59). Notable
azo dyes that contain benzidine moiety in their structure were used in industry intensively and
are probably still being used in different parts of the world. According to IACR’s
classification, all azo dyes metabolized to benzidine were classified as a category 1 carcinogen
(60). Examples of azo dyes that released benzidine after reduction are indicated in List 5.
Benzidine and its congeners such as 3, 3’,-dimethylbenzidine (o-tolidine), 3, 3’-dimethooxy-
benzidine (o-dianisidine), and 3, 3’- dichlorobenzidine are the starting materials for the
synthesis of azo dyes referred to as benzidine-based or benzidine congener-based dyes.
Examples of benzidine-based dyes are Direct Blue 6, Direct Brown 9, Direct Black 38, etc.
The production of benzidine-based dyes has significantly decreased during the last century.
Although the National Institute of Occupational Safety and Health (NIOSH) and the
Environmental Protection Agency (EPA) of the U. S. A listed many potentially available
derived dyes, only a few are found in commercial use today (58).
The major company producing 3, 3’-dimethylbenzidine in the United States stopped
production in 1975. Imports appeared to be the major source of 3, 3’-dimethylbenzidine.
The major sources of the 3, 3’-dimethylbenzidine released into the environment is the
reduction of 3, 3’-dimethylbendine-based azo dyes including Acid Black 209, Acid Red 114,
Direct Black 154, etc. It was reported that administration of dihydrochloride salt of 3, 3’-
dimethylbenzidine in drinking water induced adenoma or carcinoma of the Zymbal gland and
liver, adenoma of basal-cell, carcinoma, adenoma or papilloma of squamous-cell or carcinoma
of perputial and clitoral glands and adenomatous polyps of large intestine in rats of both sexes
(61). Exposure of rats (of unspecified sex) to 3, 3’-dimethylbenzidine by subcutaneous
injection caused primarily carcinoma of the Zymbal-gland (58). 3, 3’-Dimethyl-benzidine is
reasonably anticipated to be a human carcinogen (60).
3, 3’-Dichlorobenzidine induced carcinomas of the sebaceous gland (58), lung tumor (58),
sarcomas (58), tumor of lower jaw (58), and Zymbal gland tumors (58) in mouse. In rats (58),
3, 3’-dichlorobenzidine induced Zymbal gland tumors, skin tumors, mammary gland tumors ,
intestinal tumors, bladder tumors, tumors of hamematopoietic system, salivary gland tumors ,
liver tumors, thyroid tumors, leukemia, sarcomas, Sebaceous tumors, bone tumors. In dogs,
3, 3’-dichlorobenzidine caused lung tumors and bladder tumors (58). 3, 3’-Dichlorobenzidine
may also cause human bladder cancer (63).
3, 3’-Dimethoxybenzidine and 3, 3’-dimethoxybenzidine-hydrochloride are used as an
intermediate in the production of dyes and pigments. 3, 3’-Dimethoxybenzidine has been
reported to have damaging effects on the liver, kidneys, spleen, bladder, endocrine, and
gastrointestinal in animal studies. Increased incidences of tumors in several organs have been
reported in rats orally exposed to 3, 3'-dimethoxy-benzidine or its salt (58). EPA has
classified 3, 3'-dimethoxy-benzidine as a Group 2B, probably human carcinogen (64).
4-Aminobiphenyl [(1, 1’-biphenyl)-amine] (Cas No. 92-67-1) has been reported to be
metabolically released by deamination of benzidine (58, 65). 4-Aminobiphenyl can be
present in tobacco smoke (66), in fumes of cooking oils (67), and in contaminated food dyes
(68). It is a potent human carcinogen and induces human bladder cancer (69, 70).
4-Aminobiphenyl also causes cancer in mice. Bladder and liver tumors have also been
observed in rabbits and dogs following oral administration of 4-aminobiophenyl. Mammary
gland and intestinal tumors have been reported in rats exposed by subcutaneous injection (69,
3, 3’,-5, 5’-Tetramethylbenzidine (TMB) is a widely used chromogen (71) and
is not mutagenic by the Ames test (61, 72) and did not induce formation of tumors in a single-
arm study of rats (73). TMB seems to be the only benzidine analogues that is neither
mutagenic nor carcinogenic and has been used as a replacement for carcinogenic
compounds such as benzidine (74) and o-phenylenediamine (75).
The nitro derivatives of benzidine were usually more mutagenic than that of
benzidine in Salmonella typhimurium tester strainTA98 without S9 (76). The addition of a
sulfonic acid group to benzidine molecule reduced the mutagenicity. When both sides of
the azo linkage of azo dyes were sulfonated, the compounds were usually not carcinogenic in
any animal species (57).
1-Amino-2-naphthol can be released by the 1-amino-2-naphthol based azo dyes such as
Lithol Red and Orange II (18). 1-Amino-2-naphthol has been reported to be non-mutagenic
(16, 18); but Dillion, et al. (77) reported that 1-amino-2-naphthol was mutagenic to
Salmonella typhimurium tester strain TA100, not to strain TA98. Bonser et al. (78) also
reported that the formation of papilloma and carcinoma and an unusually high incidence
of squamous metaplasia in the surgically implanted mouse bladder in the pellets contained
1-amino-2-naphthol. The Health and Environmental Effects Profiles for 1-amino-2-naphthol
and 1-amino-2-naphthol hydrochloride reported that existing data are insufficient to determine
a Reference Dose (RfD) or carcinogenic potency factor for 1-amino-2-naphthol and
1-amino-2-naphthol hydrochloride (79).
2. Carcinogenicity of p-phenylenediamine (p-PDA)
Initially, p-PDA was postulated to be a mutagenic component in several azo dyes (21).
However, p-PDA was reported to be non-mutagenic (80); Shahin, et al. (81-83) reported
it to be only a weak mutagen. Chung, et al. (84) found it to be weakly mutagenic to
Salmonella tester strain TA98 with metabolic activation. Lin and Solodar (80) also reported
that p-PDA became mutagenic only after it was oxidized. Watanabe, et al. (85) discovered
that p-PDA became strongly mutagenic in Salmonella typhimurium tester strain TA1538 in
the presence of microsomal fraction following oxidation by H2O2. So it can be concluded that
pure fresh p-PDA is not mutagenic, but it easily becomes mutagenic after oxidation.
p-PDA is a component in hair dye, which is a public concern. Sontag (86) pointed out that
p-PDA increased the formation of liver tumors in mice. Rollison, et al. (87) reported that
there is an association between personal hair dye use and non-Hodgkin's lymphoma, multiple
myeloma, acute leukemia, and bladder cancer in at least one well-designed study. Those
associations were not consistently observed across studies. A formal meta-analysis was not
possible due to the heterogeneity of the exposure assessment across the studies. Bolt and
Golka (88) pointed out that carcinogenicity of p-PDA is under debate. The authors suggested
that since earlier exposures could have an impact decades later, the possibility of bladder
cancer in hairdressers who have intensively worked with permanent hair dyes during earlier
decades prior to 1980s should be taken into account.
Recently, Turesky, et al. (89) reported that hair dye p-PDA could be contaminated with
the carcinogenic 4-aminobiphenyl. So the reported carcinogenicity and mutagenicity of
p-PDA might be due to the contaminant, not due to p-PDA itself. It is interesting to note that
DMPD is highly mutagenic (15, 16) but has not been reported to be carcinogenic (14). So
the carcinogenicity of Methyl Yellow (DAB) studied by Miller and Miller (14) may be
activated via direct oxidation of the azo linkage to highly reactive electrophilic diazonium,
which is a free radical that induces carcinogenesis (57, 90). Therefore, azo reduction of
Methyl Yellow to generate p-PDA or N-methyl-p-phenylenediamine, both of which were
neither mutagenic nor carcinogenic, was regarded as a process of detoxification (14). p-PDA
is supplemented by other aniline analogues or derivatives such as 2,5-diaminohydroxy-
ethylbenzene and 2, 5-diaminotoluene in its uses. 2, 5-Diaminotoluenes itself is often used as
a substitute for p-PDA. No adequate information to indicate that both 2, 5-diaminohydroxy-
ethylbenzene and 2, 5-diaminotoluene were genotoxic
p-PDA is usually mixed with H2O2 for hair dyeing. Oxidized p-PDA becomes a
diaminophenazines, which are extremely mutagenic (91) The reported contamination of
p-PDA with carcinogenic 4-aminobiphenyl, would put p-PDA as a high risk compound to
humans for commercial use (89).
3. Carcinogenicity of some other monocyclic aromatic amines (MAAs)
a. Aniline (Cas No. 62-53-2)
Aniline is the prototype of aromatic amine and a primary compound of industrial
chemistry. About 2.3 million tons were produced in 1996. Aniline can also be released from
the reduction of Orange G and 1-phenylazo-2-naphthol. Aniline is used in the synthesis of
polyurethane, diphenylmethane-3, 4-diisocyanate (MDI), rubber, dyes, pesticides, fibers, and
pharmaceuticals (92). Aniline has been reported to induce tumors in the spleen of rats but
does not induce bladder cancer in humans or animals. Carcinogenicity of aniline is now
proved to be due to the contaminant β-naphthylamine (93).
b. p-Nitroaniline (Cas No.100-01-6)
p-Nitroaniline is also called 4-nitroaniline or 1-amino-4-nitrobenzene with the formula
C6H6N2O2 and is commonly used as an intermediate in the synthesis of dyes, antioxidants,
pharmaceuticals, gasoline, medicines for chickens, and as a corrosion inhibitor.
p-Nitroaniline can be released from Para Red. p-Nitroaniline was reported to be mutagenic in
the presence or absence of S9 mix activation in Salmonella typhimurium tester strain TA98,
but the results were negative for all other strains (77). P-Nitroaniline was also reported to
induce tumors in B6C3F1 mice (94). The Dutch Expert Committee on Occupational
Standards of the Health Council of the Minister of Social Affairs and Employment, the Health
Council of the Netherlands, evaluates and judges the carcinogenic properties of substances to
which workers are occupationally exposed. The committee recommends classifying
p-nitroaniline as a suspected human carcinogen (95).
c. 2, 4-Dimethylaniline
Another aniline derivative, 2, 4-dimethylaniline (Cas No. 95-68-1) is also called
m-xylidine and 2, 4-xylidine. Osano, et al. showed that 2, 4-dimethylaniline showed
teratogenic properties in developing Xenopus frogs (96). 2, 4-Dimethylaniline was
mutagenic and carcinogenic (97). 2, 4-Dimethylaniline can be released from 1-[(2, 4-
dimethyphenyl)azo]-2-naphthalenol by azo reduction.
d. o-Toluidine (Cas No. 95-53-4)
o-Toluidine is also called 2-methylaniline and is used as an intermediate in dye, rubber,
and pharmaceutical products (98, 99). It was first synthesized in 1844 and was suspected to
be a carcinogen before 1921 (100). Up to 1954, o-toluidine was still not considered as a cause
of cancer. Richter (101) reviewed historical aspects of o-toluidine in detail. Numerous
publications proved that o-toluidine induced urinary bladder cancer in animals and humans
(94 ,99, 102, 103). The German Commission for the Investigation of Health Hazards of
Chemical Compounds in the Work Area classifies o-toluidine as a proven human bladder
carcinogen (104). The IARC also upgraded o-toluidine from group 2A to group 1 carcinogen
for humans in 2010 (105).
Many monocyclic aromatic amines (MAAs) are genotoxic and impose hazards to human
health. The mutagenicity of more than 80 of these amines has been reviewed by Chung, et al.
(106) with primary emphasis on evaluation by the Ames Salmonella/microsome testing
system. Many of these amines are mutagenic in Salmonella tester strains TA98 and TA100,
but S9 mix is required for activity (106). 2, 4-Diaminotoluene, m-phenylenediamine (1, 3-
diaminobenzene) and a few amines containing a nitro-group including 4-nitro-o-
phenylenediamine (4-nitro-2-aminoaniline), 2-nitro-p-phenylenediamine (4-nitro-1,4-
diaminobenzene), 2-amino-4-nitrophenol (4-nitro-2-aminophenol), 2-amino-5-nitrophenol (3-
nitro-6-aminophenol), m-nitroaniline, 4-nitro-2-amino-6-methylaniline, 4-nitro-2-amino--
hydroxyethylaniline, 4-nitro-2-amino-6β-hydroxypropylaniline, 4-nitro-2-amino-6-
isopropylaniline, 2-nitro-6-methyl-p-phenylenediamine, 2-nitro--hydroxylethyl-p-
phenylenediamine, 4-amino-3-nitro-6-methoxylaniline, 4-amino-3-nitro-6-fluoroaniline,4-
amino-3-nitro-6-chloroaniline, 4-nitro-o-phenylenediamine are direct mutagens. Among these
mutagens, the carcinogenicity of the following compounds are noticed:
i. 2, 4-Diaminotoluene (Cas No. 95-80-7)
2, 4-Diaminotoluene has been reported to cause tumor in rats and mice. Most tumors are
hepatocellular carcinoma, fibroma, mammary gland tumors, and kidney carcinoma (107). But
no epidemiological studies evaluated the relationship between human cancer specifically and
2, 4-diaminotoluene. Based on sufficient evidence of carcinogenicity from studies on
experimental animals, the National Institute for Occupational Safety and Health (NIOSH) of
the U. S. A. listed 2, 4-diaminotoluene as a potential human occupational carcinogen.
ii. 2-Nitro-p-phenylenediamine (Cas No. 5307-14-2).
Dietary administration of 2-nitro-p-phenylenediamine was reported to be carcinogenic to
female B6C3F1 mice, causing an increased incidence of hepatocellular neoplasms, primary
adenomas. There was no convincing evidence for the carcinogenicity of the
compound in Fischer 344 rats in both sexes or in male B6C3F1 mice (108).
iii. 2-Amino-4-nitrophenol (Cas No. 99-57-0)
The use of 2-amino-4-nitrophenol in cosmetic products is prohibited in the Commission
of the European Economic Community (109). According to the National Toxicological
Program (NTP) of the U. S. A. toxicology and carcinogenesis studies, there was some
evidence of increase incidences of renal cortical (tubular cell) adenomas by treatment of
2-amino-4-nitrophenol for male F344/N rats. The incidences of renal tubular cell hyperplasia
were also increased in male rats exposed to 2-amino-4-nitrophenol; but there was no evidence
of carcinogenic activity of 2-amino-4-nitrophenol for female F344/N rats or female B6C3
mice (110).
iv. 4-Nitro-o-phenylenediamine (Cas No. 99-56-9)
The SCCCNFP/SCCP is of the opinion that the use of 4-nitro-o-phenylenediamine
itself as an oxidative hair dye substance at a maximum concentration of 0.5% in the finished
cosemetic product (after mixing with hydrogen peroxide) does not pose a risk to the health of
the consumer, yet it has a sensitizing potential. 4-Nitro-o-phenylenediamine itself is not
genotoxic in vivo. However, studies on genotoxicity/mutagenicity in hair dye formulations
should be undertaken following the relevant SCCCNFP/SCCP opinions and in accordance
with its “Notes of Guidance.”
2, 4-Diaminoanisole, 2, 5-diaminoanisole, o-PDA (1, 2-diaminobenzene),
2, 4-diaminoethoxybenzene, 2, 4-diaminopropoxybenzene, 2, 4-diaminoethylbenzene, 2, 4-
isopropoxybenzene, 4-Nβ-hydroxyethylamino-3-nitroanisole (3-nitro-4-Nβ-hydroxyethyl
aminoanisole), 4-amino-3-nitro-phenoxyethanol, p-hydroxy-m-PDA(2, 4-diaminophenol),
4-amino-3-nitro-6-methylaniline, 4-amino-3-nitro-6-isopropylaniline,
4-amino-3-nitro-5β- hydroxymethylaniline, 4-amino-3-nitro-5-methylaniline, 4-amino-3-
nitro--hydroxypropylanilne, 4-amino-3-nitro-5-isopropylaniline, 4-amino-3-nitro-5, 6-
dimethylaniline, and 4-amino-3-nitro-2, 5-dimethylaniline were mutagenic in the
Salmonella tester strain TA98, but S9 mix is required for activity (106). Among the above
mentioned compounds, 2, 4-diaminoanisole (Cas No. 615-05-04) is identified as a carcinogen,
and o-PDA is suspected to be carcinogenic.
Sufficient evidence exists for the carcinogenicity of 2, 4-diaminoanisole sulfate in
experimental animals (111). When administered in the diet, 2, 4-diaminoanisole sulfate
increased the incidences of thyroid follicular cell adenomas in mice of both sexes and thyroid
follicular cell carcinomas in female mice. When administered in the diet, 2, 4-diaminoanisole
sulfate increased the incidences of squamous cell carcinomas, basal cell carcinomas, or
sebaceous adenocarcinomas of the skin and its associated glands; malignant thyroid follicular
cell tumors; and preputial or clitoral gland adenomas, papillomas, or carcinomas in rats of
both sexes, and thyroid C-cell adenomas or carcinomas and Zymbal gland squamous cell
carcinomas or sebaceous adenocarcinomas in male rats (112). When administered in the diet
to female rats, 2,4-diaminoanisole sulfate induced mammary adenocarcinomas and
carcinomas of the clitoral gland and increased the incidences of follicular cell adenomas or
carcinomas and C-cell carcinomas of the thyroid (111). The IARC Working Group reported
that there were no adequate data available to evaluate the carcinogenicity of 2, 4-
diaminoanisole sulfate in humans. Therefore, 2, 4-diaminoanisole is classified as carcinogenic
to humans (Group 2B) in IARC volume 79 (113).
v. o-Phenylenediamine (o-PDA)
o-Phenylenediamine was found to be genotoxic in vitro and in vivo (114) and in
Salmonella mutagenicity test. Administration of o-phenylenediamine-dihydrochloride in
drinking water to F344/DuCrj rats and Crj BDF mice of both sexes for two years induced
hepatocellular adenomas in rats in both sexes and in female mice, and hepatocellular
adenomas in male mice (114). o-Phenylenediamine dihydrochloride causes both local
reactions and systemic damages to humans. Local actions include severe dermatitis and
urticarial in the eye. o-phenylenediamine dihdrochloride induces chemosis, lacrimation,
exophthalmos, ophthalmia, and even permanent blindness. Systematical damages include
asthma, gastritis, rise in blood pressure, transudation into serious cavities, vertigo, tremors,
convulsions, and comas (115). o-PDA is first oxidized to the reactive o-quinone diimine,
which reacts with another molecule of o-PDA to form 2, 3-diaminophenazine, which is found
to be mutagenic in Salmonella typhymurium strain TA100 with metabolic activation (116). In
subsequent reactions, trimer and higher oligomers can be formed from diaminophenazine. A
trimer of o-PDA is known as Bandrowski’s base, which is extremely mutagenic in reverting
strain TA1538 (117). o-PDA can be used to make tiabendazole, pyrazinamide, morinamide,
chemizole, chlormidazole, and other pharmaceuticals (118). For many applications, o-PDA
has been replaced by safer chemicals such as 3, 3’, 5, 5’-tetramethylbenzidine (119).
vi. m-Phenylenediamine (m-PDA)
m-PDA) is also called 1,3-PDA and is used in the preparation of various polymers
including aramid fibers, epoxy resin, wire aramid coating and polyurea clastomers, and as
an accelerator and for adhesive resins and components of dyes such as Basic Brown, Basic
Orange 2, Direct Black 38, and Developed Black BH. It also used as a coupling agent in
hair-dye. m-PDA is used in large quantities in the United States (120). Because no data are
available for humans, and there is inadequate evidence of carcinogenicity in animals,
m-PDA is not considered as a human carcinogen. But the oxidation products are highly
mutagenic (91)
.vii. Others
As the author postulated the nitro-group containing monocyclic aromatic amines are direct
mutagens, but 4-amino-3-nitro-6-isopropylaniline, 4-amino-3-nitro--hydroxymethylaniline,
4-amino-3-nitro-5-methylaniline, 4-amino-3-nitro--hydroxypropylanilne, 4-amino-3-nitro-
5-isopropylaniline, 4-amino-3-nitro-5, 6-dimethylaniline, and 4-amino-3-nitro-2,5-
dimethylaniline are containing nitro-group in the structure but still require S9 activation for
mutagenic activity. It is possible that the number and position of amino and/or nitro groups
are crucial for their mutagenicities (106).
Several parameters such as lowest unoccupied molecular orbital energy (Elumo), highest
occupied orbital energy (Ehomo), and hydrophobicity are important. However, what factors
determine the minimum requirement for the compound to be mutagenic and what factors
determine the extent of mutagenicity are not known (106). Since mutagenicity and
carcinogenicity are intimately related, those mutagenic monocyclic aromatic amines (MAAs)
are likely to be carcinogenic.
Besides the use as a hair dye component, p-PDA is used in engineering polymers and
composites (121). The Center of Disease Control (CDC) of the United States lists p-PDA as
a contact allergen. p-PDA induced throat irritation (pharynx and larynx), bronchial asthma,
and/or sensitization dermatitis {(NIOSH, Registry of Toxic Effects of Chemical Substances
(RTECS) entry for p- PDA.} Likewise, the potential effects of the o-phenylenediamine may
cause eye irritation, skin irritation, dermatitis, and an allergic reaction. Another malady is
methemoglobinemia, which is characterized by dizziness, drowsiness, headache, shortness of
breath, cyanosis, rapid heart rate, chocolate-brown colored blood, and liver damage.
m-PDA may cause sensitization reactions, eye irritation and injury, skin irritation,
dermatitis, blackened skin, and bronchial asthma. Other symptoms include allergic skin
reactions, irritation of mucous membranes, coughing, burning sensation, runny nose, sore
throat, methemoglobinemia, cyanosis, headache, dizziness, drowsiness, mental confusion,
pulmonary edema, kidney and liver damage, central nervous system effects, and
conjunctivitis. Eye contact may cause discomfort, tearing, blurring of vision, reddening,
partial clouding of the corneas, and swelling of the eye and surrounding tissues. Exposure
may also result in mucous membrane and respiratory tract irritation. When this compound is
heated, it will decompose to oxides of nitrogen. Some workers 30 to 50 years old who were
exposed to m-PDA for 5-10 years complained of dysuria. A scratch test with m-PDA
produced positive reactions in 8 % of the people who also suffered from eosinophiluria and
had urinary m-PDA levels of 0.3 to 40 μg/100 ml. Cystoscopy revealed edema of the mucosa,
polypous swellings and infiltration of the area of triangle and cervix of urinary bladder.
Effects were also observed in people exposed to hyperreflexia, hyporeflexia, anisoreflexia, skin
hyperesthesia and pathological changes in kidneys and liver. The eosinophilic character of these
alterations was confirmed cytologically (69).
Kleniewska and Maibach (122) studied the allergenicity of 16 aminobenzenes
including p-PDA, p-toluidine, p-sulfanilic acid, p-aminobenzoic acid, and p-nitroaniline.
Their structure-function relationships using sensitizations for 24 occlusive patches in guinea
pigs were examined. Activating chemical groups -NH2 ,-CH3 and -OH were more potent
sensitizers than compounds with deactivating groups -SO3H, -COOH, and -NO2.
Benzidine is acutely toxic to humans by ingestion. Symptoms include cyanosis,
headache, mental confusion, nausea, and vertigo. Dermal exposure may cause skin
rashes and irritation as well as bladder injury (69, 123, 124). Exposure effects on the blood,
liver, kidney, and central nervous system from oral exposure of benzidine to animals have
been reported (123).
4-Aminoazobenzene is present in yellow pigments it is also found in insecticides
lacquers, varnishes, waxes, oil stains, and pyrotechnics for yellow smoke, It can cause skin
allergenic reaction. Symtoms of exposure to 4-aminobiphenyl include redness, swelling,
itching, and fluid-filled blisters.
o-Aminoazotoluene can cause eczema of the hands and arms. When this compound is
heated to decomposition, o-aminoazotoluene emits toxic fumes of carbon monoxide, carbon
dioxide, and nitrogen oxides (125).
Exposure to Methyl Yellow through inhalation, skin absorption, ingestion, and/or skin
contact may induce an enlarged liver, kidney disturbance, contact dermatitis, cough,
wheezing, dyspnea, bloody sputum, bronchial secretions, frequent urination, and hematuria.
1-Amino-2-napththol-4-sulfonic acid may cause eye and skin irritation as well as
gastrointestinal disturbance.
Tartrazine is a certified food color, mainly yellow, and can cause allergies to humans.
Human exposure to tartrazine is usually by ingestion or cutaneous contact. Symptoms appear
after a period of time ranging from a few minutes to 14 hours. Approximately 360,000
Americans, less than 0.12% of the general population (126), are affected by tartrazine.
According to the FDA, tartrazine causes hives in fewer than 1 in 10,000 people, or 0.01%
(127). It is not clear how many individuals are sensitive or intolerant to tartrazine, but the
University of Guelph estimates that it is one to 10 out of 10, 000 people in Canada. The
advice to deal with tartrazine sensitivity is to avoid tartarazine totally (128).
There is no evidence that it had an effect on most people with asthma (130). McCann,
al. (130) reported that a mixture of tartrazine, Ponceau 4R (E124), Sunset Yellow FCF,
carmoisine, and sodium benzoate may cause hyperactivity in children. However, an
independent review of the study concluded that the clinical significance of these observations
remained unclear (131). In 1994, Rowe and Rowe conducted a study at the University of
Melbourne and suggested that children previously identified as hyperactive might exhibit an
increase in irritability, restlessness, and sleep disturbance after ingesting tartrazine (132).
Tartrazine is a permitted food coloring in Canada because Canada found that existing
scientific evidence does not show that this synthetic food color is unsafe in the general
population (133). The European Food Safety Authority allows for tartrazine to be
used in processed cheese, canned fruit or vegetables, processed fish, or fishery
products, and wine-based drinks (134). The use of tartrazine was banned in Norway and
Austria but the ban was overturned by a European Union directive (135).
Sulfanilamide, the metabolite of Prontosil studied by Gerhardt Domagk is a sulfonamide
drug (sulfur drug) that is the basis of several groups of drugs including child antibacterial
pediazole, antimicrobial sulfacetamide, sulfadiazine, sulfadimidine, sulfafurazole
sulfisomidine, sulfadoxine, sulfamethoxazole, sulfamoxole, sulfadimethoxine antidiabetic
agents sulfonylureas, diuretics, anticonvulsants, dermatologicals, and antiretrovirals (136)
(List 1). Although these synthesized sulfur drugs were not generated from azo dyes any more,
there are basically aromatic amines. Maladies include urinary tract disorders, haemopoietic
discorders, porphyria, and hypersensitivity reactions when taking these drugs. Allergies to
sulfonamide are common. The most common symtoms are rash and hives as well as life-
threatening manifestations of hypersensitivity including Stevens–Johnson syndrome, toxic
epidermal necrolysis (also known as Lyell syndrome) agranulocytosis, lymolytic anemia,
thrombocytopenia, fulminant hepatic necrosis and acute pancreatitis are reported (136, 137)
2-Amino-p-cresol, a metabolite produced from azo dye Disperse Yellow was discovered
by Stahlmann, et al. (138) to be a strong allergen causing a marked increase in lymph node
weight and cell proliferation, accompanied by a relative decrease of T-cells and relative
increases in B-cell and IA cells in a modified local lymph node assay protocols in NMRI
mice. On the other hand, the other metabolite of Disperse Yellow, 3, 4-aminoacetanilide
led to an increase in lymph node weight and cellularity at a higher concentration of 30%,
with no consistent changes in the phenotypic analysis, indicating that 4-aminoacetanilide was
a weak sensitizer.
Disperse Blue 106 and Disperse Blue 124 have been shown to cause an allergic contact
dermatitis to a variety of garments, which include underwear, blouses, pants, swimming suits,
pantyhose, shoulder pads, and materials used of leggings and body suits (139-14). Exposure
to consumers can prove fatal when these chemicals come in contact with the skin as they
might generate incurable diseases .
Trypan Blue has been shown to be carcinogenic and teratogenic (142). The reduced
amaranth (FD & C Red #2) and reduced Sunset Yellow (FD & C Yellow # 6) were reported
to induce cytoxicity when incubated with repair deficient Escherichia coli strain in the
absence of hepatic enzymes (143). Amaranth was banned to use in food in the USA in 1976
but is still a certified food colorant for other countries. Sunset Yellow is a certified food color.
Various genotoxic related illnesses of workers in textile dyeing plants have been frequently
reported in various countries (144). Yoshida and Miyakawa (145) disclosed that occupational
exposure to benzidine dyes (for kimoto painting) might have possibly resulted in bladder
cancer among kimoto painters in Japan. Usha reported (146) that eczema, contact dermatitis,
ashma, chronic bronchitis, tuberculosis, hematoma, bladder cancer, and irritation to eyes were
common among workers of textile industries in Sanganer, India. Pelclova, et al. (147) also
reported that a high incidence of chromosomal aberrations in 42 rotogravure printing plant
workers. Morikawa, et al. (148) reported triple primary cancers including kidney, urinary
bladder, and liver in dye workers. There may be more instances of multiple diseases related to
workers in azo dye industries that have not been reported.
It was estimated in the 1980’s that nearly 280,000 tons of textile dyes were annually
discharged into industrial effluents worldwide (149). Azo dyes make up approximately 70%
of weights of all dyestuffs used, the largest group of the most used synthetic dyes released into
the environment (6, 150-152). Microbial decolorization of azo dyes have been extensively
reviewed elsewhere (152). However, these dyes remain difficult to be completely degraded.
Residue azo dyes and their degradation products still damage water quality (152, 153).
Degradation products are toxic to aquatic organisms, allergenic, mutagenic, and carcinogenic
to humans and render the water unfit for its intended use. For example, Bae and Freeman
(154) demonstrated that C. I. Direct Blue 218 was very toxic to daphnids with a 48-h LC50
between 1.90 and 100 mg/L. Azo dyes decrease the passage of light penetration and gas
dissolution in lakes, rivers, and other bodies of water. The ecological impact and
environmental damage have been reviewed elsewhere (5, 154, 155); therefore, they are not
discussed in this article.
The whole life-cycle of azo dyes in colored clothes is an unavoidable source of human
exposure . The textile fibers are not necessarily allergenic; rather, the dyes used to color the
fabrics or formalin finishing resins added to make them wrinkle-resistant, shrink-proof, or
easily laundered are responsible for direct contact (156). The most common sensitizers
include the Disperse Dye application class of azo dyes, which are loosely held in the fibers
and are easily rubbed off.
Azo dyes preceded the discovery of sulfur drug medicine and facilitated the development
of the chemical industry. Azo dyes and their cleaved products, aromatic amines, are
carcinogenic, mutagenic, allergenic, and also cause various human maladies in addition to
being harmful pollutants to our environment. If we can effectively restrict the use of azo dyes
and control the spread of pollution of azo dyes and their toxic aromatic amines in our
environment, we can certainly drastically reduce the incidence of cancer and other relevant
human diseases. Regulation, prevention, and research for industrial substitution are urgently
called for by this author. Further, we should invest more in the study of the mechanisms,
remedies, and prevention of those maladies induced by azo dyes and their metabolites in order
to protect our health and environment
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XII. Tables and Figures
Figure. 1. Chemical Structures of Prontosil and Sulfanilamide
Figure. 2. Chemical structures of Methyl Yellow (p-Dimethylaminoazobenzine) and its
Table. 1. Examples of Aromatic Amines Metabolically Produced from Azo Dyes
Names of aromatic amines Sources of Azo Dyes
4-Aminobenzenesulfonic acid Ponceau BS, Methyl Orange, Orange II,
Ponceau S
1-Amino-2-Naphthol Acid Red 88, Orange II, Para Red,Ponceau
BS , Lithol
Red, 1-Phenylazonaphthol
Aniline Orange G, 1-Phenylazo-2-naphthol
4-Aminoazobenzene, Methyl Yellow
Benzidine Congo Red, Direct Blue 6, Direct Black
Direct Brown 95
2,5-Diaminobenzenesulfonic acid Ponceau BS, Ponceau S
2,4-Dimethylaniline 1-[2, 4-(Dimethylphenyl)azo]-2-
N, N-Dimethyl-p-phenelenediamine (p-PDA) Methyl Orange, Methyl Red, Methyl Yellow
p-Nitroaniline Para Red
p-Phenylenediamine (p-PDA) 4’-Hydroxy-4-aminoazobenzene, 4-
monomethylaminoazbenzene, Sudan IV
Sulphanilinic Sunset Yellow, Tartrazine
Toluidine 1-[2-Methyl-4-[(2-
2, 4, 5-Trimethyaniline Ponceau 3 R
List. 1. Examples of Sulfonamides (Sufur Drugs) ________________________
Pediazole, Sulacetyamide, Sulfadiazine, Sulfadimidine, Sulfurazole, Sulfisomidine
(aka sulfaisodimidine), Sulfadoxine, Sulamethoxazole, Sulfamoxole, Sufanitrane
Sulfadimethoxine, Sulfamethoxypyridazone, Sulfmetoxydiazine. Sulfadoxine,
Sulfamedopyrazine, Acetohexamide, Carbutamide, Chlorpropamide, Glibenclamide (also
known as Glyburide), Glibormuride, Gliclazide, Glyclopyramidine, Glimepiride, Gliprizide.
Gliquidone, Glisoxepide ,Tolazamide, Tolbutamide. Acetazolamide,
Bumetanide,Chlorthalidone, Clopamide, Dorzolamide, Flurosemide, Indapamide,
Hydrochlorothiazide (HCT, HCTZ, HZT), Mefruside, Metolazone, Xipamide.
Ethoxazolamide, Sultiame, Topiramate, Zonisamide.Mafenide, Antiretrovirals, Amprenavir,
Durunnavir, Delavirdine,(non-nucleoside reverse transcriptas inhibitor), Fosamprenavir
(protease inhibitor), Tipranavir (Protease inhibitor). Stimulant, Azabon, Apricoxib (COX-2
inbitor), Bosentan (endothelin receptor antagonist), Celecoxib (COX-2inhibitor), Dofetilide
(class III antiarrthy themic), Dronedarone (Class III antiarrthythemic), Ibutilide ( Class III
antiarrthythemic), Parecoxib (COX-2 inhibitor), Probenecid (PBN), Sotalol (beta blocker),
Sulfasalazine (SSZ), Sumatriptan (alpha blocker), Udenafil (PDE5 inhibitor).
List. 2. Reported Intestinal Microorganisms with Azo Reduction Activity
Acidaminonococcus feermentans, Acerobacter aerogenes, Bacteriodes vulgatus,
distasonis, Bacteroides fragilis, Bacteroides ovatus , Bacteroides thetaiotaomicron,
Bifidobacterium longum, Bifidobacterium adolescentis, Bifidobacterium infantis,
Butyrivibrio sp., Citrobacter sp., Clostridium nexile, Clostridium clostridiiforme,
Clostridium paraputrificum, Clostridium ramosum, Clostridium perfringens,
Clostridium difficile, Coprococcus catus, Enterococcus faecalis, Escherichia coli,
Eubacterium sp., Eubacterium aerofaciens, Eubacterium biforme, Eubacterium
hadrum, Fusobacterium prausnitzii, Fusobacterium sp., Lactobacilluscatenaforme,
Peptostreptococcus productus, Pneumococcus sp., Proteus vulgaris,Proteus sp.,
Pseudomonas aeruginosa, Pseudomonas pyocyanea, Rumonococcus bromii,
Salmonella paratyphi, Salmonella typthimurium, Shigella dysenteriae, Staphylococcus
aureus, Streptococcus faecalis, Streptococcus haemolyticus, Veillonella parvula, etc.
(20, 21).
List. 3. Azo dyes whose Carcinogenicities are not due to their Cleaved
4-Aminoazobenzene, o-Aminoazotoluene, 3’-Methyl-4-monomethylaminoazobenzene,
Methyl Yellow, 3’-Methyl-4-dimethylaminoazobenzene, 4-Ethylmethylaminoazobenezene,
Sudan I, Sudan II, Sudan III, Sudan IV, Para Red, Ponceau 3R, , Orasol Navy Blue 2RB,
2’-Nitro-4-dimethylaminoazobenzene, 4’-Chloro-4-dimethylaminoazobenzene, 3’-Chloro-4-
dimethylaminoazobenzene. Thiodiphenyl-4, 4’-diazobissalicyclic Acid
List. 4. Azo Dyes listed as Carcinogens
___Solvent Yellow 1 (Cas No. 60-09-3, also called p-(phenylazo)aniline; p-
aminoazobenzene; Solvent Yellow 2 (Cas No. 60-11-7), also called 4-
(dimethylamino)azobenzol; Solvent Yellow 3 (Cas No. 97-56-3); Pigment Orange 5 (Cas
No. 3468-63-1); Solvent Orange 2 (Cas No. 2646-17-5); Pigment Red 3 (Cas No. 24525-
85-6); Solvent Red 80 (Cas No. 6358-53-8), commonly called Citrus Red 2; Pigment Red
53 (Cas No. 2092-56-0), also called D&C Red No. 8, Pigment 53:1, barium salt (Cas No.
5160-02-1); Acid Red 26 (Cas No. 3761-53-3), also called Ponceau 26; xylidine; Ponceau
2R; Acid Dye (Cas No. 3564-09-8), also called Ponceau 3R; Direct Red 28 (Cas. No. 573-
58-0), also called Congo Red; Direct Blue 6 (Cas No. 2602-46-2); Acid Red 114 (Cas No.
6459-94-5); Direct Blue 14 (Cas No. 72-57-1); Direct Blue 53 (Cas No. 314-13-6); Direct
Blue 15 (Cas No. 2429-74-5); Direct Blue 218 (Cas No.28407-37-6); Direct Brown 95
(Cas No. 16071-86-6); Direct Black 38 (Cas No.1937-37-7); Basic Red 9 (Cas No. 479-
73-2); Basic Red 9 hydrochloride (Cas No. 569-61-9); Disperse Blue 1 (Cas No. 2475-45-
8); Pigment Yellow 34 (Cas No. 1344-37-2); and Pigment Red 104 (Cas No. 1256-85-8).
List. 5. Examples of Azo Dyes that Released Benzidine after Azo Reduction
Acid Black 29, Acid Black 232, Acid Black 94, Acid Orange 45, Acid Red 85, Azoic Diazo
Component 112, Direct Black 4, Direct Black 29, Direct Black 38, Direct Blue 2, Direct Blue
6, Direct Brown 1, Direct Brown 1:2, Direct Brown 2, Direct Briwn 6, Direct Brown 25,
Direct Brown 27, Direct Brown 31, Direct Brown 33, Direct Brown 51, Direct Brown 59,
Direct Brown 74, Direct Brown 79, Direct Brown 95, Direct Brown 101, Direct Brown 154,
Direct Dye, Direct Green 1, Direct Green 6, Direct Green 8, Direct Green 8:1, Direct Orange
1, Direct Orange 8, Direct Red 1, Direct Red 10, Direct Red 13, Direct Red, Direct Red 28,
Direct Red 37, Direct Violtet 1, Direct Violet 4, Direct Violet 12, Direct Violet 22, Direct
Yellow 1, Direct Yellow 24, Mordant Red 57, Direct Red 44.
... Se emplean en múltiples industrias como la textil, papelera, farmacéutica, recubrimientos, entre otras. La capacidad de OFI de actuar como agente de floculación, coagulación y sedimentación de contaminantes ha sido reportada como una opción viable para la remediación de aguas a pesar de que los mecanismos involucrados en estos procesos no se encuentran completamente elucidados (Chung, 2016;Ferraz et al., 2017). El objetivo de este estudio es reportar la capacidad de remoción de RC en agua de dos adsorbentes derivados de OFI en diferentes condiciones de temperatura y pH. ...
Conference Paper
En Sinaloa, anualmente se utilizan 5.4 mil millones de litros de agua en el riego. El agua residual agrícola (ARA) generada (37%), contiene altos niveles de nutrientes y plaguicidas. En el presente trabajo se evaluó la eficiencia de biofiltros empacados con “barba” de elote y roca caliza para la remoción de fósforo total (PT). Se utilizaron tubos concéntricos en dos configuraciones. En la primera el ARA estuvo en contacto con 87 cm3 de roca caliza y posteriormente con 535 cm3 de barba de elote (RCB). En el segundo biorreactor, el ARA primero se contactó con 149 cm3 de barba de elote y 311 cm3 de roca caliza (RBC). El RCB removió 50% de DQO y 10% de PT, mientras que el RBC removió 45% de DQO y 60% de PT, lo cual se atribuye a que el RBC tuvo mayor superficie y tiempo de contacto con la roca caliza lo que provoca precipitación química del nutriente además de fisiosorción. En el RBC, este proceso se lleva una vez degradada la molécula por la biopelícula bacteriana formada en la barba de elote. En ambos reactores la estabilización del sistema se suscitó a los 15 días de operación y el potencial de óxido reducción incrementó de condiciones anóxicas a aerobias (30-40 mV). Los resultados plantean un potencial uso de biofiltros empacados con medios sustentables para el eficiente tratamiento de ARA. Se recomienda escalar los resultados a nivel piloto e implementar el retrolavado del sistema.
... In addition to DNA mutations due to the formation of DNA adducts, epigenetic alterations can also arise due to chemical exposure (Chung, 2016), particularly with compounds that form G adducts. Epigenetic alterations cause changes in gene expression. ...
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Azo dyes are defined by the presence of a characteristic N=N group. Sudan I and Sudan II are synthetic azo dyes that have been used as coloring agents. Although animal toxicity studies suggest that Sudan dyes are mutagenic, their molecular mechanism of action is unknown, thus making it challenging to establish thresholds for tolerable daily intake or to understand how these molecules could be modified to ameliorate toxicity. In addition, dye metabolites, such as azobiphenyl and 4-aminobiphenyl, have been correlated with epigenetic alterations. We shed some light on the mechanisms of Sudan dye genotoxicity through a molecular modeling study of Sudan I and Sudan II dyes and two common metabolites interacting with DNA as adducts. The results suggest that all four adducts cause significant perturbations to the DNA helical conformation and structure; thus, it can be inferred that DNA repair and replication processes would be significantly impacted.
... Azo dyes have very attractive vivid colors and are the most widely used and structurally diverse group of commercial organic dyes [62]. Approximately more than 2000 azo dyes are used today which are colorants of materials such as synthetic and natural textile fibers, plastic, leather, hair dyes, waxes and certain petroleum products [63]. ...
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Organic azo dyes, which are widely used in industrial, health and cosmetic fields, pose genotoxic risks due to their chemical structures; however, the molecular details of the undesirable effects of these dyes on DNA have been poorly or insufficiently clarified. In this computational molecular docking study, the DNA binding modes and binding affinities of 14 azo dyes, previously determined to show DNA clastogenicity, were characterized using 2 different double-stranded DNA (dsDNA) conformations (an intact dsDNA and dsDNA with an intercalation gap). In this study, it was determined that 10 out of the 14 genotoxic azo dyes were strong dsDNA minor groove binders, while the remaining ones formed tight binding complexes with dsDNA through intercalation or threading intercalation modes. The azo, nitro, hydroxyl, ammonium, sulfonate, naphthalene, methoxyphenyl, bromine, nitrophenyl, imidazole, amino-phenylethanol and chloro-nitrophenyl groups were found to play primary role in the most favorable binding conformations of these dyes on dsDNA with an affinity ranging from −6.35 kcal/mol to −9.42 kcal/mol. It was determined that dsDNA sequences containing GT dinucleotides are frequently preferred in binding by these dyes, and that rings and polar groups are important features for tight binding with dsDNA. It was concluded that these dyes may be banned, or non-genotoxic congeners should be manufactured with appropriate molecular optimization for the genetic health of the human population and for future generations.
... They account for 70% of all organic colorants produced worldwide [1]. Toxicological studies show that azo colorants can have adverse health effects on the human body by causing diarrhea, eczema, allergic reactions and asthma attacks [2], cancer and low levels of dopamine in the human brain [3,4]. Primarily, this is due to the fact that the products of azo colorant decomposition (e.g., aromatic amines) are toxic and carcinogenic [5]. ...
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The paper describes the development of an electrochemical sensor to be used for the determination of synthetic food colorants such as Sunset Yellow FCF (SY) and Tartrazine (TZ). The sensor is a carbon paper (CP) electrode, manufactured by using hot lamination technology and volume modified with fine-grained graphite powder (GrP). The sensor (GrP/CP) was characterized by scanning electron microscopy, energy dispersive spectrometry, electrochemical impedance analysis, cyclic, linear sweep and differential pulse voltammetry. The mechanism of SY and TZ electrochemical oxidation on GrP/CP was studied. The developed sensor has good electron transfer characteristics and low electron resistance, high sensitivity and selectivity. Applying the differential pulse mode, linear dynamic ranges of 0.005–1.0 μM and 0.02–7.5 μM with limits of detection of 0.78 nM and 8.2 nM for SY and TZ, respectively, were obtained. The sensor was used to detect SY and TZ in non-alcoholic and alcoholic drinks. The results obtained from drink analysis prove good reproducibility (RSD ≤ 0.072) and accuracy (recovery 96–104%).
The genome of an organism is directly or indirectly correlated with its environment. Consequently, different microbes have evolved to survive and sustain themselves in a variety of environments, including unusual anaerobic environments. It is believed that their genetic material could have played an important role in the early evolution of their existence in the past. Presently, out of the uncountable number of microbes found in different ecosystems we have been able to discover only one percent of the total communities. A large majority of the microbial populations exists in the most unusual and extreme environments. For instance, many anaerobic bacteria are found in the gastrointestinal tract of humans, soil, and hydrothermal vents. The recent advancements in Metagenomics and Next Generation Sequencing technologies have improved the understanding of their roles in these environments. Presently, anaerobic bacteria are used in various industries associated with biofuels, fermentation, production of enzymes, vaccines, vitamins, and dairy products. This broad applicability brings focus to the significant contribution of their genomes in these functions. Although the anaerobic microbes have become an irreplaceable component of our lives, a major and important section of such anaerobic microbes still remain unexplored. Therefore, it can be said that unlocking the role of the microbial genomes of the anaerobes can be a noteworthy discovery not just for mankind but for the entire biosystem as well.
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Textile industry being one of the most flourishing industries keeps growing and developing every year, and the consequences are not very pleasant. Even though its contribution towards economy of a country is indisputable, there are many pros and cons associated with it that should not be brushed aside, one of them being textile dye waste which is also growing at alarming rate. Many techniques have been designed to deal with this environmental crisis including adsorption and photodegradation of dye waste by various substances, both natural and synthetic. TiO2 and clay both have gained immense popularity in this area. Over the last decade, many successful attempts have been made to design TiO2-clay-based composites to combine and make the most of their individual capabilities to degrade textile dye waste. While clay is an effective adsorbent, inexpensive, innocuous, and a great ion exchanger, TiO2 provides supplementary active sites and free radicals and speeds up the degradation rate of dyes. This review summarizes various features of TiO2-clay-based composites including their surface characteristics, their role as dye adsorbents and photocatalysts, challenges in their implementation, and modifications to overcome these challenges made over the last decade.
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This work addressed one step preparation method to form a novel nano material composite of graphene oxide nanosheet (GO) functionalized with low-cost tri-sodium citrate (C), using, teteraethylorthosilicate (TEOS) as a cross-linker. The prepared composite (GO–C) was characterized using various advanced techniques. Among these techniques, the TGA provided interesting information concerning the functionalization process. Within this process, the (–OH) groups that located at the GO-surface were consumed in the modification process which leads to increase the thermal stability of the resulted composite. Cationic organic methylene blue (MB) and crystal violet (CV), and inorganic copper (Cu ²⁺ ) and cobalt (Co ²⁺ ) pollutants were displayed as a model to assess their removal performance by the developed composite (GO–C) from aqueous solution, through batch technique. According to Langmuir isotherm the GO–C present an excellent adsorption capacity for MB (222.22 mg g ⁻¹ ), CV (270.27 mg g ⁻¹ ), Cu ²⁺ (163.4 mg g ⁻¹ ) and Co ²⁺ (145.35 mg g ⁻¹ ) which were more than the adsorption capacities found in literature. Additionally, the regenerated composite presents higher removal ability than the original composite.
In the present work, the photocatalytic potential of zinc oxide nanoparticles, prepared using extracts of Ulva lactuca (U. lactuca) and Stoechospermum marginatum (S. marginatum), has been evaluated. The effect of catalyst dosage, pH of the solution, and initial dye concentration on the degradation of methyl red under sunlight has been studied. After 180 min of solar irradiation, the S. marginatum based zinc oxide nanoparticles (Sm-ZnO) exhibited the highest degradation efficiency, 92%, at pH 7, 5 mg/L dye concentration, and 2.5 mg/mL catalyst load. Under the same conditions, U. lactuca based ZnO NP (Ul-ZnO) recorded 90% degradation. The zinc oxide nanoparticles displayed notable performance during the three degradation cycles, and the stability of the catalyst is confirmed by X-ray diffraction analysis. The dye degradation reaction followed pseudo-first-order kinetics with a rate constant of 0.0167 min⁻¹ for Sm-ZnO NPs and 0.0155 min⁻¹ for Ul-ZnO NPs. The treated dye solution at pH 7, 2.5 mg/mL catalyst, and 10 mg/L dye concentration has been further utilized for watering green gram plants, and the growth parameters were, with a maximum shoot and root lengths of 13.5 cm and 1.8 cm, respectively. The total chlorophyll content was 72.9 μg/mL, protein content was 62 mg/g and the carbohydrate content 446 mg/g.
Loose nanofiltration (LNF) membrane with exclusively high dye rejection and inorganic salt permeation are remarkable method to treatment dye/salt wastewater for the achievement of zero liquid discharge. Herein, a long molecule bis-tris propane with amines and hydroxyl groups was firstly chosen as aqueous monomer in interfacial polymerization to fabricate a novel polyester-amide LNF membrane. Noteworthily, the investigation of morphology characterization and preparation conditions revealed that the size of molecule was a vital influence factor for the formation mechanism of unique loose structure of LNF made by long molecule. A new insight about the size of long molecule to form ultrathin thickness of self-repression layer on the formation mechanism of LNF was proposed in this work to replenish the previous theory. A series of characterization verified that the polyester-amide layer is negatively charged and hydrophilic due to the carboxyl and hydroxyl groups on the surface. Meanwhile, the tailored 0.3-LNF exhibited high water permeability (114.9 L ·m⁻² h⁻¹), dye rejection (98.83% RB 5) and low salt rejection (11.72% NaCl) under 0.5 MPa, which displayed good performance for the fractionation of dye/salt mixtures. In addition, the polyester-amide LNF membrane possesses a superior antifouling and stability performance.
Azo dyes are the most common colorants in consumer products, including clothing and cosmetics. Some azo dyes and their products from reductive degradation are known to be mutagenic, so dermal exposure to these species has been studied extensively. In contrast, oxidative degradation of azo dyes in consumer products has not been studied so thoroughly. In the indoor environment, ozone is ubiquitous, so reactive uptake of ozone to azo dyes could lead to dermal exposure to other classes of degradation products. Here, we report the first measurements of the reactive uptake of ozone to thin films of three widely used commercial azo dyes: sunset yellow, amaranth, and tartrazine. Steady-state uptake was observed for all three dyes, under all conditions investigated, even at the lowest relative humidity (RH) of 0%. The uptake coefficients increased with RH. For sunset yellow at 100 ppb of ozone, the value at 80% RH, (2.0 ± 0.5) × 10-7, was 2.5 times greater than that at 0% RH, (8 ± 1) × 10-8, consistent with plasticization of the thin film due to absorption of water. The uptake coefficient of sunset yellow at 80% RH exhibited an inverse dependence on the ozone mixing ratio, approaching an asymptote of 1 × 10-7 above 250 ppb. At 80% RH and 100 ppb of ozone, the uptake coefficients for the three dyes were similar, (2.0 ± 0.5) × 10-7 for sunset yellow, (2.7 ± 0.6) × 10-7 for amaranth, and (3.2 ± 0.3) × 10-7 for tartrazine, despite differences in structural parameters related to the number of reactive sites at the surface. Together, these results are consistent with ozone diffusing into the thin film and the dye molecules mixing between the layers, such that reaction is not restricted to the surface of the film. Finally, the results are suggestive of a role for azo dyes, including the occurrence of their oxidation products, in indoor chemistry.
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The Ames Salmonella/microsome assay was employed to test the mutagenicity of benzidine and its analogs using strains TA98 and TA100 in the presence and absence of Aroclor 1254-induced rat S9 mix. 3,3*-Dichlorobenzidine-2HCl and 4,4*-dinitro-2-biphe- nylamine were directly mutagenic to TA98, while 4,4*-dinitro-2- biphenylamine was directly mutagenic to both TA98 and TA100 in the absence of S9 mix. 2-Aminobiphenyl, 3-aminobiphenyl, and 3,3*-5,5*-tetramethylbenzidine were not mutagenic in either strains in the presence or absence of S9. In the presence of S9 mix, 4-aminobiphenyl, benzidine, 3,3*-dichlorobenzidine-2HCl, 3,3*-di- methoxybenzidine, 3,3*-4,4*-tetraaminobiphenyl, o-tolidine, N, N-N* ,N *-tetramethylbenzidine, and 4,4*-dinitro-2-biphenylamine were mutagenic to TA98; 4-aminobiphenyl, 3,3*-dichlorobenzi- dine-2HCl, 3,3*-dimethoxybenzidine, and 4,4*-dinitro-2-biphe- nylamine were mutagenic to TA100. Physicochemical parameters of these compounds including oxidation potentials, the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, ionization potentials, di- pole moment, relative partition coefficient, and basicity did not
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The characteristics of wastewater from textile processing operations are comprehensively reviewed. The categorisation of wastewaters proceeds through a consideration of the nature of the various industrial processes employed by the industry and the chemicals associated with these operations. Chemical pollutants arise both from the raw material itself and a broad range of additives used to produce the finished product. The industrial categories considered include sizing and desizing, weaving, scouring, bleaching, mercerizing, carbonizing, fulling, dyeing and finishing. Pollutants of concern range from non‐biodegradable highly‐coloured organic dyes to pesticides from special finishes such as insect‐proofing. It is evident that the textile wastewater chemical composition is subject to considerable change due to both the diversity in the textile processes employed and the range of chemicals employed within each industrial category.
The development of new electrochemical and photochemical methods for the decontamination of natural water containing significant concentrations of aromatic pesticides is described. The electrochemical method is based on the electro-Fenton process, i.e. the simultaneous reduction of O2 and Fe3+ ions. Hydroxyl (OH.) radicals are electrosynthesized in aqueous solutions, followed by complete mineralization of the initial pollutants. The photochemical methods involve either a direct photodegradation reaction of pesticides by UV light, or indirect photodegradation processes including H2O2 photolysis or photo-Fenton reagents (H2O2/ Fe3+). Examples of the application of these methods to chlorophenoxy acid herbicides and four aromatic pesticides (bendiocarb, pirimiphos-methyl, coumatetralyl, chlorophacinon) in aqueous media are given. Environmental applications are also presented. The performances of electrochemical and photochemical methods are compared.
The mutagenicity of fresh solutions of p-phenylenediamine (PPD) and Aroclor 1254 was investigated. The histidine-requiring strains of Salmonella typhimurium were used in the absence and presence of uninduced and/or Aroclor-induced rat-liver homogenate. The presence of polychlorinated biphenyls (PCBs) was also examined by chromatographic methods in Aroclor-induced rat-liver homogenate.
Literature regrading azo dye carcinogenicity was examined to establish, if possible, guidelines to predict the human health risks of new azo dyes. Three different mechanisms for azo dye carcinogenicity were identified, all involving metabolic activation to reactive electrophilic intermediates that covalently bind DNA. In the order of decreasing number of published references, these mechanisms are 1. Azo dyes that are toxic only after reduction and cleavage of the azo linkage to give aromatic amines, mostly via intestinal anaerobic bacteria. The aromatic amines are met‐abolically oxidized to reactive electrophilic species that covalently bind DNA.2. Azo dyes with structures containing free aromatic amine groups that can be meta‐bolically oxidized without azo reduction.3. Azo dyes that may be activated via direct oxidation of the azo linkage to highly reactive electrophilic diazonium salts.Each mechanism may be compound specific, thus azo toxicity is probably caused by more than one mechanism. Although it is not possible to predict azo dye carcinogenicity with absolute certainty, it is possible to establish certain guidelines. Because some species of intestinal anaerobic bacteria (and in some cases, hepatic azo reductases) may reduce any azo compound to aromatic amines, those containing aromatic amine subgroups known to be carcinogenic, such as benzidines, must be suspect. Information about human carcinogenicity of other specific aromatic amines is scant, and various short‐term mutagenicity tests may provide some guidance. Other in vitro tests can directly assay new azo dyes. Although it is unlikely that azo dyes can be developed that can be guaranteed not to generate constituent aromatic amines, it may be possible to select aromatic amines that are not toxic.
1. Eighteen known or possible metabolites of the hepatic carcinogen 4- (or p-) dimethylaminoazobenzene were tested for carcinogenic activity in the rat. Of these compounds only 4-monomethylaminoazobenzene, a known metabolite, proved to be active. Eight compounds, which appear to be metabolites of the dye, were inactive; these included 4-aminoazobenzene, 4'-hydroxy-4-monomethylaminoazobenzene, 4'-hydroxy-4-aminoazobenzene, N-methyl-p-phenylenediamine, p-phenylenediamine, aniline, p-aminophenol, and o-aminophenol. Nine compounds which may possibly be metabolites also were inactive; these compounds were 4'-hydroxy-, 3'-hydroxy-, and 2'-hydroxy-4-dimethylaminoazobenzene, 4-formylaminoazobenzene, 4-hydroxyazobenzene, 2, 4'-diamino-5-dimethylaminodiphenyl, 3-dimethylaminocarbazole, N,N-dimethyl-p-phenylenediamine, and p-hydroquinone. A mixture of 9 known and possible metabolites was also found to be inactive. These data indicate that the primary carcinogen operative in tumor formation by 4-dimethylaminoazobenzene is probably an azo dye closely related to the parent carcinogen. This conclusion is supported by recent work from this laboratory which indicates that the primary carcinogen consists of either or both of the protein-bound dyes found in the liver, i.e. 4-monomethylaminoazobenzene and an unidentified polar aminoazo dye, and that the formation of bound dye constitutes one of the first steps in this carcinogenic process. 2. The carcinogenic activities of 19 other compounds related to 4-dimethyl-aminoazobenzene were tested to obtain more information on the structural features needed for a 4-aminoazo dye to possess strong activity in the rat. 3'-Methyl-4-monomethylaminoazobenzene and the corresponding dimethylamino derivative were nearly twice as active and 4-ethylmethylaminoazobenzene had the same activity as 4-dimethylaminoazobenzene. As tested 3'-nitro- and 3'-chloro-4-dimethylaminoazobenzene both had about the same activity as 4-dimethylaminoazobenzene; however, since the 3'-nitro derivative was incompletely absorbed its real activity appears to be about 1½ times that of 4-dimethylaminoazobenzene. 2'-Nitro- and 2'-chloro-4-dimethylaminoazobenzene were about one-half to one-third as active and 4'-chloro-4-dimethylaminoazobenzene was approximately one-fourth as active as the parent dye. 3'-Ethoxy-4-dimethylaminoazobenzene and 3-methyl-4-monomethylaminoazobenzene exhibited only slight carcinogenic activity. The following compounds proved inactive: the benzamide of N,N-dimethyl-p-phenylenediamine; the diethyl, monoethyl, benzylmethyl, ß-hydroxyethylmethyl, and formyl derivatives of 4-aminoazobenzene on the amino group; and the 3-methyl, 3', 5'-dimethyl, 2',5'-dimethyl, and 2',4'-dimethyl derivatives of 4-dimethylaminoazobenzene. From the available data two conditions appear to be essential if a dye is to possess high activity: (1) at least one methyl group must be attached to the amino group together with the proper second substituent, and (2) the rings must bear either no substituents or carry only certain substituents, preferably in the 3' position. 3. The data on the carcinogenicity of the 2'-, 3'-, or 4'-methyl, chloro, and nitro derivatives of 4-dimethylaminoazobenzene show that the position of these groups determines the carcinogenicity of these compounds to a greater extent than does the type of group. The activity relationship was 3' > 2' > 4'. 4. Primary, secondary, and tertiary aminoazo dyes were determined in the livers and blood of rats fed aminoazo dyes which differed in the substituents on the amino group. The data show that deethylation of 4-diethyl-, 4-monoethyl-, and 4-ethylmethylaminoazobenzene occurs in vivo just as 4-dimethyl- and 4-monomethylaminoazobenzene are demethylated in vivo. However, 4-benzylmethylaminoazobenzene and 4-ß-hydroxyethylmethylaminoazobenzene were dealkylated only slightly under similar conditions. 5. The following new compounds are described: 4-ethylmethyl-, 4-monoethyl-, 4-benzylmethyl-, and 4-ß-hydroxyethylmethylaminoazobenzene; 4'-hydroxy-, 3-methyl-, and 3'-methyl-4-monomethylaminoazobenzene; 2'-hydroxy-, 3'-hydroxy, 3-methyl-, 3'-ethoxy-, 3', 5'-dimethyl-, 2', 5'-dimethyl-, and 2',4'-dimethyl-4-dimethylaminoazobenzene.
Abstract 1. Reduction of 4-nitrobenzoic acid and 1,2-dimethyl-4-(4-carboxyphenyl-azo)-5-hydroxybenzene by the cestode Moniezia expansa occurred in the distal cytoplasm (tegumental cytoplasm) of the proglottids. No drug reduction was found in other parts of the proglottid, and no adsorbed host-derived enzymes were detected. 2. Azo- and nitro-reductase activities were found in the 75 000 g supernatant. No activity was observed in the 75 000 g pellet. 3. Both enzyme activities required as cofactors NADH2 and either glutathione or cysteine; NADPH2 gave about half the activity of NADH2. 4. The optimal pH of both reductases was about 6-5, and neither activity was inhibited by CO, O2, EDTA or sodium azide. 5. Ammonium sulphate fractionation procedures failed to separate azo- and nitro-reductase activities. 6. The molecular weight of both azo- and nitro-reductase enzymes was about 125 000.