Environmental Impact of Textile Dyes and Their Toxicity

Dye wastewater from textile and dye based industries is one of the most complex industrial wastewaters to treat. It is known that 90% of reactive textile dyes entering the activated sludge sewage treatment plants discharge into rivers and cause problems such as (a) reduction in penetration of sunlight in the streams, which is essential for photosynthesis and consequently, the ecosystem of the stream is seriously affected (b) toxicity to fish and mammals life (c) inhibition of the activity and the growth of microorganisms particularly at high concentrations (d) some cationic species (mostly triphenylmethanes) affect the flora and fauna even at lesser concentrations (Verma 2008).

Interest in the pollution potential of textile dyes has been primarily prompted by concern over their possible toxicity and carcinogenicity (Maas and Chaudhari 2005; Salony and Bisaria 2006; Revankar and Lele 2007). This is mainly due to the fact that many dyes are made from known carcinogens, such as benzidene and other

Dye Toxicity Fish

Tryp an Blue Evans Blue

Fig. 35.2 Chemical structure of common dyes used in various industries (www.wikipedia.com)

Tryp an Blue Evans Blue

Fig. 35.2 Chemical structure of common dyes used in various industries (www.wikipedia.com)

aromatic compounds (Clarke and Anliker 1980; Levin et al. 2005). Chronic effects of dyestuffs, especially of azo dyes, have been studied for several decades. Azo dyes in purified form are seldom directly mutagenic or carcinogenic (Brown and DeVito 1993), however, reduction of azo dyes, leads to formation of aromatic amines, which are known mutagens and carcinogens (Dawkar et al. 2009). Exposure to aromatic amines may cause methaemoglobinemia in which the amine oxidize the heme iron

Table 35.2 Important classes of dyes and their characteristics

Type of interaction/reactions

Dye class Color index Fiber with fiber Examples

Acid dyes Largest class -2,300 different Mainly wool. Nylon, Ionic interactions, anionic Azo dyes like Orange II, Orange G

dyes listed -40% of them Polyamide, Modified compounds of dyes bind and Carbonyl like Indigo are in current production acryl with the cationic NH4+ Carmine, Anthraquinone etc.

ions.

Basic dyes Represent -5% of all dyes Mainly synthetic fibers like Ionic interactions Triphenyl like Crystal violet listed in color index modified polyacryl and Malachite green.

and anthraquinone. triaryl-methane etc.

Reactive dyes Second largest dye class Cotton, wool, silk and nylon Covalent interactions with Reactive Orange II. Reactive etc. fibers Black5. Reactive Redl98.

and Quinine type Remazol blue

Direct dyes -1.600 are listed and about Mainly cellulose fibers like Vanderwaal forces Mostly are Azo Congo red. Direct

30%are in current cotton Blue86, Phthalocyanine etc. production

Disperse dyes Third largest group of dyes Synthetic fibers like cellulose These dyes penetrate Azo compounds like Methyl acetate, polyester, synthetic fibers yellow. Disperse Yellow 1 etc. Polyacrylamide.

Vat dyes - Cellulose fibers mainly Dyeing method based on the All vat dyes are anthraquinone or cotton and wool solubility of vat dyes in indigoid like indigo etc.

their reduced (Leuco) form

Mordant dyes -600 Mordant dyes are listed Wool. Leather. Silk. Mordant dyes fixed to fabric These are Azo. Oxazine or in the color index Paper and modified by the addition of a Triarylmethane but usually cellulose fibers mordant. these are dichromates or chromium complexes.

Pigment dyes About 25% of all commercial Used for printing diverse To interact with fiber required Mostly are Azo (Yellow to Red)

dyes name listed in the fibers. the help of dispersing or metal complexes and color index agent. Quinacridone like Acridine

NH2 OH h3co

OCH3 OH NH2

NaSOg ^^ SOgNa

Resacor Blue 2F

azoreductases in liver cells, intestinal bacteria and skin surface microflora

NH2 OH

NaSO

NH2 OH

SO3Na

OH NH

NaSO

OH NH

H3CO

och3

3,3'-Dimethoxybenzidine

SO3Na

Fig. 35.3 Reaction mechanism of degradation of dye Resacor Blue 2F to a carcinogenic compound 3,3—Dimethoxybenzidine (Hildenbrand et al. 1999)

of hemoglobin from Fe (II) to Fe (III), blocking the oxygen binding. In mammals, reduction of azo dyes is mainly due to bacterial activity in the lower gastrointestinal tract, liver and the kidney. The carcinogenicity mechanism probably includes the formation of nitremium and carbonium ions from acyloxy amines that bind to DNA and RNA, which induce mutations and tumour formation (Van der Zee 2002; Golka et al. 2004). A study carried out by Hildenbrand et al. (1999) on reduction of azo dyes in cell cultures showed that the addition of a dye, Resacor Blue 2F, to kidney and liver cells produced a carcinogenic aromatic amine 3,3'-Dimethoxybenzidine (Fig. 35.3).

Dermal and immunological effects have also been reported in workers exposed to benzidine and cancer is the documented toxic effect of benzidine in both human and animals. Direct brown, Direct black, Direct blue, are the dyes generally used in textile industries and the workers exposed to these compounds excrete high level of benzidine into their urine (Van der Zee 2002; Golka et al. 2004). Metabolic transformation of benzidine results in the formation of reactive intermediates which are thought to produce DNA adducts, which may initiate carcinogenesis by producing mutations that become fixed before DNA can be repaired (Van der Zee 2002; Golka et al. 2004). Moreover, anthraquinone based dyes, which are the most resistant to degradation when form metal -based complex can also be carcinogenic, in water supplies (Van der Zee 2002; Golka et al. 2004).

Other compounds like formaldehyde, carbon disulphide, some phenolic and sulphur containing compounds are also used in textile industries. Formaldehyde is generally used in textile industries to attain a permanent press finish. It is a well-known cause of ocular and airway irritation and it can cause certain skin reactions including contact dermatitis via either allergic or irritant mechanism (Van der Zee 2002; Golka et al. 2004). Carbon disulphide (CS2) is prominent in the production of the synthetic fiber viscose rayon. It is used in the conversion process of cellulose to rayon fibers and cellophane and high level of CS2 resulted in the severe central nervous system (CNS) disorders including acute mania and narcosis (Van der Zee 2002; Golka et al. 2004).

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