1 Introduction
Rapid urbanization and industrialization during past few decades resulted the global
economic growth by providing food security and job security to mankind. But at the
same time, nonstrategic urbanization and industrialization led to pollution due to
discharge of the large quantities of pollutants such as organic and inorganic
chemicals, metals, dyes, etc. into the environment. Textile, dying, printing, leather,
and tannery industries use various synthetic dyes for imparting color and aesthetic
value to their products and discharge large quantities of pollutants into the environment. Effluents from these industries are highly colored, contain toxic dyes and
metals, and have a deleterious effect on the environment (Saibaba et al. 2012). These
metal dyes contaminate the soil and enter into the food chain through accumulation
in plants, vegetables, grains, and fruits. Consumption of these food products create many health hazards to humans and other animals living on the earth and water.
Thus, these pollutants need to be treated before they are discharged into the water
bodies.
Textile industry is not only one of the principal users of synthetic dyes but also
the largest generator of effluent containing hazardous dyes. Textile, dyeing, and
printing industries generate large quantities of dye effluents from processes such as
textile wet processing, dyeing, washing, etc. More than 8000 chemical produces are
associated with dyes and dying processes. Over 7 Â 10
5 metric tons of dyes are
being produced annually from over 10
5 types of commercial dyes. Most of these
dyes are wasted during the textile dying and printing processes; this wastage could
be in the range of 2% for basic dyes to 50% for reactive dyes. On an average,
approximately 15% of the dyes used in the textile industry are reaching the environment through effluents and are causing severe land and water contamination.
Most of these dyes are physically, chemically, and photolytically stable, which
persist in the environment for longer periods. Bioaccumulation of these dyes in
the food chain causes serious health hazards to humans and other living animals.
Long-term exposure of these dyes is carcinogenic and mutagenic to humans and
causes skin irritation, eye blindness, nausea, cancer, etc. (Saibaba et al. 2011, 2012;
Saibaba and King 2013a; Vital et al. 2016).
Various types of synthetic dyes such as acidic dyes, basic dyes, reactive dyes,
metal complex dyes, sulfur dyes, and fluorescent dyes, are being used for various
applications. Textile industries also use dichromates or chromium complexes as
mordents (Aksu and Karabayır 2008; Arpita et al. 2015). Most of the synthetic dyes
used in the textile industry are metal complexes. Metal complex dyes are made up of
dyes and heavy metals such as Cr, Co, Cu, Pb, etc. Long-term contact of chromium
causes health problems such as irritation in the lungs, stomach ache, lowered
immunity, and also damage to the health hormones. Accumulation of chromium in
plants inhibits the photosynthesis, damages the tissue, and decreases the growth
(Shanker et al. 2005; Li et al. 2013; Arpita et al. 2015). Cobalt exposure for longer
times may create asthma, dermatitis, cancer, etc. (Min et al. 2013). Long-term
exposure of copper may result to kidney and liver failures and brain damage and
174
N. S. KV
Rapid urbanization and industrialization during past few decades resulted the global
economic growth by providing food security and job security to mankind. But at the
same time, nonstrategic urbanization and industrialization led to pollution due to
discharge of the large quantities of pollutants such as organic and inorganic
chemicals, metals, dyes, etc. into the environment. Textile, dying, printing, leather,
and tannery industries use various synthetic dyes for imparting color and aesthetic
value to their products and discharge large quantities of pollutants into the environment. Effluents from these industries are highly colored, contain toxic dyes and
metals, and have a deleterious effect on the environment (Saibaba et al. 2012). These
metal dyes contaminate the soil and enter into the food chain through accumulation
in plants, vegetables, grains, and fruits. Consumption of these food products create many health hazards to humans and other animals living on the earth and water.
Thus, these pollutants need to be treated before they are discharged into the water
bodies.
Textile industry is not only one of the principal users of synthetic dyes but also
the largest generator of effluent containing hazardous dyes. Textile, dyeing, and
printing industries generate large quantities of dye effluents from processes such as
textile wet processing, dyeing, washing, etc. More than 8000 chemical produces are
associated with dyes and dying processes. Over 7 Â 10
5 metric tons of dyes are
being produced annually from over 10
5 types of commercial dyes. Most of these
dyes are wasted during the textile dying and printing processes; this wastage could
be in the range of 2% for basic dyes to 50% for reactive dyes. On an average,
approximately 15% of the dyes used in the textile industry are reaching the environment through effluents and are causing severe land and water contamination.
Most of these dyes are physically, chemically, and photolytically stable, which
persist in the environment for longer periods. Bioaccumulation of these dyes in
the food chain causes serious health hazards to humans and other living animals.
Long-term exposure of these dyes is carcinogenic and mutagenic to humans and
causes skin irritation, eye blindness, nausea, cancer, etc. (Saibaba et al. 2011, 2012;
Saibaba and King 2013a; Vital et al. 2016).
Various types of synthetic dyes such as acidic dyes, basic dyes, reactive dyes,
metal complex dyes, sulfur dyes, and fluorescent dyes, are being used for various
applications. Textile industries also use dichromates or chromium complexes as
mordents (Aksu and Karabayır 2008; Arpita et al. 2015). Most of the synthetic dyes
used in the textile industry are metal complexes. Metal complex dyes are made up of
dyes and heavy metals such as Cr, Co, Cu, Pb, etc. Long-term contact of chromium
causes health problems such as irritation in the lungs, stomach ache, lowered
immunity, and also damage to the health hormones. Accumulation of chromium in
plants inhibits the photosynthesis, damages the tissue, and decreases the growth
(Shanker et al. 2005; Li et al. 2013; Arpita et al. 2015). Cobalt exposure for longer
times may create asthma, dermatitis, cancer, etc. (Min et al. 2013). Long-term
exposure of copper may result to kidney and liver failures and brain damage and
174
N. S. KV