include pesticides, plastics, paints, hydrocarbon fuels, soaps, detergents, and many
more substances. Each chemical has a different effect on the environment and its
organisms. Dichlorodiphenyltrichloroethane (DDT) affects the endocrine system of
birds, leading to eggshell thinning and reduced breeding. Other chlorohydrocarbons
are also highly toxic to aquatic organisms, being persistent, soluble in fat, and having
very low solubility in water; thus, they quickly accumulate in the food chain, a
process described as bioaccumulation. Many countries have banned the use of these
chemicals and have promoted the use of other chemicals such as organophosphates,
carbamates, pyrethrins, and pyrethroids. Having relatively less solubility in water
and fat, these chemicals do not bioaccumulate and thus are less toxic, having a much
lower impact on the environment. However, these chemicals can be highly toxic to
biota including mammals and aquatic organisms. Soaps and detergents, containing
surfactants, have relatively low toxicity, persistence, and bioaccumulation. Although
discharged to the environment in large quantities their effects are generally low.
Plastics, on the other hand, enter the environment as solid wastes with little toxicity
but have other adverse environmental effects. Proper management of pollutants
through bioremediation is the demand of the present time. Some important pollutants, their sources, and their effects are highlighted in Table 18.2.
3.1.1 Hydrocarbons
Hydrocarbon contamination in the environment poses a serious problem whether it
comes from petroleum products, pesticides, or other toxic organic matter. Of the
hydrocarbons, petroleum products are a great concern because these are toxic to all
forms of life. Environmental contamination by crude oil is relatively common
because of its widespread use and the associated disposal operations and accidental
spills.
3.1.2 Polychlorinated Biphenyls (PCBs)
Another group of organic pollutants, polychlorinated biphenyls (PCBs), shares a
common structure but differ in the number of attached chlorine atoms. The international treaty on Persistent Organic Pollutants, drafted by 122 nations in Johannesburg in December 2000, emphasized phase-by-phase removal of targeted PCBs from
the world. PCBs can be carcinogenic according to the International Agency for
Research on Cancer, the U.S. Environmental Protection Agency, and the National
Toxicology Program. According to the National Institute for Occupational Safety
and Health, PCBs are a potential occupational carcinogen leading to increased rates
of melanoma, liver cancer, gallbladder cancer, biliary tract cancer, gastrointestinal
tract cancer, and brain cancer. PCBs are reported to cause various types of cancer in
rats, mice, and other study animals.
440
S. K. Shekhar et al.
more substances. Each chemical has a different effect on the environment and its
organisms. Dichlorodiphenyltrichloroethane (DDT) affects the endocrine system of
birds, leading to eggshell thinning and reduced breeding. Other chlorohydrocarbons
are also highly toxic to aquatic organisms, being persistent, soluble in fat, and having
very low solubility in water; thus, they quickly accumulate in the food chain, a
process described as bioaccumulation. Many countries have banned the use of these
chemicals and have promoted the use of other chemicals such as organophosphates,
carbamates, pyrethrins, and pyrethroids. Having relatively less solubility in water
and fat, these chemicals do not bioaccumulate and thus are less toxic, having a much
lower impact on the environment. However, these chemicals can be highly toxic to
biota including mammals and aquatic organisms. Soaps and detergents, containing
surfactants, have relatively low toxicity, persistence, and bioaccumulation. Although
discharged to the environment in large quantities their effects are generally low.
Plastics, on the other hand, enter the environment as solid wastes with little toxicity
but have other adverse environmental effects. Proper management of pollutants
through bioremediation is the demand of the present time. Some important pollutants, their sources, and their effects are highlighted in Table 18.2.
3.1.1 Hydrocarbons
Hydrocarbon contamination in the environment poses a serious problem whether it
comes from petroleum products, pesticides, or other toxic organic matter. Of the
hydrocarbons, petroleum products are a great concern because these are toxic to all
forms of life. Environmental contamination by crude oil is relatively common
because of its widespread use and the associated disposal operations and accidental
spills.
3.1.2 Polychlorinated Biphenyls (PCBs)
Another group of organic pollutants, polychlorinated biphenyls (PCBs), shares a
common structure but differ in the number of attached chlorine atoms. The international treaty on Persistent Organic Pollutants, drafted by 122 nations in Johannesburg in December 2000, emphasized phase-by-phase removal of targeted PCBs from
the world. PCBs can be carcinogenic according to the International Agency for
Research on Cancer, the U.S. Environmental Protection Agency, and the National
Toxicology Program. According to the National Institute for Occupational Safety
and Health, PCBs are a potential occupational carcinogen leading to increased rates
of melanoma, liver cancer, gallbladder cancer, biliary tract cancer, gastrointestinal
tract cancer, and brain cancer. PCBs are reported to cause various types of cancer in
rats, mice, and other study animals.
440
S. K. Shekhar et al.