Continuously increasing population is leading to the intensive agriculture (to get greater
amount of food and other products on the same limited land by the use of improved varieties
of crop plants, which require higher amount of chemical fertilizers, insecticides, herbicides,
etc.), urbanization, industrialization, deforestation, and excessive utilization of various
resources (fossil fuels, underground water, etc,). This leads to the degradation of our environment
by generating various kinds of liquid, solid, gaseous and hazardous wastes, particularly in the developed
countries, where, only about 15% population consumes about 85% resources to generate about
85% of the wastes (most of which are non-biodegradable) in comparison to the developing countries.
On the other hand, in developing countries higher population, limited technological knowledge and
finance facilities for the treatment of wastes are the major causes of environmental degradation.
Earlier, when the population was small the environment was sustainable and the biodegradable wastes
generated were easily decomposed by the decomposers. But now, the amount of waste generated is
so great that the limited natural capabilities of the environment are unable to decompose it properly,
particularly the toxic non-biodegradable ones, leading to the accumulation of such wastes in food
chains (biomagnification of insecticides, like, dichloro diphenyl trichloro ethane or DDT, herbicides,
etc.) as well as in the surroundings. Large-scale production and application of synthetic chemicals
in most industrialized countries is a problem of serious concern causing serious health hazard. Organic
chemicals that cannot be easily degraded by microorganisms or totally resistant to biodegradation are
known as recalcitrants, e.g., lignin; whereas, synthetic compounds (foreign substances) not formed
by natural biosynthetic processes are called xenobiotic compounds (that can be recalcitrants) and
often have toxic effects, e.g., insecticides DDT, BHC (benzene hexa-chloride), etc.