Degradation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 48

quantify the chemical and biological processes that control the behavior of organic chemi-
cals in the environment to improve pesticidal management for minimizing contamination
of our natural resources and remediating contaminated environment. To an estimate, we
have an annual production of approximately 10 6 tons of active ingredients worldwide.
Assuming a total arable land area of 13.8 × 10 6 km 2 on earth, though unrealistic, the even
distribution of pesticides would amount to about 0.7 kg/ha year. So, much use of organic
chemicals by all sectors of the economy is affecting human health and environment as the
result of soil, air, and water contamination. These effects may range from growth retarda-
tion to physiological or behavioral deficiencies, which substantially affect the most sensi-
tive individuals or species (Atterby et al. 2002; Bollag and Liu 1990). Subsequently, it may
lead to population shift resulting in ecological changes. Pesticides, when used in agricul-
ture, are likely to enter various compartments of the environment. They may undergo
leaching by water, volatilization into atmosphere, or sorption to various surfaces. When
introduced into the environment, the fate of pesticides is influenced by three major pro-
cesses: transfer (sorption), transport (runoff, leaching, and volatilization), and transforma-
tion (chemical degradation (hydrolysis and photolysis) and microbial degradation).
Pesticide degradation : Pesticide degradation or the breakdown of pesticides is usually con-
sidered beneficial. Pesticide-destroying reactions change most pesticide residues in the
environment to nontoxic or harmless compounds. However, degradation is detrimental
when a pesticide is destroyed before the target pest has been controlled. There are three
types of pesticide degradation: (a) chemical degradation, (b) photodegradation, and (c)
microbial degradation.
During pesticide transformation brought about by physical, chemical, and biological
forces, following types of reactions generally occur.

1. Oxidation : Physical and chemical oxidation reactions involve molecular oxygen or
peroxide or singlet oxygen. Biological oxidation occurs by mixed-function oxidase
enzyme. Specific oxidative reactions in pesticide degradation are

a. Ring hydroxylation

Y

Y

OH

b. Side-chain oxidation

H OH

C R

C R

R R

c. Epoxidation

C C<

>C= C< >

O

d. O-dealkylation

OCH 3 OH