Environmental Engineering Reference
In-Depth Information
4.
Conjugation
a.
Methylation
≡
C-OH
→
≡
C-OCH
3
b.
Acetylation
O
≡
C-NH
2
→
≡
C-NH-C
-CH
3
5.
Rearrangement
: Transformation of one isomer to another, occurring by physical or
chemical agents.
a.
Cyclization
Open
→
Closed chain
b.
Dimerization
2A
→
[A-A]
3.2 Chemical Degradation
Chemical degradation is the breakdown of pesticides by processes in which living organ-
isms are not involved. Hydrolysis, oxidation-reduction, substitution, elimination, deha-
logenation, and reduction, without the influence of microbial activities, are processes
involved in chemical degradation. Hydrolysis is an important reaction that takes place in
water and soil for pesticide degradation.
3.2.1 Factors Influencing Chemical Degradation
1.
Organic matter content and clay content
: Organic matter and clay content are the two
major components that influence chemical degradation of pesticides, as organic
matter content and clay content provide larger surface area for enhancing hydro-
lytic degradation.
2.
pH
: Soil pH or pH of the medium affects the hydrolytic process of pesticide dis-
sipation, which depends on the nature of pesticides, for example, some pesticides
are acid hydrolyzed and others are base hydrolyzed.
3.
Temperature
: With the increasing temperature, the molecules in solution have more
energy, causing them to move and react faster, which causes hydrolysis reaction to
occur at a faster rate.
4.
Nature of substituents
: The reactivity of pesticides depends on the substituents present
in the pesticides used. Some substituents are easily replaced from the substrate by
hydrolysis reaction since the products formed are very stable in water. The substitu-
ents that pull electron density away from the substrate facilitate hydrolysis.
5.
Effluent irrigation
: Effluent irrigation enhances the chemical degradation of pesti-
cides by altering the pH of the soil solution and increasing dissolved organic mat-
ter content (Muller et al. 2007).
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