Environmental Engineering Reference
In-Depth Information
C 2 H 5
NH
CH
NH
CH 2
C 2 H 5
NHCH 3
NH 2
C 2 H 5
NO 2
NO 2
NO 2
NO 2
NO 2
CH 3
CH 3
CHO
CH 3
CH 3
CH 3
NH 2
NO 2
CH 3
CH 3
Propiconazole , a broad-spectrum fungicide, on photodegradation in soil and water, forms
a stable aromatic moiety, 1,2,4 triazole.
Thiamethoxam , an efficient synthetic agrochemical, neonicotinoid, on photodegradation
forms 3-(2-chloro-1,3-thiazol-5-yl methyl) 1,3,5-oxaziazinan-4-ylidene (nitrosamine).
N
NO 2
N
NO
S
S
NH
N
CH 3
N
N
Cl
Cl
N
N
O
O
The photochemical degradation of most of the pesticides follows first-order chemical
kinetics. The first-order rate equation is generally expressed as:
(
) =
ln CA CA0
k1t ,
where k 1 is the degradation constant. Plot of ln(C A /C A0 ) vs t would therefore be a straight
line passing through origin, and the slope will give the rate constant, k 1 .
3.4 Microbial Degradation
Microorganisms are known to play major roles in metabolizing pesticides in the environ-
ment, mainly in water and soil. The process can take several steps to degrade pesticides
into CO 2 , H 2 O, and mineral salts. There are four types of microbes: bacteria, fungi, proto-
zoa, and algae. Bacteria and fungi are the most abundant in nature, so they are the most
important microorganisms for biological degradation. There will always be one or more
microorganisms that are able to degrade any organic compound. Due to an enormous
number of species, mutations of a microorganism may create an organism that can degrade
the compound. So, the rate of degradation increases with time.
In the microbial degradation process, the pesticide is absorbed into the cell membrane of
the microbe. Enzymes present in the microbe breakdown the pesticide into smaller frag-
ments with minerals as the final end-product. The degradation process follows different
pathways depending on the microbes present.
 
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