Environmental Engineering Reference
In-Depth Information
Parent Compound
Degradation products
Cl
Cl
N
NHCH
2
CH
3
N
NHCH
2
CH
3
N
N
N
N
NHCH
2
CH
3
NH
2
Simazine
DES
Deethylsimazine
H
3
CO
N
NHC(CH
3
)
3
H
3
CO
N
NHC(CH
3
)
3
N
N
N
N
NHCH
2
CH
3
NH
2
Terbumeton
Deter
Deethylterbumeton
Cl
Cl
HO
N
NHC(CH
3
)
3
N
NHC(CH
3
)
3
N
NHC(CH
3
)
3
N
N
N
N
N
N
NHCH
2
CH
3
NH
2
NHCH
2
CH
3
Terbuthylazine
DETbzne
Deethylterbuthylazine
HTbzne
2-hydroxyterbuthylazine
FIGURE 4.7 (Continued)
were not detected, DK was found in concentrations as high as 1.37 μg/L and DADK was
detected in concentrations as high as 1.83 μg/L.
Alachlor, metolachlor, and acetochlor acetamide are three similar chloroacetanilide her-
bicides and are among the most commonly used preemergence herbicides of corn and
soybean crops in the United States (Graham et al. 1999). Each of these three parent com-
pounds breaks down into their ethane sulfonic acid (ESA) and oxanilic acid (OA) metabo-
lites (
Figure 4.7
). The chloroacetanilide herbicides are transformed to the ESA and OA
metabolites primarily by microbial activity in soil. The degradation of the parent com-
pounds to the ESA metabolites, for example, results in the removal of a chlorine atom and
the addition of a sulfonic acid functional group to the molecule. This greatly increases the
water solubility relative to the parent compound. In addition to the solubility, the appar-
ent higher stability than that of the parent compound contributes to the increase in their
leaching potential in groundwater. Furthermore, degradation products of chloroacetani-
lide herbicides are considered not only more mobile but also potentially persistent than the
respective parent compounds (Barrett 1996). Therefore, their extensive use and moderate
persistence make these herbicides and their degradation products accumulate in many
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