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SO 2 CH 2 CH 3 OCH 3
SO 2 CH 2 CH 3
SO 2 CH 2 CH 3
OCH 3
OCH 3
N
N
N
H
SO 2 NHCH 2 NH
N
N
N
N
N
N
N
O C
OCH 3
OCH 3
OCH 3
NH 2
Rimsulfuron
IN70941
IN70942
FIGURE 4.8
Major pathway of degradation of rimsulfuron in soil.
Rosenbom and coworkers (2010) studied the leaching of rimsulfuron and its by-products
IN70941 and IN70942 (Figure 4.8) at two sandy research fields in Denmark. Water was
sampled every month during a 4-6-year period following the application of the herbi-
cide. No rimsulfuron was detected in the water beneath the two sandy soil research
fields. By contrast, the degradation products were detected in the water or the vadose
and groundwater zones for several years following the application of rimsulfuron, thus
indicating that they are relatively stable and persist in the soil, from where they leach
into groundwater. Both degradation products exhibited continuous leaching during the
6-year monitoring period and were still detected toward the end of 2008, that is, 6 years
after the application of rimsulfuron. The observed leaching patterns seem to be consis-
tent with fate studies suggesting that rimsulfuron is nonpersistent and that the two deg-
radation products IN70491 and IN70942 are more persistent, with half-lives of 30-1100
and 101-214 days, respectively.
These authors suggest that the long-term leaching of low-dose pesticide degradation
products such as IN70941 and IN70942 can pose a potential risk to the aquatic environ-
ment, thus indicating a need to further study/monitor the long-term leaching and ecotoxi-
cological effects of low-dose pesticides and their degradation products.
The identification of new degradation products formed from the primary by-products is
gaining importance, as is shown by the identification of new degradation products of aldi-
carb, such as aldicarb sulfoxide oxime and aldicarb sulfoxide nitrile, by-products derived
from the previous degradate aldicarb sulfoxide ( Table 4.1 ). These degradation products
were detected at a concentration in the range of 22-220 μg/L for aldicarb sulfoxide nitrile
and 3.8-38 μg/L for aldicarb sulfoxide oxime (Miles and Delfino 1984).
4.6 Chemical Analysis of Pesticide Degradation Products
Analysis of polar pesticides and even more polar transformation products is quite chal-
lenging because they are extremely water-soluble and therefore difficult to be enriched
and detected by common methods such as gas chromatography (GC) coupled with mass
spectrometry (MS). Furthermore, the difficulty in determining the organic by-products
in raw and finished water is enhanced by taking into account the following issues: (a)
By-products and metabolites of some pesticides, formed in the different environmental
conditions, are still unknown; (b) A scarce number of analytical standards for the degra-
dates are available, hence there are no analytical methods for the analysis of transforma-
tion products in the aquatic environment; (c) The concentrations expected in the aquatic
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