104
N. Sethunathan et al.
HCH
(-y_. 0(-. ~-. s-)
DD T
PARATHION
DIAZINON
CARBOFURAN
CARBARYL
o 4
8
12
16
20
24
28
HALF-LIFE IN DAYS
Figure 4.3. Half-life (days) of selected pesticides in flooded soils (adapted from Sethunathan and
Siddaramappa. 1978).
pounds than in either system alone. This is especially true for molecules possessing ring moieties since ring cleavage reaction requires oxygen. Diazinon was
hydrolyzed in flooded soil, but the ring portion of its hydrolysis product was
cleaved only under aerobic conditions following anaerobiosis (Sethunathan, 1972).
Likewise, anaerobic degradation of parathion in a flooded soil led to the formation
of aminoparathion and possibly other easily soil-bound residues (Katan et ai.,
1976). p-Nitrophenol, formed readily after two or three additions of parathion
to flooded soil, was converted to soil-bound residues under continued anaerobiosis, in contrast to its almost complete mineralization to CO2 under aerobic
conditions (Sudhakar-Barik and Sethunathan, 1978b). In flooded soils, conversion of DDT to DDD occurred rapidly, but DDD persisted. Probably more
complete destruction of DDT past DDD can be accomplished in a system where
anaerobiosis is followed by aerobiosis, as demonstrated in the extensive degradation of DDT past DDD to p-chlorophenylacetic acid, formed by cleavage
of one of the aromatic rings by Hydrogenomonas sp. (Pfaender and Alexander,
N. Sethunathan et al.
HCH
(-y_. 0(-. ~-. s-)
DD T
PARATHION
DIAZINON
CARBOFURAN
CARBARYL
o 4
8
12
16
20
24
28
HALF-LIFE IN DAYS
Figure 4.3. Half-life (days) of selected pesticides in flooded soils (adapted from Sethunathan and
Siddaramappa. 1978).
pounds than in either system alone. This is especially true for molecules possessing ring moieties since ring cleavage reaction requires oxygen. Diazinon was
hydrolyzed in flooded soil, but the ring portion of its hydrolysis product was
cleaved only under aerobic conditions following anaerobiosis (Sethunathan, 1972).
Likewise, anaerobic degradation of parathion in a flooded soil led to the formation
of aminoparathion and possibly other easily soil-bound residues (Katan et ai.,
1976). p-Nitrophenol, formed readily after two or three additions of parathion
to flooded soil, was converted to soil-bound residues under continued anaerobiosis, in contrast to its almost complete mineralization to CO2 under aerobic
conditions (Sudhakar-Barik and Sethunathan, 1978b). In flooded soils, conversion of DDT to DDD occurred rapidly, but DDD persisted. Probably more
complete destruction of DDT past DDD can be accomplished in a system where
anaerobiosis is followed by aerobiosis, as demonstrated in the extensive degradation of DDT past DDD to p-chlorophenylacetic acid, formed by cleavage
of one of the aromatic rings by Hydrogenomonas sp. (Pfaender and Alexander,