100
N. Sethunathan et al.
influenced by the period of submergence prior to the addition of the insecticide
(Wahid, 1978). Thus, parathion applied to soils preflooded for 10 and 20 days
disappeared more rapidly than parathion added to soils at the time of flooding.
The more the soil was reduced by pre submergence at the time of the addition
of parathion, the more rapid was its degradation via nitro group reduction.
In equilibration studies (Wahid et al., 1980), instantaneous surface-catalyzed degradation of parathion to aminoparathion occurred when the insecticide
was shaken, even for less than 5 sec, with soils reduced by prior incubation
under flooding (Fig. 4.2). Aminoparathion was further converted by dealkylation
to desethyl aminoparathion in the acid sulfate soils, but not in other soils. Based
on persistence data with irradiated, autoclaved, and sodium-azide-treated soils,
parathion degradation in prereduced soils appeared to be mediated by soil enzymes and/or other heat-labile substances produced by soil anaerobiosis.
b
a
c
2
3
Figure 4.2. Radioautograph of parathion and its degradation products formed within 5 sec of
equilibration with anaerobic Po/ckali (acid sulfate) soil. (I) Anaerobic soil; (2) aerobic soil; (3)
standard parathion; (a) aminoparathion; (b) desethyl aminoparathion; (c) unidentified product (Wahid
et ai., 1980).
N. Sethunathan et al.
influenced by the period of submergence prior to the addition of the insecticide
(Wahid, 1978). Thus, parathion applied to soils preflooded for 10 and 20 days
disappeared more rapidly than parathion added to soils at the time of flooding.
The more the soil was reduced by pre submergence at the time of the addition
of parathion, the more rapid was its degradation via nitro group reduction.
In equilibration studies (Wahid et al., 1980), instantaneous surface-catalyzed degradation of parathion to aminoparathion occurred when the insecticide
was shaken, even for less than 5 sec, with soils reduced by prior incubation
under flooding (Fig. 4.2). Aminoparathion was further converted by dealkylation
to desethyl aminoparathion in the acid sulfate soils, but not in other soils. Based
on persistence data with irradiated, autoclaved, and sodium-azide-treated soils,
parathion degradation in prereduced soils appeared to be mediated by soil enzymes and/or other heat-labile substances produced by soil anaerobiosis.
b
a
c
2
3
Figure 4.2. Radioautograph of parathion and its degradation products formed within 5 sec of
equilibration with anaerobic Po/ckali (acid sulfate) soil. (I) Anaerobic soil; (2) aerobic soil; (3)
standard parathion; (a) aminoparathion; (b) desethyl aminoparathion; (c) unidentified product (Wahid
et ai., 1980).