Pesticide Metabolism in Plants
57
Recent studies with chioroanilines derived from herbicides indicate that these
metabolites are associated mostly with the lignin fraction (Balba and Still, 1977).
It is reasonable to expect many of the phenolic residues from herbicides and
insecticides to be found also in the same lignin fraction. However, it is difficult
to speculate how products metabolized via glutathione conjugation might be
incorporated into lignin. Perhaps products from glutathione conjugation are incorporated into various protein fractions. The study of insoluble pesticide residues
is an area of pesticide metabolism that is in need of additional research, but it
is one of the most difficult to study.
Several examples of high insoluble residue formation in plants from different
pesticides have been cited (Baldwin, 1977). However, only a few of the reported
residues have been tested for their bioavaiiability. Generally, the insoluble residues of pesticides in plants appear to be highly stable and are not readily
degraded for absorption in the gastrointestinal tract of animals.
About 21 % of the absorbed radioactivity from ring-labeled [14C]atrazine
was in the insoluble residue fraction of sorghum. This residue was highly stable
and resisted digestion by the rat and ruminant sheep, which excreted 88% and
100%, respectively, of the bound residue in the feces (Bakke et at., 1972b). In
alfalfa, 26% and 77% of the 14C found in the shoots and roots, respectively,
from root-absorbed [14C]propham was incorporated into insoluble residue after
7 days. When the insoluble residue was fed to rats, 86% of the 14C was excreted
in the feces and less than 3% remained in the carcass 96 hr after treatment
(Paulson et at., 1975). Bean plants incorporated 51 % and 7% of ring 14C-Iabeled
carbaryl and carbofuran, respectively, into insoluble residues 20 days after treatment (Marshall and Dorough, 1977). Water-soluble conjugates from carbaryl
and carbofuran accounted for 30% and 67% of the 14C, respectively (Marshall
and Dorough, 1977). When the insoluble residues of carbaryl and carbofuran
were fed to rats, 98% and 85%, respectively, of the doses were excreted in the
feces. In contrast, rats fed 14C water-soluble metabolites of carbaryl and carbofuran excreted 80% to 90%, respectively, of the radiocarbon in the urine
(Marshall and Dorough, 1977).
2.4. CONCLUSION
This review is not a complete compilation of pesticide metabolism in plants.
Important pesticide compounds such as the synthetic pyrethroids (Gaughan and
Casida, 1978; Ruzo and Casida, 1977) and other naturally occurring plant insecticides such as nicotine and rotenone have not been discussed. However,
these compounds, especially the pyrethroids, should not be overlooked because
of their potential use as important insecticides.
This short discussion on pesticide metabolism in plants indicates that most
57
Recent studies with chioroanilines derived from herbicides indicate that these
metabolites are associated mostly with the lignin fraction (Balba and Still, 1977).
It is reasonable to expect many of the phenolic residues from herbicides and
insecticides to be found also in the same lignin fraction. However, it is difficult
to speculate how products metabolized via glutathione conjugation might be
incorporated into lignin. Perhaps products from glutathione conjugation are incorporated into various protein fractions. The study of insoluble pesticide residues
is an area of pesticide metabolism that is in need of additional research, but it
is one of the most difficult to study.
Several examples of high insoluble residue formation in plants from different
pesticides have been cited (Baldwin, 1977). However, only a few of the reported
residues have been tested for their bioavaiiability. Generally, the insoluble residues of pesticides in plants appear to be highly stable and are not readily
degraded for absorption in the gastrointestinal tract of animals.
About 21 % of the absorbed radioactivity from ring-labeled [14C]atrazine
was in the insoluble residue fraction of sorghum. This residue was highly stable
and resisted digestion by the rat and ruminant sheep, which excreted 88% and
100%, respectively, of the bound residue in the feces (Bakke et at., 1972b). In
alfalfa, 26% and 77% of the 14C found in the shoots and roots, respectively,
from root-absorbed [14C]propham was incorporated into insoluble residue after
7 days. When the insoluble residue was fed to rats, 86% of the 14C was excreted
in the feces and less than 3% remained in the carcass 96 hr after treatment
(Paulson et at., 1975). Bean plants incorporated 51 % and 7% of ring 14C-Iabeled
carbaryl and carbofuran, respectively, into insoluble residues 20 days after treatment (Marshall and Dorough, 1977). Water-soluble conjugates from carbaryl
and carbofuran accounted for 30% and 67% of the 14C, respectively (Marshall
and Dorough, 1977). When the insoluble residues of carbaryl and carbofuran
were fed to rats, 98% and 85%, respectively, of the doses were excreted in the
feces. In contrast, rats fed 14C water-soluble metabolites of carbaryl and carbofuran excreted 80% to 90%, respectively, of the radiocarbon in the urine
(Marshall and Dorough, 1977).
2.4. CONCLUSION
This review is not a complete compilation of pesticide metabolism in plants.
Important pesticide compounds such as the synthetic pyrethroids (Gaughan and
Casida, 1978; Ruzo and Casida, 1977) and other naturally occurring plant insecticides such as nicotine and rotenone have not been discussed. However,
these compounds, especially the pyrethroids, should not be overlooked because
of their potential use as important insecticides.
This short discussion on pesticide metabolism in plants indicates that most