Degradation of Pesticides in the Environment
73
agents such as acetylCoA, methylcobalamine, S-adenosylmethionine, and organic acids. Conceivably, organic amines and nucleic acids could also react with
some pesticidal chemicals, but no such incidence has been reported. Some pesticidal chemicals are known to react with amino acids, particularly with an -SH
moiety.
Much less is known about the contribution of inorganic reactants to the
alteration of insecticides or derivatives. Certainly various metallic and some
nonmetallic ions and gasses, such as H2S, O2 , and H2 , are known to react with
organic chemicals, though some of the reactions require rather extreme conditions
of, for example, light, heat, and pressure. Walker and Stojanovic (1973) reported
that most of the microbial metabolic products of malathion in an Arthrobacter
sp. were in the form of potassium salts. Hydrogen sulfide is known to react with
mercuric and other metallic ions which are also used as insecticides.
Finally, microbial production of cofactors used in both enzymatic and nonenzymatic reactions should not be overlooked. Co/actors are here defined as
the organic molecules which promote the overall reactions involving an organic
chemical without becoming a part of the reaction product derived from that
chemical. For example, Miskus et al. (1965) found that dechlorination of DDT
to form TDE (DDD) proceeded nonenzymatically in the presence of reduced
porphyrins added to lake water. The presence of such porphyrin residues in
natural lake water could certainly be traced to microbial activities, particularly
to those of photosynthetic microorganisms. Other possible candidates are glutathione, NAD+ , NADP+ , NADH, NADPH, and cytochromes.
It must be pointed out that many reductive reactions proceed nonezymatically under anaerobic conditions (Esaac and Matsumura, 1980). The details of
such reactions will be covered in the section dealing with reductive reactions in
this chapter.
3.3. COMMONL Y OCCURRING METABOLIC PROCESSES IN
MICROORGANISMS
3.3.1. Hydrolytic Processes
As mentioned earlier, one of the moieties most commonly present in pesticides is the ester linkage. This includes all of the organophosphate and carbamate insecticides as well as pyrethroids. Hydrolysis of ester, halide, ether,
and amide bonds usually gives rise to nontoxic products.
There is a considerable body of evidence that hydrolytic activities are much
more prevalent in the microbial world than in any other biological group. For
instance, the normal environmental and microbial metabolic product of carbaryl
73
agents such as acetylCoA, methylcobalamine, S-adenosylmethionine, and organic acids. Conceivably, organic amines and nucleic acids could also react with
some pesticidal chemicals, but no such incidence has been reported. Some pesticidal chemicals are known to react with amino acids, particularly with an -SH
moiety.
Much less is known about the contribution of inorganic reactants to the
alteration of insecticides or derivatives. Certainly various metallic and some
nonmetallic ions and gasses, such as H2S, O2 , and H2 , are known to react with
organic chemicals, though some of the reactions require rather extreme conditions
of, for example, light, heat, and pressure. Walker and Stojanovic (1973) reported
that most of the microbial metabolic products of malathion in an Arthrobacter
sp. were in the form of potassium salts. Hydrogen sulfide is known to react with
mercuric and other metallic ions which are also used as insecticides.
Finally, microbial production of cofactors used in both enzymatic and nonenzymatic reactions should not be overlooked. Co/actors are here defined as
the organic molecules which promote the overall reactions involving an organic
chemical without becoming a part of the reaction product derived from that
chemical. For example, Miskus et al. (1965) found that dechlorination of DDT
to form TDE (DDD) proceeded nonenzymatically in the presence of reduced
porphyrins added to lake water. The presence of such porphyrin residues in
natural lake water could certainly be traced to microbial activities, particularly
to those of photosynthetic microorganisms. Other possible candidates are glutathione, NAD+ , NADP+ , NADH, NADPH, and cytochromes.
It must be pointed out that many reductive reactions proceed nonezymatically under anaerobic conditions (Esaac and Matsumura, 1980). The details of
such reactions will be covered in the section dealing with reductive reactions in
this chapter.
3.3. COMMONL Y OCCURRING METABOLIC PROCESSES IN
MICROORGANISMS
3.3.1. Hydrolytic Processes
As mentioned earlier, one of the moieties most commonly present in pesticides is the ester linkage. This includes all of the organophosphate and carbamate insecticides as well as pyrethroids. Hydrolysis of ester, halide, ether,
and amide bonds usually gives rise to nontoxic products.
There is a considerable body of evidence that hydrolytic activities are much
more prevalent in the microbial world than in any other biological group. For
instance, the normal environmental and microbial metabolic product of carbaryl