EPA-600/1-76-002
January 1976
AGENCY-*-
Environmental Health Effect
Effects Research Laboratory
Environmental Protection Agency
North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
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1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS
RESEARCH series. This series describes projects and studies relating
to the tolerances of man for unhealthful substances or conditions.
This work is generally assessed from a medical viewpoint, including
physiological or psychological studies. In addition to toxicology
and other medical specialities, study areas include biomedical
instrumentation and health research techniques utilizing animals -
but always with intended application to human health measures.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22161.
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EPA-600/1-76-002
January 1^76
ROLE OF MIXED FUNCTION OXIOASES IN INSECTICIDE ACTION
by
Robert L. Metcalf
Department of Entomology
University of Illinois
Urbana-Champaian, Illinois
R8P2022
Project Officer
Ronald L. Baron
Environmental Toxicology Division
Health Effects Research Laboratory
Research Triangle Park, North Carolina 27511
LI. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AMD DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
Research Triangle Park, north Carolina 27511
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DISCLAIMER
This report has been reviewed by the Health Effects Research
Laboratory, U.S. Environmental Protection Agency, and approved
for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the U.S. Environ-
mental Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation
for use.
H
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ABSTRACT
The role of the raicrosomal oxidase enzymes (MFO) in the
biochemistry and toxicology of insecticides has been studied.
Insects contain greatly varying titres of these enzymes. A survey
of 74 species from 40 families in 8 orders, using the topical LDrQ
of carbaryl alone and together with the inhibitor piperonyl butoxide
showed a 55,000-fold variability in LD^ largely due to MFO detoxi-
cation. In individual species of Diptera, MFO activity is highly
variable with age, sex, and stage of development.
The DDT-type molecule has been as a model for the study of
degradophores, i.e. molecular groupings that can serve as MFO
substrates. Their oxidation thus converts lipophilic compounds
into more water-partitioning moieties and thus promotes excretion
rather than lipid storage. Suitable degradophores for the DDT-
type molecule are alkyl and alkoxy groups on the aryl rings. Compounds
with judicious combinations of these provide relatively long per-
sistence on inert surfaces and ready biodegradability in vivo.
Such compounds are much less toxic to mice and to fish than DDT
but because of the generally lower MFO of insects, can be effective
insecticides. The role of degradophores incorporated into the
aliphatic moiety of DDT has also been explored, where the -CH(CH.,)_,
-CHCH_C1 and -CHCTLNO., groups are useful. Induction experiments
with the biodegradable DDT analogues in mice has demonstrated that
unlike DDT, these compounds do not elevate liver MFO.
This report was submitted in fulfillment of Project EP-826
by The Board of Trustees University of Illinois, under the partial
sponsorship of the Environmental Protection Agency. Work was
completed as of March 31, 1975.
111
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CONTENTS
Abstract \-\-\
Table of Contents jy
List of Tables V
Acknowledgements vi
Sections
I. Conclusions 1
II. Introduction 2
III. Distribution of MFO in Insecta 4
IV. Age dependent variation in insect mfo
activity 6
V. MFO oxidation of pesticides in green sunfish
and effects of piperonyl butoxide 8
VI. Role of degradophores in design of
degradable insecticides 13
VII. Degradation pathways for DDT analogues with
altered aliphatic moieties 19
VIII. Toxicity to mouse and green sunfish 24
IX. DDT analogues as inducers of MFO enzymes 27
X. Biochemistry of selective toxicity 28
XI. References 31
XII. List of publications 33
IV
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LIST OF TABLES
Table
I. Susceptibility of insects to carbaryl and
piperonyl butoxide. 5
2. Effects of age, sex, and development stage
on susceptibility of flies to carbaryl. 7
14
3. Concentration of " C-methoxychlor and degradation
products in green sunfish from treatment at
0.01 ppm. 9
14
4. Concentrations of C-aldrin and degradation
products in green sunfish from treatment at
0.01 ppm. 10
14
5. Concentrations in C-trifluralin and degrada-
tion products in green sunfish from treatment
at 0.01 ppm. 11
6. Degradation of DDT and analogues by mouse
liver microsomes. 16
7. Ecological magnification and biodegradability
of DDT analogues. 17
8. Effects of structural changes on toxicity of
DDT analogues. 20
9. Degradation of methoxychlor and analogues by
sheep liver microsomes. 22
10. Toxicity of DDT analogues to mouse and
green sunfish 25
11. Induction of mouse liver MFO by DDT
analogues. 30
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ACKNOWLEDGEMENTS
The principal investigator gratefully acknowledges the
participation and invaluable assstance of students and coworkers
in this investigation, Mr. Al Tegen faithfully reared large
numbers of insects used for study. Mrs. Penny Tegen and Mrs. Ruth
Millholin worked tirelessly at essential bioassays. Compounds
involved in the study were prepared by Dr. Inder P. Kapoor,
Dr. Asha Hirwe, and Dr. Joel Coats. Dr. W. F. Childers supplied
fish and helped conduct bioassays. Dr. Larry Hansen, Dr.
Lena Brattsten, and Dr. R. A. Metcalf carried out biochemical
studies. Portions of the thesis research of Dr. Inder P. Kapoor
"Comparative metabolism of DDT, methoxychlor and methiochlor in
mammals, insects and in a model ecosystem"; Dr. Lena Brattsten
"Role of mixed function oxidases of insects in their response to
xenobiotics"; Dr. Joel R. Coats "Toxicity and metabolism of
three methoxychlor analogues with altered aliphatic moieties,
and the development of some novel DDT analogues"; and Dr.
Keturah A. Reinbold "Effects of the synergist piperonyl butoxide
on toxicity and metabolism of pesticies in the green sunfish
(Lepomis cyanellus Rafinesque)", were involved in the studies
reported.
VI
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I. CONCLUSIONS
The mixed function oxidase enzymes play a critical role in
insecticide action both on target and non-lrargt't species. The
susceptibility of target insects appears to be inversely related
to the titre of those enzymes which is highly variable over a
wide range of insect species. The use of inhibitors of mixed
function oxidase action such as piperonyl butoxide restores
susceptibility of insects with high mixed function oxidase
levels to carbaryl. Non-target organisms such as fish accumulate
xenobiotic compounds such as pesticides in direct proportion to
the levels of mixed function oxidases and bioaccumulation of
pesticides in fish is greatly increased by exposire to mixed
function oxidase inhibitors such as piperonyl butoxide.
Molecular groupings or degradophores which can serve as
substrates for mixed function oxidase enzymes can improve the
biodegradability of pesticides by promoting in vivo conversion
to groups which are predominately water partitioning. Effective
examples include CH3~converted to -COOH, CH-jO- converted to
-OH, and CH^S converted to Ct^SO. Incorporation of these
moieties into the DDT-type compound greatly increased biodegrada-
bility and decreased ecological magnification. These biodegradable
DDT analogues were also largely inactive in the induction of
microsomal oxidase activity when given to mice.
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II. INTRODUCTION
The biological activity of nearly all o^
pesticides, and toxic-substances is determine^
vivo metabolism in living organisms by a group
introduce molecular oxygen combined with a uniqi
into readily modifiable sites of the organic molt
enzymes were termed by Mason et al (1965) as |"mixed
oxidases" and have been variously referred'
oxidases after their ubiquity of reactitoft, \m;
!
as riul'.
cros<
from their typical location in the endpplastalk: retjicu
1 ' 1
sedimentation by ultracentrifugation, oxygenafees from
biochemical mode of action, and drug metabolizing anzymqs
their typical action on xenobiotical compounds foreign to the
organism. In this report we shall refer to jlhem as MFO.
The MFO enzymes require reduced diphGspljopyriulisne -aac-le^
? I ^s"**~ **^f ^ ^
tide NADPH and cytochrome P.450 to form an ejlectioi transport
chain which can be represented in general as':
\
NADPH
NADP +
FPH
Fe++v OxfLd.
i :
protein Vcyt.:P 450 p 4^0*0
i
Fe+++
-------
The MFO enzymes are generally located In the endoplasmic
reticulum of the vertebrate liver, in the gut wall, fat body,
Afj rnalpighian tubules of invertebrates, and in uncharacterized
locations in plant tissues. Typically the MFO enzymes can be
sedimented as the "microsomal fraction" by ultracentrifugation
at 105,000 G. Brodie and Maickel (1961) believe that the MFO
enzymes arose phyllogenetically to enable terrestrial organisms
to degrade and eliminate lipid soluble foreign molecules
from the body. Thus fish and other aquatic organisms where
xenobiotic exposure was mininal in an evolutionary sense seem
to have relatively low levels of MFO compared to typical
terrestrial vertebrates (Terriere 1969), Adamson et al (1965)
view the MFO enzymes as normally present for metabolism of
endogenous products such as steroids and acting on xenobiotics
only where structural similarities permit. In any event the
MFO enzymes are under genetic control and the evolutionary
processes can be discerned by the selection of living organisms
for tolerance to various xenobiotics e.g. insecticide resistance.
In many instances survival occurs through enhanced MFO activity.
The types of biochemical reactions mediated in vivo by the
mixed function oxidases include: (a) epoxidation of C=C)
(b) hydroxylation of aromatic rings, (c) hydroxylation of alkyl
groups, (d) 0-dealkylation, (e) N-dealkylation, (f) S-dealkylation,
(g) thioether oxidation, (h) desulfuration of C-S, (i) desulfura-
tion of P=S, and (j) deamination. This great variety of reactions
is thought to occur by attack of the .OH, or .OOH radical
formed by activation of molecular oxygen in combination with
cyf.ochrome P.450. There appear to be few qualitative differences
in the nature of the various MFO induced reactions in the wide
variety of living organisms but a wide variety of quantitative
differences in the rates with which various xenobiotics are degraded.
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III. DISTRIBUTION OF MFO IN INSECTA
A rather complete survey of representative insect species
and their susceptibility to carbaryl has been made by Brattsten
and Metcalf (1970, 1973). Carbaryl is rapidly detoxified by
the MFO enzymes by attack on the aryl rings to produce the
degradation products 4-OH, 5-OH, and 6, 7-di-OH-dihydrocarbaryls.
These are readily conjugatedฑn vivo and are subject to further
N-dealkylation and subsequent hydrolysis at the carbaryl group to
give a series of hydroxylated naphthols and conjugates.
Piperonyl butoxide is very effective in retarding these reactions
and thus in synergizing the insecticidal activity of carbaryl.
Accurate quantitative LD values were obtained for carbaryl
alone and with the synergist piperonyl butoxide for 74 species
of insects from 40 families. As shown in Table 1, the variation
in susceptibility to carbaryl as determined by the typical LDcn
in micrograms per body weight is ca. 55,OOOX, ranging from the
chrysomelid beetle Trirhabda adela to the ant Pogonomyronex
barbatus. Much of this variation in susceptibility is determined
by MFO detoxication as the synergized LD values (with
piperonyl butoxide) range over only about 200X (Table 1).
It is difficult to discern any obvious correlations be-
tween the carbaryl tolerance and synergistic ratio and the
phyllogenetic position, food habits, and biological speciation
of the 74 species representing 40 families and 8 orders. In
general the Coleoptera showed high susceptibility and low
synergistic ratio, indicating very poor MFO capacity. The
Diptera showed an amazing range from an LD of 0.66 in
Stomoxys calcitrans to 4000 for Sarcophaga bullata. These
characteristics must relate to basic biochemical processes in
the insects. It is clear, however, that the performance of
carbaryl as an insecticide relates to the intrinsic MFO
activity of the insect species, and this is a basic consideration
in the use of degradophores, i.e. chemical groups which can
serve as substrates for MFO enzymes, in the design of new
biodegradable pesticides.
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Table 1. SUSCEPTIBILITY OF INSECTS TO CARBARYL AND PIPERONYL BUTUXLDE
Specie's Topical Lb,-, Pg/g Synergistic Ratio
carbaryl carbaryl + piperonyl
butoxide
Trirhabda adela
Tetraopes tetrophthalrnus
Stomoxys calcitrans
Spodoptera frugiperda
Apis raellifera
Epilachna varivestis
Chrysopa carnea
BlaLtella gennanica
Musca antuinnalis
Ostrinia nubilalis
Phorinia regina
Pcriplaneta atnericana
Musca domestica
Dermestes ater
Sarcophaga bullata
Pogonomyrmex barbatus
0.11
0.3
0.66
1.3
2.3
2.7
8.5
22
8.8
12.3
29
190
>900
3500
4000
>5800
0.14
0.11
0.46
0.3
0.8
1.6
1.6
5.3
1.2
7.2
4.3
10.5
12.5
110
10
26
0.8
2.7
1.4
4.3
2.9
1.7
5.3
4.2
7.3
1.7
6.7
18.1
>72
31.8
400
>223
data from Brattsten and Metcalf (1970, 1973).
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IV. AGE DEPENDENT VARIATIONS IN INSECT MFO ACTIVITY
The MFO enzymes have been shown to undergo dramatic
variation in levels in insects depending upon sex, stage of
development, and upon age (Brattsten and Metcalf 1973). These
factors have been investigated in detail using 6 species of
Diptera: Sarcophaga bullata, j^. crassipalpis, S^. argjrostoma,
Phormia regina, Musca autumnalis, and Stomoxys calcitrans. The
LD of carbaryl alone and when synergized with piperonyl
butoxide has been used as an indicator of MFO activity as
shown in Table 2.
In vitro assays for MFO activity in N-dealkylation, 0-
demethylation, and epoxidation were also performed with
adults and pupae of J3. bul lata, S^. crassipalpis, and P_. regina
(Brattsten and Metcalf 1973). Maximum activity was generally
associated with the microsomal pellet following 100,OOOX g
centrifugation. N-demethylase activity showed only slight
variation during pupa and adult flies of 1 to 8 days of age.
However, 0-demethylation was lowest in nearly emerged flies and
rapidly increased from 4 to 10-fold at 8 days of age. Activity
was generally lower in males than in females. Epoxidation was
low and virtually constant with age. 0-demethylation was shown
to be associated both with microsomal and soluble fractions
and several enzymes may be involved. From the data in Table
2 and supplementary evidence it can be concluded that the major
factors responsible for variations in the susceptibility to
carbaryl associated with sex and age of typical dipterous
insects are levels of MFO enzymes and related enzymes as
associated with the complex patterns of metabolism involved in
development and reproduction, rather than by other factors such
as penetration or excretion.
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Table 2. EFFECTS OF SEX, AGE, AND DEVELOPMENTAL STAGE ON
SUSCEPTIBILITY OF FLIES TO CARBARYL
Topical LDcQ yg/g
carbaryl carbaiyl + piperonyl Synergistic
Sarcophaga bullata
Sarcophaga crossipalpis
Sarcophaga argyrostoma
Phormia regina
Musca anttramalis
Stomoxys calcitrans
butoxide
Ratio
ฅ Id
8d
d* Id
8d
$ Id
8d
500
27
72
52
60
110
52
56
37
13
90
17
160
8.8
3.0
6.9
3.7
0.7
0.5
0.8
0.6
7.5
14.5
6.1
13
5.9
10.5
6.6
6.6
4.5
10
5.8
10
4.5
11
7
8.9
1.2
1.3
0.8
0.9
0.5
0.1
0.6
0.2
800
> 69
180
> 38
4.6
6.9
7.9
9.1
24.4
5.2
9.7
3.7
2.9
8.2
2.4
18
7.3
2.3
9.2
4
1.4
5
1.3
3.0
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V. MFO OXIDATION OF PESTICIDES IN
GREEN SUNFISH AND EFFECTS OF
PIPERONYL BUTOXIDE
As indicated above fish have generally low levels of MFO
enzymes and this poses severe disadvantages to them in regard
to low levels of micropollutant exposure and consequent
biomagnification. We have evaluated the role of MFO enzymes
in the green sunfish, Lepomis cyanellus by exposing the fish
14
for up to 16 days to 0.01 ppm concentrations of C radiolabeled
methoxychlor, aldrin, and trifluralin followed by quantitative
and qualitative radiochemical assay using thin-layer chromato-
graphy, radioautography, and liquid scintillation counting to
determine rates of storage and degradation of the xenobiotics.
To determine the total role of the MFO enzymes, a companion set
of fish were exposed to each of the three pesticides together
with 0.1 ppm piperonyl butoxide synergist (P.B.) which inhibits
the MFO enzymes (Casida 1971). The data obtained with the three
pesticides is shown in Tables 3-5 (Reinbold and Metcalf 1975).
Methoxychlor or 2,2-bis-(p_-methoxy phenyl)-l,l,l-trichloroethane
is degraded largely by 0-demethylation and this reaction is
greatly retarded by P.B. Thus with methoxychlor alone, the
dihydroxy degradation product was present after 16 days at
0.216 ppm but with the addition of 0.1 ppm P.B., the concentration
of this degradation product was only 0.055 ppm. Similarly, with
the methoxychlor treatment alone, the fish contained 0.04 ppm
parent compound after 16 days as compared to 0.605 ppm when
P.B. was present (Table 3).
Aldrin or l,2,3,4,10,10-hexachloro-l,4,4a,5,8,8a-hexahydro-l,
4-endo-exo-dimethanonaphthalene is readily oxidized to the
3,4-epoxide dieldrin by MFO. In the green sunfish, with aldrin
alone at 0.01 ppm the tissues contained 0.051 ppm aldrin after
16 days, but with the addition of 0.1 ppm P.B. the tissues con-
tained 1.076 ppm aldrin or a 21 fold increase (Tablet).
The effect of PB was also evident in the production of further
-------
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,~j ;M f, f. 3 13 s; ฃ -O-U3-I o sz r:
j PJ ^3 3 3 Ml S 3 -P- M 01 1 O .P- GO to ^D C H M
ฃ4 i f 3 xO *-O O --J 1 IjJ O t>^ | .ฃ> ! CO N3 |J3 -p-
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U1.P-CO JN O--JU1 ^4 ro 00 M VO H*
OOO O OOO O O O O U3-P-
MOO O OOO O O O O ONO
OO-JO O MOM M O Ul to U3M
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11
-------
metabolic products such as 9-OH aldrin and 9-C=0 dieldrin both
of which formed more slowly.
Trifluralin or a.ป ctป crtrif luro-2,6-dinitro-N,N-dipropyl-p_-
toluidine is degraded largely by N-dealkylation by MFO. With
trifluralin alone, at 0.01 ppm, the green sunfish contained
0.005 ppm parent compound after 16 days as compared to 0.225
ppm in the presence of P.B., for a 45-fold difference (Table 5).
In summary the MFO enzymes of the green sunfish provide
substantial protection against storage and accumulation of
these xenobiotics. The inhibition of these MFO enzymes with
piperonyl butoxide resulted in the accumulation of 15X as much
methoxychlor, 21X as much aldrin, and 45X as much trifluralin.
These data stress the importance of MFO enzymes in the survival
of fish in polluted aquatic environments and demonstrate the
danger of traces of MFO inhibitors, such as P.B., which may also
be present as aquatic pollutants in blocking normal biochemical
survival mechanisms. The value of degradophore groups which
can be oxidized by MFO reactions such as 0-dealkylation or N-
dealkylation in the design of biodegradable pesticides is
readily apparent.
12
-------
I-'OLE OF DEGRADOPHORES IN DESIGN OF DEGRADABLE INSECTICIDES
The experience of the past 25 years with DDT, dieldrin and ocher
persistent non-degradablc organot hi urine insecticides has shown the
gross incompatibility of those materials with desirable environ-
mental quality. Their u;,u has resulted in definition of and focus
UT the phenomenon of b i omagnif i cation whereby trace amounts of
these micropollutants below the limits of water solubility have
been absorbed and concentrated by living organisms and deposited
in their body lipids. The importance of this phenomenon is shoxm
by the experience in Lake Michigan where DDT at an average concentra-
tion in the open lake of 6 ppt is found in mature lake trout
at an average of 18.8 ppm, bioconcentration
3.13 x 10 . The corresponding values for dieldrin are 2 ppt in
water and 0,26 ppm in trout, bioconcentration 1.30 x 105 (EPA 1972).
Bioconcentration in Lake Michigan has nearly destroyed the commercial
fishing industry because the contaminated fish are unsafe for
consumption. Moreover because of the carcinogenic properties
of DDT and dieldrin, the ubiquitous presence of tissue residues
in humans, averaging about 11 ppm DDT plus DDE, and about 0.29
ppm dieldrin (Durham 1969) is most disquieting from a public
health viewpoint. Nevertheless, there is clearly a need for
insecticides which are of some degree of environmental persistence
on inert surfaces yet which are readily degradable in vivo.
We refer to these compounds as persistent biodegradable insecticides.
In this research grant we have concentrated study on the
DDT- type molecule:
This has been shown to be generally of low cost, relatively stable
on inert surfaces and modifiable in a large number of ways while
preserving substantial insecticidal properties. In DDT itself
13
-------
12 3
R and R are Cl and R is -CC1ป. The presence of the very stable
C-C1 bonds in these three areas of the DDT molecule is largely
responsible for the high jm vivo stability of DDT and its storage
in tissue lipids of animals. The DDT-type molecule in which other
less environmentally stable molecular groupings are substituted
for Cl atoms, is an ideal tool for studying the principles of
biodegradability. The problems of developing biodegradable
analogues of DDT are two-fold: (1) incorporating molecular
groups or degradophores which can serve as suitable substrates
for MFO enzymes, and (2) preserving an overall configuration to
the molecule so that it will have DDT-like biological activity.
The second phase falls outside the scope of this grant research
but has been discussed by Metcalf et al (1971) and by Coats and
Metcalf (1975).
Development of Degradophores
From the state of the art in 1969 when this research began
we considered potential degradophores for DDT-like action to be:
(a) for R and R2 CH30, C HjO, C^O, OCH^O, CH^C^, C^ ,
and CH3S, C2H,-S, CJUS; e.g. groups that would be readily
oxidized by MFO enzymes in the verteb,rate liver, thus converting
the compounds into water partitioning moieties which would be
excreted rather than stored in tissue lipids. We also considered
3
(b) for R degradophores with stereochemistry resembling that of
the CC13 groups i.e. CMe3> CMe2Cl, CMe2N02, CHMeCl,
Methoxychlor and Methylchlor . The simplest degradophores
for incorporation into the DDT molecule are ฃ,ฃ'-CH_0, and
groups. Methoxychlor or 2,2-bis-(jD-methoxyphenyl)-l,
-
1,1-trichloroethane was developed at the same time as DDT
(Muller 1944) and was known as a very safe DDT analogue which
did not accumulate in milk or store in animal fat as did DDT.
However, these were no satisfactory studies of its degradative
3
pathways in animals. Using H-radiolabeled methoxychlor,
Kapoor et al (1970) showed that methoxychlor was readily dealkylated
14
-------
by MFO enzymes in mouse liver, to give i.iono- and di-hydroxy
.'<-irivat 1 vr-s (Table 6), The result jf this biochemical conversion
was ;. o change methoxychlor, H00 solubility 0.&2 ppm, to 2,2-
b is- (p_-hydroxyphenyl)-l, 1,1-t ri chloroethane, HO solubility 76 ppm.
Similar study with methylrhlor or 2,2-bis- (p_-tolyl)-
1,1,j~trichloroethane showed the conversion of methylchlor,
H?0 solubility 2.21 ppm, to 2,2-bis-(p-carboxyphenyl)-l,!,1-
trichloroethane, HO solubility 50 ppm. (Table 6) Methiochlor
or 2,2-bis-(ฃ-methylthiophenyl)-l,l,l~trichloroethane, HO
solubility 0.57 ppm was converted by M'FO enzymes to 2,2-bis-(p-
methylthiophenyl)!,1,1-trichloroethane, H90 solubility 29 ppm
(Table 6).
Studies of these radiolabeled DDT analogues in the laboratory
model ecosystem (Metcalf et al ]971, Kapoor et al 1972) showed that
the analogues incorporating degradophores were truly biodegradable
and accumulated in the tissues of fish and other organisms to substan-
tially lower levels than did DDT (Table 7 ). The degradative
pathways found in the model ecosystem investigations were
predominately those predicted from the microsomal enzyme incu-
bation studies (Table 6).
Further investigations of this nature (Kapoor et al 1973)
showed that the presence of a single degradophore e.g. CH_, in
the DDT-type molecule to form 2-(j>-chlorophenyl)- 2-(p_-tolyl)
-1,1,l~trichloroethane was sufficient to produce a desirable degree
of biodegradability and to prevent the compound from bioaccumulating
to high levels in aquatic organisms (Table 1 ). Evaluation of
the insecticidal properties (Metcalf et al 1971) and biodegradability
of additional DDT analogues with asymmetrical arrangement of
degradophores (Kapoor et al 1973) indicated that the most favorable
combination of insecticidal properties and biodegradability was
obtained with asymmetrical DDT analogues containing two different
types of degradophores, e.g. 2-(p-methoxyphenyl)-2-(jp_-tolyl)-l,1,1-
trichloroethane , and 2-(p_-ethoxyphenyl)-2-(ฃ-tolyl)-l,1,1-trichloro-
ethane, as shown in Table 7.
15
-------
Table 6. DEGRADATION OF DDT AND ANALOGUES BY MOUSE LIVER
MICROSOMES -
R
Cl (DDT)
CH30 (methoxychlor)
C2H50 (ethoxychlor)
CH3 (methylchlor)
CH-S (methiochlor)
21
products recovered
DDT with traces of a-OH compound
HOC ,H. CHCC1ปC,H. OCH.,
64 364 3
HOC,H.CHCC1,.C,H/OH
64 364
HOC,H . CHCCl-CJS. OC0H,.
64 36425
HOOCC,H, CHCC1,,C ,H . CHป
64 3643
HOCH0C,H . CHCC1,C ,H, CH0OH
264 3642
HOOCC,H . CHCC10C,H. COOH
64 364
CH.SOC ,H. CHCC1QC,H, SCH,
3 64 364 3
CHQSOC,H . CHCC1QC,H , SOCH,
3 64 364 3
-1 Kapoor et al (1970, 1972)
21
by TLC and radioautography after 2 hours incubation with
microsomal suspension
16
-------
,'able 7. hCUl.OOKAL MAGN1FICATLON AND BIOOEGRADABIl [ I'Y OF DDT ANALOGUES lj
1 V" x ^ '' /S"~\\ 2
g\^:^K
v r-f 1C]
Cl
o 2/ 3/
R" ecological magni t :' cat ion biodegradability index -
01
oii3o
C2H50
CH3
r,H3S
CH-^0
CM3
CH3
Cl
CH30
C2H50
GH3
CH3S
CH3S
C2H50
Cl
fish
34,500
1 ,545
1,536
140
5.5
UO
400
1,400
snail
3/;5500
120,000
97,645
120,270
300
3,400
42,000
21,000
fish
0,015
0.94
2 . 69
7.14
47
2.75
1.20
3.43
snail
0,045
0.13
0.39
0.08
0.77
105
0.25
2.0
L- Kapoor et al (1973)
?/
rat Lo of concentration in organism/concentration in water
ratio of polar/nonpolar metabolites
17
-------
Development of Synergaphores
Molecular moieties which inhibit the MFO enzymes are termed
synergaphores. The best known is the -OCH-O- or methylenedioxy
group. Methylenedioxyphenyl derivatives are widely used as in-
secticide synergists, e.g. piperonyl butoxide, sesamex, propyl
isome; and it appears that these compounds combine or complex
with cytochrome P.450 to prevent its function as a carrier of
the .OH radical (Casida 1971). Another molecular moiety which
has this property is the propynyloxy group -OCHซC=CH (Sacher et
al 1968). Synergaphores attached to various active insecticidal
groupings have been shown to substantially increase the toxicity
of phenyl N-methylcarbamates by aut osynergism (Metcalf 1968)
and this technique has also been used with the DDT-type molecule
(Metcalf et al 1971). Attachment of the 3,4-methylenedioxy
group to the methoxychlor type molecule as in 2 Cp_-methoxyphenyl)
-2-(3,4-methylenedioxyphenyl)-l,l,l-trichloroethane reduced the
LDijQ values to the house fly from 45 to 22 yg per g. and reduced
the synergistic ratio from 12.8 to 4.9. The addition of the propynyl
group as in 2- (p-methoxyphenyl)-2-(^-propynyloxy phenyl) 1,1,1-
trichloroethane reduced the LD5Q value to 34 and the synergistic
ratio to 10.3, indicating a lesser degree of au tosynergism.
When the 2-(p_-methoxyphenyl)-2-(3,4-methylenedioxyphenyl)-
1,1,1-trichloroethane was compared with methoxychlor in toxicity
studies to the green sunfish at 0.1 ppm the former compound was
found to be concentrated and persistent in fish tissues with an
average residue of 18.0 ppm after 4 weeks compared to 1.75 ppm
for methoxychlor. Thus although the -OCl^O- group may increase
the insecticidal potency of specific compounds it may also have
adverse environmental effects in increasing persistence and bio-
accumulation.
18
-------
VII, DEGRADATION PATHWAYS FOR DDT ANALOGUES
WITH Al. LKRKD Ai I PPATIC MOTET IF?
The most important dufieLoney ot DOT as an Insecticide Is the
environmental dehydrochlorinatI on of the -CC1ซ group to form the
very stable ethyiene DDE ( CC1,,). iJDT analogues incorporating
icuL.rc>r_'c groups such as --l,Me, and CH(Me)N09 in place of -CC1_
have typical DDT-like biological activity (Table 8 ). Although
Holan (1971) has proposed the use of such compounds as biodegradable
substitutes for DDT, little or no information is available about
their degradative pathways ,md the effects of MFO enzymes on these
moieties.
M^nJr^yJ^ne_ogentan_e - We have investigated the metabolism and degrada-
^ _
tion of H-labeled dianisylneopentane (l,l-~bis-p_-methoxyphenyl)-2,
2-diniethylpropaiie in the house fly, the salt marsh caterpillar, by
mouse liver microsomes and in a laboratory model ecosystem (Coats
et al 1974). All of the results were in agreement in showing the
remarkable biological stability of the neopentyl moiety. In the
mouse, the major metabolites were the mono- and bis-phenols produced
by microsomal 0--dealkylation (see Table 9). The neopentyl group
was only slightly attacked. In the model ecosystem, substantial
amounts of dianisylneopentane persisted in snail and fish and this
compound behaved almost identically to methoxychlor. Thus the
neopentyl group is not a satisfactory substrate for the MFO enzymes.
Pro Ian or 1,1-bis-(p_-chlorophenyl)-2-nitropropane is another DDT
isostere with good insecticidal activity. Investigation of its
14
metabolic and environmental fate using C radiolabeled compound
has been undertaken (Hirwe et al 1975). Prolan is substantially more
degradable than DDT and although it accumulated to high levels in
the snail Physa, was readily degraded in the fish Ciambusia, of the
model ecoystem. Degradation of Prolan occurred by two general
mechanisms (a) dehydrogenation of the ot-H and release of the NO^
19
-------
Table 8. EFFECTS OF STRUCTURAL CHANGES ON TOXICITY
OF DDT ANALOGUES
123
R R R
Cl Cl CC13
CH3 CH3 CC13
CH30 CH30 CC13
CTT r\ (~* IT f\ /"*f "I
rtii^U v-irtllj-U V*V_ป.Lrt
Cl Cl
J
CH3 CH3 CMe3
CH30 CH30 CMe
C2H50 C2H50 CMe3
Cl Cl HC(Me)N02
CH3 HC(Me)N02
HC(Me)NO
HC(Me)NO
CH30 CH30 HC(Me)N02
2
topical
Musca
alone
14.0
100
45
7.0
85
1250
95
37.5
20.5
145
>500
5.0
LD50
(S)
p.b.
5.5
17.5
3.5
1.75
15.5
35
19
9.0
7.0
1.9
2.75
1.25
yg per g.
Phormia
alone p
11.5
61.2
10.0
6.9
70
17
100
11.0
13.0
12.5
32.5
.b.
8.25
21.5
4.6
7.4
55
5.75
92.5
11.0
6.0
7.75
1.35
20
-------
Table 8 (continued)
Cl
C-H 0
2 5
Cl
CH0
3
CH00
3
C0H,.0
2 5
CL
CH-
3
CH00
3
C0H 0
Cl
CH 0
C0H,0
2 5
Cl
CHQ
3
CH-0
3
C H 0
2 5
Cl
CH0
3
CH 0
3
C H 0
HCMeCl
HCMeCl
HCMeCl
HCMeCl
HCMe
HCMe
HCMe
HCMe
HCC1
HCC1
HCC1
HCC1
2
2
2
2
2
2
o
180
500
>500
9.5
>500
>500
>500
21.5
72.5
120
>500
9.0
37.0
24.5
3.5
2.0
500
300
36
3.5
35
11.5
10.0
2.15
->250
>250
>250
4.
>250
>250
122.
14.
15.
10.
250
3.
6
5
5
2
7
75
107.5
125
40
4.6
>250
>250
95
6.
9.
8.
7.
2.
7
0
5
5
75
I/
Coats (1974) and Coats and Metcalf (1975)
21
-------
Table 9. DEGRADATION OF METHOXYCHLOR AND ANALOGUES BY SHEEP
LIVER MICROSOMES -
OCR-
R
CC13 (methoxychlor)
o (dianisylneopentane)
HC(Me)NO,
HC(Me)Cl
products
parent
tnonophenol
diphenol
polar
parent
monophenol
diphenol
polar
parent
monophenol
diphenol
polar
parent
monophenol
diphenol
polar
recovi
86.6%
8.1%
3.4%
1.9%
93.5%
3.8%
0.8%
91.5%
5.7%
0.3%
trace
90.0%
5.8%
1.0%
1.2%
2/
- Coats (1974)
21
by TLC and radioautography after 30 minutes incubation
with microsomal suspension
22
-------
moiety to produce the ethylene I,l~bis-(p_-ch1 orophenyl)-~propene and
(b) by oxidation of the propyl GIL, group to produce 2,2-bis(p_-
ohlorophenyl)--pyruvic acid and eventually bis~(p-~rhlorophenyl,)-
acet.ic acid. These pathways were demonstrated, in fly, mouse, and
in the model ecosystem. In the .nouse Che principal excretory products
were bis- (p_--chlorophenyl) ace tone, bi s- (j>~ehlorophenyl)-pyruvic acid,
.n.'l M 3-(ฃ--c;iJorophenyl)--aeelic acid. (DDA) The ultimate environmental
degradation products from ?t:olan are thus DDA and 4,4'~dichlorober.zo-
phenone both of which are also formed from DDT. The ultimate environ-
mental distinction is that Prolan forms a biodegradable propene while
DDT forms the non-biodegradable dichloroethylene DDE. Thus the
nitropropane moiety CHMeNO^ is a suitable degradophore.
23
-------
VIII. TOXICITY TO MOUSE AND GREEN SUNFISH
An important feature of use of new DDT-type analogues is
their relative toxicity to mammals and to fish. The high toxicity
of DDT to a variety of fish has been a major drawback of its use
and this toxicity extends to methoxychlor and many other analogues.
Evidently, as discussed in the Introduction, 0-dealkylation and
certain other MFO catalyzed processes are not readily carried
out in the fish.
We have explored, in a preliminary way, the toxicity of a number
of the DDT-type analogues incorporating degradophores to the
Swiss mouse, as measured by the oral LD,_n of solutions in olive
oil. In addition we have studied the toxicity of the analogues
at 0.1 ppm in water from acetone, using the duration of toxicity
to the green sunfish Lepomis cyanellus. These latter studies
were carried out in 1700 1. tanks at both summer (average
70-90ฐF) and winter temperatures (average 40-50ฐF) and are
so reported in Table 10. It is apparent from this data that the
12 3
nature of the aryl and alkyl substituents R , R , and R has a
pronounced effect on the toxicity of the compound to both mouse
and fish. Surprisingly, the most toxic DDT analogue evaluated to
the mouse was the C-H 0-C.,H70 analogue which was more than twice
as toxic as DDT. The least toxic was the CH-j-CH., analogue
followed by CH 0-CH3, and methoxychlor CH3-CH30. All of the
combinations of CyRrQ-CJ*^ฎ were safer than DDT and enhanced
safety over CC1- (ethoxychlor) was gained by other alkyl groupings,
showing that these do function as degradophores.
The toxicity picture to the green sunfish is more complex and
reflects the generally low level of MFO enzymes. Thus groups such
as aryl CปH_0 which function as degradophores in the mouse are not
as effective in fish and all combinations of C H 0-C2H 0 except
with CMe^Cl showed prolonged toxicity to the green sunfish
especially in winter. The marked enhancement of safety to fish
provided by a single aryl CH~ is demonstrated in Table 10 , by
comparing the C H 0-C?H,.0 compounds with their CTL-C-H 0 analogues
for CC13, HCMeCl, and HCMe^
24
-------
Table 10. TOXTC1TY OF DDT ANALOGUES TO MOUSE AND GRELN SUNFTSH
R1
Cl
CH3
CH3C
C2H5
C2H5
CH3
CH3
R2
Cl
CH3
) CH30
.0 C2H50
.0 C3H70
CH3ฐ
C2H50
R3
CC13
cci3
CC13
cci3
cci3
cci3
cci3
uiax IjJJ50 ma
Swiss tnoui
200
3350
1850
300-325
75-100
>1000
1000
duration of toxicity
kg at 0.1 ppm - days
18 (S)
2 (S) 41 (W)
22 (S)
41 (W)
0(S) 15 (W)
0(S) 15 (W)
C9H,.0 C9H 0 CMe >1000 76 (W)
*-. J ฃ~ _? J
C2H5ฐ C2H5ฐ HCMe2 >2100 52 (W)
CH, C9H 0 HCMe9 >1000 0(S)
J ฃ~ J ฃ..
C2H50 C2H 0 HCMeCl 1000 4(S) 60(W)
CH3 C2H5ฐ HCMeC1 >1000 0(W)
C2H50 C2H50 HCMeN02 >1000 64 (W)
C2H5ฐ C2H5ฐ ccl2Me 80ฐ 80 ^W^
C7H,0 C7H,-0 CMe?Cl >1000 0(W)
/.. J ฃ J ฃ-
Metcalf et al (1974), Coats (1974)
fish used per tank, when killed re
(Metcalf et al 1974), (s) summer (w) winter
21
5 fish used per tank, when killed restocked at weekly intervals.
25
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Altered Aliphatic Moieties. An important objective was the
evaluation of the effects of alterations in the CC1,, group of the
DDT-type compound. As shown in Table 8, a considerable variety
of other groupings can be substituted with preservation of the
insecticidal activity. However, the biological effects of the
DDT-type molecule are a function of the size and shape of the
entire molecule and optimum activity for a given aliphatic
moiety will require one set of ฃ,jDf-substituents while another
set will be required for a different aliphatic moiety (Table 8 ).
The effects of molecular groupings readily attacked by MFO
enzymes are shown by the comparisons between LD,-n to Musca alone
and LD after pretreatment with piperonyl butoxide (p.b.)
which inhibits most of the MFO activity. Aliphatic moieties for
which MFO detoxication was maximal were CHMeCl and CHMe2. This
is well demonstrated also by the fish toxicity data in Tab ]e 10.
However, when exposed to MFO enzymes directly in microsomes, the
part of the DDT-type molecule subjected to initial attack is the
degradaphores on the aromatic rings rather than the aliphatic
moiety. This is clearly shown by the experiments with sheep
liver microsomes as shown in Table 9. Regardless of the nature of
the aliphatic moiety, 0-dernethylation was the dominant reaction.
26
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IX. DDT ANALOGUES AS INDUCERS OF MFO ENZYMES
A major objection to persistent residues of DDT concentrating
in living organisms is ihe role of DDT and similar lipophilic substances
as inducers of MFO enzyme activity. This effect has been deemed
responsible for tbe syndrome of egg-shell thinning and lowered
reproductive efficiency in birds and may give rise to abnormal
jielabolism of both endogenous steroids and hormones as well as exogenuous
drugs (Corney and Baines (1973). DDT and some of its analogues are potent
inducers of microsomal enzymes in mouse liver (Hart and Fouts 1965,
Abernathy et al 1971). We have compared the inductive effects of a
variety of DDT analogues some incorporating degradophores upon the
induction of mouse liver microsomal enzymes producing 0-dealkylation,
N-dealkylation, sulfoxidation, epoxidation and ring hydroxylation
as shown in Tableil. (Nigg et al 1975). The analogues were injected
intraperitoneally into Swiss mice at 100 ug per kg. per day for
5 days before assay of liver homogenates.
The data shows the importance of degradophores in reducing
accumulation of the compound in the endoplasmic reticulum and
consequent induction. Both the COOH and OH derivatives formed by
degradation of alkyl or alkoxy groups were non-inducers. However
CH.,S which is a degradophore was highly inductive because of metabolism
to the inducer CH..SO .
27
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X. BIOCHEMISTRY OF SELECTIVE TOXICITY
The concept of degradophores and the possibilities of building
them into toxic moieties to enhance biodegradability has enhanced
interest in the comparative biochemistry of selective toxicity.
Clearly selective and biodegradable insecticides incorporating this
principle will be effective only if detoxication in vertebrates
is substantially more rapid than in invertebrates. We have
investigated this area by studying 0-dealkylation, a typical
microsomal process on a comparative basis. In a comparison of
rates of 0-demethylation and 0-deethylation of j3-nitrophenyl
ethers and DDT analogues it was found that Culex mosquito larva,
Physa and Lymnaea snails, and the fish Gambusia affinis and
Pimephales promelas were all more active in deethylation of _p_-
nitrophenetol than in demethylation of _p_-nitroanisole. Longer chain
propyl and butyl ethers were less readily 0-dealkylated. Within
the organisms, Gambusia was most active in 0-dealkylatioa deter-
mined on a body weight basis, followed by Physa, Lymnaea , Culex,
and Pimephales (Hansen et al 1972). The toxicity of methoxychlor
and ethoxychlor was correlated with metabolism data except for
snails which were naturally tolerant to these organochlorine
insecticides.
The comparative in vivo and microsomal 0-dealkylation of
both _p_-nitrophenyl ethers and methoxychlor and ethoxychlor was
studied by Hansen et al (1974) using the house fly Musea domestica,
the flesh fly Sarcophaga bullata, and the white mouse. The rates
of p- nitrophenyl alkyl ether 0-dealkylation were found to vary
with chain length: house fly-methyl>ethyl>n-propyl>ii-butyl,
flesh fly methyl=ethyl>n-propyl>n-butyl; mouse ethyl>methyl>n~propyl
>n-butyl. When a comparison was made with DDT analogues, methoxy=
chlor was 0-dealkylated by both house fly and mouse at substantially
28
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greater rates than ethoxychlor. Detailed kinetic studies showed
the presence of both high and low affinity sites in microsomes
of mouse liver and house fly abdomen. The mouse liver microsomes
had a greater capacity for 0-dealkylation than the fly abdomen
microsomes and also converted more of the primary product to
dihydroxy and polar metabolites (Hansen et al 1974).
These studies illustrate the importance of comparative
biochemistry in understanding the relative effectiveness of various
xenobiotics to specific organisms. There are astonishing qualitative
and quantitative differences in the manner in which organic compounds
are degraded by various species and the subject is of considerable
complexity.
29
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XI- REFERENCES
Abernathy, C.O., E. Hodgson, and F. E. Guthrie. Biochem. Pharmacol.
20, 2385 (1971).
Adamson, R. H., R. L. Diekson, F. L. Francis, and D. P. Rawl.
Proc. Nat. Acad. Set. _54_, 1386 (1965).
Brattsten, L. A. and R. L. Metcalf. Jour. Econ. Entomol. 63,
101 (1970).
Brattsten, L. A. and R. L. Metcalf. Jour- Econ. Entomo1. ^6,
.1347 (1973).
Brattsten, L. A. and R. L. Metcalf. Pest. Biochem. Physiol.
J3, 189 (1973).
Brodie, B. B. and R. P. Maickel. Proc.. First Itvt. Pharmacol.
Meeting 6^, 299 (1961).
Casida, J. E. J. Agr. Food Chem. 18, 753 (1971).
Coats, J. R., R. L. Metcalf, and I. P. Kapoor. Pest. Biochem.
Physiol. 4., 201 (1944).
Coats, J. and R. L. Metcalf. Ms. in preparation (1975).
Conney, A. H. and J. J. Burns. Science 178, 576 (1972).
Durham, W. F. Ann. N.Y. Acad. Sci. 160, 183 (1969).
EPA. An evaluation of DDT and dieldrin in Lake Michigan.
Ecoj-ogical Research Series EPA-R3-72-003, Washington, D.C.
(1972).
Hansen, L. G., I. P. Kapoor, and R. L. Metcalf. Comp. Gen. Pharmacol.
3>, 339 (1972).
Hansen, L. G. , R. L. Metcalf, and I. P. Kapoor. Comp. Gen. Pharmacol.
5., 157 (1974).
Hart, L. G. and J. R. Fouts. Arch_. Pa^th. Pharmacol. 249, 486 (1965).
Holan, G. ffull. World Health Or_ฃ. 44, 355 (1971).
Hirwe, A. S., R. L. Metcalf, Po-Yung Lu, and Li-Chun Chio. Pest.
Biochem. Physiol. 5, 65 (1975).
Kapoor, I. P., R. L. Metcalf, A. S. Hirwe, J. R. Coats, and M. S.
Khalsa. .J.. Aฃr_. Food Chem. 21, 310 (1973)
31
-------
Mason, H. S., J. C. Noilh, and M. Vanneste. Fed, Proc. 24_, 1172
(1965).
Metcalf, R. L., G. K. Sangha, and I. P. Kapoor. Environ. Sci.
Technol_. _5, 709 (1971).
Metcalf, R. L., I. P. Kapoor, and A. S. Hirwe. Bull^. World Health
Org. 44, 363 (1971).
Mu'ller, P. Helv. Chim. Acta 29, 1560 (1946).
Nigg, H. N., R. L. Metcalf, and I. P. Kapoor. In Press. Arch.
^BZil- Contain. T_qxlc_ol.. (1975).
Reinbold, K. A. and R. L. Metcalf. Ms. in preparation. (1975).
Terriere, L. C. The oxidation of pesticides:the comparative
approach, p. 175 in E. Hodgson ed. Enzymatic oxidation of
toxicants N. Carolina State Univ., Raleigh, N.C. (1968).
32
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XIT. LIST OF PUBLICATIONS
Kapoor, I. P,, R. L, Metcalf, R, F. Nystrom, and G. K.
Sangha. Comparative Metabolism of Methoxychlor ,
Methiochlor and DDT in Mouse, Insects, and a Model
Ecosystem. J_. Agr. Food Chem. 1.8:1145-52, 1970.
Brattsten, L. A. and R. L. Metcalf. The Synergistic
Ratio of Carbaryl with Piperonyl Butoxide as an
Indicator of the Distribution of Multifunction Oxidases
in the Insecta. Jour. Econ. Entomol. jx}:101-104, 1970.
Sacher, R. M. , R. L. Metcalf, E. R. Metcalf, and T. R.
Fukuto. Structure Activity Relationships of Methyl-
enedioxynaphthyl Derivatives as Synergists of Carbaryl
in House Flies. -Jour. Econ. Entomol. 64:1011-1014, 1971.
Metcalf, R. L. Structure-activity Relationships for
Insecticidal Carbamates. Bull . World Health Org.
44:43-78, 1971
Hansen, L., I. P. Kapoor, and R. L. Metcalf. Bio-
chemistry of selective toxicity and biodegradability:
comparative 0-dealkylation by aquatic organisms.
Physiol . 3, 339-344 (1972).
6. Metcalf, R. L. "Development of selective and biode-
gradable insecticides pp 137-156 in Pest Control
Strategies for the Future. Nat. Acad. Sci. , Washington,
D.C. (1972).
7. Metcalf, R. L., I. P. Kapoor, and A. S. Hirwe. Develop-
ment of biodegradable analogues of DDT. Chemical
Technol. Feb. 1972, pp 105-109.
8. Nigg, H. N., I. P. Kapoor, R. L. Metcalf and J. R. Coats.
A glc assay for microsomal thioether oxidation. J..
Agr. Food Chem. 20, 446-448 (1972).
9. Kapoor, I. P., R. L. Metcalf, A. S. Hirwe, Po-Yung Lu,
J. R. Coats, and R. F. Nystrom. Comparative Metabolism
of DDT, Methylchlor, and Ethoxychlor in Mouse, Insects,
and a Model Ecosystem. ฃ. Agr. Food Chem. ^0:1-6, 1972.
33
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10. Metcalf, R. L. A Model Ecosystem for the Evaluation
of Pesticide Biodegradability and Ecological Magnifi-
cation. Outlook on Agriculture 71:55-59, 1972.
11. Yu, Ching-Chieh, C. W. Kearns, and Robert L. Metcalf.
Acetylcholinesterase Inhibition by Substituted Phenyl
N-alkyl Carbamates. J._ Agr. Food Chem. .20:537-40, 1972.
12. Brattsten, L.B. and R. L. Metcalf. Age-dependent
Variations in the Response of Several Species of Diptera
to Insecticidal Chemicals. Pesticide Biochem. Physiol.
1:189-98, 1973.
13. Metcalf, R. A. and R. L. Metcalf. Selective Toxicity
of Analogues of Methyl Parathion. Pesticide Biochemistry
Physiology 1:149-59, 1973.
14. Kapoor, I. P.,R. L. Metcalf, A. S. Hirwe, J. R. Coats,
and M. S. Khalsa. Structure Activity Correlations of
Biodegradability of DDT Analogues. J_. Agr. Food Chem.
21:310-315, 1973.
15. Coats, J, R., R. L. Metcalf, and I. P. Kapoor. Metabolism
of the Methoxychlor Isostere Dianisyl Neopentane, in
Mouse, Insects, and a Model Ecosystem. Pesticide Bio-
chemistry Physiology 4_:201-211, 1974.
16. Metcalf, R. L. A Laboratory Model Ecosystem to Evaluate
Compounds Producing Ecological Magnification. Essays
IS. Toxicology 5.: 17-38, 1974.
17. Yu, Ching-Chieu, K. S. Park, and R. L. Metcalf.
Correlation of Toxicity and Acetylcholinesterase
(AChE) Inhibition in 2-Alkyl Substituted 1,3-Benzo-
dioxolyl-4 N-Methylcarbamates and Related Compounds.
Pesticide Biochemistry Physiology 4^:178-184, 1974.
18. Hansen, L. G., R. L. Metcalf, and I. P. Kapoor.
Biochemistry of Selective Toxicity and Biodegradability
II Comparative in Vivo and Microsomal 0-dealkylation by
Mice and Flies. Comparative General Pharmacology 5_:
157-163, 1974.
34
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19. Hansen, L, G. , I, P, Kapoor, and R. L. Metcalf. Biochemistry
of selective toxicity and biodegradabiiity: comparative
O-dealkylation by aquatic organises. Comฃarat_iye General
Pharmacology 1- 339-344 (1972).
20, Hirwe, A. S.,R. L, Metcalf, Po--YUrig Lu, and Li-Chun Chio.
Comparative metabolism of l,l--bis-(p_-chlorophenyl)-2-
nitropropane (Prolan) in mouse, insects, and in a model
ecosystem, PjLsticide_ J3ipche_sn:Lst_ry^ ?llY,s.i^lp_gjy_ 5_, 65-72 (1975) .
21. Metcalf, R. 1,., J. R. Sanbcrn, Po-Yung Lu, and D. Nye.
Laboratory Model Ecosystem Studies of the Degradation and
Fate of Radiolabeled Tri~, Tetra-, and Pentachlorobiphenyl
compared with DDE. Archives Envirorrmen_Ea_l Contaminat ion
Toxicology 3:151-165,1975.
22. Nigg, H. S., R, L. Metcalf, and I. P. Kapcor. DDT and
Selected Analogues as Microi-omal Oxidase Tnducers in the
Mouse. ArcJli.Y^s. E n y j r grime n t a 1 Con t am in at i on Toxicology.
In Press.
23. Reinbold, K. A. and R. L. Metcalf. Effects of the
Synergist Piperonyl Butoxide on Metabolism of Pesticides
in Green Sunfish. Pesticide Biochem. Physipl. In Press.
35
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO.
EP7H5QQ/ 1-76 -002
'
2.
3. RECIPIENT'S ACCESSION NO.
Role of Mixed Function Oxidases in Insecticide
Action
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Robert I. Met calf
8. PERFORMING ORGANIZATION REPORT NO.
5 REPORT DATE _ ^
January 1976
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Entomology
University of Illinois
Urban a-Champaign, IL
10. PROGRAM ELEMENT NO.
1EA078 (ROAP 21AYL)
11. GON-T-ซACT/GRANT NO.
R802022
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The role of the microsomal oxidase enzymes (MFO) in the biochemistry and toxicology
of insecticides has been studied. Insects contain greatly varying titres of these
enzymes. A survey of 74 species from 40 families in 8 orders, using the topical
of carbaryl alone and together with the inhibitor piperonyl butoxide showed a 55,
fold variability in LD5Q largely due to MFO detoxication. In individual species of
Diptera, MFO activity Ts highly variable with age, sex, and stage of development
The DDT-type molecule has been as a model for the study of degradophores, i.e. molecul
groupings that can serve as MFO substrates. Their oxidation thus converts lipophilic
compounds into more water-partitioning moieties and thus promotes excretion rather
than lipid storage. Suitable degradophores for the DDT-type molecule are alkyl and
alkoxy groups on the aryl rings. Compounds with judicious combinations of these pro-
vide relatively long persistence on inert surfaces and ready biodegradability in vivo.
Such compounds are much less toxic to mice and to fish than DDT but because of~the
generally lower MFO of insects, can be effective insecticides. The role of degrad-
ophores incorporated into the aliphatic moiety of DDT has also been explored, where
the -CH(CH3)2ป -CHCHoCl and -CHCHaNO? groups are useful. Induction experiments with
the biodegradable DDT analogues in mice has demonstrated that unlike DDT, these com-
pounds do not elevate liver MFO.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
*Insecticides
*Enzymes
Biochemistry
Toxicology
Microsomal-Oxidase-
Enzymes
a6A
Q6T
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
42
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
36
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