DICHLORVOS JMPR 1977
This pesticide was evaluated by the 1965, 1966, 1967, 1970 and 1974
Joint Meetings (FAO/WHO, 1965, 1967, 1968, 1971, 1975). Since the
previous evaluation additional data have become available and are
summarized and discussed in the following monograph addendum.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
Absorption, distribution and excretion
Dichlorvos is rapidly absorbed, distributed and excreted in mammals.
Studies utilizing 32P-labelled dichlorvos have been previously
discussed (FAO/WHO 1967; FAO/WHO, 1971). Additional biochemical
studies utilizing methyl-14C, vinyl-14C, 3H and 36Cl-labelled
dichlorvos have become available since these previous evaluations.
Three male rats were given a single oral dose of 0.99 mg of
vinyl-1-14C dichlorvos in oil to determine the metabolism, excretion
and distribution of the vinyl moiety of dichlorvos. Similarly, three
female rats were treated with 0.72 mg of vinyl-1-14C dichlorvos. In
both sexes, over a 4 day period approximately 40% of the administered
radioactivity was expired as CO2, 10-20% was excreted in the urine
and 3-5% in the faeces. Of the retained radioactivity, approximately
5% was found in the liver, 2% in the gut, 8% in the skin and 14% in
the carcass. In this same report similar results were found when three
male rats were exposed to similar dose levels of vinyl-l-14C
dichlorvos vapour for one hour. In contrast, the intraperitoneal
injection of 0.6 mg of vinyl-1-14C dichlorvos two male rats resulted
in less of the administered radioactivity being expired as CO2 (19%)
and a higher level of excretion in the urine (35%) and retention in
the carcass (23%) (Huston et al., 1971).
Intramuscular injection of a female rat with a single 19 mg dose of
36 Cl-labelled dichlorvos in the right groin, after atropine and
obidoxime injection into the left groin, resulted in a 64% excretion
of radioactivity in the urine during the first 9 days (Hutson et al.,
To study the metabolism, distribution and excretion of the methyl
groups of dichlorvos rats were given a single oral dose of
approximately .35 mg/kg 14C-methyl-labelled dichlorvos. During the
next four days, approximately 60% of the administered radioactivity
was excreted in the urine, 5% in the faeces and 15% as expired CO2.
The carcass, skin and gut contained approximately 5, 2 and 1% of the
administered radioactivity respectively. No differences were observed
between the sexes. In male and female mice receiving a single oral
dose of approximately 2 mg/kg a similar excretion and residue pattern
was observed (Hutson and Hoadley, 1972).
Three male pigs were fed 40 mg/kg vinyl-1-14C dichlorvos encapsulated
in polyvinyl chloride pellets. After 14 days approximately 60% of the
administered radioactivity was recovered in the encapsulated pellets
in the faeces. The expired CO2 accounted for approximately 15% of the
administered dose, 5% was excreted via the urine, 5% via the faeces
and the carcass contained approximately 10% of the administered dose.
Of 20 tissues examined, the highest level of radioactivity was found
in liver tissue and the lowest in brain tissue (Potter et al., 1973a).
Pregnant sows were given multiple 4 mg/kg doses of vinyl-14C or
36Cl-labelled dichlorvos in polyvinyl chloride pellets. In this
experiment less of the administered 14C radioactivity was expired as
CO2 and more was released from the polyvinyl chloride pellets than in
the feeding study with male pigs described above.
Dichlorvos-36Cl recoveries from the sows comprised approximately 60%
recovered in pellets in the faeces, 6% in faeces, 25% in urine and 8%
in the carcass. In the newborn piglets, 14C tissue residues were
increased in the femur, as were 36Cl residues. This increase is
apparent up to sacrifice at 21 days of age. Heart 36Cl residues (no
data on 14C) were also elevated. By 21 days, 14C residues were
reduced for kidney, liver, lungs, muscle, spleen and stomach as
compared with residues in the sow. 36Cl residues are reduced at birth
and up to 21 days, as compared with the sow, in the kidney, liver,
lungs, muscle, salivary gland, spleen and stomach. The 36Cl residues
in the piglets are maximal for all tissues at 9 days of age (Potter et
Pigs were exposed for 24 days to an atmosphere of vinyl-1-14C
dichlorvos (0.1-0.15 µg/). Twice as much 14C was excreted in the
urine as in the faeces, (Loeffler et al., 1976).
Rats and mice were treated with unlabelled dichlorvos to study the
distribution in tissues by inhalation or intravenous administration.
No dichlorvos was detected in the blood, liver, kidney, renal fat or
lung tissues of rats exposed to 0.5 or 0.05 µg/1 for 14 days: the
kidney, trachea and fat tissue from male rats exposed to 90 µg/1
contained detectable quantities. In female rats treated similarly the
trachea, fat, blood and brain tissue contained detectable quantities
of dichlorvos. Intravenous administration of 0.25 mg dichlorvos/rat in
males and females with autopsies 10 and 30 mins. after dosing,
indicates rapid destruction of dichlorvos, based on kidney residues in
the male. In females, dichlorvos was not detectable in the kidney
(Blair et al., 1975).
The metabolic fate of dichlorvos in rats, mice and swine following
oral ingestion, inhalation exposure, or intraperitoneal injection were
similar. Biotransformations occurred primarily as a result of
hydrolytic, oxidative or demethylating enzymes which detoxified the
Analysis of the urine of rats orally dosed with vinyl-1-14C labelled
dichlorvos indicated that the major urinary metabolites are hippuric
acid (8%), 2,2-dichlor-vinyl-methyl-phosphate (11%), dichloroethanol
glucuronide (27%) and urea (3.1%). Three other unidentified
metabolites were noted. No unchanged dichlorvos was detected in the
urine. Inhalation exposure resulted in a similar pattern of
metabolites in the urine. Intraperitoneal administration resulted in
dichloroethanol glucuronide as the major urinary metabolite (76%) and
small amounts of hippuric acid and 2,2-dichlorovinyl methyl phosphate
(Hutson et al., 1971).
When 14C-methyl-labelled dichlorvos was administered orally to rats
and mice the major urinary metabolites were dimethyl phosphate (77% in
rats, 64% in mice) and 2,2-dichlorovinyl methyl phosphate (3.5% in
rats, 25% in mice). Minor metabolites were S-methyl-L-cysteine oxide,
S-methyl-L-cysteine and methylmercapturic acid (Hutson and Hoadley,
When pigs were treated orally with 14C-methyl-labelled dichlorvos in
a slow release polyvinyl chloride pellet, no dichlorvos,
2,2-dichlorovinyl phosphate, dichloroacetaldehyde or dichloroacetic
acid was detected in any tissue samples (Potter et al., 1973a).
When pigs were exposed to 1-vinyl-14C-labelled dichlorvos by
inhalation (0.1-0.15 µg/1), the major metabolites identified were
glycine, serine and adenine (Loeffler et al., 1976).
Pregnant sows were treated with 4 mg/kg of 14C-methyl-or
36Cl-labelled dichlorvos orally in a slow release polyvinyl chloride
pellet. No dichlorvos, dichloroacetaldehyde, 2,2-
dichlorovinylmethyl-phosphate, dichloracetic acid or dichloroethanol
was found in the tissues. (Potter et al., 1973b).
Other Biochemical Parameters
Several studies have been carried out to determine the potential for
direct methylation of nucleic acids by dichlorvos.
C14-methyl-dichlorvos was found to be a weak methylating agent in DNA
pre-isolated from E. coli and Salmon sperm. The principal products
were 7-methylguanine, 3-methyladenine, 3-methylguanine and trace
levels of other methylated bases. Methylation was also found when
14C-methyl dichlorvos was incubated with intact cells of E. coli
and the HeLa tumour line. However, the principal product was
7-methylguanine and no 3-methylguanine was found in these cells
(Lawley et al., 1974).
E. coli cells were incubated with methyl-14C-dichlorvos to study
the methylation of DNA and RNA. 14C-labelled 7-methylguanine was
found in DNA and RNA isolated from treated cells (Wennerberg and
Mice were exposed to 14C-methyl dichlorvos by inhalation or i.p.
injection. Analysis of the urine collected from two successive 24 hour
periods from these mice showed the excretion of 14C-labelled
7-methylguanine (Wennerberg and Lofroth, 1974).
Mice and rats were exposed to methyl-14C-labelled dichlorvos by
inhalation or i.p. injection. Analysis of the hydrolysate from the
mouse liver protein showed incorporation of 14C activity into amino
acids. Labelled 7-methylguanine, 3-methyl adenine and
1-methylnicotinamide was found in the urine of treated rats. 14C
labelled guanine and adenine were found in the DNA and RNA from liver
and lung tissues of treated mice. However, no detectable amount of
7-methylguanine was found in the DNA or RNA from lung or liver tissues
Rats were exposed to an atmosphere containing 0.064 µg/1 of
methyl-14C-labelled dichlorvos for 12 hours to study the methylation
of DNA and RNA in vivo. Traces of radioactivity were found in the
DNA, RNA and protein fractions from brain, heart, lung, liver, spleen,
kidney and testes. The 14C activity was not associated with any
UV-absorbing component. The 7-methylguanine fraction from the pooled
tissue samples was assayed for 14C activity by 20 repeated 7 hour
counts. No significant difference was detected between the test and a
blank 7-methylguanine fraction. The purine fraction of the urine from
treated rats contained no detectable 14C as 7-methylguanine (Wooder
et al., 1977).
Special studies on mutagenicity
Two review papers on the alkylating and mutagenic properties of
dichlorvos in microorganisms, drosophila, tissue culture, host
mediated assays and humans were submitted for consideration.
Conclusions drawn in both papers are essentially the same. Under
conditions of normal use as an insecticide, dichlorvos cannot exert
significant mutagenic effects in mammals, including humans. This view
is based mainly on the mutagenicity for microbes, the DNA alkylating
property of dichlorvos at high concentrations and the results from
analytical determinations in issues of treated mammals. Tissue
concentrations in mammals are lower than 10-3 to 10-5 times the
lowest concentrations mutagenic for microbes in vitro (Wild, 1975).
Various types of study performed with dichlorvos in in vivo host
mediated assay, dominant lethals assays, bone marrow cytogenetic
analysis and chromosome analysis of spermatocytes in mice treated by
inhalation have all been negative. On the basis of these results
dichlorvos does not represent a mutagenic risk for humans domestic
doses (Loprieno, undated).
Special studies on carcinogenicity
Two groups of 50 male and 50 female mice (age not specified) were fed
1000 and 2000 ppm 94% minimum purity dichlorvos in the diet for 2
weeks. Because of severe signs of toxicity, levels were reduced to 300
and 600 ppm for the remaining 78 weeks of administration. Mice were
autopsied 12-14 weeks after cessation of dosing. Matched controls
comprised 10 mice/sex maintained for 92 weeks. The minimum survival
(low dose females) was 74% at 90 weeks. Average weights of high dose
level mice were slightly depressed. Analysis of tumours at autopsy did
not reveal any compound- or dose-related effects (Anon, 1977).
Two groups of 50 male and 50 female rats were run 4 weeks apart. Group
1 consisted of rats 43 days of age, which were fed 1000 ppm in the
diet for 3 weeks, which because of signs of toxicity was reduced to
300 ppm for the subsequent 77 weeks of administration. Autopsy was
performed 30-31 weeks after cessation of dosing. Five rats/sex were
maintained for 110 weeks as controls. Group 2 consisted of 36 day old
rats which were fed 150 ppm in the diet for 80 weeks, with autopsy 30
weeks after cessation of dosing. Again controls comprised 5 rats/sex
maintained for 110 weeks. Body weights of high dose rats were
constantly reduced. Analysis of tumours at autopsy did not reveal any
compound- or dose-related effects (Anon, 1977).
Four groups of 50 male and 50 female rats were exposed to nominal air
concentrations of 0, 0.05, 0.5 or 5 mg dichlorvos/m3 air for 23
hours/day for 2 years. (Groups of 10 M and 10 F/dose level commenced
exposure each week for 5 weeks. Average actual dichlorvos
concentrations were 0.05, 0.48 and 4.70 mg/m3. Necropsies were
performed on all rats dying naturally, or killed at termination of the
study. Data on tumour incidence was analyzed using actuarial analysis,
comparing observed with expected tumour incidence, and then performing
a risk assessment. No gross pathological changes were noted which were
related to dichlorvos exposure. Microscopic examination of animals
dying in the study was frequently difficult, owing to autolysis
resulting from inability to examine animals more than once daily,
without upsetting the vapour exposure requirements. Tumour incidence
data were therefore analyzed with respect to all rats in the study and
also with respect to those dead animals where microscopic examination
was possible in detail. Results indicated a higher incidence of
tumours in the latter group. Thus, considering all rats, percentage
occurrence of tumours in males was 36, 60, 52 and 48% and in females
77, 60, 77 and 72% at 0, 0.05, 0.5 and 5.0 mg/m3. The breakdown of
these data indicate that 31, 48, 49 and 43% of male rats dying during
the experiment had tumours at 0, 0.05, 0.5 and, 5 mg/m3.
Corresponding figures for females are 68, 60, 57 and 67%, for males
surviving until termination 55, 76, 60 and 56%, and for females 86,
59, 92 and 74% (Blair at al., 1976).
Short term studies
In a study of the anthelmintic efficacy of dichlorvos for schislosome
and filarial infections, 32 rhesus monkeys, sex undisclosed, were
treated with pelleted polyvinyl chloride resin formulations of
dichlorvos at dosages ranging from 5 to 80 mg/kg daily or 8 and 20
mg/kg twice daily for 10 to 21 consecutive days. None of the monkeys
developed clinical signs which could be attributed to treatment.
Plasma and erythrocyte cholinesterase activities were significantly
inhibited in all animals (Hass at al., 1972).
Long term studies
Groups of rats (50/sex/group) were exposed to 97% technical dichlorvos
at nominal concentrations of 0, 0.05, 0.5 and 5.0 mg/m3 of air for 2
years. The details of experimental design are given in the second rat
study in "Special studies on carcinogenicity".
No signs of organophosphorus toxicity nor consistent differences in
food intake were seen in any group. In 3 female rats/group, brain
tissue examined for acethylcholine and choline revealed no
compound-related effects. Cholinesterase activity in plasma and brain
was significantly reduced in both sexes exposed to 0.5 and 5.0 mg/m3.
Erythrocyte activity was significantly reduced in both sexes at 5.0
mg/m3 but only in females at 0.5 mg/m3. Enzyme activity in males
exposed to 0.05 mg/m3 was not significantly different from that of
controls. Female erythrocyte activity was significantly different at
this level but plasma and brain cholinesterase values were not. Body
weights of both series of the 5.0 mg/m3 group were significantly
depressed for the major portion of the study as they were for the 0.5
mg/m3 males. There were no compound-related effects on organ body
weight ratios or haematological or blood chemistry values except for
some increase in PGPT and PGOT activities and a decrease in plasma
chloride concentration in males exposed to 5.0 mg/m3.
Minor lesions of the respiratory tract did not correlate with exposure
levels. Ultra-structural examination of bronchi and alveoli of small
numbers of 0 and 5 mg/m3 rats showed no differences between groups.
Necropsies revealed no gross microscopic tissue damage related to
compound effect in the respiratory tract or elsewhere and no increased
incidence of tumours was found (Blair et al., 1976).
OBSERVATIONS IN HUMANS
No new data were submitted.
On the basis of recent and earlier studies, the metabolic patterns of
dichlorvos in animals are clearly elucidated. It is rapidly broken
down in mammals to products which are excreted or incorporated into
natural biosynthetic pathways.
Several new studies have examined the potential for direct methylation
of nucleic acids by dichlorvos. It has been shown to cause the
methylation of bacterial and mammalian DNA and RNA in vitro. Also
the urine from dichlorvos-treated mice and rats was found to contain
methylated purines. The alkylating properties of dichlorvos led to the
suspicion that dichlorvos might be mutagenic and/or carcinogenic.
However, no methylated 7-methyl-guanine has been detected in the DNA
or RNA from liver or kidney tissue or other soft tissues of rats or
mice treated with 14C-methyl-labelled dichlorvos.
Although dichlorvos is a potential alkylating agent of DNA and RNA
in vitro, this potential is apparently not realized in vivo owing
to the rapid degradation of dichlorvos in mammals. The presence of
14C-labelled purines in the urine of animals treated with 14C-
labelled methylating agents is not conclusive proof of the methylation
of DNA and RNA at the polymeric level. The 14C may be incorporated
into the free purine bases. Thus, animals treated with 14C-labelled
guanine excreted 14C-labelled 7-mehtylguanine in the urine.
These studies and the negative results in mammalian mutagenicity and
carcinogenicity studies support the view that dichlorvos has an
extremely low potential for producing mutations or cancer in humans.
None of the recent studies have changed the basis for establishing an
Level causing no toxicological effect
Humans: 0.033 (mg/kg bw)/day
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR
0-0.004 mg/kg bw
Anonymous, (1977) Bioassay of dichlorvos for possible carcinogenicity.
Unpublished report from National Cancer Institute, submitted by Shell
Chemical Co., USA.
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