ETHION JMPR 1972
Explanation
Ethion was evaluated by the Joint Meeting in 1968 (FAO/WHO, 1969), and
residues in meat (FAO/WHO, 1970) and tea (FAO/WHO, 1971) were
re-evaluated by subsequent meetings. Since the previous evaluation
additional information has become available on toxicology of this
compound, and new experimental work on residues in food has been
reported.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Absorption, distribution and excretion
When 14C-methylene labelled ethion was administered orally to rats,
88% of the 14C was excreted in the urine in four days; the remainder
was found in the faeces and in respiratory CO2 to the extent of 3.7
and 3.4%, respectively. No metabolite identification was attempted in
this experiment, and 78% of the dose was excreted in the urine within
the first 24 hours (Brandav et al., 1971).
Effect on enzymes of the oxygen analogues of ethion
The in vitro inhibitory effects of the oxygen analogues of ethion
that might possibly occur in foods have been measured in human plasma
and erythrocyte cholinesterase. The I50 values showed that both
ethion monooxon and ethion dioxon were more active than ethion, with
the dioxon being the most active, as shown in Table 1 (Greco et al.,
1970).
TABLE 1
Anticholinesterase activity of ethion and its oxygen analogues
Compound Plasma I50 (M) RBC I50 (M)
Ethion 6.95 × 10-8 3.29 × 10-6
Ethion monooxon 1.15 × 10-9 6.1 × 10-8
Ethion dioxon 5.76 × 10-10 3.0 × 10-9
TOXICOLOGICAL STUDIES
Special studies on mutagenicity
A dominant lethal test was carried out in albino mice. Groups of 12
male mice were each treated with a single intraperitoneal injection of
50 and 100 mg/kg. A third group of 12 male mice were each injected
with 300 mg/kg of ethyl methanesulfonate to act as positive control.
The males were mated with untreated females on a weekly schedule for
six consecutive weeks. The mutation rates for the ethion treated
animals did not differ from the controls. The mutation rates with
positive control animals were significantly increased. Measurements
were made for implantations, resorptions and number of embryos. In
addition, ethion did not reduce the ability of males to mate
successfully (Arnold et al., 1972).
Special studies on neurotoxicity
No demyelination was noted in six adult hens treated orally with acute
median lethal dose (4 290 mg/kg) of ethion technical. The dose level
was at the LD50. TOCP administered at 500 mg/kg was used as a
positive control. Measurements included histopathological examination
of the brain, spinal cord and sciatic nerve (Fletcher et al., 1972).
Special studies on teratogenicity
One group of 18 female rats was dosed with ethion at 1.5 mg/kg/day,
and a second group of 16 female rats received 3.0 mg/kg/day on days 6
to 15 of gestation. Measurements were made for maternal body-weight,
maternal mortality, implantation sites, resorption sites, viable
foetuses, foetal external abnormalities, foetal skeletal development
and foetal internal development. No teratogenic effects were noted in
the offspring of these female rats (Haley et al., 1972).
Acute toxicity
LD50 of ethion in female rats was found to be 24.4 mg/kg (Kretchmar
et al., 1971).
The acute oral LD50 of the oxygen analogues were measured in albino
rats and found to be 35.1 mg/kg for the monooxon and 12.8 mg/kg for
the dioxon (Mastri et al., 1970).
Long-term studies
Rat
Four groups, each containing 50 male and 50 female rats, were fed
ethion at dietary levels of 0, 2, 6 and 20 ppm for two years. Slight
depression of RBC, plasma and brain cholinesterase activities were
noted in female rats fed 20 ppm throughout the investigation. Male
rats fed 20 ppm and all rats fed 2 and 6 ppm exhibited no significant
inhibition of cholinesterase activity during the study. Results
obtained during the investigation disclosed no changes which could be
attributed to the ingestion of ethion in body-weight gains, food
consumption, blood chemistry, urine analyses, organ weights and ratios
and gross and microscopic pathologic studies. Erythrocyte and plasma
cholinesterase activities were determined at ´, 1, 1´, 2, 3, 6, 12, 18
and 24 months and brain cholinesterase activity after 1, 2, 3 and 24
months of feeding (Smith et al., 1972).
Dog
Four groups of 4 male and 4 female dogs, were fed ethion at dietary
levels of 0, 2, 6 and 20 ppm for two years. Animals fed 6 and 20 ppm
displayed depression of plasma cholinesterase activity, which was
noted through the first 26 weeks of test in the animals receiving 6
ppm and for the entire 104 weeks in the animals receiving 20 ppm. No
significant depression was noted in RBC or brain cholinesterase
activity at the 6 and 20 ppm levels. Animals fed 2 ppm displayed no
significant depression of plasma, RBC or brain cholinesterase activity
at any time. Body-weights, food consumption, behavioural reactions,
mortality, haematologic studies, blood chemistry studies and
histopathologic studies all gave normal results. Plasma and RBC
cholinesterase determinations were made on all animals at 0, 2, 4, 6,
9, 13, 26, 78 and 104 weeks of testing. Brain cholinesterase
determinations were made on each animal immediately after sacrifice at
the end of the study (Hartke et al., 1972).
OBSERVATIONS IN MAN
Ethion was administered to a group of six male volunteers at levels of
0, 0.05, 0.075, 0.1 and 0.15 mg/kg/day for a period of three weeks at
each dose level, with the exception of the highest one which was given
for three days only. The control group consisted of four individuals.
The material was administered in divided doses in gelatin capsules as
solution in corn oil three times a day. Plasma and RBC cholinesterase
activities were determined five times during two weeks of the pretest
period and three weeks of the test period. No statistically
significant depression in RBC cholinesterase was noted. A
statistically significant depression in plasma cholinesterase of 21%
and 29% was noted at dose level of 0.1 and 0.15 mg/kg/day,
respectively. Plasma cholinesterase activity at the highest dose level
returned to pretest values in seven days. The 0.075 mg/kg/day level
was considered borderline, with the mean inhibition being about 15%.
The 0.05 mg/kg/day dose was a definite no-effect level. No adverse
effects were noted in any of the other parameters studied, which
included haemoglobin concentration, haematocrit, RBC count, total
differential leukocyte counts, blood pressure, pulse rate, pupil size,
light reflex, eye accommodation, chest sound, muscle tone, knee jerk
and tongue and finger tremor (Palazzolo et al., 1970; 1971).
COMMENT
The toxicological data available at the 1968 Meeting were supplemented
by new information on ethion excretion, acute short and long-term
toxicity, neurotoxicity, mutagenicity, teratogenicity and
cholinesterase inhibition. Information was provided on the effects on
human volunteers.
Following oral administration of 14C-ethion-methylene to rats, most
of the radioactivity was found in the urine. Results of a dominant
lethal test in mice, a teratogenicity test in rats and a neurotoxicity
test in hens were negative.
Two-year feeding studies in rats and dogs indicated plasma, RBC and
brain cholinesterase inhibition at 20 ppm in rats and plasma
cholinesterase inhibition at 6 ppm and above in dogs. Exposure of
humans for three weeks indicated a no-effect level on plasma
cholinesterase at 0.05 mg/kg/day.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 6 ppm in the diet, equivalent to 0.3 mg/kg
body-weight/day.
Dog: 2 ppm in the diet, equivalent to 0.05 mg/kg
body-weight/day.
Man: 0.05 mg/kg/day.
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN
0 - 0.005 mg/kg body-weight
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Ethion preparations have been registered for use in cattle dips and
sprays in the following countries: Australia, Argentina, Brail,
Colombia, Costa Rica, Cuba, Mexico, Paraguay, Rhodesia, South Africa
Uruguay and Venezuela.
Ethion is approved for application to apples, pears and citrus (often
to other crops as well) at a maximum rate of 2.5 kg/ha in the
following countries: Australia, Argentina, Colombia, Iran, Israel,
Italy, Japan, Mexico, New Zealand, Peru, Spain, Uruguay, U.S.A.,
Venezuela.
Additionally, ethion is used extensively on cotton in U.S.A., Pakistan
and probably in several other countries. An important field of use
occurs in Ceylon, India and Indonesia where tea is treated at the rate
of 600 g/ha three times per year. It is not practicable to specify an
interval between application and harvest, but normally two weeks would
elapse.
In Australia, in addition to use on cattle for the control of cattle
ticks, ethion is registered for the control of specific pests of
apples, peaches, nectarines, peers, plums, prunes, cherries, almonds
and quinces where a dormant spray in oil emulsion is applied, and
passionfruit, grapes, citrus, figs, avocados and onions, where a
foliage spray in oil emulsion is used.
In U.S.A. ethion is registered for the uses shown in Table 2, at the
rates and with the withholding periods indicated.
TABLE 2 Use of ethion in the United States
Use Rate Applications Withholding
(kg/ha) (no.) period (days)
Almonds 2.5 - 30
Apples 5.0 4 60
2 40
2.5 4 40
2 20
Apricots 3.0 1 dormant
Beans 0.5 - 2
1.5 1 10
Cherries 3.0 1 dormant
Chestnuts 2.5 2 before husks split
Corn 1.0 1 50
Cotton 1.6 not after bolls open
TABLE 2 (Cont'd.)
Use Rate Applications Withholding
(kg/ha) (no.) period (days)
Cucumbers 0.5 - no time limitation
Eggplant 0.5 - no time limitation
Filberts 2.5 2 before nuts visible
Garlic 2.0 1 at planting
Grapes 1.25 - 60
2 30
2.2 1 30
1.2 (dust) 2 15
Grapefruit 7.5 - no time limitation
10.0 - 30
Lemons 7.5 1 21
Limes 7.5 1 21
Melons 1.6 - no time limitation
Nectarines 1.5 - dormant
Onions 2.0 1 at planting
Oranges 7.5 - no time limitation
10.0 - 30
Peaches 1.75 2 30
5.0 3 60
Pears 2.7 2 35
Pecans 2.5 2 not after husks split
1.0 3 21
Pimentos 0.5 - no time limitation
Plums and 2.5 2 45
prunes 1.75 3 21
TABLE 2 (Cont'd.)
Use Rate Applications Withholding
(kg/ha) (no.) period (days)
Sorghum 0.5 3 30
Strawberries 1.0 - 2
Squash 0.5 - no time limitation
Tangelos and 7.5 - no time limitation
tangerines
Tomatoes 0.5(spray - 2
0.8(dust) - 2
Walnuts 2.0 - dormant
2.5 2 before husks split
RESIDUES RESULTING FROM SUPERVISED TRIALS
In citrus fruit
Oranges from Florida receiving three foliar sprays of ethion
emulsifiable concentrate were analysed to determine if ethion residues
would conform to the 1 ppm tolerance proposed by the Joint Meeting
when treated according to standard practice for Florida (Niagara,
1971b).
Hamlin oranges sampled on the same day after a 1 kg/ha treatment
yielded maximum ethion and ethion monooxon residues of 0.34 ppm and
0.015 ppm, respectively. Valencia oranges sampled on the same day
after a 2.4 lb a.i./acre treatment yielded maximum ethion and ethion
monooxon residues of 0.60 ppm and 0.060 ppm respectively. No ethion
dioxon residues were found in either study by a method capable of
determining 0.025 ppm of dioxon.
The data indicate that ethion residues would be less than the proposed
1 ppm tolerance when the emulsifiable formulation is used.
The orange trees had been treated in summer, autumn and spring at
intervals of 3 - 6 months.
Residue studies involving two formulations of ethion were conducted on
Valencia oranges grown in California (Niagara, 1972a). Application
rates conformed to registered use patterns in U.S.A. The object of
these experiments was to determine whether it was possible to comply
with the tolerance of 1 ppm recommended in 1968 within the time
interval which would be practicable under normal conditions of
agriculture.
Single applications of ethion wettable powder and ethion emulsifiable
concentrate, each at the rate of 5.0 and 7.5 kg/ha, were made to
mature Valencia oranges.
Samples were collected from the wettable powder treated plots at
intervals of 0, 7 and 14 days after treatment. Average zero day
residues of 0.75 ppm were found in the 5 kg/ha plot, these residues
diminished to 0.26 ppm on day 14. In the case of the 7.5 kg/ha
treatment, initial average residues of 1.50 ppm diminished to 0.63 in
the same period. Ethion monooxon was found only in the 7- and 14-day
samples and comprised 16%-17% of the total residue. Ethion dioxon was
not detected.
Sampling of the plots treated with emulsifiable concentrate was
conducted over a 21 day period. Average initial residues of 1.38 ppm
diminished to 0.63 ppm in the case of the 5 kg/ha treatment. Samples
from the 7.5 kg/ha application rate showed residues of 1.49 ppm and
0.65 ppm at day 0 and 21, respectively. Ethion dioxon and ethion
monooxon were not detected on these samples.
The time required to bring about a 50% reduction in the residue levels
varied from 14 to 21 days, but it appeared that, having reached a
level of 0.5 ppm, the rate of dissipation decreased sharply. In view
of the fact that some citrus varieties, including Valencias, must be
sprayed when both mature and immature fruit are on the trees, residues
above 1.0 ppm may sometimes occur.
In pome fruit
Harvest samples of ethion treated apples and pears were analysed for
the presence of ethion dioxon, ethion monooxon and ethion residues
(Niagara, 1972b). In all cases, the chemical was applied as the 25%
wettable powder in accordance with registered use patterns.
The two apple studies (in California and Washington) showed combined
oxygen analogue residues which comprised 10-20% of the total residue.
However, the total residue did not exceed 1 ppm on any of the samples.
The pear study conducted in Washington showed a maximum residue of
2.76 ppm, 20% of which was combined dioxon and monooxon. In contrast,
the California pear study (which involved only one application)
yielded a maximum residue of 1.21 ppm; of this total, 10% was present
as the combined oxons.
In a submission to the U.S. Food and Drug Administration, Niagara
(1962) showed that the application of ethion wettable powder to pears
at the rate of 5 kg/ha and 8 kg/ha seven days before harvest gave rise
to residues of 1.6 ppm (1.08 - 2.2) and 2.5 ppm (2.2 - 2.8) ethion on
the fresh fruit. When this fruit was dried experimentally, the dried
fruit contained from 1.12 to 4.8 ppm ethion, but it was shown that
normal commercial drying would have a more pronounced effect on
concentrating the residues.
In stone fruit
Harvest samples of plum and prune from a maximum ethion treatment
programme were analysed for the presence of ethion dioxon, ethion
monooxon and ethion residues (Niagara, 1972c). Both crops had received
three applications at the registered rate of 1.75 kg/ha as the
wettable powder and were sampled at an interval of 21 days after the
final treatment. Total residues did not exceed 0.5 ppm on either fruit
at this interval. However, the combined oxygen analogues contributed
approximately 25% of the total residue. Apricots and cherries analysed
at harvest following previous winter and spring treatment with 0.025%
and 0.05% solutions in petroleum oil showed no detectable residues by
a method capable of determining 0.05 ppm (Niagara, 1972d).
Results of trials carried out by Niagara (1962) and submitted to the
U.S. Food and Drug Administration show that there is relatively little
loss of ethion residues in nine days elapsing between application to
mature fruit, and harvesting of ripe fruit. Following application of
two sprays three weeks apart (as is typical for the control of
oriental fruit moth, the total being 4 kg ethion/ha) peaches were
picked immediately after the second spray and again nine days later.
The fruit collected immediately after spraying were found to have a
mean residue of 2.6 ppm (2.4 - 2.8) while those which had remained on
the trees for nine days still had 1.3 ppm (1.27 - 1.34).
Peaches from the above trial were subjected to a simulation of the
normal drying process involving exposure to sulphur dioxide and then
sun drying for 13 days. The first pickings after drying contained 8.8
ppm (8.6 - 9.0) while the second still had 4.2 ppm (3.2 - 5.1) after
drying. This represents a loss of only 15 - 37% of the theoretical
residue when allowance is made for the loss of moisture. It was
considered that under drying conditions more in keeping with normal
practice the loss would have been considerably less.
In the same submission results are given of trials on fresh and dried
apricots. Immediately following application of 1.3 kg ethion/ha,
apricots were found to have 2.8 ppm ethion (2.5 - 3.1). In other
trials nearby, fruit picked 12 and 14 days after the application of
the same rate of the same formulation contained 0.65 (0.58 - 0.72) ppm
and 1.42 (1.16 - 1.77) ppm ethion. Fruit from each of these trials was
subjected to a normal treatment with SO2 and then sun dried for 14
days. The residues ranged from 1.2 to 4.7 (average 3.0) ppm ethion.
The loss of ethion on drying ranged from 31 to 80%.
In grapes, raisins and grape by-products
In order to determine the level of residues in grapes following normal
treatment, the loss between application and harvest and the subsequent
loss in drying grapes (for raisins and muscats) Niagara (1972e) found
that though there was a loss of more than 50% in the seven days
following application the rate of loss thereafter declined, as is
shown in Table 3.
Grapes from experiments 4 - 7 were dried in the sun for 35 days and
the dried muscatels were again analysed. The residue levels in the
dried fruit ranged from 1.25 - 10.4 ppm. Allowing for the loss of
water from the fruit, this represented a loss of from 70 - 91% of the
amount of ethion originally present.
Samples of ethion treated grapes, raisins, raisin stems and grape
pomace were analysed for the presence of ethion dioxon, ethion
monooxon and ethion residues (Niagara 1972e).
In one location, ethion wettable powder and ethion emulsifiable
concentrate were applied to separate lots at the maximum registered
rate and frequency, i.e., 1.25 kg/ha; two applications, the last 32
days before harvest. Total residues averaged 1.3 ppm on harvest
samples of the grapes treated with wettable powder, and 0.4 ppm on the
samples treated with emulsifiable concentrate. When the grapes were
field dried to raisins, total residues averaged 0.47 ppm with no
significant difference between the two formulations. Residues on the
raisin stems were in the range of 0.8 - 0.9 ppm with the combined
oxygen analogues contributing 45 - 50% of the total residue.
A similar schedule was used at a second location, but in this case
only the emulsifiable concentrate was applied. Total residues on the
fresh grapes at harvest (32 days after the final treatment) averaged
0.95 ppm (range 0.93 - 0.95). Dry pomace prepared from this fruit in
the laboratory showed an average total residue of 6.2 ppm with only 2
ppm present as the oxygen analogue. Raisins obtained from this study
contained an average total residue of 1.1 ppm (range 1.07 - 1.16).
Residues on the corresponding stem samples averaged 2.9 ppm of which
30 - 35% was present as the combined oxygen analogues.
During the experiment, samples of the wet pomace were fortified with
ethion, ethion dioxon and ethion monooxon. Subsequent analysis of the
dried samples showed the following losses had occurred: dioxon 92%,
monooxon 75% and ethion 67%. These results show the more rapid
degradation of the dioxon.
Cucumbers and squash
In order to demonstrate the level of residues in cucumbers and squash
following approved use of ethion sprays, Niagara (1962) treated
cucumbers from two to seven times with from 1.0 to 3.5 kg/ha of ethion
as wettable powder and as emulsion. The results are summarized in
Table 4.
TABLE 3 Ethion residues on grape
Rate Residue when sampled x days after application (ppm)
Location Variety ethion
(kg/ha) 0 7 14 21 28 35
Fredonia, N.Y. 2.25 4.8-5.8 2.1-3.0 1.1-1.7 0.9-1.2 0.7-0.9 0.6-1.0
Fredonia, N.Y. 0.75 10.1 3.4 2.4 2.2 1.9
Modesto, Cal. Seedless 1.4 0.65 0.63 0.33 0.12
Clovis, Cal. Muscat 5.4 3.3-4.0
Biola, Cal. Muscat 5.4 4.9-5.8
Clovis, Cal. Muscat 5.4 2.5-3.8
Biola, Cal. Muscat 5.4 6.3-6.7
TABLE 4 Ethion residues on cucumbers and squash
Total ethion Application Residues found x days after application (ppm)
applied (no.)
(kg/ha) 0 5 8 11
3.0 6 0.12 0.09 0.01 0.04
3.5 7 0.12 0.09 0.01 0.0
1.0 2 - - - 0.0
1.5 3 0.05 0.02 0.02 0.04
Cottonseed
In support of a petition to the U.S. Environmental Protection Agency,
Niagara (1971a) showed from several trials that the application of
ethion (several formulations) at the approved rate (1.6 kg/ha), and at
double rate prior to the opening of bolls, produced residues in the
ginned seed ranging from non-detectable to 0.25 ppm. The residues
found were thought to be the maximum likely to occur, to be present on
the lint only and probably to be due to contamination and/or
inefficient ginning. The location of the residues in lint was
confirmed, and it was shown that the acid delinting process removed
all detectable residues from the cottonseed. Further studies showed
that any ethion residues present on the seed were mainly in the lint,
less in hulls and only 4% in the crude cottonseed oil. The maximum
level of ethion found in crude cottonseed oil was 0.33 ppm.
Maize (grain, forage and fodder)
Niagara (1971d) carried out trials in three different regions of
U.S.A. following the application of ethion emulsifiable concentrate at
the rate of 1 kg/ha to maize. Samples of forage collected 0, 7, 14 and
21 days after application contained 20.2 ppm, 5.7 ppm, 3.2 ppm and 1.9
ppm ethion (total ethion and oxons), respectively. Ethion comprised
95% of the residues at day 0 and 70 - 80% at day 21. Maximum ethion
monooxon residues of 0.71 ppm were detected at day 0, and these
declined to 0.27 ppm at day 21. Maximum ethion dioxon residues of 0.30
ppm were detected at day 7 and 14, after application. There were wide
variations in the residue levels between different samples from
different sites. The maximum level of ethion likely to be found in
maize forage following approved use would be 15 ppm.
In separate studies for the same petition Niagara (1971d) showed that
the application of 1 kg ethion/ha to maize 50 days before harvest
produced minimum residues in the maize grain. No residues exceeding
the limit of determination were found.
In nuts
Chestnuts, filberts, pecans and walnuts were treated with 0.05% ethion
in petroleum oil emulsions during the dormant season and again twice
with ethion wettable powder at the rate of 1.5 - 2.5 kg/ha during the
growing period, but before the husk split. Analysis of the kernels of
nuts from six trials showed no detectable residues by a method capable
of determining 0.05 ppm ethion or metabolites (Niagara, 1972d).
In dairy cattle
An indication of the levels of ethion residue found in milk from
individual cows or an individual herd is shown by a trial conducted by
the New South Wales Department of Agriculture (Watts, 1969). Four
dairy cows were dipped once in 0.068% ethion emulsion (slightly less
than the recommended 0.075% dip). Milk samples were collected,
pre-dipping and over a period of 12 days post dipping, with the
results shown in Table 5.
TABLE 5 Ethion residues in milk after dipping of dairy cattle1
Samples collected Mean ethion level Range ethion
(ppm) (ppm)
Pre-dip nil nil
5 h post-dip 3.36 2.66 - 4.10
1 d post-dip 1.95 1.70 - 2.14
2 d post-dip 1.37 1.14 - 1.58
3 d post-dip 0.77 0.56 - 0.84
4 d post-dip 0.66 0.50 - 0.81
5 d post-dip 0.52 0.49 - 0.56
6 d post-dip 0.44 0.39 - 0.58
10 d post-dip 0.06 0 - 0.25
12 d post-dip 0.02 0 - 0.06
1 Expressed as ppm in butterfat
FATE OF RESIDUES
In animals
Studies were conducted to determine the effect and fate of ethion in
the ration of cows in order to gauge whether animals grazing treated
orchards or fed pomace from treated citrus, grapes or apples or
cottonseed meal would excrete residues in milk or retain residues in
meat, fat or meat by-products (Niagara, 1971c).
Groups of four mature Holstein cows were fed ethion at 5, 10 and 20
ppm in their daily feed ration for 30 consecutive days. Milk samples
were collected periodically during the feeding period. At the end of
the 30-day test feeding period, three cows from each group were
sacrificed and tissue samples taken.
A 30-day recovery period followed during which the remaining cows were
not fed ethion in their daily feed ration. Milk samples were collected
at weekly intervals. At the end of the recovery period, the cows were
sacrificed and tissue samples taken.
Milk samples from the 5 and 20 ppm ethion feeding levels and tissue
samples (muscle, kidney, liver and fat) from all three feeding levels
were analysed. Ethion was the only residue detected in any of the milk
or tissue samples.
Analysis of milk from the 5 ppm ethion feeding level yielded maximum
ethion residues of 0.009 ppm at day 8. Milk from the 20 ppm ethion
feeding level yielded maximum ethion residues of 0.034 ppm at day 4.
No ethion residues were detected in any of the recovery period milk
samples.
It is notable that no oxygen analogues of ethion occurred in any of
the milk, meat or fat samples. The fat of animals was the only tissue
to contain significant residues. This study supplements the previous
study done with radioactive ethion (FAO/WHO, 1969).
White Leghorn hens were fed ethion at 10 ppm as a portion of their
daily feed ration for nine consecutive weeks (Niagara, 1969). Egg
samples were collected from day 54 of ethion feeding through day 60.
At the end of the nine week test feeding period, one half of the
chickens were sacrificed and tissue samples taken.
A four-week recovery period followed during which the remaining
chickens were not fed ethion in their daily feed ration. Egg samples
were collected periodically. At the end of the recovery period the
remaining chickens were sacrificed and tissue samples taken.
No ethion residues approaching the method sensitivity of 0.01 ppm were
detected in any of the egg or tissue samples analysed following the
feeding and recovery periods. Although the analytical method was not
the newer version that measures extremely low levels of the oxygen
analogues, no residues would be expected since there were no traces of
ethion.
In plants
An improved analytical method for the measurement of oxidized forms of
ethion (ethion monooxon and ethion dioxon) has been developed since
the 1968 review (FAO/WHO, 1969). Apples, pears, plums, prunes, grapes
and oranges have been treated with ethion formulations at the maximum
allowable rate to determine the magnitude of the oxidized forms by
this newer method (Niagara, 1972b,c,d,e). These data are summarized in
Table 6.
TABLE 6 Ethion residues in various crops
Crop Pre-harvest Total residue-ethion Residue present as
interval + oxons (ppm) oxygen analogue
(days) (% of total)
Apples 20 - 28 0.71 - 0.75 13 - 16
Pears 20 - 23 1.2 - 2.6 15 - 18
Plums 21 0.40 25
Prunes 21 0.25 22
Grapea 30 - 32 0.35 - 1.8 0 - 15
Oranges 0 1.50 0
Oranges 7 0.92 16
14 0.62 18
Residues of oxygen analogues resulted only from treatments with
wettable powders. No oxygen compounds were detected from emulsifiable
concentrate treatments.
In storage and processing
Simulated commercial processing of ginned cottonseed (Niagara, 1970)
showed that 64% of the residue present on cottonseed from useful
application of ethion was contained on the lint. The bulk of the
remainder was present on the hulls (29%). Transfer to the oil was only
4%.
This represented a level of 0.33 ppm on the cottonseed oil when the
total on the ginned seed was 0.84 ppm.
Evidence of residues in food, in commerce or at consumption
Duggan et al. (1971), in a report on residues in food in the United
States from July 1963 to June 1969, reported that ethion was found in
0.3 to 1.7% of composite samples, with an average daily intake below
0.003 mg/day. The only samples reported containing residues were large
and small fruits. The incidence was 11.9% in the case of large fruits
and 5% in the case of small fruits.
Corneliussen (1970) reported on a total diet study for the period of
June 1968 through April 1969. Ethion occurred on six of the 30 fruit
composites. This was the only category in which ethion residues were
found. The maximum value was 0.27 ppm. Processing of the fruits
reduced the residues by 42%. Details of the processing procedure were
not given.
The New South Wales Department of Agriculture (Watts, 1972) reported
results of a critical survey of 1 063 samples of butter produced in
1971 within the cattle tick quarantine areas and analysed by the Board
of Tick Control. The residues were found only during the period when a
compulsory dipping program was being undertaken, i.e., from September
until March. Of the samples, 54% were reported to contain ethion
residues ranging from 0.01 to 0.62 ppm. A similar pattern was reported
for 1970 although, due to less intensive dipping, the number of
samples with residues was then only 39% of the total analysed. During
this period, 286 000 head of cattle were being dipped in ethion
emulsion every 17 - 21 days.
In a survey of 879 butter samples collected in 1971 from regions where
cattle tick is endemic, the Australian Department of Primary Industry
(Snelson, 1972) reported that 17.4% of the samples contained ethion
residues at levels ranging from 0.05 to 0.5 ppm.
METHODS OF RESIDUE ANALYSIS
A gas chromatographic method utilizing a flame photometric detector
specific for phosphorus has been developed for the analysis of ethion
residues (Niagara, 1972b). Ethion and the two oxygen analogues can be
determined simultaneously in the same sample. A limit of determination
as low as 0.005,ppm has been achieved. The key factor in achieving
this improvement was the elimination of charcoal absorbents in cleanup
steps. This method has not been published.
The EPA multi-residue procedure determines ethion but will not
determine the oxygen analogues. There are two points in the
multi-residue procedure where these substances are lost: firstly in
the hexane/acetonitrite partition where the oxygen analogues do not
partition quantitatively into the hexane; secondly the oxygen
analogues are not eluted from the cleanup column with the solvents
used to isolate the organophosphate materials.
The multi-detection methods published in the EPA Analytical Manual
Vol. 1 have been used successfully for the determination of ethion
residues in many substrates and are recommended for regulatory
purposes even though not determining oxygen analogues.
NATIONAL TOLERANCES
Since the review in 1968 (FAO/WHO, 1969d) the tolerances shown in
Table 7 have been established for ethion residues.
TABLE 7
Examples of national tolerances reported to the meeting
ppm
U.S.A. Maize, forage and fodder 14
Cottonseed 0.5
Milk fat (reflecting negligible
residues in whole milk) 0.5
Eggs 0.2
Meat, fat and meat by-products
of goats, pigs, horses, poultry
and sheep 0.2
Maize grain, apricots, cherries,
chestnuts, filberts, pecans and
walnuts (kernel) 0.1
Australia Fruit and vegetables 1
Fat of meat of cattle 2.5
Meat of cattle 0.75
APPRAISAL
Ethion is a non-systemic organo-phosphorus insecticide and acaracide
introduced in 1956 and widely used, especially as an acaracide and
scale control agent, for many fruit crops, tea and some vegetables,
often in combination with petroleum oils. It is also used for dipping
cattle against cattle ticks in many countries.
Since the review in 1968 (FAO/WHO, 1969), improved methods of analysis
have enabled studies to be made of the fate of ethion residues on a
number of fruits. Foliar applications of wettable powder formulations
can give rise to small amounts of ethion monooxon and ethion dioxon,
but the amount is usually less than 20% of the total residue. The
oxygen analogues do not occur when emulsifiable formulations are used.
Studies made following the feeding of dairy cattle with ethion,
simulating feeding of contaminated or treated fodder, show that small
amounts of ethion, but no oxygen analogues, are to be found in milk
and fatty tissues. Poultry, on the other hand, do not have residues
either in body fat or eggs when receiving rations containing small
amounts of ethion.
Ethion residues have only been found infrequently at low levels in
composites of the average diet examined in the U.S.A. Butter samples
taken from areas where cattle must be dipped to control cattle ticks
show that ethion residues occur frequently at significant levels.
Analytical procedures suitable for regulatory purposes are available.
These are capable of determining the oxygen analogues as well as the
parent compound.
RECOMMENDATIONS
The previously recommended temporary tolerances are amended and are no
longer classified as temporary. The following residue limits are based
on residues likely to be found at harvest, or in the case of fat of
meat from cattle, dairy produce and tea, also at the retail level,
following currently approved use patterns.
The residue levels are unlikely to decline significantly during
storage but, except in fat of meat and dairy produce, processing or
cooking will largely destroy any residues prior to consumption.
PRACTICAL RESIDUE LIMITS
ppm
Apples, grapes, lemons, limes, oranges 2
Plums, prunes, strawberries 2
Nectarines, peaches, pears 1
Apricots, cherries 0.1*
Melons, tomatoes, beans 2
Cucumbers, squash 0.5
Eggplant, garlic, onions 1
Pimentos, peppers 1
Cottonseed 0.5
Maize (grain) 0.05*
Almonds, chestnuts, filberts,
pecans, walnuts (shelled) 0.1*
Fat of meat of cattle 2.5
Edible offal of cattle 0.75
Fat of meat of goats, horses, pigs,
poultry and sheep 0.2*
Edible offal of goats, horses, pigs,
poultry and sheep 0.2*
Milk and milk products (fat basis) 0.5
Eggs 0.2*
Tea (dry manufactured) 7
* at or about the limit of determination
Remarks
Residues of ethion and its oxygen analogues should each be determined
and the sum expressed as ethion.
FURTHER WORK OR INFORMATION
DESIRABLE
Determination of the metabolic fate in animals.
REFERENCES
Arnold, D., Kennedy, G. and Keplinger, M.L. (1972) Report NCT 461.99,
Industrial Bio-Test Laboratories, Inc. Mutagenic study with ethion in
albino mice. (unpublished)
Brandav, E.G., Knaak, J.B. and McCarthy, J.F. (1971) Excretion of
ethion-methylene-14C by the rat. Report M2819 Niagara Chemical
Division, FMC Corporation. (unpublished)
Corneliussen, P.E. (1970) Pesticide residues in total diet samples
(V). Pest. Mon. J., 4(3): 89 - 105.
Duggan, R.E., Lipscomb, G.Q., Cox, E.L., Heatwole, R.E. and Kling,
R.C. (1971) Pesticide residue levels in foods in the United States
from 1963 - 1969. Pest. Mon. J., 5(2): 73 - 212.
FAO/WHO. (1969) 1968 evaluations of some pesticide residues in food.
FAO/PL:1968/M/9/1; WHO/Food Add./69.35.
FAO/WHO. (1970) 1969 evaluations of some pesticide residues in food.
FAO/PL/1969/M/17/1; WHO/Food Add./70.38.
FAO/WHO. (1971) 1970 evaluations of some pesticide residues in food.
FAO/AGP: 1970/M/12/1; WHO/Food Add./71.42
Fletcher, D., Jenkins, D.H. and Keplinger, M.L. (1972) Report NCT
646.22 Industrial Bio-Test Laboratories, Inc. Neurotoxicity study with
ethion technical in adult hens. (unpublished)
Greco, R.A., Keplinger, M.L. and Fancher, O.E. (1970) The in vitro
inhibitory effects of ethion, ethion monooxon and ethiondioxon on
human plasma and erythrocyte cholinesterase activity. Report NCT
402.21 Industrial Bio-Test Laboratories, Inc. (unpublished)
Haley, S., Plank, B.J. and Wright, P.L. (1972) Teratogenic study with
ethion technical in albino rats. Report NCT 463.42 Industrial Bio-Test
Laboratories, Inc. (unpublished)
Hartke, K., Wright, P.L. and Keplinger, M.L. (1972) Two-year chronic
oral toxicity study with ethion technical in beagle dogs. Report NCT
386.32 Industrial Bio-Test Laboratories, Inc. (unpublished)
Kretchmar, B., Mastri, C. and Keplinger, M.L. (1971) Acute oral
toxicity study with ethion technical in female albino rats. Report NCT
422.01 Industrial Bio-Test Laboratories, Inc. (unpublished)
Mastri, C., Keplinger, M.L. and Fancher, O.E. (1970) Acute oral
toxicity studies with ethion dioxon and ethion monooxon in albino
rats. Report NCT 404.01 Industrial Bio-Test Laboratories, Inc.
(unpublished)
Niagara. (1962) Pesticide Petition No. 351 to U.S. Food and Drug
Administration, Niagara Chemicals Division, FMC Corporation.
Niagara. (1969) Determination of ethion residues in eggs and poultry
tissues. Report M2548 filed with FAO. Niagara Chemicals Division, FMC
Corporation. (unpublished)
Niagara. (1970) Ethion residues on cottonseed; process study. Report
R-1156 filed with FAO. Niagara Chemicals Division, FMC Corporation.
(unpublished)
Niagara. (1971a) Pesticide Petition OF0920 to U.S. Environmental
Protection Agency. Niagara Chemicals Division, FMC Corporation.
Niagara. (1971b) Determination of ethion, ethion monooxon and ethion
dioxon residues in or on oranges. Report M-3035 filed with FAO.
Niagara Chemicals Division, FMC Corporation (unpublished)
Niagara. (1971c) Residue determination of ethion and its oxygen
analogues in milk and cow tissue. Report M-2808 filed with FAO.
Niagara Chemicals Division, FMC Corporation. (unpublished)
Niagara. (1971d) Pesticide Petition 1F1104 to U.S. Environmental
Protection Agency. Niagara Chemicals Division, FMC Corporation.
Niagara. (1972a) Ethion residues in or on Valencia oranges. Report
R-1207 filed with FAO. Niagara Chemicals Division, FMC Corporation.
(unpublished)
Niagara. (1972b) Ethion residues in or on apples and pears. Report
R-1187 filed with FAO. Niagara Chemicals Division, FMC Corporation.
(unpublished)
Niagara. (1972c) Ethion residues in or on plums and prunes. Report
R-1188 filed with FAO. Niagara Chemicals Division, FMC Corporation.
(unpublished)
Niagara. (1972d) Pesticide Petition No. OF0918 to U.S. Environmental
Protection Agency. Niagara Chemicals Division, FMC Corporation.
Niagara. (1972e) Ethion residues in or on grapes, raisins and grape
by-products. Report R-1196 filed with FAO. Niagara Chemicals Division,
FMC Corporation. (unpublished)
Palazzolo, R.J., Fancher, O.E. and Calandra, J.C. (1970) A study on
the effects of ethion on plasma and erythrocyte cholinesterase
activity in human subjects during subacute administration. Report NCT
380-21 Industrial Bio-Test Laboratories, Inc. (unpublished)
Palazzolo, R.J., Fancher, O.E. and Calandra, J.C. (1971)
Cholinesterase inhibition studies in man with ethion. Society of
Toxicology Meetings, 5 - 9 March 1972. Paper No. 29.
Smith, P.S., Wright, P.L. and Keplinger, M.L. (1972) Two-year chronic
oral toxicity study with ethion technical in albino rats. Report NCT
385.32 Industrial Bio-Test Laboratories, Inc. (unpublished)
Snelson, J.T. (1972) Results of residue surveys in Australia. Report
filed with FAO. Department of Primary Industry, Canberra, Australia.
Watts, R.M. (1969) Report of dipping trials with ethion. New South
Wales Department of Agriculture.
Watts, R.M. (1972) Analysis of butter by Board of Tick Control. Report
to Co-ordinating Committee on Pesticides, Canberra, Australia.