ETHEPHON JMPR 1978
Explanation
Residue aspects of ethephon were evaluated by the Joint
Meeting in 1977 (FAO/WHO, 1978b) at which time only guideline
residue levels could be proposed owing to constraints on data and
the lack of an ADI. Some data on short term toxicological work and
additional information on use patterns, residues from supervised
trials and methods of analysis are summarized in this monograph
addendum.
Short-term studies
Rat
In 1 90-day test, rats (8/group) were dosed by gavage with
1500, 750, 375, 190, 90 and 45 mg/kg on five days per week. Death
occurred at the highest dose. Reduced weight gain and some decrease
in urinary pH occurred in the two highest dosage groups only. Food
consumption did not differ in any of the groups. Hematology studies
revealed no abnormalities. Urinary protein, sugar or sediment were
unaffected, and serum glutamic-oxaloacetic-transaminase and
leucine-aminopeptidase were within normal ranges. Relative liver,
kidney, adrenal, spleen and thymus weights did not differ between
test groups and control and no gross pathology was detected. In the
1500 mg/kg dose group histological studies revealed some vaculation
in liver parenchymal cells. A tendency towards diminished size of
liver cell nuclei, an increased size of the Kupffer cells and some
renal tubular necrosis was also observed at the highest dose.
Exposures at the 375 mg/kg dosage or less were associated with
little or no effects under the conditions tested (Weisbrod et al.,
1973).
COMMENTS
Ethephon was reviewed by the 1977 Joint Meeting (FAO/WHO,
1978b) at which time it was reported that long-term studies were in
progress the reports of which would be made available by 1978. The
results of such studies were not available to the Joint Meeting. A
short-term study was available to the Meeting.
In a short-term 90-day study in rats, ethephon was
administered by gavage at dosage levels varying from 0 to 1500
mg/kg/day five days/week. Growth depression was noted at 750 mg/kg
and above. Mortality and histopathological changes were observed at
1500 mg/kg Clinical chemistry and gross examination of several
tissues showed no specific adverse effects.
The available data were insufficient to allocate an ADI.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
In Australia ethephon in used to initiate flowering of
pineapple, peaches, tomatoes and apples, It has undergone trials
for use as a harvest aid (to accelerate ripening and loosen fruits)
in grapes, cherries, pears, and black currants. In the Netherlands
it is used for sprout inhibition of bulb onions.
Ethephon in available as a 480 g/l concentrate and in applied:
(i) to pineapple plants at 1 kg/2000 l or half
this concentration (depending on the time of
year) to initiate flowering; the pre-harvest
interval in about 9 months;
(ii) to pineapple fruits at 2.2 kg/ha at 200g/100l
(0.2%) concentration to accelerate ripening;
it in applied one week before harvest;
(iii) to tomato fruits, pre-harvest, at 875g/ha at
200g/100l concentration (0.2%) or half this
concentration, to accelerate ripening of
pink-red fruit, it is applied 7 days before
harvesting;
(iv) to apples at 24-48g/100l (0.24-0.48%)
concentration to advance fruit maturity and
coloring; it is applied 7-14 days prior to
harvesting;
(v) to peaches at 864g/ha at 200g/100l (0.2%)
concentration to advance maturity; it is
applied about 6 weeks before harvest;
(vi) to bulb onions at 500 l spray/ha in 280 g
ai/100 l concentration to inhibit sprouting;
it is applied 4 weeks before harvest.
Post-harvest treatments
Ethephon is applied to tomato fruits post-harvest as a
192-288 g/100l (0.19-0.29%) concentration dip to ripen picked
mature green fruits.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Ciba-Geigy Australia, Ltd. (1978a) have made field trials
with an ethephon formulation (48% liquid concentrate) on
pineapples, tomatoes, apples, peaches, cherries, pears, grapes and
black currants.
The residues are summarized below. All residues were determined by
an adaptation of the method of Bache (1970).
Pineapples (i) Residues in fruit following spraying of
plants to initiate flowering: single
trial data, 1971; no residues were
detected (limit of detection, 0.05 mg/kg)
in the whole fruit or flesh of pineapples
9 months after the plants had been
sprayed with 6 concentrations of ethephon
varying from 5 to 25g/100l. Each plant
was treated with 28ml of spray, i.e. the
actual amount of ethephon applied per
plant ranged from 14 to 70 mg. All
treatments were replicated 3 times, and
the plot size was 20 pineapples plants. 2
plants per plot were sampled.
(ii) In a 1972 trial, in which ethephon was
applied to ripening fruits (a fortnight
before harvest) in concentrations of 50,
100 and 200 g/100l at 1120l/ha the
residues found ranged from 0.81-0.28
mg/kg one day after treatment to
0.28-0.12 mg/kg fifteen days after.
Tomatoes (i) Pre-harvest spraying, 1972: after a single
treatment at 896g/ha using an ethephon
concentration of 400g/100l (0.4%) the
residues found in whole fruit bush
tomatoes, sampled 1, 4, 7 and 11 days
after application, did not exceed 0.5
mg/kg.
(ii) Post-harvest dip 1976 trial: after
dipping three concentrations of ethephon,
(100, 200 and 300g/100l) the tomatoes
were analysed 0, 3, 4, 7, 10 and 14 days
after treatment. The initial residues,
1.3, 2, 3 and 4 mg/kg, were in proportion
to the ethehpon concentrations applied,
and they hardly varied during the 14
days.
Apples In a 1974 trial In New South Wales,
three varieties of apples were sprayed
some 3 weeks before harvest. Following
application of 50g/100l ethephon
concentration at 13.5 litres/tree to two
of the varieties the residue found ranged
from 0.75-1.1 mg/kg immediately after
treatment to 0.25-0.28 mg/kg 21 days
later. The third variety as sprayed with
ethephon at 25g/100l concentration and
22.5 litres/tree and a single
determination nine days later showed
0.26-0.72 mg/kg residue.
Peaches In a 1974 trial in NSW, a variety of
peach was sprayed with two concentrations
of ethephon, 20g/100l and 40g/100l, at
27-31.5 litres/tree some two to three
weeks before harvest. The residues found
16 and 23 days after application ranged
from 0.26-0.72 mg/kg (lower rate - higher
rate of application) to 0.24 mg/kg (lower
rate), respectively.
Cherries In a 1972 trial in Victoria, a variety
of cherry as sprayed with two
concentrations of ethephon, 25g/100l and
50g/100l, at 23-27 litres/tree one week
before harvest. The residues found in the
fruit flesh ranged from 3.6-5.1 mg/kg
(low rate - high rate of application)
immediately after spraying to 9.5 - 14.3
mg/kg (low-high rates) fourteen days
later.
Grapes (viii) Two trials were made in NSW in 1975. In
one, ethephon at 80g/100l (0.08%) was
applied to grapes at 10001/ha five days
before harvest; the mean residues found
in the fruit ranged from 7.2 mg/kg
immediately after application to 4.2
mg/kg at harvest. In the other, two
concentrations of ethephon, 50 and
100g/100l were sprayed to `run-off' on
fruiting vines seven days before harvest;
mean residues found in the fruit juice at
harvest ranged from 3.8-8.5 mg/kg (low
rate - high rate of application).
Black-currants (ix) In a trial in Tasmania in 1974, 6g/100l
ethephon was sprayed on black currants
fruiting-bushes at 600ml/bush;, residues
found in the fruit harvested 1, 2, 4, 7
and 12 days after application hardly
varied, ranging from 0.11-0.18 mg/kg.
Onions (x) In the Netherlands in 1977, 4 plots of
onions were treated once each with 0,
960, 1440 or 1920 kg ai/ha using a 480 g
ai/l liquid formulation. At 20 days after
application, residues were 0.1 mg/kg
(mean of 3 replicates) for the untreated
samples, 0.1 mg/kg (mean of 3) for the
960 kg treatment, 0.14-0.35 mg/kg for the
1440 kg treatment, and 0.14-0.35 mg/kg
for the 1920 kg treatment.
FATE OF RESIDUES
In plants
In connection with the development of a new method of analysis
for ethephon in tomatoes, cherries and apples, Hurter et al.,
(1978) described results obtained when tomatoes were treated once
in the field with a 0.2% solution at a time when fruits of the
first cluster turned from green to yellow. A steady increase in
ethephon concentration in treated tomatoes occurred for
approximately seven days post-treatment rising from about 3 mg/kg
to about 7 mg/kg then declining slowly thereafter for about 2
months. This observation was interpreted as indicating the systemic
transport of ethephon from leaves into the fruit. The
characteristic increase in ethephon residues were found also in
apples and cherries within 2 and 8 days after application, reaching
maximum values of 1.2 mg/kg in apples and 4.1 mg/kg in cherries.
RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
No new information was available to the Meeting.
METHODS OF RESIDUE ANALYSIS
Information on two adaptations of the Bache method and a
completely new rapid method for residues in tomatoes, cherries, and
apples was available to the Meeting.
Ernst et al., (1976) developed a rapid method for residues of
ethephon in tomatoes by changing the extraction step and
eliminating the clean-up step of the Bache method. Samples were
extracted with ethyl acetate and the extract was methylated with
diazomethane, decolourized with carbon and analysed by GC with a
flame photometric detector. Recoveries ranked from 78 to 98% at the
0.1 to 11 mg/kg level and the limit of determination was 0.1 mg/kg.
In Australia, the Bache method was modified to be suitable for
a large range of crops by Ciba-Geigy Australia, Ltd. (1978b). The
macerated crop was extracted with methanol and acetone was used to
precipitate some interfering co-extractives and dry the extracted
residue. The residue was then methylated under acidic conditions
with diazomethane and analysed by CG with a thermionic detector.
Recoveries at 0.1 to 5 mg/kg levels ranged from 70-100% for a wide
variety of crops with an overall limit of detection of 0.05 mg/kg.
Hurter et al., (1978) developed a new and rapid method for
ethephon residues based on degradation to ethylene at high pH
values. The ethylene gas is determined by gas-solid chromatography
with a flame-ionisation detector using head-space sampling
techniques. The extraction and purification steps of other
procedures (see above) are omitted. Results are consistent with the
direct determination of methylated ethephon by GLC. The natural
ethylene content of fruit was found to be less than 5% of that which
can be expected from residues of ethephon. However, this limits the
level of determination to about 0.1 mg/kg ethephon, whereas the
absolute limit would be about 0.002 mg/kg. The method has sufficient
merit to warrant further investigation and validation for possible
regulatory use for ethephon.
NATIONAL MRLs REPORTED TO THE MEETING
The following list of maximum residue limits currently in
force in Australia was available to the Meeting.
Crop Limit, mg/kg Pre-harvest interval
Cherries 15 7 days
Pineapples 2 7 days
Tomatoes 2 7 days
Tomatoes 5 (Provisional for Post-harvest use)
Black currants 1 7 days
Apples 1 7 days
Peaches 0.5 6 weeks
Wine grapes 10 (provisional)
APPRAISAL
The Joint Meeting evaluated ethephon in 1977. Only guideline
residue levels could be recorded owing to insufficient data for
allocating an ADI and inadequate data on residue levels from field
trials.
New information was available to the Meeting on use patterns,
residues resulting from supervised trials, and established maximum
residue limits in Australia and the Netherlands. Data on peaches,
onions and grapes which were not included in the previous
evaluation, were sufficient to record additional guidelines residue
levels for these commodities.
Information was available on modified and improved methods of
residue analysis. The modifications to the previous method have the
merit of shortening or eliminating some of the procedures and
should be further studied with a view to regulatory use. The new
method developed by Hurter et al., (1978) which measures the
ethylene gas liberated by ethephon under basic conditions, although
indirect, has considerable promise for the rapid screening of
fruits and vegetables and should be thoroughly investigated as a
possible replacement for existing methods.
EVALUATION
The following guideline levels are additional to those
previously recorded.
Commodity Guideline level, mg/kg Intervals on which
levels are based
Grapes 10 7 days
Onions (bulb) 0.5 4 weeks
Peaches 0.5 6 weeks
FURTHER WORK OR INFORMATION
Desirable
1. Additional and more comprehensive residue data resulting from
field trials on commodities not included in present recommendations
and for which registered uses exist in various countries.
REFERENCES
Anonymous. Information paper on ethephon from Australia.
(1978)
Anonymous. Information paper on ethephon from the Netherlands.
(1978)
Bache, C.A. J.A.O.A.C. 53 (4) 730-732.
(1970)
Ciba-Geigy Australia, Ltd. Reports on field trials of ethephon in
(1978a) Australia. Attachments I through VIII.
Ciba-Geigy Australia, Ltd. R. & D. Analytical Method No. 110A, The
(1978b) Determination of Ethephon Residues in Crops.
Ernst, G.F. and Anderegg, M.J.P.T. Rapid Gas-Liquid Chromatographic
(1976) Method for Determining Residues of Ethephon
(2-Chloroethyl Phosphoric Acid) in Tomatoes.
J.A.O.A.C. 59 (5): 1185-1187.
FAO/WHO. Working paper on ethephon prepared by the FAO Panel on
(1978b) Pesticide Residues and the environment.
Hunter, J., Manser, M. and Zimmerli, B. A Rapid and Simple
(1978) Method for the Determination of Residues of
2-Chloroethyl Phosphoric Acid (Ethephon) in
Tomatoes, Cherries and Apples. J. Agric. Food Chem.
26 (2): 472-475.
Weisbrod, D., Leine, J. and Ponsald, W. Untersuchungen zur
(1973) Toxizitat des Präparats; CKB 1080 Wirkstoff
(Ethephon); 90-Tage-Test an wachsenden Ratten. VEB
Chemisch-Pharmazentisches Werk Oschersleben
Forachunge-und-Entwicklungsstelle Blankenburg
(Harz) and CKB Bittefeld (CDR). Unpublished report.
See Also:
Toxicological Abbreviations
Disulfoton (ICSC)
Disulfoton (WHO Pesticide Residues Series 3)
Disulfoton (WHO Pesticide Residues Series 5)
Disulfoton (Pesticide residues in food: 1979 evaluations)
Disulfoton (Pesticide residues in food: 1981 evaluations)
Disulfoton (Pesticide residues in food: 1984 evaluations)
Disulfoton (Pesticide residues in food: 1991 evaluations Part II Toxicology)