THIABENDAZOLE JMPR 1977
Explaination
Thiabendazole was evaluated by the Joint Meeting in 1970, 1971, 1972
and 1975 (FAO/WHO 1971, 1972, 1973, 1976). An ADI was allocated in
1970 and maximum residue limits have been proposed for apples, pears,
bananas, citrus fruits and potatoes. In view of the evidence that the
administration of thiabendazole to livestock or the feeding of
livestock on treated commodities or food wastes containing
thiabendazole residues produces no significant residues in milk, meat
and edible offals a maximum residue limit at or about the limit of
determination was recommended.
Some additional data were obtained on residues from both pre-harvest
and post-harvest treatments and on the fate of these residues in
processing: further data were obtained on the fate of thiabendazole
residues in livestock. Results of a study with human volunteers were
also received. This monograph addendum is an evaluation of the new
data.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Tissue residue studies in animals
These are described in the section "Fate of residues", "In animals".
OBSERVATIONS IN HUMANS
A double blind study was carried out with about 100 male volunteers,
half of them receiving 250 mg/day thiabendazole during 6 months and
half of then a placebo. Each subject was interviewed weekly and any
potential side effect was recorded. General physical examination and
laboratory examinations (haematology, cholesterol, glucose, urea,
alkaline phosphatase, thymol turbidity, bilirabin in serum and
urinalysis) were carreid out before the test and after 4, 12 and 24
weeks. PBI in serum and BOG were carried out only at the beginning and
after 24 weeks. 36 subjects on thiabendazole and 41 on placebo
completed the study (none was removed from the study in relation with
the drug). As thiabendazole has a possible influence on the thyroid
the values for PBI were evaluated carefully. No indication, however,
was found of a decrease or increase in PBI values under influence of
thiabendazole. Under the conditions of the study thiabenclazole was
well tolerated at a dosage of 250 mg/clay during 24 weeks. go effect
on any of the parameters studied could be clearly ascribed to the drug
(Colmore, 1965).
COMMENTS
A study in human volunteers with a dose of 250 mg/day corresponding to
3-4 mg/kg bw was reviewed. No effects could be ascribed to the
thiabendazole administration, although many parameters were measured
including a thyroid function test.
In 1970 an ADI for humans established of 0.05 mg/kg bw based on a
no-effect level in the rat of 10 mg/kg bw. Observations on humans
allowed the meeting to increase the ADI for humans.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat. 10 (mg/kg bw)/day
Dog: 20 (mg/kg bw)/day
Humans: 3 (mg/kg bw)/day
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR HUMANS
0-0.3 mg/kg bw
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
The world-wide use of thiabendazole as an agricultural fungicide has
grown greatly since it was first introduced as a post-harvest
treatment for citrus, bananas and pome fruit in the late 1960s.
Thiabenclazole products are now registered for 40 or more uses as
pre-plant and pre-harvest treatments as well as for post-harvest use.
Table 1 gives a comprehensive review of current use patterns. Not all
uses are registered in all countries. Many applications are limited to
the control of only a few diseases on each crop.
A wide variety of formulations are available including dusts, wettable
powders, flowable pastes and thermal dusting tablets (smoke
generators). Thiabendazole is often formulated along with other
fungicides to increase the range of diseases controlled.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Bananas
In addition to the data evaluated in 1970 (FAO/WHO 1971) extensive
data are available from the study of pre-harvest applications of
thiabendazole to bananas in Brazil, Costa Rica, Dominican Republic,
Equador, Guadeloupe and Honduras. These are summarized in Table 2.
For the control of important fungal diseases of bananas, thiabendazole
is applied as a suspension in mineral oil emulsified in water. These
sprays are applied every four weeks throughout the year. Bananas take
many months to develop to maturity and they may be harvested
throughout the year. Extensive studies from many trials in all of the
above countries indicate that the residue from the pre-harvest
application of thiabendazole seldom exceeds 0.1 mg/kg. Only
insignificant amounts are found in the pulp, indicating relatively
little systemic transfer.
Bananas analysed after both pre-and post-harvest application of
thiabendazole were found to contain increased quantities of residue
with the maximum in the range of 1 mg/kg. In this case the
concentration in the peel was usually about 20 times higher than in
the pulp, the concentration in the pulp seldom exceeding 0.1 mg/kg.
There appears to be a trend for unripe fruit to take up slightly more
thiabendazole than ripe fruit. In the case of ripe fruit there appears
to be no tendency for migration of the deposit from the peel into the
pulp whereas in unripe fruit a small but measurable migration occurs.
Cabbage
Thiabendazole has proved effective for use as a fungicide in red and
white cabbage, applied post-harvest as a mist spray to protect the
cabbage in store prior to the production of sauerkraut. Two sprays are
recommended, to be used soon after harvest and 60 days later. In
practice, the use rate amounts to 0.34 mg/kg on the cabbage. An
extensive experiment carried out in Germany revealed residues ranging
from 0.06 to 2.6 mg/kg.
Cereals
Thiabendazole has proved effective for use as a fungicide in cereals,
applied as a foliar spray to control footrots and ear diseases. It is
generally applied in combination with contact fungicides to broaden
the spectrum of activity. Although a number of applications may be
made the last application is generally not later than 6 weeks before
harvest.
Extensive residue trials carried out in the Netherlands, Germany and
the United Kingdom indicate that for the most part the residues in
grain following such treatments are less than the limit of
determination though several studies revealed residues ranging up to
0.25 mg/kg. The data indicate that the residue in straw is not
significantly greater than in the grain.
Thiabendazole has found application for the control of seed-borne
diseases of meat, oats, barley and rice.
TABLE 1. Thiabendazole - use pattern
Crop Pre-plant applications Pre-harvest applications Post-harvest applications
No. Rate No. Rate No. Rate
Apples and pears - 2-10 450-1350 g/ha 1 500-2000 mg/l
Asparagus - 3 280 g/ha -
Avocado - 1 - 1 1000-3250 mg/l
Bananas - 10 30-150 g/ha 1 150-300 mg/l
Berries - 3 270-1200 g/ha -
Cabbage - - 1 0.34 g/tonne
Celery - 3 270-1200 g/ha -
Cereals 1 60-200 g/100kg seed 2 500-100 g/ha -
Cherries - 1 270-360 mg/l -
Citrus - 1 300-900 mg/l 1 500-5000 mg/l
Cotton 1 265 g/100 kg seed - -
Cucurbits - 1 600-1350 mg/l 1 650-1000 mg/l
Grapes - 3 900-1350 mg/l -
Mango - - 1 1000-2500 mg/l
Mushrooms - 3 12-24 g/100m3 -
Onions and garlic 1 900-1800 mg/l 1 1260-1800 g/ha -
Pastures - 1 140-280 g/ha -
Potatoes 1 40-150 g/tonne - 1 42 g/tonne
Rice 1 60-150 g/100 kg seed 2 112-315 g/ha -
Soybeans 1 30-240 g/100 kg seed 2 225-315 g/ha -
Sugar beet - 2 200-400 g/ha -
Sweet potato 1 400 mg/l - -
Tobacco - 1 1350 mg/l 1 600 mg/l
Tomato - 3 225-450 g/ha -
Turf 2 20-36 g/100m2 -
TABLE 2. Thiabendazole - residues resulting from pre-harvest uses
Application Residues (mg/kg) at intervals (days) after application
Crop Country Year no. rate formulation 1 2 5 10 20 40 60
g.a.i/ha
Bananas Costa Rica 1973 12 146 flowable 0.01
(WHOLE) Dominica Rep. 1974 14 145 flowable 0.05
1975 10 145 flowable 0.05
Honduras 1972 1 158 flowable 0.06
Brazil 1976 6 135 flowable 0.06
1977 8 135 flowable 0.14
Ecuador 1976 10 125 flowable 0.03
Bananas Various Various 0.0 0.0 0.0 0.0
(PULP)
Onions Netherlands 1974 2 300 WP <0.1 <0.1
Soybean USA 1974 3 200 flowable 0.01
4 350 flowable 0.02
4 1100 flowable 0.04
Strawberries Netherlands 1974 4 3200 fumigant 0.24
1975 6 2400 fumigant <0.05
1976 7 2400 fumigant <0.05
Sugar beet USA 1967 2 200 flowable 0.07
1967 4 200 flowable 0.18
1967 6 200 flowable 0.01
Tomatoes Netherlands 1973 1 1200 fumigant <0.1 <0.1 <0.1
2 1800 fumigant <0.1 <0.1
4 1200 fumigant <0.1 <0.1
1973 1 300 WP <0.1
TABLE 2. Thiabendazole - residues resulting from pre-harvest uses
Application Residues (mg/kg) at intervals (days) after application
Crop Country Year no. rate formulation 1 2 5 10 20 40 60
g.a.i/ha
Wheat Netherlands 1974 1 300 WP <0.2
(GRAIN) Germany 1975 1 675 flowable 0.23
UK 1976 1 300 WP 0.03
Wheat Netherlands 1974 1 300 WP <0.2
(STRAW) Germany 1975 1 675 flowable 0.15
UK 1976 1 300 WP 0.25
Extensive trials carried out over several years in a number of
different regions of the USA have indicated that when a variety of
thiabendazole formulations are applied to seed wheat the highest
residue of thiabendazole recovered from grain harvested from various
cultivar seed was 0.03 mg/kg. This residue resulted only when the
application rate was increased to 2.5 times the recommended rate.
There is some reason to believe that even this residue is possibly an
artifact due to interference with the fluorophotometric method used
for the determination of thiabendazole residues.
Onions
Several studies carried in the Netherlands on onions grown from seed
treated with thiabendazole seed dressing and thereafter by two foliar
sprayings, indicated that the residues were below the limit of
determination (0.1mg/kg) 40 and 60 days after the application of the
foliar spray.
Potatoes
In addition to the extensive data evaluated in 1975 (FAO/WHO 1976),
further studies carried out in Canada, the United Kingdom, USA, the
Netherlands and Germany on potatoes treated with various formulations
of thiabendazole at rates ranging from 10 to 45 g/tonne indicates that
the residue on the unwashed whole potato may range from 1 to 16 mg/kg.
The thiabendazole residues found on potatoes treated by a mist spray
application at the recommended rate of 42 g/tonne ranged from 4.3 to
13 mg/kg with an average of 9.2 mg/kg.
This level is much higher than the residues found following spray
application conditions used in the US, which apply 6 to 12 g/tonne and
leave a residue of 1.8 to 2.3 mg/kg on the potatoes (see Table 3). In
Germany and the Netherlands the treatment of potatoes by fog
application is popular. Residue levels on potatoes treated with this
fogging technique tend to be quite low ranging from 2.2 to 4.4 mg/kg
following the application of 25 and 75 g thiabendazole per metric ton
respectively.
Obviously the residue detected on potatoes treated with a given rate
of thiabendazole will vary widely with the application technique. In
addition, the amount of residue found on the potato will depend on
whether the tuber is washed or not before analysis. Reduction in
residues of 20-50% have been shown in various trials after washing the
treated potatoes (see "Fate of residues" "In storage and processing".
Soybean
Thiabendazole is effective against a range of diseases which affect
soybeans and during 1974, 27 field trials were conducted in 14 states
which involved from 1 to 4 applications and a range of application
rates. Harvested seed was found to contain from 0.0 to 0.04 mg/kg of
thiabendazole. The highest residue was found in harvested soybean seed
from crops treated with 6 times the recommended rate.
TABLE 4. Thiabendazole residues in potatoes
Application Storage Unwashed Washed
Country Year No. g ai/tonne Formulation (days) Whole Peel Edible Whole Peel
portion
Canada 1974 1 - WP - 4.2
(Estey) 1 - WP - 6.2
UK
(Tisdale
and Lord) 1972 1 - WP - 16.2
UK
(Tisdale
and Lord) 1972 1 45 Dust - 2.3
22 Dust - 4.8
UK
(Logan) 1974 1 42 WP - 11.0
42 WP - 8.4
USA 1975 1 12 Flowable - 2.38
Netherlands 1976 1 10 WP 8 days 4.6 1.1
20 WP 8 days 14.0 1.8
40 WP 8 days 16.0 4.3
30 WP 5 months 5.8 1.5
UK 1976 1 40 WP 0 days 18.0
USA 1973 1 9.7 WP - 1.8 0.64
Germany 1975 1 27 Flowable 1 day 7.6 14.8 0.6 1.3
14 days 6.3 16.2 0.7 1.9
28 days 6.2 13.0 0.7 2.2
56 days 9.7 17.8 0.4 3.6
Strawberries
Thiabendazole has proved effective for use as a fungicide on
strawberries in greenhouses, applied by fumigation. In trials made in
the Netherlands treatments were made weekly applying 24 g of
thiabendazole per 100 m2. Strawberries harvested 3 and 4 days after
the last Treatment were mostly found to contain less than 0.05 mg/kg
of residue though in one trial a residue of 0.24 mg/kg was found.
Sugar beet
The manufacturers have demonstrated the usefulness of thiabendazole as
a post-harvest application on sugar-beet roots as they enter pile
storage for protection against beetrotting fungi and official approval
has been given for this use in the USA. Use on sugarbeets pre-harvest
has been approved in several countries. In an extensive trial in the
USA 5,000 tons of sugar beets were treated with a thiabendazole
suspension containing 1,500mg/l at the rate of 4 litres per ton. The
treated sugar beets going into storage were systematically sampled and
analysed as were sugar beets from the stock pile during removal for
processing 120 days later. Although the theoretical application rate
was 6 mg/kg, analysis revealed only 1.75 mg/kg immediately following
application though the concentration an individual samples ranged from
0.6 to 4.7 mg/kg. Apparently much of the spray w" absorbed on dirt
clinging to the sugar beet roots. After the sugar beets had been in
storage for 120 days the concentration of thiabendazole had declined
to approximately one-third (0.65 mg/kg), Individual samples indicating
residues in the range 0.2 to 2.1 mg/kg (See Tables 4 and 5).
Tomatoes
Thiabendazole has proved effective for use as a fungicide on tomatoes
in greenhouses, applied by fumigation. The rate of application is
12-18 g/100 m2
Trials carried out at a number of locations in the Netherlands
indicated that the residues on the tomato fruit were less then
0.1 mg/kg at all stages following repeated treatments.
FATE OF RESIDUES
In animals
Thiabendazole is rapidly metabolized and excreted in all species and
concentrations of the drug and its metabolites in tissues and excreta
diminish quickly to control levels. The major metabolite is the
5-hydroxy analogue generally found as its glucuronide or sulphate
ester.
The levels of thiabendazole or its metabolites are readily determined
in the various tissues and excreta of animals by a photofluorometric
procedure which, as used, is quite specific for these substances. A
description of the procedure used in the preparation of tissues and
the results of extensive investigations are given by
Tocco et al., (1965).
Additional data were supplied by the manufacturers (Merck Sharp and
Dohme, 1975); this information is summarized as follows.
Pigs
8 Pigs were given a single oral dose of 100 mg thiabendazole per kg
b.w. Four pigs were killed after 7 days, and 4 after 28 days. The
residue was determined in liver, kidneys and skeletal muscle by the
fluorimetric method of Tocco et al. (1965). No tissue residues of
thiabendazole or 5-hydroxythiabendazole (limit of detection
0.05 mg/kg) were found.
Three pigs received 1000 ppm thiabendazole in the feed during 2 weeks
and were killed at 0, 2 and 7 days after withdrawal. In 16 organs and
tissues thiabendazole and metabolites were determined. At day 0 tissue
residues ranged from 1.6-8 mg/kg, the highest levels being in kidney
and liver. At day 2 in muscle, livery kidney and brain, values of
0, 0.12, 0.19 and 0.31 mg/kg were found respectively, while at day
7 thiabendazole and metabolites were absent (< 0.05 mg/kg).
Cattle
The kidney, liver and muscle tissues of cattle become rapidly free of
thiabendazole and metabolite residues. Three day after an oral dose of
50 or 110 mg/kg thiabendazole no residues were detected in these
tissues (limit of detection 0.1 mg/kg). Thiabendazole was given to
3 lactating cows in dosages of 66, 110 or 220 mg/kg body weight.
Residues of thiabendazole and metabolites were determined in milk.
After 0-24 hr the highest residues were found, mainly as metabolites,
varying between 0.2-0.67 mg/kg. Approximately 0.1% of the total dose
was excreted in the milk. No residues were detectable 60 hr after
administration of the thiabendazole (Tocco et al., 1965).
5 Calves were fed continuously for 14 weeks a grain diet containing 0,
0.031, 0.10, 0.32 and 1.0% thiabendazole. When the animals were
sacrificed after 14 weeks, relatively high tissue levels of
thiabendazole plus metabolites could be determined: at a dose of
1% 16.7, 11.6 and 12.1 mg/kg in muscle, liver and kidney respectively.
At the lower dose levels the highest concentration was found in the
kidneys.
TABLE 4. Thiabendazole residues resulting from post-harvest uses
Application Residues (mg/kg) at intervals (days) after application
Crop Country Year no. rate formulation 1 5 10 20 120 150
g.a.i./ha
Pears Israel 1974 1 500 1.04
1000 2.0
2000 3.5
Bananas Costa Rica 1973 1 200 flowable 0.36
(WHOLE) Doninica Rep. 1974 1 400 flowable 0.75
1975 1 400 flowable 0.21
Honduras 1972 1 200 flowable 0.03
Brazil 1974 1 400 flowable 1.22
Bananas Various 1 200-400 flowable 0.02-0.05
(PULP)
Sugar beet USA 1976 1 1500 flowable 0.6-4.7 0.2-2.1
(6 g/tonne) (1.75) (0.65)
Sheep
Thiabendazole was orally administered to sheep in dosages of 60, 82
and 100 mg/kg body weight. After 4 hr the sheep receiving 60 mg/kg was
killed, the other 2 sheep after 7 days. At 7 days no residues were
detectable (thiabendazole only)q except for a residue of 0.09 mg/kg in
the liver of the sheep that received 100 mg/kg body weight.
In storage and processing
Studies carried out in Germany in 1975 (Table 3) indicate that there
is no significant change in the level of thiabendazole deposits on
potatoes treated post-harvest and kept in store for up to 56 days. The
level of residues in the whole potato, in the peel and in the edible
portion remain much as they were on the day following application.
However there seems to be a slight but significant trend for the
deposit to become transferred from the surface into the potato since
the residue in the whole washed potato increased from 1.3 mg/kg to
3.6 mg/kg over the 56 day period.
In separate experiments carried out in the United Kingdom in 1976,
when potatoes were treated at 40 and 80 g/tonne, a similar trend could
be observed. Although the concentration of thiabendazole in the
unwashed potatoes did not change significantly over a 21 day storage
period the concentration in the washed potatoes increased from 1.7 to
6.3 mg/kg and 2.2 to 7.5 mg/kg between days 4 and 21 of this period
(Table 5).
The effect of washing potatoes treated post-harvest with thiabendazole
is clearly demonstrated in Tables 3 and 5. In the UK experiments,
washing in running water removed approximately 90% of the residue when
carried out 4 days after treatment and approximately 75% when carried
out 21 days after treatment. It is assumed that after 21 days more
thiabendazole had been absorbed into the skin surface. Washing,
peeling and boiling removed approximately 99% of the thiabendazole
residues on the unwashed tubers. This was not influenced by the time
which elapsed after treatment. There was a slight but probably
insignificant increase in the residue in the chips prepared from
potatoes held 21 days following treatment.
The results from the experiments with boiled and chip potatoes suggest
that thiabendazole is only absorbed into the outer skin layer of the
tubers. This is confirmed by further experiments where the washed
tubers were baked without removing the skins. The residue in the whole
baked potato was considerably higher than in the corresponding potato
which were peeled before cooking. The baking of washed potatoes does
not significantly reduce the residue level present prior to cooking.
TABLE 5. Effect of processing on thiabendazole residues in potatoes; UK, 1976
Rate of application
40 g/tonne 80 g/tonne
Held in store 4 days 21 days 4 days 21 days
Unwashed 22.6 mg/kg 24.9 mg/kg 25.2 mg/kg 28.5 mg/kg
Washed 1.7 " " 6.3 " " 2.2 " " 7.5 " "
Washed, peeled,
chipped 0.1 " " 0.2 " " 0.2 " " 0.5 " "
Washed, peeled,
chipped 0.2 " " 0.2 " " 0.4 " " 0.3 " "
Washed, baked 1.7 " " 3.8 " " 2.3 " " 11.9 " "
TABLE 6. Effect of processing sugar beets on thiabendazole residues
Rate of application 6 g/tonne
Residue level at application 0.6-4.7 (mean 1.75± 0.68) mg/kg
Residue level after 120 days storage 0.2-2.1 (mean 0.65± 0.39) mg/kg
Residues in flume water 0.2 mg/kg
wet pulp 0.08 mg/kg
diffusion juice 0.1 mg/kg
pressed pulp 0.2 mg/kg
dried pulp 2.5 mg/kg
thick juice 0.44 mg/kg
sugar 0.00 mg/kg
molasses 0.70 mg/kg
pellets 1.26 mg/kg
Studies on the fate of thiabendazole applied to sugar beet going into
storage indicate that approximately two-thirds of the residues
disappear during 120 days storage. This appears to be due to the
sorption of the thiabendazole on the fine soil particles adhering to
the beet roots. This sorted material is not recovered by analysis and
in commercial practice is removed from the roots before processing.
The extensive study carried out under commercial conditions in the USA
(Merok Sharp and Dohme, 1977b; Table 6) indicates that thiabendazole
can be traced in most fractions of the sugar beet process through to
but not including the finished sugar. Since the thiabendazole content
of the sugar beet molasses was 0.7 mg/kg, it is clear that not all of
the residue is removed during the activated carbon and lime treatment
stages.
The sugar beet pellets, which are formed by adding about 4.2 tons of
molasses to 10.8 tons of dried pressed pulp and further drying the
composite back to 10.8 tons of extruded pellets, contain thiabendazole
residues from both pulp and molasses.
RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
Monitoring of fruit in the Netherlands in 1976 revealed that none of
137 samples of various varieties of citrus fruits, plums and
pineapples examined contained thiabendazole residues at levels above
national (and Joint Meeting) maximum residue levels. Only 16 of the
137 samples contained no thiabendazole (Netherlands Food Inspection
Services, 1976).
Data from the US Food and Drug Administration indicate that of eight
samples of citrus fruits examined four contained thiabendazole
residues at levels ranging from 0.02 to 1.0 mg/kg.
NATIONAL MAXIMUM RESIDUES LIMITS REPORTED TO THE MEETING
National maximum residue limits reported to the Meeting as established
or amended since the 1972 Joint Meeting are listed below.
Country Commodity MRL (mg/kg)
Australia apples, pears citrus 10
bananas whole) 3
bananas (pulp) 0.4
meat 0.2
milk 0.05
Country Commodity MRL (mg/kg)
Canada bananas (pulp) 0.4
potatoes 4
apples, citrus, pears 10
Israel citrus, pears 10
celery 5
bananas, strawberries 3
Netherlands tomato 0.1
grain 0.2
banana 3
citrus fruit 10
apples 6
New Zealand bananas, citrus 3
South Africa all food products 3
Sweden fruit and Vegetables except
potatoes 6
Switzerland banana (whole) 3
banana (pulp) 0.4
citrus fruit 6
USA dried citrus pulp 35
dried apple pomace 33
potato processing waste 30
citrus molasses 20
apples, citrus fruit, pears,
sugar beet tops 10
dried sugar beet pulp 3.5
bananas, potatoes 3
hubbard squash 1
sugar beets 6
wheat straw 0.2
milk, fat, meat, meat
by-products
of cattle, goats,
hogs, horses, sheep 0.1
soybeans, wheat grain 0.1
sweet potatoes 0.02
APPRAISAL
The world-wide use of thiabendazole as an agricultural fungicide has
grown greatly since it was first introduced as a post-harvest
treatment for bananas, citrus and pome fruit in the late 1960s. It is
now applied to many classes of crop and commodity in preplant and
pre-harvest as well as post-harvest treatments. Information was
available on many of these new applications together with data from
residue studies related to many of these uses.
The residue data indicate that the residues resulting from the
pre-plant and pre-harvest application of thiabendazole are generally
low to very low, some of the more important applications resulting in
no detectable residues.
Among the more important uses is the application of thiabendazole
alone or with other fungicides as seed dressings for a wide variety of
cereals and cotton. These uses do not give rise to residues in the
harvested crop. The use of thiabendazole, either alone or in
conjunction with other fungicides, pre-harvest on bananas, rice,
soybeans and teat has been studied and data on the residues arising
from such applications were evaluated. The use of thiabendazole as a
fumigant in glasshouses and similar situations has become increasingly
important. The residues resulting from such uses on tomatoes and
strawberries are remarkably low.
Thiabendazole has become increasingly important for the treatment of
stored potatoes to protect them against a variety of fungal rots. The
method of application has an important bearing on the level of the
resulting residue which is largely confined to the outer part of the
skin. Much of this residue is removed by washing. The amount removable
by washing decreases as the potatoes remain longer in storage. Farther
evidence has become available to demonstrate the fate of thiabendazole
residues in processed potatoes. This shows that up to 99% of the
residue present in the unwashed potato is removed prior to
consumption.
Extensive studies have been carried out with a view to proposing the
use of thiabendazole on sugar beets as they enter pile storage for
protection against beet rotting fungi whilst stored outdoors. These
studies revealed that a large proportion of the applied thiabendazole
becomes bound in the soil coating the beet roots. There is a further
loss during storage. The fate of the thiabendazole during the various
stages of beet sugar production has been studied. Whilst a significant
residue remains in the sugar beet pulp and in the molasses, no
residues remain in the beet sugar. These studies provide an adequate
basis for recommending maximum residue limits in sugar beet, sugar
beet pulp and sugar beet molasses.
Since a number of the commodities treated with thiabendazole, or food
wastes from such treated commodities, form the basis of a variety of
animal feedstuffs, the meeting considered further information on the
fate of thiabendazole in a variety of livestock. These studies showed
that when thiabendazole is administered to livestock, even at levels
vastly in excess of those likely to occur in practice, significant
residues occur in animal tissues but these disappear completely within
a few days of withdrawing the thiabendazole. These new studies serve
to confirm the recommendations made for a maximum residue limit in
milky meat and edible offal of cattle, goats, horses, pigs and sheep
at or about the limit of determination (0.1 mg/kg).
The meeting took note that a number of countries have extended or
amended their maximum residue limits for thiabendazole in a variety of
commodities.
Whereas in 1974 it was stated that residues resulting from the use of
thiabendazole consisted of thiabendazole and 5-hydroxythiabendazole,
it is recognized that this applies only to residues in foods of animal
origin such as meat, edible offal, milk and eggs. An analytical method
for measuring both parent compound and metabolite in such commodities
is available. Residues in foods of plant origin consist entirely of
thiabendazole. The recommendations are amended accordingly.
RECOMMENDATIONS
In the light of the new and previously available data, the following
additional or amended maximum residue limits are recommended. They
refer to thiabendazole only. The limits for potatoes (unwashed) and
potatoes (washed) have been replaced by a recommendation which directs
that potatoes be washed before analysis.
Commodity Limit, mg/kg
Sugar beet tops 10
Potatoes (washed before analysis) 5
Sugar beets 5
Sugar beet pulp 5
Sugar beet molasses 1
Raw grain 0.2
Onions 0.1
Strawberries 0.1
Tomatoes 0.1
FURTHER WORK OR INFORMATION
DESIRABLE
1. Information on the use pattern m cereals and an indication as to
whether the residue pattern on rice, barley and oats is similar to
that on wheat.
REFERENCES
Colmore, J.P. (1965) Chronic toxicity study of thiabendazole in
volunteers. Merok, Sharp and Dohme, unpublished report.
Estey. (1977) Results of Canadian potato trials 1974/75. Analysis
performed by Merok, Sharp and Dohme, Rahway, N.J., U.S.A.
Logan, C. Potato tuber disinfestation by thiabendazole mist
application. Agriculture in Northern Ireland, 48:, 438-440.
Logan, C. Tuber disinfestation by mist application. Potato Research,
17: 347.
Merok, Sharp and Dohme. (1975) Thiabendazole tissue residue studies in
animals. (Unpublished report).
Tisdale, M.J. and Lord, K.A. (1973) Uptake and distribution of
thiabendazole by seed potatoes. Pestic. Sci., 4: 121-130.
Tocco, D.J., Egerton, J.R., Bowers, W., Christensen, V.W. and
Rosenblum, C. (1965) Absorption, metabolism and elimination of
thiabendazole in farm animals and a method for its estimation in
biological materials. J. Pharmacol and Exp. Therapeutics 149 (2)
263-271.
FAO/WHO (1971) 1970 evaluations of some pesticide residues in food.
FAO/AGP/1970/M/12/1; WHO/Food Add/71.42.
FAO/WHO (1972) 1971 evaluations of some pesticide residues in food.
FAO/AOP/1971/M/9/1, WHO Pesticide Residue Series No. 1.
FAO/WHO (1973) 1972 evaluations of some pesticide residues in food.
FAO/AGP/1972/M/9/1; WHO Pesticide Residues Series No. 2.
FAO/WHO (1976) 1975 evaluations of some pesticide residues in food.
FAO/AGP/1975M/9/1; WHO Pesticide Residues Series No. 6.