THIABENDAZOLE JMPR 1972
In 1970 the Joint Meeting evaluated the available data on
thiabendazole, and an ADI of 0.05 mg/kg/day was recommended (FAO/WHO,
1971). Tolerances were proposed for citrus fruit and bananas to take
account of the use of this fungicide for post harvest treatments. In
1971 recommendations were made for the residues resulting from the
treatment of pome fruit (FAO/WHO, 1972). Since that time, considerable
quantities of citrus fruit and bananas have been treated with
thiabendazole and much of this has entered international trade.
Studies have shown that for satisfactory inhibition of sporulation of
moulds which stain citrus fruit and produce unacceptable odour, taste
and appearance, every fruit must be treated in such a way that an
adequate deposit of thiabendazole is left on the skin. The minimum
effective concentration on the skin is equivalent to 6-7 ppm on the
whole fruit. To ensure that this level is maintained, some fruit
should receive up to 10 ppm thiabendazole, the level depending on skin
texture, fruit size and method of applying the wax.
RESIDUES IN FOOD AND THEIR EVALUATION
The application of thiabendazole to citrus fruit, including dipping
and spraying with suspensions and the incorporation in the wax used
for preventing moisture loss during storage, shipment and marketing,
is extensively practised in the U.S.A., Israel, Australia and South
The citrus fruit industry in several countries, including the U.S.A.,
Israel and South Africa, has found that the dipping process is not
compatible with production methods and equipment used routinely in
packing houses. The installation of equipment, space and drying
facilities to allow the introduction of a dipping process would entail
additional costs and slow down fruit processing. Admixture with wax
emulsions is therefore preferred (Anon., 1972).
One of the objectives in applying thiabendazole to citrus fruit is to
avoid the necessity of using diphenyl impregnated wraps, liners or
inserts in the packages (Eckert and Kolbezen, 1971a). To date, citrus
fruit packing houses - at least in the U.S.A. - have been reluctant to
discontinue the use of diphenyl while there was a possibility that
citrus fruit treated with thiabendazole at rates below the tolerance
limit of 6 ppm might allow the development of some mouldy fruit. To
avoid significant spoilage and soiling, all thiabendazole treated
fruit has also been protected by diphenyl.
Work at the University of California (Eckert and Kolbezen, 1971b) has
shown that citrus fruit treated with thiabendazole in wax emulsion is
as well protected against sporulation as similar fruit protected with
diphenyl, provided the concentration on the skin is sufficiently high.
Data on extensive trials were supplied to the Joint Meeting (Anon.,
1972) with a request that the 6 ppm tolerance be revised to
accommodate the higher rate of application needed. The results of
these trials indicate that a significant proportion of the fruits in
any consignment will contain residues of thiabendazole approaching 10
ppm on the whole fruit.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Results of packing house trials carried out in Israel with fruit
shipped to and analysed in the Netherlands in 1970 show that when 150
fruit from 13 consignments (10 - 20 from each) were analysed for
thiabendazole residues, the overall average was just under 3.0 ppm.
The variation in residue levels on individual fruits ranged from
0.43 - 7.35 ppm (FAO/WHO, 1971).
The Netherlands Delegation to the Codex Committee on Pesticide
Residues carried out a statistical analysis of the data and showed
(Kruysse, 1971) that for each of the 13 consignments the upper 95%
confidence limit ranged from 1.18 to 8.92 ppm. Six of the 13
consignments were estimated to contain fruit with residues above the
tolerance limit of 6 ppm notwithstanding the average of 3 ppm. This
indicates that under practical conditions many consignments would
violate the tolerance if it remained at 6 ppm.
Trials carried out at the University of California (Eckert and
Kolbezen, 1971a and 1971b) on numerous varieties of citrus fruit
demonstrated that wax emulsion containing approximately 5 000 ppm
(0.5%) thiabendazole would give surface residues of sufficient
magnitude to inhibit the growth and sporulation of Penicillium
digitatum on the surface of decaying oranges. The lack of uniformity
of residue from one fruit to another in any lot of fruit which has
been treated by commercial equipment makes it necessary to recommend
concentrations well above the minimum effective levels determined in
Table 1 gives the level of thiabendazole residues found on citrus
fruit treated with a water-emulsion wax containing several levels of
thiabendazole (Anon., 1972).
Fourteen large citrus fruit packing houses took part in officially
supervised trials to determine the efficiency of thiabendazole/wax
treatment for reducing sporulation and preventing wastage. The fruit
was stored under conditions typical of shipping, and portions were
exported to Europe where the cartons and contents were inspected by
inspectors from the U.S. Department of Agriculture.
TABLE 1 Residues of thiabendazole on citrus fruits treated
with a water emulsion wax
Formulation1 mg TBZ/kg fresh fruit2 3
(mg TBZ/kg wax) Orange Lemon Grapefruit
Initial 1965 1.25 1.94 2.79
Final 1965 1.06 1.97 2.61
1.22 1.85 2.74
1.08 2.32 2.35
1.06 1.80 2.74
1.30 1.92 3.29
Mean 1.16±0.11 1.96±0.18 2.75±0.30
Initial 3065 3.53 5.32 3.51
Final 4244 3.69 4.23 3.48
4.41 4.96 4.59
4.38 6.02 4.95
3.58 4.13 4.48
3.37 5.47 4.82
Mean 3.82±0.44 5.02±0.73 4.30±0.64
Initial 5784 5.65 8.41 4.68
Final 6206 5.65 9.19 4.86
5.80 7.77 4.86
5.71 7.39 5.49
8.32 8.41 5.73
5.36 10.25 5.84
Mean 6.08±1.09 8.57±1.04 5.31±0.48
Initial 8869 11.4 14.0 9.6
Final 8383 9.4 13.6 11.4
11.8 13.4 8.9
12.2 15.2 11.6
12.8 14.1 9.6
12.9 13.3 10.5
Mean 11.7±1.3 13.9±0.7 10.2±1.1
1 Samples collected at spray nozzle before and after fruit treated.
2 Values obtained by analysis of individual fruit. Value following
mean is the standard deviation.
3 Average surface areas: orange - 141 cm2, lemon - 128 cm2,
grapefruit - 231 cm2.
It was demonstrated that all varieties of citrus can be protected
during shipment, provided the total thiabendazole deposit exceeds
6 - 9 ppm on the whole citrus fruit. It was concluded that the
residues on most fruit would not exceed 10 ppm. Table 2 gives results
of assays for thiabendazole residues on citrus from the commercial
packing houses taking part in the above trial (Anon., 1972).
TABLE 2 Summary of assays for thiabendazole (TBZ) residues
on citrus fruit1
Experiment Citrus TBZ TBZ residue
(no.) variety concentration in in the fruit
or species the coating (ppm) (ppm)2
1 Valencia 6 2003 4.7
2 Valencia 6 000 3.0
3 Valencia 5 500 4.8
4 Grapefruit 6 4003 3.3
5 Lemon 6 000 5.2
6 Valencia 7 800 7.4
7 Navel 5 500 9.0
8 Lemon 7 7443 7.4
9 Lemon 7 9203 7.1
10 Navel 7 800 5.6
11 Navel 6 000 5.1
12 Lemon 6 000 8.3
13 Lemon 10 000 5.2
14 Lemon 12 000 5.7
1 Based on actual present practices of a selection of packing
houses, and reflecting a highly variant usage pattern. Data
obtained from fourteen commercial packinghouse trials
conducted from 26/3/71 through 25/3/72.
2 Average residue values of data obtained from 1-4 analytical
laboratories involved in the study.
3 Values obtained from actual analysis of coating samples, other
values are calculated theoretical concentrations.
The size, skin texture and species of citrus fruit influences the
amount of wax coating, and hence the amount of thiabendazole,
deposited on the skin. Equipment and method of application are also
important. Table 3 indicates the effect of fruit size, species and
concentration of thiabendazole on the level of the deposit on the
fruit (Anon., 1972).
TABLE 3 Effect of size and species on residues of thiabendazole (TBZ)
on citrus fruits
% TBZ Species Size Diameter mg/kg g/cm2
in wax (gm) (cm)
0.3 Orange 180 5.6 3.24 ± 1.25 3.33
138 6.1 3.45 ± 1.45 3.68
113 6.6 2.75 ± 0.78 3.06
88 7.2 2.59 ± 1.03 3.29
Lemon 200 5.1 3.45 ± 1.35 3.57
140 5.6 3.06 ± 1.41 3.03
115 6.1 3.65 ± 0.52 3.67
95 6.5 3.63 ± 0.22 4.22
0.5 Orange 180 5.6 6.22 ± 2.10 6.29
138 6.1 6.99 ± 0.96 7.28
113 6.6 5.75 ± 2.04 6.57
88 7.2 6.93 ± 2.46 8.55
Lemon 200 5.1 9.15 ± 2.53 8.12
140 5.6 6.95 ± 2.01 6.75
115 6.1 7.58 ± 1.64 7.76
95 6.5 6.98 ± 1.24 7.79
1 Mean and standard deviation of six analyses.
Oranges treated in South Africa with a wax emulsion containing 16 000
ppm (1.6%) thiabendazole were analysed in the Netherlands to determine
the degree of penetration of thiabendazole into edible portion. Table
4 indicates that approximately 9% of the total is found in the edible
portion with a level of approximately 1 ppm (Anon., 1972).
TABLE 4 Thiabendazole (TBZ) residues in the edible portion
of oranges treated with high doses1
Fruit TBZ residue TBZ residue TBZ residue
(no.) in whole in peel (ppm) in edible
fruit (ppm) portion (ppm)
1 9.0 34.3 1.16
2 7.7 26.6 1.19
3 6.2 25.0 0.63
4 7.3 23.8 0.99
5 6.2 19.1 0.83
6 7.7 26.0 0.39
7 5.3 22.4 0.74
8 8 3 35.4 0.84
Mean 7.2 26.6 0.85
1 16 000 ppm thiabendazole brush on, FMC wax.
In data submitted to the U.S. Environmental Protection Agency (Merck,
Sharpe and Dohme Co., 1972) it was shown that the average
concentration of thiabendazole in fresh orange juice (single strength)
was 0.14 ppm when fruit with an average residue of 5.10 ppm was
converted commercially into juice.
The thiabendazole residue in dried citrus pulp prepared from unwashed
fruit, previously treated with thiabendazole in wax so as to leave a
residue of 10 ppm, is calculated to be 35 ppm. Fruit with a residue of
5.10 ppm produced dried pulp containing 17.43 ppm thiabendazole. Dried
citrus pulp is used for cattle feed at a rate not above 20% of the
mixed ration. Studies reported earlier (FAO/WHO, 1971) indicate that
when thiabendazole is fed to cattle at rates up to 20 ppm in the whole
ration no detectable residues appear in the milk.
New data were available for consideration by the Joint Meeting,
including a statistical analysis of analytical data showing that many
individual fruit will contain residues greatly in excess of 6 ppm when
thiabendazole is used for the effective control of post harvest decay
and for the suppression of sporulation. In view of the importance of
finding alternatives to diphenyl for this purpose, the Meeting
considered that the tolerance should be raised to provide for these
higher residue levels. Due consideration was given to the data
indicating that only a small proportion of the residue was in the pulp
or would find its way into citrus fruit juice and other citrus
The recommendation proposed in 1970 for a tolerance of 6 ppm
thiabendazole on whole citrus fruit is amended as follows:
Citrus fruit 10 ppm
This tolerance applies to residue levels likely to be found in samples
of all types of citrus fruit immediately following the application of
thiabendazole in wax emulsion. Due to the stability of the deposit it
is not expected that any significant change in residue level will
occur during storage, shipment and distribution of citrus fruits.
FURTHER WORK OR INFORMATION
Anon. (1972) Joint submission by citrus industries of
California - Arizona, Israel and South Africa and by Merck, Sharp and
Dohme International to FAO. (unpublished)
Eckert, J.W., and Kolbezen, K.J. (1971a) Chemical treatments for the
control of post harvest diseases of citrus fruit. Proc. 6th British
Insectic. Fungic. Conf., p.683 - 693.
Eckert, J.W. and Kolbezen, M.J. (1971b) Effect of levels of
thiabendazole residues on sporulation of Penicillium digitatum on
citrus fruit. Report dated 11 June 1971, University of California,
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.
Kruysse, A. (1971) The determination of an acceptable quality level of
thiabendazole in citrus fruit and the selection of a standard sampling
inspection plan. Paper submitted to the Ad Hoc Working Group, Codex
Committee on Pesticide Residues, Copenhagen. CX/PR/WG 71/10 Add. 2.
Merck, Sharp and Dohme Co. (1972) Petition to the U.S. Environmental
Protection Agency for the establishment of tolerances for
thiabendazole on citrus fruits (30/10/72).