PESTICIDE RESIDUES IN FOOD - 1979
Sponsored jointly by FAO and WHO
EVALUATIONS 1979
Joint meeting of the
FAO Panel of Experts on Pesticide Residues
in Food and the Environment
and the
WHO Expert Group on Pesticide Residues
Geneva, 3-12 December 1979
FENBUTATIN OXIDE
Explanation
Fenbutatin oxide was evaluated by the meeting in 1977 and an ADI was
established. MRLs on a range of fruits and vegetables were
recommended and the fate when feeding food wastes to livestock was
evaluated.
The 11th Session of the CCPR (ALINORM 79/24) considered these
recommendations and requested that the Joint Meetings should:
a) review the MRL proposed for peaches (paragraph 154)
b) reduce the MRL for apples and pears (paragraph 155)
c) define the residue resulting from the use of fenbutatin oxide
(paragraph 155)
d) propose an MRL for grapes (paragraph 165).
RESIDUES IN FOOD AND THEIR EVALUATION
The summary of residue data on peaches in the 1977 monographs reflects
a cross section of data from supervised trials considered by the
Meeting. Whilst many of the data indicate that the residues on fruit
harvested 14 days after the last application range from 0.5 to 3.5
mg/kg, 60% of the residue levels are above 2 mg/kg and 22% are above 4
mg/kg. The meeting recognized that since the data from trials in
three distinctly different regions, California, South Carolina, and
South Africa, indicate residues ranging from 4 to 8 mg/kg it was not
unlikely that good agricultural practice in many other regions would
yield residues near to 7 mg/kg, the figure chosen for the MRL.
The meeting notes that in several trials, heavy rain (up to 75 mm) had
fallen only a few days before harvest, and this would have had a
tendency to lower the residue level. It also recognized that some
national governments had established MRLs in the range of 1.5 to 3.0
mg/kg. This raised the question as to whether the same data had been
available to all authorities. On the strength of the data available,
the meeting agreed that the MRL recommended in 1977 should not be
reduced.
So far as apples are concerned, the meeting confirmed the observations
of the 1977 Meeting that "in most instances residues in whole fruit
were below 3 mg/kg following a pre-harvest interval of 14 days. In a
few instances however, residues at harvest exceeded this figure, but
were essentially below 5 mg/kg". In fact, 33% of the residue trials
yielded residue levels above 2.0 mg/kg at harvest, 14 days after the
last application. Of these, 15% were above 3 mg/kg. There was little
or no reduction whether the apples were treated 28 days or 14 before
harvest. In the data presented in the 1977 monographs, over 20% of
the trials yielded residues above 2 mg/kg 28 days after application.
Residue levels 28 days after application ranged up to 5.7 mg/kg.
Recognizing the many varieties of apples, the widely differing
cultural practices and the wide range of climatic conditions in
apple-growing areas of the world, the meeting agreed that there was no
justification for reducing the MRL below the 5 mg/kg recommended in
1977.
In reviewing the data on pears, it was recognized that although the
number of trial results indicating residues above 2 mg/kg was less
than with apples, there were a number of cases recorded in the data
from the U.S.A. Since a significant proportion of the results from
trials harvested 28 days after application ranged well above 3 mg/kg
the meeting recommended to retain the MRL of 5 mg/kg.
As with other fruits, fenbutatin oxide residues on grapes decline only
slowly. A number of the trials considered in 1976 show residues at
30-56 days not significantly lower than the residues found 3 and 7
days after application. The pre-harvest intervals approved in various
countries range from 7 to 42 days. On the strength of these data, the
meeting recommended a MRL for grapes of 5 mg/kg.
Definition of Residue
The residue was defined in 1977 as fenbutatin oxide, excluding any
metabolites. This recommendation is supported by studies with
radio-labelled compounds an well as regular chemical analysis. It has
been shown that less than 5% of the total radioactivity originates
from the principal metabolites with less than 0.7% due to other
organo-tin metabolites. Inorganic tin represents approximately 10% of
the total tin in the residue. Studies on apples have shown that the
metabolites are degraded more rapidly than the parent, and thus
disappear from the residue. With citrus, the metabolites represent
approximately 3% of the residue, whereas on many different crops the
residue of metabolites is generally below the limit of determination
(0.04 mg/kg).
All of the residue data considered in support of the recommendations
made by the 1977 meeting were generated by sensitive analytical
methods designed to measure the parent compound, fenbutatin oxide,
alone.
The main additional relevant data relate to residue levels of the
degradation products 1,1,3,3 tetrakis
(ß,ß-dimethylphenethyl)-1,3-dihydroxydistannoxane (SD31723) and
ß,ß-dimethylphenethylstannoic acid polymer (SD 33608) in crops and
their significance in relation to the incidental residues in products
of animal origin. As a result of studies carried out on methods for
the analysis of these compounds, a method was developed by Shell (see
later) using glc and having a normally-achievable limit of
determination of 0.02 mg/kg for both degradation products. This method
was used in most of the new studies reported here.
Data obtained with this method and a few additional data obtained with
the previous method are given below. The crops include apples,
peaches and grapes which were included in the original review and also
a series of nuts which were not covered previously. These latter data
are included here since it is considered that they assist the
evaluation of the significance of degradation products in the total
residue present in treated crops. The data are summarised in Table 1.
With fruit samples the overall picture is the same as suggested by
data presented to the 1977 JMPR. For apples, where the method of
analysis employed was similar to that given in the 1977 submission, a
positive residue, at the limit of determination of 0.1 mg/kg, was
reported in only one of 21 treated samples examined.
The more sensitive method used for the grape and peach samples showed
the presence of small residues in several samples. These amounted to
a total of 0.11 mg/kg in a dried peach sample 15 days after the second
of two treatments and 0.08 mg/kg in the corresponding fresh material.
Grape samples harvested 14 days after three applications at the
recommended rate contained no measurable residues of either
degradation product, but a sample treated at an excessive rate under
similar conditions contained 0.21 mg/kg SD 31723 and 0.06 mg/kg SD
33608 against a content of 5.5 mg/kg fenbutatin oxide itself. In
dried grape pomace prepared from the same samples, residues were
correspondingly higher, but residue levels of the degradation products
were in total below 5% of the fenbutatin oxide level.
Data for nuts show that residues of parent acaricide in the non-edible
parts of the nuts are in some instances considerably higher than have
generally been reported in the edible parts of crops analysed. In
these nut samples easily measurable levels of SD 31723 and SD 33608
were also found. However, these did not exceed 5% of the level of
fenbutatin oxide present. Hence, the current residue situation for
crops in respect of degradation products indicates that the levels of
these products are small in relation to those of the parent product
and unlikely to exceed 5% of the fenbutatin oxide level. There is no
evidence from these data that these degradation products may exceed
the levels of parent acaricide.
Table 1. Residues of Fenbutatin Oxide breakdown products in Fruits and Nuts (Additional Data)
Interval between Ref.
Crop Dose Rate No. of last treatment Fenbutatin SD 31723 SD 33608 (Shell)
(Location) treatments and harvest Oxide
Apples 0.025% 3 0 days 1.8 0.1 - (A)
(Germany) 7 days 1.3 <0.1 -
14 days 1.8 <0.1 -
21 days 1.2 <0.1 -
28 days 1.0 <0.1 -
0.025% 3 0 days 1.7 <0.1 - (B)
7 days 1.2 <0.1 -
14 days 1.1 <0.1 -
21 days 0.95 <0.1 -
0.025% 3 0 days 2.6 <0.1 -
(SC formn.) 7 days 1.5 <0.1 -
14 days 0.65 <0.1 -
21 days 0.5 <0.1 -
0.025% 3 0 days 1.3 <0.1 -
7 days 1.1 <0.1 -
14 days 1.0 <0.1 -
21 days 0.5 <0.1 -
0.025% 3 0 days 2.3 <0.1 -
(SC form.) 7 days 1.5 <0.1 -
14 days 1.3 <0.1 -
21 days 1.0 <0.1 -
Peaches 0.0625% 2 15 days 1.1 (fresh) 0.08 <0.02 (D)
(California) 8.2 (dried) 0.08 0.03
Grapes 0.0625% 3 14 days 0.7 <0.02 <0.02 (E)
(California) 0:125% 5.5 0.2 0.06
Table 1. Continued...
Interval between Ref.
Crop Dose Rate No. of last treatment Fenbutatin SD 31723 SD 33608 (Shell)
(Location) treatments and harvest Oxide
Dried grape 0.0625% 3 14 days 5.3 0.1 0.05
pomace 0.125% 3.9 1.4 0.40
Walnut Hulls 0.03% 2 14 days 5.8 0.16 0.09 (F)
(California) 0.06% 2 14 days 6.0 0.12 0.05
0.03% 2 14 days 12.0 0.32 0.13 (G)
0.06% 2 14 days 5.1 0.15 0.07
Walnut Shells 0.03% 2 14 days 1.5 0.06 <0.02 (F)
(California) 0.06% 2 14 days 0.9 0.03 <0.02
0.03% 2 14 days 1.0 0.05 <0.02 (G)
0.06% 2 14 days 0.05 <0.02 <0.02
Walnut Meats 0.03% 2 14 days 0.05 <0.02 <0.02 (F)
(California) 0.06% 2 14 days 0.05 <0.02 <0.02
0.03% 2 14 days 0.04 <0.02 <0.02 (G)
0.06% 2 14 days <0.02 <0.02 <0.02
Almond Hulls 0.03% 2 14 days 24 1.1 0.34 (H)
(California) 0.06% 2 14 days 39 1.7 0.58
0.03 2 14 days 56 2.7 0.78 (I)
0.06 2 14 days 170 7.1 1.3
0.06% 2 14 days 29 1.5 0.25 (C)
0.125% 2 14 days 36 1.7 0.26
Almond Shells 0.03% 2 14 days 8.3 0.31 0.15 (H)
(California) 0.06% 2 14 days 3.5 0.10 0.07
Table 1. Continued...
Interval between Ref.
Crop Dose Rate No. of last treatment Fenbutatin SD 31723 SD 33608 (Shell)
(Location) treatments and harvest Oxide
Almond Shells 0.03% 2 14 days 13 0.3 0.12 (I)
(cont'd) 0.06% 2 14 days 36 1.3 0.30
0.06% 2 14 days 40 1.9 0.27 (C)
0.125% 2 14 days 45 2.2 0.35
Almond Meats 0.03% 2 14 days 0.16 <0.02 <0.02 (H)
(California) 0.06% 2 14 days 0.12 <0.02 <0.02
0.03% 2 14 days 0.13 <0.02 <0.02 (I)
0.06% 2 14 days 0.58 <0.02 <0.02
0.06% 2 14 days 0.16 <0.02 <0.02 (C)
0.125% 2 14 days 0.23 <0.02 <0.02
Pecan Shells 1.4 kg/ha 1 14 days 1.6 0.03 <0.02 (J)
(S.Carolina) 2.8 kg/ha 1 14 days 1.4 0.03 <0.02
Pecan Nut Meat 1.4 kg/ha 1 14 days 0.03 <0.02 <0.02
2.8 kg/ha 1 14 days 0.03 <0.02 <0.02
Residues in Products of Animal Origin
Additional experiments have been carried out in which cattle and hens
were fed high levels of fenbutatin oxide in their diet in order to
obtain further information on the residue consequences of using
treated crops as feed. For these experiments radio-labelled material
was not used and fenbutatin oxide and its degradation products were
determined using a sensitive recently developed glc procedure.
Cattle (ref. M)
In this experiment fenbutatin oxide was added to dairy concentrate at
two levels; 85.7 mg/kg and 857.5 mg/kg. This concentrate was then fed
daily to two batches of lactating Guernsey cows so that they either
received a total feed containing 11 mg/kg or 96 mg/kg. The experiment
was carried out over a period of three weeks during which levels of
fenbutatin oxide, SD 31723 and SD 33608 in the milk were monitored.
No residues of any of the three compounds were found in samples of
cream or skim milk of cows fed at 11 mg/kg or in skim milk from
animals receiving 96 mg/kg in their diet. Cream from the latter group
of cows was, however, reported to contain residues up to a maximum of
0.11 mg/kg fenbutatin oxide, but no SD 31723 or SD 33608 were found.
The limit of determination in this study was 0.02 mg/kg for each
compound (See Table 2).
At the end of the three-week experimental feeding period, the animals
were slaughtered and tissue samples (liver, kidney, muscle, fat, bone
and brain) taken for analysis. No residues of SD 33608 were found in
any sample. Similarly no SD 31723 was found in any tissue from cattle
given feed treated at the 11 mg/kg rate, nor in muscle, fat, bone or
brain at the 96 mg/kg intake level. Again the limits of determination
were 0.02 mg/kg. Only in liver and kidney from animals at the higher
feeding level were small residues of SD 31723 reported - up to a
maxima of 0.12 and 0.04 mg/kg respectively.
Fenbutatin oxide itself was found in kidney (0.08 mg/kg max.), liver
(0.07 mg/kg max.) and fat (0.06 mg/kg max.) at the higher level of
feeding, but was absent from samples from the lower rate animals (see
Table 2).
Grape pomace is not fed to cattle, but nut hulls are occasionally fed
at levels up to 15-20% in the diet. Hence, on the basis that cattle
will be given feed with hulls containing the highest residue so far
observed following recommended treatments, residue levels on feed are
unlikely to exceed 11 mg/kg on a whole feed basis. Thus, it is
unlikely that measurable levels of fenbutatin oxide or its two
degradation products would occur in milk, milk products or in meat.
Table 2. Maximum residue levels of fenbutatin oxide, SD31723 and SD33608 in milk and tissues of cattle
receiving fenbutatin oxide in the daily ration (values in mg/kg)
Sample Cream Skim milk Liver Kidney Fat
Feeding Level 11 96 11 96 11 96 11 96 11 96
Fenbutatin oxide <0.02 0.11 <0.02 <0.02 <0.02 0.07 <0.02 0.18 <0.02 0.06
SD 31723 <0.02 <0.02 <0.02 <0.02 <0.02 0.12 <0.02 0.04 <0.02 <0.02
SD 33608 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02
The results on bone, brain and muscle samples were all <0.02
Poultry (Ref. L)
White Leghorn laying hens were given fenbutatin oxide at 5 or 25 mg/kg
in their daily ration for up to 28 days. At the end of this period
some of the birds were given untreated feed for a short period.
Throughout the experiment, samples of eggs were taken. Birds were also
sacrificed at intervals and tissue samples taken for analysis.
None of the samples of light or dark meat, or fat were found to
contain fenbutatin oxide, SD 31723 or SD 33608 at a limit of
determination of 0.02 mg/kg. In the remaining tissue samples and in
eggs, maximum levels were found as shown in Table 3.
Hence, following use of grape pomace in poultry feed, residues of SD
31723 and SD 33608, but not fenbutatin oxide, may occur at measurable
levels in liver and kidney, but are unlikely to be present in other
tissues. Eggs may conversely contain small levels of fenbutatin
oxide, but not its degradation products. Nut hulls are not fed to
poultry.
Table 3. Residues in poultry tissues and eggs
Sample Eggs Liver Kidney
Feeding level 5 25 5 25 2 25
Fenbutatin oxide 0.02+ 0.12++ <0.02 0.04 <0.02 0.03
SD 31723 <0.02 <0.02 0.03 0.12 <0.02
0.04
SD 33608 <0.02 <0.02 <0.02 0.04 <0.02
<0.02
Levels in meat and fat all <0.02.
+ 0.17 in yolk; ++ 0.25 in yolk.
Conclusions
The new evidence presented confirms earlier data showing that residues
of the two degradation products of fenbutatin oxide, SD 31723 and SD
33608, are unlikely to exceed 10% of the residue of fenbutatin oxide
in crops. When treated crops are fed to cattle residue levels of the
degradation products are unlikely to rise above the limit of
determination of the analytical method in milk or tissues. However,
in experiments where residues have been found in milk, they have
occurred entirely as fenbutatin oxide. In animal tissues, residues
have also been found following feeding at an excessive rate. These
residues have been shown to consist of fenbutatin oxide and SD 31723.
SD 33608 has not been found.
With poultry, the experiments have shown that small residues may occur
in eggs and that these will consist entirely of fenbutatin oxide.
Poultry meat, apart from liver and kidney, are unlikely to contain
measurable levels. In the two tissues mentioned, however, small
residues consisting of fenbutatin oxide and SD 31723 may occur.
It is thus only in some animal tissues that appreciable amounts of
degradation products of fenbutatin oxide may be found. Apart from
liver and kidney, these are unlikely to be at measurable levels and
where they do occur they are likely to consist of SD 31723 with
fenbutatin oxide at roughly the same order of magnitude.
METHODS OF RESIDUE ANALYSIS
The method previously used to obtain data on SD 31723 submitted to the
1977 JMPR, was based on thin-layer chromatography and was capable of
achieving a limit of detection between 0.1 and 0.4 mg/kg, depending on
the nature of the sample.
Recently, a technique for determining residues of SD 31723 and SD
33608 together with fenbutatin oxide, by gas-liquid chromatography
using a tin sensitive flame photometric detector, has been developed
(Ref. K). The samples are extracted with chloroform and HCl, and the
chloroform extract evaporated to dryness. The residue is dissolved in
hexane and partitioned repeatedly into acetonitrile and finally into
ether. The ether solution is then methylated with methyl lithium.
Excess of the latter is destroyed with isopropanol and water and the
aqueous phase is extracted with hexane. Clean-up is effected by
chromatography on Florisil and the appropriate fractions of eluate
analysed by glc. A limit of determination of 0.02 mg/kg for each
product is normally achievable with this method.
NATIONAL LIMITS REPORTED TO THE MEETING
The following limits, additional to those recorded in 1977, were
reported to the meeting:
Canada mg/kg
Apples, pears 3
Citrus fruit 3
New Zealand mg/kg
Pome fruit 1
Stone fruit 1
APPRAISAL
Fenbutatin oxide has been reviewed at the request of the 11th Session
of the CCPR. The meeting examined new residue data together with that
considered previously and confirmed the maximum residue limit for
peaches, apples and pears.
It was noted that metabolites of fenbutatin oxide disappeared from
treated fruit and vegetables at a more rapid rate than the parent
compound and were generally present only in insignificant
concentrations. Though these metabolites could be found in liver and
kidney of experimental animals fed excessive concentrations of the
pesticide, they did not occur after feeding levels likely to be
encountered in practice. The determination of metabolites requires
separate analytical procedures and the meeting confirmed that the
definition of the residue included only the parent fenbutatin oxide.
On the strength of the residue data published in the 1977 monograph,
the meeting recommended a MRL for fenbutatin oxide on grapes. Because
the residue level is not significantly influenced by the interval
between application and harvest, the meeting recommended that the MRL
for grapes not be linked with a preharvest interval.
RECOMMENDATIONS
The following additional maximum residue limit for fenbutatin oxide is
recommended. It refers to fenbutatin oxide, excluding any
metabolites:
Commodity Limit, mg/kg
Grapes 5
FURTHER WORK OR INFORMATION
Desirable
The further information listed in 1977.
REFERENCES
The references in the Tables are to a series of unpublished Reports
received from the Shell International Chemical Co. and indexed from A
to M.