434. Cyhexatin (Pesticide residues in food: 1978 evaluations)

CYHEXATIN JMPR 1978

Explanation

The 1973 Joint Meeting (FAO/WHO, 1974b) set a practical
residue limit, now called an extraneous residue limit (ERL), for
milk of 0.05 mg/kg (fat basis). This level was at or about the
limit of determination. The present Meeting considered new data
which indicated that the limit should now apply to whole milk and
milk products. The use of cyhexatin to control certain pests of
animals by direct application requires that the maximum residue
levels should be re-examined in the light of new residue data from
supervised trials, and that limits for meat, milk and milk products
should now be MRLs rather than ERLs.

New information was also received on some of the toxicological
requirements listed at the 1970 Meeting, and on uses and residue
levels in countries other than the U.S.A.

EVALUATION FOR ACCEPTABLE DAILY INTAKE

TOXICOLOGICAL STUDIES

Special studies on carcinogenicity

Sprague-Dawley rats (50 m + 50 f per group) were fed a diet
with 0, 1, 3 and 6 mg cyhexatin¹/kg b.w./day for 2 years.
Parameters evaluated included general appearance, mortality, body
weight, food consumption, absolute and relative organ weights,
gross morphology and detailed microscopy. Body weight and food
consumption were decreased and general debilitation noted in males
and females at the 3 and 6 mg/kg/day dosage, and body weights were
decreased in females in the 1 mg/kg/day group after about 450 days
on the diet. The 3 and 6 mg dose groups also showed atrophy of the
skeletal muscles of hip and thigh, particularly in females of the
highest dose group accompanied by a mild to moderate degenerative
myophathy. These changes in many rats were associated with variable
degrees of microscopic degenerative lesions of the lumbar spinal
cord and nerve roots. All dose groups showed prominent and
dose-related, pale mottled liver. Focal bile duct hyperplasia and
biliary fibrosis, both in males and females; in addition some areas
of focal cellular alterations were found. Focal bile duct
hyperplasia occurred at incidence rates of 8%, 39%, 62% and 72% in
males fed 0, 1, 3 and 6 mg/kg/day respectively and at rates of 8%,
50%, 72% and 72% in females fed the same dosage of cyhexatin.
Dose-related increases in relative weights (compared to body
weights) of brain, heart, kidneys, pituitary, liver and spleen were
found in males and/or females, the increases being significant for
all organs at the highest dose group, for the brain and heart also

¹ purity: 98.6% uncorrected, 97.2% corrected; impurities: related
tin compounds 2.9% and chlorine 0.1%.

for the 3 mg group and, for the heart of females only, also at the
1 mg group. However, since the absolute organ weight changes were
generally decreases, the increased relative organ weights is a
reflection of the proportionately greater reduction in body weights
of the exposed groups. The tumor incidence was not increased (Warner
et al., 1977).

Short-term studies

Cyhexatin given to young male mice for 7 days at
concentrations of 100 mg/kg diet gave a decrease in body weight of
24%. Absolute weights of heart, liver and spleen were also
decreased with 21, 32 and 61% respectively. Cyhexatin given to
mature male mice for 4 days at concentrations of 30, 100 and 300
mg/kg diet gave a decrease in body weight and relative weight of
spleen at the highest dose group. A considerable decrease in the
number of leucocytes was also found at this dose group (32% of
control); on the other hand, a slight increase was noted in the
level of haemoglobin, haematocrit and erythrocytes. All these
effects were also present at 200 mg but less pronounced. There was
no significant effect on the adrenal adrenalin level or on the
percentage of dry matter of the brain (Ishaaya et al., 1976).

COMMENTS

Cyhexatin did not increase the number of benign or malignant
tumors in a two-year rat feeding study with rats. Therefore the
original finding of an increased incidence of liver adenomas in
rats, could not be confirmed. However, the incidence of focal bile
hyperplasia was increased in a dose-dependent fashion and was
statistically significant at all dose levels (1,3 and 6 mg/kg),
both in males and females. This was a more detailed study using
more sophisticated methods than the study which was conducted 10
years earlier. Since this study did not reveal a no toxic effect
level, the previous indication that 3 mg/kg bw/day, causes no
toxicological effects in rats was withdrawn. Further studies to
elucidate the pathophysiological significance of focal bile
hyperplasia are required before a firm ADI can be allocated.

TOXICOLOGICAL EVALUATION

Level causing no toxicological effects

Dog: level in the diet adjusted to give 0.75 mg/kg bw

Estimated temporary acceptable daily intake for man

0.008 mg/kg bw

RESIDUES IN FOOD AND THEIR EVALUATION

USE PATTERN

Crop use-outside USA

Australia - cyhexatin is applied:

(i) to pome and stone fruits at 20g/100l (0.02%) concentration
two or more times throughout the season, and a
pre-harvest interval of 2 days in established;

(ii) to strawberries at 20g/100l at 2-week intervals throughout
the growing season, and a pre-harvest interval of 1 day
is established;

(iii) to various vegetables such as peas, beans, cucurbits at
20g/100l.

Netherlands - for the control of Red Spider mites

(i) to apples, pears, cherries (sweet and sour) and plums at a
concentration of 25g/100l water, and a rate of 0.4-0.5
kg/ha. The pre-harvest interval is 28 days.

(ii) to blackberries, raspberries, strawberries and red- and
black currants at the same concentration and a rate of
0.25-0.4 kg/ha. Spraying is carried out before
blossoming and after harvest.

(iii) to bell peppers, cucumbers, eggplants, gherkins, melons and
tomatoes (glasshouse only) at the same concentration and
application rate as (ii). The pre-harvest interval is 3
days.

South Africa - for the control of Red Spider mites cyhexatin is
applied:

(i) to apples and pears a concentration of 30 g ai/100l and a
rate of 0.9-1.5 kg ai/ha. The per-harvest interval (PHI)
is 3 days.

(ii) to peaches at 30g ai/100l and 0.75-0.9 kg ai/ha. The PHI is
21 days.

(iii) to plums at the rate of 30g ai/100l and 0.75-0.9 kg ai/ha.
The PHI is 14 days.

(iv) to tomatoes at the rate of 0.38-0.45 kg ai/ha, with a PHI
of 3 days.

Livestock Use

A wettable powder spray containing 500 mg cyhexatin per litre
of water is applied in the following dosages; 3l per cow 1 1/2l per
pig; 1l per goat; 1l per sheep (or dip in bath containing 250 mg
chyexatin/l).

The animals are treated totally. Repetition of the treatment
after 8 days is mandatory to kill mites that have survived the
previous treatment as eggs. No interval between treatment of cows
and use of milk is specified.

RESIDUES RESULTING FROM SUPERVISED TRIALS

Crops

In trials by Dow Chemical (Australia) Ltd. before 1971,
strawberries and beans were sprayed with cyhexatin. Strawberry
plots on two sites were sprayed fourteen times with either one
concentration (18.7g/100l or 0.02%) or two concentrations
(18.7g/100l and 25g/100l or 0.025%) of cyhexatin. Samples were
taken 0, 2, 4 and 10 days (Site 1) or 0, 5 and 10 days (Site 2)
after the last treatment. Results are presented in Tables 1.

Recovery tests carried out on the Site 1 samples gave 96% and
101% for organic and total tin respectively. The average total tin
values in strawberries, calculated as cyhexatin range from 0.43 to
0.78 mg/kg for the 18.7 g/100l rate and 0.56 to 1.05 mg/kg for the
25 g/100l rate.

Beans were treated once with one concentration (20 g/100l or
0.02%) cyhexatin and samples were taken four weeks after treatment.
Results are presented in Table 1 section D. Tin residues in treated
beans tour weeks after spraying did not differ significantly from
control.

In field trials in the Republic of South Africa apples, pears,
peaches, plums and tomatoes were sprayed with cyhexatin and
analysed for residues at various intervals after the last
treatment. The results of these tests are presented in Table 2.

Animals

To provide data in support of a proposed use of cyhexatin for
the control of mange mites on sheep (Getzendaner et al., 1972)
fifteen sheep were dipped twice in a vat containing 0.026% ai of a
25% w.p. formulation, with 10 days between dips. Samples of tissues
taken at slaughter 2, 7, 14, 28 and 60 days after the second dip
were analysed for total tin. Essentially no residue was found in
either omental or renal fat. Residues in muscle increased for 28

TABLE 1. Tin residues on strawberries and beans (A, B, C refer to strawberries - D refers
to beans)

Residue, mg/kg*
Days Organic tin* Total tin*
After As tin As cyhexatin Inorganic As tin As cyhexatin
Application tin

A. Source: Victorian Silvan.
Application Rate: 18.7 g/100l

Control 0.016 0.024 0.040
0 0.190 0.617 0.013 0.203 0.660
2 0.082 0.266 0.067 0.149 0.480
4 0.070 0.227 0.076 0.146 0.470
10 0.044 0.143 0.090 0.134 0.430

B. Source: South Australia
Application Rate: 18.7 g/100l

Control 0.019 0.010 0.029
0 0.220 0.714 0.022 0.242 0.785
5 0.140 0.456 0.027 0.167 0.542
10 0.111 0.361 0.027 0.138 0.448

C. Source: South Australia
Application Rate: 25 g/100l

Control 0.019 0.029
0 0.268 0.927 0.036 0.322 1.045
5 0.160 0.518 0.048 0.208 0.675
10 0.107 0.346 0.072 0.179 0.558

TABLE 1. (Cont'd)

Residue, mg/kg*
Days Organic tin* Total tin*
After As tin As cyhexatin Inorganic As tin As cyhexatin
Application tin

D. Source: N.S.W.
Application Rate: 0.02% a.i.

Control 0.028 0.07 - 0.048 0.15
28 0.031 0.10 - 0.050 0.16
28 0.015 0.05 - 0.015 0.05
28 0.030 0.08 - 0.036 0.12

* Results corrected for control and recovery.

TABLE 2. Tin residues on apple, pear, peach, plum and tomato

Residues (mg/kg) at intervals (days) after last application
Number of
Crop Rate Applications
0 1 2 3-4 7 14 16 21 28 29

Apple 35g ai/100l 2 1.23 0.54 1.0
" 4 1.04 0.83 0.73 0.67 0.50 0.59

Pear " 1 1.15 0.49 0.46
" 4 0.9 0.7 0.76 0.64 0.41 0.43

Peach " 1 3.05 1.09 0.77
" 4 3.33 3.88 3.74 2.58 1.81 1.11

Plum 30g ai/100l 2 3.74 0.41 0.32

Tomato 0.5 kg ai/ha 4 0.55 1.12 0.61 0.50 0.28 0.32
1 kg ai/ha 1 1.86 1.75 1.15 1.05 0.52 0.66

days to an average of 0.07 mg/kg of tin, then dropped to < 0.04 mg/kg.
The highest residue in liver was at two days after dipping averaging
0.07 mg/kg, dropping to < 0.04 mg/kg in 60 days. Kidney retained
about the same level of 0.06 to 0.09 mg/kg tin for 28 days, with
< 0.04 mg/kg after 60 days.

In another experiment, nine pigs were treated with a 500 mg/kg
spray to obtain information on residue levels of cyhexatin (Bant et
al., 1977). The animals were slaughtered 3, 15 or 30 days after
treatment and samples of diaphragm, liver, neck fat, neck skin and
kidneys were analysed. It was found that 3 and 15 days after treatment
the residues of cyhexatin in liver and kidney were just above the
limit of detection (0.04 mg/kg cyhexatin). In muscle, fat and skin
tissue, residues were below the limit of detection throughout the
sampling period.

Milk

One study has been conducted (Verschuuren, 1976) by the National
Dairy Station, Leiden, Holland. Seven cows were treated twice, with a
7-day interval between treatments, with 3l of spray containing 500 mg
cyhexatin/l. Milk from the cows was analyzed for both organic and
inorganic tin. The udders of 2 cows were washed before milking to
eliminate potential environmental contamination. As shown in Table 3,
the amounts of organotin and inorganic tin found in the milk are below
or just above the limit of detection (0.002 mg/kg) with an average of
0.003 mg/kg organic tin, and a maximum of 0.012 mg/kg. This is
equivalent to 0.01 mg/kg average and 0.04 mg/kg maximum residue,
calculated as cyhexatin.

In another study (Hollick et al., 1978) three cows were treated
twice with 31 of spray containing 500 mg/kg cyhexatin. Residues of
organotin were determined after 1 or 2 days to investigate
partitioning between butter fat and the aqueous phase. Residues in
whole milk were below or just above the limit of detection (0.02 mg/kg
as chyexatin), while after correction for control values mean residues
in butter fat were 0.02 mg/kg or less (Table 7). Hence, under
conditions of good veterinary practice, no real tendency has been
shown for the cyhexatin residue to concentrate in fat. This indicates
a need to revise the conclusions of the 1973 and 1975 Joint Meetings
(FAO/WHO, 1974b, 1976b).

The limit of detection depends on the quantity of the samples.
For routine analysis in food control laboratories, limits of
determination of 0.02 ppm for whole milk and 0.04 ppm for butter fat
are reasonable.

TABLE 3. Organotin residues in milk

Cow Organotin (mg/kg as Sn) at intervals (days)
after treatment

7 8 8 9
(p.m.) (a.m.) (p.m.) (a.m.)

1 n.d. 0.009 n.d. n.d.

2 n.d. 0.005 n.d. 0.012

3 0.006 0.008 n.d. 0.003

4 n.d. 0.005 n.d. 0.005

5 0.005 0.008 n.d. n.d.

6 (udder washed before
milking) 0.002 0.001

7 (udder washed before
milking) 0.012 0.002

n.d. = not detectable ( < 0.002 mg Sn/kg)

TABLE 4. Organotin residues in milk following spray treatment of cows with cyhexatin

Location : L.J. Boere, Holland

Animal Breed : Friesian

Treatment Data : Cattle were sprayed with 31 of a formulation
containing 500 mg a.i./l i.e. 1.5 g ai/animal

Treatment Dates : 7th February and 14th February 1978

Cow Day after Organotin residue, mg/kg calculated as
treatment cyhexatin ^{1) 2)}

Milk Butter
Treated Control Treated Control

1 1 0.03- <0.02 0.08- 0.04
0.03 0.04

2 1 0.02- <0.02 0.08- 0.04
0.02 0.04

3 1 0.02- 0.02 0.06- <0.04
0.02 0.04

1 2 0.03- - <0.04- -
0.03 <0.04

2 2 0.03- - <0.04- -
0.02 <0.04

3 2 <0.02- - <0.04- -
<0.02 <0.04

¹⁾ Results not corrected for control or recovery.
385
²⁾ Cyhexatin mg/kg = corrected Sn mg/kg X 118.7; corrected tin is tin found minus
reagent blank.

RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION

In a 1975 market basket survey in Australia, canned peaches
(among other commodities) were examined for contamination of the food
contents by tin compounds. The total tin content ranged from 5 to 83
mg/kg with the mean at 44.2 mg/kg, in the 72 samples examined. The
analysis did not identify the tin compounds determined. The mean and
range of tin residues found in canned peaches were of the same order
of magnitude as were found for the other canned fruits examined, none
of which had been sprayed with cyhexatin (as far as is known).
Cyhexatin residues have not been reported, though not specifically
sought, in raw produce (meaty grain, dairy products, fruit and
vegetables) examined continuously in routine national surveys.

METHODS OF RESIDUE ANALYSIS

There are no new methods of residue analysis to report, but a
discussion of the residue analysed is appropriate.

Definition of residue

In the methods of analyzing crops or animals for residues on
which national MRLs are established and on which the present
recommended MRLs are based, all of the organic tin including cyhexatin
and di- and mono- cyclohexyltin compounds are determined. This was
recognized by the 1970 Joint Meeting (FAO/WHO, 1971b). However, in the
recommendations for temporary MRLs the degradation products were
excluded by the description of the residue, although in fact they are
included by the methods of analysis.

In the 1973 evaluations (FAO/WHO, 1974b), it was stated that
practically all the organotin residue in oranges was present as
cyhexatin. For tea leaves, all the data were for cyhexatin per se.
Data on meat and milk were obtained by methods which determine total
organic tin.

In the 1974 evaluations (FAO/WHO, 1975 b), data are given on
gherkins, cucumbers, bell peppers and tomatoes, all based on total tin
determination.

To define the residues possibly present in the meat of animals
consuming cyhexatin, Smith and Fischer (1970, cited in FAO/WHO, 1971b)
determined that both cyhexatin and dicyclohexyltin oxide were present
in the tissues of rats given cyhexatin ^-119Sn for 90 days, with the
ratio of from 1:3 (dicyclohexyltin oxide:cyhexatin) 2 days after
cessation of feeding cyhexatin, to 3:1 after 80 days. This was also
true of rats fed cyhexatin for 2 years. (Anon. 1970a, cited in
FAO/WHO, 1971b).

Thus, a definition to cover all cases should include the
cyclohexyltin and organic tin derivatives of cyhexatin, and the
following definition is proposed.

Definition (to apply to all post and future recommendations for MRLs
for cyhexatin)

Cyhexatin residue: cyhexatin and its organotin metabolites
calculated as cyhexatin.

NATIONAL MRLs REPORTED TO THE MEETING

New information was received from Australia, South Africa and the
Netherlands, on maximum residue limits for cyhexatin in effect in
those countries. These are:

Australia Stone fruits - 3 mg/kg
Strawberries - 3 mg/kg
Apples, pears - 2 mg/kg

South Africa Apples, pears - 2 mg/kg
Peaches - 2 mg/kg
Plums - 2 mg/kg
Tomatoes - 2 mg/kg

Netherlands Apples, cherries
(sour and sweet)
pears, plums - 1 mg/kg
Blackberries, raspberries,
red and black currants,
strawberries - 0.2 mg/kg
Gherkins - 1 mg/kg
Bell peppers, cucumbers,
melons, tomatoes - 0.5 mg/kg

APPRAISAL

A need for the direct application of cyhexatin sprays to dairy
animals for the control of mites causing mange has necessitated a
re-examination of residues in milk. Data were available from trials on
dairy cows showing that, following recommended treatment practices,
organotin residues in milk (and butter) were at or just about the
limit of determination 0.02 mg/kg (0.04 butter) as cyhexatin 24 hours
after the last treatment. In addition, the data provided evidence that
accumulation of cyhexatin in butterfat did not occur. These new data
are contrary to the interpretation reported in 1975 (WHO/FAO, 1976b)
after re-examination of data presented in 1973 (WHO/FAO, 1974b). It is
appropriate, therefore, to express the recommended limit on the basis
of whole milk and milk products rather than on a fat basis. The
previously recommended limit of 0.05 mg/kg (as cyhexatin) in milk is
supported by the available data and because of the need for direct
application to animals, the previous temporary extraneous residue
limits (ERLs) for meat and milk should be converted to temporary MRLs.

Data were available on residues of cyhexatin in tissues of sheep
dipped twice at 10 day intervals in the miticide and on residues in
meat of pigs sprayed once with a cyhexatin solution. These data did
not indicate a need to revise the previously recommended temporary
limit of 0.2 mg/kg in meat.

Additional information was available to the Meeting on the use
patterns and results of field trials on fruits and vegetables from
Australia, the Netherlands and South Africa. Residue data from
Australia indicate that residues on strawberries would not exceed 1
mg/kg on the day of application and on beans would not exceed 0.2
mg/kg by 28 days post-treatment. Residue data from South Africa on
apples, pears, peaches, plums and tomatoes indicate that residues
would not exceed 2 mg/kg on each commodity after the recommended
pre-harvest interval.

In the first evaluation of cyhexatin by the 1970 Joint Meeting,
the recommendations for temporary maximum residue limits excluded the
organotin degradation products although they are determined by the
methods of analysis in use then and now. Subsequent reevaluations of
cyhexatin did nothing to clarify the situation. Therefore, a
definition of the residue is proposed which will cover those cases
where cyhexatin is essentially the only residue and also those in
which other organic derivatives of tin are present. This new
definition does not require a change in the values of previously
recommended limits.

RECOMMENDATIONS

The following temporary maximum residue limits are in addition to
those previously recommended except those for meat, milk and milk
products which replace the extraneous residue limits previously
recommended. The limits refer to cyhexatin and its organotin
metabolites determined as total organic tin and expressed as
cyhexatin. This definition applies also to all previous
recommendations.

Commodity Temporary Maximum
Residue Limits, mg/kg

Peaches, plums, strawberries 2

Beans 0.5

Meat 0.2

Milk (whole), milk products (whole) 0.05

FURTHER WORK OR INFORMATION

Required by 1980

1. Clarification of the no effect level in the rat with respect
elucidating the significance of focal bile hyperplasia at low dose
levels.

Desirable

1. A study to elucidate the possible effect on the immune system.

REFERENCE

Anonymous Information on cyhexatin from Australia.
(1978)

Anonymous Information on cyhexatin from South Africa.
(1978)

Bant, S., Braunius, W.W. and Hollick, C.B. Examination of pig
(1977) meat for the residue content of the anti-mange product
Dow Cyhexatin Miticide. Report provided by Dow
Chemical, Gouda, Holland.

CCPR Report of the Tenth Session of the Codex Committee on Pesticide
(1978) Residues May 29 - June 5, 1978. Alinorm 79/24.

Dow Chemical (Australia), Lt. Report No. 149. Plictran Residues in
(1971) Strawberries and Beans.

Dow Chemical, USA. Information on use pattern for cyhexatin on dairy
(1978) animals and definition of a residue of cyhexatin.

Getzendauer, M.E., Shover, R.J. and Corbin, H.B. A study of residues
(1972) of tin in tissues of sheep dipped twice in a vat
containing plictran R miticide. Report provided by the
Dow Chemical, U.S.A.

Hollick, C.B., Braunius, W.W. and Iosson, D.I. Report of Dow Chemcial
(1978) Company, Ltd., Kings Lynn, England, GHE-A-204. Residues
of cyhexatin in milk and butter from cow treated with
cyhexatin miticides.

Iahaaya, I., Engel, J.L. and Casida, J.E, Dietary triorganotins
(1976) affect lymphatic tissues and blood composition of mice.
Pestic. Biochem. and Physiol., 6: 270-279.

Verschuuren, A.G. Report of Dow Chemical Europe, GHE-P-425. Residue
(1976) analysis of cyhexatin in milk after application on cows
following the recommended dose level. Report based on
data obtained from National Dairy Research Station,
Leiden. Netherlands. Original report in Dutch by Dr.
W.G. de Ruig.

Warner S.D., Ayers, K.M. Gerbig, C.G. and Strebing, R.J. Results of
(1977) a two-year chronic toxicity study of tricylohexyltin
hydroxide administered to rats by the dietary route.
Unpublished report by Dow Chemical Co., U.S.A.

WHO/FAO 1980 evaluations of some pesticide residues in food.
(1971)

WHO/FAO 1973 evaluations of some pesticide residues in food.
(1974)

WHO/FAO 1975 evaluations of some pesticide residues in food.
(1976)

    See Also:
       Toxicological Abbreviations
       Cyhexatin (WHO Pesticide Residues Series 4)
       Cyhexatin (WHO Pesticide Residues Series 5)
       Cyhexatin (Pesticide residues in food: 1980 evaluations)
       Cyhexatin (Pesticide residues in food: 1981 evaluations)
       Cyhexatin (Pesticide residues in food: 1983 evaluations)
       Cyhexatin (Pesticide residues in food: 1989 evaluations Part II Toxicology)
       Cyhexatin (Pesticide residues in food: 1991 evaluations Part II Toxicology)
       Cyhexatin (JMPR Evaluations 2005 Part II Toxicological)