PESTICIDE RESIDUES IN FOOD - 1984
Sponsored jointly by FAO and WHO
EVALUATIONS 1984
The monographs
Data and recommendations of the joint meeting
of the FAO Panel of Experts on Pesticide Residues
in Food and the Environment and the
WHO Expert Group on Pesticide Residues
Rome, 24 September - 3 October 1984
Food and Agriculture Organization of the United Nations
Rome 1985
BENDIOCARB
Explanation
Bendiocarb was evaluated by the Joint Meeting in 1982 at which
time a temporary ADI was allocated. 1/
The 1982 JMPR required submission of 1) historical data of total
lymphoreticular tumours in the CFY strain of rats used in the long-
term study, and 2) a short-term (28 days) study in dogs to clarify the
relationship between dietary intake of Bendiocarb and terminal
erythrocyte and brain cholinesterase activity, using an appropriate
method for cholinesterase determination. Additional data have been
submitted and are reviewed in this monograph addendum.
Corrigenda: The NOEL for the dog in the 1982 evaluations is
incorrect. It should be 0.7 mg/kg bw/day.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Absorption, Distribution and Excretion
Man
An area on the forearm of each of six male volunteers was exposed
for 3 h to 14C- Bendiocarb (as an aqueous suspension) at a dosage of
0.01-0.02 mg/kg bw under occluded conditions in a warm environment and
non-occluded conditions in a cooler environment. The data indicate
that Bendiocarb was absorbed (as measured by 14C- urinary excretion)
more rapidly and to a greater extent (18 percent total urinary
excretion) under an occlusive dressing than on non-occluded skin
(6 percent total urinary excretion). The study also showed that
Bendiocarb was incompletely removed by washing and formed a depot in
the skin. Some Bendiocarb (generally less than 1 percent of that
applied) remained on or in the skin 48 h after treatment. The only
urinary metabolite formed was 2,2-dimethyl-l,3-benzoxodiol-4-ol in
conjugated forms (Challis, 1982).
1/ See Annex 2 for FAO and WHO documentation
TOXICOLOGICAL STUDIES
Special Study on Carcinogenicity
Rat
Evaluation by trend analysis of historical data on the incidence
of total lymphoreticular tumours was done in the CFY strain of rats
used in the long-term study. It demonstrated that the incidences of
lymphoreticular tumours in treated and untreated groups of each sex
were not significant, with a calculated chi-square value of 2.45 at
one degree of freedom. None of the tumour types was observed more than
twice in one sex at any dose level, indicating the absence of any
consistent tendency for the recurrence of tumourigenicity in a
particular organ, and there was no demonstrated decrease in latency.
There was no evidence that tumours adversely affected survival.
Moreover, as shown in Tables 1 and 2, the incidence of lymphoreticular
tumours among untreated control groups in concurrent studies, at the
same laboratories (Huntingdon Research Centre) and in the same CFY rat
strain, are comparable to the overall incidences observed among
treated groups in the present study and, therefore, are not compound-
related.
Short-term Toxicity
Dogs
A series of investigations of the factors influencing assessment
of effects of Bendiocarb on blood and brain cholinesterase in the dog,
including controlled alterations of feeding conditions, sampling
times, sample storage and the analytical method, led to the
development of an experimental model for monitoring cholinesterase
effects of Bendiocarb. The principal features of this test system are:
1. A 1-h feeding period following overnight fasting recording the
dose ingested.
2. Blood samples within 1.5 h after the end of the feeding period.
3. Blood samples rapidly chilled and assayed virtually immediately
for whole blood cholinesterase.
4. Brain samples within 2 h after the end of the feeding period,
with chilled homogenate prepared and assayed immediately after
death.
5. Reference (normal) activity for whole blood obtained from
pre-exposure sample and for brain from 24-h recovery sample at
room temperature.
6. Modification of the Ellman analytical technique, adjusting sample
volume and buffer strength.
TABLE 1. Observed Incidence of Lymphoreticular Tumours
Tumour Type Sex Dose Level (ppm)
0 2/10 20 200
No. Examined/Group 200 100 100 100
Reticulum cell sarcoma M 1 1 1 2
F 0 1 0 0
Myeloid leukaemia M 1 0 2 1
F 1 0 0 0
Lymphatic leukaemia M 0 0 1 2
F 0 0 0 0
Thymic lymphosarcoma M 1 2 1 1
F 0 1 0 0
Mediastinal lymphosarcoma M 0 0 0 0
F 0 1 0 0
Mast cell leukaemia M 0 1 0 0
F 0 0 0 0
Total L.R. Tumours (%) M 3 8 10 12
F 1 6 0 0
M+F 2 7 5 6
TABLE 2. Historical Incidence of Lymphoreticular Tumours
Study 1 2 3 4 5 6 7 8 9
Males 0/35 2/40 0/48 1/49 0/38 2/38 1/50 1/49 1/49
% 0 5 0 2 0 5 2 2 2
Females 0/50 0/50 1/48 1/50 1/49 1/49 3/50 3/50 1/50
% 0 0 2 2 2 2 6 6 2
These features were developed during successive studies on Bendiocarb.
The refinement of cholinesterase monitoring is evidenced by the
consistency of the effects on cholinesterase activity observed in the
chronic dog study, i.e. recurrent reductions over the 2-year treatment
period of whole blood cholinesterase activity at least 30 percent
below pre-exposure levels in individuals administered 500 ppm
Bendiocarb in the diet. Previous acute and sub-chronic studies
demonstrated complete recovery from anticholinesterase effects
following feeding at dietary levels of 500 or 1000 ppm. Brain
cholinesterase activity was also similarly decreased after 52 and 104
weeks of treatment at 500 ppm and complete recovery was observed after
24 h at room temperature. No consistent effects were detected at 100
or 20 ppm.
All animals were fasted overnight at each monitoring stage in
order to minimize the expected and unavoidable wide variation in the
amount of diet ingested by individuals in the same group.
A uniform dose-effect correlation can be demonstrated when the
amount of Bendiocarb actually ingested in the feeding period is
considered, with statistically significant reductions in
cholinesterase activity repeatedly associated with doses greater than
5 mg/kg. This uniformity of response to a given dose of Bendiocarb can
also be shown to extend to the degree of effect, with more than 70
percent of all instances of ingestion of at least 5 mg/kg being
associated with anticholinesterase activity falling within a narrow
range that equates to 2-5 percent cholinesterase inhibition per mg/kg
Bendiocarb dose.
It is further evident that the individual variation in response
within and between dose groups observed in both the 16-week and
chronic dog studies was related to the amount of Bendiocarb ingested
rather than to the dietary level, given uniform conditions of feeding,
sampling, analysis, etc. The variability in individual food intake
during short feeding periods is a consequence of normal daily
fluctuations in appetite and can produce very different degrees of
cholinesterase inhibition. Thus, both the daily variation in amount of
food ingested, as well as the pattern of eating, present limitations
to the uniformity of response achievable experimentally in dogs.
However, since blood samples were taken 1.5 h after feeding, and
considering the rapid reversibility of cholinergic effects from methyl
carbonates, it was considered adequate to evaluate the inhibitory
effect on cholinesterase enzymes in the dog. Therefore, the original
concerns of the 1982 Meeting were alleviated.
COMMENTS
Bendiocarb was evaluated in 1982, at which time a temporary ADI
was allocated with a request for further information on historical
data on the incidence of total lymphoreticular tumours in rats in the
long-term study, and for a short-term study in dogs.
Historical control data and considerations on the statistical
analysis of incidences of lymphoreticular tumours provided indications
that the observed differences among control and treated groups are of
insufficient extent and consistency to indicate any treatment-related
effect on tumourgenicity. Furthermore, according to the 1982
Evaluation, the latency period of these tumours was not modified by
the treatment.
The required short-term dog study was not provided. However,
clarifications made available to the meeting alleviated the concerns
expressed by the 1982 Meeting with respect to the cholinesterase
activity determination, and a dog study is no longer required.
The meeting agreed to estimate a full ADI.
TOXICOLOGICAL EVALUATION
Level Causing no Toxicological Effect
Rat: 10 ppm in the diet, equal to 0.38 mg/kg bw
Dog: 20 ppm in the diet, equal to 0.7 mg/kg bw
Estimate of Acceptable Daily Intake for Man
0 - 0.004 mg/kg bw
FURTHER WORK OR INFORMATION
Desirable
1. Further investigations on the cataractogenic activity of
Bendiocarb at low dosage levels in rats.
2. Observations in humans.
REFERENCES
Challis, J.R. Dermal absorption of Bendiocarb in man. Report
1982 Method/12/35 submitted by FBC Limited to WHO,
(Unpublished)