TECNAZENE JMPR 1978
Explanation
Limited available information was reviewed in 1974 (FAO/WHO,
1975) but the meeting reported that before an ADI or residue limits
could be recommended the following data were required.
1. Adequate toxicological data.
2. Full information on specifications for the chemical and the
formulated products (including impurities,
e.g., HCB), present use patterns, residue data
from supervised trials, fate of residues in
crops other than potatoes and in soils, etc.
The data received in response to these published requirements
are evaluated in this monograph.
IDENTITY
Chemical name
1,2,4,5-Tetrachloro-3-nitrobenzene
Synonyms
2,3,5,6-Tetrachloronitrobenzene, TCNB, FusarexR, FumiteR,
Folosan DB 905.
Structural formula
Other information on identity and properties
Molecular weight: 261
Physical state: Colourless, odourless, crystalline solid
Melting point: 99°C
Volatility: Appreciably volatile at room temperature
Solubility: Practically insoluble in water; soluble
in ethanol; readily soluble in acetone,
benzene, carbon disulphide, chloroform,
etc.
Stability: Generally very stable; can be dispersed
by pyrotechnic mixtures. Decomposes
slowly in solution when irradiated with
ultra-violet light.
Purity of technical material: The test material was more then 99% pure
and contained less than 0-1% of
hexachlorobenzene. Full information was
available to the Meetings.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Biotransformation
One of the major metabolites identified in the urine following
oral administration of 1-3 g of 2,3,5,6-tetra-chloronitrobenzene to
rabbits was mercapturic acid, being excreted at a rate of 11%
within 48 hours after application. Further metabolites excreted
were an ether glucuronide (12%), 2,3,5,6-tetrachloroaniline (10%),
unconjugated 4-amino-2,3,5,6-tetrachlorophenol (2%) and an etheral
sulphate (1%) (Bray et al., 1953; Betts et al., 1955). Similar
amounts of mercapturic acid were excreted in the urine of rats
(Barnes et al., 1959).
Rat liver contains an enzyme catalysing the formation of
glutathione S-conjugates with replacement of the active halogen of
aromatic compounds, known to be excreted as mercapturic acid.
Evidence was presented by Al-Kassab et al., 1963, that the enzyme,
that catalyses the displacement of halogen will also replace the
labile nitro group of polychloronitrobenzenes with glutathione and
of the carcinogen 4-nitroquinoline-N-oxide.
Studies in pigeons showed that orally administered
2,3,5,6-tetrachloronitrobenzene is also converted to mercapturic
acid (Wit et al., 1969).
TOXICOLOGICAL STUDIES
Special studies on carcinogenicity
Tests were performed to study the carcinogenic action of
polychloronitrobenzenes, its tumour initiating activity and its
action on carcinogenesis induced by benz(a) pyrene: one of the
reasons for performing these tests was the similarity in
biotransformation of TCNB and the carcinogenesis
4-nitroquinoline-N-oxide.
Skin application of 0.2 ml of 0.3% acetone solutions to 10
males and 10 females twice weekly for 12 weeks was followed by
croton oil treatment for 20 weeks. Controls (10 of each sex) were
treated according the same schedule, instead of tecnazene only
acetone was given in the first phase. By the end of the croton oil
treatment, 41 papillomas had been observed in treated males and 13
in treated females versus 7 and 5 in controls.
Tecnazene (> 99% pure) was administered continuously in the
diet to 65 male and 65 female CD-1 animals in each dose group at
dietary levels of 09 750 and 1500 ppm for a period of 80 weeks. The
treatment did not adversely affect the general condition,
behavioural patterns, body weight gain and food intake. Survival in
males was poorer in the controls than in treated groups; mice alive
at 80 weeks were 16, 17 and 31 males and 27, 37 and 25 females at
0, 750 and 1500 ppm respectively. Several macroscopic pathological
alterations with increased incidences in the dose-groups were
observed, but because no distinct dose-relationship is found, no
biological significance could be attached to these changes. No
dose-related group distribution of neoplasms was observed, with the
only exception of a higher frequency of pulmonary adenoma in the
male animals of the 1500 ppm group; 8 animals showing this lesion
compared to 4 animals in the control and low dose group (Ben-Dyke
et al., 1978b). Skin carcinogenesis by benzo(a)pyrene was not
affect by TCNB (Searle, 1966).
Groups of 65 male and 65 female rats were fed with a diet
containing tecnazene (purity > 99%) at concentrations of 0, 750
and 1500 ppm for a period of 104 weeks. The feeding did not affect
general appearance, behaviour, mortality and food consumption. In
all groups survival at 78 weeks was 50% or more. In the first half
of the treatment period body-weights were unaffected, whereas in
the second half a slight reduction of body weights was observed in
treated males at 1500 ppm. The macropathological findings and
non-neoplastic histologic changes were those commonly found in the
rat strain used; they were not considered to be treatment-related and
did not show clear dose-relationships. Liver hyperplastic nodules
were seen in one female at 750 ppm and in 3 males and 2 females at
1500 ppm. Benign or malignant tumours of the mammary glands were
seen in 39 females of the control group versus 48 females given 750
ppm and 50 animals given 1500 ppm. Adenocarcinomas were found in 4
females of the control group compared to 5 and 8 females at the 750
and 1500 ppm level respectively. These differences are of
borderline statistical significance (p approx. 0.05). Only one
liver-cell tumour was seen and this was in a control rat (Ben-Dyke
et al., 1978a).
Special studies on teratogenicity
2,3,5,6-tetrachloronitrobenzene did not show embryotoxic or
teratogenic properties when orally administered at doses of up to
200 mg/kg b.w. to CD rats and C 57 B 1/6 mice on gestation day 7-18
or to CD-1 mice on day 7-16 (Courtney et al., 1976).
Acute toxicity
The acute intraperitoneal LD50 of
2,3,5,6-tetrachloronitrobenzene in the rat is approximately 3500
mg/kg (Wit et al., 1960)
Short Term Studies
Pig
Groups of two pigs were maintained an a diet containing
potatoes that have been treated with a dust-mixture of tecnazene at
levels of 0, 60, 400 and 600 mg/lb potatoes for 26 weeks. The
highest dose level of 600 mg/lb potatoes being ten times as high as
that which will be used for the routine dressing of potatoes,
corresponds to 7.1 g tecnazene per pig per day or approximately to
50 mg/kg b.w. and caused reduction in body weight gains in the
first half of the study. No other abnormal findings with respect to
general health condition, haematological parameters or gross and
microscopic examination of liver and kidney were detected. No
methaemoglobinanaemia was produced by the treatment (Abrams et al.,
1950).
Rat
In a 10 week-feeding study rats were maintained on a diet with
2000 ppm tecnazene. No abnormalities in general health, blood
picture, autopsy findings and histological picture of liver and
kidney were detected. In the male animals increased liver- and
testis-weights were observed (no other details described) (Wit et
al., 1960).
COMMENTS
Following oral administration of tecnazene to rabbits the
material absorbed is excreted mainly as an ether glucuronide,
2,3,5,6-tetrachloraniline and mercapturic acid. The study of the
biotransformation of some polychloronitrobenzenes in rats and
rabbits showed that these compounds were converted to mercapturic
acids; the formation of S-substituted glutathione by replacing the
labile nitro groups with glutathione seems to be the first stage in
mercapturic acid formation.
An experiment on mice on skin carcinogenesis is suggestive of
a tumour-initiating effect of tecnazene, but, a full evaluation is
impaired by the small number of animals used. The results of the
carcinogenicity tests with feeding of the test compound over 104
weeks to rats and 80 weeks to mice gave no clear indication of a
carcinogenic activity in tecnazene. The increased number of mammary
tumours in female rats was of borderline statistical significance.
In the study on mice the tumour incidence was not increased.
In the 80 week study in mice with 750 and 1500 ppm tecnazene
in the diet no treatment revealed effects were noted. In the two
year study on rats with dose levels of 750 and 1500 ppm a slight
reduction of weight gain occurred in the males of the high dose group.
Tecnazene showed no teratogenic activity in mice. No studies
relating to mutagenicity, effects an reproduction or metabolism in
different mammalian species were made available since the last
evaluation by the 1974 Meeting.
In view of come uncertainties in regard to the carcinogenic
potential of tecnazene and the lack of adequate reproduction data
only a temporary ADI was allocated.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 750 ppm in the diet equivalent to 38 mg/kg bw
Mouse: 1500 ppm in the diet equivalent to 200 mg/kg bw
Dog: 15 mg/kg bw
Estimate of temporary acceptable daily intake for man
0 - 0.01 mg/kg bw
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Tecnazene is used on potatoes after harvest, as a 3% dust
formulation at the rate of 10 1b product per ton,(4.5g product/kg),
to reduce sprouting during storage. This recommendation produces a
theoretical initial loading on the potatoes of 134 mg/kg. Tecnazene
displays the additional merits of not inhibiting would healing in
freshly-clamped potatoes and of controlling dry rot, Fusarium
caeruleum (Brown, 1947; Reavill, 1954). Tecnazene is also used as
a smoke generator formulation at 15 mg/m3 to control Botrytis
spp. on tomatoes, lettuce, chrysanthemums and other ornamental
plants, and as a dust in chicory (witloff) culture.
RESIDUES RESULTING FROM SUPERVISED TRIALS
When potatoes were treated at 4.5g kg with 3% tecnazene dust,
stored for 4-5 months, commercially graded and transported, mean
residues on the tubers were of the order of 2 mg/kg. Increasing the
storage period to six months caused a farther reduction to
approximately 1 mg/kg. The original concentration applied (134
mg/kg) is reduced mainly by handling, both before and after
storage, but losses by evaporation were shown to occur during
storage. Washing reduced residues still further and no tecnazene
was detected in the flesh of peeled potatoes (limit of
determination approximately 0.1 mg/kg) (Wilson and Dawson, 1953).
In a similar study (Bullock, 1973), when potatoes treated as
above were stored commercially for 4-5 months, tecnazene residues
on tubers with adhering soil were normally less than 10 mg/kg; the
mean residue was approximately 3 mg/kg. Washing the potatoes
reduced residues to below 1 mg/kg (mean approximately 0.4 mg/kg).
Residue levels in stored potatoes treated with a 30% liquid
tecnazene formulation by means of a fogging machine have been
reported (Wheatley Chemical Co., 1978). Three application rates
were chosen, giving the recommended rate of 15 mg a.i./kg and one
half and twice this rate (i.e. 25, 50 and 100 ml/ton); results are
shown in Table 1.
TABLE 1. Residues of tecnazene in treated potatoes
Tecnazene residue (mg/kg)
Day 1 Day 60 Day 100
Application Whole Whole Whole
rate (mg ai/kg) tuber skin tuber tuber skin
7.5 6.4 76.8 4.05 1.0 7.6
15 13.2 151.8 6.8 2.6 24.2
30 23.3 276.0 17.3 3.1 41.0
Data from trials usage of tecnazene on 7 samples of glasshouse
grown lettuce in 1972 showed residues ranging from 1.3 to 2.2 mg/kg
(mean 1.7 mg/kg) at 11-19 days after treatment (Race, 1978).
Fodderbeets treated at 90 mg/kg with tecnazene and stored for
five months contained residues of 0.1-13 mg/kg, with most samples
containing less than 5 mg/kg tecnazene (Wit et al., 1960).
In the culture of chicory (witloff) tecnazene can be used as a
fungicidal powder on the roots when they are forced. Residues were
determined in the sprouts, and in the remaining roots which are used
as fodder, six weeks after treatment at 150 g product per m2 (4.5 g
a.i. per m2). Residues in the sprouts did not exceed 0.05 mg/kg and
in the roots were less than 3 mg/kg (Wit et al., 1960). Confirmatory
studies at a 3 g m2 treatment rate showed residues not exceeding 0.11
mg/kg in the sprouts and less than 0.3 mg/kg in the roots
approximately seven weeks after treatment (Bullock, 1973).
FATE OF RESIDUES
In plants
As reviewed above, tecnazene residues on potatoes are readily lost by
evaporation. Under commercial conditions the major losses occur by
handling, both before and after storage, although some losses also
occur during storage, Washing treated potatoes reduces residues
significantly (Wilson and Dawson, 1953; Bullock, 1973). Limited
evidence indicated that washing chicory (witloff) roots was much less
effective in reducing the residue content (Netherlands, 1978),
In soil
Tecnazene was rapidly lost from a sandy soil; over 50% in two
months and all but 2% in ten months. Volatility of tecnazene is likely
to have been a major contributory factor. The rate of loss was similar
from both sterile and non-sterile sandy soil and at 100 mg/kg in this
soil tecnazene had no effect on respiration or nitrification (Caseley,
1968: Caseley and Broadbent, 1968).
EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
Washing, peeling and cooking potatoes all cause considerable
reductions in tecnazene residue levels. As stated above, when potatoes
treated at 4.5 g kg with 3% tecnazene dust were stored commercially
for 4-5 months, mean tecnazene residues on tubers with adhering soil
were approximately 3 mg/kg. Washing the potatoes reduced residues to
below 1 mg/kg (mean approximately 0.4 mg/kg). After peeling, residues
in uncooked edible flesh were normally below 0.1 mg/kg (mean
approximately 0.04 mg/kg) (Bullock, 1973), Boiling reduces the level
of tecnazene in peeled edible flesh by 50% or more (Bullock, 1973;
Dalzeil and Duncan, 1974). Although baking unpeeled potatoes caused a
slight increase in residues in edible flesh (up to two-fold), it
caused a major reduction of tecnazene levels in peel and an overall
reduction in the residue level in the potato (Bullock, 1973).
Potatoes grown in the U.K. in 1976 and 1977 were purchased on the
market and examined for residues of tecnazene. In addition to the
whole tubers analysed from both crops, some samples from the 1977 crop
were washed and peeled before analysis. Results obtained are shown in
Table 2. Although most results on whole tubers were below 10 mg/kg, an
appreciable number were greater than 5 mg/kg in both years (Anon,
1978).
TABLE 2. Residues of tecnazene in marketed potatoes
Year Commodity No. of Tecnazene residue (mg/kg)
samples
Range Mean
1976 Whole tubers 3 10.5 - 19.3 15.3
Whole tubers 13 3.0 - 9.0 5.7
Whole tubers 7 0.6 - 1.5 1.1
1977 Whole tubers 17 2.2 - 7.6 4.6
Whole tubers 26 <0.1 - 1.7 0.3
Washed and peeled
tubers 19 <0.1 - 0.25 <0.1
Over a 10 year period (June 1964 - August 1974), about 300
samples of potatoes were collected during a series of market basket
surveys in the USA. Of these 14 were found to contain detectable
residues of tecnazene, ie 0.001 mg/kg or above; the highest level
found was 0.37 mg/kg, Over 3500 samples of other foodstuffs were also
analysed in which trace residues (0.01 mg/kg or less) were reported in
15 samples representing a wide range of foodstuffs (Corneliussen,
1969, 1970, 1972; Duggan et al., 1966, 1967; Johnson and Manske 1975;
Manske and Corneliussen, 1974; Manske and Johnson, 1975, 1977; Martin
and Duggan, 1968).
Of 60 samples of lettuce examined in Belgium in 1972, 52
contained less than 0.01 mg/kg and only one contained more than 2
mg/kg of tecnazene. Similarly, of 54 samples of chicory examined, only
two contained more than 0.01 mg/kg but none more than 2 mg/kg
(Valange, 1974). No tecnazene was detected in 17 samples of maize, and
only one of 23 samples of dried sugar beet pulp contained a detectable
residue of 0.03 mg/kg (Valange and Henriet, 1974). A survey of canned
peas, haricot beans, carrots, celery, salsify, asparagus and cherries
in Belgium showed no residues of tecnazene above 0.001 mg/kg (Biston
et al., 1975).
Westöö and Noren (1973) examined about 2500 samples of fresh and
canned, home grown and imported foods in Sweden during the period 1968
to June 1972. Of the foods analysed, detectable residues of tecnazene
appeared most commonly in lettuces; of 230 samples tested 15 contained
0.02 to 0.1 mg/kg, 14 contained 0.11 to 0.5 mg/kg and 9 contained 0.51
to 1.4 mg/kg of tecnazene. A few samples of carrots (6 of 140),
tomatoes (3/240), paprika (1/65) and parsley (4/13) had residues of
tecnazene in the range 0.02 to 0.1 mg/kg.
Similar studies in Sweden in 1976-77 showed no residues of
tecnazene above 0.1 mg/kg in mushrooms (9 samples), carrots (187),
sweet peppers (166), parsley (16), beetroots (4) tomatoes (467) or
apples (931). Of 253 samples of potatoes, 2 were in the range 0.11 to
0.5 mg/kg, 2 from 0.51 to 1.0 mg/kg and 4 between 1.1 and 5.0 mg/kg
(Sweden, 1973).
METHODS OF RESIDUE ANALYSIS
Gas chromatography with an electron-capture detector is the
preferred method of residue analysis. Crop samples are macerated with
light petroleum, dried and filtered, and an aliquot is injected into
the gas chromatograph. The limit of determination is 0.01 mg/kg or
better. Recoveries in excess of 90% are normally obtained from
potatoes and chicory, for which the method is suitable for use as a
regulatory method. Confirmation of the residue can be obtained by
clean-up of the extract by thin-layer chromatography and further gas
chromatographic determination (Bullock, 1973).
The use of gas chromatography with a flame ionisation detector
has also been reported. Tecnazene residues could be determined in
hexane extracts applied directly to the gas chromatograph; however,
the accumulation of charred plant residues on the column and overlap
with natural components using this detector limited the value of this
approach. Solvent partition and an alumina column were used
successfully to clean-up the extracts and a method of avoiding the
formation or troublesome emulsions has been described (Dalziel and
Duncan, 1974).
Polarographic and colorimetric methods have also been described
(Webster and Dawson, 1952; Auerbach, 1950; Canbäck and Zajaczkowska
1950; Higgons and Toms, 1957).
NATIONAL MRLs REPORTED TO THE MEETING
National MRLs reported to the meeting are shown in Table 3.
TABLE 3. National MRLs for tecnazene reported to the meeting
Country Commodity MRL (mg/kg)
Belgium Vegetables and strawberries 2
Federal Republic Strawberries, chicory, lettuce,
of Germany tomatoes 0.03
Other vegetables 0.05
Netherlands Vegetables and strawberries 2
United States Potatoes
of America 25
Zambia Potatoes 25
APPRAISAL
Tecnazene is used on potatoes as a post-harvest sprout
suppressant and as a fungicide on chicory (witloof) and glasshouse
grown tomatoes and lettuce. Residue data were available from
supervised trials on potatoes, lettuce and chicory (witloof). Some
data from marketed samples, and market basket surveys showed
detectable residues in potatoes and, occasionally, in other crops such
as lettuce, tomatoes, carrots, etc. No information was forthcoming on
the fate of residues in crops other than potatoes. Information
concerning the purity specification for the technical material was
available and acceptable to the Meeting; the content of
hexachlorobenzene in this material was below 0.1%. Sufficient data
were available to allow the following recommendations to be made for
temporary maximum residue limits in certain crops. Gas chromatographic
methods of analysis are available and suitable for regulatory
purposes.
RECOMMENDATIONS
The following temporary maximum residue limits apply to
tecnazene.
Commodity Temporary MRL, mg/kg
Lettuce 2
Potatoes (washed before analysis) 1
Chicory (witloof) 0.2
Other vegetables 0.1
Tomatoes 0.1
FURTHER WORK OR INFORMATION
Required (by 1981)
1. Clarification of the tumour initiating activity observed in a
skin painting experiment on mice.
2. Adequate study on reproduction.
Desirable
1. Short-term tests on mutagenicity.
2. Metabolism in different mammalian species.
3. Information regarding levels of residues occurring in meat and
milk resulting from consumption of treated chicory roots or potatoes
by cattle.
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