HEXACHLOROBENZENE JMPR 1978
Explanation
Following evaluations at the 1969 and 1973 meetings (FAO/WHO,
1970b, 1974b) when some Practical Residue Limits were recorded, the
1974 Meeting allocated a Conditional ADI to hexachlorobenzene. The
latter meeting also urged that:
1. support be given to an international monitoring programme to
identify the source and extent of contamination;
2. the presence of HCB as an impurity in other pesticides be
monitored and minimized;
3. the recommendations for use as a seed-dressing be carefully
adhered to; and
4. HCB should be used only as a seed-dressing and only when no
suitable substitute is available.
The results of further toxicological studies have become
available and are evaluated in the following monograph amendment.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Orally administered HCB was slowly absorbed from the gut in
rats, mainly via the lymphatic system and was stored in the fat
(Iatropoulos et al., 1975). Recovery of orally administered 14C-HCB
in rats was dose-dependent, more 14C being recovered from faeces
than from urine. Several investigations on the metabolic pathway of
HCB were performed in the rat and pentachlorophenol,
pentachlorothiophenol, tetrachlorohydroquinone,
tetrachlorothiophenol and 2,4,5-trichlorophenol could be identified
as major urinary metabolites (Mehendale et al., 1975., Koss et al.,
1976; Renner and Schuster, 1977). Unchanged HCB was found mainly in
faeces and fat (Engst et al., 1976).
After the administration of 14C-HCB in the diet to rhesus
monkeys over a period of 10-15 months 99% of the radioactivity
excreted in faeces was unchanged HCB, whereas the major urinary
metabolites were identified as pentachlorophenol and
pentachlorobenzene (Rozman et al., 1977).
HCB was found in milk of cows and rats (Fries and Marrow,
1976; Mendoza et al., 1976; Mendoza et al., 1975).
TOXICOLOGICAL STUDIES
Special studies on carcinogenicity
Mouse
Groups of 30-50 male and 30-90 female Swiss mice were
maintained on a diet supplemented with 0, 50, 100 or 200 ppm HCB
for life. Survival was impaired in the group given 200 ppm in which
more than 50% animals of both sexes died before 50 weeks of age and
only 2 males were alive at 90 weeks. The incidence of liver-cell
tumours was 10% in both sexes given 100 ppm and 34% in males and
16% in females at 200 ppm. No liver tumours were found in the
control and lowest dose group. In treated animals, incidence of
other tumours did not differ from controls or were decreased
because of shortening of lifespan. In a further group of 30 mice of
each sex fed a diet containing 300 ppm HCB for 15 weeks, survivors
at 90 weeks were 17 females and 4 males, among which 1 mouse of
each sex developed liver-cell tumours (Cabral et al., 1978).
In another study the production of lung adenomas in strain A
mice was investigated following multiple i.p. injections of HCB,
three times weekly at doses of 0, 8, 20 and 40 mg/kg for 8 weeks.
24 weeks after the first injection the survivors were killed. The
only organ microscopically examined was the lung. Incidences of
lung adenomas in treated animals were not significantly increased
compared to the control. This test system is relatively unsensitive
to hepatocarcinogens (Theiss et al., 1977).
Hamster
Groups of 30-60 female and 30-60 male Syrian golden hamsters
were fed a diet containing 0, 50, 100 and 200 ppm HCB for lifespan.
After 50 weeks the survival rate of the treated animals was
comparable to the controls, after 70 weeks however shorter lifespan
occurred in both sexes at the highest dose level of 200 ppm; marked
weight reduction was observed at this dose level. Tumours of the
thyroid, hepatomas and haemangioendotheliomas of the liver were
found only in the treated animals, a dose-relationship of
incidences was evident. Hepatomas occurred in 47% of the male and
female animals in the 50 ppm group, in 57% of female and 87% of
male animals in the 100 ppm group and in 85% of males and females
in the 200 ppm group. Liver haemangioendotheliomas were found in 0
and 3% at 50 ppm, in 7 and 20% at 100 ppm and 12 and 35% at 200 ppm
in female and male animals respectively. Three of the
haemangioendotheliomas occurring in the highest dose group
metastasised. The incidence of thyroid adenomas was significantly
increased compared to control in males treated with 200 ppm (Cabral
et al., 1977).
Special study on reproduction
Rat
The effect of HCB on reproduction was studied by feeding the
test compound to groups of 20 females and 10 males at dietary
levels of 0, 10, 20, 40, 80, 160, 320 and 640 ppm over 4
generations. Dose levels of 320 and 640 ppm caused the death of 20
and 50% respectively of the females of the Fo generation.
Fertility was reduced at 320 ppm and above, the average litter size
was decreased from 160 ppm onwards. Marked reduction of the
survival to day 5 after birth of the pups in various generations
was observed; less than 60% of the pups of the F1 generation fed
160 ppm and only about 40% of the pups of the F2 generation fed
160 ppm survived the 5-day period. None of the pups of females fed
320 and 640 ppm HCB survived. Lactation was also adversely affected
by the treatment in the dose groups of 80 ppm and above and a
significant decrease in birth weights was observed at this dose
levels. Relative liver weight for pups from dame fed 40 ppm were
significantly increased. No gross abnormalities were found in the
pups (Grant et al., 1977).
Special study on teratogenicity
Mouse
The oral administration of HCB at a dose level of 100 mg/kg
b.w. on gestational day 7-16 to 10 CD-1 mice resulted in 13%
abnormal fetuses per litter compared to 7% in the litters of 7
untreated mothers; cleft palates, small-sized kidneys and renal
agenesis were found only in treated animals (Courtney et al.,
1976).
Placental transfer of HCB was reported by Andrews and
Courtney, (1976).
Special study on mutagenicity
Hexachlorobenzene did not indicate mutagenic activity in
Saccharomyces cerevisiae (Guerzoni et al., 1976).
Short term studies
Rat
Groups of 70 male and female rats were maintained on a diet
with HCB added at does levels of 0, 0.5, 2, 8 and 32 mg/kg b.w.
over a period of 15 weeks. Part of the animals was observed during
a recovery period of another 18 weeks. At 32 mg/kg reduction of the
average body weight of male rats was noted; mortality of 40%
occurred in females only by the end of treatment. Urinalyses did
not reveal abnormal findings except for a red color in females at
32 mg/kg after 9 weeks of feeding, presumably due to the presence
of high concentrations of uroporphyrins. At 8 and 32 mg/kg the
relative liver weights were significantly increased compared to
control. After 16 weeks on the recovery diet only liver weights
in females at the highest dose level were still significantly
higher than controls. Reversible increase of the relative kidney
and spleen weights was found in both sexes at 32 mg/kg. Gross
pathological and histopathological changes were found in liver
and spleen. The livers were enlarged and an increase in the size
of centrilobular heaptocytes was found accompanied by an increase
in smooth endoplasmic reticulum. These changes were particularly
marked in animals treated with 8 and 32 mg/kg. Spleens of many
females at 32 mg/kg were enlarged, sometimes accompanied by
hyperplasia. At 8 and 32 mg/kg females developed porphyria with
high levels of liver porphyrin (> 800 nmol/g) even during the
recovery period. Porphyrin also accumulated in the kidney and
the spleen.
Tissue residues of HCB reached a plateau before 15 weeks and
were dose-related with concentrations in adipose tissue > liver
> brain > serum. Maximum residues of approximately 6000 ppm were
measured in the adipose tissue of females treated with 32 mg/kg
HCB. A no effect level of 0.5 mg/kg was established in this study
(Kuiper-Goodman et al., 1977).
Similar results with respect to porphyrin accumulation in
organs were reported by Doss et al., (1976).
Pig
A 90-day toxicity study was carried out with pigs receiving
the test compound in the diet at concentrations to give dose levels
of 0, 0.05, 0.5, 5 and 50 mg/kg b.w. Animals treated with 50 mg/kg
showed porphyria and died before termination of the experiment. A
dose-related increase in the urinary excretion of coproporphyrin
was found at does levels of 0.5 mg/kg and above as well as
induction of microsomal liver enzymes (mixed-function oxidases)
accompanied by increased liver weight at 5 mg/kg; significant
increase of kidney and thyroid weights were also found at this dose
level. Histopathological examination of the liver revealed
centrilobular hypertrophy of the cells at dose levels of 0.5 mg/kg
and above. At 50 mg/kg kidneys showed degenerative changes and
lymph nodes atrophy. HCB residues in the 5 mg/kg group after 12-13
weeks of feeding were 2.5 ppm in blood, 1300 ppm in fat, 42 ppm in
the liver and approximately 20 ppm in kidney and brain. Residue
levels at 50 mg/kg determined after 8 weeks of feeding were 30 ppm
in blood and 15'000 ppm in fat.
A no effect level of 0.05 mg/kg was found (Den Tonkelaar,
1978).
Further short term studies:
- Rats were fed low levels of HCB for 4 weeks; subsequent food
deprivation enhanced the toxic response, thus indicating
mobilization of HCB residues from fat (Villeneuve et al., 1977).
- Immuno-suppression was observed in mice treated with 167 mg
HCB/kg diet for 6 weeks (Loose et al., 1977).
- In a 90 day feeding study in Japanese quails using dietary
concentrations of 0, 1.5, 20 and 80 ppm, the treatment with 80 ppm
caused mortality, tremors, liver damage consisting of enlargement
of nuclei and nucleoli, proliferation of bile ductules and necrosis
of hepatocytes, an well an reduction in egg production and
hatchability. Increased liver weight, slight liver damage and
increased faecal excretion of coproporphyrin were already observed
at the 5 ppm dose level (Vos et al., 1971).
Observation in Man
Abnormal high plasma coproporphyrin levels of 3.6 ppb were measured
in people not exposed occupationally but living near an
HCB-manufacturing plant. There was no evidence of porphyria (Burns
and Miller, 1975).
COMMENTS
Carcinogenicity tests in mice and hamsters were available. In
mice HCB caused an increase in the incidence of hepatomas when fed
at dose levels of 100 and 200 ppm. In hamsters feeding with 50, 100
and 200 ppm caused an increase of hepatomas, haemangioendotheliomas
and thyroid adenomas. No long-term studies in rats are available.
The Meeting concluded that the maintenance of a conditional
ADI was no longer justified. The Meeting further stressed the need
to lower the human exposure to HCB as much as possible. The Meeting
was aware of the fact that the use of HCB as a acid-dressing has
declined considerably during recent years. It expressed the hope
that the use of HCB in agriculture will completely cease in the
near future.
The Meeting stressed especially the importance of efforts to
identify the various agricultural and non-agricultural sources of
environmental contamination by HCB and of programmes directed to
its diminution.
TOXICOLOGICAL EVALUATION
Because the toxicity of HCB is such that the contamination of
food should be kept as low as possible the previously allocated
conditional ADI was withdrawn.
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See Also:
Toxicological Abbreviations
Guazatine (Pesticide residues in food: 1980 evaluations)
Guazatine (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)