BUTYLATED HYDROXYANISOLE (BHA)
EXPLANATION
This substance was evaluated for acceptable daily intake for man
by the Joint FAO/WHO Expert Committee on Food Additives at its sixth,
ninth, seventeenth, twentieth, twenty-fourth, twenty-sixth and
twenty-seventh meetings (Annex 1, references 6, 11, 32, 41, 53, 59,
and 62). Toxicological monographs or monographs addenda were published
after the sixth, seventeenth, twentieth, twenty-fourth, and
twenty-seventh meetings (Annex 1, references 6, 33, 42, 54 and 63).
At the twenty-seventh meeting of the Committee (Annex 1,
reference 62), the temporary ADI of 0-0.5 mg/kg b.w. (group ADI with
BHT and TBHQ) was maintained pending adequate studies to determine if
the induction of hyperplasia, papilloma, and carcinoma by BHA in the
forestomach of the rat and hamster are relevant for evaluating the
safety of BHA for man. It was specifically requested that studies be
submitted to show whether or not the hyperplasia is induced in the
stomach of species that do not have a forestomach, such as the dog,
pig, and monkey, as well as studies to determine the mechanisms
involved in the effect of BHA on the forestomach. A multigeneration
reproduction study was also requested.
Since the previous evaluation additional data, including the
results of some of the studies requested by the twenty-seventh
Committee, have become available and are summarized and discussed in
the following monograph addendum.
BIOLOGICAL DATA
Biochemical aspects
Effects on enzymes and other biochemical parameters
Mice fed diets containing 0.75% BHA showed no change in hepatic
cytochrome P-450 levels, aminopyrine demethylase activity, or
benzo(a)pyrene monooxidase activity. However, there were significant
increases in other microsomal mixed-function oxidases (NADPH
cytochrome reductase and aniline hydroxylase) and other enzyme
activities (glutathione reductase and hepatic cytosol glutathione
S-transferase). There was also a marked increase in the level of
nonprotein thiol levels in the liver, lung, kidneys, and small
intestine (Cha et al., 1983).
Liver microsomal preparations from rats fed BHA did not show an
increased rate of formation of reactive products from benzo(a)pyrene
that bind to calf thymus DNA, as has been observed with microsomal
preparations from rats fed other antioxidants (Dock et al., 1982a;
Kahl & Kahl, 1983).
Addition of BHA to the diet of mice altered the components of the
monooxygenase system in liver nuclei and inhibited binding of
benzo(a)pyrene metabolites to nuclear macromolecules on incubation
with liver nuclei from the BHA-fed mice. However, there was no
inhibition of binding of benzo(a)pyrene metabolites to macromolecules
when benzo(a)pyrene with added DNA was incubated with liver microsomes
from BHA-fed mice (Hennig et al., 1983).
Dietary BHA (7.5 g/kg b.w. of diets of mice for 14 days) resulted
in a 12-fold increase in the concentration of the predominant hepatic
glutathione S-transferase. Its rate of synthesis and the mRNA for this
protein were also increased (Pearson et al., 1983).
In a study comparing the effects of dietary BHA on liver
microsomal enzymes and benzo(a)pyrene metabolism in male and female
mice, both sexes appeared to respond similarly to BHA feeding
(Dock et al., 1982b).
Lung microsomal preparations from female mice fed diets
containing 0.5% BHA showed decreased benzo(a)pyrene metabolism and
altered ratios of the different metabolites (Sydor et al., 1984).
Dietary or topically-applied BHA caused an inhibition in
epidermal ornithine decarboxylase activity induced by
12-1-tetradec-anoylphorbol-13-acetate in mice (Kozumbo et al.,
1983).
BHA suppresses murine in vitro immune responses by inhibiting
guanylate cyclase function. The suppression was reversed by addition
of either exogenous dibutyryl cGMP or Ca+2 to the cultures
(Wess & Archer, 1982).
Toxicological studies
Special studies on the effect of BHA on the stomach
Rats
Groups of 50 male F344 rats from Charles River Japan, Inc., 6
weeks of age, were maintained on powdered diets containing 0, 0.125,
0.25, 0.5, 1, or 2% BHA. After 104 weeks the surviving animals were
killed. These animals plus all other animals that died during the
study were autopsied. The oesophagus and stomach from all animals were
examined histologically.
No treatment-related clinical signs were observed during the
course of the study. Reduction in weight gain in BHA-treated animals
was dose-related. Average food intake of test and control animals was
comparable. BHA had no effect on survival. Histologically, the
epithelial lesions which were observed in the forestomach were
classified into three categories, hyperplasia, papilloma, and squamous
cell carcinoma. No metastases were reported. The incidences of
proliferative and neoplastic lesions in the forestomach were
dose-related, as summarized in the following table (Ito et al.,
1986):
Number (%) of rats with changes
in the forestomach
Effective
number Squamous cell
% BHA in diet of ratsa Hyperplasia Papilloma carcinoma
0 50 0(0) 0(0) 0(0)
0.125 50 1(2) 0(0) 0(0)
0.25 50 7(14)b 0(0) 0(0)
0.5 50 16(32)c 0(0) 0(0)
1.0 50 44(88)c 10(20)b 0(0)
2.0 50 50(100)c 50(100)c 11(22)c
a Rats surviving to > 50 weeks.
b Significantly different from control group at p < 0.01.
c Significantly different from control group at p < 0.001.
Special studies on mutagenicity
BHA was shown to cause genetic alteration in S. aureus strain
W46. The variant, obtained following incubation in S. aureus W46, is
characterized on the basis of its hemolytic properties, its production
of staphylokinase, and its sensivity to bacitracin (Degre & Saheb,
1982).
BHA showed no evidence of genotoxicity in V79 Chinese hamster
lung cells at concentrations up to 0.3 mM with and without
hepatocyte-mediated activation (Rogers et al., 1985).
BHA was examined in 4 in vitro systems for genotoxicity:
(1) Salmonella/microsome mutation test at doses between
0.01-10 mg/plate using 5 tester strains with and without S-9
fractions; (2) hepatocyte primary culture/DNA repair, using 10 doses
ranging from 10-5 to 1 mg/ml; (3) adult rat liver epithelial
cell/hypoxanthine guanine phosphoribosyl transferase mutagenesis assay
(rat liver line 18) using 6 doses ranging from 0.05 to 0.1 mg/ml; and
(4) Chinese hamster ovary/sister chromatid exchange (SCE) assay, at 4
dose levels ranging from 1 to 10-3 mg/ml. BHA was without mutagenic
activity in any of the systems (Williams et al., 1984).
Pre-treatment of E. coli H/r30R strain with BHA had no
anti-mutagenic effect on UV-induced mutagenesis (Kawazoe & Kato,
1982).
Addition of 25-500 µg of BHA/plate was shown to inhibit
3,2'-dimethyl-4-aminobiphenyl-induced mutagenicity in Salmonella
strains TA98 and TA100 (Reddy et al., 1983).
BHA caused a dose-dependent reduction in revertant yield in
benzidine-induced mutagenesis in Salmonella strain TA98 activated
with hamster liver S-9 preparation (Josephy et al., 1985).
BHA substantially increased aflatoxin-B 1-induced mutagenesis in
Salmonella strains TA98 and TA100 (Shelef & Chin, 1980).
The addition of BHA to beef patties prior to broiling resulted in
significantly-reduced formation of mutagens detectable by
S. typhimurium TA98 (Wang et al., 1982).
Special studies on potentiation or inhibition of carcinogenicity
Colon
The effect of dietary BHA on methylazoxymethanol acetate-induced
carcinogenesis was studied in female mice fed NIH-07 open formula diet
or AIN-76A semi-purified diet. Lung tumour incidence was lower in mice
fed the NIH-07 diet than in mice fed the AIN-76A diet whereas colon
tumour incidence and tumour multiplicy were higher in animals fed the
NIH-07 diet than animals fed the AIN-76 diet. BHA inhibited
methylazoxymethanol-induced colon cancer and lung tumours in a
dose-related fashion. Treated mice fed AIN-76A diet plus BHA developed
fewer colon adenocarcinomas than did mice fed the NIH-07 diet plus BHA
(Reddy et al., 1983a; Reddy & Maeura, 1984).
Dietary BHA given after the post-initiation phase of colon tumour
development in male F344 rats treated with 1,2-dimethylhydrazine did
not modify tumour development (Shirai et al., 1985).
In a study in mice, BHA decreased the incidence and multiplicity
of 1,2-dimethylhydrazine-induced colon cancer (Jones et al., 1984).
Forestomach and bladder
Rats were treated with methylnitrosourea (MNU) for 4 weeks and
then maintained on a diet containing 0 or 2% BHA for 32 weeks. BHA in
the diet resulted in a significant increase in the number per rat of
papillomas and papillary and nodular hyperplasia of the urinary
bladder and in the number of cancers per rat. There was also a
significant increase in the incidence of cancer and papillomas in the
forestomach of the MNU-induced rats (Imaida et al., 1984).
Gastric tumours
BHA and BHA plus NaCl exerted a promoting activity on
N-methyl-N'-nitro-N-nitrosoguanidine-induced forestomach
carcinogenesis in rats. The promotion was more marked in the BHA plus
NaCl group, suggesting a synergistic effect on tumour promotion
(Shirai et al., 1984).
Liver
BHA fed to rats for 5 weeks after administration of
N-ethyl-N-hydroxyethylnitrosamine resulted in an inhibition of the
induction of preneoplastic and neoplastic lesions (Ito et al.,
1983b).
Sequential administration of BHA resulted in a dose-dependent
inhibition of hepatic tumourigenesis in rats treated with
diethylnitrosamine (as measured by gamma-glutamyltranspeptidase and
the placental form of glutathione S-transferase, as markers of altered
focal populations of liver cells) (Thamavit et al., 1985).
Rats were fed diets containing aprofibrate alone or in
combination with BHA. There was a significant reduction in the number
of hepatic tumours greater than 5 mm, but not in the overall number of
tumours. Peroxisome proliferation was seen in the liver cells of
non-tumorous portions of the liver in rats fed aprofibrate with or
without BHT (Rao et al., 1984).
Liver and bladder
Rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine for 4
weeks, and then administered 2% BHA in the diet for 32 weeks, showed a
significant increase in the incidence of cancer and papillomas, in the
average number of papillomas, and in papillary or nodular hyperplasia
of the urinary bladder. In another study, dietary BHA significantly
inhibited the induction of gamma-glutamyl transpeptidase-positive foci
in the livers of rats treated with diethylnitrosamine (Imaida et al.,
1983).
Lung
Dietary administration of BHA to mice treated with hydrazine
sulfate had no effect on induction of lung tumours. However, BHA
inhibited the formation of lung tumours in mice receiving isoniazide
(Maru & Bhide, 1982).
BHA did not significantly increase the multiplicity of lung
tumours induced in mice treated with urethane, 3-methylcholanthrene,
or dimethylnitrosamine (Witschi et al., 1981).
In another study, dietary BHA did not enhance the development of
lung tumours in A/J mice treated with urethane, benzo(a)pyrene, or
dimethylnitrosamine. Pre-feeding mice with diets containing BHA prior
to treatment with urethane or benzo(a)pyrene did not affect tumour
incidence, but caused a marked decrease in tumour multiplicity.
Neither 3-BHA nor 2-BHA stimulated the proliferation of mouse lung
cells (Witschi & Doherty, 1954).
Mammary tumours
The incidence of mammary tumours induced in rats by
7,12-dimethylbenz(a)anthracene (DMBA) was shown to be increased when
the level of polyunsaturated fat in the diet was increased. BHA
supplementation of the diet was not effective in inhibiting the
DMBA-induced tumors. However, in another study, dietary BHA fed up to
1 week prior to, and even 1 week after, administration of DMBA was
effective in reducing the incidence of rat mammary tumours (King &
McCay, 1983; McCormick et al., 1984).
Pancreas
Rats maintained on diets containing 0.45% BHA were each given an
i.p. injection of 30 mg azaserine once a week for 3 weeks. Evaluation
of the pancreas 4 months after treatment showed dietary BHA resulted
in a 42% reduction in the number of acidophilic foci per pancreas, but
it was without effect on focal size (Roebuck et al., 1984).
Perinatal effects
Perinatal administration of BHA to pregnant mice treated with a
single dose of 7,12-dimethylbenz(a)anthracene resulted in substantial
reduction in tumour incidence in the F1, F1 and F2 generations
(Rao, 1982).
Special studies on reversibility of the effect of BHA on the rat
forestomach
BHA (food grade) was mixed dry into powdered diet, incorporated
into the diet in corn oil, or incorporated into a pelleted diet at 0
or 2% and fed to male F344 rats for 9 or 27 days. The increase in the
3H-thymidine labelling index (a standardized measure of
methyl-3H-thymidine labelling of squamous cells of the stomach
epithelium) in the forestomach region adjacent to the fundic
epithelium at 9 and 27 days were comparable for BHA in the ground and
pelleted diet, while larger increases were observed at 9 days than at
27 days for BHA in corn oil. Stomach lining thickness increases due to
BHA were markedly higher at 27 days than at 9 days. When BHA was mixed
dry into powdered diet at dose levels of 0, 0.1, 0.25, 0.5, 1, or 2%
and fed to rats for 9 days the no-effect level for the proliferative
effect, as measured by the 3H-thymidine labelling index, was 0.25%
(Nera et al., 1984).
Male F344 rats were fed diets containing 0, 0.1, 0.25, 0.5, or 2%
BHA, which was mixed dry into the powdered diet, for 13 weeks. Rats
fed 2% BHA showed lower food consumption and weight gain than animals
in the other groups and in the control group. At the end of the test
period, proliferative lesions were observed in the forestomach of the
2% group, but not in the other test groups. Elevation of the
3H-thymidine labelling index showed a dose-related response, and a
no-effect level of 0.25% BHA in the diet. Only the 2% group showed
histological changes of the forestomach. Removal of BHA from the diet
after 13 weeks, and maintenance on the control diet, resulted in a
rapid decline in the labelling index, and after 1 week was comparable
with the controls in all test groups. After 9 weeks on the normal
diet, the mucosae in the 2% treatment group had reverted almost to
normal (Iverson et al., 1985).
Groups of male and female Wistar Han/BGA rats were fed diets
containing 2% BHA for periods of 1, 2, or 4 weeks. Control groups were
pair-fed BHA-free diets. After one week epithelial damage, mild
hyperplasia, and hyperkeratosis of the forestomach mucosa were
reported. The hyperplasia and hyperkeratosis increased in severity at
weeks 2 and 4, but the other epithelial changes had decreased by that
time. The hyperplastic changes occurred in the region of the limiting
ridge. After a 4-week recovery period on a BHA-free diet, the
epithelial changes and mild hyperplasia induced in animals maintained
on the test diet for one week had completely disappeared, and only a
minimal increase in cellularity and basophilic staining of the
limiting ridge was noted. The more severe hyperplastic changes
observed in the groups maintained 2 and 4 weeks on the test diets
regressed only partially during a 4-week recovery period. In another
study, male rats were dosed daily by gavage with a solution of BHA in
arachis oil (5 ml/kg b.w.) of a dose equivalent to 1 g BHA/kg b.w./day
for periods of 1, 2, 4, 8, 16, and 32 days. Forestomach changes
occurred mainly in the area remote from the limiting ridge. After 1
dose mild inflammation, minor epithelial defects, and increased
mitotic activity were observed in the forestomach. Mild hyperplasia
and hyperkeratosis, with a marked increase in mitotic activity, were
apparent after 2 days. Epithelial hyperplasia became more marked with
4 and 8 daily intubations, but mitotic activity that was markedly
increased after 4 doses was less pronounced after 8 doses. After 16 or
32 daily intubations the hyperplastic lesions in the forestomach
appeared to have regressed (Altmann et al., 1985).
Groups of Wistar rats were fed diets containing 0, 0.125, 0.5, or
2% BHA in crystalline form for 90 days. At the highest level fed there
were marked changes in the forestomach, characterized as
hyperkeratosis and massive papillary hyperplasia with epithelial
changes in the basal area. Less-pronounced effects were observed at
the lower dose levels. Another group of rats was fed diets containing
2% BHA for 90 days, and then maintained on a BHA-free diet for 4
weeks. After the recovery period only mild hyperkeratosis and moderate
hyperplasia of the forestomach were observed. In another study, groups
of Wistar rats were fed diets containing 0, 0.125, 0.5, or 2% BHA
dissolved in arachis oil for 90 days. In the highest-dose group,
pronounced hyperplasia and in some cases papillary hyperplasia of the
forestomach were observed. In contrast to the study in which the BHA
in the diet was in the crystalline form, the lesions were confined to
the limiting ridge. No changes of the forestomach were observed at the
lower dose levels. When rats were maintained on 2% BHA for 90 days and
then maintained on a BHA-free diet for 4 weeks or 8 weeks, only 1/10
rats showed any effect on the forestomach (mild hyperplasia), and this
effect persisted in 2/10 rats after an 8-week recovery period. None of
the rats in these studies showed any changes in the oesophagus
(Altmann, 1986).
In another feeding study, rats were maintained on diets with 2%
BHA dissolved in arachis oil for periods of 6, 12, or 15 months with
or without a subsequent 2 or 7-month period of BHA-free diet.
Histological studies were carried out on (1) the oesophagus near the
cardiac orifice, (2) forestomach and glandular stomach at the greater
curvature adjacent to the limiting ridge, and (3) forestomach and
glandular stomach near the oesophageal entry. Generalized hyperplasia
with hyperkeratosis or parakeratosis were observed, especially in the
vicinity of the limiting ridge. After 12 months of exposure, BHA
induced focal dysplasia of the forestomach epithelium in 3/10 rats and
generalized dysplasia of the forestomach epithelium in 4/10 rats. The
type and extent of lesions were similar in the different sections of
the forestomach. After 12 months on the test diet and a recovery
period of 2 months, lesions at the greater curvature had almost
completely regressed, whereas lesions in the stomach near the
oesophageal entry were still present. After a recovery period of 7
months following a 15-month period on the test diet, there was a
nearly complete regression of the forestomach changes that included
extensive hyperplasia, papillomas, dysplastic changes, and invasive
growth (which did not reach the muscularis mucosae to become malignant
under the conditions of this study) (Altmann, 1986).
Special studies on species differences
Mice
NMRI mice were dosed daily by gavage with BHA dissolved in
arachis oil at dose levels equivalent to 0 or 1000 mg BHA/kg b.w./day
for 28 days. When examined macroscopically, visible lesions were
observed in the forestomach, which were similar to hyperkeratosis
observed in rats (Altmann, 1986).
Hamsters
Male Syrian golden hamsters were maintained on a diet containing
0 or 2% BHA (pelleted) or 1% BHA (powdered) for 24 weeks. Tumours of
the forestomach were observed in all hamsters in the treated group. No
tumours were reported in the control group or in other organs examined
(Ito et al., 1983).
In another study, groups of Syrian golden hamsters were
maintained on powdered diets containing 0 BHA, 1% "crude BHA" (98%
3-tert isomer and 2% 2-tert isomer), 3-tert BHA, or 2-tert BHA
for 1 to 4 weeks. Hyperplasia of the forestomach was found to be more
progressive and severe in hamsters fed 3-tert BHA or "crude BHA"
than those fed 2-tert BHA (Ito et al., 1984).
Groups of hamsters were fed diets containing 0 or 2% BHA for a
period of 90 days. The forestomach changes differed from those
observed in rats and mice, showing no hyperkeratosis when examined
macroscopically. When examined histologically, mild epithelial
hyperplasia and hyperkeratosis were observed. The effects were more
marked in the females (Altmann, 198b).
Guinea pigs
Test animals were dosed daily by gavage with BHA dissolved in
arachis oil at dose levels equivalent to 0 or 1000 mg BHA/kg b.w./day
for 28 days. No gross changes were observed in the stomach. (Note: The
guinea pig is a rodent species that does not have a forestomach)
(Altmann, 1986).
Dogs
Beagle dogs were fed diets containing 0, 1.0, or 1.3% BHA for 180
days. At autopsy no gross or microscopic lesions were found in the
stomach that could be attributed to the presence of BHA in the diet.
Neither hyperplasia nor cellular proliferation were observed. Electron
microscopic examination of the oesophagus (above the stomach and at
the cardio-oesophageal junction), of the cardia area, and of the main
body of the stomach revealed no differences in ultrastructure between
the tissues from test and control animals. Enzyme analysis of hepatic
tissues showed a significant increase in mixed-function oxidases, UDP
glucuronyltransferase, glutathione-S-transferase, and epoxide
hydrarase activities in the BHA-treated animals (Ikeda et al., 1986).
Groups of 3 or 4 male and female beagle dogs were maintained on
diets containing 0, 0.25, 0.5, or 1% BHA for 6 months. A dose-related
retardation of growth was observed. Serum biochemical analyses carried
out at 1, 3, and 6 months showed a slight decrease in albumin content
and increases in alkaline phosphatase and leucine aminopeptidase
activities in the high-dose groups. At autopsy, liver weights were
increased in the test groups, but no histological changes were
reported. Histopathological and histometrical studies showed no
significant mucosal alterations in the stomach (fundic and pyloric
areas), oesophagus, or duodenum in the test animals. The mitotic index
in the basal layer of the squamous epithelium of the distil part of
the oesophagus was similar in test and control groups (Tobe et al.,
1986).
Pigs
Pregnant pigs (Danish landacre) were fed diets containing 0,
0.5, 1.9, or 3.7% BHA for 16 weeks. At necropsy, epithelial changes in
the oesophageal part of the stomach were similar in test and control
groups. No papillomas and no changes in the glandular part of the
stomach were reported. Linear yellow-brown rough epithelium was seen
in the whole length of the oesophagus in a few pigs in the middle- and
high-dose groups. Microscopic examination of these tissues showed
proliferative and parakeratotic changes of the epithelium. The changes
in the oesophagus were not seen in the low-dose or control groups and
have not been observed in historical controls (Wurtzen & Olsen, 1986).
Monkeys
Monkeys (Macaca fascicularis) were given 0, 125, or 500 mg
BHA/kg b.w./day by gavage in corn oil 5 times/week for 20 days, after
which time the high dose was halved. After 85 days the study was
terminated. Histopathology of the stomach showed no treatment-related
effects. However, there was a significant increase in the mitotic
index of the squamous epithelial cell lining of the distal oesophagus
in the high-dose group (Iverson et al., 1985b).
Special studies on the effect of structurally-related substances
on the forestomach of the rat
Groups of 5 to 10 male and female rats were fed diets containing
2% BHA, tert-butylhydroquinone (TBHQ), 1,4-dimethoxybenzene,
hydroquinone, 4-methoxyphenol, 3-methxyphenol, 2-methoxyphenol,
anisol, rho-cresol, or phenol or 1% BHT for 28 days. BHT did not
induce forestomach lesions. TBHQ-treated animals showed mild
hyperplasia of the forestomach mucosa with locally-increased
hyperplasia of the basal cells. 4-Methoxyphenol caused circular deep
ulceration parallel to the limiting ridge, with hyperplasia and mild
hyperkeratosis in the adjoining mucosa. Neither 3- nor 2-methoxyphenol
nor 1,4-dimethoxy-benzene had any effect on the forestomach,
rho-cresol and phenol also failed to cause any effect on the
forestomach epithelium (Altmann, 1986).
Weanling male F344 rats were maintained on diets containing one
of the following phenols or acids: 2% 3-BHA, 4% 4-hydroxybenzoic acid,
4% methyl-4-hydroxybenzoic acid ester, 4% ethyl-4-hydroxybenzoic acid
ester, 4% n-propyl-4-hydroxybenzoic acid ester, 4% n-butyl-
4-hydroxybenzoic acid ester, 2% 4-methoxyphenol, 4% propionic acid, or
0.5% acetylsalicylic acid for periods ranging from 9 to 27 days. At
the end of the test period studies were carried out to determine the
effects of administration of these compounds on the methyl-3H-
thymidine labelling index and histological appearance of the
forestomach.
3-BHA was as effective as food grade BHA in inducing cellular
proliferation in the prefundic region. Methyl-4-hydroxybenzoic acid
ester did not increase the thymidine labelling index in the
forestomach epithelium in the prefundic area or the main body of the
tissue. However, the thymidine labelling index in the prefundic region
was progressively increased in going from the ethyl to the n-butyl
ester, the 4% n-butyl ester being as active as 2% BHA in this system.
Propionic acid was without effect after 9 days, but it caused a 2-fold
increase in the labelling index in the main body of the forestomach
epithelium after 27 days. Acetylsalicylic acid alone did not affect
thymidine labelling of either the prefundic or midregion of the rat
stomach. However, simultaneous administration of 2% BHA and 0.5%
acetylsalicylic acid resulted in a marked reduction (43%) of the
proliferative effect of BHA in the prefundic region and appeared to
protect the midregion of the forestomach. Histopathological changes
paralleled the results obtained from the thymidine labelling index
studies (Rodrigues et al., 1986).
Human studies
Metabolism
Two males were given 100 mg BHA. There was a significant
conversion of BHA to TBHQ (0-demethylation) prior to its conjugation
and excretion, primarily as the glucoronide with lesser amounts as the
O-sulphate (El-Rashidy & Niazi, 1983).
Comments
Studies have been conducted that provide additional information
on the proliferative changes observed in the forestomach of rats fed
BHA, and also the effect of BHA on the stomach and oesophagus of
species that do not have a forestomach. The data show that induction
of hyperplasia in the forestomach of the rat is dose-dependent, and
can be reversed when BHA is removed from the diet. In one species that
does not have a forestomach, the dog, levels of BHA that produced
effects in the forestomach of the rat had no effect on either the
stomach or oesophagus. However, in monkey and pig studies there was
some evidence that BHA produced effects in the oesophagus. In the case
of the monkey, an increased mytotic rate was reported, and in the case
of the pig largely macroscopically-diagnosed hyperkeratosis was
reported.
In both these cases the Committee believes that the studies
should be repeated. In particular, studies should be performed in the
monkey in which BHA is administered in the diet (only gavage data are
presently available in the monkey).
The results of several tests on the genotoxicity of BHA,
involving both bacterial and mammalian cells, lend additional support
to previous evaluation of several in vitro and in vivo systems
which do not show BHA to be mutagenic.
New data were not submitted to meet the requirements for a
multigeneration reproduction study.
The present evaluation is based upon the results of long-term
feeding studies showing that rats can be maintained on diets
containing up to 0.125% BHA without any significant adverse effect
(summarized under "Special studies on the effect of BHA on the
stomach").
EVALUATION
Level causing no toxicological effect
Rat: 1250 ppm (0.125%) in the diet, equivalent to 62.5 mg/kg
b.w./day
Estimate of temporary acceptable daily intake for man
0-0.3 mg/kg b.w.
Further work or information
Required (by 1988)
1. Studies in pigs and monkeys to explore the potential for BHA
to cause oesophageal hyperplasia in these species. These studies
should be carried out with dietary BHA. The Committee recognizes the
technical difficulties in carrying out this study in the monkey due to
potential diet rejection, but emphasizes that it should be attempted.
2. Mutigeneration reproduction study.
Desirable
Studies to determine the mechanism involved in the effects of BHA
on the forestomach.
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See Also:
Toxicological Abbreviations
Butylated hydroxyanisole (WHO Food Additives Series 5)
Butylated hydroxyanisole (WHO Food Additives Series 10)
Butylated hydroxyanisole (WHO Food Additives Series 24)
BUTYLATED HYDROXYANISOLE (JECFA Evaluation)