Mutagenicity of hydroquinone and phenol
COM statement COM/00/S1 - January 2000
Introduction
1. The Health and Safety Executive (HSE) asked for advice from the Committee
during 1994 and 1995 and most recently in 1999 on the interpretation of
the mutagenicity data on hydroquinone and phenol. The advice from COM
was required by HSE as part of its regulatory reviews of occupational
exposure limits to hydroquinone and phenol.
2. The principal use for hydroquinone is in the manufacture of black and
white film developers. Other uses include the manufacture of antioxidants
and polymerisation inhibitors; as a chemical intermediate in the manufacture
of pharmaceutical, agrochemicals and dyes; in the production of cosmetics
and topical creams; and as a laboratory reagent. Occupational exposure
to hydroquinone in the UK is mainly via inhalation of airborne concentrations
usually below 1 mg m-3 and averaging about 0.15 mg.m-3
(8 hour time weighted average (TWA)). Dermal exposure to hydroquinone
in the occupational setting is low. [The current UK occupational inhalation
exposure limits for hydroquinone are 2 mg.m-3 as an 8-hour
TWA and 4 mg.m-3 as a 15 minute short-term exposure limit (STEL).(1)]
3. Phenol is mostly used in the manufacture of phenolic resins, and is
also used in the manufacture of disinfectants, some shampoos and in the
preparation of soaps. The highest occupational exposures would be expected
to occur in the paint stripping of aircraft, where exposures are controlled
to below 8 mg.m-3 (8 hour TWA). The other possible circumstances
where high exposures may occur is in the use of phenolic resins in foundries.
The resins contain small amounts of free phenol and whilst most exposures
are very low, in some special cases exposures of up to 12 mg.m-3
(8-hour TWA) may occur. There are no data available for occupational
dermal exposure to phenol. However, as personal protective equipment is
known to be extensively used, it is considered that exposure via the skin
will be very low. [The current UK occupational inhalation exposure limits
for phenol are 20 mg.m-3 as an 8-hour TWA and 39 mg.m-3
as a 15 minute STEL.(2)]
Overview of COM considerations.
4. A brief overview of the Committee's discussions held in 1994, 1995
and 1999 is given below. Full details of the Committee's considerations
in 1994 and 1995 have been published in the Annual reports.(2,3)
5. In 1994, the COM agreed that both hydroquinone and phenol should be
regarded as somatic cell in-vivo mutagens.(4-11) The Committee agreed
that for exposure to these two compounds by the oral route there was potential
for a threshold of activity as there was good evidence that two protective
mechanisms (namely rapid conjugation and detoxification via the glutathione
pathway) would substantially reduce systemic exposure to any active metabolites
formed. However, Members agreed that there were insufficient data on inhalation
and dermal exposure and it was not possible to assume that a threshold
existed for activity when exposure was via the respiratory tract or the
skin. The Committee noted the information from one published paper that
when radiolabelled phenol was given intratracheally, initially all the
radiolabel in the plasma was present as phenol.(12) These data suggested
that there was little conjugation of phenol on the "first-pass"
from airways to the circulation. The Committee recommended that appropriate
toxicokinetic studies were needed.
6. In 1995, a submission from industry to the HSE provided some additional
studies on the metabolism of hydroquinone and phenolic derivatives in
the lung and skin, HSE requested the Committee's assessment of these new
data.(13-20)
7. The Committee agreed that the new data on the metabolism of hydroquinone
and phenol in animals and in humans were valuable but appropriate studies
to determine the extent of pre-systemic metabolism following either inhalation
or dermal exposure had not been undertaken. It was agreed that the following
studies were needed to answer this question.
i) Further in-vivo studies in rats or dogs using administration
of hydroquinone or phenol via a bronchoscope with very early sampling
for free and conjugated test substance in the blood.
ii) It was essential that the method be sensitive enough to measure both
free and conjugated substance.
iii) Additional investigations in volunteers following dermal administration
would also be useful but should be undertaken using higher doses of hydroquinone
and early sampling times. (Members acknowledged that the skin irritancy
of phenol would limit the dose level of this compound that could be studied.)
8. In 1999, further data from published papers on the kinetics of hydroquinone
in rats following intratracheal instillation and on its percutaneous absorption
in in-vitro studies using rat skin and human stratum corneum were provided
to the Committee.(21,22) A number of additional in-vivo mutagenicity studies
including an investigation of site of contact mutagenicity in skin and
respiratory tract of MutaTM mice using the LacZ transgene
were also considered.(23-25)
9. Regarding the new data on hydroquinone,(23) the Committee agreed that
a positive result had been obtained in a new bone-marrow micronucleus
assay and that these results were consistent with previous studies considered
in 1994. The new toxicokinetic study in which rats were given a single
intratracheal dose of 14C-hydroquinone showed detectable free hydroquinone
in arterial blood within 5-10 seconds after dosing.(21) This new information
suggested a potential risk of site-of- contact and systemic mutagenic
effects following inhalation exposure to hydroquinone.
10. Regarding the new data on phenol, the new bone-marrow micronucleus
studies showed that a small but consistent positive result with phenol
could be identified in studies conducted according to OECD guidelines
at intraperitoneal dose levels of around 100-160 mg/kg.(23,24)
11. The Committee considered the new transgenic mutagenicity test with
phenol using the LacZ transgene in MutaTM mice.(25)
Animals were given either dermal doses of 100 mg/kg bw or exposed for
a period of 2 hours to a vapour containing 100 ppm phenol (390 mg.m-3)
on five consecutive days. Samples of tissues (liver, bone marrow, and
blood, and also for inhalation exposure to nasal epithelia and lung) were
taken at a number of time points after dosing and the DNA extracted and
packaged for analysis of LacZ mutants. Members noted that a positive
control chemical (benzo(a)pyrene) had been used for the dermal studies
but no positive control had been used for the inhalation studies presumably
because of the potential hazards involved in handling and controlling
exposures to test animals. Members acknowledged that there would be an
observable degree of inter-animal variation in results for in-vivo mutation
assays such as LacZ, which complicates the assessment of data but
agreed that the results reported for the study concerned could not be
assessed in view of the failure to obtain acceptable levels of DNA packaging
in many of the trials. The Committee considered that inhalation exposure
to phenol followed by assessment of mutation frequency in nasal tissue
were critical to the identification of site-of-contact mutagenicity and
felt that a further study with acceptable levels of DNA packaging would
be needed before any conclusions on site-of-contact mutagenicity could
be reached.
Overall conclusions
12. The Committee reached the following conclusions based on all the available
information.
Hydroquinone
a. Hydroquinone is an in-vivo mutagen in somatic cells,(4-11) but there
is no convincing evidence for effects in germ cells in vivo.(26-28) Any
risk to human health by ingestion would be likely to be greatly reduced
by rapid conjugation and detoxification via the glutathione pathway. Furthermore,
mutagenicity appeared to be positively related to peroxidase activity
while catalase could also have a protective role.(29) Actual systemic
exposure levels in humans would be very much lower than levels at which
positive results had been achieved in studies in animals.
b. The Committee concluded that by the oral route there was potential
for a threshold of activity based on the protective mechanisms outlined
at (a).
c. However, there is insufficient evidence to support a threshold approach
to risk assessment for inhalation or dermal exposure to hydroquinone.
d. The Committee concluded that the available data showed that occupational
exposure to hydroquinone was associated with a mutagenic hazard but it
was not possible to quantify the risk.
Phenol
a. In-vitro mutagenicity data on phenol were of poor quality and results
difficult to interpret, but in-vivo data show phenol to be a somatic cell
mutagen following intraperitoneal doses of approximately 100-160 mg.kg.(5,8,23,24)
No conclusions can be drawn from the one available study in transgenic
animals (MutaTM mice) on site-of-contact mutagenicity following
dermal or inhalation exposure.(25) The Committee felt that a further study
in transgenic animals, with acceptable levels of DNA packaging, would
be helpful before any conclusions on site-of-contact mutagenicity could
be reached. Data from germ cell studies in vivo were inadequate to allow
any definite conclusions to be drawn.(30,31)
b. Any risk to human health by ingestion would be likely to be greatly
reduced by rapid conjugation and detoxification via the glutathione pathway.
Furthermore mutagenicity also appeared to be positively related to peroxidase
activity while catalase could also have a protective role. Actual systemic
exposure levels in humans would be very much lower than levels at which
positive results had been achieved in studies in animals.
c. The Committee concluded that by the oral route there was potential
for a threshold of activity based on the protective mechanism outlined
at (b).
d. However, there is insufficient evidence to support a threshold approach
to risk assessment for inhalation or dermal exposure to phenol.
e. The Committee concluded that the available data showed that occupational
exposure to phenol was associated with a mutagenic hazard but it was not
possible to quantify the risk.
2. Department of Health (1994). Annual report of the Committees on Toxicity,
Mutagenicity, Carcinogenicity of Chemicals in Food, Consumer Products
and the Environment. Published HMSO, London.
3. Department of Health (1995). Annual report of the Committees on Toxicity,
Mutagenicity, Carcinogenicity of Chemicals in Food, Consumer Products
and the Environment. Published HMSO, London.
4. Xu W and Adler ID (1990). Clastogenic effects of known and suspect
spindle poisons studies by chromosome analysis in mouse bone marrow cells.
Mutagenesis, 5, 371-374.
5. Ciranni R, Barale R, Ghelardini G and Lopriene N (1988). Benzene and
the genotoxicity of its metabolites. II. The effect of the route of administration
of the micronuclei and bone marrow depression in mouse bone marrow cells.
Mutation Research, 209, 23-28.
6. Adler ID, Kliesch U, Van Hummelen P and Kirsh-Volders M (1991). Mouse
micronuceleus tests with known and suspect spindle poisons: results from
two laboratories. Mutagenesis, 6, 47-53.
7. Adler ID and Kliesch U (1990). Comparison of single and multiple treatment
regimes in the mouse bone marrow micronucleus assay for hydroquinone and
cyclophosphamide. Mutation Research, 234 115-123.
8. Ciranni R, Barale R, Marrazzini A and Leprieno N (1988). Benzene and
the genotoxicity of its metabolites. I. Transplacental activity in mouse
fetuses and in their dams. Mutation Research, 208, 61-67.
9. Van Hummelen P, Deleener A, Vanparys A and Kirsch-Volders M (1992).
Discrimination of aneuploidogens from clastogens by C-banding, DNA and
area measurements of micronuclei from mouse bone marrow. Mutation Research,
271, 13-28.
10. Gocke E , Wild D, Eckhardt K and King MT (1983). Mutagenicity of cosmetics
ingredients licensed by the European Communities. Mutation Research,
90, 90-109.
11. Barale R, Marrazzini A, Betti C, Vangelisti V, Loprieno N and Barrai
I (1990) Genotoxicity of two metabolites of benzene: phenol and hydroquinone
show strong synergistic effects in vivo. Mutation Research, 244,
15-20.
12. Hogg SE, Curtis CG, Upshall DG and Powell GM (1981). Conjugation of
phenol by rat lung. Biochemical Pharmacology, 30, 1551-1555.
13. Barber E, Hill T and Schun DB (1979). Percutaneous absorption of hydroquinone
(HQ) through rat and human skin in-vitro. In confidence report provided
by Kodak Ltd.
14. Lockhart HB, Fox JA (1985). Metabolic fate of 14C-hydroqunione administered
by intratracheal instillation to male fischer 344 rats. In confidence
report provided by Kodak Ltd.
15. Fox JA, English JC, Lockhart HB (1980). Blood elimination kinetics
of 14C-hydroquinoneadministered by intragastric intubation, intracheal
instillation or intravenous injection to male fischer 344 rats. In confidence
report provided by Kodak Ltd.
16. Lockhart HB, Fox JA, DiVincenzo GD (1984). The metabolic fate of 14C-hydroquinone
administered by gavage to male fischer 344 rats. In confidence report
provided by Kodak Ltd.
17. Cassidy MK and Houston JB (1984). In-vivo capacity of hepatic and
extra-hepatic enzymes to conjugate phenol. Drug Metabolism and Disposition,
12, 619-624.
18. Cassidy MK, Houston JB (1980). In-vivo assessment of extrahepatic
conjugative metabolism on first pass effects using the model compound
phenol. Communications in Journal of Pharmacy and Pharmacology,
32, 57-59.
19. Deisenger PJ, Hill TS and English JC (1994). Human exposure to naturally
occurring hydroquinone. In confidence report provided by Kodak Ltd.
20. Hui X, Wester RC, and Maibach HI (1994). In-vivo percutaneous absorption
of hydroquinone in normal human volunteers: Absorption, excretion, skin
tape stripping, ipsilateral and contralaterial blood profile. In confidence
report provided by Kodak Ltd.
21. Deisenger and English CJ (1999). Bioavailability and metabolism of
hydroquninone after intratracheal instillation in male rats. Drug Metabolism
and Disposition, 27, 442-448.
22. Barber ED, Hill T and Schum DB (1995). The percutaneous absorption
of hydroquinone (HQ) through rat and human skin in-vitro. Toxicology
Letters, 80, 167-172.
23. Marrazini A, Chelotti L, Barrai I, Loprieno N, Barale R (1994). In
vivo genotoxic interactions among three phenolic benzene metabolites.
Mutation Research. 341 29-46.
24. Chen H, Eastmond DA (1995). Synergistic increase in chromosomal breakages
within the euchromatic induced by interactions of benzene metabolites
phenol and hydroquinone in mice. Carcinogenesis, 16, 1963-1969.
25. Covance (1999). Phenol: Induction of LacZ mutation in tissues of treated
MutaäMice. In-confidence unpublished draft report of Covance report
No 501/2-D5140.
26. Miller BM and Adler ID (1992). Aneuploidy induction in mouse spermatocytes.
Mutagenesis, 7, 69-76.
27. Ciranni R and Alder ID (1991). Clastogenic effects of hydroquinone:
induction of chromosomal aberrations in mouse germ cells. Mutation
Research, 263, 223-229.
28. Eastman Kodak Company (1984). Hydroquinone: a dominant lethal study
in male rats. In-confidence Report 189299E, TX-84-23.
29. Levay G, Ross D and Bodell WJ (1993). Peroxidase activation of hydroquinone
results in the formation of DNA adducts in HL-60 cells, mouse bone marrow
macrohpages and human bone marrow. Carcinogenesis, 14, 2329-2334.
30. Bulsiewicz H (1977). The influence of phenol on chromosomes in mice
(musmusculus) in the process of spermatogenesis. Folia Morphol (Warsz),
36, 13-22.
31. Skare JA, Schrotel KR (1984). Alkaline elution of rat testicular DNA:
detection of DNA strand breaks after in vivo treatment with chemical mutagens.
Mutation Research, 130, 283-294.
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