VOL.: 71 (1999) (p. 691)
Chem. Abstr. Name: 1,4-Benzenediol
5.1 Exposure data
Exposure to hydroquinone may occur during its production, its use as an inhibitor, antioxidant and intermediate in the production of dyes, paints, motor fuels and oils, and in black-and-white photographic processing. Hydroquinone occurs naturally in certain plant species. It is used as a topical treatment for skin hyperpigmentation.
5.2 Human carcinogenicity data
A cohort of workers with definite and lengthy exposure to hydroquinone had low cancer rates compared with two comparison populations; the reason for the lower than expected rates is unclear. A cohort of lithographers, some of whom had worked with hydroquinone, had an excess of malignant melanoma based on five cases; only two of the cases had reported exposure to hydroquinone.
5.3 Animal carcinogenicity data
Hydroquinone was tested for carcinogenicity in two studies in mice and two studies in rats by oral administration. It was also tested in rats for promoting activity in assays for bladder, stomach, liver, lung, oesophagus and kidney carcinogenesis and in one study in hamsters for pancreatic carcinogenesis.
In mice, hydroquinone induced hepatocellular adenomas in females in one study and in males in another study. In rats it induced renal tubule adenomas in males in two studies.
Hydroquinone had no promoting activity in most assays; an increase in the multiplicity of oesophageal tumours was observed in one study and in the multiplicity of renal cell tumours in another study. No promoting effect on pancreatic carcinogenesis was observed in the study in hamsters.
5.4 Other relevant data
Hydroquinone is metabolized mainly to conjugates, but a small percentage may be converted to 1,4-benzoquinone, conjugated with glutathione or form DNA adducts in vitro.
It caused toxicity in several organs, notably the kidney and forestomach.
Hydroquinone was mutagenic in many in-vitro systems using a variety of end-points. Also, after intraperitoneal administration, it caused genotoxicity or chromosomal aberrations in bone marrow.
There is inadequate evidence in humans for the carcinogenicity of hydroquinone.
There is limited evidence in experimental animals for the carcinogenicity of hydroquinone.
Hydroquinone is not classifiable as to its carcinogenicity to humans (Group 3).For definition of the italicized terms, see Preamble Evaluation.
Previous evaluations: Vol. 15 (1977); Suppl. 7 (1987)
See Also: Toxicological Abbreviations Hydroquinone (EHC 157, 1994) Hydroquinone (HSG 101, 1996) Hydroquinone (ICSC)