International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 3)

For definition of Groups, see Preamble Evaluation.

VOL.: 68 (1997) (p. 267)

CAS No.: 18307-23-8
Chem. Abstr. Name: Sepiolite (Mg3H2(SiO3)4 . xH2O

CAS No.: 15501-74-3
Chem. Abstr. Name: Sepiolite (Mg2H2(SiO3)3 . H2O)

CAS No.: 63800-37-3
Chem. Abstr. Name: Sepiolite (Mg2H2(SiO3)3 . xH2O)

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Sepiolite is a hydrated magnesium silicate that occurs as a fibrous chain-structure mineral in clays in several areas of the world. The major commercial deposits of sepiolite are in Spain. Sepiolite fibre characteristics vary with the source, but fibre lengths in commercial samples are generally less than 5 mm. Sepiolite has been mined since the 1940s, finding its greatest use as an absorbent, particularly for pet waste, and oils and greases. It is also used as a drilling mud and as a carrier for fertilizers and pesticides. Meerschaum, a compact form of sepiolite, has been used for centuries for the production of smokers' pipes. Occupational exposure occurs during the mining, milling, production and use of sepiolite.

5.2 Human carcinogenicity data

No data were available to the Working Group.

5.3 Animal carcinogenicity data

In one inhalation study in rats using sepiolite from Vicálvaro-Vallecas, Spain, in which all fibres were shorter than 6 mm, no significant increase in tumour incidence was found.

In one study by intrapleural injection to rats, sepiolite from China (fibre length, 1-100 mm) induced pleural mesotheliomas. In similar studies by intrapleural injection using samples from Turkey and Vicálvaro-Vallecas (all fibres shorter than 6 mm), no increases in tumour incidence were observed.

In two studies in rats by intraperitoneal injection using samples (0.9% of fibres > 5 mm) from Vicálvaro-Vallecas, no significant increases in the incidences of abdominal tumours were found.

In one study in mice by intraperitoneal injection, sepiolite from China (fibres, 1-100 mm in length) produced a small increase in the incidence of peritoneal mesotheliomas but sepiolite from Turkey (fibre length, 3-5 mm) did not.

5.4 Other relevant data

One study in sepiolite-exposed workers demonstrated clinical evidence of pulmonary function deficits. The results of one in-vitro study indicated that sepiolite was relatively potent in inducing superoxide anion release from both hamster and rat alveolar macrophages. Sepiolite is strongly haemolytic in some in-vitro assays.

In a single study, samples of sepiolite from China, Japan, Spain and Turkey induced polyploidy, but not chromosomal aberrations, in cultured Chinese hamster lung cells.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of sepiolite.

There is limited evidence in experimental animals for the carcinogenicity of long sepiolite fibres (> 5 mm).

There is inadequate evidence in experimental animals for the carcinogenicity of short sepiolite fibres (< 5 mm).

Overall evaluation

Sepiolite cannot be classified as to its carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.

Previous evaluation: Suppl. 7 (1987) (p. 71)


Last updated 05/23/97

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