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

(Group 3)

For definition of Groups, see Preamble Evaluation.

VOL.: 68 (1997) (p. 409)

CAS No.: 24938-64-5
Chem. Abstr. Name: Poly(imino-1,4-phenyleneiminocarbonyl-1,4-phenylenecarbonyl)

CAS No.: 25035-37-4
Chem. Abstr. Name: 1,4-Benzenedicarboxylic acid, polymer with 1,4-benzenediamine

CAS No.: 26125-61-1
Chem. Abstr. Name: 1,4-Benzenedicarbonyl dichloride, polymer with 1,4-benzenediamine

5. Summary of Data Reported and Evaluation

5.1 Exposure data

para-Aramid fibres are long-chain synthetic polyamides, most commonly poly(para-phenyleneterephthalamide), and have been produced commercially since the early 1970s. The combination of high strength, high temperature resistance and light weight make these fibres useful in the reinforcement of composite materials for the aerospace and sports equipment industries, in woven fabrics used in protective apparel and in automotive brake pads and gaskets.

During abrasive processing operations, small-diameter respirable fibrils can be released into the air. Highest occupational exposures to para-aramid fibrils have been measured in the processing of shorter (staple) fibres in yarn.

5.2 Human carcinogenicity data

No data were available to the Working Group.

5.3 Animal carcinogenicity data

para-Aramid fibrils were tested for carcinogenicity in one study in rats by inhalation exposure. An increased incidence of cystic keratinizing squamous-cell carcinomas was reported. However, subsequent re-examinations and evaluation of these lesions revealed a diagnosis of pulmonary keratinizing cysts. The biological significance of these lesions is unclear. para-Aramid fibrils were also tested in two experiments in rats by intraperitoneal injection. No intra-abdominal tumours were observed.

5.4 Other relevant data

Inhalation exposure of rats to para-aramid fibrils for two years produced minimal pulmonary fibrosis. Chronic inhalation studies demonstrate that inhaled para-aramid fibrils are biodegradable in the lungs of rats. Similarly, two-week inhalation studies in rats and hamsters demonstrate transient pulmonary inflammatory and cell proliferative responses and biodegradability of inhaled fibrils in the lungs of exposed animals. para-Aramid fibrils demonstrate some cytotoxic activity to cells under in-vitro conditions.

para-Aramid fibril extracts were not mutagenic to Salmonella typhimurium or to Chinese hamster V79 fibroblasts.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of para-aramid fibrils.

There is inadequate evidence in experimental animals for the carcinogenicity of para-aramid fibrils.

Overall evaluation

para-Aramid fibrils cannot be classified as to their carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.


Last updated 05/27/1997

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       Toxicological Abbreviations