Evaluation of chemical flame retardants for carcinogenic potential

Tetrakis(hydroxymethyl)phosphonium chloride (THPC) and Pyroset TKP, which is the mixed acetate/phosphate of the same phosphonium base, are widely used in flame-retardant cotton fabrics, particularly in children's sleepwear. THPC degrades thermally and under certain chemical conditions to yield hydrochloric acid and formaldehyde (CH2O). In solution, the latter two compounds are in equilibrium with the known potent carcinogen bis(chloromethyl)ether (BCME). A sample of commercial THPC contained from 4% (at pH 0.4) to 14% (at pH greater than 4.5) free CH2O. The material, as supplied by the manufacter, showed pH 0.4. Gas chromatographic analysis of aqueous commercial THPC did not reveal any peak chracteristic of BCME under conditions where 0.1 ppm of the material can be detected. Application to mouse skin of THPC ( 2 mg in 0.1 ml DMSO) and of Pryset TKP (7 mg in 0.1 ml DMSO), three times per week for 400 days with 20 female ICR/Ha Swiss mice per group, gave one squamous carcinoma in the THPC-treated group. THPC was inactive as an initiating agent in two-stage mouse skin carcinogenesis with phorbol myristate acetate as promoter. Both agents were active as tumor promoters, using a single application of 7,12-dimethylbenz[a]anthracene (20 microng in 0.1 ml acetone) as initiator. With THPC as promoter (2 mg in 0.1 ml DMSO, thrice weekly) 3 of 20 mice bore papillomas which progressed to squamous carcinoma. With Pyroset TKP as promoter (7 mg in 0.1 ml DMSO) 7 of 20 mice bore papillomas of which two progressed to squamous carcinoma.