Carcinogenicity of boiling water extract of bracken, Pteridium aquilinum.

Carcinogenicity of an aqueous extract of bracken was studied in inbred strain ACI rats. In Experiment 1, Group 1 rats received a diet containing unprocessed dry bracken powder for 3 months, Group 2 received the boiling water extract of dry bracken as drinking water for 16 months, Group 3 received the cold water extract of dry bracken as drinking water for 16 months, and Group 4 received a diet containing the concentrated boiling water extract of dry bracken during the whole experimental period. Rats in Experiment 2 also received a diet containing the boiling water extract of dry bracken. A control group was fed a normal diet. Majority of the animals in Group 1 developed multiple ileal tumors, such as adenomas and adenocarcinomas. In Group 2, 6 of 11 rats which survived beyond 7 months developed tumors in either the ileum or urinary bladder, or in both. Rats in Group 3 had no tumor. In Group 4 and in Experiment 2, all the animals except 1 rat in Experiment 2 had urinary bladder tumor. Furthermore, almost all the rats in these groups had simultaneously ileal tumors. Based on these results, it may be assumed that the carcinogen in bracken is extractable in boiling water and is most probably also water-soluble.