Estimated intakes of pyrrolizidine alkaloids by humans. A comparison with dose rates causing tumors in rats.

Pyrrolizidine alkaloid poisoning in humans is associated with the consumption of plants containing the alkaloids, either as contaminants of grains or as infusions for medicinal purposes. The alkaloids are carcinogenic in rats but have not been associated, so far, with tumors in humans. For the known instances of human intake of pyrrolizidine alkaloids, the main alkaloids involved and estimated consumption rates have been tabulated. These rates are compared with the dose rates of the same or similar alkaloids that lead to a significant tumor incidence in experimental rats. In the more chronic poisoning outbreaks, the intake rate is comparable with a carcinogenic dose in rats. The long-term observation of survivors of these outbreaks would offer an opportunity for determining whether pyrrolizidine alkaloids are carcinogenic in humans.