The plant kingdom has developed an arsenal of poisons to deter predation. Among these are pyrrolizidine alkaloids. Some 3 percent of all flowering plants produce these chemicals, including such herbal-garden favorites as borage and comfrey. When bees pollinate such plants, the little buzzers risk seeding the honey they produce with worrisome concentrations of the poisons, a new study charges.
In 1988, the World Health Organization designated pyrrolizidine alkaloids as a serious health threat. Even persistent, low-dose exposure to the poisons can cause cirrhosis of the liver or other diseases, notes John A. Edgar, a consulting organic chemist and toxicologist in Melbourne, Australia. The alkaloids have k