Plant-produced 1,2-dehydropyrrolizidine ester alkaloids and their N-oxides (PAs) not only cause acute poisoning of humans and livestock, but also the likely harmful cryptic effects of chronic exposure pose particular food safety risks that need to be addressed for consumer protection. In natural contexts, however, PAs cause few or no problems. Rather, these plant secondary metabolites are important elements of ecosystems and plant-animal relationships; the existence and persistence of many PA-adapted organisms, in various ways, depends on the presence of PA-containing plants or even on PAs as such. PA plants are widely distributed among unrelated families of the plant kingdom; there is great structural diversity of PAs, and the amounts of PAs produced are subject to great variation due to multiple causes. These realities, coupled with many deficiencies in our scientific understanding, make the presence and roles of PAs in nature a subject with limited potential for valid generalisations and predictions, and complex and difficult to summarise. PAs, their producer plants and their users are integral parts of ecosystems worldwide, and we have to learn to live with these allelochemicals by accepting the presence of some harmful natural chemicals in the environment and by taking regulatory action to reduce health risks to humans. Regulations for consumer protection are long overdue. However, any such measures must be flexible enough to accommodate the findings of future research. Transdisciplinary efforts are required to fill gaps in the knowledge and to come up with additional means to monitor the presence of PAs in food and feed.
