1. INTRODUCTION

This informational general chapter is intended to provide an overview of pyrrolizidine alkaloids (PAs), heterocyclic organic compounds that are synthesized by many plant species (1–2) and can contaminate or be present in many plant-related products. The most potent PAs exhibit hepatotoxic, genotoxic, carcinogenic, or mutagenic activities. PAs can be found as contaminants in botanical drugs, herbal medicines, botanical dietary ingredients, and botanical dietary supplements, thereby posing a potentially serious threat to human health. PAs are derived from ornithine and are characterized by bicyclic pyrrolizidine moieties that are referred to as “necines” (3–4). PAs occur in two forms: pyrrolizidine alkaloids N-oxide (PANO) and tertiary bases (4–5). More than 660 PAs have been identified in approximately 6000 plant species (2) or in 3% of the world’s flowering plants (6–7). PAs are reported to be present mainly in the Boraginaceae (all genera), Asteraceae or Compositae (specifically in the tribes Senecioneae and Eupatorieae), and Leguminosae or Fabaceae (genus Crotalaria) families (5,8–9). PAs are mainly concentrated in the seeds and flowering parts of plants and, in lesser amounts, the leaves, stems, and roots (5). PAs of concern have been detected in dietary supplements (6); teas and herbal infusions (2); honey and pollen (4,10), predominantly due to the presence of PA-containing plants growing near plants of interest and being accidentally coharvested with plants used in these products. Because of the wide distribution of PAs in many plant species, dietary exposures to potent PAs are a safety concern (6). Published literature reports suggest that tea and herbal infusions were the main contributors to total unsaturated PA exposure. Therefore, efforts should be made to obtain information specifically on the sources of PA contamination in tea, such as the adventitious PA-containing plants responsible for the contamination, and to use measures to control infestation and coharvest (11).