Semi-natural products and related substances as alleged botanical pesticides

Plants are a virtually inexhaustible source of structurally diverse biologically active substances. In some cases, however, xenobiotics or their biotransformed derivatives can also be found in extracts from botanical sources. Whilst it is not improbable that plants are able to biosynthesise such compounds, the fact that they have similar, or even identical, structures to those of synthetic materials used in practice indicates a problem in determining their origin and blurs the borderline between natural and man-made substances. The recent identification of a herbicide-like 1,3,5-triazine (halimedin) from an algal source illustrates the difficulty of separating a natural from a semi-natural product, the latter being defined as substance of apparently man-made origin that is re-isolated from natural sources. Additional literature reports shown here demonstrate that pesticide contamination can turn up in unexpected locations. Although these cases appear to be only curiosities, they have the potential of toxicological or ecological risks.