Uptake and accumulation of pyrrolizidine alkaloids in the tissues of maize (Zea mays L.) plants from the soil of a 4-year-old Chromolaena odorata dominated fallow farmland.

ABSTRACT

In an attempt to maximize yields of food crops, smallholder farmers have, over the years, increasingly employed agricultural practices such as slash-and-burn and slash-and-mulch on Chromolaena odorata dominated fallow farmlands. However, owing to recently introduced "Horizontal Natural Product Transfer" concept, concerns have been raised over how these common agricultural practices could potentially lead to toxic pyrrolizidine alkaloids (PAs), from decaying or burnt C. odorata residues, taken up by food crops and subsequently accumulate in the food chain. A field experiment was therefore conducted to analyze the PA contents in the tissues of maize (Zea mays L.) plants grown on slash-and-burn and slash-and-mulch plots, previously dominated with Chromolaena odorata, using liquid chromatography mass spectroscopy (LC-ESI-MS/MS). The results revealed, in general, trace amounts of PAs in the maize tissues (i.e. roots, leaves and grains) at maturity while significantly higher levels were detected in the surface soils sampled before sowing (for both plots), 45 days after sowing (slash-and-burn plot) and 90 days after sowing (slash-and-mulch plot). These findings demonstrate, for the first time, the leaching out of PAs from C. odorata residues (e.g. mulch and ash particles) and taken up by maize tissues. In spite of its air polluting and farmland degrading effects, slash-and-burn agricultural practices could lead, in the long term, to relatively lower accumulation of PAs in maize cultivated on PA-plant dominated fallow farmlands, hence smallholder farmers are encouraged to frequently employ this farming system.