Biodegradation and utilization of crop residues contaminated with poisonous pyrrolizidine alkaloids

Disposal of noxious plant residues is a challenge for farmers and land management dealing with contaminated biomasses. Recent studies confirm the potential threat of transferring toxic plant constituents like pyrrolizidine alkaloids (PAs) from plant residues to non-toxic succeeding agricultural crops via the soil. We studied the degree of biochemical degradation of PAs in the two most important processes, composting and biomethanization. We used lab composting and biogas batches to investigate the potential of PA-degradation of two common PA-containing plants, Lappula squarrosa and Senecio jacobaea. The experiments demonstrated a virtually complete loss of PAs in three months during the composting process and a rapid decomposition of PAs from 3112.6 μg/kg to less than 21.5 μg/kg in L. squarrosa and from 6350.2 μg/kg to less than 539.6 μg/kg in S. jacobaea during biomethanization. The information obtained is a first guide on how to re-utilize PA-contaminated plant matter in a circular bioeconomy.