Accumulation and Metabolization of Caffeine in Lettuce.

Land application of biosolid and irrigation with reclaimed water in agricultural fields could result in the uptake of pharmaceuticals in crops and vegetables, which has raised concern on public health. The accumulated pharmaceuticals in plants could undergo metabolization. In this study, the uptake kinetics of caffeine by lettuce was conducted in a hydroponic system. The results showed that the mass distribution of caffeine in lettuce roots and shoots kept on decreasing with time, and more than 50% of caffeine lost in the system after 144 hours of uptake, which suggest the formation of metabolites in the lettuce. To identify the metabolites in lettuce, a scan mode of enhanced mass scan with information dependent acquisition criteria and followed by product ion scan (EMS-IDA-EPI) was utilized in a liquid chromatography-QTRAP mass spectrometry. After subtracting the pharmaceutical-free control, the obtained fragment ions was matched to the spectra in ChemSpider database. The results of the identified metabolites revealed that caffeine underwent demethylation reactions by forming theobromine, methylxanthine and xanthine in lettuce shoots. This results highlighted that pharmaceuticals could be metabolized in plants, the formed metabolites could be still bioactive posing risks to human health.