Background
Microcystin congeners are produced by cyanobacteria when these organisms proliferate in freshwater systems, forming cyanobacterial blooms. Studies in the laboratory have shown the accumulation of these hepatotoxins in crops, raising the possibility of human health risks. While providing valuable data, these conditions do not always reflect the occurring variability in plant growth during larger-scale production of crops.
Methods
Therefore, larger greenhouse experiments were performed where different crops (carrots, strawberries and lettuce) were exposed to 100 µg/L of the most microcystin congener (MC-LR) through irrigation water for 4 to 5 weeks. For lettuce, a combination of spray- and drip irrigation was used to water the plants, whereas for carrots and strawberries, batches of the plants received water through either spray- or drip- irrigation. After harvest, MC-LR was quantified in the samples using a validated UHPLC-MS/MS method. Also, the MC-LR concentration in the irrigation water was monitored at 8 intervals during the experiments using UHPLC-MS/MS.
Results
The presence and overall stability of MC-LR in the irrigation water throughout the experiment were confirmed. For lettuce, the outer leaves contained higher concentrations of MC-LR compared to the inner leaves. Accumulation in carrots was limited with only a few plants showing detectable levels of MC-LR in either the taproot or leafy greens. On the other hand, strawberry plants showed an accumulation of MC-LR in all plants when spray irrigation was used, with the highest accumulation found in the roots, followed by the greens and fruits. For drip irrigation, MC-LR was only quantified in the roots and the greens, implying the transport of the MC-LR from the roots to the other plant parts.
Conclusions
Accumulation of MC-LR was observed in this study for different crops and was dependent on the crop and irrigation method used. Further research including more microcystin congeners would be recommended to evaluate the potential risks.
