Toxic cyanobacterial blooms are commonly observed in freshwater reservoirs, ponds, lakes and canals. These waterbodies are also well-known irrigation water sources for crop production. This overlap has resulted in the accumulation of cyanotoxins, particularly microcystin congeners (MCs), in fruits, vegetables, and culinary herbs. Yet, data on the influence of accumulation based on crop type, irrigation methods, and the prevalence of the MCs in products on the consumer market is incomplete.

Initiating our studies, a UHPLC-MS/MS method was validated in strawberries, carrots, lettuce, and basil to quantify eight MCs and Nodularin. Thereafter, multiple lab and mid-scale greenhouse experiments were performed to assess the MCs accumulation. Specifically, the accumulation and depuration of MCs was investigated at lab-scale for basil. Additionally, strawberries were exposed to MC-LR or naturally obtained toxic cyanobacteria biomass using the same setup. Drip and/or spray irrigation were evaluated for strawberries, carrots, and lettuce exposed to MC-LR fortified irrigation under relevant greenhouse conditions. Furthermore, fruit, vegetable, and basil samples were collected from the consumer market.

Accumulation of MCs in crops was established for most irrigation approaches. MCs were quantified in basil roots and leaves after 7 days. Strawberries grown in the lab or undergoing drip irrigation in a greenhouse showed accumulation in the roots and the foliage. These results show that MCs can be transported through the roots, to the subsequent plant parts. Moreover, MC-LR was quantified on strawberries after spray irrigation. Similarly, a combination of spray and drip irrigation resulted in MC-LR accumulation in lettuce. The consumer market sampling demonstrated the presence of MC-LR in one basil food item, indicating that the prevalence of MCs contamination in crops might still be low. However, MCs accumulation should be monitored as the contamination frequency might change in different regions due to climate change, resulting in additional human exposure to MCs.