Root vegetables bioaccumulate microcystins-LR in a developmental stage-dependent manner under realistic exposure scenario: The case of carrot and radish

Cyanotoxins are secondary metabolites of the ubiquitous cyanobacteria and exert their toxicity to plants and humans. Human health can be impacted by cyanotoxin bioaccumulation in crops via irrigation from contaminated water reservoirs. In the present study we conducted an ecologically relevant experiment in terms of toxin dose, cultivation time and the use of agricultural soil and naturally contaminated irrigation water. We investigated the growth response, protection potential, bioaccumulation profile and the related health risk of two widely consumed root vegetables, radish and carrot, when the exposure to microcystins-rich water commences at different developmental stages, from seed to 4 true leaves stage. Additionally, carrot was subjected to a prolonged depuration phase in order to evaluate its recovery potential. The results indicate a developmental stage-dependent profile of all measured parameters. Severe growth reduction was evident for plants receiving degraded water from the seed stage which reached 50% and 70% for radish and carrots, respectively. The impact was less pronounced when degraded water was first received at subsequent developmental stages. The protection response, in terms of phenolic content, was considerably insufficient to mitigate the stress at the tissue level. The earlier in its life cycle a plant confronts the exposure, the greater microcystins content occurs in its tissue, particularly in the edible parts, posing considerably high health risk for humans upon consumption. Estimated daily toxin intake after consuming treated taproots exceeded the World Health Organization safety threshold by 4 and 5 times for adults and children, respectively. The experimental depuration in carrot only partially alleviated the problem of bioaccumulation and growth impairment, thus, pointing to irreversible hazards. The results highlight the importance of monitoring the major cyanotoxins content in irrigation water and emphasize the necessity to re-visit the regulation/guidelines concerning the origin and quality of the irrigation water in the frame of effective agricultural water management.