Water availability and quality are two crucial factors contributing to a healthy and well-functioning society. However, due to climate change and pollution, access to safe freshwater sources diminishes. Increasing salinization, increasing sea levels and the presence of organic and non-organic pollutants are some of the causes of the problem. Moreover, due to the increasing human population, water demand is also increasing, while water reserves in aquifers, groundwater and fossil water are decreasing. These resources can only slowly be replenished. An increase in water storage deficits in Europe was observed after the dry summers of 2018 and 2019 compared to the water storage deficits after the droughts during the summers of 2003 and 2015, as shown by the GRACE and GRACE-FO data record . A high water storage deficit was also observed in Belgium in 2018 and 2019 . Freshwater is not only used for consumption but also for industrial processes, agriculture and other activities. In Flanders, 10% of the total consumed water is used for agriculture . Currently, to produce tap water, ground and surface waters are used equally in Flanders, while in Wallonia, up to 80% of tap water originates from groundwater [3,4,5]. The remaining 20% is captured from the river Meuse, old mining sites and six dams [6,7]. Increasing the use of surface water could be necessary to meet the current and future water demand. However, the switch to surface water is accompanied by certain pitfalls, as mentioned by the Flanders Environment Agency .
One of these pitfalls is the development of cyanobacterial blooms in these water bodies. These proliferations of certain cyanobacterial taxa are favored by environmental and meteorological factors and their prediction is still under study [9,10,11,12]. The presence of these blooms can have a detrimental effect on the water quality by producing compounds that lead to foul tastes and odors, or possibly worse, toxic compounds also known as cyanotoxins.
A major group of cyanotoxins are the hepatotoxins, categorized as such due to their main toxicological effect. Two other structurally related hepatoxins are the microcystin congeners (MCs) and nodularin (NOD) (Figure 1). Both contain in their structure an (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid (ADDA) group connected to a peptide ring. However, NOD’s ring contains five peptides, whereas the MCs have a heptacyclic peptide ring [13,14]. Both toxins inhibit protein phosphatase 1 (PPI) and 2A (PPIIA), disrupting cell growth and metabolism [15,16]. When ingested, these toxins are transported by the bile salts to the liver, potentially causing liver damage [17,18,19].