Increased awareness in the media and strict control by competent authorities resulted in an overall risk perception of toxic cyanobacteria blooms among the global population in Belgium. There is a general concern about the negative impact of the blooms and their toxins on the environment and public health. Yet, limited data about cyanotoxins in food, drinking and recreational water are available in Belgium. Among the main reasons for this data shortage is a lack of publicly sourced, reliable methods to analyze cyanotoxins in food and environmental samples. This has a negative downstream effect on possible risk assessment studies that would establish the exposure and influence of the different cyanotoxins on public health, and on the final risk management through concrete policy measures. This doctoral dissertation discusses the development and validation of fit-for-purpose analytical methodologies to quantify the most prevalent cyanotoxin group worldwide, the microcystin congeners (MCs). After method validation, the quantitative UHPLC-MS/MS approaches were applied to Belgian samples to characterize potential human exposure sources in conjunction with and compared to other research tools. The MCs prevalence data was then used to make a preliminary assessment of human exposure and associated public health risk. Initially, methodologies were successfully validated and applied to quantify MCs in drinking water and environmental samples. Drinking water has the highest potential to be an exposure source of MCs, as assumed by the World Health Organization. Yet, no toxins were found in Belgium’s drinking water. However, the situation is very different for the Belgian fresh waterbodies (lakes, ponds, canals). There, MCs ranging from 0.11 µg L−1 to 2798.81 µg L−1 total microcystin, were quantified in 68 out of 79 samples during the monitoring of five lakes in Wallonia and occasional blooms in Flanders and Brussels, including a canal. MCs prevalence in Belgian waterbodies indicated the potential for exposure through recreational activities and also potential contamination of drinking water from reservoirs. The risk of the latter is aggravated by water shortages and droughts that will require the increased use of surface water for drinking water production in Belgium. Dominant cyanobacterial strains and the presence of the mcy gene cluster were also identified in the waterbody samples to better characterize the cyanobacteria blooms. Algal-based food supplements were also identified as a potential exposure source. The presence of toxin-producing cyanobacteria during the production or harvesting of these products may cause health risks. However, data concerning sales and consumption of algal-based food supplements on the Belgian market, as well as possible contaminations with cyanotoxin, are scarce. Again, a quantitative UHPLC-MS/MS approach was optimized, validated and applied. Overall, 35 algal-based food supplement samples were collected and analyzed, whereof nine samples contained MCs. Moreover, three samples exceeded the concentration of 1 µg g−1 total microcystins, previously proposed as a guideline value. Microcystis sp. were determined as the producers of these toxins by amplification and sequencing of the mcyE gene. Yet, data on the MCs prevalence is not sufficient to accurately assess human exposure and risk. Additional consumption data were needed. Therefore, a consumption survey for algal-based food supplements was launched, showing that 13.00 % of the 554 respondents used these products. The majority of the users consumed these food supplements daily and all year round. Additionally, most users confirmed that they adhered to the recommended dose for consumption as advertised on the label of the product. This result supports our suggestion that the recommended dose values can be used as a measure for the consumption of algal-based food supplements since quantitative consumption data is not available for these products. The collected data were cumulated in a new exposure assessment for adults and children and a reaffirmation of the proposed guideline values. Vegetables and fruits might also become a potential exposure source for MCs. These products can potentially accumulate cyanotoxins when contaminated water is used for irrigation, pesticide spraying or other pre- and post-harvest operations. Therefore, their potential role in foodborne exposure was studied. A new quantitative UHPLC-MS/MS approach was developed and validated to quantify MCs in strawberries, carrots and lettuce. These three matrices represented three groups of crops, fruits/berries, leafy and root vegetables, sequentially. Afterwards, a sampling of nine different kinds of fruits and vegetables from the Belgian market was accomplished. In total, 103 samples were analyzed with the method. Yet, MCs were not detected. However, the quality controls during the analysis reported acceptable recoveries for the different products, confirming the appropriateness of the method. Finally, the results from the 79 samples from algal blooms, 75 drinking water samples, 35 algal-based food supplements, and 103 fruits and vegetable samples were combined with consumption data from the different sources to make a preliminary aggregated exposure and risk assessment for different exposure scenarios. Currently, our data suggest that algal-based food supplements and contaminated recreational water are the major exposure sources, with the food supplements posing a potential risk to public health, especially in children. Of course, this preliminary assessment should be complemented with additional data on the MCs prevalence in the different products. Moreover, other exposure sources, like freshwater foods (fish), and other cyanotoxins should be included in the future to further develop their risk assessment. The approaches described in this thesis can hopefully be used as a toolbox to guide and support continuing research.
