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Occurrence of microcystin congeners in surface waters and food in Belgium as a source of exposure to humans
No full textIncreased 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
Characterization of salinity in the southwest coastal alluvial terrain in Bangladesh evaluated through hydrogeochemical and geophysical study
No full textPeople in the southwest coastal region of Bangladesh suffer from a severe potable water crises due to saltwater at shallow depth (200 m. There is still a lack of exact causes, origin, and processes controlling the hydrogeochemistry of groundwater in the study area. Several aquifers such as the upper shallow aquifer (<100 m) is characterized by mostly brackish saline NaCl type of water due to infiltration of dissolved evaporite salts, not laterally from the Bay of Bengal. These salt-waters infiltrate into the brackish lower shallow aquifer (100-200 m). The deep aquifer (DA) below 200 m depth, is dominated by fresh NaHCO3+ type of water suggesting freshening conditions. The NaHCO3+ facies originated by cation exchange. The freshwater-saltwater interface varies in depth between 190 to 285 m. The shallowest depth is due to upward migration of fresh groundwater from the DA. Numerical modelling revealed that no fundamental changes in flow direction occur with a diffuse abstraction rate of 10.24 l/person/day from DA. This integrated study has helped to understand the characteristics and hydrogeochemical processes of the complex aquifer systems as well as to make sustainable use of water resources, especially from the DA
Exploring biochemical and biophysical methods for the delivery of biologics to the corneal epithelium
No full textMost of the time visual impairments due to corneal issues can be treated using corneal transplantations. Unfortunately, there is a lack of suitable donor material. Delivery of biologics to the cornea could alleviate this need through alternative treatments. However even though the cornea seems readily available it is still difficult to overcome pre-corneal, corneal and cellular barriers. New innovative treatments overcoming these barriers can be classified into two groups: biochemical and physical methods. Here, cationic amphiphilic drugs as adjuvant therapy are investigated in in an effort to overcome lysosomal degradation. Commercially available cationic amphiphilic drugs among which ophthalmic formulations are examined on their ability to induce lysosomal membrane permeabilization for the enhanced delivery of siRNA’s. Photoporation, a physical method, is also investigated where light absorbing particles irradiated with pulsed laser light lead to bubble formation which upon collapse release a mechanical force able to permeate cell membranes. In one method biocompatible and biodegradable polydopamine nanoparticles are synthesized to be used as photosensitizers. These are employed to deliver the model compound FITC-dextrans and mRNA into primary bovine corneal epithelial cells and fully intact corneas of ex vivo bovine eyes. This treatment was also investigated to deliver FITC-dextrans in an in vivo rabbit model. In a second method, iron oxide nanoparticles embedded in PLA films were explored as photosensitizers in an effort to limit the diffusion of particles to surrounding tissues during photoporation. The force released after irradiation could be used to kill or permeabilize cells. High resolution killing by targeting specific areas for the treatment of superficial tumors as well as safe delivery of macromolecules are explored using these films
Design and evaluation of advanced virtual reality applications in healthcare
No full textKwalitatieve gezondheidszorg wordt een steeds grotere uitdaging, omdat de vraag naar zorg stijgt, waardoor de tijd die een zorgverstrekker per patiënt kan spenderen daalt. Tegelijk weten we uit onderzoek dat een gepersonaliseerde behandeling veel effectiever is dan een generieke aanpak. Virtual Reality is een technologie waarbij de gebruiker compleet wordt ondergedompeld in een virtuele wereld. Ondertussen kan een operator of computersysteem volledige controle over deze wereld hebben. Om deze redenen heeft Virtual Reality zeker en vast een plaats in de behandeling van verschillende medische aandoeningen. In dit doctoraat worden drie Virtual Reality applicaties ontworpen en ontwikkeld voor de mentale gezondheidszorg en revalidatietherapie. Hierbij wordt steeds rekening gehouden met de noden van de patiënten en zorgverleners door hen vanaf het begin te betrekken bij het ontwikkelingsproces. Er wordt ook telkens onderzocht in welke mate Virtual Reality een toegevoegde waarde kan bieden aan bestaande therapieën. Dit uit zich in de ontwikkeling van intelligente algoritmen die het gedrag van de patiënt analyseren en vervolgens, in combinatie met bijkomende informatie en domeinkennis van zorgverleners, de virtuele wereld aanpassen naar de noden van de patiënt in hun behandeling
Studying the impact of the gastrointestinal bacteria on the brain, focusing on the blood-cerebrospinal fluid barrier and Alzheimer's disease
No full textDevelopment of low-cost and low-power wearable sensor nodes based on bluetooth low energy
No full textDit proefschrift beschrijft de ontwikkeling van draadloze sensor nodes (WSN) die Bluetooth Low Energy als communicatieprotocol gebruiken en wordt toegepast op drie verschillende topics. Het eerste onderwerp gaat over dodehoekdetectie bij vrachtwagens. Er worden enkele nodes op een vrachtwagen gemonteerd en de zwakke weggebruiker draagt een zelfontworpen wearable. Deze maakt gebruik van een energiezuinig regel-gebaseerd algoritme dat bepaalt of een zwakke weggebruiker te dicht in de buurt komt van de vrachtwagen. Het volledige systeem wordt getest in een real-life situatie. Later wordt een van deze nodes geminiaturiseerd. De tweede topic handelt over valdetectie bij ouderen in woonzorgcentra. Een kleine onopvallende wearable wordt ontwikkeld dat op basis van accelerometer data zal bepalen of er zich een val heeft voorgedaan. Op basis van drie vrij beschikbare databanken is het zelfontworpen regel-gebaseerde algoritme getest en vergeleken met een CNN algoritme. In een volgende stap werden de resterende nodes van het systeem ontwikkeld en getest in laboratoriumomstandigheden. Monitoren van trein integriteit is de laatste topic in dit proefschrift. Er worden verschillende metingen uitgevoerd op en rond een locomotief met verschillende wagons. Op basis van deze metingen wordt het uitgerolde WSN energie-efficiënt gemaakt en voorzien van een antenne voor stabiele communicatie
Marine phytoplankton response to environmental stressors associated with climate change
No full textThe open ocean accounts for nearly 70% of Earth’s surface and represents the largest habitat in the biosphere. Phytoplankton, which are drifting microorganisms with the capacity to perform oxygenic photosynthesis, support life in this vast environment. Besides, they are a key component of marine ecosystems as they drive the oceanic biological pump, influence biogeochemical cycles and modulate fishing yields. However, climate change modifies the environmental drivers governing phytoplankton photosynthesis and consequently alters their productivity, diversity and community structure. Understanding the phytoplankton response to environmental stressors is mandatory to ascertain the implications of current and future climate changes on marine ecosystems in general.
Important tools in this respect are remote sensing satellite observations and mathematical models. The former provide high-resolution spatial-temporal observations of key ocean variables, while the latter allow to extrapolate knowledge from the laboratory and sparse field observations to global and regional scales. Hence, the main focus of this thesis is the assessment of the marine phytoplankton response to environmental stressors associated with climate change on the basis of multi-platform datasets, i.e. satellite observations and outputs of mathematical models. More specifically, the response of dominant phytoplanktonic cyanobacteria genera on Earth (Prochlorococcus and Synechococcus) to ultraviolet (UV) radiation is investigated as well as the perturbations induced by hurricanes (strongest tropical cyclones (TCs)) on phytoplankton assemblages in several areas of the western North Atlantic Basin in the period 1998–2019.
On the basis of biological weighting function (BWF)/photosynthesis-irradiance (P-E) models, we found that UV accounts for roughly two-thirds of the potential photosynthetic inhibition of Prochlorococcus and Synechococcus in the oceanic photoactive layer in the latitudinal band 40º N/S. Prochlorococcus showed a higher inhibition and integrated photosynthetic potential throughout the water column than Synechococcus, since the former is more vulnerable to UV damage at the surface and more successful at greater depths compared to the latter. On the other hand, we demonstrated that hurricanes trigger vertical and horizontal transport of phytoplankton and nutrients leading to an increased satellite chlorophyll (Chl) a concentration (a proxy for phytoplankton biomass) in the waters surrounding Cuba, the eastern Gulf of Mexico and the western Sargasso Sea. Besides, we illustrated that hurricanes drive connectivity of phytoplankton assemblages between coastal and oceanic environments. Climatological analyses showed that the strongest TC-induced Chl a increases in the western Sargasso Sea have been mainly associated with consecutive TCs as they superimpose effects on the upper-ocean response.
Finally, data of phytoplankton functional types (PFTs) derived from a biogeochemical ocean general circulation model revealed that Prochlorococcus and Synechococcus respond modestly to post-storm nutrient enrichment in the tropical Sargasso Sea as compared to coccolithophores, diatoms, diazotrophs, mixotrophic dinoflagellates, and picoeukaryotes, whose concentrations increase significantly after a hurricane passage. Besides, a significant post-storm increase of the Shannon diversity index values was also observed indicating that a moderate post-storm nutrient increase in this oligotrophic area positively impacts phytoplankton diversity limiting exacerbated productivity of opportunistic species. Overall, this thesis provides a baseline against which future phytoplankton responses to environmental stressors can be evaluated. Its findings fit the needs of future studies on climate change, ecological variability, environmental protection and fisheries oceanography
