ESR13 Natasa Skrbic

Project: Removal of natural toxins at groundwater fed water works

Principal supervisor: Dr. Sarah Christensen

Intro to project: For a long period of time, focus of environmental organic chemistry has been on anthropogenic substances and their occurrences in the environment, particularly in ground and drinking water. However, it is estimated that approximately 99% of the toxic substances that humans are exposed to have a natural origin. Thus, there is a clear need to put great attention on this still not enough explored group of hazard substances.
 
Natural toxins are compounds that by definition have toxicological effects and their exposures can be orders of magnitude higher in anthropogenically affected ecosystems. This is chemically very diverse group of compounds encompassing tannins, coumarins, quinones, flavonoids, polyketides, terpenes, saponins, steroids, alkaloids, cyanogenic glucosides and glucosinolates. Natural toxins, such as phytotoxins, have been studied in food for decades, but little attention has been paid to their occurrence in the natural environment.
 
Bracken fern (Pteridium aquilinum) is a globally distributed plant species, which is long known for its toxicity and carcinogenicity toward livestock. Among the group of potent illudane carcinogens that have been identified from bracken, the most abundant is patquiloside (PTA), a nor-sesquiterpene glycoside. A recent study has shown that that PTA and its degradation product ptersoin B (PTB) are present in the surface water and pore water in the upper soil layers in bracken dominated areas in Denmark. It was found that a considerable pool of PTA can accumulate in the soil profile. These findings raised an important question whether local water sources supplied by either groundwater or surface water in bracken-infested areas may be at risk of ptaquiloside or even other natural toxin contamination.
 
The overall objective of this PhD project is to address these concerns. In particular, this project aims to understand if the natural toxins (e.g. ptaquiloside, cyanogenic glucosides and glucosinolates toxins) are present in the ground water that serves as a drinking water abstraction source in Denmark. Since natural toxins have not been detected in Danish drinking water sources, the effect of standard water treatment procedures has not been explored yet. Therefore, this study will also investigate natural toxin fate/removal through the water treatment processes.

Major conclusions
Ptaquiloside (PTA) is highly water soluble carcinogenic compound with almost no sorption to soil and sediment, and hence it is of great concern if it is present in drinking water wells in bracken dominated regions. We developed a simple yet reliable method that can be used by water supply companies for monitoring the PTA in drinking water. The presented method was successful in PTA preservation and pre-concentration and its degradation product PtB in various groundwater samples. The method has the desired limit of detection of 0.001 µg L-1, which enables sensitive monitoring relevant for toxicity assessment. Furthermore, we investigated the presence of PTA, and structurally similar CAU (caudatoside), PTE (ptesculentoside) and their corresponding hydrolysis products pterosins B (PtB), A (PtA) and G (PtG) in 77 water wells in Denmark, Sweden and Spain. We detected at least one illudane glycoside or pterosin from bracken fern in seven of the 77 studied wells. Thereby we demonstrated that leaching of illudane glycosides to shallow drinking water wells is possible and could pose a threat to human health. The concentrations in these drinking water wells were 0.27 – 0.75 µg L-1, which violate the maximum estimated tolerable PTA concentration in drinking water by approximately 100 – 300 fold. Finally, we investigated natural toxin removal potential of five biological sand filters used for drinking water treatment. While very fast degradation was observed for illudane glycosides, alkaloids (jacobine N-oxide, senecionine N-oxide, sparteine and gramine) exhibit recalcitrant character in this study and further investigations on their removal are needed.

Scientific profile
Natasa completed Bachelor and Master studies in Biology, after what she was selected as one of ten scholarship laureates for Erasmus Mundus Master Programme in Ecohydrology. She did her Master Thesis at the Water Unit of European Commission Research Centre, working on developing of molecular tools for detecting toxigenic cyanobacteria in surface water. Natasa is currently employed at Greater Copenhagen Utility (HOFOR) and completing her final year as PhD student of the University of Copenhagen. Her role is to investigate the presence of natural toxins in drinking water wells and evaluate the risk they might pose to drinking water quality. As a PhD researcher, she has balanced academic and industry experience in the environmental sector with a focus on water quality. She has experience in performing experimental work in the laboratory, working with analytical chemistry methods (e.g. LC-MS). Besides, she tests conventional drinking water treatment (e.g. biological rapid sand filters) capacity to remove natural toxins.