ESR9 Carina Schönsee

Project: Physicochemical property determination of natural toxins

Principal supervisor: Dr. Thomas Bucheli

Project Summary and Conclusions:

Natural toxins have not been commonly regarded as environmental contaminants of concern for water quality. However, within NaToxAq we could show that natural toxins indeed can be found in water bodies. In our first suspect screening study for phytotoxin occurrence in swiss surface waters (https://doi.org/10.2533/chimia.2020.129), we could demonstrate the presence of isoflavones and different alkaloid subclasses (indole alkaloid, pyrrolizidine alkaloids) in a grab sampling campaign during summer. The detected compounds are representatives of compound classes already prioritized based on predicted physicochemical properties characterizing persistence, mobility and toxicity and combined with plant abundance data (https://doi.org/10.1021/acs.jafc.8b01639). Thus, stressing the importance of having reliable natural toxin physicochemical property data for use in subsequent exposure and risk assessment.

Until recently, hardly any experimental physicochemical property data were available that could adequately describe natural toxin aquatic mobility though. We were able to determine partitioning and sorption coefficients for 123 natural toxins (phytotoxins, mycotoxins) from 36 compound classes.

In a first extensive experimental study, we could show pH-dependent octanol-water partitioning behavior for 45 natural toxins (https://doi.org/10.1021/acs.jced.9b01129). In a second study, we have assessed sorption to soil organic carbon by deriving the soil organic carbon sorption coefficient Koc for an extended set of 117 natural toxins under changing environmental conditions. By changing pH, ionic strength and ions in the aqueous solution, we were able to gain detailed mechanistic insights that are of great value for understanding transport and fate processes in the environment. Those mechanisms hold true for both natural toxins and other multifunctional, ionizable organic compounds. We could demonstrate that the chosen method, using HPLC columns manually packed with the sorbent of interest, allows reliable, highly reproducible determination of sorption coefficients. Additionally, it is an excellent choice to study sorption behavior of large sets of compounds under various experimental settings. Thus, we further applied the approach to study sorption of 52 phytotoxins to two different clay minerals and revealed further specific sorption mechanisms of N-containing phytotoxins in particular. Publications containing the full datasets and the detailed sorption mechanisms of natural toxins to both soil organic carbon and clay minerals are currently under review.

Finally, we could demonstrate the high value of experimental data by comparison with predicted property data. Improved models are urgently needed and our data is now used for setting up a new model for predicting the sorption of multifunctional organic compounds to soil organic carbon. Overall, we conclude that natural toxins are highly mobile compounds and therefore, should be included in monitoring campaigns to ensure continuous high quality of drinking water resources.