ESR9 Carina Schönsee

Project: Physicochemical property determination of natural toxins

Principal supervisor: Dr. Thomas Bucheli

Intro to project:

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. 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). Additionally, we were able to highlight the limitations of commonly used prediction tools such as EPISuite, ACD/Percepta and Chemicalize for assessing natural toxins. Thus, additionally stressing the need for better models to reliably predict natural toxin environmental mobility. Derived octanol-water partitioning data can now be used as a first proxy estimating natural toxin mobility in the aquatic environment.

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 about 100 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. The publication of the full dataset and detailed mechanistic study is currently in preparation.

Experimental sorption data is also currently used for setting up a new model for predicting the sorption of multifunctional organic compounds to soil organic carbon. The work jointly performed with ESR1 from Stockholm University was initiated during ESR9s secondment in Stockholm in late 2019 and a publication is planned for the near future.