Target Screening of Plant Secondary Metabolites in River Waters by Liquid
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Nanusha et al. Environ Sci Eur (2020) 32:142 https://doi.org/10.1186/s12302-020-00399-2 RESEARCH Open Access Target screening of plant secondary metabolites in river waters by liquid chromatography coupled to high-resolution mass spectrometry (LC–HRMS) Mulatu Yohannes Nanusha1,2, Martin Krauss1, Carina D. Schönsee3,4, Barbara F. Günthardt3, Thomas D. Bucheli3 and Werner Brack1,2* Abstract Background: Substantial eforts have been made to monitor potentially hazardous anthropogenic contaminants in surface waters while for plant secondary metabolites (PSMs) almost no data on occurrence in the water cycle are available. These metabolites enter river waters through various pathways such as leaching, surface run-of and rain sewers or input of litter from vegetation and might add to the biological activity of the chemical mixture. To reduce this data gap, we conducted a LC–HRMS target screening in river waters from two diferent catchments for 150 plant metabolites which were selected from a larger database considering their expected abundance in the vegetation, their potential mobility, persistence and toxicity in the water cycle and commercial availability of standards. Results: The screening revealed the presence of 12 out of 150 possibly toxic PSMs including coumarins (bergapten, scopoletin, fraxidin, esculetin and psoralen), a favonoid (formononetin) and alkaloids (lycorine and narciclasine). The compounds narciclasine and lycorine were detected at concentrations up to 3 µg/L while esculetin and fraxidin occurred at concentrations above 1 µg/L. Nine compounds occurred at concentrations above 0.1 µg/L, the Threshold for Toxicological Concern (TTC) for non-genotoxic and non-endocrine disrupting chemicals in drinking water. Conclusions: Our study provides an overview of potentially biologically active PSMs in surface waters and recom- mends their consideration in monitoring and risk assessment of water resources. This is currently hampered by a lack of efect data including toxicity to aquatic organisms, endocrine disruption and genotoxicity and demands for involvement of these compounds in biotesting. Keywords: Natural toxins, Bioactive compounds, Mixture toxicity, Surface water, Emerging contaminants Background plant while secondary metabolites play an important role, Plants produce a large variety of chemical compounds, for example as defence (against herbivores, microbes, which may be categorized as primary and second- viruses or competing plants) and signal compounds to ary metabolites. Primary metabolites are necessary for attract pollinating or seed dispersing animals [26, 36, growth and maintenance of cellular functions of the 53]. Many PSMs can be seen as nature’s own pesticides and have the potential to contribute to adverse efects of *Correspondence: [email protected] chemical mixtures in aquatic ecosystems together with 1 Department of Efect-Directed Analysis, Helmholtz Centre anthropogenic chemicals [47]. Often, the production of for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, PSMs is specifc for taxonomic groups, species, genera or Germany Full list of author information is available at the end of the article families. Te amounts produced are typically lower than © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. Nanusha et al. Environ Sci Eur (2020) 32:142 Page 2 of 11 those of primary metabolites [36]. Secondary metabo- in Suwannee River fulvic acid isolates, USA [41]. Tus, lites are diverse in their chemical nature. Most of them PSMs may add to the complex mixtures of anthropogenic belong to four major classes of compounds, namely ter- organic micropollutants in water resources. Terefore, penoids, phenolic compounds, alkaloids and sulfur-con- there are indications that some PSMs, which exhibit tox- taining compounds [13]. Due to their biological activity, icity at environmental concentrations, may jeopardize PSMs have been used for drug development including water quality and afect aquatic ecosystems and human anti-infammatory, antioxidant and antiviral agents. health in concert with anthropogenic compounds. However, many medicinally active PSMs also show toxic Te objective of the present study was to perform a side efects [10, 11, 26, 39]. For instance, bergapten, a frst river water target screening of PSM selected from a furanocoumarin, has shown antitumor efects in a variety larger database for their expected mobility, persistence of cell types, but is also a potential photosensitizer that and toxicity, their expected abundance and their com- can cause severe phytophotodermatitis after either skin mercial availability as standards in two selected catch- contact or ingestion followed by sun UV exposure [9, 43, ments with primarily natural vegetation and agricultural 51]. Some PSMs detected in the water cycle have been land use, respectively. We focused particularly on sam- shown to cause severe impacts on human health such as pling during or after rain events in the vegetation season aristolochic acids from Aristolochia clematitis causing to enhance the probability of detection of PSMs leaching Balkan endemic nephropathy [48] and the potent car- to the river water. Since hardly any quantitative toxicity cinogen ptaquiloside. Te latter is produced by bracken data for PSMs is available, we compared water concen- fern and emitted into the water cycle particularly during trations with TTC suggested for drinking water contami- rain events at toxicologically relevant concentrations [7, nants for which no toxicity data exist for a preliminary 35]. Recently, natural carboline alkaloids have been dem- estimate of risks [29]. onstrated to exhibit synergistic mutagenic efects with anthropogenic aromatic amines [31]. Experimental section Plants produce toxic PSMs particularly under envi- Study site and water sampling ronmental stress and release these compounds to the Te investigated catchments are located in the north- environment through various means such as root exu- west part of the federal state of Saxony (close to the city dates, volatilization and animal contact as part of their of Leipzig) and in Saxony-Anhalt (Bode catchment), defence mechanism [2, 4, 10, 26]. Previous research Germany. Both catchments were selected due to their demonstrated their pharmacological efect and toxic- land coverage with natural and/or agricultural vegeta- ity by isolating them from plants [3, 42] and their con- tion along the river banks. Te 50 km2 large foodplain tribution to mixture toxic risk in river water [5, 34]. In forest in Leipzig reaches along the rivers Elster, Pleiße silico predictions suggest that many PSMs are persistent and Luppe (EPL catchment) together with some smaller and mobile in the environment [14]. Te authors identi- tributaries. Te natural old-growth deciduous forest was fed priority phytotoxins characterized based on in silico- historically used for the extraction of coppice and clay. predicted values of half-life longer than 20 days, a log It is mainly characterized by Quercus robur, Fraxinus DOC (organic carbon–water partition coefcient) below excelsior, Acer pseudoplatanus, Ulmus minor, Alnus glu- 4.5, rodent or aquatic toxicity and high abundance of the tinosa, Tilia cordata, Carpinus betulus, Acer platanoides producing plant in Switzerland [14]. Assuming similar and Acer campestre. In spring, the forest scrub is domi- vegetation in Germany, these priority phytotoxins were nated by monocotyledonous and tuberous plants such used as a basis for target selection in the present study. as Allium ursinum, Anemone nemorosa, Galanthus niva- PSMs may be transported to river water through leach- lis and Leucojum vernum [22]. Tus, during their peri- ing, rain sewers and surface run-of and might pose a risk odic growth and decay, they might leave their secondary not only to aquatic organisms, but also to human health metabolite footprints in the environmental components in case of exposure, if the water is used for human con- (e.g., soil, river). Te Bode catchment is characterized sumption and recreational purposes. Recently, target and by large diversity of natural and agricultural vegetation. suspect screening of PSMs identifed 12 compounds in Land use is dominated by forest (such as broad-leaved Swiss small creeks from three compound classes includ- forest, coniferous forest and mixed forest) in the moun- ing formononetin, an estrogenic isofavone, the indole tain areas and agriculture in the lowland areas. Main alkaloid gramine and several pyrrolizidine alkaloids [15]. crops include winter wheat, triticale, winter barley, rye, Formononetin in concert with other isofavones has been rape, sugar beet and corn. detected in Swiss and USA surface waters already earlier Grab water samples were collected