Sorption and Mobility of Charged Organic Compounds: How to Confront and Overcome Limitations in Their Assessment.

Permanently charged and ionizable organic compounds (IOC) are a large and diverse group of compounds belonging to many contaminant classes, including pharmaceuticals, pesticides, industrial chemicals, and natural toxins. Sorption and mobility of IOCs are distinctively different from those of neutral compounds. Due to electrostatic interactions with natural sorbents, existing concepts for describing neutral organic contaminant sorption, and by extension mobility, are inadequate for IOC. Predictive models developed for neutral compounds are based on octanol-water partitioning of compounds (Kow) and organic-carbon content of soil/sediment, which is used to normalize sorption measurements (KOC). We revisit those concepts and their translation to IOC (Dow and DOC) and discuss compound and soil properties determining sorption of IOC under water saturated conditions. Highlighting possible complementary and/or alternative approaches to better assess IOC mobility, we discuss implications on their regulation and risk assessment. The development of better models for IOC mobility needs consistent and reliable sorption measurements at well-defined chemical conditions in natural porewater, better IOC-, as well as sorbent characterization. Such models should be complemented by monitoring data from the natural environment. The state of knowledge presented here may guide urgently needed future investigations in this field for researchers, engineers, and regulators.

Disentangling Mechanisms in Natural Toxin Sorption to Soil Organic Carbon.

Natural toxins are multifunctional, often ionizable organic compounds increasingly detected in the environment. Surprisingly little is known about their interactions with soil organic carbon, although sorption largely controls transport, bioavailability, and dissipation. For a set of 117 natural toxins from 36 compound classes the pH-dependent organic carbon-water distribution coefficient (Doc) was quantified using a soil column chromatography approach under changing conditions with regards to pH, ionic strength, and the major inorganic cation in solution. Natural toxins could be assigned to groups with either hydrophobic partitioning or specific interactions (complexation reactions, cation exchange) as dominating sorption mechanisms. The complex interplay of interactions in the sorption of natural toxins was equally influenced by sorbate, sorbent, and solution specific characteristics. High variability in sorption was particularly observed in the presence of Ca2+ resulting in Doc being enhanced by a factor of 10 when the pH was increased from 4.5 to 6. Sorbates following this trend contain either functional groups able to form ternary complexes via Ca2+ or aromatic moieties adjacent to protonated N presumably stabilizing cation exchange reactions. Although sorption was often stronger than predicted, investigated natural toxins were highly mobile under all considered conditions.

"Is there anybody else out there?" - First Insights from a Suspect Screening for Phytotoxins in Surface Water.

To protect themselves, plants can produce toxic secondary metabolites (phytotoxins) that appear with widely varying structures and negative effects. These phytotoxins often show similar properties as known aquatic micropollutants in terms of mobility, persistence, toxicity, and possibly also ecotoxicity. However, their occurrence in surface waters remains largely unknown, which is also due to unknown ability of available screening approaches to detect them. Therefore, we performed a target and suspect screening based on a persistence-mobility prioritization for phytotoxins in small Swiss creeks using high resolution mass spectrometry. In total, three of 26 targets were detected, three of 78 suspects tentatively identified, and six suspects fully confirmed by reference standards. To the best of our knowledge, it is the first time that three different plant secondary metabolite classes are detected in the same surface water sample. Estrogenic isoflavones were detected at 73% of the sites with formononetin as main toxin, which is in agreement with previous studies. Furthermore, pyrrolizidine alkaloids and the indole alkaloid gramine were detected. Especially pyrrolizidine alkaloids might be critical due to their production by various plants including the invasive Senecio inaequidens, and their known importance in food and feed safety. Based on these first screening results, different phytotoxin classes should be assessed for their ecotoxicological effects and considered in future water monitoring.

Evaluating the influence of wastewater composition on the growth of Microthrix parvicella by GCxGC/qMS and real-time PCR.

This study underlines the significance of long chain fatty acid (LCFA) content in wastewater influents as an influencing factor promoting the growth of Candidatus 'Microthrix parvicella' (M. parvicella), the most common filamentous bacteria causing foam in activated sludge systems worldwide. Quantification of M. parvicella by real-time polymerase chain reaction (real-time PCR) and analysis of LCFAs by means of two-dimensional gas chromatography coupled with mass spectrometry (GCxGC/qMS), involving solid phase micro-extraction (SPME) to enhance sensitivity, were combined for the first time as a monitoring tool. The results indicate a highly significant correlation between the abundance of M. parvicella and the total LCFA loading (r = 0.96) and linolenic acid C18:3 (r = 0.98) in particular. Additionally, comparison of slope values for the direct correlations of all significant LCFAs found in the analyses showed that the influence of LCFAs on M. parvicella growth increases with an increasing degree of unsaturation of carbon chains. These findings suggest that by removing lipid compounds from the incoming waters, substrate availability would be limited for M. parvicella.