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Storm events lead to agricultural and urban runoff, to mobilization of contaminated particulate matter, and to input from combined sewer overflows into rivers. We conducted time‐resolved sampling during a storm event at the Ammer River, southwest Germany, which is representative of small river systems in densely populated areas with a temperate climate. Suspended particulate matter (SPM) and water from 2 sampling sites were separately analyzed by a multi‐analyte liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for 97 environmentally relevant organic micropollutants and with 2 in vitro bioassays. Oxidative stress response (AREc32) may become activated by various stressors covering a broad range of physicochemical properties and induction of aryl hydrocarbon receptor–chemical‐activated luciferase gene expression (AhR‐CALUX) by hydrophobic compounds such as dioxins and dioxin‐like molecules. Compound numbers, concentrations, their mass fluxes, and associated effect fluxes increased substantially during the storm event. Micropollutants detected in water and on SPM pointed toward inputs from combined sewer overflow (e.g., caffeine, paracetamol), urban runoff (e.g., mecoprop, terbutryn), and agricultural areas (e.g., azoxystrobin, bentazone). Particle‐facilitated transport of triphenylphosphate and tris(1‐chloro‐2‐propyl) phosphate accounted for up to 34 and 33% of the total mass flux even though SPM concentrations were <1 g L–1. Effect fluxes attributed to SPM were similar or higher than in the water phase. The important role of SPM‐bound transport emphasizes the need to consider not only concentrations but also mass and effect fluxes for surface water quality assessment and wastewater/stormwater treatment options. Environ Toxicol Chem 2021;40:88–99. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Understanding groundwater–surface water (GW–SW) interactions is vital for water management in karstic catchments due to its impact on water quality. The objective of this study was to evaluate and compare the applicability of seven environmental tracers to quantify and localize groundwater exfiltration into a small, human‐impacted karstic river system. Tracers were selected based on their emission source to the surface water either as (a) dissolved, predominantly geogenic compounds (radon‐222, sulphate and electrical conductivity) or (b) anthropogenic compounds (predominantly) originating from wastewater treatment plant (WWTP) effluents (carbamazepine, tramadol, sodium, chloride). Two contrasting sampling approaches were compared (a) assuming steady‐state flow conditions and (b) considering the travel time of the water parcels (Lagrangian sampling) through the catchment to account for diurnal changes in inflow from the WWTP. Spatial variability of the concentrations of all tracers indicated sections of preferential groundwater inflow. Lagrangian sampling techniques seem highly relevant for capturing dynamic concentration patterns of WWTP‐derived compounds. Quantification of GW inflow with the finite element model FINIFLUX, based on observed in‐stream Rn activities led to plausible fluxes along the investigated river reaches (0.265 m3 s−1), while observations of other natural or anthropogenic environmental tracers produced less plausible water fluxes. Important point sources of groundwater exfiltration can be ascribed to locations where the river crosses geological fault lines. This indicates that commonly applied concepts describing groundwater–surface water interactions assuming diffuse flow in porous media are difficult to transfer to karstic river systems whereas concepts from fractured aquifers may be more applicable. In general, this study helps selecting the best suited hydrological tracer for GW exfiltration and leads to a better understanding of processes controlling groundwater inflow into karstic river systems. [ABSTRACT FROM AUTHOR]

Organic micropollutants of anthropogenic origin in river waters may impair aquatic ecosystem health and drinking water quality. To evaluate micropollutant fate and turnover on a catchment scale, information on input source characteristics as well as spatial and temporal variability is required. The influence of tributaries from agricultural and urban areas and the input of wastewater were investigated by grab and Lagrangian sampling under base flow conditions within a 7.7‐km‐long stretch of the Ammer River (southwest Germany) using target screening for 83 organic micropollutants and 4 in vitro bioassays with environmentally relevant modes of action. In total, 9 pesticides and transformation products, 13 pharmaceuticals, and 6 industrial and household chemicals were detected. Further, aryl hydrocarbon receptor induction, peroxisome proliferator–activated receptor activity, estrogenicity, and oxidative stress response were measured in the river. The vast majority of the compounds and mixture effects were introduced by the effluent of a wastewater‐treatment plant, which contributed 50% of the total flow rate of the river on the sampling day. The tributaries contributed little to the overall load of organic micropollutants and mixture effects because of their relatively low discharge but showed a different chemical and toxicological pattern from the Ammer River, though a comparison to effect‐based trigger values pointed toward unacceptable surface water quality in the main stem and in some of the tributaries. Chemical analysis and in vitro bioassays covered different windows of analyte properties but reflected the same picture. Environ Toxicol Chem 2020;39:1382–1391. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Some environmental pollutants impair mitochondria, which are of vital importance as energy factories in eukaryotic cells. Mitochondrial toxicity was quantified by measuring the change of the oxygen consumption rate (OCR) of HepG2 cells with the Agilent Seahorse XFe96 Analyzer. Various mechanisms of mitochondrial toxicity, including inhibition of the electron transport chain or adenosine triphosphate (ATP) synthase as well as uncoupling of oxidative phosphorylation, were differentiated by dosing the sample in parallel with reference compounds following the OCR over time. These time–OCR traces were used to derive effect concentrations for 10% inhibition of the electron transport chain or 10% of uncoupling. The low effect level of 10% was necessary because environmental mixtures contain thousands of chemicals; only few of them interfere with mitochondria, but the others cause cytotoxicity. The OCR bioassay was validated with environmental pollutants of known mechanism of mitochondrial toxicity. Binary mixtures of uncouplers or inhibitors acted according to the mixture model of concentration addition. Uncoupling and/or inhibitory effects were detected in extracts of river water samples without apparent cytotoxicity. Uncoupling effects could only be quantified in water samples if inhibitory effects occurred at lower concentrations because no uncoupling can be detected without an appreciable membrane potential built up. The OCR bioassay can thus complement chemical analysis and in vitro bioassays for monitoring micropollutants in water. Environ Toxicol Chem 2019;00:1–12. © 2019 SETAC [ABSTRACT FROM AUTHOR]

Abstract Interpreting the fate of wastewater contaminants in streams is difficult because their inputs vary in time and several processes synchronously affect reactive transport. We present a method to disentangle the various influences by performing a conservative-tracer test while sampling a stream section at various locations for chemical analysis of micropollutants. By comparing the outflow concentrations of contaminants with the tracer signal convoluted by the inflow time series, we estimated reaction rate coefficients and calculated the contaminant removal along a river section. The method was tested at River Steinlach, Germany, where 38 contaminants were monitored. Comparing day-time and night-time experiments allowed distinguishing photo-dependent degradation from other elimination processes. While photo-dependent degradation showed to be highly efficient for the removal of metroprolol, bisoprolol, and venlafaxine, its impact on contaminant removal was on a similar scale to the photo-independent processes when averaged over 24 h. For a selection of compounds analyzed in the present study, bio- and photodegradation were higher than in previous field studies. In the Steinlach study, we observed extraordinarily effective removal processes that may be due to the higher proportion of treated wastewater, temperature, DOC and nitrate concentrations, but also a higher surface to volume ratio from low flow conditions that favorizes photodegradation through the shallow water column and a larger transient storage than observed in comparable studies. Graphical abstract Unlabelled Image Highlights • Studying reactive processes in river channels is inherently difficult. • Tracer tests allowed separating conservative transport from the measured signal. • Comparison of day and night experiments highlighted photodegradation. • Photodegradation is weaker than photo-independent elimination on the long term. [ABSTRACT FROM AUTHOR]

Anthropogenic organic micropollutants enter river systems mainly via wastewater treatment plants (WWTP). Characterization of turnover processes and fate of these compounds including temporal and spatial resolution at the same time remains challenging. Still, published results rely frequently on grab samples that do not account adequately for advection, dispersion and transformation along the studied reach. This study aims to compare degradation rates calculated from a Lagrangian Sampling concept in two different sequential reaches with calculations from arbitrary grab samples.Field investigations took place at two sequential reaches at the Ammer River close to Tübingen in the southwest of Germany that differ in (hydro-) morphology, slope and amount of groundwater inflow. Time-series measurements of organic chemical compounds (target screening), accompanied by electrical conductivity (EC), and conservative ions were conducted over a period of 24 hours. A lumped parameter model approach accounting for advection and dispersion was applied to the time-series measurements to calculate degradation rate constants affecting water parcels entering and leaving the same reach. In an alternative approach, degradation rate constants were calculated from arbitrary grab samples of the time series, representative for samples not properly considering travel time of water in the river. The influence of dilution caused by tributary and groundwater inflow was included for the overall attenuation rate in both approaches. The Lagrangian sampling approach integrates temporal dynamics such as the changed solar radiation or input of the WWTP into the river throughout the whole day and thus leads to representative degradation rates and characterization of turnover processes. In contrast, results from arbitrary grab samples may be misleading and indicating unrealistic processes and rates.The different results of the tested approaches show the relevance of identifying and including temporal and spatial aspects of river systems for characterization of the fate of organic micropollutants. They highlight the need to consider hydrological processes in the river for future field-based attenuation investigations. [ABSTRACT FROM AUTHOR]