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Attenuation of trace organic compounds (TrOCs) in a river occurs to a large extent in its hyporheic zone. A major part of the attenuation of polar TrOCs is of microbial origin. As microbial activity depends on temperature and redox conditions, seasonal differences in TrOC attenuation are likely. We investigated TrOC attenuation at a river influenced by treated wastewater during two sampling campaigns, one in summer and one in winter. In addition to redox conditions and temperature, we also determined residence times of porewater in sediment using three methods: (a) non‐parametric deconvolution of electrical conductivity time series, (b) the model VFLUX 2.0 based on temperature time series (only summer), and (c) applying Darcy's law to differences in hydraulic heads (only summer). Contrary to our expectations, we found higher attenuation for 12 out of 18 TrOCs in winter, while three TrOCs were better attenuated in summer. Sediment conditions varied between seasons as more of the top sandy layer with a higher hydraulic permeability accumulated on the river bed in summer. As a result, residence times in the sediment were shorter in summer. In winter, longer residence times, lower temperatures, and a steeper oxygen gradient in sediment coincided with higher TrOC attenuation. Further research is needed to understand our unexpected findings and underlying mechanisms. Key Points: The attenuation of 12 out of 18 trace organic compounds (TrOCs) in the hyporheic zone was higher in winter while three TrOCs were attenuated better in summerResidence times in sediment were longer and more diverse in winterThe extent of the oxic sediment was similar between seasons but the gradient from the oxic to anoxic zone was steeper in winter [ABSTRACT FROM AUTHOR]

Triiodinated benzoic acid derivatives are widely used as contrast media for medical examinations and are found at high concentrations in urban aquatic environments. During bank filtration, deiodination of iodinated contrast media has been observed under anoxic/anaerobic conditions. While several bacterial strains capable of dechlorination and debromination have been isolated and characterized, deiodination has not yet been shown for an isolated strain. Here, we investigate dehalogenation of iodinated contrast media (ICM), triiodobenzoic acids (TIBA), and analogous chlorinated compounds by Dehalococcoides mccartyi strain CBDB1 and its corrinoid co-factor vitamin B12. No cell growth of CBDB1 was observed using iodinated compounds as electron acceptor. Only negligible deiodination occurred for ICM, whereas 2,3,5-TIBA was nearly completely deiodinated by CBDB1 without showing cell growth. Furthermore, TIBA inhibited growth with hexachlorobenzene which is usually a well-suited electron acceptor for strain CBDB1, indicating that TIBA is toxic for CBDB1. The involvement of CBDB1 enzymes in the deiodination of TIBA was verified by the absence of deiodination activity after heat inactivation. Adding iodopropane also inhibited the deiodination of TIBA by CBDB1 cells, indicating the involvement of a corrinoid-enzyme in the reductive TIBA deiodination. The results further suggest that the involved electron transport is decoupled from proton translocation and therefore growth. [ABSTRACT FROM AUTHOR]

Elevated levels of adsorbable organic bromine compounds (AOBr) have been detected in German lakes, and cyanobacteria like Microcystis, which are known for the synthesis of microcystins, are one of the main producers of natural organobromines. However, very little is known about how environmental realistic concentrations of organobromines impact invertebrates. Here, the nematode Caenorhabditis elegans was exposed to AOBr-containing surface water samples and to a Microcystis aeruginosa-enriched batch culture (MC-BA) and compared to single organobromines and microcystin-LR exposures. Stimulatory effects were observed in certain life trait variables, which were particularly pronounced in nematodes exposed to MC-BA. A whole genome DNA-microarray revealed that MC-BA led to the differential expression of more than 2000 genes, many of which are known to be involved in metabolic, neurologic, and morphologic processes. Moreover, the upregulation of cyp- and the downregulation of abu-genes suggested the presence of chronic stress. However, the nematodes were not marked by negative phenotypic responses. The observed difference in MC-BA and microcystin-LR (which impacted lifespan, growth, and reproduction) exposed nematodes was hypothesized to be likely due to other compounds within the batch culture. Most likely, the exposure to low concentrations of organobromines appears to buffer the effects of toxic substances, like microcystin-LR. [ABSTRACT FROM AUTHOR]

Brominated organic compounds are known as disinfection byproducts. Very recently, however, even natural brominated organic compounds (analyzed as adsorbable organic bromine; AOBr) have been found in decaying freshwater cyanobacteria blooms. Among the identified compounds was dibromoacetic acid (DBAA), which has proven to be neurotoxic at rather high concentrations in mammalian assays. Currently it is open how single compounds as well as complex mixtures impact organisms at environmentally realistic concentrations. Furthermore, it is also unclear how natural organic matter, mainly humic substances (HS), which are present in all freshwater systems, modulates the toxic impact of AOBr. Therefore, two AOBr compounds (DBAA and tetrabromobisphenol-A; TBBP-A) and AOBr-containing water samples were tested using a Caenorhabditis elegans neurotoxicity assay that measured autonomic and sensory functions. TBBP-A had an impact on three response variables of C. elegans and can be classified neurotoxic. In contrast to our expectations, DBAA led to neurostimulation of two autonomic functions, but had a temporary impact on the defecation interval. All surface water samples contained measurable amounts of AOBr. Exposure of C. elegans to concentrated water samples – one in particular – increased three of the four locomotion traits and left defecation activity and both sensory variables unchanged. This stimulation might be due to unidentified compounds in the samples or to a hormetic effect of the AOBr compounds. Thermotactic behavior was characterized by a temporary preference for the colder environment, indicating a temporary mild neurotoxicity. Overall, the set of relative simple phenotypic tests used in the current study revealed a meaningful neurotoxic or neurostimulative profile in response to chemical compounds or natural samples. Furthermore, it shows that the resulting response to natural AOBr compounds at environmentally realistic concentrations was not necessarily adverse, but instead, that the mixtures of natural AOBr were neurostimulatory. [Copyright &y& Elsevier]

This research examined whether treatment with zero-valent iron in the presence of oxygen is a suitable process for the degradation of pharmaceuticals (antibiotics, cytostatic drugs) and diagnostic agents. It was shown that the concentration of all selected compounds was decreased efficiently by treatment with iron. The compounds exhibited a pseudo-first-order decay with a linear dependence on ln(c/c0) on time. The observed reaction rate strongly depended on pH, the amount of added iron, and the stirring speed. The influence of temperature on the reaction rate was small. Comparison of detected transformation products with those obtained after catalytic hydrogenation and treatment with Fenton's reagent revealed that reductive and oxidative processes are responsible for the transformations observed. [ABSTRACT FROM AUTHOR]

Abstract: Many rivers and streams worldwide are impacted by pharmaceuticals originating from sewage. The hyporheic zone underlying streams is often regarded as reactive bioreactor with the potential for eliminating such sewage-born micropollutants. The present study aims at checking the elimination potential and analyzing the coupling of hydrodynamics, biogeochemistry and micropollutant processing. To this end, two sites at the lowland stream Erpe, which receives a high sewage burden, were equipped and sampled with nested piezometers. From temperature depth profiles we determined that at one of the sites infiltration of surface water into the aquifer occurs while exfiltration dominates at the other site. Biogeochemical data reveal intense mineralization processes and strictly anoxic conditions in the streambed sediments at both sites. Concentrations of the pharmaceuticals indomethacin, diclofenac, ibuprofen, bezafibrate, ketoprofen, naproxen and clofibric acid were high in the surface water and also in the subsurface at the infiltrating site. The evaluation of the depth profiles indicates some attenuation but due to varying surface water composition the evaluation of subsurface processes is quite complex. Borate and non-geogenic gadolinium were measured as conservative wastewater indicators. To eliminate the influence of fluctuating sewage proportions in the surface water, micropollutant concentrations are related to these indicators. The indicators can cope with different dilutions of the sewage but not with temporally varying sewage composition. [Copyright &y& Elsevier]

For the detection of unknown organic bromine compounds, a liquid chromatography-mass spectrometry (LC-MS) method with negative-ion electrospray ionization (NI-ESI) and induced in-source fragmentation (IISF) was established. After LC separation, the molecules are fragmentized in the source, and bromide is detected via m/z 79 and m/z 81 based on the isotopic occurrence of bromine. In this way, the retention times of the unknown organobromine compounds are determined, and this can be used to extract additional structural information (number of bound bromine atoms, molecular mass and fragmentation scheme) from measurements in the commonly used but less sensitive scan mode. The analysis of known organobromine compounds shows that LC/NI-ESI-IISF mass spectrometry with detection of m/z 79 and 81 is more sensitive than the detection of daughter ions (LC/ESI/MS-MS). Therefore, we present a method not only for the detection of unknown organic bromine compounds, but also for the selective and sensitive detection and quantification of known organobromine compounds. [ABSTRACT FROM AUTHOR]

Berlin surface waters are characterized by elevated concentrations of organic bound bromine (up to 35 µg/L) in late summer. Organic bromine compounds in lakes are of significant importance because human life is closely connected to fresh water. Apart from recreational use, fresh water is frequently used for the production of drinking water, e.g., after bank filtration. Therefore the source, particularly the mechanism responsible for the formation is studied. Field studies indicate that the organic bromine compounds, measured as adsorbable organic bromine (AOBr), are autochthonous. Staggered maxima concentrations of chlorophyll-a, DOC and AOBr indicate that phototrophic organisms might contribute to the AOBr after death. The involvement of phototrophic organisms was established in the laboratory using surface water and/or cultures of organisms. Light and the presence of phototrophic organisms are essential for an AOBr production. Phototrophic organisms incorporate bromide, which is released randomly and after cell death. A part of the incorporated bromide is used for the formation of organic bromine compounds in the cell. After death of the organisms the brominated compounds and the incorporated bromide are released into the water phase, and an extracellular AOBr production can lead to a further formation of AOBr, most probably due to the parallel release of haloperoxidases. [ABSTRACT FROM AUTHOR]

Monitoring of organic halogen compounds, measured as adsorbable organically bound bromine (AOBr), in an eutrophic lake, which is influenced by treated waste water, revealed repeatedly high concentrations of organobromine compounds in late summer, whereas five times lower values were measured during the rest of the year. It was possible to reproduce the in situ observed AOBr increase in the laboratory. Batch experiments were performed with lake water from two different lakes and an algae culture. It could be shown that the AOBr production is not limited to strong waste water influenced lakes. Furthermore, the AOBr formation requires light and the presence of algae, and thus is most probably biotic in nature. A low content of nutrients favours the formation of organic bromine compounds. To our knowledge this is the first report about the seasonally occurrence of naturally produced organic bromine compounds in lakes/surface waters. [Copyright &y& Elsevier]

Iodinated contrast media (ICM) are found at considerably higher concentrations than any other pharmaceutical in waste water, surface water and bank filtrate. While the compounds are persistent to deiodination in aerobic environments, field data from bank filtration transects have demonstrated a partial deiodination in reducing soil–water environments. In a previous lab study, we have shown that this reductive deiodination is abiotically catalyzed by (free) corrinoids. To achieve a better understanding of the incomplete deiodination in the environment, we now investigated the reaction kinetics based on the decrease of the iodinated compound, the formation of deiodinated transformation products and the iodide release. The deiodination follows first-order kinetics and consists of three partial reactions for the release of three iodine atoms. The deiodination rate decreased with decreasing iodination degree with the deiodination rate constants k 1 > k 2 > k 3. In contrast to the ICM, 2,4,6- and 2,3,5-triiodobenzoic acid, 5-amino-2,4,6-triiodoisophthalic acid and monoiodobenzoic acids did not show a complete deiodination under the same test conditions. Our results show that the deiodination strongly depends on the substitution pattern of the bound iodine atoms as well as on adjacent functional groups. Iodine atoms in ortho -position to another iodine atom or a carboxyl group were released more easily while an amino group in ortho -position inhibited the deiodination. Tests in tap water in the presence of B 12 showed a much slower deiodination than in ultrapure water, most likely caused by competitive electron acceptors in the water matrix. Image 1 • Deiodination of ICM follows first-order kinetics with rate constants k 1 > k 2 > k 3. • Complete deiodination of contrast media but not of tri- and monoiodobenzoic acids. • An iodine atom in ortho -position to another is released more easily than in meta. • Carboxyl groups ortho to iodine promote deiodination while amino groups inhibit it. • Deiodination in ultrapure water is substantially faster than in tap water. [ABSTRACT FROM AUTHOR]

Iodinated X-ray contrast media (ICM) as well as their aerobic transformation products (TPs), are highly polar triiodobenzoic acid derivatives, ubiquitously found in the urban water cycle. Based on their polarity, their sorption affinity to sediment and soil is negligible. However, we hypothesize that the iodine atoms bound to the benzene ring play a decisive role for sorption, due to their large atom radius, high electron number and symmetrical positioning within the aromatic system. The aim of this study is to investigate, if the (partial) deiodination, occurring during anoxic/anaerobic bank filtration, improves the sorption to aquifer material. Tri, di, mono and deiodinated structures of two ICMs (iopromide and diatrizoate) and one precursor/TP of ICM (5-amino-2,4,6-triiodoisophtalic acid) were tested in batch experiments, using two aquifer sands and a loam soil with and without organic matter. The di, mono and deiodinated structures were produced by (partial) deiodination of the triiodinated initial compounds. The results demonstrated that the (partial) deiodination increases the sorption to all tested sorbents, even though the theoretical polarity increases with decreasing number of iodine atoms. Whereas lignite particles positively affected the sorption, mineral components decreased it. Kinetics tests show biphasic sorption for the deiodinated derivatives. We have concluded that iodine affects the sorption by sterical hindrance, repulsive forces, resonance and inductive effects, depending on the number and position of iodine, side chain characteristics and composition of the sorbent material. Our study has revealed an increased sorption potential of ICMs and their iodinated TPs to aquifer material during anoxic/anaerobic bank filtration as a result of (partial) deiodination, whereby a complete deiodination is not necessary for efficient removal by sorption. Furthermore, it suggests that the combination of an initial aerobic (side chain transformations) and a subsequent anoxic/anaerobic (deiodination) redox milieu supports the sorption potential. [Display omitted] • Batch tests using real aquifer material and standard loam soil. • (Partial) deiodination increases the sorption despite increased polarity. • Sorption kinetics of the deiodinated compounds is biphasic. • Iodine affects sorption by sterical, repulsive, resonance and inductive effects. [ABSTRACT FROM AUTHOR]

Abstract: Leaf litter processing is one major pathway of the global organic carbon cycle. During this process, a variety of small reactive organic compounds are released and transported to the aquatic environment, and may directly impact aquatic organisms as natural xenobiotics. We hypothesize that different forest stockings produce different leachate qualities, which in turn, stress the aquatic communities and, eventually, separate sensitive from tolerant species. Particularly, leachates from coniferous trees are suspected to have strongly adverse impacts on sensitive species. We exposed individuals of a clone of the model organism, Moina macrocopa, to comparable concentrations (approximately 2mM) of litter leachates of Norway spruce, Picea abies, Colorado blue spruce, Picea pungens, black poplar, Populus nigra, and sessile oak, Quercus petraea. The animals were fed ad libitum. The following life trait variables were recorded: growth, lifespan, and lifetime offspring. To identify, whether or not exposure to litter leachates provokes an internal oxidative stress in the exposed animals we measured the superoxide anion radical scavenging capacity via photoluminescence. Except of P. abies, exposure to the leachates reduced this antioxidant capacity by approximately 50%. Leachate exposures, except that of Quercus, increased body size and extended lifespan; furthermore, particularly the leachates of both Picea species significantly increased the offspring numbers. This unexpected behavior of exposed Moina may be based on food supplements (e.g., high carbohydrate contents) in the leachates or on yet to be identified regulatory pathways of energy allocation. Overall, our results suggest that the potentially adverse effects of litter leachates can be overruled by either bacterial-growth supporting fractions in the leachates or an internal compensation mechanism in the Moina individuals. [Copyright &y& Elsevier]

Abstract Iodinated X-ray contrast media are known for their stability concerning deiodination in the aquatic environment under aerobic conditions. In this study, we demonstrate the abiotic reductive deiodination of the iodinated contrast media iopromide, iopamidol and diatrizoate in the presence of corrinoids. In addition, triiodinated benzoic acid derivatives with iodine atoms bound at different positions were investigated. Corrinoids like cyanocobalamin (vitamin B 12) and dicyanocobinamide served as electron shuttles and as catalysts between the reducing agent (e.g., titanium (III) citrate) and the electron accepting iodinated compound. The concentration decrease of the iodinated compounds followed first-order kinetics with rate constant k obs depending on the iodinated compound. A linear correlation between the rate of iodide release and the corrinoid concentration was observed, with deiodination rates for dicyanocobinamide twice as high as for vitamin B 12. Reducing agents with a less negative standard redox potential like dithiothreitol or cysteine caused slower deiodination as the cobalt center was only reduced to its CoII oxidation state. With a temperature increase from 11 to 23 °C, the concentrations of released iodide doubled. A complete deiodination was only observed for the iodinated contrast media but not for structurally similar iodinated benzoic acid derivatives. Graphical abstract Image 1 Highlights • Deiodination of iodinated contrast media can be catalyzed by B 12 derivatives. • Linear correlation between iodide release rate and corrinoid concentration. • Deiodination degree depends on the oxidation state of the cobalt center of B 12. • Decrease of the iodinated compounds follows first-order kinetics. • Deiodination is influenced by the substitution pattern of bound iodine. [ABSTRACT FROM AUTHOR]

The hyporheic zone (HZ) is often considered to efficiently remove polar trace organic compounds (TrOCs) from lotic systems, mitigating potential adverse effects of TrOCs on ecosystem functioning and drinking water production. Predicting the fate of TrOCs in the hyporheic zone (HZ) is difficult as the in-situ removal rate constants are not known and the biogeochemical factors as well as hydrological conditions controlling the removal efficiency are not fully understood. To determine the in-situ removal efficiency of the HZ for a variety of TrOCs as a function of the biogeochemical milieu, we conducted a field study in an urban river near Berlin, Germany. Subsurface flow was studied by time series of temperature depth profiles and the biogeochemical milieu of the HZ by concentration depth profiles. These results, in conjunction with a 1D advection-dispersion transport model, were used to calculate first-order removal rate constants of several polar TrOCs in the HZ. For the majority of TrOCs investigated, removal rate constants were strongly dependent on redox conditions, with significantly higher removal rates observed under predominantly suboxic (i.e. denitrifying) compared to anoxic (i.e. Fe and Mn reducing) conditions. Compared to previous studies on the fate of TrOCs in saturated sediments, half-lives within oxic/suboxic sections of the HZ were relatively low, attributable to the site-specific characteristics of the HZ in a stream dominated by wastewater treatment plant effluent. For nine out of thirteen investigated TrOCs, concentrations decreased significantly in the HZ with relative removal percentages ranging from 32% for primidone to 77% for gabapentin. For many TrOCs, removal efficiency decreased drastically as redox conditions became anoxic. For the majority of compounds investigated here, the HZ indeed acts as an efficient bioreactor that is capable of removing TrOCs along relatively short flow paths. Depending on the TrOC, removal capacity may be enhanced by either increasing the magnitude of groundwater-surface exchange fluxes, by increasing the total residence time in the HZ or the exposure time to suboxic zones, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved organic matter (DOM) has been shown to affect phytoplankton species directly. These interactions largely depend on the origin and molecular size of DOM and are different in prokaryotes and eukaryotes. In a preceding study, however, two humic substance preparations did not adversely affect coccal green algae or cyanobacterial growth even at high concentrations of dissolved organic carbon (DOC). These results contradicted previous findings, showing a clear, negative response of different phototrophs to much lower DOC concentrations. To test whether or not at least defined building blocks of humic substances (HSs) are effective algicidal structures, we enriched two humic preparations with hydroquinone and p-benzoquinone, respectively, and exposed two different green algae, Pseudokirchneriella subcapitata and Monoraphidium braunii, and two cyanobacterial species, Synechocystis sp. and Microcystis aeruginosa, to the unmodified and enriched HSs. As response variables, growth rates in terms of biomass increase, chlorophyll-a content, and photosynthetic yield were measured. The highest concentration (4.17mM DOC) of the modified HSs clearly inhibited growth; the cyanobacterial species were much more sensitive than the green algal species. However, realistic ecological concentrations did not adversely affect growth. Aerating the exposure solution for 24h strongly reduced the inhibitory effect of the modified HSs. The algicidal effect was obviously caused by monomers and not by polymerised high molecular weight HSs themselves. Furthermore, the maximum quantum yield (Φ PSII max) was stimulated in the green algal species by low and medium DOC concentrations, but reduced in the cyanobacterial species upon exposure to higher HS concentrations. The quinone- and phenol-enriched HSs only showed algicidal activity at high concentrations of 4.17mM DOC and lost their effects over time, presumably by oxidation and subsequent polymerisation. This study confirms that the applied humic substances themselves are not effective algicides even if enriched in effective structures. [Copyright &y& Elsevier]

In fresh waters cyanobacterial blooms can produce a variety of toxins, such as microcystin variants (MCs) and anatoxin-a (ANA). ANA is a well-known neurotoxin, whereas MCs are hepatotoxic and, to a lesser degree, also neurotoxic. Neurotoxicity applies especially to invertebrates lacking livers. Current standardized neurotoxicity screening methods use rats or mice. However, in order to minimize vertebrate animal experiments as well as experimental time and effort, many investigators have proposed the nematode Caenorhabditis elegans as an appropriate invertebrate model. Therefore, four known neurotoxic compounds (positive compounds: chlorpyrifos, abamectin, atropine, and acrylamide) were chosen to verify the expected impacts on autonomic (locomotion, feeding, defecation) and sensory (thermal, chemical, and mechanical sensory perception) functions in C. elegans. This study is another step towards successfully establishing C. elegans as an alternative neurotoxicity model. By using this protocol, anatoxin-a adversely affected locomotive behavior and pharyngeal pumping frequency and, most strongly, chemotactic and thermotactic behavior, whereas MC-LR impacted locomotion, pumping, and mechanical behavior, but not chemical sensory behavior. Environmental samples can also be screened in this simple and fast way for neurotoxic characteristics. The filtrate of a Microcystis aeruginosa culture, known for its hepatotoxicity, also displayed mild neurotoxicity (modulated short-term thermotaxis). These results show the suitability of this assay for environmental cyanotoxin-containing samples.

The detection of unknown organic compounds, e.g., transformation products of known trace pollutants in environmental samples, is a difficult task which can be simplified if the compounds of interest are characterized by a functional group or a heteroatom which can selectively be detected. For the detection of iodinated benzene derivatives, used as X-ray contrast media, we have studied whether such compounds can be selectively detected by negative ion (NI) electrospray ionization via iodide as a product ion of in-source fragmentation, generated by applying a high cone voltage. It was found that selective detection of iodinated benzene derivatives is possible by liquid chromatography/negative ion electrospray ionization (LC/NI-ESI) if the compounds are destroyed before entering the mass spectrometer. To our knowledge this is the first report of the use of NI in-source fragmentation MS for analyses traditionally performed with inductively coupled plasma (ICP)-MS. The novel application of NI in-source fragmentation MS is a tool for those who do not possess the facilities to perform ICP-MS. Furthermore, NI-ESI at varying cone voltages provides both structural information and elemental detection, whereas ICP-MS can only provide elemental detection., (Copyright 2003 John Wiley & Sons, Ltd.)