Stefan Höger - Academia.edu (original) (raw)

Papers by Stefan Höger

Environmental Health Perspectives, Mar 1, 2000

Cyanobaeteria (blue-green algae) produee toxins that may present a hazard 101' drinking water saf... more Cyanobaeteria (blue-green algae) produee toxins that may present a hazard 101' drinking water safety, These toxins (mieroeystins, nodularins, saxitoxins, anatoxin-a, anatoxin-a(s), eylindrospermopsinl are strueturally diverse and their effeets range from liver damage, including liver cancer, to neurotoxicity, The oecurrenee of eyanobaetsria and their toxins in WeHer bodies used for tlle procluction 01 drinking water poses a tsehnieal cllallenge lor water utility managers, With respeet to their removal in water treatment procedures, of the more than 60 microcystln congeners, microeystin-LR (L, L-Ieucine; R, L-arglnine) is the best studied cyanobacterial toxin, whereas srudies thae have beeIl conducted co date (7,13-16). Cyanobacterial Toxins Cyallobacteria pl'l'ldllCe a val'iety 01" toxins, sllbseqlletltly called cyanoroxins, that are dassiEicd funetionally inw hepaw., lH:UI'O-, and cytornxins. Additionally, cyanobacteria producc lipopolysacclult'ides (LPS) as weil as sccondary merabolites that arc poren tially pharmacologically useful. '['he former are l'espotlsible fot' the irriranl nawre 01' cyanobaeterial tnaterinl. Ddlned hy their chemic~tl strtu.:tllre, cyatlo(()xitls fall itlHI three groU))s: cydic peptides (the heparoroxins microcystins alld !1odularin), alkaloids (thc ncurotoxins atH\toxin and saxitoxins), and LPS. The specics mosr ,!fren itnplicated wirh toxicity are MiC1'()qstis lumgill()SIl, Nllllkt()tlni.\• ('" (Jscillflt!)/,ill) /'ubt'Sel'NS, Aphanizomenrm./los-rlquae, ilnllbfll:JJrl jlosaqulle, P!rwktflthrix f/gardhii, alld I.yngliia spp. (Table 1).

Julius-Kühn-Archiv, Jul 26, 2018

was reached in the treatment were group feeding took place and then mating. It is very likely tha... more was reached in the treatment were group feeding took place and then mating. It is very likely that the consumption did not increase due to the mating process but due to the additional starvation phase after the bees had learned how to feed, as mating itself does not seem to have an effect. Conclusions Not only the type of food or feeder offered to Osmia can make a difference in the consumption rates, but the way the bee is treated before the test can have a large influence. This data shows that bees being exposed to a certain type of feeder in a group setting before the experiment will have better consumption rates when that same feeder is used during the experiment.

Cyanobacteria produce a variety of unusual secondary metabolites, the function of some of them st... more Cyanobacteria produce a variety of unusual secondary metabolites, the function of some of them still remains unclear. Research in the last years has primarily focused on cyanobacterial microcystins that have severe impact on humans and livestock. While at the beginning the main focus point was on the structure elucidation and functionality of microcystins, in recent years also cyanopeptolins and cyclamides have become important issues. Today also the possible ecological role of these metabolites is an attractive goal of research. In this protocol methods for the extraction, determination, and quantification using high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), and gas chromatography-mass spectrometry (GC-MS) are described as well as methods (bioassay-guided fractionation, enzyme linked immunosorbent assay) to find toxins and protease inhibitors in cyanobacterial extracts. In addition, methods for the determination of the molar absorption coefficient, necessary for the quantification of small amounts of the oligopeptides, are described.

Chemosphere, Mar 1, 2022

The impact of pesticide mixtures on various soil parameters has been extensively studied, whereas... more The impact of pesticide mixtures on various soil parameters has been extensively studied, whereas research on effects in the aquatic environment is scarce. Furthermore, investigations on the consequences of chemical mixtures on the biodegradation kinetics of parent compounds remain deficient. Our research intended to evaluate potential effects by combined application of an agriculturally employed tank mixture to aquatic sediment systems under controlled laboratory conditions. The mixture contained two fungicides and one radiolabeled herbicide of which the route and rate of degradation was followed. One set of aquatic sediment vessels was incubated in the dark. A second set of vessels was controlled under identical conditions, except for being continuously irradiated to promote algal growth. In addition, the algal biomass in irradiated aquatic sediment was monitored to determine its effects and a potential role in the biodegradation of iodosulfuron-methyl-sodium. The study results showed that the herbicide, although hydro- and photolytically stable throughout the study, metabolized faster (DT50 1.1-1.2-fold and DT90 2.8-4.5-fold) when continuously irradiated in comparison to dark aquatic sediment. Both fungicides had a significant prolonging effect on the biodegradation rate of the herbicide. In the presence of fungicides, DT90 values increased 1.5-fold in the irradiated, and 2.5-fold in the dark systems. Additionally, algae may have influenced the metabolization of the herbicide in the irradiated systems, where shorter DT90 values were evaluated. Even so, the algal influence was concluded to be indirect.

American Chemical Society eBooks, Oct 14, 2021

Aquatic Toxicology, 2006

The microcystin-producing cyanobacterium Planktothrix is one of the most widespread genera amongs... more The microcystin-producing cyanobacterium Planktothrix is one of the most widespread genera amongst toxin producing cyanobacteria in European lakes. In particular, the metalimnic blooms of Planktothrix rubescens have been associated with growing problems in the professional freshwater fishery as a decrease in yearly yields in the important coregonids fishery often coincides with the appearance of P. rubescens. P. rubescens is a cyanobacterial species known to produce toxic compounds, e.g. microcystins. Although microcystins have been reported to affect fish health, behaviour, development and growth and have also been associated with feral fish kills, there is currently no specific information on the effects of toxic Planktothrix filaments in fish and especially coregonids. Therefore, the aim of this study was to investigate the effects of an environmentally relevant dose of P. rubescens filaments orally applied to coregonids and to discuss the findings in the context of microcystin toxicity previously reported in carp and trout. A single dose of P. rubescens culture, at a density of 80,000 cells per 120 l, was applied to coregonids thus corresponding to 0.6-0.9 g microcystin-LR equiv. /kg body weight. Behavioural changes and opercular beat rates, growth, hepatosomatic index, condition and plasma glucose were determined. Liver, kidney, gill and the gastrointestinal tract were assessed histopathologically and immunhistologically. Exposed fish showed behavioural changes, increased opercular beat rates and elevated plasma glucose levels, possibly representing a physiological stress response. Histopathological alterations in liver, gastrointestinal tract and kidney, also immunopositive for microcystin suggested causality of tissue damage and the in situ presence of microcystins. The observed combination of stress and organ damage may explain the frequently reduced weight and thus the fitness noted in coregonids subjected to regular occurrences of stratified and dispersed P. rubescens blooms, e.g. in lake Ammersee,

Biochemical Journal, 2003

Recent functional studies have suggested that, in addition to simple diffusion, carrier-mediated ... more Recent functional studies have suggested that, in addition to simple diffusion, carrier-mediated transport may play an important role in foetal unconjugated bilirubin (UCB) uptake by the placenta. We have investigated the role of organic anion-transporting polypeptides (OATPs) in UCB transport by the placenta–maternal liver tandem. RNA was obtained from human liver (hL), human placenta (hPl) at term, and purified (> 80%) cytokeratin-7-positive mononucleated human trophoblast cells (hTCs). By analytical reverse transcription (RT)-PCR, agarose gel electrophoresis separation and sequencing, the mRNA of OATP-A (SLC21A3) and OATP-8 (SLC21A8) was identified in hL, hPl and hTCs, whereas that of OATP-C (SLC21A6) was detectable only in hL. Real-time quantitative RT-PCR revealed that in hL the abundance of mRNA was OATP-8 > OATP-C ≫ OATP-A, whereas in hPl and hTCs this was OATP-8 ≫ OATP-A ≫ OATP-C. Expression levels for these OATPs were hL ≫ hTCs > hPl. Injection of mRNA of OATP-A, O...

CHIMIA International Journal for Chemistry, 2020

Just recently the problem of pharmaceutical residues in the environment has been emphasized by OE... more Just recently the problem of pharmaceutical residues in the environment has been emphasized by OECD. Especially antibiotics are of concern due to their widespread use and diverse modes of actions including ones that can affect the photosynthetic activity of primary producers and subsequently primary biomass production and carbon dioxide fixation. The EU regulatory authority, the European Medicines Agency (EMA), has therefore proposed to implement a new tailored environmental risk assessment scheme, published in a new draft guideline 2018. Threshold effect levels to three fixed representative species of green algae and cyanobacteria will be required. This article reviews and compares the contamination of waters with antibiotics in Switzerland and Germany and also presents an overview of published effect data on eukaryotic algae and prokaryotic cyanobacteria in order to discuss the representativeness of the selected species. Since no full datasets as demanded by the EMA were publicall...

Toxicon, 2006

Cyanobacteria are well known for their production of non-ribosomal cyclic peptide toxins, includi... more Cyanobacteria are well known for their production of non-ribosomal cyclic peptide toxins, including microcystin, in temperate and tropical regions, however, the production of these compounds in extremely cold environments is still largely unexplored. Therefore, we investigated the production of protein phosphatase inhibiting microcystins by Antarctic cyanobacteria. We have identified microcystin-LR and for the first time [D-Asp 3 ] microcystin-LR by mass spectrometric analysis in Antarctic cyanobacteria. The microcystins were extracted from a benthic microbial community that was sampled from a meltwater pond (Fresh Pond, McMurdo Ice Shelf, Antarctica). The extracted cyanobacterial cyclic peptides were equivalent to 11.4 ng MC-LR per mg dry weight by semi-quantitative analyses using HPLC-DAD and the protein phosphatase inhibition assay. Furthermore, we were able to identify the presence of cyanobacterial non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes in total DNA extracts from the mat community.

Harmful Algae, 2009

Regular occurrences of the cyanobacterium Plankcotlllix rubescens have been observed in several l... more Regular occurrences of the cyanobacterium Plankcotlllix rubescens have been observed in several lakes that have undergone recent re-oligotrophication, e.g. Lake Ammersee. Planktothn",~ species are known to produce microcystins, potent pllOsphatase inhibitors that have been associated with morbidities and mortalities in hUinans and animals. The aim of this study was to characterise the temporal and spatial abundance and toxicity of r. rubescens in Lake Ammersee. P. rubescens cell densities and biovolumes were calculated via fluorescence image analyses. P. rubescens was present during the entire observation period from 1999 to 2004, albeit at different cell densities. Maximum biovolumes of 45 cm) m-2 were observed in May 2001. Filaments were regularly distributed over the entire water column during winter and stratified in distinct metalimnic layers during summer, reaching maximum cell densities of ::; 15,000 (winter) and ::;77,000 cells ml-' (summer). The results demonstrate that r. rubescens abundance is strongly influenced by water transparency, i.e. illumination in the mNalimnion. Moreover, the r. rubescens abundance appears to result from regular phosphate depletion in the epilimnion. possibly additionally benefiting from high nitrogen loads. Microcystin (MC) was detectable in 27 and 38 of 54 seston samples via HPLC and Adda-EUSA measurements, respectively. The main microcystin congeners in the seston samples were ]Asp I]-MC-RR and [Asp),Dhb 7 ]-MC-RR. Microcystin concentrations correlated significantly with the respective phycoerythrin (PE)-concentrations. The variation in the MC/PE-ratios was low suggesting that the JJO Table 1 Size and nutritional status in (pre-) alpine lakes with documented P. rubescens abundance during the last decade Country/lake Size (km 2) Trophic status Abundallce Referellces

Environmental Toxicology, 2005

Cyanotoxins, particularly microcystins (MCs), have been shown to be a hazard to human health. MCs... more Cyanotoxins, particularly microcystins (MCs), have been shown to be a hazard to human health. MCs accumulate in aquatic organisms probably as a result of irreversible binding to liver protein phosphatases. The aim of this study was to describe the recovery of MC from fish liver using various detection methods, with MC-LR as the representative congener. These findings are discussed in conjunction with the current procedures and limit values used for human risk assessment. Following incubation of liver homogenates with various MC-LR concentrations, the homogenates were extracted by a water/ methanol/butanol mixture via different treatments and subsequently analyzed via the colorimetric protein phosphatase inhibition assay (cPPA), HPLC, and anti-Adda ELISA. Detection via cPPA appeared to yield the highest recovery of MC-LR, although the presence of unspecific background may have resulted in overestimation of the true recovery. The recoveries determined via HPLC and anti-Adda ELISA were comparable to each other. The limits of detection were 0.01-2.4 g MC-LR/g liver tissue, depending on the method used. Maximum MC-LR recovery from samples incubated with 10 and 100 g MC-LR/g ranged between 44% and 101%. Recovery from samples incubated with 1 g MC-LR/g liver tissue was below 3%. Lower recovery is assumed to result from irreversible, covalent MC protein binding, as confirmed by Western blotting of liver homogenates with anti-Adda immunoprobing. The results demonstrate that further investigation of and improvement in routinely applied MC methods for fish tissue and/or food analyses are needed for a reliable risk assessment.

Environmental Health Perspectives, 2002

Water treatment plants faced with toxic cyanobacteria have to be able to remove cyanotoxins from ... more Water treatment plants faced with toxic cyanobacteria have to be able to remove cyanotoxins from raw water. In this study we investigated the efficacy of ozonation coupled with various filtration steps under different cyanobacterial bloom conditions. Cyanobacteria were ozonated in a laboratory-scale batch reactor modeled on a system used by a modern waterworks, with subsequent activated carbon and sand filtration steps. The presence of cyanobacterial toxins (microcystins) was determined using the protein phosphatase inhibition assay. We found that ozone concentrations of at least 1.5 mg/L were required to provide enough oxidation potential to destroy the toxin present in 5 × 10 5 Microcystis aeruginosa cells/mL [total organic carbon (TOC), 1.56 mg/L]. High raw water TOC was shown to reduce the efficiency of free toxin oxidation and destruction. In addition, ozonation of raw waters containing high cyanobacteria cell densities will result in cell lysis and liberation of intracellular toxins. Thus, we emphasize that only regular and simultaneous monitoring of TOC/dissolved organic carbon and cyanobacterial cell densities, in conjunction with online residual O 3 concentration determination and efficient filtration steps, can ensure the provision of safe drinking water from surface waters contaminated with toxic cyanobacterial blooms.

Aquatic Toxicology, 2007

Planktothrix rubescens belongs to the most ubiquitous cyanobacterial species in mesotrophic and o... more Planktothrix rubescens belongs to the most ubiquitous cyanobacterial species in mesotrophic and oligotrophic lakes in the pre-alpine regions. In most of these lakes, coregonids are among the dominant species of the ichthyofauna with great importance for the professional fishery. A possible link between the occurrence of toxic Planktothrix blooms and the recurrent slumps in coregonid yields has been suggested. Indeed, acute toxic effects of microcystins and other cyanobacterial toxins have been shown for various fish species. However, chronic exposure scenarios appear to be more common and thus more environmentally realistic than acute intoxications. The aim of this study was therefore to investigate the physiological stress response and organ pathology in coregonids sub-chronically exposed to ambient water containing low, medium and high P. rubescens densities, known to be typical of pre-alpine lakes. Coregonid hatchlings were exposed in four tanks containing 0 (sham-control) and approximately 1500 (low), 15,000 (medium) and 55,000 (high) P. rubescens cells/ml for up to 28 days. Temperature, oxygen concentration, pH-value, P. rubescens cell density and microcystin concentration were recorded and the fish were observed for behavioural changes and examined for parasite infestations. Gill ventilation rates, general condition factors and mortalities were determined and liver, kidney, gut and gill were assessed histopathologically and immunhistologically. Depending on the cell density, exposed fish showed behavioural changes, including increased ventilation rates possibly representing a physiological stress response. Susceptibility to ectoparasitic infestation and increased mortality in exposed fish suggested P. rubescens associated effects on fish fitness. Histopathological alterations in liver, gastrointestinal tract and kidney, which were also immunopositive for microcystin suggested causality of tissue damage and the presence of microcystins. In contrast, observed gill pathology appeared to result primarily from mechanical abrasion and irritation due to ectoparasitic infestation. The current exposure experiment confirmed the hypothesis that subchronic and chronic exposure to low cyanobacterial cell densities and hence microcystins can exacerbate physiological stress and sustained pathological alterations in exposed coregonids. The study therefore supports the theory that P. rubescens blooms may be causal to the observed weight reduction and hence fitness of coregonids in pre-alpine lakes such as Lake Ammersee (Germany).

Toxicology and Applied Pharmacology, 2005

Toxin-producing cyanobacteria (blue-green algae) are abundant in surface waters used as drinking ... more Toxin-producing cyanobacteria (blue-green algae) are abundant in surface waters used as drinking water resources. The toxicity of one group of these toxins, the microcystins, and their presence in surface waters used for drinking water production has prompted the World Health Organization (WHO) to publish a provisional guideline value of 1.0 Ag microcystin (MC)-LR/l drinking water. To verify the efficiency of two different water treatment systems with respect to reduction of cyanobacterial toxins, the concentrations of MC in water samples from surface waters and their associated water treatment plants in Switzerland and Germany were investigated. Toxin concentrations in samples from drinking water treatment plants ranged from below 1.0 Ag MC-LR equiv./l to more than 8.0 Ag/l in raw water and were distinctly below 1.0 Ag/l after treatment. In addition, data to the worldwide occurrence of cyanobacteria in raw and final water of water works and the corresponding guidelines for cyanobacterial toxins in drinking water worldwide are summarized.

Environmental Science: Advances, 2022

The presented research illustrates the importance of assessing pesticide mixtures in the environm... more The presented research illustrates the importance of assessing pesticide mixtures in the environment by showing that the aerobic degradation of a herbicide in four different soils was significantly retarded in the presence of fungicides.