Marius Majewsky

Antibacterial Activity of Sulfamethoxazole Transformation Products (TPs): General Relevance for Sulfonamide TPs Modified at the para Position

Sulfonamide antibiotics undergo transformation in the aquatic environment through biodegradation, photolysis, or hydrolysis. In this study, the residual antibacterial activity of 11 transformation products (TPs) of sulfamethoxazole (SMX) was investigated with regard to their in vitro growth and luminescence inhibition on Vibrio fischeri (30 min and 24 h exposure). Two transformation products, 4-hydroxy-SMX and N(4)-hydroxy-acetyl-SMX, were synthesized in-house and confirmed by nuclear magnetic resonance and high-resolution mass spectrometry. Results of individual compound experiments showed that TPs modified at the para amino group still exhibit clear antibacterial effects, whereas TPs resulting from breakdown of the SMX structure lost this mechanism of action. 4-NO2- and 4-OH-SMX were found to inhibit growth to a clearly greater extent than the parent compound, SMX. In contrast, the N(4)-acetyl- and N(4)-hydroxy-acetyl-derivatives retain less than 10 and 5% of the effect of SMX on growth and luminescence inhibition, respectively. The effect of a mixture of para-modified TPs was observed to be additive. Considering the homologous series of sulfa drugs widely prescribed and their common mechanism of action, the potential environmental impact must consider the total amount of sulfonamide antibiotics and their derivative TPs, which might end up in a water body. Extrapolating the results obtained here for the para TPs of SMX to other sulfa drugs and determining the persistence and occurrence of these compounds in the aquatic environment is required for improved risk assessment.

Active heterotrophic biomass and sludge retention time (SRT) as determining factors for biodegradation kinetics of pharmaceuticals in activated sludge.

The present study investigates the biodegradation of pharmaceutically active compounds (PhACs) by active biomass in activated sludge. Active heterotrophs (X(bh)) which are known to govern COD removal are suggested as a determining factor for biological PhAC removal as well. Biodegradation kinetics of five polar PhACs were determined in activated sludge of two wastewater treatment plants which differed in size, layout and sludge retention time (SRT). Results showed that active fractions of the total suspended solids (TSS) differed significantly between the two sludges, indicating that TSS does not reveal information about heterotrophic activity. Furthermore, PhAC removal was significantly faster in the presence of high numbers of heterotrophs and a low SRT. Pseudo first-order kinetics were modified to include X(bh) and used to describe decreasing PhAC elimination with increasing SRT.

Xenobiotic removal efficiencies in wastewater treatment plants: Residence time distributions as a guiding principle for sampling strategies

The effect of mixing regimes and residence time distribution (RTD) on solute transport in wastewater treatment plants (WWTPs) is well understood in environmental engineering. Nevertheless, it is frequently neglected in sampling design and data analysis for the investigation of polar xenobiotic removal efficiencies in WWTPs. Most studies on the latter use 24-h composite samples in influent and effluent. The effluent sampling period is often shifted by the mean hydraulic retention time assuming that this allows a total coverage of the influent load. However, this assumption disregards mixing regime characteristics as well as flow and concentration variability in evaluating xenobiotic removal performances and may consequently lead to biased estimates or even negative elimination efficiencies. The present study aims at developing a modeling approach to estimate xenobiotic removal efficiencies from monitoring data taking the hydraulic RTD in WWTPs into consideration. For this purpose, completely mixed tanks-in-series were applied to address hydraulic mixing regimes in a Luxembourg WWTP. Hydraulic calibration for this WWTP was performed using wastewater conductivity as a tracer. The RTD mixing approach was coupled with first-order biodegradation kinetics for xenobiotics covering three classes of biodegradability during aerobic treatment. Model simulations showed that a daily influent load is distributed over more than one day in the effluent. A 24-h sampling period with an optimal time offset between influent and effluent covers less than the half of the influent load in a dry weather scenario. According to RTD calculations, an optimized sampling strategy covering four consecutive measuring days in the influent would be necessary to estimate the full-scale elimination efficiencies with sufficient accuracy. Daily variations of influent flow and concentrations can substantially affect the reliability of these sampling results. Commonly reported negative removal efficiencies for xenobiotics might therefore be a consequence of biased sampling schemes. In this regard, the present study aims at contributing to bridge the gap between environmental chemistry and engineering practices.

Cometabolic degradation of organic wastewater micropollutants by activated sludge and sludge-inherent microorganisms.

Municipal wastewaters contain a multitude of organic trace pollutants. Often, their biodegradability by activated sludge microorganisms is decisive for their elimination during wastewater treatment. Since the amounts of micropollutants seem too low to serve as growth substrate, cometabolism is supposed to be the dominating biodegradation process. Nevertheless, as many biodegradation studies were performed without the intention to discriminate between metabolic and cometabolic processes, the specific contribution of the latter to substance transformations is often not clarified. This minireview summarizes current knowledge about the cometabolic degradation of organic trace pollutants by activated sludge and sludge-inherent microorganisms. Due to their relevance for communal wastewater contamination, the focus is laid on pharmaceuticals, personal care products, antibiotics, estrogens, and nonylphenols. Wherever possible, reference is made to the molecular process level, i.e., cometabolic pathways, involved enzymes, and formed transformation products. Particular cometabolic capabilities of different activated sludge consortia and various microbial species are highlighted. Process conditions favoring cometabolic activities are emphasized. Finally, knowledge gaps are identified, and research perspectives are outlined.

Determination of microplastic polyethylene (PE) and polypropylene (PP) in environmental samples using thermal analysis (TGA-DSC)

Microplastics are increasingly detected in the environment and the consequences on water resources and ecosystems are not clear to date. The present study provides a cost-effective and straightforward method to determine the mass concentrations of polymer types using thermal analysis. Characteristic endothermic phase transition temperatures were determined for seven plastic polymer types using TGA-DSC. Based on that, extracts from wastewater samples were analyzed. Results showed that among the studied polymers, only PE and PP could be clearly identified, while the phase transition signals of the other polymers largely overlap each other. Subsequently, calibration curves were run for PE and PP for qualitative measurements. 240 and 1540mg/m(3) of solid material (12µm to 1mm) was extracted from two wastewater effluent samples of a municipal WWTP of which 34% (81mg/m(3)) and 17% (257mg/m(3)) could be assigned to PE, while PP was not detected in any of the samples. The presented application of TGA-DSC provides a complementary or alternative method to FT-IR analyses for the determination of PE and PP in environmental samples.

Impact of approach used to determine removal levels of drugs of abuse during wastewater treatment.

In this study the levels of 19 drugs of abuse were estimated throughout a wastewater treatment plant using polar organic chemical integrative samplers (POCIS), 24h composite samples and grab samples. Overall removal efficiencies and removals in between each treatment unit were calculated using load data for each sampling technique as well as removals that take into account the hydraulic residence time distribution of the treatment plant (time-shifted mass balancing approach). Amphetamine-type stimulants, cocaine and its major metabolite, benzoylecgonine and opioid levels determined with 24h composite samples were generally comparable to those obtained with POCIS and grab samples. Negative mass balances resulting from the estimation of overall removal efficiencies by POCIS, day-to-day mass balancing of 24h composite and grab sample data did not occur when the hydraulic retention time (HRT) distributions of the plant were taken into account for calculation. Among the compounds investigated, cocaine exhibited the highest overall removal (90%) while codeine had the lowest with 13%, respectively. Sampling between the treatment units revealed that highest removal occurs during biological treatment as compared to primary or secondary clarification. Methylenedioxyamphetamine (MDA), fentanyl, dihydrocodeine and heroin were not detected in wastewater at any of the sampling locations at the treatment plant regardless of the sampling technique. The study demonstrates the benefits of applying the time-shifted mass balancing approach to the calculation of removals of drugs of abuse during wastewater treatment.

Systematic suspect screening and identification of sulfonamide antibiotic transformation products in the aquatic environment

The formation of environmental sulfonamide transformation products (TPs) has only been investigated for very selected compounds, and their transformation pathways are incompletely elucidated. Given their homologous series, it is likely that similar transformation reactions occur for all sulfonamides. It has recently been demonstrated for sulfamethoxazole (SMX) that its derivative TPs retain antibiotic activity. Unfortunately, TP reference standards are often not available and a number of TPs are still unknown. Therefore, in the present study, a generic scheme was developed to predict 29 potential TPs of sulfonamide antibiotics via identification of the major transformation and breakdown reactions. Mass shifts were calculated for each transformation allowing for a suspect screening using LC/QTOF. Based on the structural elucidation of the parent sulfonamide product ion spectra, five characteristic product ions could be predicted for each of 15 derivative TPs. The predictions were confirmed with reference standards of SMX TPs as well as with data of TPs of further sulfonamides reported in literature. In a final step, samples of activated sludge biotransformation experiments were screened for suspect TPs of two sulfonamides. In total, 13 ecotoxicologically relevant TPs could be tentatively identified by use of the product ion predictions and LC/QTOF.

Phototransformation of sulfamethoxazole under simulated sunlight: Transformation products and their antibacterial activity toward Vibrio fischeri

Sulfamethoxazole (SMX) is a bacteriostatic antibiotic ubiquitously found in the aquatic environment. Since conventional biological wastewater treatment is not efficient to remove SMX, photolysis in natural waters can represent an important transformation pathway. It was recently shown that SMX transformation products can retain antibiotic activity. Therefore, it is crucial to better understand photochemical processes occurring in natural water just as the formation of active transformation products (TPs). During long-term SMX photolysis experiments (one week), nine TPs were identified by reference standards. Moreover, five further TPs of photodecomposition of SMX were found. For the first time, a TP with m/z 271 [M+H](+) was observed during photolysis and tentatively confirmed as 4,x-dihydroxylated SMX. The DOC mass balance clearly showed that only around 5 to 10% were mineralized during the experiment emphasizing the need to elucidate the fate of TPs. Bacterial bioassays confirmed that the mixture retains its antibiotic toxicity toward luminescence (24h) and that there is no change over the treatment time on EC50. In contrast, growth inhibition activity was found to slightly decrease over the irradiation time. However, this decrease was not proportional to the transformation of the parent compound SMX.

How benchmarking in science can lead to a reversal of priorities.

M funding institutions, research organizations, and universities nowadays base their decision to fund a project or to fill a research position on personal metrics, rather than on a thorough and critical review of the content of the articles themselves. At first glance, this approach of “stimulation by competition” appears highly effective insofar as it has undoubtedly contributed to fuel the increase in the number of scientific publications observed in the last decades. Our opinion, however, is that the increase in the amount of published material does not necessarily mean an advance in knowledge and in mankind’s wellbeing, and that scientific progress is made possible in spite of the competitive model, rather than thanks to it. We recognize two negative consequences of a model based on competition: on the one hand, it distracts the members of the scientific community from the real purpose of the scientific method, which is to solve relevant problems, and just as importantly, it weakens the ability to think creatively. Both phenomena find their origin in a form of benchmarking specific to science we shall call “publication pressure”, and which proposes to stimulate scientists by placing them within a dynamic hierarchy based on competition. Scientific work is seen from an industrial perspective in terms of output, and summarized by the number of articles produced, a number meaning either success (i.e., many publications) or failure (i.e., few publications). The relevance and usefulness of a given article − commonly termed “impact” − is calculated by adding up the number of times it is cited in other articles. These indicators can then be used in a worldwide classification system for scientific excellence. Implicitly, the indicator method assumes that usefulness can be measured in terms of popularity. We think that this is an erroneous assumption because this very pressure may distort a scientist’s view of what is useful. Since project funding so crucially depends upon previous achievements, which are in turn mostly measured in terms of publication record, some scientists come to view publications as the “raison d’et̂re” of any scientific study. We argue this is false and misleading, and that the aim of all research is problem solving. Whether the given problem has been solved or not by a certain hypothesis, the experience gained should indeed be made accessible to all and shared in a spirit of mutual help. But that does not mean that publishing in itself is the final aim of the scientist’s efforts. Publishing is an essential part of the method of scientific inquiry, but a part only. In a competitive model, however, the personal publication record becomes a precious commodity which, through clever investments, needs to be tended and grown. Co-authorship and citations can be bargained for data or reciprocal citation, and investment decisions can range from investigating trendy subjects to joining particular research groups known or supposed to be efficient paper “producers”. In this way, the number of publications per year, number of citations, honours and prizes received, and so on become over time more important than the problems to be solved, while a scientific article is turned into an abstract object, a mere currency whose value lies solely in its academic weight, and not in its practical contribution to mankind’s wellbeing. Thus, one should not take for granted that an increased production of scientific articles means an increase in useful knowledge, as a large part of that published material may turn out to be useless verbiage and endless variations of the same theme. Verbiage and repetition find another origin in the stifling constraint benchmarking imposes on the process of creative thinking. Since indicators are recalculated at regular intervals, scientific articles must be published at a predetermined pace: one publication a year, for instance. As a consequence, instead of writing according to one’s capacity, one’s taste, and at one’s leisure, authors are forced to follow restrictive guidelines

Estimating the trend of micropollutants in lakes as decision-making support in IWRM: a case study in Lake Paranoá, Brazil

Reservoir water becomes increasingly important as a drinking water resource in densely populated areas that have to respond to the challenge of water scarcity and quality. The Lake Paranoá in Central Brazil is under discussion to be used as a reservoir for drinking water production. There is concern regarding the water quality since the two largest wastewater treatment plants discharge into the lake. This issue raised the question about the need and efficiency of additional treatment to remove micropollutants. In this context, the present study aims to derive decision-making support by estimating the future concentration trends of five selected micropollutant markers in Lake Paranoá based on a minimum measured data set of three years. Results indicated slowly increasing trends and no steady-state situation until 2060 for persistent compounds. A quasi steady state is reached for degradable micropollutants. Furthermore, scenario analyses showed that a reduction of micropollutant emissions by advanced wastewater treatment would only be observable and detectable in the lake after around one decade due to the inertia of the lake. This agrees well with the observed total phosphorus reduction after the installation of phosphorus removal treatment.