An ecotoxicological view on neurotoxicity assessment.

The numbers of potential neurotoxicants in the environment are raising and pose a great risk for humans and the environment. Currently neurotoxicity assessment is mostly performed to predict and prevent harm to human populations. Despite all the efforts invested in the last years in developing novel in vitro or in silico test systems, in vivo tests with rodents are still the only accepted test for neurotoxicity risk assessment in Europe. Despite an increasing number of reports of species showing altered behaviour, neurotoxicity assessment for species in the environment is not required and therefore mostly not performed. Considering the increasing numbers of environmental contaminants with potential neurotoxic potential, eco-neurotoxicity should be also considered in risk assessment. In order to do so novel test systems are needed that can cope with species differences within ecosystems. In the field, online-biomonitoring systems using behavioural information could be used to detect neurotoxic effects and effect-directed analyses could be applied to identify the neurotoxicants causing the effect. Additionally, toxic pressure calculations in combination with mixture modelling could use environmental chemical monitoring data to predict adverse effects and prioritize pollutants for laboratory testing. Cheminformatics based on computational toxicological data from in vitro and in vivo studies could help to identify potential neurotoxicants. An array of in vitro assays covering different modes of action could be applied to screen compounds for neurotoxicity. The selection of in vitro assays could be guided by AOPs relevant for eco-neurotoxicity. In order to be able to perform risk assessment for eco-neurotoxicity, methods need to focus on the most sensitive species in an ecosystem. A test battery using species from different trophic levels might be the best approach. To implement eco-neurotoxicity assessment into European risk assessment, cheminformatics and in vitro screening tests could be used as first approach to identify eco-neurotoxic pollutants. In a second step, a small species test battery could be applied to assess the risks of ecosystems.

Influence of the Ag concentration on the medium-range order in a CuZrAlAg bulk metallic glass.

Fluctuation electron microscopy of bulk metallic glasses of CuZrAl(Ag) demonstrates that medium-range order is sensitive to minor compositional changes. By analyzing nanodiffraction patterns medium-range order is detected with crystal-like motifs based on the B2 CuZr structure and its distorted structures resembling the martensitic ones. This result demonstrates some structural homology between the metallic glass and its high temperature crystalline phase. The amount of medium-range order seems slightly affected with increasing Ag concentration (0, 2, 5 at.%) but the structural motifs of the medium-range ordered clusters become more diverse at the highest Ag concentration. The decrease of dominant clusters is consistent with the destabilization of the B2 structure measured by calorimetry and accounts for the increased glass-forming ability.

Quantum speed limit for physical processes.

The evaluation of the minimal evolution time between two distinguishable states of a system is important for assessing the maximal speed of quantum computers and communication channels. Lower bounds for this minimal time have been proposed for unitary dynamics. Here we show that it is possible to extend this concept to nonunitary processes, using an attainable lower bound that is connected to the quantum Fisher information for time estimation. This result is used to delimit the minimal evolution time for typical noisy channels.

Quantum metrological limits via a variational approach.

The minimum achievable statistical uncertainty in the estimation of physical parameters is determined by the quantum Fisher information. Its computation for noisy systems is still a challenging problem. Using a variational approach, we present an equation for obtaining the quantum Fisher information, which has an explicit dependence on the mathematical description of the noise. This method is applied to obtain a useful analytical bound to the quantum precision in the estimation of phase-shifts under phase diffusion, which shows that the estimation uncertainty cannot be smaller than a noise-dependent constant.

Ozonation and biological activated carbon filtration of wastewater treatment plant effluents.

This study investigates the fate of trace organic chemicals (TrOCs) in three full-scale reclamation plants using ozonation followed by biological activated carbon (BAC) filtration to treat wastewater treatment plant effluents. Chemical analysis was used to quantify a wide range of TrOCs and combined with bioanalytical tools to assess non-specific toxicity (Microtox assay) and estrogenicity (E-SCREEN assay). Limited dissolved organic carbon (DOC) removal (<10%) was observed in the ozonation stages showing that oxidation leads to the formation of transformation products rather than mineralization. The quantified TrOCs were removed to a degree highly dependent on the compounds' structures and the specific ozone dose (mg(O3) mg(DOC)(-1)). Non-specific toxicity was reduced by 31-39%, demonstrating that the mixture of remaining parent compounds and their transformation products as well as newly formed oxidation by-products had an overall lower toxic potential than the mixture of parent compounds. Estrogenicity was reduced by more than 87% indicating that the transformation products of the estrogenic chemicals lost their specific toxicity potential. The subsequent BAC filtration removed between 20 and 50% of the DOC depending on the plant configuration, likely due to biodegradation of organic matter. The filtration was also able to reduce the concentrations of most of the remaining TrOCs by up to 99%, and reduce non-specific toxicity by 33-54%. Overall, the combination of ozonation and BAC filtration can achieve removals of 50% for DOC and more than 90% for a wide range of TrOCs as well as a reduction of 70% of non-specific toxicity and more than 95% of estrogenicity. This process combination is therefore suggested as an effective barrier to reduce the discharge of TrOCs into the environment or their presence in water recycling schemes.

Biofiltration of wastewater treatment plant effluent: effective removal of pharmaceuticals and personal care products and reduction of toxicity.

This study investigates biofiltration for the removal of dissolved organic carbon (DOC), pharmaceuticals and personal care products (PPCPs), and for the reduction of non-specific toxicity expressed as baseline toxicity equivalent concentration (baseline-TEQ). Two filtering media, sand and granular activated carbon, were tested. The influence of pre-ozonation and empty-bed contact time (EBCT, from 30 to 120 min) was determined. The experiments were performed at a pilot-scale with real WWTP effluent. A previous study showed that biological activity had developed on the filtering media and dissolved organic removal had reached a steady state before sampling commenced. The results show that biological activated carbon (BAC) has a good potential for the removal of DOC (35-60%), PPCPs (>90%) and baseline-TEQ (28-68%) even without pre-ozonation. On the contrary, the sand shows limited improvement of effluent quality. Varying the EBCT does not influence the performance of the BAC filters; however, dissolved oxygen concentration could be a limiting factor. The performances of the BAC filters were stable for over two years suggesting that the main mechanism of organic matter and PPCPs removal is biodegradation. It is concluded that BAC filtration without pre-ozonation could be implemented as a low cost advanced treatment option to improve WWTP effluent chemical quality.

Monitoring the biological activity of micropollutants during advanced wastewater treatment with ozonation and activated carbon filtration.

A bioanalytical test battery was used to monitor the removal efficiency of organic micropollutants during advanced wastewater treatment in the South Caboolture Water Reclamation Plant, Queensland, Australia. This plant treats effluent from a conventional sewage treatment plant for industrial water reuse. The aqueous samples were enriched using solid-phase extraction to separate some organic micropollutants of interest from metals, nutrients and matrix components. The bioassays were chosen to provide information on groups of chemicals with a common mode of toxic action. Therefore they can be considered as sum indicators to detect certain relevant groups of chemicals, not as the most ecologically or human health relevant endpoints. The baseline toxicity was quantified with the bioluminescence inhibition test using the marine bacterium Vibrio fischeri. The specific modes of toxic action that were targeted with five additional bioassays included aspects of estrogenicity, dioxin-like activity, genotoxicity, neurotoxicity, and phytotoxicity. While the accompanying publication discusses the treatment steps in more detail by drawing from the results of chemical analysis as well as the bioanalytical results, here we focus on the applicability and limitations of using bioassays for the purpose of determining the treatment efficacy of advanced water treatment and for water quality assessment in general. Results are reported in toxic equivalent concentrations (TEQ), that is, the concentration of a reference compound required to elicit the same response as the unknown and unidentified mixture of micropollutants actually present. TEQ proved to be useful and easily communicable despite some limitations and uncertainties in their derivation based on the mixture toxicity theory. The results obtained were reproducible, robust and sensitive. The TEQ in the influent ranged in the same order of magnitude as typically seen in effluents of conventional sewage treatment plants. In the initial steps of the treatment chain, no significant degradation of micropollutants was observed, and the high levels of dissolved organic carbon probably affected the outcome of the bioassays. The steps of coagulation/flocculation/dissolved air flotation/sand filtration and ozonation decreased the effect-based micropollutant burden significantly.

Removal of micropollutants and reduction of biological activity in a full scale reclamation plant using ozonation and activated carbon filtration.

Pharmaceutical compounds are found in secondary treated effluents up to microg L(-1) levels and therefore discharged into surface waters. Since the long term effects of these compounds on the environment and human health are, to date, largely unknown, implementation of advanced treatment of wastewaters is envisaged to reduce their discharge. This is of particular relevance where surface waters are used as drinking water sources and when considering indirect potable reuse. This study aimed at assessing the removal of organic micropollutants and the concurrent reduction of their biological activity in a full scale reclamation plant treating secondary effluent. The treatment consists of 6 stages: denitrification, pre-ozonation, coagulation/flocculation/dissolved air flotation and filtration (DAFF), main ozonation, activated carbon filtration and final ozonation for disinfection. For that purpose, representative 24-hour composite samples were collected after each stage. The occurrence of 85 compounds was monitored by LC/MS-MS. A battery of 6 bioassays was also used as a complementary tool to evaluate non-specific toxicity and 5 specific toxic modes of action. Results show that, among the 54 micropollutants quantified in the influent water, 50 were removed to below their limit of quantification representing more than 90% of concentration reduction. Biological activity was reduced, depending on the specific response that was assessed, from a minimum of 62% (AhR response) to more than 99% (estrogenicity). The key processes responsible for the plant's performances were the coagulation/flocculation/DAFF, main ozonation and activated carbon filtration. The effect of these 3 processes varied from one compound or bioassay to another but their combination was almost totally responsible for the overall observed reduction. Bioassays yielded complementary information, e.g. estrogenic compounds were not detected in the secondary effluent by chemical analysis, but the samples had an estrogenic effect. The main ozonation formed oxidation by-products of the organic micropollutants but decreased the level of non-specific toxicity and other specific toxic modes of action, demonstrating that the mixture of oxidation by-products was less potent than the mixture of the parent compounds for the considered effects.

Mode of action-based classification and prediction of activity of uncouplers for the screening of chemical inventories.

A new approach for classification of uncouplers of oxidative and photophosphorylation, also suitable for screening of large chemical inventories, is introduced. Earlier fragment-based approaches for this mode of toxic action are limited to phenols but weak acids of extremely diverse chemical classes can act as uncouplers. The proposed approach overcomes the limitation to phenolic uncouplers by combining structural fragments with the global information of physico-chemical descriptors. In a top-down approach to reduce the number of candidate chemicals, firstly substructure definitions for the detection of weak acids were applied. Subsequently, conservative physico-chemical thresholds for the two most important properties for the uncoupling activity were defined: an acid dissociation constant (pK(a)) between 3 and 9, and a sufficiently low energy barrier for the internal permeability of anions (17 kcal/mol). The later was derived from a novel approach to calculate the distribution of compounds across membranes. The combination of structural and physico-chemical criteria allowed a good separation of active from inactive chemicals with high sensitivity (95%) and slightly lower (more than 75%) specificity. Applying this approach to several thousand high and low production volume chemicals retrieved a surprisingly small number of 10 compounds with a predicted excess toxicity above 10. Nevertheless, uncoupling can be an important mode of action as highlighted with several examples ranging from pesticide metabolites to persistent organic compounds.

Reducing micropollutants with source control: substance flow analysis of 212 pharmaceuticals in faeces and urine.

Pharmaceuticals in the aquatic environment are raising concern. It is expected that many anthropogenic pharmaceuticals are largely excreted via urine; a popular argument for introducing urine source separation. However, to date, this assumption lacks verification. We close this gap with quantitative screening of official pharmaceutical data. We analysed the excretion pathways of 212 pharmaceuticals' active ingredients (AI), equalling 1,409 products. On average, 64% (+/-27%) of each AI was excreted via urine, and 35% (+/-26%) via faeces. In urine, 42% (+/-28%) of each AI was excreted as metabolites. However, these numbers need cautious interpretation. We found an extreme variability (1) between different therapeutic groups, (2) within some groups and (3) sometimes even between products of the same AI. We discuss various therapeutic groups and include Swiss sales' quantities. For instance, urine source separation could very effectively remove the highly sold and non-degradable x-ray contrast media: 94% (+/-4%) are excreted via urine. However, for different pharmaceuticals belonging to cytostatics, excretion via urine was 6-98%. Because of such large variability we advise caution to introduce the still imperfect urine separation technology solely because of pharmaceuticals. Nonetheless, together with other good arguments for this innovation, removal of pharmaceuticals is a welcome side effect.

Pilot experiments with electrodialysis and ozonation for the production of a fertiliser from urine.

Pilot tests were performed with a process combination of electrodialysis and ozonation for the removal of micropollutants and the concentration of nutrients in urine. In continuous and batch experiments, maximum concentration factors up to 3.5 and 4.1 were obtained, respectively. The desalination capacity did not decrease significantly during continuous operation periods of several weeks. Membrane cleaning after 195 days resulted in approximately 35% increase in desalination rate. The Yeast Estrogen Screen (YES), a bioassay that selectively detects oestrogenic compounds, confirmed that about 90% of the oestrogenic activity was removed by electrodialysis. HPLC analysis showed that ibuprofen was removed to a high extent, while other micropollutants were below the detection limit. In view of the fact that ibuprofen is among the most rapidly transported micropollutants in electrodialysis processes, this result indicates that electrodialysis provides an effective barrier for micropollutants. Standardised plant growth tests were performed in the field with the salt solution resulting from the treatment by electrodialysis and subsequent ozonation. The results show that the plant height is comparable to synthetic fertilisers, but the crop yield is slightly lower. The latter is probably caused by volatilisation losses during field application, which can be prevented by improved application technologies.

Elimination of beta-blockers in sewage treatment plants.

beta-Blockers are used to treat high blood pressure as well as patients recovering from heart attacks. In several studies, they were detected in surface water, thus indicating incomplete degradability of these substances in sewage treatment plants (STPs). In this study, we determined the sorption coefficients (K(D)) and degradation rates of the four beta-blockers sotalol, atenolol, metoprolol and propranolol in sludge from an STP operating with municipal wastewater. The sorption coefficients (K(D), standard deviations in brackets) were determined as 0.04(+/-0.035), 0.04(+/-0.033), 0.00(+/-0.023) and 0.32(+/-0.058) Lg(-1)(COD), and the pseudo-first-order degradation rate constants were estimated to be 0.29(+/-0.02), 0.69(+/-0.05), 0.58(+/-0.05) and 0.39(+/-0.07) Ld(-1)g(-1)(COD) for sotalol, atenolol, metoprolol and propranolol, respectively. These values translate into a typical elimination in STPs (sludge concentrations of 4g(COD)L(-1) and a hydraulic retention time of 6h) of 25%, 37%, 44% and 50% for sotalol, propranolol, metoprolol and atenolol, respectively. These results are also confirmed by measurements in two municipal STPs for atenolol, sotalol and propranolol. The estimated eliminations are slightly too high for metoprolol.

pH dependence of the partitioning of triphenyltin and tributyltin between phosphatidylcholine liposomes and water.

Triorganotin compounds are very toxic contaminants. The site of their basic mechanism of action of acute toxicity is the biomembrane. Liposome-water distribution ratios of triphenyltin and tributyltin were determined between pH 3 and pH 8 with the equilibrium dialysis method in the micromolar concentration range, which is the concentration range where acute toxicity is observed. In addition, biomembrane-water distribution ratios of tributyltin were determined with chromatophores of Rhodobacter sphaeroides that contain approximately 70% protein intercalated in the lipid bilayer. The liposome-water distribution of both compounds showed only weak pH dependence. For tributyltin, the apparent distribution ratio decreased from 4100 at low pH to 2000 at high pH, while this ratio decreased from 70 000 to 22 000 for TPT. The distribution ratio of the triorganotin cation exceeded that of the neutral hydroxo complex by a factor of 2. The distribution ratio of both the cation and the hydroxo complex of triphenyltin exceeded that of tributyltin by a factor of 10. It is postulated that the sorption of the cation is governed by complex formation with ligands in the phospholipids, presumably the phosphate group. The biomembrane-water distribution ratio of tributyltin was found to be lower than the liposome-water distribution ratio at high pH. The hydroxo complex appears to partition only to the lipid fraction of the biomembrane. Yet, at low pH the biomembrane-water distribution ratio exceeded the liposome-water distribution ratio, which is attributed to complex formation of the cationic species with ligands of the protein fraction.

Interaction of phenolic uncouplers in binary mixtures: concentration-additive and synergistic effects.

The uncoupling activities of 14 binary mixtures of substituted phenols and of 4 binary mixtures of phenols and anisols were investigated at different pH values. Experiments were performed with time-resolved spectroscopy on membrane vesicles (chromatophores) of the photosynthetic bacteria Rhodobacter sphaeroides. Phenols are known to destroy the electrochemical proton gradient in energy-transducing membranes by a protonophoric mechanism. Anisols do not have protonophoric activity but disturb membrane structure and functioning as a nonspecific baseline toxicant. It was postulated in the literature that, for certain substituted phenols, the formation of a dimer between the phenoxide and the neutral phenol may contribute significantly to the overall protonophoric activity. In 13 of 14 mixtures of substituted phenols but in none of the mixtures of phenols with anisols, such a dimer appears to be formed between two different mixture partners. An extended shuttle mechanism of uncoupling, which includes a term for the contribution of such a mixed dimer, provided a good description of all experimental data. Opposite speciation favors interaction and ortho substituents abate interaction, which adds evidence for the dimerformation via a hydrogen bond between the phenol-OH and the phenoxide. These findings are significant not only regarding the mechanism of protonophoric action but also for the risk assessment process of chemical mixtures in the environment. When assessing the effect of mixtures, concentration addition is regarded as a reference X concept to estimate effects of similarly acting compounds. The substituted phenols in this work act according to the same action mechanism of uncoupling. Nevertheless, the overall effect of four of the investigated mixtures, which exhibit stronger dimer formation as compared to the single compounds or for which the resulting dimer is intrinsically more active, exceeded the effect calculated according to concentration addition considerably. In future work, this synergistic effect observed in-vitro has to be validated in-vivo to deduce its implications for the risk assessment process.

Acute toxicity of (chloro-)catechols and (chloro-)catechol-copper combinations in Escherichia coli corresponds to their membrane toxicity in vitro.

(Chloro-)catechols are toxic for bacteria and higher organisms, but the mode of action is not yet clearly understood. We have compared the acute toxicity of different chlorinated catechols to Escherichia coli with membrane toxic effects, namely narcosis and uncoupling that we have determined in an in vitro assay. In vitro membrane toxicity was quantified by measuring the accelerated decay of the membrane potential of chromatophores isolated from Rhodobacter sphaeroides. Both acute and membrane toxicity increased with increasing degree of chlorination. Analysis of dose-response curves, pH dependence, and estimated membrane concentrations gave a consistent picture of the mechanisms of membrane toxicity: At pH 7, the higher-chlorinated catechols acted as uncouplers of oxidative and photophosphorylation, and the lower-chlorinated catechols and catechol acted as narcotics. In the case of 3,5-dichlorocatechol and 4-monochlorocatechol at pH 8.8, both mechanisms appeared to contribute to the overall toxicity. Copper exhibited a diverging effect on the toxicity of catechols and of (chloro-)catechols to E. coli. Whereas the presence of copper increased the toxicity of catechol and 4-monochlorocatechol, the toxicity of 3,5-dichlorocatechol, 3,4,5-trichlorocatechol, and tetrachlorocatechol decreased. Again, the results obtained with in vitro assays agreed with the acute toxicity observed in E. coli: The presence of copper accelerated decay of the membrane potential of catechol and 4-monochlorocatechol; however, the effect was reversed by copper in experiments with 3,5-dichlorocatechol, 3,4,5-trichlorocatechol, and tetrachlorocatechol. We have proposed a mechanistic model to explain the diverging effects of copper on the uncoupling activities of the different catechols.