Background, aim and scope For reliable environmental risk assessment of pollutants, knowledge on the effects at different levels of biological organisation is needed. During the early days of biomarker research in environmental studies approximately two decades ago, biochemical biomarkers were considered as the most promising tool for such purposes. Among these, three enzymes have often been studied: catalase (CAT), glutathione S-transferase (GST) and cholinesterase (ChE). However, despite their intensive research, their measurements in invertebrates have not been commonly applied in environmental risk assessment (ERA) or for regulatory purposes. Main features In the present review, we summarise our past experiences in biochemical biomarker research in two crustacean species: water flea Daphnia magna and terrestrial isopod Porcellio scaber. This is to orientate their use and to provide recommendations for the use of novel biomarkers in environmental studies, such as proteomic or genomic responses. Results and discussion We assessed the intrinsic properties of biochemical biomarkers CAT, GST and ChE in the D. magna and the isopod P. scaber. It was found that they are not in agreement with the expectations that were previously given for their use in environmental studies. To advance their use in environmental risk assessment, we suggest that based on their properties, their role should be more specifically defined. ERA includes several distinct steps, among them hazard identification, effect assessment and finally risk characterisation, each of which requires a different type of toxicity data. We recommend that the use of biochemical markers is most appropriate for hazard identification because this is a procedure whose purpose is to characterise the potential hazard of the substance in question and is more flexible in terms of using different tools. Furthermore, our results imply that biochemical markers are not always more sensitive than whole-organism responses, as was anticipated. Their sensitivity depends on the mode of action, duration of exposure and test species. Therefore, we suggest that combining both a battery of biomarkers from different levels of biological organisation and an array of biomarkers within a single level could identify hazard adequately. Conclusions The lesson learnt from biochemical biomarkers in environmental studies utilizing crustacean model species is that, for successful application of each group of biomarkers, their intrinsic properties are needed to be known before an (eco)toxicity study is designed. We suggest that a substantial body of experience obtained with biochemical biomarkers should be exploited to new emerging biomarkers in environmental studies in order to facilitate their application. Recommendations and perspectives The future of biomarkers lies in a combination of traditional biochemical and new-generation biomarkers. The latter are not only a potential replacement for existing biomarkers but will also provide new knowledge which might encourage renewed research and development of traditional biomarkers. For research purposes, complete ecotoxicity information should include contributions from molecular fingerprint of an organism, as well as whole organism, population and ecosystem responses. Still, the type of biomarkers used for routine purposes will depend on their reproducibility, their ease of use, robustness, affordability of the methodology and the type of chemicals, organisms and ecosystem of interest.

Introduction Isotope ratios of lead (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) in Japanese women's hair of the twentieth century were measured to evaluate lead contamination of human proximate environment of those days. Materials and Methods The historic hair samples (n = 40) were collected in 1980s by staffs of Department of Human Ecology, University of Tokyo, from Japanese women who cut their hair in 1910s to 1968 by themselves for hair piece or needle pad and who had stored it by the time of collection. Additional five contemporary hair samples (one from male and four from females) were also included. The hair samples were digested with HNO₃, diluted with water to Pb concentration of 10 µg/kg, and isotope ratios were measured by inductively coupled plasma mass spectrometry. Results and Discussion Isotope ratios as well as Pb concentration in the hair samples of the twentieth century varied to a considerable extent depending on the period of hair cut. The oldest hair samples (1910-1920s) had the highest concentration and the most distinct isotope ratios from those of Japanese domestic Pb indicating serious contamination of proximate environment of people of those days with Pb originated from mines in other regions of the world, probably through the usage of Pb-containing face powder. The concentration and isotope ratios of Pb decreased thereafter indicating less serious contamination of proximate environment of Japanese which, in turn, should have affected by environmental contamination of mid-twentieth century due to industrial activities and leaded gasoline. Contemporary Pb level was quite low (<1 mg/kg); however, isotope ratios were close to those in 1960s when hair concentration was assumed to be strongly affected by leaded gasoline.

Purpose China's freshwater subtropical shallow lakes are increasingly eutrophic and susceptible to production of heavy growths or water blooms of cyanobacteria. One example was the heavy water bloom that occurred for the first time in Lake Xuanwu, in 2005, an urban lake located in Nanjing city. The aim of the present study was to determine dynamics of water bloom dominating Microcystis in this lake. Meanwhile, the relationship between environmental factors and Microcystis populations was also analyzed. Materials and methods Molecular detection, using quantitative polymerase chain reaction, was used in this lake to study the dynamics of the cyanobacterial community, its Microcystis populations, and the microcystin-producing Microcystis genotypes from August 2005 to November 2006. Results It was shown that Microcystis wesenbergii and Microcystis aeruginosa were the main components of the cyanobacterial blooms in Lake Xuanwu, and they coexisted with species of the filamentous cyanobacterial genera Anabaena, Planktothrix, and Anabaenopsis. Microcystis cells were detected during the entire survey period and in all sample sites. The cell abundance of Microcystis ranged from 3.6 × 10² cells ml⁻¹ to a peak of 3.8 × 10⁶ cells ml⁻¹. The ratio of mcyB-containing Microcystis subpopulations to the total Microcystis varied, ranging from 0.1% to 12.8%. The abundance of Microcystis containing the mcyB microcystin gene was shown to be significantly correlated with concentrations of total phosphorus and phosphate. Conclusions Water temperature was the primary factor affecting Microcystis abundance in the lake, and phosphorus loading was shown to be a main factor in governing the growth of both microcystin-producing genotype and total Microcystis population. Higher Microcystis cell counts at the bottom of the water column before and after appearance of water blooms in Lake Xuanwu suggested that Microcystis numbers in the water column, especially at the bottom of the water column, play an important role in forming the next water bloom.

Purpose To protect the environmental quality of soil, groundwater, and surface water near the landfill site, it is necessary to make an accurate assessment of the heavy metal mobility. This study aims to present the bio-immobilization behavior of heavy metals in landfill and provide some reference suggestion for the manipulation of heavy metal pollution control after closure. Materials and methods Two simulated bioreactor landfill system loaded with real municipal solid waste (MSW), namely, conventional bioreactor landfill (CL) and leachate recirculated bioreactor landfill (RL), were operated. Cu and Zn, the two conventional heavy metals with the highest contents in MSW, were chosen to track the heavy metal bio-immobilization behavior in landfill. Results The MSW in landfill is a great threat to environment because much of the heavy metal is “hidden” in different components. The weight ratio of Cu and Zn in landfill amounts to 0.00427% and 0.00437%, respectively. The accumulated effluent masses of Cu and Zn in CL increased all along, while they still kept at a stable level after day 105 in RL. Conclusions The microbes like sulfate-reducing bacteria mediate the behavior of Cu and Zn in bioreactor landfill system. Cu and Zn can be bio-immobilized in bioreactor landfill system with leachate recirculation like RL.

Background, aim, and scope Chlorinated volatile organic compounds (CVOCs), widely used in industry as solvents and chemical intermediates in the production of synthetic resins, plastics, and pharmaceuticals, are highly toxic to the environment and public health. Various studies reported that Fenton's oxidation could degrade a variety of chlorinated VOCs in aqueous solutions. In acidic conditions, ferrous ion catalyzes the decomposition of H₂O₂ to form a powerful •OH radical. In this study, wastewater from wash of ion-exchange resin containing typical CVOC, 1,2-dichloroethane, was treated using Fenton's oxidation. To reduce environmental load and processing costs of wastewater, Fenton process as a simple and efficient treatment method was applied to degrade 1,2-dichloroethane of wash water. Materials and methods The water samples were collected from three different washing stages of ion-exchange resin. The degradation of 1,2-dichloroethane and total organic carbon (TOC) of wash water of ion-exchange resin by Fenton process was studied with response surface method (RSM). Design of the experiments was conducted by central composite face, and factors included in three models were Fe²⁺ and H₂O₂ doses and treatment time. Relevant quadratic and interaction terms of factors were investigated. Results According to ANOVA, the model predicts well 1,2-dichloroethane reduction of all water samples and TOC reduction of samples 2 and 3. The Fe²⁺ and H₂O₂ doses used in the present study were most suitable when 1,2-dichloroethane concentration of the wash water is about 120 mg L⁻¹. In that case, Fenton's oxidation reduced 1,2-dichloroethane and TOC up to 100% and 87%, respectively, according to the RSM model. With 90-min reaction time and H₂O₂ dose of 1,200 mg L⁻¹, the required Fe²⁺ doses for 1,2-dichloroethane and TOC were 300 and 900 mg L⁻¹, respectively. The optimal H₂O₂/Fe²⁺ stoichiometric molar ratio was between 4-6. Then, concentration of Fe²⁺ was low enough and the amount of residual sludge can thus be reduced. It seems that most of TOC and part of 1,2-dichloroethane were removed by coagulation. Discussion Up to a certain extent, increase of Fe²⁺ and H₂O₂ doses improved the removal of 1,2-dichloroethane and TOC. High Fe²⁺ doses increased the formation of ferric-based sludge, and excessive H₂O₂ doses in sample 2 decreased the degradation of 1,2-dichloroethane. Excess amount of hydrogen peroxide may scavenge hydroxyl radicals, thus leading to loss of oxidative power. Also, the residual hydrogen peroxide of different samples increased with increasing H₂O₂ dose and H₂O₂/Fe²⁺ molar ratio and decreasing treatment time probably also due to scavenging reactions. Due to the saturated nature of 1,2-dichloroethane, the oxidation mechanism involves hydrogen abstraction before addition of hydroxyl radical, thus leading to lower rate constants than for direct hydroxyl radical attack, which for one increases the treatment time. Conclusions Complete removal of 1,2-dichloroethane was attained with initial concentration <120 mg L⁻¹. Also, TOC degraded effectively. Wash water with higher concentration of 1,2-dichloroethane requires longer treatment times and higher concentrations of Fe²⁺ and H₂O₂ for sufficient 1,2-dichloroethane removal. Recommendations and perspectives Due to the results achieved in this study, Fenton's oxidation could be recommended to be used for organic destruction of wash water of ion-exchange resin. Residual sludge, the main disadvantage in Fenton process, can be reduced by optimizing the ferrous dose or by using heterogeneous treatment where most of the reusable iron remains in the solid phase.

Background, aim, and scope The occurrence and fate of pharmaceuticals in the aquatic environment is recognized as one of the emerging issues in environmental chemistry and as a matter of public concern. Existing data tend to focus on the concentrations of pharmaceuticals in the aqueous phase, with limited studies on their concentrations in particulate phase such as sediments. Furthermore, current water quality monitoring does not differentiate between soluble and colloidal phases in water samples, hindering our understanding of the bioavailability and bioaccumulation of pharmaceuticals in aquatic organisms. In this study, an investigation was conducted into the concentrations and phase association (soluble, colloidal, suspended particulate matter or SPM) of selected pharmaceuticals (propranolol, sulfamethoxazole, meberverine, thioridazine, carbamazepine, tamoxifen, indomethacine, diclofenac, and meclofenamic acid) in river water, effluents from sewage treatment works (STW), and groundwater in the UK. Materials and methods The occurrence and phase association of selected pharmaceuticals propranolol, sulfamethoxazole, meberverine, thioridazine, carbamazepine, tamoxifen, indomethacine, diclofenac, and meclofenamic acid in contrasting aquatic environments (river, sewage effluent, and groundwater) were studied. Colloids were isolated by cross-flow ultrafiltration (CFUF). Water samples were extracted by solid-phase extraction (SPE), while SPM was extracted by microwave. All sample extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the multiple reaction monitoring. Results and discussion Five compounds propranolol, sulfamethoxazole, carbamazepine, indomethacine, and diclofenac were detected in all samples, with carbamazepine showing the highest concentrations in all phases. The highest concentrations of these compounds were detected in STW effluents, confirming STW as a key source of these compounds in the aquatic environments. The calculation of partition coefficients of pharmaceuticals between SPM and filtrate (observed partition coefficients, [graphic removed] , [graphic removed] ), between SPM and soluble phase (intrinsic partition coefficients, [graphic removed] , [graphic removed] ), and between colloids and soluble phase (K coc) showed that intrinsic partition coefficients [graphic removed] are between 25% and 96%, and between 18% and 82% higher than relevant observed partition coefficients values, and are much less variable. Secondly, K coc values are 3-4 orders of magnitude greater than [graphic removed] values, indicating that aquatic colloids are substantially more powerful sorbents for accumulating pharmaceuticals than sediments. Furthermore, mass balance calculations of pharmaceutical concentrations demonstrate that between 23% and 70% of propranolol, 17-62% of sulfamethoxazole, 7-58% of carbamazepine, 19-84% of indomethacine, and 9-74% of diclofenac are present in the colloidal phase. Conclusions The results provide direct evidence that sorption to colloids provides an important sink for the pharmaceuticals in the aquatic environment. Such strong pharmaceutical/colloid interactions may provide a long-term storage of pharmaceuticals, hence, increasing their persistence while reducing their bioavailability in the environment. Recommendations and perspectives Pharmaceutical compounds have been detected not only in the aqueous phase but also in suspended particles; it is important, therefore, to have a holistic approach in future environmental fate investigation of pharmaceuticals. For example, more research is needed to assess the storage and long-term record of pharmaceutical residues in aquatic sediments by which benthic organisms will be most affected. Aquatic colloids have been shown to account for the accumulation of major fractions of total pharmaceutical concentrations in the aquatic environment, demonstrating unequivocally the importance of aquatic colloids as a sink for such residues in the aquatic systems. As aquatic colloids are abundant, ubiquitous, and highly powerful sorbents, they are expected to influence the bioavailability and bioaccumulation of such chemicals by aquatic organisms. It is therefore critical for colloids to be incorporated into water quality models for prediction and risk assessment purposes.

Background, aim, and scope The chemical substance 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) is a non-ionic surfactant used as an industrial defoaming agent and in various other applications. Its commercial name is Surynol 104® and the related ethoxylates are also available as Surfynol® 420, 440, 465 and 485 which are characterized by different grades of ethoxylation of TMDD at both hydroxyl functional groups. TMDD and its ethoxylates offer several advantages in waterborne industrial applications in coatings, inks, adhesives as well as in paper industries. TMDD and its ethoxylates can be expected to reach the aquatic environment due its widespread use and its physico-chemical properties. TMDD has previously been detected in several rivers of Germany with concentrations up to 2.5 µg/L. In the United States, TMDD was also detected in drinking water. However, detailed studies about its presence and distribution in the aquatic environment have not been carried out so far. The aim of the present study was the analysis of the spatial and temporal concentration variations of TMDD in the river Rhine at the Rheingütestation Worms (443.3 km). Moreover, the transported load in the Rhine was investigated during two entire days and 7 weeks between November 2007 and January 2008. Materials and methods The sampling was carried out at three different sampling points across the river. Sampling point MWL1 is located in the left part of the river, MWL2 in the middle part, and MWL4 in the right part. One more sampling site (MWL3) was run by the monitoring station until the end of 2006, but was put out of service due to financial constrains. The water at the left side of the river Rhine (MWL1) is influenced by sewage from a big chemical plant in Ludwigshafen and by the sewage water from this city. The water at the right side of the river Rhine (MWL4) is largely composed of the water inflow from river Neckar, discharging into Rhine 14.9 km upstream from the sampling point and of communal and industrial wastewater from the city Mannheim. The water from the middle of the river (MWL2) is largely composed of water from the upper Rhine. Water samples were collected in 1-L bottles by an automatic sampler. The water samples were concentrated by use of solid-phase extraction (SPE) using Bond Elut PPL cartridges and quantified by use of gas chromatography-mass spectrometry (GC-MS). The quantification was carried out with the internal standard method. Based on these results, concentration variations were determined for the day profiles and week profiles. The total number of analyzed samples was 219. Results The results of this study provide information on the temporal concentration variability of TMDD in river Rhine in a cross section at one particular sampling point (443.3 km). TMDD was detected in all analyzed water samples at high concentrations. The mean concentrations during the 2 days were 314 ng/L in MWL1, 246 ng/L in MWL2, and 286 ng/L in MWL4. The variation of concentrations was low in the day profiles. In the week profiles, a trend of increasing TMDD concentrations was detected particularly in January 2008, when TMDD concentrations reached values up to 1,330 ng/L in MWL1. The mean TMDD concentrations during the week profiles were 540 ng/L in MWL1, 484 ng/L in MWL2, and 576 ng/L in MWL4. The loads of TMDD were also determined and revealed to be comparable in all three sections of the river. The chemical plant located at the left side of the Rhine is not contributing additional TMDD to the river. The load of TMDD has been determined to be 62.8 kg/d on average during the entire period. By extrapolation of data obtained from seven week profiles the annual load was calculated to 23 t/a. Discussion The permanent high TMDD concentrations during the investigation period indicate an almost constant discharge of TMDD into the river. This observation argues for effluents of municipal wastewater treatment plants as the most likely source of TMDD in the river. Another possible source might be the degradation of ethoxylates of TMDD (Surfynol® series 400), in the WWTPs under formation of TMDD followed by discharge into the river. TMDD has to be considered as a high-production-volume (HPV) chemical based on the high concentrations found in this study. In the United States, TMDD is already in the list of HPV chemicals from the Environmental Protection Agency (EPA). However, the amount of TMDD production in Europe is unknown so far and also the biodegradation rates of TMDD in WWTPs have not been investigated. Conclusions TMDD was found in high concentrations during the entire sampling period in the Rhine river at the three sampling points. During the sampling period, TMDD concentrations remained constant in each part of the river. These results show that TMDD is uniformly distributed in the water collected at three sampling points located across the river. ‘Waves' of exceptionally high concentrations of TMDD could not be detected during the sampling period. These results indicate that the effluents of WWTPs have to be considered as the most important sources of TMDD in river Rhine. Recommendations and perspectives Based also on the occurrence of TMDD in different surface waters of Germany with concentrations up to 2,500 ng/L and its presence in drinking water in the USA, more detailed investigations regarding its sources and distribution in the aquatic environment are required. Moreover, the knowledge with respect to its ecotoxicity and its biodegradation pathway is scarce and has to be gained in more detail. Further research is necessary to investigate the rate of elimination of TMDD in municipal and industrial wastewater treatment plants in order to clarify the degradation rate of TMDD and to determine to which extent effluents of WWTPs contribute to the input of TMDD into surface waters. Supplementary studies are needed to clarify whether the ethoxylates of TMDD (known as Surfynol 400® series) are hydrolyzed in the aquatic environment resulting in formation of TMDD similar to the well known cleavage of nonylphenol ethoxylates into nonylphenols. The stability of TMDD under anaerobic conditions in groundwater is also unknown and should be studied.

Background, aim, and scope High mountain soils constitute a long-term cumulative record of atmospherically deposited trace elements from both natural and anthropogenic sources. The main aims of this study were to determine the level of major and trace metals (Al, Ti, Mn, Fe, and Zr) of lithologic origin and airborne contaminating trace elements (Ni, Cu, Zn, As, Cd, and Pb) in soils in the Central Pyrenees as an indication of background contamination over SW Europe, to establish whether there is a spatial pattern of accumulation of trace elements in soils as a function of altitude, and to examine whether altitude-related physicochemical properties of soils affect the accumulation of major metals and trace elements. Methods Major metals and trace elements were measured in “top” (i.e., first 10 cm) and “bottom” (i.e., below 10 cm) soil samples along an altitudinal transect (1,520-2,880 m a.s.l.) in the Central Pyrenees. Total concentrations were determined by X-ray fluorescense spectrometry. Total major metal concentrations were analysed by conventional X-ray fluorescence spectrometry (XRF) with a Siemens SRS 303 instrument. Total trace element concentrations were determined with an energy-dispersive multielement miniprobe XRF analyser. Acid-extractable concentrations were measured by inductively coupled plasma after previous extraction with nitric acid and hydrogen peroxide in closed beakers. Acid-extractable major metal concentrations were measured by inductively coupled plasma (ICP)-Optic Emission Spectrometry with a Perkin Elmer 3200 RL Instrument. Acid-extractable trace element concentrations were determined by ICP-Mass Spectrometry with a Perkin Elmer ELAN 6000. Results Trace element concentration ranges were (in mg kg⁻¹, inventories in g m⁻² between parenthesis) <2-58 (0.5-6.6) for Ni, 6-30 (0.2-3.4) for Cu, 38-236 (1.6-32.4) for Zn, 6-209 (0.2-12.8) for As, 0.02-0.64 (<0.04) for Cd, and 28-94 (0.6-13.0) for Pb. These concentrations were, in general, comparable to those recorded in soils from other European mountainous areas and were in many cases above the threshold recommended for ecosystem protection by regional and European environmental authorities. The highest concentrations were found at lower altitudes, indicating an effect of local contamination up to ∼2,300 m a.s.l. Only above this altitude can trace elements in soils be considered representative of a background, long-range atmospheric contamination. Conclusions None of the storage capacity properties of soils examined were determinant of the differences in elemental concentrations along the altitudinal transect. At the upper altitude range, Ni, Cu, and Pb showed a approximately two- to fivefold increase over the average concentration of the local dominant lithology, reflecting the regional and global background of atmospheric contamination in the area.

Background, aim, and scope Solid surfaces in contact with water have been found to be biofouled due to the attachment of various organisms. For better understanding of the biofilm formation, the important initial stage of bacterial attachment was investigated with Pseudomonas aeruginosa PAO1 as a model microorganism. Effects of the biosurfactant rhamnolipids and the shear conditions were particularly examined. Materials and methods A highly reproducible procedure was employed. The procedure involved monitoring and counting the number of attached cells on glass walls of the flow chambers, through which a PAO1 suspension was circulated and, subsequently, a saline solution was passed for washing. The experiments were made under different circulation rates (exerting different shear on the bacteria) and rhamnolipid concentrations. Results and discussions Reproducibility of the procedure was confirmed. The velocity profiles near the flow chamber wall were determined. Rhamnolipids, even at a very low concentration of 13 mg/l, were found to deter the bacterial attachment substantially. Prewashing the cells with a 100 mg/l rhamnolipid solution, however, did not affect the attachment significantly. As for the effect of shear, the PAO1 attachment showed an increasing-then-decreasing trend in the range investigated, i.e., 1.0 to 26 mN/m² shear stresses at the chamber wall. The diffusion-limited transport of cells to the chamber wall might have contributed to, but could not fully explain, the increasing attachment observed in the very low shear range (up to 3.5-5.0 mN/m²). Conclusions As compared to static systems, the flow chamber systems significantly improved the reproducibility of initial attachment results. Flow chamber systems were more suitable for experimental investigations of bacterial attachment to surfaces. Rhamnolipids were found to be potent antifoulants for PAO1 attachment on glass. The initial cell attachment increased with increasing shear at the very low shear range (up to 3.5-5.0 mN/m²), but the attachment could be minimized with further increase of the shear.

Background, aim and scope The applicability of the Whole Effluent Assessment concept for the proof of compliance with the “best available techniques” has been analysed with paper mill wastewater from Germany by considering its persistency (P), potentially bio-accumulative substances (B) and toxicity (T). Materials and methods Twenty wastewater samples from 13 paper mills using different types of cellulose fibres as raw materials have been tested in DIN or ISO standardised bioassays: the algae, daphnia, luminescent bacteria, duckweed (Lemna), fish-egg and umu tests with lowest ineffective dilution (LID) as test result. The potentially bio-accumulative substances (PBS) were determined by solid-phase microextraction and referred to the reference compound 2,3-dimethylnaphthalene. Usually, a primary chemical-physical treatment of the wastewater was followed by a single or multi-stage biological treatment. One indirectly discharged wastewater sample was pre-treated biologically in the Zahn-Wellens test before determining its ecotoxicity. Results No toxicity or genotoxicity at all was detected in the acute daphnia and fish egg as well as the umu assay. In the luminescent bacteria test, moderate toxicity (up to LIDlb = 6) was observed. Wastewater of four paper mills demonstrated elevated or high algae toxicity (up to LIDA = 128), which was in line with the results of the Lemna test, which mostly was less sensitive than the algae test (up to LIDDW = 8). One indirectly discharged wastewater sample was biodegraded in the Zahn-Wellens test by 96% and was not toxic after this treatment. Low levels of PBS have been detected (median 3.27 mmol L⁻¹). The colouration of the wastewater samples in the visible band did not correlate with algae toxicity and thus is not considered as its primary origin. Further analysis with a partial wastewater stream from thermomechanically produced groundwood pulp (TMP) revealed no algae or luminescent bacteria toxicity after pre-treatment of the sample in the Zahn-Wellens test (chemical oxygen demand elimination 85% in 7 days). Thus, the algae toxicity of the respective paper mill cannot be explained with the TMP partial stream; presumably other raw materials such as biocides might be the source of algae toxicity. Discussion Comparative data from wastewater surveillance of authorities confirmed the range of ecotoxicity observed in the study. Wastewater from paper mills generally has no or a moderate ecotoxicity (median LID 1 and 2) while the maximum LID values, especially for the algae and daphnia tests, are considerably elevated (LIDA up to 128, LIDD up to 48). Conclusions Wastewater from paper mills generally is low to moderately ecotoxic to aquatic organisms in acute toxicity tests. Some samples show effects in the chronic algae growth inhibition test which cannot be explained exclusively with colouration of the samples. The origin of elevated algae ecotoxicity could not be determined. In the algae test, often flat dose-response relationships and growth promotion at higher dilution factors have been observed, indicating that several effects are overlapping. Recommendations and perspectives At least one bioassay should be included in routine wastewater control of paper mills because the paper manufacturing industry is among the most water consuming. Although the algae test was the most sensitive test, it might not be the most appropriate test because of the complex relationship of colouration and inhibition and the smooth dose-effect relationship or even promotion of algae growth often observed. The Lemna test would be a suitable method which also detects inhibitors of photosynthesis and is not disturbed by wastewater colouration.