Recent results show that cylindrospermopsin is more frequent and widespread in surface waters than previously assumed. Studies on the fate of CYN in sediments are lacking, but this is important if these resources are used for drinking-water production via sediment passage. Therefore, the aim of our study was to determine a) CYN retention in two sandy sediments as a function of flow rate, CYN concentration, the presence of DOM and the content of fines (1% and 4%, respectively) and b) the influence of sediment preconditioning and DOM composition of the water (aquatic DOM versus DOM released from lysed cells) on CYN degradation. Retention of CYN proved negligible under the investigated conditions. Degradation in virgin sediments showed the highest lag phases (20 days). Preconditioned sediments showed no lag phase. The presence of aquatic DOM yielded highest degradation rates (k1 ¼0.46 and 0.49 day 1) without a lag phase. Readily available organic carbon sources were preferentially metabolized and hence induced a lag phase. Thus, the presence and composition of DOM in the water proved important for both CYN degradation rates in preconditioned sediments and for the lag phase. Cylindrospermopsin degradation took place solely in the sediment and not in the water body.

Microcystins (MCYSTs) are a group of structurally similar toxic peptides produced by cyanobacteria (“blue-green algae”) which occur frequently in surface waters worldwide. Reliable elimination is necessary when using these waters as drinking watersources.Bankfiltrationandartificial groundwaterrecharge utilize adsorption and degradation processes in the subsurface, commonlythroughsandandgravel aquifers, for the elimination of a wide range of substances during drinking water (pre-) treatment. To obtain parameters for estimating whether MCYST breakthrough is likely in field settings, we tested MCYST elimination in laboratory experiments (batch experiments, column experiments) under a range of conditions. Adsorption coefficients (kd-values) obtained from batch studies ranged from 0.2 mL/g for filter sand to 11.6 mL/g for fine grained aquifer materials with 2% fine grains (<63 µm) and 0.8% organic matter. First order degradation rates in column studies reached 1.87 d-1 under aerobic conditions and showed high variations under anoxic conditions (<0.01-1.35 d-1). These results show that, next to sediment texture, redox conditions play an important role for MCYST elimination during sediment passage. Biodegradation was identified as the dominating process for MCYST elimination in sandy aquifer material.

Management models for aquatic systems can be used to determine which measures in the watershed or in the water body have been effective and/or which one should be used in future. The newly developed management models presented in the following for Lake Tegel and Schlachtensee are empirical and lake specific. The values for the unknown factors are estimated by an iterative process using optimisation routines and sensitivity analysis methods. The resulting models describe the water and phosphorus balance of each lake. The Lake Tegel water balance model calculates the unknown water inflow from the River Havel depending on the other main in- and outflows with very good validation results. The phosphorus models of both lakes quantify mixing of the upper and lower water body as well as sedimentation and release from the sediment as functions of measured variables. For Lake Tegel, management scenarios were run indicating effective management interventions. For Lake Schlachtensee, the phosphorus model captured the variations in the hypolimnion well but produced poorer results for the epilimnion because of unknown external phosphorus loads. For these the model indicated possible sources and magnitudes.

Tropical cyanobacteria in German waters: Causes and consequences - Toxic cyanobacteria of tropical origin have spread to water bodies in northern Germany. Here their population size is determined by the onset of germination: the earlier the time of germination, the larger the summer population. Climate-related early increase in water temperatures over the course of the years has promoted their spreading to temperate regions. Toxins known from these species in tropical regions were also found in German lakes. Surprisingly, these toxins are not produced by the invaders but by native species. Thus, the invasion have drawn our attention to an old problem. However, the invaders itself potentially also poses a health risk in German lakes since they produce other – so far unidentified – toxic substances.

The project “Organic Trace Substances Relevant for Drinking Water – Assessing their Elimination through Bank Filtration (TRACE)” aims at giving an up-to-date overview of the potential risk resulting from the occurrence of chelating agents, perfluorinated compounds (PFCs) and selected pesticides in surface waters and to show if there is a potential for the substances to persist during bank filtration and artificial recharge. During the first phase of the project which is subject of this paper, a literature study was conducted addressing their occurrence (in the Berlin region and elsewhere), amounts produced as well as data on their persistence in the subsurface. This was the basis for a decision on the substance applied in the field scale experiments at the UBAs experimental field during the following project phase. Using freely available databases (e.g. ULIDAT, DIMDI, Tiborder) 1148 references were screened for their relevance to these topics, and 450 of these were classified as relevant. Of these, so far the 223 most important references have been compiled in an ACCESS database which comprises data on the data origin as well as on specific values (e.g. measured concentrations, amounts produced, use, main metabolites, sources, pathways in the environment). The database links this information so that output forms (“fact sheets”) can be created that summarize all data for one specific substance. The regarded substances were subsequently classified according to the criteria: usage / production, occurrence in surface water (if possible also in groundwater and bank filtrate), degradation potential, biological degradability, production of relevant metabolites and toxicity. For the chelating agents three substance groups were examined closely: aminocarboxylates, hydrocarboxylates and phosphonates (all other substance groups were found to be irrelevant due to total biodegradability). The aminocarboxylates are produced in highest numbers and occur most frequently (especially EDTA, PDTA, NTA and DTPA). There are, however, already extensive investigations on this field so that few knowledge gaps were identified. Hydrocarboxylates are produced in lesser amounts and for some ready biological degradability has been shown. For these reasons further investigations were not seen as a priority. Phosphonates produce relevant metabolites (phosphates that enhance eutrophication) and are produced in high amounts (> 1000 t/a). This substance group was therefore recommended for further investigations. Currently a variety of research projects cover the field of perfluorinated compounds (PFCs) that occur in aquatic environments world wide and whose toxicity and persistence is not yet clearly determined. Most investigations aim at the main substances of this group: PFOA and PFOS. These are, however, currently being replaced by shorter chained PFCs on which investigations are lacking. This substance group is therefore also of interest for further investigations. For the pesticides glyphosate and isoproturone high production rates and frequent occurrence in surface and groundwater world wide were determined. Due to this fact and to the presence of relevant metabolites (e.g. AMPA) as well as to limited knowledge on their fate during underground passage these substances were classified as highly interesting for further investigations.

Cyanobacterial toxins are toxic substances produced by cyanobacteria or blue-green-algae. The can occur in surface waters wordwide and have to be removed sufficiently when using infested surface waters as drinking water source. Bank filtration has been used since 150 years for drinking water (pre-)treatment and utilizes natural elimination processes like sorption and degardation in the sub-surface. During several research projects the German Federal Environmental Agency (Umweltbundesamt, UBA) carried out field investigations and experiments in different scales in order to assess under which conditions secure elimination of microcystins (the most common group of cyanobacterial toxins) takes place. Filtration of cells on the sediment surface is the most prominent process for eliminating the primarily cell-bound toxins. Middle to coarsly grained sands eliminated more than 99.9 % of intracellular toxins within the first 10 centimeters. Elimination of extracellular microcystin during underground passage is mainly due to biodegradation. Reversible adsorption processes do not reduce the total load but lead to longer contact times for extended biodegradation. Laboratory experiments showed that high clay and silt content is crucial for maximum adsorption. However, redox conditions play an important role for degradation rates: under aerobic conditions half lives of less than one day occured frequently whereas anoxic conditions resulted in lag phases of one day and more as well as in half lives of up to 25 days. Field experiments could show that temperature is crucial for degradation velocity under natural conditions.

In Berlin – wie auch in anderen Regionen Deutschlands – wird ein Großteil des Trinkwassers durch Uferfiltration gewonnen. Durch eine Untergrundpassage mit einer Dauer von meist mehreren Wochen erhält es eine Aufreinigung, die den Aufwand der konventionellen Trinkwasseraufbereitung verringert und eine zusätzliche Barriere gegenüber Schadstoffen darstellt (Kühn 2001). Das Ziel eines interdisziplinären Forschungsvorhabens mit dem Titel NASRI (Natural and Artificial Systems for Recharge and Infiltration) war, die Reinigungsprozesse für verschiedenste Substanzen zu ermitteln und Empfehlungen für das zukünftige Wassermanagement in Berlin abzuleiten (Fritz 2003). Aufgabe der Arbeitsgruppe des Umweltbundesamtes war dabei zu klären, wie wirksam Microcystinen (MCYST) als wichtigste Gruppe der Cyanobakterientoxine durch die Bodenpassage eliminiert werden. Im Folgenden werden einige Schlüsselergebnisse berichtet. Für eine ausführliche Ergebnisdarstellung siehe Grützmacher et al. (2006). MCYST sind in der Regel überwiegend (> 90 %) zellgebunden, so dass die physikalische Filtration der Zellen an der Sedimentoberfläche als Eliminationsprozess im Vordergrund steht (Grützmacher et al. 2003). Das extrazelluläre MCYST wird dagegen überwiegend biologisch abgebaut (Lahti et al. 1998, Grützmacher et al. 2005a). Um unter naturnahen Bedingungen Extremfälle für den biologischen Abbau zu simulieren, wurden i) Freilandversuche unter variierenden Redoxbedingungen und ii) Laborsäulenversuche bei unterschiedlichen Temperaturen durchgeführt. Ferner wurde die Freisetzung von MCYST aus sedimentierten Zellen untersucht.

Cylindrospermopsis raciborskii, a cyanobacterium of tropical origin, can produce the toxin cylindrospermopsin (CYN). This originally tropical cyanobacterium (bluegreen algae) has now spread to the distant waters of the Berlin area. Cylindrospermopsin has been detected in two lakes in the area, but none of the C. raciborskii strains isolated here so far were found to produce the toxin. The main objectives of the CYLIN project were therefore to analyze the distribution and regulation of C. raciborskii and cylindrospermopsin and to determine which cyanobacteria are producing this toxin in order to establish a basis with which to predict the further course of development of this species and the related health hazards for humans. The CYLIN project was implemented as a three-part program. A screening program was first conducted in 2004 to test regional water bodies for the presence of cylindrospermopsin and potential CYN-producing cyanobacteria in order to obtain an overview of their distribution in the study region. A total of 142 regional water bodies were sampled once each in this qualitative analysis cylindrospermopsin and cyanobacteria. The screening program was followed by a monitoring program designed to generate quantitative data on the concentrations of dissolved CYN, particulate CYN, cyanobacteria and target environmental parameters at 20 selected lakes, which were sampled 3 times each. Last but not least, we investigated the seasonal dynamics of these parameters at two selected lakes in 2004 and 2005. Apart from this we isolated different cyanobacterial strains and conducted chemical and molecular biological analyses of CYN and CYNcoding genes, in order to identify CYN-producing cyanobacteria. The results show that C. raciborskii and CYN are much more widespread than was previously assumed. C. raciborskii was detected in 22 % of the investigated water bodies, and cylindrospermopsin in 52 %. Additionally, two other toxic cyanobacteria of tropical origin were found for the first time in the BerlinBrandenburg region, Anabaena bergii and Aphanizomenon aphanizomenoides. The mean and maximum CYN concentrations were 1 µg L-1 and 12 µg L-1, respectively. Since the particulate CYN fraction did not exceed 0.5 µg L-1, the dissolved CYN fraction was found to be responsible for the high CYN concentrations. The proposed guideline safety value for cylindrospermopsin in drinking water (1 µg L-1) was exceeded 18 times at 8 different lakes. Although Aphanizomenon flos-aquae (Nostocales) has been unequivocally identified as a producer of cylindrospermopsin, the observed cylindrospermopsin concentrations cannot be attributed to this cyanobacterial species alone. Aphanizomenon gracile was also identified as a potential CYN-producing cyanobacterium. Based on the findings of the CYLIN project, we recommend that cylindrospermopsin be included as a risk factor in drinking and bathing water quality assessments. To identify hazard conditions associated with this cyanotoxin, further investigations are needed to identify all cyanobacteria that produce cylindrospermopsin and to elucidate the mechanisms regulating the occurrence of CYN-producing cyanobacteria, CYN synthesis by these organisms, and CYN decomposition in aquatic ecosystems. Our analysis of C. raciborskii population dynamics showed that its germination is temperature-dependent and its population growth light-dependent. Population size was determined by the time of germination, that is, the earlier the time of germination, the bigger the population. Based on these findings, it appears highly likely that the climate-related early rise in water temperatures over the course of the years has promoted the spread of this species to temperate regions. Our hypothesis for the future course of cyanobacterial and cyanotoxin development in German waters is as follows: The combination of trophic decline and global warming works to the general benefit of cyanobacteria of the order Nostocales and leads to a shift in cyanobacterial species and toxin composition. This may ultimately lead to an increase in the incidence of neurotoxins as well as cylindrospermopsin.

Cylindrospermopsis raciborskii, a cyanobacterium of tropical origin, can produce the toxin cylindrospermopsin (CYN). This originally tropical cyanobacterium (blue-green alga) had spread to the waters of the Berlin area. Cylindrospermopsin had been detected in two lakes in the area, but none of the C. raciborskii strains isolated here so far were found to produce the toxin. The main objectives of the CYLIN project were therefore to analyze the distribution and regulation of C. raciborskii and cylindrospermopsin and to determine which cyanobacteria are producing this toxin in order to establish a basis to predict the further course of development of this species and the related health hazards for humans. The CYLIN project was implemented as a three-part program. A screening program was first conducted in 2004 to test regional water bodies for the presence of cylindrospermopsin and potential CYN-producing cyanobacteria in order to obtain an overview of their distribution in the study region. A total of 142 regional water bodies were sampled once each in this qualitative analysis of cylindrospermopsin and cyanobacteria. The screening program was followed by a monitoring program designed to generate quantitative data on the concentrations of dissolved CYN, particulate CYN, cyanobacteria and target environmental parameters at 20 selected lakes, which were sampled 3 times each. Furthermore, we investigated the seasonal dynamics of these parameters at two selected lakes in 2004 and 2005. Apart from this we isolated different cyanobacterial strains and conducted chemical and molecular biological analyses of CYN and CYN-coding genes, in order to identify CYN-producing cyanobacteria. The results show that C. raciborskii and CYN are much more widespread than was previously assumed for the region. C. raciborskii was detected in 22 % of the investigated water bodies, and cylindrospermopsin in 52 %. Additionally, two other toxic cyanobacteria of tropical origin were found for the first time in the Berlin-Brandenburg region, Anabaena bergii and Aphanizomenon aphanizomenoides. The mean and maximum CYN concentrations were 1 µg L-1 and 12 µg L-1, respectively. Since the particulate CYN fraction did not exceed 0.5 µg L-1, the dissolved CYN fraction was found to be responsible for the high CYN concentrations. The proposed guideline value for cylindrospermopsin in drinking water (1 µg L-1; Humpage and Falconer 2003) was exceeded 18 times at 8 different lakes. Although Aphanizomenon flos-aquae (Nostocales) has been unequivocally identified as a producer of cylindrospermopsin, the observed cylindrospermopsin concentrations cannot be attributed to this cyanobacterial species alone. Aphanizomenon gracile was also identified as a potential CYN-producing cyanobacterium. Based on the findings of the CYLIN project, we recommend that cylindrospermopsin be included as in hazard analyisis for drinking and bathing water quality assessments. To identify risk conditions associated with this cyanotoxin, further investigations are needed to identify all cyanobacteria that produce cylindrospermopsin and to elucidate the mechanisms regulating the occurrence of CYN-producing cyanobacteria, CYN synthesis by these organisms, and CYN decomposition in aquatic ecosystems. Our analysis of C. raciborskii population dynamics showed that its germination is temperature-dependent and its population growth light-dependent. Population size was determined by the time of germination, that is, the earlier the time of germination, the bigger the population. Based on these findings, it appears highly likely that the climate-related early rise in water temperatures over the course of the years has promoted the spread of this species to temperate regions. Our hypothesis for the future course of cyanobacterial and cyanotoxin development in German waters is as follows: The combination of trophic decline and global warming works to the general benefit of cyanobacteria of the order Nostocales and leads to a shift in cyanobacterial species and toxin composition. This may ultimately lead to an increase in the incidence of neurotoxins as well as cylindrospermopsin.

The frequent occurrence of the cyanobacterial toxin cylindrospermopsin (CYN) in the (sub)-tropics has been largely associated with cyanobacteria of the order Nostocales of tropical origin, in particular Cylindrospermopsis raciborskii. C. raciborskii is currently observed to spread northwards into temperate climatic zones. In addition, further cyanobacteria of the order Nostocales typically inhabiting water bodies in temperate regions are being identified as CYN-producers. Therefore, data on the distribution of CYN in temperate regions are necessary for a first assessment of potential risks due to CYN in water used for drinking and recreation. A total of 127 lakes situated in the northeastern part of Germany were investigated in 2004 for the presence of the toxin CYN and the phytoplankton composition. The toxin could be detected in half of the lakes (n ¼ 63) and in half of 165 samples (n ¼ 88). Concentrations reached up to 73.2 _g CYN/g DW. CYN thus proved more widely distributed than previously demonstrated. The analyses of phytoplankton data suggest Aphanizomenon sp. and Anabaena sp. as important CYN producers in Germany, and confirm recent findings of Aphanizomenon flos-aquae as CYN-producing species frequently inhabiting water bodies in temperate climatic regions. The data shown here suggest that CYN may be an important cyanobacterial toxin in German water bodies and that further data are needed to assess this.