Open Access

Deichbau und andere flussbautechnische Maßnahmen haben dazu geführt, dass die Mittlere Elbe ihre ursprünglichen Überschwemmungsgebiete verloren hat. Um die Auswirkungen der alljährlich auftretenden Hochwasserereignisse einzudämmen, wurden große Bereiche der Talniederung durch Deiche vom Überflutungsgeschehen abgetrennt. Diese Eingriffe in den Naturhaushalt ermöglichten gleichfalls eine intensive ackerbauliche Nutzung oder eine hochwassersichere Bebauung der Auen. Die natürliche Auendynamik ist heute weitestgehend auf einen schmalen Bereich entlang der Elbe beschränkt. Hinter den Deichen sind die für die Elbeauen typischen Lebensräume von der lebenswichtigen Auendynamik abgeschnitten. Angepasste Auenarten und -lebensgemeinschaften treten zugunsten von Allerweltsarten zurück. Eine Wiederanbindung von Altauenbereichen an das Überflutungsgeschehen ist deshalb eine der vordringlichsten Maßnahmen zur Revitalisierung gefährdeter Auenlebensräume und stellt eine Chance dar, einen nachhaltigen und modernen Hochwasserschutz mit Naturschutzzielen zu verbinden. An der Elbe entspricht das aktuelle Hochwasserschutzsystem nicht den heutigen Anforderungen an den Hochwasserschutz. Um jedoch jederzeit auf mögliche große Hochwasserereignisse reagieren zu können, entstanden Anfang der 1990er Jahre in den Anliegerländern der Elbe zahlreiche Pläne für Deichrückverlegungen.

Highlights • Comprehensive pesticide monitoring at 105 sites over two application periods. • RAC exceedances occurred for majority of small streams. • Rainfall increases pesticide concentrations in streams by factor of 10. • 2,4-D, MCPA, terbuthylazine, and nicosulfuron increased most strongly during rainfall. • Sum concentration of pesticide metabolites factor 10 higher than pesticides. Abstract Few studies have examined the exposure of small streams (< 30 km2 catchment size) to agriculturally used pesticides, compared to large rivers. A total of 105 sites in 103 small agricultural streams were investigated for 76 pesticides (insecticides, herbicides, fungicides) and 32 pesticide metabolites in spring and summer over two years (2018 and 2019) during dry weather and rainfall using event-driven sampling. The median total concentration of the 76 pesticides was 0.18 µg/L, with 9 pesticides per sample on average (n = 815). This is significantly higher than monitoring data for larger streams, reflecting the close proximity to agricultural fields and the limited dilution by non-agricultural waters. The frequency of detection of all pesticides correlated with sales quantity and half-lives in water. Terbuthylazine, MCPA, boscalid, and tebuconazole showed the highest median concentrations. The median of the total concentration of the 32 metabolites exceeded the pesticide concentration by more than an order of magnitude. During dry weather, the median total concentration of the 76 pesticides was 0.07 µg/L, with 5 pesticides per sample on average. Rainfall events increased the median total pesticide concentration by a factor of 10 (to 0.7 µg/L), and the average number of pesticides per sample to 14 (with up to 41 in single samples). The concentration increase was particularly strong for 2,4-D, MCPA, terbuthylazine, and nicosulfuron (75 percentile). Metabolite concentrations were generally less responsive to rainfall, except for those of terbuthylazine, flufenacet, metamitron, and prothioconazole. The frequent and widespread exceedance of the regulatory acceptable concentrations (RAC) of the 76 pesticides during both, dry weather and rainfall, suggests that current plant protection product authorization and risk mitigation methods are not sufficient to protect small streams.

Schistosomiasis is a severe neglected tropical disease caused by trematodes and transmitted by freshwater snails. Snails are known to be highly tolerant to agricultural pesticides. However, little attention has been paid to the ecological consequences of pesticide pollution in areas endemic for schistosomiasis, where people live in close contact with non-sanitized freshwaters. In complementary laboratory and field studies on Kenyan inland areas along Lake Victoria, we show that pesticide pollution is a major driver in increasing the occurrence of host snails and thus the risk of schistosomiasis transmission. In the laboratory, snails showed higher insecticide tolerance to commonly found pesticides than associated invertebrates, in particular to the neonicotinoid Imidacloprid and the organophosphate Diazinon. In the field, we demonstrated at 48 sites that snails were present exclusively in habitats characterized by pesticide pollution and eutrophication. Our analysis revealed that insensitive snails dominated over their less tolerant competitors. The study shows for the first time that in the field, pesticide concentrations considered “safe” in environmental risk assessment have indirect effects on human health. Thus we conclude there is a need for rethinking the environmental risk of low pesticide concentrations and of integrating agricultural mitigation measures in the control of schistosomiasis.

Highlights • Interaction between one chemical and two non-chemical stressors was studied. • Food limitation and elevated temperature showed additive interactions. • Environmental stressors substantially increase the effects of esfenvalerate. • Multiple stressors induced strong latent synergistic effects. • Combined effects of multiple stressors were predicted by the Stress Addition Model. Abstract Global biodiversity is declining at an unprecedented rate in response to multiple environmental stressors. Effective biodiversity management requires deeper understanding of the relevant mechanisms behind such ecological impacts. A key challenge is understanding synergistic interactions between multiple stressors and predicting their combined effects. Here we used Daphnia magna to investigate the interaction between a pyrethroid insecticide esfenvalerate and two non-chemical environmental stressors: elevated temperature and food limitation. We hypothesized that the stressors with different modes of action can act synergistically. Our findings showed additive effects of food limitation and elevated temperature (25 °C, null model effect addition (EA)) with model deviation ratio (MDR) ranging from 0.7 to 0.9. In contrast, we observed strong synergistic interactions between esfenvalerate and food limitation at 20 °C, considerably further amplified at 25 °C. Additionally, for all stress combinations, the synergism intensified over time indicating the latent effects of the pesticide. Consequently, multiple stress substantially reduced the lethal concentration of esfenvalerate by a factor of 19 for the LC50 (0.45–0.024 μg/L) and 130 for the LC10 (0.096–0.00074 μg/L). The stress addition model (SAM) predicted increasing synergistic interactions among stressors with increasing total stress.

Highlights • 307 chemicals identified, 18 proposed for regular monitoring and abatement. • Forty-six chemicals detected in >50 % of the sites. • Ecotoxicological risk on aquatic organisms driven by pesticides. • Dry seasons pose high risk for crustaceans and algae. • Seasonal variation of chemical occurrence and concentrations reported. Abstract The release of chemicals into the environment presents a significant threat to aquatic ecosystems dependent on the proximity to emission sources and seasonal dynamics of emission and mobilization. While spatial-temporal information on water pollution in Europe is increasing, there are substantial knowledge gaps on seasonal pollution dynamics in tropical countries. Thus, we took Lake Victoria South Basin in western Kenya as a case study to identify spatial and seasonal hot spots of contamination, quantified toxic risks to different groups of organisms, and identified seasonal risk drivers. For this purpose, we analyzed grab water samples from five rivers with agricultural and wastewater treatment plants in their catchment in four different seasons. We used liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) with a target list of 785 organic micropollutants. A total of 307 compounds were detected with concentrations ranging from 0.3 ng/L to 6.6 μg/L. Using a Toxic Unit (TU) approach based on mixture toxicity to standard test organisms, crustaceans were identified as the most affected group followed by algae and fish. For crustaceans, chronic risk thresholds were exceeded in 96 % of all the samples, while 56 % of all samples are expected to be acutely toxic, with the highest risk in February during the dry season. High toxic unit values for algae and fish were recorded in July dry season and May wet season. Diazinon, imidacloprid, clothianidin and pirimiphos-methyl were the major drivers for crustacean toxicity while triclosan and different herbicide mixtures drive risks to algae in dry and wet seasons, respectively. A total of 18 chemicals were found to exceed acute and chronic environmental risk thresholds. With this study, strong spatial-temporal patterns of pollution, risks and risk drivers could be confirmed informing prioritization of monitoring and abatement to enhance water quality and reduce toxic risks.