Impairment of trophic interactions between zebrafish ( Danio rerio ) and midge larvae ( Chironomus riparius ) by chlorpyrifos

The effects of chemicals on biotic interactions, such as competition and predation, have rarely been investigated in aquatic ecotoxicology. This study presents a new approach for the investigation of predator-prey interactions between zebrafish (Danio rerio) and midge larvae (Chironomus riparius) impaired by chlorpyrifos (CHP), a neurotoxic insecticide. With a simple experimental design including four different treatments: (1) control, (2) predator exposed, (3) prey exposed and (4) both, predator and prey, exposed, we were able to detect by visual observation an increase in the feeding rate of zebrafish preying on exposed chironomids after acute (2h) exposure to 6μg/l CHP. Previously, a decrease in the burrowing behaviour of exposed chironomid larvae was observed. However, when pre-exposing simultaneously both predators and prey, no significant differences in the feeding rate of zebrafish were observed. This suggests an impairment in prey recognition of the exposed zebrafish. At a lower CHP concentration (1μg/l), no differences in feeding rate of zebrafish were observed. We therefore propose the use of trophic interactions as parameters in higher tier studies for chemical testing and evaluation of ecotoxicological risk assessmen

Integrated toxicity evaluation of a pulp deposit using organisms of different trophic levels

Purpose: In order to assess possible adverse effects originating from pulp deposits in a Swiss lake, a sediment quality triad approach was applied with chemical, ecotoxicological and ecological assessment methods. Materials and methods: To obtain an integrative picture of the potential ecotoxicological effects on organisms of different trophic levels, four test procedures were applied. The acute effects of pulp deposit pore water on a decomposer, the amphipod Gammarus fossarum, were monitored. Chronic toxicity of the pore water was evaluated on primary producers via a growth inhibition test with unicellular green algae (Pseudokirchneriella subcapitata) and on secondary consumers in a reproduction test with the water flea Ceriodaphnia dubia. To evaluate the effects of the pulp deposit on sediment inhabitants, a whole-life-cycle test with the non-biting midge Chironomus riparius was undertaken. Chemical assessment included dissolved organic carbon, extractable organic halogenic compounds, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals. The composition of the macrozoobenthos community was analysed in order to assess the ecological effects. Results and discussion: G. fossarum displayed increased locomotor activity at 12.5% but not at 25% sample concentration during a short-time exposure of 20h. Chronic effects compromised the reproduction and growth of C. dubia (lowest observed effect concentration, 12.5% sample concentration) with zero population growth in 100% pulp deposit pore water. In 100% pulp deposit, C. riparius exhibited increased mortality at 10 and 17days after oviposition. Pulp deposits of 50% and 100% concentration caused a significantly lower emergence compared with the reference treatments (lake sediment and quartz sand). Additionally, the locomotor activity of chironomids decreased significantly in 25-100% pulp deposit. No chronic effects of pulp deposit pore water on algae photosynthesis and growth could be detected. The bioassay results were in accordance with an elevated content of PAHs, PCBs and metals in the pulp deposit. Significantly more organisms known to be tolerant to organic pollution were present within the macrozoobenthos community. Conclusions: In general, for sediment inhabitants such as chironomids, the pulp deposit has to be classified toxic. In the present test setup, the toxicity of the pulp deposit was reflected better by the chronic test systems applied than by the acute ones. The applied testing framework could be a suitable tool to assess the risk of contaminated sites, and this information will help decide whether risk mitigation measures should be taken. In addition, with a similar approach, the success of any mitigation measures taken can be assesse

Effects of chemicals on chironomids and fish as their predators

Im Rahmen der Dissertation wurden in mehreren Teilprojekten die Auswirkungen von Umweltchemikalien auf Chironomiden als Schlüsselorganismen in aquatisch-benthischen Lebensräumen untersucht. Dabei lag der Fokus besonders auf der Erfassung von nicht-standardisierten Endpunkten und Bioindikatoren sowie auf der Bearbeitung einer weiterführenden ökologisch relevanten Fragestellung zum Räuber-Beute-Verhältnis unter Schadstoffeinfluss. Im ersten Teil der Dissertation wurde das herkömmliche Standardtestsystem mit Chironomus riparius erweitert, um die Informationslage von Thiacloprid als Vertreter der neuen Insektizidklasse der Neonikotinoide im subletalen und letalen Bereich auf Nicht-Zielorganismen zu erweitern. Die etablierten Testparameter aus den anerkannten OECD Testrichtlinien wurden dabei mit einer Batterie von weiteren Testparametern kombiniert, um den Test sensitiver und aussagekräftiger zu gestalten. Somit wurde eine große Bandbreite an zusätzlichen Parametern, nämlich biochemische (Induktion von Stressproteinen), entwicklungsbiologische (z.B. Larvalentwicklung) und organismische (Verhalten) als Endpunkte integriert, quantifiziert und deren Sensitivität miteinander verglichen. Mit diesem erweiterten Testsystem wurden exemplarisch die Auswirkungen des Insektizids Thiacloprid auf die verschiedenen biologischen Ebenen des Nicht-Zielinsekts C. riparius untersucht. Allgemein ist es mit diesem Testsystem möglich, die Auswirkungen von Einzelsubstanzen, Substanzmischungen und natürlichen Proben zu testen. Im zweiten Teil der Dissertation wurde untersucht, ob sich Deformationen der Mundwerkzeuge von Chironomiden als Bioindikator bei Schadstoffbelastungen eignen. Es sollte dabei geklärt werden, ob Schadstoffe mit verschiedenen Wirkweisen Deformationen der Mundwerkzeuge bei C. riparius induzieren können und ob die Anzahl bzw. die Intensität der Deformationen mit der Schadstoffmenge korreliert. Zusätzlich wurde getestet, ob Einzelsubstanzen die gleiche Reaktion induzieren wie Substanzgemische. Dies wurde mit dem gleichen Testdesign anhand von vier verschiedenen Schadstoffen (Imidacloprid, Thiacloprid, Nickelchlorid und Chlorpyrifos) und deren Mischungen getestet. Darüber hinaus wurden die Ergebnisse in den Kontext der aktuellen, zum Teil widersprüchlichen Literatur gestellt. Im dritten Teil der Dissertation wurden die Auswirkungen des Insektizids Chlorpyrifos auf Räuber-Beute-Beziehungen anhand eines Modellsystems mit Zebrabärblingen als Räuber und Chironomidenlarven als Beute untersucht. Ziel war es, auf einem höheren biologischen Niveau die eventuell indirekten Auswirkungen von einer kurzzeitigen umweltrelevanten Schadstoffexposition zu untersuchen. Dabei wurden in verschiedenen Ansätzen die Räuber, die Beute oder beide kurzzeitig dem Schadstoff gegenüber exponiert. Es wurde als Hypothese formuliert, dass Prädatoren das Räubervermeidungsverhalten (Vergraben) bei Chironomiden stimulieren, unabhängig davon ob die Beute vorexponiert war oder nicht. Dabei wurde jedoch angenommen, dass vorexponierte Chironomiden ein vermindertes Räubervermeidungsverhalten aufweisen, weshalb sie anfälliger für Prädation sind. Bei gleichzeitiger Vorexposition von Räuber und Beuteorganismen sollte sich die verringerte Fähigkeit des Räubers, die Beute zu erkennen und die der Beute, sich zu vergraben, aufheben und somit zu keinen deutlichen Unterschieden in der Fressrate im Vergleich zur Kontrolle führen. Allgemein sind Räuber-Beute-Beziehungen sehr komplex, weshalb als Versuchsaufbau bewusst ein einfaches und unmissverständlich zu interpretierendes System entwickelt wurde.The effects of chemicals on chironomids as key organisms in aquatic-benthic systems were investigated in three subprojects. The main focus was on the evaluation of non standard endpoints and bioindicators, as well as on ecologically relevant predator-prey systems under pollutant stress. Since data documentation on neonicotinic toxicity to nontarget organisms should be enhanced, the effects of thiacloprid, a novel neonicotinoid insecticide, on the sediment-dwelling non target insect Chironomus riparius was investigated. Further we wanted to validate the sensitivity of end points on different biological levels and obtain the greatest amount of information regarding the effects of this compound by using a battery of several end points such as larval mortality, behavior, body weight gain, emergence rate, time of development, gender ratio, the Hsp70 stress protein level and larval mouth part deformities after exposure at a concentration range of 0.1 to 1000 µg/L thiacloprid. C. riparius was impacted starting at concentrations of 0.5 µg/L, a concentration which can be considered as environmentally relevant. Larval mortality, behavior, emergence, and Hsp70 protein level were sensitive indicators for the toxic effect of thiacloprid, whereas gender ratio and mouthpart morphology were not affected. In our case life cycle endpoints like the survival rate (LC50: 1.57 µg/L) or emergence rate (EC50: 0.54 µg/L) proved to be more sensitive than tested physiological endpoints for the neurotoxic insecticide. The significance of chironomids mouth part deformities as suitable indicators for pollutant contamination of natural waters and sediments has been investigated and discussed for several decades. Uncertainties still exist as further laboratory studies, with different pollutants and with the same experimental design are required. In this study, the effects of four substances (i.e. nickelchloride, chlorpyrifos, imidacloprid, and thiacloprid) were tested on the mouth part deformity rates and patterns in Chironomus riparius. These compounds were investigated either individually or in mixtures. No significant increase in the frequency of mouth part deformities was found using different single substance treatments when compared to the controls. Consequently no concentration-effect relationships between substance concentration and deformity frequency were detected. In mixture experiments an increase in mouth part deformities of C. riparius exposed to imidacloprid-thiacloprid mixtures was detected. This indicated that the effects of single substances and mixtures on mouth part deformity frequency may differ considerably. The findings in this study from different laboratory approaches in combination with the published literature questions the reliability of chironomids mouth part deformities as indicators of freshwater and sediment contamination by toxic substances. The effects of chemicals on biotic interactions, such as competition and predation, have rarely been investigated in aquatic ecotoxicology. This study presents a new approach for the investigation of predator-prey interactions between zebrafish (Danio rerio) and midge larvae (Chironomus riparius) impaired by chlorpyrifos (CHP), a neurotoxic insecticide. With a simple experimental design including four different treatments: (1) control, (2) predator exposed, (3) prey exposed and (4) both, predator and prey, exposed, we were able to detect by visual observation an increase in the feeding rate of zebrafish preying on exposed chironomids after acute (2 h) exposure to 6 µg/L CHP. Previously, a decrease in the burrowing behaviour of exposed chironomid larvae was observed. However, when pre-exposing simultaneously both predators and prey, no significant differences in the feeding rate of zebrafish were observed. This suggests an impairment in prey recognition of the exposed zebrafish. At a lower CHP concentration (1 µg/L), no differences in feeding rate of zebrafish were observed. We therefore propose the use of trophic interactions as parameters in higher tier studies for chemical testing and evaluation of ecotoxicological risk assessment