Dominic Englert

Ecotoxicological impact of the fungicide tebuconazole on an aquatic decomposer‐detritivore system

Leaf litter breakdown is a fundamental process in aquatic ecosystems that is realized by microbial decomposers and invertebrate detritivores. Although this process may be adversely affected by fungicides, among other factors, no test design exists to assess combined effects on such decomposer-detritivore systems. Hence, the present study assessed effects of the model fungicide tebuconazole (65 µg/L) on the conditioning of leaf material (by characterizing the associated microbial community) as well as the combined effects (i.e., direct toxicity and food quality-related effects (=indirect)) on the energy processing of the leaf-shredding amphipod Gammarus fossarum using a five-week semistatic test design. Gammarids exposed to tebuconazole produced significantly less feces (≈ 20%), which in turn significantly increased their assimilation (≈ 30%). Moreover, a significantly reduced lipid content (≈ 20%) indicated lower physiological fitness. The conditioning process was altered as well, which was indicated by a significantly reduced fungal biomass (≈ 40%) and sporulation (≈ 30%) associated with the leaf material. These results suggest that tebuconazole affects both components of the investigated decomposer-detritivore system. However, adverse effects on the level of detritivores cannot be explicitly attributed to direct or indirect pathways. Nevertheless, as the endpoints assessed are directly related to leaf litter breakdown and associated energy transfer processes, the protectiveness of environmental risk assessment for this ecosystem function may be more realistically assessed in future studies by using this or comparable test designs.

Effects of nano-TiO2 in combination with ambient UV-irradiation on a leaf shredding amphipod

Production and use of engineered nanoparticles, such as titanium dioxide nanoparticles (nTiO(2)), is increasing worldwide, enhancing their probability to enter aquatic environments. However, direct effects of nTiO(2) as well as ecotoxicological consequences due to the interactions of nTiO(2) with environmental factors like ultraviolet (UV) irradiation on representatives of detrital food webs have not been assessed so far. Hence, the present study displayed for the first time adverse sublethal effects of nTiO(2) at concentrations as low as 0.2 mg L(-1) on the leaf shredding amphipod Gammarus fossarum both in presence and absence of ambient UV-irradiation following a 7-d exposure. In absence of UV-irradiation, however, the effects seemed to be driven by accumulation of nTiO(2) at the bottom of the test vessels to which the gammarids were potentially exposed. The adverse sublethal and lethal effects on gammarids caused by the combined application of nTiO(2) and ambient UV-irradiation are suggested to be driven by the formation of reactive oxygen species. In conclusion, both the accumulation of nTiO(2) at the bottom of the test vessel and the UV induced formation of reactive oxygen species clearly affected its ecotoxicity, which is recommended for consideration in the environmental risk assessment of nanoparticles.

Inorganic fungicides as routinely applied in organic and conventional agriculture can increase palatability but reduce microbial decomposition of leaf litter

Summary The application of fungicides is considered an indispensable measure to secure crop production. These substances, however, may unintentionally enter surface waters via run-off, potentially affecting the microbial community. To assess such risks adequately, authorities recently called for suitable test designs involving relevant aquatic micro-organisms. We assessed the structural and functional responses of leaf-associated microbial communities, which play a key role in the breakdown of allochthonous leaf material in streams, towards the inorganic fungicides copper (Cu) and elemental sulphur (S). These substances are of particular interest as they are authorized for both conventional and organic farming in many countries of the world. We used the food choice of the amphipod shredder Gammarus fossarum (indicative for micro-organism-mediated leaf palatability) as well as microbial leaf decomposition as functional endpoints. Moreover, the leaf-associated microbial communities were characterized by means of bacterial density, fungal biomass and community composition facilitating mechanistic understanding of the observed functional effects. While Gammarus preferred Cu-exposed leaves over unexposed ones, microbial leaf decomposition was reduced by both Cu and S (up to 30%). Furthermore, Cu exposure decreased bacterial densities (up to 60%), stimulated the growth of leaf-associated fungi (up to 100%) and altered fungal community composition, while S did not affect any of the assessed structural endpoints. Synthesis and applications. We observed both structural and functional changes in leaf-associated microbial communities at inorganic fungicide concentrations realistic for surface water bodies influenced by conventional and organic farming. Our data hence justify a careful re-evaluation of the environmental safety of the agricultural use of these compounds. Moreover, inclusion of an experimental design similar to the one used in this study in lower tier environmental risk assessments of antimicrobial compounds may aid to safeguard the integrity of aquatic microbial communities and the functions they provide.

The relative importance of diet-related and waterborne effects of copper for a leaf-shredding invertebrate

Copper (Cu) exposure can increase leaf-associated fungal biomass, an important food component for leaf-shredding macroinvertebrates. To test if this positive nutritional effect supports the physiological fitness of these animals and to assess its importance compared to waterborne toxicity, we performed a 24-day-bioassay in combination with a 2×2 factorial design using the amphipod shredder Gammarus fossarum and a field-relevant Cu concentration of 25 μg/L (n = 65). Waterborne toxicity was negligible, while gammarids fed leaves exposed to Cu during microbial colonization exhibited a near-significant impairment in growth (∼30%) and a significantly reduced lipid content (∼20%). These effects appear to be governed by dietary uptake of Cu, which accumulated in leaves as well as gammarids and likely overrode the positive nutritional effect of the increased fungal biomass. Our results suggest that for adsorptive freshwater contaminants dietary uptake should be evaluated already during the registration process to safeguard the integrity of detritus-based ecosystems.

Combined effect of UV-irradiation and TiO2-nanoparticles on the predator–prey interaction of gammarids and mayfly nymphs

Although nanoparticle production and application increases continuously, their implications in species interactions, especially in combination with other environmental stressors, are rarely assessed. Therefore, the present study investigated the influence of 2 mg/L titanium dioxide nanoparticles (nTiO2; <100 nm) on the interaction between the prey Ephemerella ignita (Ephemeroptera) and the predator Gammarus fossarum (Amphipoda) over 96 h considering UV-irradiation at field relevant levels (approximately 11.4 W/m(2)) as an additional environmental factor (n = 16). At the same time, gammarids consumption of an alternative food source, i.e. leaf discs, was assessed. All endpoints covered were not affected by nTiO2 alone, while the combination of nTiO2 and UV caused a reduction in gammarids predation (68%), leaf consumption (60%) and body weight (22%). These effects were most likely triggered by the UV-induced formation of reactive oxygen species by nTiO2. The present study, hence, highlights the importance to cover UV-irradiation during the risk assessment of nanoparticles.

Modeling Remobilization of Neonicotinoid Residues from Tree Foliage in Streams—A Relevant Exposure Pathway in Risk Assessment?

Systemic neonicotinoid insecticides are increasingly used as a crop protection measure to suppress insect pests on trees. However, senescent foliage falling from treated trees represents a rarely studied pathway through which neonicotinoids may enter nontarget environments, e.g., surface waters. To estimate risk posed by this pathway, neonicotinoid residues were analyzed in foliage from black alder trees treated with one of three neonicotinoid insecticides (imidacloprid, thiacloprid, or acetamiprid) at five concentrations, each ranging from 0.0375-9.6 g active ingredient/cm trunk diameter at breast height (n = 3). Foliar residues measured at the time of leaf fall were used as input parameters for a model predicting imidacloprid water concentrations over a 100-m-long stream stretch as a consequence of remobilization from introduced foliage (input: 600 g foliage/m2 containing 80 μg imidacloprid/g). The water concentration (up to ∼250 ng/L) predicted by the model exceeded the recently proposed Maximum Permissible Concentration of 8.3 ng/L for ∼6.5 days. Moreover, dietary uptake was identified as an additional exposure route for aquatic organisms. The alternative pathway (i.e., introduction via leaf fall) and exposure route (i.e., dietary uptake) associated with the systemic nature of neonicotinoids should be accounted for during their registration process in order to safeguard ecosystem integrity.

Relative importance of dietary uptake and waterborne exposure for a leaf-shredding amphipod exposed to thiacloprid-contaminated leaves

Systemic neonicotinoids are commonly used in forest pest management programs. Senescent leaves containing neonicotinoids may, however, fall from treated trees into nearby streams. There, leaf-shredding invertebrates are particularly exposed due to their diet (feeding on neonicotinoid-contaminated leaves) or collaterally via the water phase (leaching of a neonicotinoid from leaves) – a fact not considered during aquatic environmental risk assessment. To unravel the relevance of these pathways we used leaves from trees treated with the neonicotinoid thiacloprid to subject the amphipod shredder Gammarus fossarum for 21 days (n = 40) either to dietary, waterborne or a combined (dietary + waterborne) exposure. Dietary exposure caused – relative to the control – similar reductions in gammarids’ leaf consumption (~35%) and lipid content (~20%) as observed for the waterborne exposure pathway (30 and 22%). The effect sizes observed under combined exposure suggested additivity of effects being largely predictable using the reference model “independent action”. Since gammarids accumulated – independent of the exposure pathway – up to 280 ng thiacloprid/g, dietary exposure may also be relevant for predators which prey on Gammarus. Consequently, neglecting dietary exposure might underestimate the environmental risk systemic insecticides pose for ecosystem integrity calling for its consideration during the evaluation and registration of chemical stressors.

News from the SETAC Europe Student Advisory Council (April 2013) - the 3rd Young Environmental Scientists (YES) meeting at the Jagiellonian University, Poland

This article reports on the 3rd Young Environmental Scientists Meeting that was hosted from 11 to 13 February 2013 by the Institute of Environmental Sciences at the Jagiellonian University in Kraków, Poland. This student-only meeting under the theme of ‘interdisciplinary discourse on current environmental challenges’ was again organized by the Student Advisory Council of the Society of Environmental Toxicology and Chemistry Europe. An abstract book of the meeting is freely available as supplemental material of this article.

News from the SETAC Europe Student Advisory Council - September 2012

The Student Advisory Council is the speaking tube of SETAC Europe’s students aiming to support young researchers in becoming fully-fledged members of the Society. In this article we report our latest activities during the 6th SETAC World Congress/SETAC Europe 22nd Annual Meeting in Berlin, Germany, and the upcoming 3rd Young Environmental Scientists (YES) Meeting in Krakow, Poland.