The influence of season, hunting mode, and habitat specialization on riparian spiders as key predators in the aquatic-terrestrial linkage.

Freshwater ecosystems subsidize riparian zones with high-quality nutrients via the emergence of aquatic insects. Spiders are dominant consumers of these insect subsidies. However, little is known about the variation of aquatic insect consumption across spiders of different hunting modes, habitat specializations, seasons, and systems. To explore this, we assembled a large stable isotope dataset (n > 1000) of aquatic versus terrestrial sources and six spider species over four points in time adjacent to a lotic and a lentic system. The spiders represent three hunting modes each consisting of a wetland specialist and a habitat generalist. We expected that specialists would feed more on aquatic prey than their generalist counterparts. Mixing models showed that spiders' diet consisted of 17-99% of aquatic sources, with no clear effect of habitat specialization. Averaged over the whole study period, web builders (WB) showed the highest proportions (78%) followed by ground hunters (GH, 42%) and vegetation hunters (VH, 31%). Consumption of aquatic prey was highest in June and August, which is most pronounced in GH and WBs, with the latter feeding almost entirely on aquatic sources during this period. Additionally, the elevated importance of high-quality lipids from aquatic origin during fall is indicated by elemental analyses pointing to an accumulation of lipids in October, which represent critical energy reserves during winter. Consequently, this study underlines the importance of aquatic prey irrespective of the habitat specialization of spiders. Furthermore, it suggests that energy flows vary substantially between spider hunting modes and seasons.

Making the Invisible Visible? Using Stable Isotope Analysis to Detect Indirect Toxicant Effects.

Although stable isotope analysis (SIA) is widely used to address ecological research questions, its application in an ecotoxicological context has been limited. Recent studies have proposed an effect of chemical stressors on an organism's isotope signature, questioning the use of SIA in food webs impacted by toxicants. Against this background, the present study investigates 1) whether trophic enrichment factors (TEFs; i.e., the offset in stable isotope signatures of a consumer to its diet) are altered by the neonicotinoid thiacloprid, and 2) whether tracking toxicant effects on an organism's diet composition (i.e., indirect effect) with SIA fits direct observations of consumption. To address the former, the amphipod Gammarus fossarum (Koch) was exposed to three levels (0, 0.75, and 5 µg L-1 ) of thiacloprid and fed with either black alder leaves or Baetis rhodani (Pictet) larvae over 6 weeks (n = 35). The thiacloprid-induced changes in TEFs that we found were statistically significant but small compared with other factors (e.g., resource quality, consumer, and physiological condition) and thus likely of minor importance. To address the latter issue, gammarids were exposed to two levels of thiacloprid (0 and 0.75 µg L-1 ) and fed with either black alder leaves, live B. rhodani larvae, or both over 2 weeks (n = 10). Dietary proportions as suggested by SIA were indeed in agreement with those derived from direct observation of consumption. The present study consequently suggests that SIA is as a robust tool to detect indirect toxicant effects especially if TEFs are assessed in parallel. Environ Toxicol Chem 2023;42:1937-1945. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Infochemicals Influence Neonicotinoid Toxicity-Impact in Leaf Consumption, Growth, and Predation of the Amphipod Gammarus fossarum.

Infochemicals act as inter- or intraspecific messengers. The literature suggests complex interactions between infochemicals (mainly predator cues) and chemical (e.g., pesticide) effects, with their direction and magnitude depending on the cue origin, pesticide identity, and test species. With the present study we assessed the impact of alarm cues alone and in combination with the neonicotinoid insecticide thiacloprid on leaf consumption, predation on Baetis nymphs, and dry weight of the amphipod Gammarus fossarum. Alarm cues (ground gammarids) and thiacloprid alone decreased gammarid leaf consumption with increasing intensities. At a defined alarm cue intensity, which alone did not cause a significant reduction in gammarid feeding, thiacloprid-induced feeding effects were additive. During an experiment targeting gammarid predation on Baetis nymphs (120 h), thiacloprid and alarm cues alone did increase and reduce predation significantly, respectively. Moreover, alarm cues led to a lower final gammarid dry weight. However, alarm cues did not affect response variables during a second predation experiment performed at a higher thiacloprid concentration (2 vs 0.75 µg/L). This discrepancy in alarm cue effects highlights either a varying susceptibility of the test species to these cues among experiments or that cue quality is fluctuating. Thus, the present study highlights a considerable variability in the individual and interactive effects of infochemicals and chemical stressors on aquatic biota, an insight relevant in the assessment of multiple stressors. Environ Toxicol Chem 2020;39:1755-1764. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Nanoparticles transported from aquatic to terrestrial ecosystems via emerging aquatic insects compromise subsidy quality.

Nanoparticle contaminants enter aquatic ecosystems and are transported along the stream network. Here, we demonstrate a novel pathway for the return of nanoparticles from aquatic to terrestrial ecosystems via cross-boundary subsidies. During their emergence, trichopteran caddisflies carried titanium dioxide and gold nanoparticles into their terrestrial life stages. Moreover, their emergence was delayed by ≤30 days, and their energy reserves were depleted by ≤25%. Based on worst case estimates, it is suggested that terrestrial predators, such as bats feeding on aquatic prey, may ingest up to three orders of magnitude higher gold levels than anticipated for humans. Additionally, terrestrial predator species may suffer from alterations in the temporal availability and nutritional quality of their prey. Considering the substantial transfer of insect biomass to terrestrial ecosystems, nanoparticles may decouple aquatic and terrestrial food webs with important (meta-)ecosystem level consequences.

Effects of a Systemic Pesticide Along an Aquatic Tri-Trophic Food Chain.

Systemic pesticides, such as the neonicotinoid imidacloprid, can be introduced into aquatic ecosystems through contaminated plant material, which is the basis for detrital (brown) aquatic food-webs. With the aim of exemplarily assessing for indirect effects on the level of predators, we first offered imidacloprid contaminated and uncontaminated alder leaves to the stonefly shredder Protonemura sp. for 72 h. Shredder survival, leaf decomposition, body length and biomass were all between 20% and 50% lower under imidacloprid exposure compared to uncontaminated conditions, indicating physiological implications. Subsequently, these shredders were provided as prey to stonefly predators (Isoperla sp.) kept in cages in a stream. Predator biomass and length decreased by up to 11% and 4.3%, respectively, when feeding on imidacloprid exposed prey. Our study hence suggests that plant material contaminated with systemic pesticides can exert adverse effects in aquatic predators when preying on shredders consuming such leaves, which warrants a further consideration of this pathway.

Is Hyalella azteca a Suitable Model Leaf-Shredding Benthic Crustacean for Testing the Toxicity of Sediment-Associated Metals in Europe?

The leaf-shredding crustacean Hyalella azteca, which is indigenous to Northern and Central America, is used to assess environmental risks associated with (metal-)contaminated sediments and to propose sediment quality standards also in Europe. Yet, it is unknown if H. azteca is protective for European crustacean shredders. We thus compared the sensitivity of H. azteca with that of the European species Asellus aquaticus and Gammarus fossarum towards copper- and cadmium-contaminated sediments (prepared according to OECD 218) under laboratory conditions employing mortality and leaf consumption as endpoints. H. azteca either reacted approximately fourfold more sensitive than the most tolerant tested species (as for cadmium) or its sensitivity was only 1.6 times lower than the highest sensitivity determined (as for copper), which should be covered by safety factors applied during risk assessments. Therefore, the results for the sediment type and the two heavy metals tested during the present study in combination with the existence of standardized testing protocols, their ease of culture, and short generation time, suggest H. azteca as suitable crustacean model shredder for assessing the toxicity of sediment-associated metals in Europe.

The evil within? Systemic fungicide application in trees enhances litter quality for an aquatic decomposer-detritivore system.

Waterborne exposure towards fungicides is known to trigger negative effects in aquatic leaf-associated microbial decomposers and leaf-shredding macroinvertebrates. We expected similar effects when these organisms use leaf material from terrestrial plants that were treated with systemic fungicides as a food source since the fungicides may remain within the leaves when entering aquatic systems. To test this hypothesis, we treated black alder (Alnus glutinosa) trees with a tap water control or a systemic fungicide mixture (azoxystrobin, cyprodinil, quinoxyfen, and tebuconazole) at two worst-case application rates. Leaves of these trees were used in an experiment targeting alterations in two functions provided by leaf-associated microorganisms, namely the decomposition and conditioning of leaf material. The latter was addressed via the food-choice response of the amphipod shredder Gammarus fossarum. During a second experiment, the potential impact of long-term consumption of leaves from trees treated with systemic fungicides on G. fossarum was assessed. Systemic fungicide treatment altered the resource quality of the leaf material resulting in trends of increased fungal spore production and an altered community composition of leaf-associated fungi. These changes in turn caused a significant preference of Gammarus for microbially conditioned leaves that had received the highest fungicide treatment over control leaves. This higher food quality ultimately resulted in a higher gammarid growth (up to 300% increase) during the long-term feeding assay. Although the underlying mechanisms still need to be addressed, the present study demonstrates a positive indirect response in aquatic organisms due to systemic pesticide application in a terrestrial system. As the effects from the introduction of plant material treated with systemic fungicides strongly differ from those mediated via other pathways (e.g., waterborne exposure), our study provides a novel perspective of fungicide-triggered effects in aquatic detritus-based food webs.

UV-irradiation and leaching in water reduce the toxicity of imidacloprid-contaminated leaves to the aquatic leaf-shredding amphipod Gammarus fossarum.

Systemic neonicotinoid insecticides such as imidacloprid are increasingly applied against insect pest infestations on forest trees. However, leaves falling from treated trees may reach nearby surface waters and potentially represent a neonicotinoid exposure source for aquatic invertebrates. Given imidacloprid's susceptibility towards photolysis and high water solubility, it was hypothesized that the leaves' toxicity might be modulated by UV-irradiation during decay on the forest floor, or by leaching and re-mobilization of the insecticide from leaves within the aquatic ecosystem. To test these hypotheses, the amphipod shredder Gammarus fossarum was fed (over 7 d; n = 30) with imidacloprid-contaminated black alder (Alnus glutinosa) leaves that had either been pre-treated (i.e., leached) in water for up to 7 d or UV-irradiated for 1 d (at intensities relevant during autumn in Central Europe) followed by a leaching duration of 1 d. Gammarids' feeding rate, serving as sublethal response variable, was reduced by up to 80% when consuming non-pretreated imidacloprid-contaminated leaves compared to imidacloprid-free leaves. Moreover, both leaching of imidacloprid from leaves (for 7 d) as well as UV-irradiation reduced the leaves' imidacloprid load (by 46 and 90%) thereby mitigating the effects on gammarids' feeding rate to levels comparable to the respective imidacloprid-free controls. Therefore, natural processes, such as UV-irradiation and re-mobilization of foliar insecticide residues in water, might be considered when evaluating the risks systemic insecticide applications in forests might pose for aquatic organisms in nearby streams.

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.

Transient effects following peak exposures towards pesticides - An explanation for the unresponsiveness of in situ measured functional variables.

Invertebrate-mediated leaf litter decomposition is frequently used to assess stress-related implications in stream ecosystem integrity. In situ measures such as the mass loss from leaf bags or the feeding of caged invertebrates deployed for days or weeks may, however, fail to detect transient effects due to recovery or compensatory mechanisms. We assessed the relevance of transient effects using the peak exposure towards an insecticide (i.e., etofenprox) as a model scenario at three levels of complexity. These were 1) the assessment of the decomposition realised by invertebrate communities in stream mesocosms over 21 days via leaf bags, 2) 7-days lasting in situ bioassays quantifying the leaf consumption of Gammarus fossarum, and 3) a laboratory experiment determining the daily feeding rate of the same species over 7 days. Etofenprox did not trigger a significantly altered decomposition by invertebrate communities during the leaf bag assay, while in situ bioassays detected a significant reduction in gammarids' feeding rate at the highest tested concentration. The laboratory bioassay suggests that observed mismatches might be explained by recovery and post-exposure compensation. As leaf-shredding invertebrates are likely in a vulnerable state following transient effects, biomonitoring for implications of peak exposures and other pulsed stress events must happen at an adequate temporal resolution.

History Matters: Pre-Exposure to Wastewater Enhances Pesticide Toxicity in Invertebrates.

Disturbance regimes determine communities' structure and functioning. Nonetheless, little effort has been undertaken to understand interactions of press and pulse disturbances. In this context, leaf-shredding macroinvertebrates can be chronically exposed to wastewater treatment plant effluents (i.e., press disturbance) before experiencing pesticide exposure following agricultural runoff (i.e., pulse disturbance). It is assumed that wastewater pre-exposure alters animals' sensitivity to pesticides. To test this hypothesis, we exposed model-populations of the shredder Gammarus fossarum to wastewater at three field-relevant dilution levels (i.e., 0%, 50%, and 100%). After 2, 4, and 6 weeks, survival, leaf consumption, dry weight, and energy reserves were monitored. Additionally, animals were assessed for their sensitivity toward the neonicotinoid insecticide thiacloprid using their feeding rate as response variable. Both wastewater treatments reduced gammarids' survival, leaf consumption, dry weight, and energy reserves. Moreover, both wastewater pre-exposure scenarios increased animals' sensitivity toward thiacloprid by up to 2.5 times compared to the control. Our results thus demonstrate that press disturbance as posed by wastewater pre-exposure can enhance susceptibility of key players in ecosystem functioning to further (pulse) disturbances. Therefore, applying mitigation measures such as advanced treatment technologies seems sensible to support functional integrity in the multiple-stress situation.

Does Waterborne Exposure Explain Effects Caused by Neonicotinoid-Contaminated Plant Material in Aquatic Systems?

Neonicotinoids are increasingly applied on trees as protection measure against insect pests. Consequently, neonicotinoids are inevitably transferred into aquatic environments either via spray drift or surface runoff or (due to neonicotinoids' systemic nature) via senescent leaves. There particularly leaf-shredding invertebrates may be exposed to neonicotinoids through both the water phase and the consumption of contaminated leaves. In 7 day bioassays (n = 30), we examined ecotoxicological differences between these two exposure scenarios for an amphipod and an insect nymph with their feeding rate as the response variable. Organisms either experienced waterborne neonicotinoid (i.e., imidacloprid, thiacloprid, and acetamiprid) exposure only or a combined exposure (waterborne and dietary) through both the consumption of contaminated leaves and neonicotinoids leaching from leaves into water. The amphipod (7 day EC50s from 0.3 to 8.4 µg/L) was more sensitive than the insect nymph (7 day EC50s from 7.0 to 19.4 µg/L). Moreover, for both species, concentration-response models derived from water concentrations indicated higher effects under the combined exposure. Together with the observed inability of shredders to avoid neonicotinoid-contaminated leaves, our results emphasize the relevance of dietary exposure (e.g., via leaves) for systemic insecticides. Thus, it would be prudent to consider dietary exposure during the registration of systemic insecticides to safeguard ecosystem integrity.

Long-term effects of fungicides on leaf-associated microorganisms and shredder populations-an artificial stream study.

Leaf litter is a major source of carbon and energy for stream food webs, while both leaf-decomposing microorganisms and macroinvertebrate leaf shredders can be affected by fungicides. Despite the potential for season-long fungicide exposure for these organisms, however, such chronic exposures have not yet been considered. Using an artificial stream facility, effects of a chronic (lasting up to 8 wk) exposure to a mixture of 5 fungicides (sum concentration 20 µg/L) on leaf-associated microorganisms and the key leaf shredder Gammarus fossarum were therefore assessed. While bacterial density and microorganism-mediated leaf decomposition remained unaltered, fungicide exposure reduced fungal biomass (≤71%) on leaves from day 28 onward. Gammarids responded to the combined stress from consumption of fungicide-affected leaves and waterborne exposure with a reduced abundance (≤18%), which triggered reductions in final population biomass (18%) and in the number of precopula pairs (≤22%) but could not fully explain the decreased leaf consumption (19%), lipid content (≤43%; going along with an altered composition of fatty acids), and juvenile production (35%). In contrast, fine particulate organic matter production and stream respiration were unaffected. Our results imply that long-term exposure of leaf-associated fungi and shredders toward fungicides may result in detrimental implications in stream food webs and impairments of detrital material fluxes. These findings render it important to understand decomposer communities' long-term adaptational capabilities to ensure that functional integrity is safeguarded. Environ Toxicol Chem 2017;36:2178-2189. © 2017 SETAC.

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.

Variability in ecosystem structure and functioning in a low order stream: Implications of land use and season.

Human activity can degrade the habitat quality for aquatic communities, which ultimately impacts the functions these communities provide. Disentangling the complex interaction between environmental and anthropogenic parameters as well as their alteration both along the stream channel, over the seasons, and finally their impact in the aquatic ecosystem represents a fundamental challenge for environmental scientists. Therefore, the present study investigates the implications of successive land uses (i.e., vineyard, urban area, highway and wastewater treatment plant (WWTP)) on structural and functional endpoints related to the ecosystem process of leaf litter breakdown during a winter and summer season in a five km stretch of a second-order stream in southern Germany. This sequence of the different land uses caused, among others, a downstream decline of the ecological status from "high" to "bad" judged based on the SPEARpesticides index together with significant shifts in the macroinvertebrate community composition, which coincided with substantial impairments (up to 100%) in the macroinvertebrate-mediated leaf decomposition. These effects, seem to be mainly driven by alterations in water quality rather than morphological modifications of the stream's habitat since the key shredder Gammarus was not in direct contact with the local habitat during in situ bioassays but showed similar response patterns than the other endpoints. While the relative effect size for most endpoints deviated considerably (sometimes above 2-fold) among seasons, the general response pattern pointed to reductions in energy supply for local and downstream communities. Although the present study focused on a single low-order stream with the main purpose of describing the impact of different land uses on various levels of biological organization, which limits the direct transferability and thus applicability of results to other stream ecosystems, the findings point to the need to develop adequate management strategies mitigating land use specific exposures during all seasons to protect ecosystem integrity.

Does the current fungicide risk assessment provide sufficient protection for key drivers in aquatic ecosystem functioning?

The level of protection provided by the present environmental risk assessment (ERA) of fungicides in the European Union for fungi is unknown. Therefore, we assessed the structural and functional implications of five fungicides with different modes of action (azoxystrobin, carbendazim, cyprodinil, quinoxyfen, and tebuconazole) individually and in mixture on communities of aquatic hyphomycetes. This is a polyphyletic group of fungi containing key drivers in the breakdown of leaf litter, governing both microbial leaf decomposition and the palatability of leaves for leaf-shredding macroinvertebrates. All fungicides impaired leaf palatability to the leaf-shredder Gammarus fossarum and caused structural changes in fungal communities. In addition, all compounds except for quinoxyfen altered microbial leaf decomposition. Our results suggest that the European Union's first-tier ERA provides sufficient protection for the tested fungicides, with the exception of tebuconazole and the mixture, while higher-tier ERA does not provide an adequate level of protection for fungicides in general. Therefore, our results show the need to incorporate aquatic fungi as well as their functions into ERA testing schemes to safeguard the integrity of aquatic 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, gammarid's 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 gammarid's 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.

Effects of municipal wastewater on aquatic ecosystem structure and function in the receiving stream.

During recent years, increasing incidences of summer droughts - likely driven by climate change - reduced the dilution potential of low-order streams for secondary treated wastewater also in temperate Europe. Despite the potential risks to ecosystem integrity, there is a paucity of knowledge regarding the effects of different wastewater dilution potentials on ecosystem functions. The present study investigated the implications of secondary treated wastewater released into a third-order stream (Queich, southwest Germany) during a season with low dilution potential (summer; ~90% wastewater) as compared to a season with high dilution potential (winter; ~35% wastewater) in terms of leaf litter decomposition and macroinvertebrate communities. Adverse effects in macroinvertebrate mediated leaf mass loss (~65%), gammarids' feeding rate (~80%), leaf associated fungal biomass (>40%) and shifts in macroinvertebrate community structure were apparent up to 100 and 300 m (partially 500 m) downstream of the wastewater treatment plant effluent during winter and summer, respectively. In addition, a Gammarus fossarum laboratory feeding trial demonstrated the potential of powdered activated carbon to reduce the ecotoxicity of released wastewater. These results urge the development and evaluation of adequate management strategies, e.g. the application of advanced wastewater treatment technologies, to protect the integrity of freshwater ecosystems, which is required by the European Water Framework Directive - also considering decreasing dilution potential of streams as projected by climate change scenarios.

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-TiO(2) 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.