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.

No abstract

Ecosystem functions in streams (e.g., microbially mediated leaf litter breakdown) are threatened globally by the predicted agricultural intensification and its expansion into pristine areas, which is associated with increasing use of fertilizers and pesticides. However, the ecological consequences may depend on the disturbance history of microbial communities. To test this, we assessed the effects of fungicides and nutrients (four levels each) on the structural and functional resilience of leafassociated microbial communities with differing disturbance histories (pristine vs.previously disturbed) in a 2 9 4 9 4-factorial design (n = 6) over 21 days. Microbial leaf breakdown was assessed as a functional variable, whereas structural changes were characterized by the fungal community composition, species richness, biomass, and other factors. Leaf breakdown by the pristine microbial community was reduced by up to 30% upon fungicide exposure compared with controls, whereas the previously disturbed microbial community increased leaf breakdown by up to 85%. This significant difference in the functional response increased in magnitude with increasing nutrient concentrations. A pollution-induced community tolerance in the previously disturbed microbial community, which was dominated by a few species with high breakdown efficacies, may explain the maintained function under stress.Hence, the global pressure on pristine ecosystems by agricultural expansion is expected to cause a modification in the structure and function of heterotrophic microbial communities, with microbially mediated leaf litter breakdown likely becoming more stable over time as a consequence of fungal community adaptions. . One billion hectares of these natural ecosystems is predicted to be lost to agricultural production between 2000 and 2050(Tilman et al., 2001, driven by the doubling of the global food demand (Godfray et al., 2010). These modifications in land use are accompanied by a 2.4-to 2.7-fold increase in nutrient (fertilizers) and pesticide contamination in these regionsThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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.