title: Effects of a triazole fungicide and a pyrethroid insecticide on the decomposition of leaves in the presence or absence of macroinvertebrate shredders.
abstract: Previously, laboratory experiments have revealed that freely diluted azole fungicides potentiate the direct toxic effect of pyrethroid insecticides on Daphnia magna. More ecologically relevant exposure scenarios where pesticides are adsorbed have not been addressed. In this study we exposed beech leaves (Fagus sylvatica) to the azole fungicide propiconazole (50 or 500 μg L(-1)), the pyrethroid insecticide alpha-cypermethrin (0.1 or 1 μg L(-1)) or any combination of the two for 3h. Exposed leaves were transferred to aquaria with or without an assemblage of macroinvertebrate shredders, and we studied treatment effects on rates of microbial leaf decomposition, microbial biomass (using C:N ratio as a surrogate measure) and macroinvertebrate shredding activity during 26 days post-exposure. Microbial leaf decomposition rates were significantly reduced in the propiconazole treatments, and the reduction in microbial activity was significantly correlated with loss of microbial biomass (increased C:N ratio). Macroinvertebrate shredding activity was significantly reduced in the alpha-cypermethrin treatments. In addition, the macroinvertebrate assemblage responded to the propiconazole treatments by increasing their consumption of leaf litter with lower microbial biomass, probably to compensate for the reduced nutritional quality of this leaf litter. We found no interaction between the two pesticides on macroinvertebrate shredding activity, using Independent Action as a reference model. In terms of microbial leaf decomposition rates, however, alpha-cypermethrin acted as an antagonist on propiconazole. Based on these results we emphasise the importance of considering indirect effects of pesticides in the risk assessment of surface water ecosystems.
authors.affiliation: Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark. Electronic address: jr@dmu.dk.
authors.forename: Jes Jessen
authors.initials: JJ
authors.lastname: Rasmussen
authors.affiliation: Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark; Department for Forest and Landscape, University of Copenhagen, Rolighedsvej 23, 1958 Frederiksberg C, Denmark.
authors.forename: Rikke Juul
authors.initials: RJ
authors.lastname: Monberg
authors.affiliation: Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark.
authors.forename: Annette
authors.initials: A
authors.lastname: Baattrup-Pedersen
authors.affiliation: Department of Basic Sciences and Environment, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Nina
authors.initials: N
authors.lastname: Cedergreen
authors.affiliation: Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Wiberg-Larsen
authors.affiliation: Department of Basic Sciences and Environment, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Bjarne
authors.initials: B
authors.lastname: Strobel
authors.affiliation: Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark.
authors.forename: Brian
authors.initials: B
authors.lastname: Kronvang
mesh_terms: D000818:Animals; D018533:Biomass; D029964:Fagus / Q000187:drug effects / Q000378:metabolism; D005659:Fungicides, Industrial / Q000633:toxicity*; D007448:Invertebrates / Q000378:metabolism*; D007700:Kinetics; D010575:Pesticides / Q000633:toxicity*; D018515:Plant Leaves / Q000187:drug effects* / Q000378:metabolism; D011722:Pyrethrins / Q000633:toxicity*; D014230:Triazoles / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D005659:Fungicides, Industrial; D010575:Pesticides; D011722:Pyrethrins; D014230:Triazoles; D014874:Water Pollutants, Chemical; C045950:propiconazole; C017160:cypermethrin