Dissipation of pesticides by stream biofilms is influenced by hydrological histories

Abstract

To evaluate the effects of hydr ological v aria bility on pesticide dissipation capacity by stream biofilms, we conducted a microcosm study. We exposed biofilms to short and frequent droughts (daily frequency), long and less frequent droughts (weekly frequency) and permanently immersed controls, prior to test their capacities to dissipate a cocktail of pesticides composed of tebuconazole, terbuthy- lazine, imidacloprid, glyphosate and its metabolite aminomethylphosphonic acid. A range of structural and functional descriptors of biofilms (algal and bacterial biomass, extracellular polymeric matrix (EPS) concentration, microbial respiration, phosphorus uptake and comm unity-lev el physiological pr ofiles) wer e measur ed to assess dr ought effects. In addition, v arious par ameters w er e measur ed to c har acterise the dynamics of pesticide dissipation b y biofilms in the different h ydr ological tr eatments (% dissipation, peak asym- metry, bioconcentration factor, among others). Results showed higher pesticide dissipation rates in biofilms exposed to short and fr equent dr oughts, despite of their low er biomass and EPS concentr ation, compar ed to biofilms in immersed contr ols or exposed to long and less frequent droughts. High accumulation of hydrophobic pesticides (tebuconazole and terbuthylazine) was measured in biofilms despite the short exposure time (few minutes) in our open-flow microcosm approach. This resear c h demonstr ated the stream biofilms capacity to adsorb hydrophobic pesticides even in stressed drought environments