Environmental concentrations of pharmaceuticals alter metabolism, denitrification, and diatom assemblages in artificial streams

Our understanding of the effects of pharmaceuticals on key biogeochemical processes and biofilm assemblage composition in surface waters is limited despite the prevalence of ng/L to lg/L concentrations of these compounds. We examined the effects of 3 commonly-prescribed pharmaceuticals: ciprofloxacin (140 ng/L), diphenhydramine (300 ng/L), and fluoxetine (20 ng/L); both individually and as a mixture, on key ecosystem processes at environmentally-realistic concentrations. We used mesocosms to expose naturally-occurring biofilm communities and artificial benthic substrates to these pharmaceuticals and measured the effects of exposure on biofilm, seston, and sediment communities. Established biofilm functions were unaffected by pharmaceutical treatments. However, successional biofilms experienced 42 to 81% reductions in primary production and 59 to 83% reductions in community respiration. Denitrification in sediment communities was reduced by 41 to 73% in shaded conditions, but was not affected when left in ambient light. Diatom assemblage structure was unaffected by pharmaceuticals in successional biofilms, whereas the composition of established biofilm assemblages changed with exposure to treatments that contained ciprofloxacin, diphenhydramine, and all 3 pharmaceuticals. Our study adds to a growing body of evidence indicating that chronic exposure to sub-lethal concentrations of pharmaceuticals may substantially alter key ecosystem processes and communities.