LAUSR

ABSTRACT Pharmaceuticals and personal care products (PPCPs) are a contaminant class of worldwide concern and a potential source of global change. To better understand the impact of low levels of PPCPs on stream biofilm structure and function, we conducted laboratory mesocosm experiments in which biofilms cultivated in streams draining areas of different land use (natural, agricultural, and urban) were exposed to low levels (5 µg L−1) of several common pharmaceuticals. We performed several functional assays and assessed differences in biofilm bacterial community composition among pharmaceutical treatments and streams. Pharmaceutical treatments altered the functional capacity and diversity of biofilms, but had no significant effect on carbon uptake or photosynthetic potential. Biofilm bacterial communities differed with land use, and pharmaceutical treatments decreased the relative abundances of Alcanivorax and Halioglobus and increased the relative abundance of Pseudomonas, indicating a shift to more drug-tolerant groups. Overall, our results provide evidence that PPCPs may act as ecological disruptors even at low levels, altering biofilm structure and some aspects of ecosystem function, and potentially influencing important biogeochemical processes in streams.