17a-Estradiol limits the impact of ibuprofen upon community respiration by streambed biofilms in a sub-urban stream

Pharmaceuticals compounds such as the non-steroidal anti-inflammatory drug ibuprofen and the artificial estrogen 17a-estradiol are contaminants of emerging concern in freshwater systems. Globally, the use of these compounds is growing by around ~3 % per year, yet we know little about how interactions between different pharmaceuticals may affect aquatic ecosystems. Here we test how interactions between ibuprofen and 17a-estradiol affect the growth and community metabolism of streambed biofilms. We used contaminant exposure experiments to quantify how these compounds affected biofilm growth (biomass), respiration and gross primary production, both individually and in combination. Within our study, we found no effects of either ibuprofen or 17a-estradiol on biofilm biomass (using ash free dry mass as a proxy) or gross primary production. Ibuprofen significantly reduced biofilm respiration. However, concomitant exposure to 17a-estradiol counteracted the depressive effects ibuprofen upon biofilm metabolism. Our study, thus, demonstrates that interactions between pharmaceuticals in the environment may have complex effects upon microbial contributions to aquatic ecosystem functioning.