Many contaminants found in surface waters are the residuals of pharmaceuticals and personal care products excreted from humans. The impact of these contaminants on benthic stream communities is not well understood, particularly their interactive effects. Two commonly detected pharmaceuticals are the anticonvulsant carbamazepine (CBZ) and the serotonin reuptake inhibitor fluoxetine (FLX). The community-level effects on freshwaters from chronic exposure to environmentally relevant concentrations of CBZ and FLX on macroinvertebrates collected from a headwater stream at Malcolm Knapp Research Forest in Maple Ridge, BC was investigated using 12.5 L of water and 2 L of gravel in 38 L microcosms to model in-stream conditions. Microcosms were treated with a single dose of 100 ng/L CBZ, 20 ng/L FLX, a combination of the two chemicals, or neither (n = per treatment). After 14 days of treatment, community composition of treatment groups was compared to the control and stream community composition. The chemicals tested resulted in significant changes in functional feeding groups between treatments. CBZ had a significant impact on %predators (CBZ p = 0.008; CBZ:FLX p = 0.01), The presence of CBZ alone decreased predator abundance (2.38 times lower than other treatments) while shredder abundance was greater. FLX alone showed a significant reduction in overall taxa abundance (p = 0.01), which may suggest detrimental consequence of FLX alone. Further experiments focusing on single taxa responses to exposure to CBZ and/or FLX will aid in explaining the differences between treatments observed in this study. It is possible that longer exposure to environmentally relevant concentrations of CBZ and FLX will result in significant differences in taxa responses, which may cause community shifts not observable during the duration of this experiment.
