Pharmaceuticals are biologically active organic contaminants frequently detected in aquatic ecosystems. There are multiple pathways for pharmaceuticals to reach aquatic ecosystems, such as human waste-water following excretion, incorrect disposal, manufacturing waste and agricultural runoff. These compounds can be incorporated by aquatic biota and may have a variety of direct and indirect effects on aquatic ecosystem functions including respiration, primary production and nutrient cycling. Recent research has demonstrated that environmentally relevant concentrations (ng L-1) of individual pharmaceuticals can inhibit these functions in aquatic biota. However, the effects of an environmentally-relevant pharmaceutical mixture on whole-ecosystem structure and functioning is largely unknown.
Our research examines the effects of an environmentally relevant pharmaceutical mixture on whole-ecosystem endpoints in artificial streams under both open and shaded canopy conditions.
We colonised 60 L fibreglass artificial streams with leaf packs, rocks and sediment balls which had been incubated in a nearby forested stream. We shaded half of the artificial streams with shade cloth to reduce incident light by ~60%. Half of both sets of streams were then dosed with a pharmaceutical mixture throughout the three week experiment. Primary production, respiration, microbial biomass and denitrification were quantified.
Results/Conclusions
We predicted that pharmaceuticals would inhibit endpoints in both open and shaded streams, albeit to different degrees. However, most endpoints tested exhibited no significant changes. This lack of an effect may be due to the oligotrophic conditions within the stream, meaning that stream were already under stress and thus the impact of pharmaceutical stressors was limited. The lack of response may also be due to antagonistic interactions of the mixture of pharmaceuticals lowering the cumulative effects below what would be expected from individual compounds. Despite these factors, some significant effects of pharmaceuticals on ecosystem endpoints were observed. Seston biomass was supressed by 33% in shaded streams and 34% in open streams on day 6 of the experiment, while seston community respiration efficiency was increased by 31% in shaded streams and 46% in open streams (in streams dosed with the pharmaceutical mixture). Pharmaceutical treatment increased denitrification potentials by up to 45% in sediment balls on day 19 of the experiment. nMDS ordination of algal pigments determined from HPLC indicated that both pharmaceuticals and canopy cover caused differences in algal pigment variability. This research indicates that pharmaceutical mixtures can have subtle, sub-lethal effects on ecosystem structure and function.