Pharmaceuticals enter freshwater ecosystems via multiple sources including disposal of surplus drugs, human
excretion into sewage, and runoff associated with therapeutic treatment of livestock. Previous studies consistently
demonstrate the prevalence of pharmaceuticals in freshwater but we do not yet know how concentrations vary
over time within a given system. Two sites in central Indiana with varying land use in the surrounding watershed
were sampled monthly for pharmaceutical concentrations and stream physiochemical parameters. Sediment
samples were also collected at each sampling event for measurement of 15N content.
Results/Conclusions
Significant differences in pharmaceutical compounds detected and total concentrations were identified both
between sites (spatial variation) and within each site (temporal variation). Pharmaceutical compounds detected
included acetaminophen (2.1-460 ng/L), carbamazepine (1.1-2.7 ng/L), caffeine (11-400 ng/L), cotinine (2.1-12
ng/L), DEET (23-150 ng/L), gemfibrozil (1.2-4.9 ng/L), ibuprofen (1.8-42 ng/L), sulfamethoxazole (1.4-15 ng/L),
sulfamethazine (1.8 ng/L), triclosan (9.1-22 ng/L), and trimethoprim (3-9.7 ng/L). Across sites, water column
dissolved oxygen correlated with caffeine (p=0.026), carbamazepine (p=0.006), cotinine (p=0.026), and
sulfamethoxazole (p=0.056) concentrations. Overall, total pharmaceutical concentrations within the agriculturally
influenced site were highest in winter whereas the urban site had the highest in summer. Pharmaceuticals present
in freshwater may not only affect aquatic organisms, but may also enter drinking water intakes resulting in
unintentional consumption by humans. A more comprehensive understanding of spatial and temporal variability of
these contaminants is needed to mitigate potential effects.