Geographic and temporal distributions of agricultural pharmaceuticals measured in surface water at several locations in Grand River watershed in Southern Ontario, Canada showed 5 pharmaceuticals with pulses occurring between May and November at similar but varying times. Compared to species sensitivity distributions of acute toxicity values, pharmaceuticals detected in the surface waters presented small risks to aquatic organisms from acute effects. Effects on population and community responses in microcosms support the observation of low risk to the environment. In vitro bioassays of twelve pharmaceuticals on the arbuscular mycorrhizal fungi, Glomus intraradices grown on Daucus carota root organ cultures showed that, doxycycline, 17-α- ethinyl estradiol, and carbamazepine were selectively toxic to G. intraradices with 28-d EC50s less than 100 μg/L. Risks to plants and mycorrhizal fungi from estimated environmental concentrations were small.