Predicting the toxicity of permethrin to Daphnia magna in water using SPME fibers.

Multiple factors can influence bioavailability, which can make predictions of toxicity in natural systems difficult. The current study examined the potential use of solid-phase microextraction fibers as a matrix-independent approach to predict the toxicity of permethrin to Daphnia magna across various water sources, including a laboratory reconstituted water, two natural waters, and a modified natural water. Water source strongly affected the toxicity of permethrin as well as the concentration-response relationships. Although permethrin concentrations in the water were predictive of toxicity to D. magna for individual water sources, there was no relationship between permethrin concentrations among water sources and mortality. This indicated that compositional differences among water sources can greatly influence toxicity, suggesting that benchmarks established using reconstituted water may be overly conservative for some natural waters. In addition, although permethrin tissue residues were predictive of mortality for individual waters, the correlation among waters was not as clear. Finally, both 48-h and equilibrium-based SPME fiber concentrations adequately predicted toxicity independent of water properties. This demonstrated that bioavailability-based estimates provided a more accurate prediction of toxicity than water concentrations and that SPME fibers could be used in environmental monitoring as a rapid and accurate means of predicting toxicity in natural waters.

Distribution of nonprescription pharmaceuticals in central Indiana streams and effects on sediment microbial activity.

Since the discovery of trace concentrations of pharmaceuticals in streams and treated drinking water around the world, a call has been made by both the scientific community and the general public to increase understanding of the potential effects these compounds may have on freshwater integrity. We measured abundance and distribution of pharmaceuticals in headwater streams across the Upper White River Watershed of central Indiana. Four nonprescription pharmaceuticals (1,7-dimethylxanthine, caffeine metabolite; acetaminophen; caffeine; cotinine, nicotine metabolite) were found at one or more sites with mean concentrations of 0.038, 0.109, 0.057 and 0.041 µg/l, respectively. Caffeine was measured at trace concentrations at all sites sampled. Higher pharmaceutical concentrations were associated with streams having >90% agricultural land use in the sub watershed, suggesting that nonpoint sources, such as septic tanks, may contribute to stream pharmaceutical contamination. To assess the influence of these pharmaceuticals on stream microbial activity, we measured changes in sediment respiration and nutrient uptake in response to pharmaceuticals using both in vitro and in situ techniques. For in vitro experiments, respiration rates were not significantly different from controls with pharmaceutical exposure. However, net NO(3) (-)-N uptake increased significantly with nicotine concentrations. Net NH(4)(+)-N uptake was reduced in response to caffeine and nicotine exposure. In situ experiments indicated nicotine exposure increased microbial respiration. Our data show pharmaceuticals are ubiquitous in headwater streams of central Indiana and likely influence stream microbial activity depending on the pharmaceutical compound and history of exposure.