Environmental Health - Toxic Substances Hydrology Program
U.S. Geological Survey (USGS) scientists have developed a new approach for evaluating the toxicity of metals to fish in streams when the chemistry fluctuates on a daily cycle. The approach intergrates innovative field water-quality sampling, computer simulation models, and data on the toxicity of metals to cutthroat trout.
Previous work by USGS scientists and their colleagues has shown that metal concentrations in streams typically exhibit substantial and systematic daily variation (diel cycles). This varation makes evaluating water quality and the health of aquatic organisms challenging. To help understand how to evaluate environmental health in these dynamic streams, USGS scientists conducted field studies in two Montana streams affected by historical metal contamination–Silver Bow Creek in southwestern Montana, and High Ore Creek north of Butte, Montana. To understand the timing of metal exposure, water–quality samples were collected using traditional methods (to represent instantaneous conditions) and also using a type of water-quality sampler called a DGT (Diffusive Gradients in Thin Films) sampler. DGT samplers accumulate contaminants by diffusion through a thin film to represent time–integrated water–quality conditions. Water compositions determined from both types of samples were evaluated using computer models of the water chemistry in the streams and then combined with previously collected toxicity data on cutthroat trout. The scientists were then able to derive a relationship that predicts the relative survivability of these fish at a given location in a stream.
This approach provides way to overcome a new challenge to toxicity of metals to aquatic organisms in streams – substantial natural daily fluctuations in water chemistry. The approach provides a linkage among water chemistry, exposure time, and biological response; it has the potential for use by water and wildlife resource managers to assess the impact of metal contamination in areas of historical mining.
Balistrieri, L.S., Nimick, D.A., and Mebane, C.A., 2012, Assessing time-integrated dissolved concentrations and predicting toxicity of metals during diel cycling in streams: Science of the Total Environment, v. 425, p. 155–168, doi:10.1016/j.scitotenv.2012.03.008.