Toxicity of heavy metals to aquatic life in mountain streams

The Colorado Water Quality Control Commission estimates that over 2080 km of streams in Colorado are impacted by metals. The Colorado Division of Wildlife Aquatic Toxicology Laboratory has studied the effects of metals on aquatic organisms for over 35 years. Early investigations focused on the effects of metals on salmonids which led to the development of numeric hardness-based metal standards for the protection of aquatic life in Colorado. Colorado is the first state to implement numeric metal standards.

About our Aquatic Toxicology Laboratory:

The laboratory utilizes an onsite well, dechlorinated municipal tap water and water purified by reverse osmosis for toxicology tests. By mixing these waters, toxicity tests can be conducted over a wide range of water quality conditions.

Laboratory toxicity tests use continuous flow-through diluters to deliver a gradient of concentrations to test organisms.

Larval and juvenile trout are frequently used as test organisms because these species and life stages are very sensitive to the effects of metals. The Division of Wildlife is one of the few laboratories that conduct tests using brown trout, which are an important fish species in Colorado headwaters where metal contamination from abandoned mines can impact aquatic communities.

Test organisms also include other sensitive species that indicate the health of aquatic ecosystems such as mottled sculpin and mayflies.

Recent Laboratory Studies on Heavy Metals toxicity:

• Effects of water hardness on toxicity of cadmium and zinc to early life stage and juvenile brown trout
  
• Acclimation and deacclimation of brown trout to cadmium, copper, zinc and their mixtures
  
• Toxicity of zinc to mottled sculpin at different levels of water hardness
  
• Toxicity of zinc, copper and cadmium to the mayflies Rhithrogena hageni, Baetis tricaudatus, and Drunella doddsi (ongoing)
  

Field Studies Documenting Recovery of Aquatic Life from Metals Impacts:

In addition to laboratory studies, the toxicology laboratory has been monitoring water quality and the fish community in the upper Arkansas River since 1994. Water samples and fish are sampled from several sites on the Arkansas River and major tributaries. Water samples are analyzed for metals at the laboratory. Fish are captured, counted, weighed, marked with a fluorescent dye, and then released. Remediation of historic mining sites has improved water quality in the upper Arkansas River resulting in dramatic improvement of fish populations.

We are currently exploring how heavy metals pollution interacts with natural variation in streamflow to impact trout populations in several mine-impacted rivers of Colorado, including the Eagle River near Minturn and the Arkansas River near Leadville. Results of this study will be used to explore the utility of using biocriteria to determine protective water quality standards for these rivers.

Impacts of reduced water quality on native plains fish communities

Great Plains fishes in river basins of eastern Colorado have been declining and many are now listed as threatened or endangered, including the Common Shiner, Brassy Minnow, Arkansas Darter, Stonecat, and others (go to http://ndis.nrel.colostate.edu/wildlife.asp to learn more about native Plains fishes). Several factors have been identified as contributing to declines of Plains fishes, including altered flow regimes through diversions and impoundments, predation by non-native fish, channelization and simplification of riverbeds, and general loss of habitat. Reduced water quality from increased urbanization and intense agricultural use likely contribute to population declines, however, the impacts of chemical stressors have not been well studied. We are investigating the impacts of two prominent urban and agricultural stressors, ammonia and endocrine disrupting chemicals, on native Plains fish species.

Toxicity Studies:

In 2006-2007, CDOW will conduct laboratory toxicity tests to investigate the effects of ammonia and endocrine disrupting chemicals on several listed fish species, including the Arkansas Darter, Central Stoneroller, Common Shiner and Red Shiner. We are also collaborating with researchers from Colorado State University, University of Colorado, and USGS to specifically address how endocrine disruptors influence mating behavior, sex ratios and gonadal development of several Plains fish species.

Arkansas Darter

Central Stoneroller

Common Shiner

Red Shiner

Endocrine disrupting chemical elicits reproductive failure in red shiners

Endocrine disrupting compounds (EDCs) are prevalent in aquatic ecosystems worldwide and can lead to developmental and reproductive problems in fishes. Concern exists regarding how exposure to EDCs may be contributing to declines in Great Plains fishes in eastern Colorado.  We conducted a study using the red shiner as a model organism to examine how estrogenic EDCs might adversely affect Plains fish populations.  Male red shiners were exposed to 17β-estradiol (estradiol), a natural estrogen found in wastewater effluent.  Our objectives were to characterize the effects of estradiol exposure on morphometric and behavioral reproductive traits of males, to investigate changes in female mate choice, and to determine whether estradiol exposure reduces fecundity.  We also measured reversibility in these reproductive responses when exposures were discontinued.  For this purpose, adult males were exposed to nominal concentrations of 120 ngL-1 estradiol, 2.4 ngL-1 estradiol, a solvent control, or a water control for at least one month.  Exposures to the highest estradiol concentration resulted in alterations in plasma vitellogenin concentrations, changes in gonadal tissues, and inhibition of mating coloration and tubercles.  Furthermore, mating behaviors were altered and reproductive success was reduced; exposed males fertilized fewer eggs and produced no viable progeny.  All reproductive endpoints improved when males were removed from the estradiol treatment and allowed to mate in control water.  Estradiol had significant adverse effects on adult male red shiners, indicating that wild populations may have low reproductive success if they are chronically exposed to estrogenic compounds in the field.

Michelle M. McGree
Department of Fish, Wildlife, and Conservation Biology
Colorado State University
Fort Collins, CO 80523
Spring 2008

Read McGree's Thesis for more information.

Field Studies:

CDOW is conducting research to determine effects of urban and agricultural contaminants on Plains fish communities. This effort will include a multivariate analysis of native fish distributions in the South Platte and Arkansas River basins in relation to water quality in those basins. Results from our research will assist with identifying potential causes for the decline of native fish in Colorado and help with development of management, conservation and recovery plans.