Conductivity and Selenium–Laboratory Approaches to Understanding the Impacts of Chemical Stressors Released From Mountaintop Mining/Valley Fill on Aquatic Insects

EPA Grant Number: FP917322
Title: Conductivity and Selenium–Laboratory Approaches to Understanding the Impacts of Chemical Stressors Released From Mountaintop Mining/Valley Fill on Aquatic Insects
Investigators: Conley, Justin M
Institution: North Carolina State University
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Pesticides and Toxic Substances


Mountaintop removal-valley fill coal mining practices bury headwater streams and significantly change water chemistry in downstream reaches. It is unclear which contaminants are most responsible for observed ecological damage (dramatic reductions in aquatic insect abundance and diversity); however, elevated concentrations of selenium and total dissolved solids (as measured by specific conductance) are strongly correlated with ecological effects in the field. Little is known about how these contaminants affect aquatic insects, as laboratory data presently are limited. This research program will assess the potential toxicity of elevated selenium and specific conductance (individually and jointly) to aquatic insects by using a laboratory-based periphyton-mayfly test system.


To assess the toxicity of elevated selenium and total dissolved solids, a representative mayfly (Centroptilum triangulifer) will be used in controlled laboratory exposures conducted at environmentally relevant exposure levels and through ecologically relevant exposure pathways. C. triangulifer will be exposed in full life-cycle assays to a range of selenium contaminated periphyton diets and to waters with a range of conductivities that mimic the ionic composition of valley fill impacted streams. A combined experiment will determine if exposure to both dietary selenium and high total dissolved solids produces an increased toxic response, or if one of these stressors is the primary driver of toxic effects. This research further will seek to characterize the uptake kinetics of different inorganic selenium species into periphyton as well as identify the individual ions in high TDS waters that are most toxic to mayflies.

Expected Results:

The expected outcome of this research program will be a much more environmentally relevant understanding of the toxic effects exerted by selenium and high total dissolved solids on aquatic insects, which currently are unknown. Characterization of selenium toxicity will be leveraged with experiments designed to describe the bioavailability of selenite versus selenate to primary producers, which dictate the bioaccumulation of selenium in food webs. Further, it is unknown whether any particular anion or cation in valley fill impacted streams is particularly toxic or whether the full assortment of ions present is necessary to produce effects. This research program will seek to clarify these uncertainties.

Potential to Further Environmental/ Human Health Protection

The focus of this research program is on aquatic macroinvertebrates, which are sentinels of water quality and aquatic ecosystem health. Recent research has shown a direct link between the health of these systems and cancer rates in residents of the Central Appalachians. This is a socio-economically depressed region and many consider mountaintop removal to be an environmental justice issue. By providing additional support to EPA administrators to set scientifically defensible water quality standards for specific conductance and Se, environmental improvements in water quality may potentially lead to improvements in human health in the area. Nationally, the EPA has for years been attempting to implement an updated Se standard. This research will fill significant data gaps in the science of understanding how Se moves through aquatic food webs towards upper trophic level organisms such as fish. Further, the issue of salinization of freshwater is a global issue with the encroachment of marine waters due to sea level rise, the extraction of natural gas from Marcellus shale brines, and evaporation of inland waters from climate change. Understanding the toxicity of specific ions to a representative sensitive aquatic insect will bolster the greater scientific understanding of how conductivity perturbs natural systems and aids in improving water quality globally.

Supplemental Keywords:

mountaintop removal, valley fill, coal mining, selenium, total dissolved solids, conductivity, mayfly, insect, toxicity

Progress and Final Reports:

  • 2012
  • 2013
  • Final