Ionic Stress in Appalachian Headwater Streams Are Total Dissolved Solids Toxic?

1
Ionic Stress in Appalachian Headwater StreamsAre
Total Dissolved Solids Toxic?
Gregory J. Pond and Margaret E. Passmore, U.S.
EPA Region 3, Wheeling, WV 26003 Teresa
Norberg-King, U.S. EPA ORD, Duluth, MN
Background
Not an Acute Effect? Most Sensitive Life Stage?
Region 3 and our component states are currently
struggling to develop Total Maximum Daily Loads
(TMDLs) for total dissolved solids (TDS). The
toxicity testing literature indicates that
changes in the concentrations and types of major
cations and anions can be both acutely and
chronically toxic to aquatic life, in the absence
of any other toxicant. These tests are typically
conducted using synthetic salt solutions. Some
of these tests mimic the makeup of various types
of effluents, but lack other toxicants found in
the effluents. Adverse endpoints include death,
and effects on reproduction and growth. In the
southern coal fields of Region 3, where alkaline
coal mine drainage is common, TDS and/or elevated
conductivity have been identified as a primary
stressor to aquatic life in many
biologically-impaired streams. These streams are
naturally very dilute with conductivities
measured at lt 40 uS/cm. However, alkaline coal
mine drainage routinely increases conductivity to
500-2000 uS/cm due to increased mineralization of
the mine overburden on the mined areas and in
associated valley fills. The elevated
conductivity and ionic changes are thought to
interfere with normal osmoregulation in
invertebrates. Field studies of
macroinvertebrate communities from Kentucky,
Virginia, and West Virginia coal fields have
shown that conductivity explains the most
variance in commonly used benthic assessment
metrics. Because macroinvertebrates have evolved
in and are adapted to very dilute streams in the
region, ionic imbalance is a probable
physiological mechanism of impairment. Empirical
data from the West Virginia and Kentucky
coalfields suggest that 90-100 of
macroinvertebrate IBIs score below established
impairment thresholds (based on the reference
condition) when conductivity is greater than 500
uS/cm. Mayflies (Ephemeroptera) appear to be
highly sensitive to TDS in the region. Acute and
chronic endpoints of particular ions have been
established for commonly used test organisms such
as Ceriodaphnia however, few toxicological
studies have been carried out using sensitive
Appalachian macroinvertebrates. Furthermore, the
toxicity testing literature indicates No Observed
Effects Concentrations (NOECs) that are typically
23 times higher than the TDS thresholds
suggested by the empirical data. Our research
interests include testing organisms that are more
representative of the native Appalachian fauna,
taking into account various life stages,
temperatures, and other variables that may define
the critical exposures.
Indicator Species Analysis (Headwater/Spring
Season)
This analysis found many taxa significantly
related to high or low conductivity. The KY and
WV datasets yielded similar taxa lists, but some
differences were noted. The tables below are
sorted by highest Indicator Value (IV). Two
metrics were created from these lists and boxpots
showing their relation to conductivity are shown
below.
2006-2007 RARE Project

• Region 3 has been awarded a grant to work with
  ORD-Duluth and USGS to conduct laboratory
  experiments to determine toxicity of various ions
  or total dissolved solids to indigenous aquatic
  life.
• Research Objectives/Outcomes
• 1. A literature review of the bioassay research
  on TDS or conductivity.
• 2. An analysis and summary of available
  empirical datasets in Region 3 and surrounding
  states to develop empirical relationships between
  TDS/conductivity and the condition of aquatic
  life.
• 3. Bioassay results using synthetic salts that
  mimic typical southern Appalachian coal field
  ambient samples (but lack other potential
  stressors like Selenium) and several commonly
  cultured species to establish both acute and
  chronic endpoints (eg. LC50s, LOECs and NOECs).
  Longterm research objectives may include more
  relevant species of Appalachian mayflies,
  stoneflies and caddisflies , various life stages
  (e.g. nymphs and eggs), and various temperatures.
• Recommendations for defensible TDS/conductivity
  thresholds that would be protective of the
  typical Appalachian macroinvertebrate community.
• We have been also testing for metals associated
  with periphyton/ aufwuchs scrapings on rocks
  below valley fills to explore routes of exposure
  other than the water column. Many of the
  conductivity intolerant taxa are scrapers and
  eat the periphyton/aufwuchs.

Response to Conductivity (KY WV headwater
streams)
10th percentileimpairment threshold
High Conductivity
High Conductivity
CONCLUSIONS
WV EPT vs. Conductivity
It is obvious, from the empirical data, that
elevated conductivity has strong effects on
sensitive Appalachian benthic communities.
Although TDS may serve as a surrogate to actual
toxicants, it is logical to conclude that
conductivity can affect osmoregulation or cause
dehydration in freshwater taxa. However,
preliminary toxicity and growth (molting) tests
showed that sensitive Epeorus and Peltoperla were
not affected by mine effluent after a 6d exposure
period. Because these and other taxa are absent
from waters with high TDS, we think there are
chronic effects or toxicity to other life stages
(eggs, early instar nymphs). Moreover, there is
evidence that higher temperatures (e.g., 20 C)
causes lower toxicity thresholds in Isonychia
mayflies (Kennedy 2000). Thus, the effect of
temperature will be addressed in the future
rounds of bioassay tests.
10th percentileimpairment threshold