Ambient
Toxicity Assessments of Clark Fork River Water-Toxicity Tests
and Metals Residues in Brown Trout Organs
Glenn
Phillips and Ron Spoon
Montana Department of Fish, Wildlife and Parks
Abstract:
Trout population densities decline dramatically in the Clark Fork River
from nearly 2,000 catchable brown trout per mile just downstream of mine waste
settling ponds to 50 trout Instream toxicity tests (1986-89), and analyses of
metals infish organs (1989) were conducted in various river reaches to try to
understand how metals influence trout density patterns.
Instream toxicity tests with swim-up stage rainbow trout
fry demonstrate that river water induces chronic mortality during spring
runoff when metals concentration, particularly copper, exceed chronic criteria
for protection of aquatic life. Concentration of copper in livers of adult
brown trout (salmo trutta) are higher than those in laboratory fish
populations exposed for several generations to chronically toxic
concentrations of copper. Both acute and chronic stress from metals,
particularly copper, are implicated as contributing to poor fish production in
the Clark Fork.
INTRODUCTION
Fish kills have occurred frequently in the upper Clark Fork River over the
last several years. Six were documented between 1983 and 1989-some killing
several thousand fish. Kills occur during high intensity summer thunderstorms
that flush metals sails accumulated on the surface of streamside mine tailings
into the river. Tailings are rich in cadmium, copper, zinc, arsenic, iron and
other metals.
During late winter and spring, concentrations of metals
(particularly copper) in the Clark Fork frequently exceed criteria for
protection of freshwater aquatic life (USEPA 1985). Fish kills have not been
documented during these events but they may chronically stress trout
populations by causing toxicity to sensitive early life stages -occurrences
that could cagily go unnoticed.
To evaluate effects on early life stages, we conducted
instream toxicity tests using fry and fingerling rainbow trout (1986-89) and
measured concentrations of metals in brown trout organs (1989). Data were
collected in the Clark Fork drainage between Anaconda and Clinton to gain a
better understanding of factors influencing the distribution and abundance of
brown trout in this segment of the river.
METHODS AND
MATERIALS
Toxicity Tests Beginning in 1986, in stream toxicity tests were conducted in
the Clark Fork River for four consecutive years. Tests included at least six
sites and up Lo nine sites including one or two control sites (Figure 1).
Fingerling rainbow trout were tested during 1986 and 1987 and swim-up stage
fry were tested from 1987-1989. All test fish were the progeny of Eagle Lake
brood stock obtained from the Creston National Fish Hatchery. U.S. Fish and
Wildlife Service. Creston. Montana.
Tests began in early to mid-April and continued through
spring runoff - terminating in early July fish were kept in cube-shaped
vessels, approximately 30 cm on a side, constructed with a wooden frame
covered with 3 mesh nylon netting. Vessels were suspended with floats,
tethered to a fence post and positioned in low velocity areas near the edge of
the current -typical rearing areas for young fish. The fry test containers
were equipped with an automatic feeding device (Sweeney Enterprises Inc.
Bourne, TX 78006) that included a timer, rheostat and battery.
Equipment was calibrated so that fry were fed commercial
trout food four times daily; fingerlings were not fed during the tests. Tests
included 40 fingerlings or 100 fry per vessel. Two vessels per site were used
during fingerling tests.
Mortality was monitored three times weekly and alkalinity,
hardness and pH were measured in the field each week (Table
1). Additionally,
water samples were collected three Limes each week and analyzed for total
recoverable, copper and zinc. A pair wise multiple comparison technique was
used to determine if mortality in the mainstem was statistically different
from the control site (Fleiss 1981).
Metals in fish organ
During April 1989, brown trout were sampled from five locations along the
Clark Fork River and one location in Rock Creek. Sampling sites included
reaches near Warm Springs, Sager Lane, Deer Lodge, Gold Creek and Beavertail.
Rock Creek was sampled approximately two miles upstream from its mouth as a
control site (Figure 1).
Approximately 30 adult brown trout were sampled from each
site. Trout were weighed, measured and sacrificed in the field and liver,
kidney and gill tissue were dissected, placed in glass containers and iced;
tissues were frozen later the same day. At a given site, fish were
intentionally selected to include a range of sizes. Mean lengths (mm) of fish
sampled were: Warm Springs -328, Sager Lane -334, Deer Lodge -358, Gold Creek
-324, Beaverk1il -331 and Rock Creek 372.
Prior to analyses, frozen tissues were vacuum freezed dried in a lyophilizer. Freeze dried tissues were microwave digested in concentrated nitric acid and analyzed for copper, cadmium and zinc using either induction coupled "plasma spectrophotometry or graphite furnace atomic absorption spectrophotometry. Quality control measures included analyses of duplicates, spikes, and reference materials (EPA fish samples and NBS bovine liver). The instrument was calibrated initially and recalibrated after every twenty samples using three reference standards and a blank. Each calibration was cross-checked with an EPA reference water sample.
RESULTS &
DISCUSSION
During all four years of testing, mortality was observed In Silver Bow Creek
and at several Clark Fork River sites that was significantly higher
(P<0.05) than at control sites (Table
2). Mortality in Silver Bow Creek was
at or near 100 percent during all four years of testing and was associated
with extremely high concentrations of copper and zinc.
In some instances high mortality corresponded with low fish
population densities. For example, the Beavertail section, where significant
mortality occurred each year, supports less than fifty catchable brown trout
per mile -the lowest trout density in the Clark Fork River (Johnson and
Schmidt 1988). Similarly the Silver Bow Creek site, where mortality was nearly
complete is unable to support trout. Comparatively, mortality at the Clinton
site, downstream of the confluence with Rock Creek, was not statistically
different from the control- reflective of lower metals concentrations
downstream of Rock Creek (Table 2).
High mortality in the Gold Creek section observed during
1987 was associated with a local thunderstorm that apparently washed mine
wastes into the river. Most of the mortality occurred the day of the
thunderstorm and coincided with a local fish kill in the table 2rnble 2briver.
Water monitoring conducted the day after the storm was too late to detect
elevated concentrations of metals.
Several investigators have evaluated the toxicity of river
water in the Clark Fork drainage (Table
3) and have observed mortality.
Bionomics (1979) tested the toxicity of water discharged from Warm Springs
Pond-2 to early life stages of rainbow trout (eggs and fry) and to Daphnia
middendorffiana -a native daphnid. Rainbow trout survival and hatchability
were not reduced by exposure to pond water but all fry, including those
exposed to dilutions of 50 and 75% pond water, experienced reduced growth.
Copper and zinc concentrations in a 50% dilution of pond-2 watertable 3
averaged 25 and 65 ug/l, respectively. Additionally, Daphnia middendorffiana
reproduction was significantly impaired by exposure to 100% pond water but not
by exposure to 50% pond water (Bionomics 1979). Copper and zinc concentrations
in 100% pond water were 33 and 77 ug/l, respectively. Identical tests with
Daphnia magna produced a similar result (Bionomics 1978); numbers of young per
female were reduced by exposure to 27 ug Cull and 31 ug Zn/l (measured as
total recoverable).
Janik and Melancon (1982), during a site-specific water
quality assessment of Silver Bow Creek and the upper Clark Fork, completed a
few bioassay tests with Daphnia and bluegill. In these tests Daphnia were not
adversely affected by Clark Fork River water nor was ventilation rate in
bluegill. However, bluegill in Clark Fork River water showed evidence of
acetylcholinesterase inhibition. Total and dissolved copper and zinc
concentrations during the survey averaged 30 and 22 ug Cu/1 and 101 and91
ug Zn/l; the report did not include specific information on metal
concentrations that were present in the bioassay water.
Parrish and Rodriguez (1985) tested the chronic toxicity of
Clark Fork River water in the Deer Lodge vicinity to early life stages of
rainbow trout including separate tests using green eggs, eyed eggs, and
fingerlings. Tests were conducted in May and early June to coincide with run
off, however, unusually dry spring conditions resulted in lower than normal
streamflows and concomitantly low metals concentrations. Percent mortality of
both eyed eggs and fingerlings were higher in 100% Clark Fork River water that
in various dilutions of Clark Fork River water but results were not
conclusive. During the test, acid soluble copper concentrations ranged from
10- 78 ug/l. For the water hardnesses that were present, EPA chronic and acute
criteria for copper were calculated to be approximately 20 and 31 ug/1
respectively. It is noteworthy that most of the mortality occurred during the
last week of the tests when copper concentrations exceeded the acute criteria
(when the weekly average concentration reached 7R ug Cu/l).
Concentrations of copper and zinc measured in previous
tests where mortality occurred are similar to those measured during our tests
{Table 2). Plausibly, copper is present in much of the Clark Fork during most
years at concentrations that affect larval survival but not adults. Unpolluted
tributaries and possibly springs that upwell in the mainstem may be necessary
for recruitment to the population. Additional work is needed to identify
spawning areas and spawning success in the Clark Fork.
Metals in Fish Organs
Cadmium, copper and zinc residues found in kidney, liver and gill of adult
brown trout collected from various reaches of the Clark Fork River and Rock
Creek are summarized in Figures 2-4. All metals concentrations are expressed
on a dry weight basis.
Cadmium
Laboratory toxicity tests show that brook trout accumulate cadmium in liver,
kidney, and gill and that residues increase with exposure concentration
(Benoit et al. 1976). All tissues reached an equilibrium after approximately
20 weeks of exposure to cadmium.
The concentration of cadmium in organs of Clark Fork brown
trout decreased from upstream to downstream. Cadmium concentrations in liver
and kidney were higher than published reports of background concentrations
(Benoit et al. 1976) but lower than those measured in brook trout exposed in
the laboratory for 39 weeks (Benoit et al. 1976) to cadmium concentrations
that were just above the chronic toxicity threshold of 3.4 ug Cd/1. Cadmium in
gill was near or below reported background concentrations at all sites. Data
suggest that Clark Fork River brown trout are exposed to cadmium
concentrations that are above background but lower than required to elicit
chronic toxicity. Concentrations of cadmium measured in the gills of Clark
Fork fish which died during fish kills also indicate that cadmium is not as
important as copper and zinc during acute toxicity events in the Clark Fork
(Phillips 1985).
Zinc
Zinc concentrations in organs of Clark Fork River fish were similar at all
sites sampled including the control site in Rock Creek (Figure
3).
Concentrations in kidney and gill were higher and in liver similar to
concentrations reported as baseline for rainbow trout (Goettl et al. 1971).
Mount (1964) showed that the concentration of zinc in gill and kidney
increased with exposure concentration but liver did not accumulate zinc. This
may account for zinc concentrations in livers of Clark Fork fish being near
reported background concentrations.
Water monitoring of Clark Fork River water conducted by the
Water Quality Bureau (Gary Ingman, unpublished data) indicate that water
quality criteria for zinc are only occasionally exceeded. Although zinc is
present at high concentrations during fish kills and may contribute to acute
mortality, residues of zinc in organs are not indicative of exposure to
concentrations of zinc that would be cxpcc1cd 10 be chronically toxic.
Copper
Benoit (1975) observed that fish begin to accumulate copper in organs when
exposed to concentrations at and above the chronic toxicity threshold,
suggesting that any accumulation of copper may be indicative of exposure Lo
chronically toxic concentrations. Liver has a tendency to retain accumulated
copper (Solbe and Cooper 1976) thus liver residues of copper may be an index
of chronic exposure to low concentrations.
Copper concentrations in liver and gill of Clark Fork fish
were highest near Warm Springs and decreased downstream (Figure
4). Kidney
copper concentrations were similar at all sites including the Rock Creek
control site. Concentrations in liver were extremely high at all Clark Fork
sites with average concentrations as high as 1663 ug/g at Warm Springs and]
517 ug/g at Sager Lane. These concentrations are much higher than those
reported as background (McKim and Benoit 1974) and exceed by several-fold
concentrations found in laboratory fish populations experiencing chronic
toxicity due to copper (Benoit 1975). Rainbow trout exposed to 59ug Cu/l for
107 weeks accumulated a maximum concentration in Jiverof738 ug Cu/g (Goettl et
al. )(1974). Bluegill exposed for 24 months to f62 ug Cu/l in water averaged
480 ug Cu/g in their livers. This concentration in water caused reduced
survival, growth, and spawning success in adult bluegill. Concentrations in
water as low 3S 40 ug Cu/l caused reduced surviva1 in larval bluegill.
Concentrations of copper in gill also exceeded those in
gills of fish suffering from chronic copper toxicity (Benoit 1975). Solbe and
Cooper (1976) found that fish eliminate copper rapidly from gill after return
to copper free water. The high concentration of copper in gill from trout
collected from the Clark Fork near Warm Springs indicate that they were being
exposed to copper at the time they were collected. Indeed, copper
concentrations in water were high near Warm Springs immediately before trout
were collected for organ testing (Gary Ingman, unpublished data).
Results indicate that Clark Fork brown trout are exposed to
large amounts of bioavailable copper. While there is no direct evidence that
adult trout were adversely affected, residues of copper in liver are
indicative of exposure to concentrations that have proven to be chronically
toxic to sensitive life stages of fishes including salmonids.