Page 807 - The Toxicology of Fishes

Mining Impacts on Fish in the Clark Fork River, Montana: A Field Ecotoxicology Case Study 787

115° 114° 113° 112°

48° Removal of tailings
Berms installed
In situ treatment of tailings
Streambank stabilization
Recipient stations Donor stations
Kilometers
190 180 160 140 120 100 90 80 70 60 50 40 30 20 10 0 downstream

Clark
Fork Blackfoot River
47°
Milltown
Dam
C
190
River 130
B
85
Rock 45
Montana Creek 29
18 A
11
5
Idaho –2
Warm Springs Creek
Silver Bow Creek
46°
Butte

0 20 mi
0 30 km

FIGURE 19.4 Map locating different remediation activities in the floodplain of the Clark Fork River below Warm Springs
tailings ponds. Black bars indicate the reach of the upstream river along which different remediation activities took place.
The upstream stations are the primary source of contamination (donor stations) for the downstream stations (recipient
stations).

Small episodes of toxicity could still occur from pulses of inflow from the floodplain, but they are
difficult to document. Typically, dissolved concentrations from a water body are compared to laboratory-
derived measures of toxicity to determine if organisms (fish) are at risk for metal toxicity. For example,
the U.S. Environmental Protection Agency (USEPA) defined hazard quotients (HQs) for different local-
ities in the Clark Fork River from the ratio of “site exposure levels” (dissolved metal concentrations) to
“levels believed to cause no or minimal effects” based on the dissolved toxicity database for trout
(USEPA, 1999). From toxicity testing data, the USEPA concluded that acute lethality to trout occurs at
dissolved copper concentrations greater than 30 to 40 µg/L (USEPA, 1999). The chronic effects of a
dissolved metals mixture was studied in the experiments specific to Clark Fork conditions (Woodward
et al., 1994, 1995). They verified that concentrations of copper, cadmium, and lead at the water quality
criteria resulted in chronic effects, manifested as decreased growth of brown trout fry at 26 through 88
days. The limits of toxicity testing for defining the well-being of fish are well known (Luoma, 1995).
Less appreciated are the challenges of identifying the ambient exposure in the water body.
The most widely collected dissolved metal data for the Clark Fork River are the quarterly analyses
from water quality monitoring stations (Dodge et al., 2003). Such infrequent sampling is insufficient to