Page 691 - The Toxicology of Fishes

Fish Toxicity Studies 671

144

120

96
LT50 (hr) 72 incipient lethal concentration (LC50)
Time-independent threshold or

48

24

0
100 150 200 250 300
Exposure Concentration (µg/L or ppb)
C
0.010

0.008
1/LC50 (µg/L) 0.006 incipient lethal concentration (LC50)

Time-independent threshold or
0.004

0.002

0.000
0 25 50 75 100 125 150
Exposure Time (hr)
D
FIGURE 15.4 (cont.) (C) Plot of LT 50 (median time to death) vs. exposure concentration (LT 50 values from part A). (D)
Plot of the inverse of LC 50 vs. exposure time (LC 50 values for low-fat fish exposed to pentachlorphenol). (From van den
Heuvel, M.R. et al., Aquat. Toxicol., 20, 235–252, 1991. With permission.)

of organisms (fish, invertebrates, algae). The utility of single-species fish tests is a function of the criteria
used to select test organisms (see below). The main limitation is that effects in the laboratory may not
occur at all or to the same degree at similar concentrations in the environment. Effects measured in the
laboratory are a result of the inherent variability of the test fish population under constant conditions.
Furthermore, bioavailability of chemicals is optimized because filtered laboratory waters are used instead
of natural waters. These tests do not consider species interactions and environmental influences. Because
most tests are conducted with water exposures, sediment and food exposures are rarely considered. The
latter exposure routes become particularly relevant with chemicals that are hydrophobic.
Small simulated model microcosm tests can also be conducted in the laboratory using a multispecies
approach. Laboratory microcosms are small-scale enclosures (e.g., fiberglass, glass, plastic) containing
a multitude of samples (e.g., water, sediment, one or more species of fish, invertebrates, and plants).
Any combination or all of the latter samples may be incorporated into the test depending on study
objectives. The advantage of this approach is that effects beyond the level of direct effects on a single
species can be studied, including indirect effects. Results provide information more predictive of the
ecological consequences of chemical release; however, environmental conditions are still controlled in
laboratory microcosms but replication may be easily obtained. Although cause-and-effect relationships