Biology 313
Background information: Ecotoxicology Lab
Ecotoxicology is the study of the fate and effects of chemicals in the environment
through the application of ecological principles (ecology + toxicology). A Toxicant
(poison) is any substance that causes a harmful effect when administered to a living
organism. Toxicant refers to an anthropogenic (human-made) contaminant
Toxin: A poison produced by a living organism. Toxin should never be used as a
synonym for toxicant (e.g. snake venom, Botulinum toxin).
In the environment, contaminants move within and among the environmental
compartments (atmosphere, hydrosphere, lithosphere) and may have an adverse impact
on biota and fauna.
Take a few minutes to list some of the toxicants that are likely present in Lake Winona
and the Mississippi River.
What you will soon realize is that each of these habitats contains a complex mixture of
many toxicants. Furthermore, each ecosystem has unique inputs. A challenging problem
for toxicologists is that it is not possible to test all combinations of chemical mixtures in a
habitat. Instead single chemicals are tested and the impacts on ecosystems and
organisms are characterized. This simplistic approach does not reflect the reality of
multiple contaminants that are likely present in contaminated ecosystems or the
interactions of different chemicals. It does, however, provide a starting point to assess
impacts to biota, to regulate use of chemicals, and to control chemical use.
The dose-response relationship is a premise of toxicology. Simply stated, the greater the
dose of chemical, the greater the response of the organism.
A toxicity test is used to generate an LC50 = lethal concentration in which 50% of the
test organisms do not survive or an EC50 = effective concentration in which 50% of the
test organisms exhibit some non-lethal endpoint that may compromise overall fitness
(e.g. changes in behavior, swimming, reproduction). The LC50 and EC50 provide a
concentration that can then be used to compare to other biota. However, a concentration
of a contaminant that causes mortality of 50% of organisms is not acceptable-it is used as
a point of comparison. Note: LC50 and EC50 values for the same chemical will vary
between different test organisms (i.e. fish, freshwater mussels, aquatic invertebrates) due
to the variation of sensitivities to the chemical.
To quantify a dose-response relationship of a contaminant through toxicity testing:
1. a test organism must be selected
2. a series of doses must be tested
3. a response or endpoint must be measured and quantified
4. an exposure period must be established
In toxicity testing acute toxicity tests are usually 24 or 48 hours in duration while
subchronic (90 days) and chronic (6 months to one year) tests are much longer.
Individual dose-response
100relationship
%
R
e
s
p
o
n
s
e
50
“lethal concentration”
“effective concentration”
0
LC50/EC50
Low
DOSE
High
Figure 1: The dose-response relationship
In this ecotoxicity study, you will be assessing the impact of road salt (NaCl) to aquatic
biota. Road salt can impact adjacent ecosystems as a component of runoff from winter
de-icing measures. NaCl can enter the groundwater or surface water and impact plants,
invertebrates and vertebrates. Road salt is approximately 60% chloride and 40% sodium.
In aquatic systems, NaCl dissociates into chloride ions (Cl-) and sodium ions (Na +).
Chloride is of greater concern to aquatic biota than sodium. The EPA and MPCA
(Minnesota Pollution Control Agency) have a chloride standard of 230mg/L limit for
chronic toxicity. This chloride level is equivalent to a conductivity of 960 uS/s.
Table 1: Amount of NaCl added to each treatment.
Treatment
N
No NaCl
10 mg/L
23 mg/L
100 mg/L
230 mg/L
500 mg/L
6
6
6
6
6
6
NaCl added
to tank (g)
0.0
0.624
1.44
6.24
14.4
31.2
Experimental design (Note: Treatments will be randomly distributed)
Control
sample
1
sample
2
sample
3
sample
4
sample
5
sample
6
10 mg/L
Cl
23mg/L
Cl
100 mg/L
Cl
230 mg/L
Cl
500 mg/L
Cl