Investigation - Biomonitoring Assay
Background
Toxins are chemical compounds that are harmful to cells or organisms. Different toxins can affect aquatic organisms in very different ways. These effects include behavioral, bioaccumulation, developmental, growth, reproduction, and mortality (which you will be observing in this investigation).
Biomonitoring is the use of living organisms to assess the quality of the environment. It includes using indicator species to reveal physio-chemical environmental conditions of a habitat and the use of bioassays to provide an integrated picture of overall toxicity of an effluent or a sample of water, sediment, or soil from a contaminated site.
A bioassay can indirectly measure the toxicity of an effluent or pollutant by exposing test organisms to several concentrations of a suspected toxin and observing mortality or death rate. The idea behind these bioassays is that the test organism will react in a predictable way to various types of environmental contaminants.
An old and commonly known example is the canary in the coalmine. Traditionally, coal miners have taken caged canaries down into the mines to help ensure a safe air supply. Canaries are more sensitive than humans to methane, an odorless gas released during the mining process, so they were used to provide an advanced warning of when methane was building up to dangerous levels in the mines. If the canary died, it meant the miners should leave the mine as quickly as possible.
Many types of bioassays exist. The simplest one is called an acute static test. Acute tests measure lethal effects over a short period of time and static tests use a known amount of test solution during the experiment. We will use this type of test in our investigation.
The object of a bioassay is to determine the concentration of toxin that kills 50% of the organisms exposed to it during a given amount of time. This concentration is known as the lethal concentration for 50% of the population and is termed the LC50 (median lethal concentration).
Time to Investigate
In Core Lake it has been recently observed that fish are having difficulty breathing and as a result have been dying. As a researcher you are to discover why this is happening.
Water samples collected at the lake stations have been analyzed for chemical data. The data can be found at Core Lake Water Quality Data.
In this investigation you will use a modified acute static toxicity bioassay to test for suspected toxins in Core Lake. You will have several test organisms at your disposal to test for suspected toxins.
Many aquatic organisms can be used as our indicator species such as fish, amphibians, and macroinvertebrates to test for various potential toxic substances.
In our investigation we will be testing some of these potential toxins:
| Ammonia | Copper | DDT | Mercury | Lead |
These will be our test species:
| Waterflea | Scud | Tubifex worm | Fingernail clam | Bluegill |
Finding the LC50 for toxins with a selected species:
In this modified bioassay, you will expose a single selected test species to a range of concentrations for all toxins available for a simulated time interval of 24-hours. Each assay will consist of six(6) concentrations plus a control for a total of seven(7) treatments.
The test concentrations will be 0.05 ppm, 0.1 ppm, 1.0 ppm, 2.0 ppm, 5.0 pp, and 10.0 ppm of toxin. The control will be 0 ppm concentration. (seen here)
| Culture dish # | Toxin Concentration (ppm) | Organism # (time=0) | 1 | 0.05 | 10 | 2 | 0.1 | 10 | 3 | 1.0 | 10 | 4 | 2.0 | 10 | 5 | 5.0 | 10 | 6 | 10.0 | 10 | 7 (control) | 0 | 10 |
|---|
PPM = parts per million, or milligrams of toxin per liter of water (mg/L)
This simulated assay will be based on this method:
Ten(10) test organisms are placed into each of seven different culture dishes (each labeled according to test toxin concentration).
The appropriate test concentration of toxin is then added to the culture dishes containing the organisms.
After 24 hours, the culture dishes are examined and the number of living and dead test organisms are counted in each dish.
Your data should be recorded in table form (as shown below). You should have one table for each toxin tested on your organism.
| Organism: ______________ | Toxin: ________________ | |||
| Toxin Concentration | 0rganism # (t=0) | # living (t=24) | # dead (t=24) | % mortality | 0.05 | 10 | 0.1 | 10 | 1.0 | 10 | 2.0 | 10 | 5.0 | 10 | 10.0 | 10 | control | 10 |
|---|---|---|---|---|
| LC50 = ______________ | ||||
From your recorded data you will create a graph to calculate the LC50 value of each toxin for your test organism.
- First, you must convert the Toxin Concentrations to natural log (ln) values. Calculate ln here
Logarithms are just transformations. They are used because sometimes it's easier to analyze or visualize something in terms of log transformed data than in terms of the original values.
- Plot the Log value for Toxin concentration on the Y-axis (vertical axis).
- Percent mortality should be plotted on the X-axis (horizontal axis)
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To plot your data on graph paper:
Click graph for larger image ...
- Now figure out the LC50:
- On your graph draw a vertical line at the 50% mortality level
- Now locate the toxin concentration to the left of the 50% line, this is the LC50 for the toxin.
- Record the LC50 in your table.
- To be handed in:
- Tables for each of your bioassay results.
- Graph of your results.
- Answers to the Biomonitoring Assay Questions.
--> --> Start Bioassay! <-- <--
Questions
- Summarize your results.
- Which toxin is the most harmful to the species you have chosen?
- Would you get the same reults if you used a different test organism? Why?
- What is the purpose for the 'Control' in your assays?
- If 50% of the population of the organism you studied was killed, how might that affect the ecosystem?
- Define the term: bioaccumulation.
- If you increased the Study Time (the length of time organisms are exposed to the given dose of toxin) would your results differ. How?