Volume 50, Number 1, December 2003:
A Toxicology Primer for Student Inquiry: Biological Smoke Detectors

Text-only version

ISSUE HOME PAGE

ABOUT THIS ISSUE
- about KSN
- about the author
- acknowledgements

IN THIS ISSUE
- disclaimer, objectives
- "biological smoke detectors"
- purpose of invertebrate toxicity testing
- lethal and sublethal effects
- some wormy ideas for toxicity testing
- sublethal chemical effects in lumbriculus
- selecting the chemical(s)
- safety
- exposure methods
- preliminary experiments and concentration range-finding
- final stages of toxicity testing
- typical equipment and supplies
- other organisms, other ideas
- obtaining background information
- references
- glossary of toxicological terms

A Toxicology Primer for Student Inquiry:
Biological Smoke Detectors
by Charles Drewes

PRELIMINARY EXPERIMENTS AND CONCENTRATION RANGE-FINDING   

Sublethal effects of some chemicals may occur within a narrow range of concentrations.  High concentrations may rapidly kill organisms while lower ones may cause no effect.  Since concentration ranges for sublethal effects differ among chemicals, an important step in toxicity testing for a chemical is to determine its threshold concentration, NOEL, and dose-response relationship (see Glossary).  This requires preliminary range-finding experiments which are time-consuming but lead to more meaningful results during final stages of toxicity testing. 

To make a stock solution, dissolve a known amount of pure chemical (liquid or solid) in a small, known volume of water or other suitable solvent (such as, ethanol or isopropyl alcohol for non-water soluble chemical).  Typically, a few milligrams or milliliters of the chemical are dissolved in 100-1000 ml of solvent.  The concentration should be expressed as:  mg of chemical per liter of solvent if the chemical is a solid.  This is the same as “parts per million” (see Glossary).  If the chemical is a liquid, then concentrations will be in milliliters of chemical per liter of solvent.  This concentrated stock solution is used to make a series of weaker stock solutions by serial dilution (see Glossary).  Each concentration step may be several times weaker than the preceding one, such as 25, 5, and 1 ppm.

Sometimes the exact amount of chemical may be unknown because it is present in an unpurified, crude form.  In this case, the volume or weight of crude material should still be measured and recorded in making a stock solution.  Then, dilutions of stock solution are used for range-finding experiments, with concentrations expressed as percentages of the original stock solution.