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

LETHAL AND SUBLETHAL EFFECTS

Toxicity testing in the past 20 years has moved away from lethality (or LC50) studies and toward studies of sublethal effects (see Glossary). This is because sublethal effects occur at relatively low concentrations and are thus more sensitive indicators of toxicity (Figure 2).

Figure 2.  Comparison of lethal and sublethal treatment effects in a hypothetical organism.  Treatment with high chemical concentrations may be lethal in some or all treated organisms.  Lethal effects are easy to recognize and tabulate.  Treatment with lower concentrations may produce sublethal effects which are sometimes difficult to discern but, nevertheless, important from a behavioral or ecological standpoint. 

 One hurdle for a student toxicology project is deciding what sublethal effects to study.  This is a challenge because such effects seldom have been described in invertebrates and there are few standard methods for measuring them.  Thus, it is advisable to begin by carefully observing an organism’s normal behavior prior to any toxicity testing.  Then, during preliminary testing, look for obvious effects, such as changes in an organism’s color, posture, or spontaneous movements... or perhaps changes in its reaction to stimuli such as light, touch, or body inversion.  Some effects may only be seen under magnification, such as rhythmic movements of the organism’s heart or respiratory system.  To systematically study behavioral effects, students may need to design and build simple devices for handling, observing, or testing organisms.  In addition, they may need to develop criteria for scoring or measuring effects.  From such observation and testing, students will likely gain new insights about the biology and behavior of normal as well as treated organisms.