Environmental Engineering: Fundamentals and Design - Chapter 5

BOOK TABLE OF CONTENTS
CHAPTER TABLE OF CONTENTS
TOC > Ch. 5 > 5.6 Ecosystem health

# Chapter 5 Biology

Martin T. Auer, James R. Mihelcic and Michael R. Penn

## Ecosystem health

### Toxicity Testing

Sometimes it is not the concentrations of individual chemicals which cause problems, but rather interactions among them and with the receiving water. These effects are determined through toxicity testing. U.S. EPA has identified 10 common freshwater and marine organisms for use in the test. Among the most common "lab rats" for toxicity tests are the water flea (Daphnia pulex) and the fathead minnow (Pimephales promelas). | Water Flea
Fathead Minnow

### Toxicity Testing Activity

Test organisms are placed in glass or plastic bottles containing the water to be tested and left there for 2-4 days. Bottles are set up for pure effluent, several dilutions of that effluent and a control water (where no more than 10% of the organisms should die). The percentage of organisms surviving exposure in each bottle is determined and the toxicity of the effluent is expressed as the effluent dilution which is lethal to 50% (LC50) of the population. An acute toxicity unit is defined as 100/LC50. The State of Michigan limits discharges to 1 acute toxic unit. If the effluent contains more than that, the treatment plant must add new processes to reduce the toxicity of their discharge.

#### Credits

Fathead Minnow image: U. S. Fish and Wildlife Service, Duane Raver.
Daphnia Pulex (Water Flea) photo: Cornuet, BIODIDAC.
Toxicity Testing animation: © 2005 State of Michigan.