Toxicity of Herbicides-Modeling Experimental Approaches

Adapted from Janet Lanza, University of Arkansas

 

            As human populations grow and increase our use of technology has impacted our physical and biological environment.  Many of the new substances produced despite their benefits have proven to he harmful to organisms.  Examples of such pollutants are DDT, dioxin, and asbestos.

            We have many environmental regulations to safeguard the health of humans and the environment; the Clean Water Act is such an example.  In order to determine how much of a chemical is safe various tests of dosages and duration of exposure are undertaken.  In trying to estimate the toxicity of a substance.  A common method is to measure the concentration of a toxin that causes death in 50% of the treated organisms. This value is the LC50. 

            This laboratory exercise is designed to increase your understanding of the measurement of toxicity.  We will use a common herbicide and vary the dosage using dilutions on the herbicide and measure the effects on plants.

 

Methodology

1.                  Design an experiment in which only one factor is varied e.g., concentration or exposure.  You can use a null hypothesis or an experimental hypothesis.

2.                  Decide on a measurement e.g., number of leaves that change color, growth, etc

3.                  Your experiment will run for 48-96 hours.

4.                  Your design must be safe; spraying outdoors, wash hands, etc.

5.                  You must have a control.

6.                  You must decide on a statistical method to accept or reject your hypothesis.

 

Report

1.                  Your report should be typed or written neatly with ink.

2.                  Your report must include; Preliminary background information,  hypothesis, experimental design, data table, graphs/charts/calculations, a conclusion accepting or rejecting your hypothesis.

 

Please answer the following questions in your report:

  1. How do the results you obtain relate to vertebrates? Would you expect vertebrates to have the same level of toxicity?

 

  1. What is the purpose of the control in this experiment?

 

 

  1. The level at which you first detect an effect is called the threshold level.  Was there a concentration below which you could not detect an effect on the plants?  What is the threshold level?