NURS 735 - APPLIED TOXICOLOGY

In this module, we will cover the toxicology of pesticides. Pesticides include the broad groupings of insecticides, herbicides, fungicides, rodenticides and acaricides. The chemical stuctures differ within these categories as well as between categories. We will focus on discerning how these different classes of pesticides vary with respect to thier history, structure, mechansism of action and relative toxicities to different target organisms.

By completing this module, you should understand that:

• The term "pesticide" includes chemicals that are insecticides, herbicides, fungicides and rodenticides.
• There are many different classes of pesticides, with very different structures, mechanisms of action and levels of toxicity.
• Some pesticides are very acutely toxic in humans, while others have a lower acute toxicity but can still cause chronic health effects at some exposure levels.
• Organochlorine insecticides have been banned in the US due to their persistence in the environment and ecological effects.
• Organophosphate and carbamate pesticides function as acetylcholinesterase inhibitors and are extremely toxic in humans.
• Pyrethroid insecticides are rapidly metabolize in mammals, which lowers their toxicity
• The toxicity of herbicides in mammals is generally low, but specific compounds show high toxicity due to their unique structure.
• The primary human health effects of chlorophenoxy herbicides are due to contaminant chemicals.
• The acute toxicity of fungicides is generally low in mammals, however health effects have been observed in cases of human exposure.
  

To guide your understanding of key concepts throughout this module, the following assigned resources are available:

• PowerPoint Presentation:

Overview of Pesticides (Flash presentation on Pesticides with narration by Dr. Katherine Squibb)

Overview of Pesticides (Same presentation in PowerPoint with notes, in pdf format for printing)

• Textbook readings:
  Pesticides (pages 109-120)
  On your own answer the three questions at the end of the pesticides chapter.

• Websites for further reading on pesticide toxicology:

EXTOXNET (Extension Toxicology Network)
Search for "pesticides" or specific pesticide name

ATSDR ToxFAQs
For example, Pyrethrins ToxFAQs: http://www.atsdr.cdc.gov/tfacts155.html

• Video interview with Dr. Ruth Berlin, Director of the Maryland Pesticides Network

Assignment:

Homework: Read the article in the Environmental Toxicology Newsletter, Vol 23, No. 1, January 2003: "Study Affirms Water Effective for Reducing Trace Pesticide Residues on Produce, Finds Produce Washes Not Effective as They Claimed" available through: http://ace.orst.edu/info/extoxnet/newsletters/ucdnl.htm, (also provided below)

This study tested two pesticides. Do you think their results can be extrapolated to the many other pesticides in use today? Why or why not?
Hint: Need to do some research on this relative to water/lipid solubility.

Study Affirms Water Effective for Reducing
Trace Pesticide Residues on Produce,
Finds Produce Washes Not Effective as They Claimed

    A new study by Dr. Robert Krieger at the University of California, Riverside has found that produce washes are not as effective as they claim.  The study looked to see if produce washes were more effective in removing pesticide residues than water.  "Since we knew that water is effective in removing pesticide residues, it seemed very unlikely that produce washes would be as effective as they advertise," said Dr. Krieger. The study will be published in the February 2003 edition of Bulletin Environ Contam Toxicol.

    In the first part of the study, crops that had been normally treated with captan were separated into three groups.  The first group was rinsed with water, the second with water and produce wash, and the third was not rinsed.  The unrinsed produce had a residue level of 6.7 parts per million.  The group that was rinsed with water had a residue level of 4.1 parts per million, 39% less than the unrinsed group.  The group that was rinsed with water and produce wash had a residue level of 3.7 parts per million, 45% less than the unrinsed group. 

    In the second part of the study, fruit that had been treated in the field with a tank mix of captan on methomyl were separated and treated as in the first part of the study.  The fruit that was unrinsed had a residue level of 0.52 for captan and 0.87 for methomyl.  The fruit that was rinsed with water had a residue level of 0.10 for captan and 0.71 for methomyl, 81% and 18% less than the unrinsed fruit respectively.  The fruit that was rinsed with water and produce wash has a residue level of 0.053 for captan and 0.53 for methomyl, 90% and 39% less than the unrinsed fruit respectively.

    The claims that produce washes are much more effective than water is not supported by this study.  "Our concern about these claims is that they are misleading a public that is already concerned about pesticide residues," said Dr. Krieger.  "Clearly, this study shows that there is no reason to spend extra money on these washes when water is just as effective."

    Dr. Krieger also stressed that all of these residue levels are well below federal standards.  "All levels of residues were well within the EPA levels and far below levels that could cause adverse health effects in rats or humans," said Dr. Krieger.  "These studies simply reaffirm the effectiveness of water for trace pesticide residue reduction.  In no case were residues of health significance."