Public Health 462: Toxic Effects of Pesticides and Pesticide Residues (Part 1)

Overview

• Focus on herbicides and insecticides.
• Discussion includes glyphosate, 2,4-D, paraquat, rodenticides, fungicides.

Pesticides

• Types: Herbicides, Insecticides, Fungicides, Rodenticides.
• Pests include any harmful species to humans, health, and crops.
• Examples: Zebra mussels in California aqueducts.

Pesticide Usage

• Over 900 active ingredients commercially used.
• 1.1 billion pounds applied in the US (2012).
• Herbicides are the most used, particularly in agriculture.

Toxicity

• Pesticides should ideally target only pests but often affect non-target species and humans.
• Balance benefits (e.g., controlling vector-borne diseases, preventing crop loss) vs. risks.

Pesticides Classification

• EPA classifies chemicals into four categories based on toxicity.
  • Category 1: Most toxic (LD50 ≤ 50 mg/kg).
  • Category 4: Least toxic.
• Labeling requirements vary by category (Danger, Warning, Caution).

Key Herbicides

Glyphosate

• Non-selective systemic herbicide, affects broadleaf plants and grasses.
• Inhibits synthesis of essential amino acids.
• Low toxicity to humans, eliminated without bio-transformation.

2,4-D (Dichlorophenoxyacetic Acid)

• Mimics plant growth hormone (auxin), causing uncontrolled growth.
• Low dermal absorption, rapidly eliminated.
• Linked to Agent Orange (Vietnam War contaminant TCDD).

Paraquat

• Disrupts cell membranes, photosynthesis inhibitor.
• Highly toxic, requiring a license for use.
• Accumulates in lungs, generates harmful free radicals.

Atrazine

• Used on corn, sugarcane, pineapples.
• Potential endocrine disruptor, banned in EU.

Rodenticides

• Mainly target rats, mice, moles.
• Warfarin: Causes internal bleeding, narrow therapeutic range.

Fungicides

• Control fungi, impossible without chemical applications.
• Low acute mammalian toxicity.
• Examples:
  • Captan: Probable human carcinogen, low dermal absorption.
  • Copper sulfate: Low toxicity, widely used.
  • Triphenyltin acetate: Moderate to high toxicity.
  • Organic mercury: No longer used, highly toxic.

Summary

• Pesticides are essential for controlling pests but pose risks to non-target species.
• Understanding the types, usage, and toxicity is crucial for safe application.