Public Health 462: Toxic Effects of Pesticides and Pesticide Residues - Part 2

Introduction

• Focus on insecticides
• Insecticides are used to kill insects causing crop damage and vector-borne diseases
• Reduction in use due to increased toxicity, specificity, and preference for organic products

Classes of Insecticides

1. Organochlorines
2. Pyrethroids
3. Organophosphates and Carbamates
   • Both target the enzyme acetylcholine esterase

Mechanism of Action

Organochlorines and Pyrethroids

• Example: DDT
• Activate sodium channels, disrupting nervous system processes
• Cause spasms and death
• Related to action potential in neurons

Action Potential in Neurons

• Involves sodium and potassium ion channels
• Positive charge moves along axon due to Na+ influx
• Resting state restored by K+ efflux
• Pyrethroids keep Na+ channels open, causing continuous stimulation

Pyrethroids

• Synthetic chemicals similar to natural pyrethrins
• Derived from flowers, modified for insecticidal properties
• Break down readily in sunlight
• Low dermal toxicity, rapid metabolism in humans
• Commonly found in products like Raid
• Low chronic toxicity

Organochlorines

• Derived from chlorinated hydrocarbons
• Example: DDT
• Lipophilic, stable, fat-soluble
• Long environmental persistence
• Associated with cancer and immune system damage
• Examples: Lindane, Aldrin

DDT Use and Impact

• Effective in reducing malaria cases
• Persistent environmental presence
• Concerns over endocrine disruption
• Banned in many countries but still used in some for malaria control

Organophosphates and Carbamates

• Inhibit acetylcholine esterase
• Prolonged stimulation of nerve synapses
• Acetylcholine remains active, causing overstimulation

Mechanism at Synapse

• Vesicles release neurotransmitters into synaptic cleft
• Acetylcholine esterase breaks down neurotransmitters post-stimulation
• Inhibition leads to continued nerve firing

Differences Between Organophosphates and Carbamates

• Organophosphates tend to be more toxic, longer duration
• Carbamates less toxic, reversible inhibition

Toxicity Effects

• Symptoms: Diarrhea, urination, muscle spasms

Pesticide Policy

• Regulations require evaluation of toxicity on human health
• Users must be trained for safe application

Key Legislation

• FIFRA: Controls manufacturing, sale, and use of pesticides
• EPA sets allowances for pesticide residues in food
• Food Quality Protection Act (1996): Sets new safety standards, especially for children

Pesticide Residues

• Monitoring by USDA and FDA
• Most foods tested contain residues below EPA tolerance levels
• Imported foods more likely to exceed tolerance levels

Conclusion

• Lecture covered insecticides' toxic effects, regulatory policies, and residue monitoring
• Encouraged to review materials and watch recommended videos for deeper understanding