Pesticides

Definition of Pesticide

  • Definition: "Any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating pests. Pests can be insects, rodents, weeds, and a host of other unwanted organisms."

Types of Pesticides

Insecticide

  • Definition: Compound specifically used to kill or prevent the growth of insects.

Herbicide

  • Definition: Chemical pesticide designed to control or destroy plants, weeds, or grasses.

Fungicide

  • Definition: Pesticide that is used to control fungi.

Nematicide

  • Definition: A chemical agent that is destructive to nematodes.

Rodenticide

  • Definition: Agent used to destroy rats and other rodent pests or to prevent them from damaging food, crops, etc.

Four Major Classes of Organic Pesticides & Insecticides

  1. Organophosphates (OPs)

  2. Organocarbamates (also called carbamates)

  3. Organochlorides (also called organochlorines)

  4. Pyrethroids (from the class of pyrethrins)

Organophosphate Pesticides (Anticholinesterases)

  • Characteristics:

    • Inexpensive compared to alternatives

    • Effective to control a wide range of insects

    • Eliminates the need to use multiple pesticides

    • Not weakened by the resistance of insects

    • Tend not to persist in the environment

    • Frequent cause of fatal poisonings

Effects of Organophosphate Poisoning

  • Acute Effects:

    • Anticholinesterase activity

    • Causes impairment of the neural impulse transfer mechanism

  • Long-Term Effects:

    • Organophosphate-induced delayed polyneuropathy

    • Manifested by numbness, loss of sensory abilities, and weakness

Examples of Organophosphate Pesticides

  • Notable Examples:

    • Diazinon

    • Malathion

    • Methyl parathion

    • Parathion

  • Forms of Application:

    • Sprays, baits, indoor foggers/bombs, flea collars, pet shampoos, powders, animal dips, granules

    • Malathion: Approved for direct application to food crops such as fruits, row crops, and vegetables.

Carbamates

  • Characteristics:

    • Close relatives of organophosphate pesticides

    • Dissipate quickly from the environment by breaking down into other substances

    • Some approved for controlling garden pests (e.g., wasps, hornets, snails)

    • Ingredient in some products applied to pets to control ticks and fleas

Examples of Carbamates

  • Notable Examples:

    • Carbaryl

    • Aldicarb

    • Fenoxycarb

    • Propoxur

    • Metham sodium

Methyl Isocyanate (MIC)

  • Description: Intermediate chemical used for the manufacture of carbamate pesticides.

  • Toxicity: Acute exposure is extremely toxic to life forms (e.g., humans, aquatic organisms, and plants).

MIC Release in Bhopal, India

  • Incident: Accidental release of MIC during a 1984 industrial accident.

    • Over 3,800 people were killed.

Organochlorines

  • Definition: Derived from chlorinated hydrocarbons, containing chlorine, carbon, and hydrogen.

  • Characteristics:

    • Stable and fat-soluble

    • Persist in the environment

    • Bioaccumulate in the food chain

    • Associated with suppression of the immune system and cancer

Examples of Organochlorine Pesticides

  • Notable Examples:

    • DDT

    • Lindane

    • Chlordane

    • Mirex

    • Hexachlorobenzene

    • Methoxychlor

DDT (Dichlorodiphenyltrichloroethane)

  • History:

    • Widespread use began in the early 1940s, with maximum use in the 1960s and prohibited in the US in 1972.

  • Reason for Prohibition: Concerns about potential adverse effects on human and wildlife health.

  • Current Status:

    • Banned in most developed nations.

    • Still used in some countries.

Facts about DDT

  • Not regarded as a highly toxic pesticide.

  • Formerly used worldwide for insect control and credited with saving millions from malaria.

Human Health Effects of DDT

  • Linked Conditions:

    • Cancer (pancreatic, non-Hodgkin’s lymphoma, and breast cancer)

    • Reproductive effects

    • Impaired lactation

    • Falling sperm counts

    • Impaired neurologic function (irritability, dizziness, and numbness)

Pyrethrins

  • Source: Derived from certain varieties of chrysanthemum flowers.

  • Mechanism: Great ability to paralyze and kill flying insects by interfering with transmission of neural impulses via action on sodium channels.

Use of Pyrethrin Insecticides

  • Application Forms:

    • Low concentrations used in homes in aerosol cans, insecticide bombs, insecticidal pet shampoos, and treatments for lice.

    • May be inhaled during spraying or ingested through food.

Herbicides/Defoliants

Examples

  • Common Herbicides:

    • Atrazine

    • Paraquat

    • Agent Orange (2,4-D and 2,4,5-T)

Agent Orange

  • Background: Used during the Vietnam War (1962–1971), approximately 19 million gallons sprayed on 3.6 million acres in Vietnam and Laos.

  • Contents: Contained small amounts of dioxins, known human carcinogens.

Health Effects of Agent Orange

  • Conclusions: Institute of Medicine (US) concluded it was associated with several forms of cancer including:

    • Soft tissue sarcoma

    • Non-Hodgkin’s lymphoma

    • Hodgkin’s disease

    • Chronic lymphocytic leukemia

Pesticide Exposure: Who Is at Risk?

  • Vulnerable Populations:

    • Agricultural workers

    • Pets

    • Children

    • Livestock

    • Sensitive subpopulations (e.g., pregnant women or individuals with suppressed immune systems)

Organic Chemicals

  • Definition: Naturally occurring or synthetic substances containing mainly carbon, hydrogen, nitrogen, and oxygen (e.g., table sugar).

Hydrocarbons

  • Definition: Organic compounds containing only carbon and hydrogen.

  • Examples: Acetylene, benzene, butane; often found in petroleum, natural gas, coal, and bitumens.

Volatile Organic Compounds (VOCs)

  • Definition: Organic compounds that readily evaporate into the air.

  • Examples: Benzene, toluene, methylene chloride, methyl chloroform.

Aromatic Compounds

  • Definition: Organic molecules that contain a benzene ring.

  • Examples: Benzene and toluene.

Persistent Organic Pollutants (POPs)

  • Definition: Toxic chemicals that adversely affect human health and the environment globally.

    • Can be transported by wind and water, affecting people and wildlife far from their release point.

  • Example: Pesticide DDT is classified as a POP.

Polycyclic Aromatic Hydrocarbons (PAHs)

  • Definition: Group of over 100 chemicals formed during incomplete burning of organic substances (e.g., coal, oil, garbage).

  • Example: Benzopyrene.

Dioxins

  • Definition: Family of chemical compounds that are unintentional byproducts of certain processes, typically involving combustion.

  • Facts:

    • Number of Compounds: 419 known, with 30 considered most poisonous.

    • Bioaccumulate in the food chain.

Natural Events Producing Dioxins

  • Sources: Forest fires and volcanic eruptions.

  • Dioxins from these sources are termed "natural background" dioxins.

Human Activities Producing Dioxins

  • Activities:

    • Incineration of industrial and municipal wastes

    • Burning of certain fuels

    • Bleaching of wood pulp

    • Manufacture and application of some herbicides

    • Tobacco combustion (minute dioxin amounts present in cigarette smoke).

Factors Affecting Health Effects of Dioxin Exposure

  • Factors:

    • Duration of exposure

    • Frequency of exposure

    • Timing of exposure

    • Concentration of the agent

    • Route of entry into the body

Health Effects of Exposure to Dioxin

  • Symptoms include:

    • Chloracne

    • Skin rashes

    • Skin discoloration

    • Excessive body hair growth

    • Liver damage

    • Possible cancer risks

    • Endocrine effects

    • Reproductive and developmental effects

Polychlorinated Biphenyls (PCBs)

  • Uses:

    • Insulating fluid in transformers and capacitors, lubricant.

  • Bioaccumulation: Present in environmental settings, bioaccumulate in fish and animals consumed by humans.

PCB Contamination

  • Extent: Present at approximately 500 sites, indicated on the EPA's National Priorities List.

  • Manufacturing Status: Terminated in 1977 due to environmental and health concerns.

Health Effects of PCBs

  • Health Risks:

    • Causes cancer in animals

    • Designated as probable human carcinogen

    • May impact immune system, reproductive system, and children's intellectual development

    • May limit immune responses to Epstein-Barr virus and other infections.

Hazardous Chemicals

  • Overview: Omnipresent in the environment, essential to modern society, but pose potential risk to all living organisms.

Advantages of Hazardous Chemicals

  • Benefits: Essential for society; about 15,000 chemicals are produced and used in high volume in the US for various products (clothing, electronics, building materials, furnishings, etc.).

Disadvantages of Hazardous Chemicals

  • Health Implications: Implicated as human health hazards, notably in the etiology of cancer and adverse birth outcomes.

    • Exposure occurs through environmental dissemination.

  • Public Awareness: Silent Spring by Rachel Carson heightened public awareness of potential hazards.

Organic Solvents

  • Definition: Liquid substances capable of dissolving other substances without changing in forming a solution.

  • Example: Goo Gone adhesive remover.

Solvents: Modes of Exposure

  • Exposure Routes Include:

    • Breathing vapors

    • Ingesting through contaminated food and water

    • Use of food/cosmetics packed in certain plastics

    • Smoking cigarettes

    • Chronic exposure in factories

    • Inhaling vapors from industrial facilities

    • Drinking groundwater contaminated with solvents.

Examples of Solvents

  • Notable Examples:

    • Tetrachloroethylene

    • Trichloroethane

    • Trichloroethylene (TCE)

    • Toluene

    • Acetone

    • Benzene

Chemicals Used in Plastics Manufacture

Styrene

  • Uses: For manufacture of polystyrene resins, components of various plastics.

  • Short-term Exposure Effects:

    • Central nervous system effects (muscle weakness, concentration problems)

    • Respiratory tract irritation

    • Possibly carcinogenic.

Vinyl Chloride

  • Uses: Mainly for manufacture of polyvinyl chloride (PVC), used in products like pipes, siding, and coatings.

  • Classification: Human carcinogen.

Environmental Estrogens

  • Context: Some organic chemicals may exhibit estrogenic activity (e.g., chlorinated hydrocarbon pesticides).

  • Specifically: DDT and its metabolites are termed endocrine disruptors, impacting androgen.

Effects of Environmental Estrogens

  • Potential Effects on Reproduction: May exert abnormal influences on reproductive systems of exposed humans and animals and act as cancer promoters related to female cancers influenced by estrogenic activity.