Toxic Organic Compounds in Chemicals

Toxic Organic Compounds

• Most toxic organic compounds are derived from petroleum or natural gas
• Types of toxic organic compounds include:
  • Polycyclic aromatic hydrocarbons (PAHs)
  • Organochlorine insecticides
  • Organophosphate and carbamate insecticides
  • Organic herbicides
  • Dioxin contaminant of herbicides and wood preservatives

Polycyclic Aromatic Hydrocarbons (PAHs)

• PAHs consist of fused benzene rings
• Examples of PAHs include:
  • Naphthalene
  • Benzo[a]pyrene
• PAHs are found in:
  • Incomplete combustion of carbon-based fuel (e.g. coal, wood, diesel)
  • Diesel engine exhaust
  • Cigarette smoke
  • Surface of charred or burnt food
• PAHs are carcinogenic to test animals and probable human carcinogens
• PAHs bioaccumulate in the food chain and are a worrisome pollutant

Mechanism of PAH Carcinogenity

• PAHs themselves are not carcinogenic, but their metabolic products are
• Chemical transformation of PAHs involves:
  • Oxidation into an epoxide ring
  • Subsequent hydration
• Addition of H+ forms a stable cation that can bind to DNA, inducing mutations and cancer

Environmental Chemistry of PAHs

• Transport in the atmosphere:
  • ≤ 4 fused ring PAHs remain gaseous
  • > 4 fused ring PAHs have low vapor pressure and condense onto surface of soot and ash
  • They become respirable
• Transport in the hydrosphere:
  • Creosote, a coal tar derivative used as wood preservative, contains PAHs
  • PAHs leach out and cause water pollution

Organochlorine Insecticides

• Characteristic properties:
  • Stable towards environmental degradation
  • Low solubility in water
  • High solubility in fatty materials
  • Relatively high toxicity to insects
  • Low toxicity to humans
• Examples:
  • HCB (hexachlorobenzene)
  • DDT (para-dichlorodiphenyltrichloroethane)
• DDT:
  • Used as insecticide and fungicide
  • Persistent and bioaccumulative
  • Carcinogenic to lab rodents and probable human carcinogen
  • Banned in 1973 except for essential public health uses

DDT Analogs

• Same insecticidal properties as DDT
• Reasonably biodegradable
• No bioaccumulation
• Example: Methoxychlor (insecticide)

Other Organochlorine Insecticides

• Lindane:
  • Contains one of 8 isomers of hexachlorocyclohexane
  • Used to control pests and treat seeds and seedlings
• Chlorinated cyclodienes:
  • Aldrin, Dieldrin, Chlordane, Heptachlor, etc.
  • Used to control various pests
  • Persistent chemicals that bioaccumulate and cause liver cancer in test animals

Modern Insecticides: Organophosphates and Carbamates

• Organophosphate insecticides:
  • Nonpersistent
  • Decompose within days or weeks
  • Much more acutely toxic to humans and other mammals than organochlorines
  • Function as nerve poisons to insects
• Carbamate insecticides:
  • Nonpersistent
  • Decompose upon reaction with water, forming nontoxic products
  • Low dermal toxicity
  • Examples: Carbaryl, Aldicarb, Carbofuran

Naturally-Occurring Pesticides

• Manufactured by plants as a defensive mechanism against insects
• Examples: Nicotine, Rotenone, Pheromones, and Juvenile hormones
• Pyrethrins:
  • Obtained from chrysanthemum flowers
  • Have been used by humans for centuries
  • Paralyze insects

Organic Herbicides

• Triazines:

  • Alternating N and C atoms in a six-membered ring
  • Useful triazine herbicides contain Cl and -NH2 or -NHR groups bonded to the ring carbon
  • Example: Atrazine

• Atrazine:

  • Mode of action: Blocks photosynthesis
  • Uses: Kills grassy weeds in corn and soybean fields
  • Undesirable properties: Can build up in dry soil, eradicates all plants, and is a possible human carcinogen

• Phenoxy herbicides:

  • Introduced as weed-killers after WWII
  • Prepared from phenol
  • Examples: 2,4-D and 2,4,5-T

• Dioxin contamination:

  • Synthesis of 2,4,5-T and other herbicides produces dioxin as a contaminant
  • Dioxin is a highly toxic and persistent environmental pollutant### Dioxin and Furan Levels in Breast Milk

• Dioxin and furan levels in breast milk collected from women in the Aluoi Valley in central Vietnam (1996-1999) were about six times higher than those in breast milk collected in 1988 in Hanoi, northern Vietnam.

• This suggests that Agent Orange, which was sprayed in the Aluoi Valley, had a significant impact on dioxin and furan levels in breast milk.

Polychlorinated Biphenyls (PCBs)

Structure and Properties of PCBs

• PCB molecules have a ring structure similar to dioxins.
• PCBs have high chemical, thermal, and biological stability.
• They have low vapor pressure and are insoluble in water but soluble in fatty/oily substances.
• PCBs are inexpensive and excellent electrical insulators.

Uses of PCBs

• PCBs were used as coolant-insulation fluids in transformers and capacitors.
• They were used as plasticizers to make other materials more flexible.
• PCBs were used as a deinking solvent for recycling newsprints.
• They were used as a heat-transfer fluid in machinery.

Environmental Contamination of PCBs

• PCBs can contaminate the environment through discarded electrical equipment, incineration plants, and waste discharges from capacitor manufacturing plants.
• The Hudson River is a source of PCB contamination, which has led to bioaccumulation in fish and other aquatic organisms.

Toxic Alkaloids

• Alkaloids are naturally-occurring complex amines, usually isolated from plants.
• They have medical uses as stimulants, analgesics, and tranquilizers.
• Alkaloids can be addictive, and some are toxic, such as coniine (cup of hemlock) and nicotine.
• Some alkaloids, like opioids, have pain-killing and tranquilizing effects.

Alkaloids from Nature

• The opium poppy is a natural source of alkaloids, such as opioids.
• The opium poppy's seed capsules contain a milky sap that, when air-dried and kneaded, forms a soft material known as opium.

This quiz covers toxic organic compounds, including polycyclic aromatic hydrocarbons, organochlorine insecticides, and more. Learn about the types and sources of these chemicals.