Toxic Organic Compounds in Chemicals

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

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

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

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

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

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

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

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.

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.

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.

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.

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.