Environmental Toxicology: Air Pollution Sources

Environmental Toxicology

• Focuses on the effects of pollution on wildlife and ecosystems.

Air Pollution Sources & Types

• Main causes of air pollution:
  • Carbon Monoxide (CO)
  • Sulfur Dioxide (SO2)
  • Hydrocarbons
  • Particulate Matter
  • Nitrogen Dioxide
• Major sources of air pollution:
  • Transportation
  • Industry and Industrial disposal
  • Electric power generation
  • Space heating
• Types of air pollution:
  • Outdoor pollution:
    • Reducing type pollution: Characterized by sulfur dioxide (SO2) and smoke, typically resulting from incomplete coal combustion, often associated with fog and cool temperatures.
    • Oxidative type pollution: Caused by atmospheric reactions of automobile exhaust, particularly intense in areas with high sunlight. Examples include photochemical smog.
  • Indoor pollution:
    • Sick-Building Syndromes: Symptoms include eye, nose, and throat irritation, headaches, fatigue, reduced attention span, irritability, nasal congestion, difficulty breathing, nosebleeds, dry skin, and nausea. Often associated with poorly ventilated or newly furnished buildings.
    • Building-related illnesses: Caused by biological agents, often found in poorly ventilated buildings. Examples include Legionnaires' disease, hypersensitivity pneumonitis, humidifier fever, allergies to animal dander, dust mites, and cockroaches.

Effects of Reducing Type Pollution

• Sulfur dioxide (SO2): Chronic exposure in animals causes thickening of the trachea's mucosa layer and hypertrophy of goblet cells and mucous glands.
• Sulfuric acid: Animals are more sensitive at younger ages (1-2 months) than older (18 months). Rapid exposure in animals can lead to bronchoconstriction and death. Ammonium carbonate can protect against sulfuric acid effects by providing excess ammonia.
• Particulate sulfates & particulate matter: Zinc ammonium sulfate acts as an irritant, similar to histamine, causing constriction in alveolar ducts and terminal bronchioles. Particulate matter size (5μm) can lead to respiratory diseases like asbestosis or silicosis.

Effects of Oxidative Type Pollution

• Carbon Monoxide (CO): Toxicologically a chemical asphyxiant, CO binds to hemoglobin, forming carboxyhemoglobin (CoHb).
  • Normal CoHb levels in non-smokers are around 0.5%.
  • CoHb levels below 2% are generally not associated with health effects.
  • CoHb levels above 2% (median value for smokers is 5%) can impact the central nervous system, causing Anoxia (Silent killer).
• Ozone: Toxic effects include:
  • Mortality and lung pathology: Ozone can cause death through pulmonary edema and increase histamine production.
  • Pulmonary function: Causes shallow and rapid breathing, decreased lung compliance, and increased sensitivity to bronchoconstrictors like histamine and acetylcholine.
  • Susceptibility to bacteria: Inhibits clearance mechanisms, affecting mucociliary streaming and phagocytosis, reducing macrophage number and activity.
  • Biochemical and genital effects: Can cause chromosomal aberrations in plants and animals, its effects are additive to those of X-irradiation. Antioxidants, like quinines, ascorbic acid, and α-tochopherol, offer protection against ozone toxicity. Ozone exposure can lead to lipid peroxidation.
• Nitrogen Dioxide: Acts as a deep lung irritant, potentially leading to pulmonary edema. A significant concern for farmers as it can be released from ensilage, causing Silo-Fibers disease. Exposure can alter pulmonary function, increasing respiratory frequency and decreasing lung compliance.
• Aldehydes:
  • Formaldehyde: Highly soluble in water, irritating to mucous membranes of the nose, upper respiratory tract, and eyes. Detectable by odor at 0.5-1 ppm.
  • Acrolein: More irritant than formaldehyde due to its unsaturated nature. Concentrations below 1 ppm can irritate eyes and respiratory tract mucous membranes. Its irritant action stimulates the pituitary-adrenal system, leading to increased glucocorticoid secretion and enzyme synthesis in the liver.

Indoor Pollution

• Sources include:
  • Unvented space heaters, poorly vented fire places, and wood stoves.
  • Fuels used for heating and cooking.
  • Secondhand tobacco smoke.
  • Carpets and furnishings.
  • Dry cleaner clothes and household cleaning products (VOCs).
  • Overcrowded homes and insufficient living space.
• Sick-Building Syndromes: A collection of non-specific ailments including eye, nose, and throat irritation, headaches, fatigue, reduced attention span, irritability, nasal congestion, difficulty breathing, nose bleeds, dry skin, and nausea. Often relieved after leaving the building. Suspect causes include combustion products, furnishings, and poor ventilation.
• Building-related illnesses: Caused by biological agents, including:
  • Legionnaires' disease
  • Hypersensitivity pneumonitis
  • Humidifier fever
  • Allergies to animal dander, dust mites, and cockroaches.
  • Some toxic inhalants, like carbon monoxide, nitrogen dioxide, and volatile organic compounds.
  • Inhalants like nitrogen dioxide and trichloroethylene (from chlorinated water or dry-cleaned clothes) can suppress host defenses and allow opportunistic pathogens to proliferate in the lungs.
  • Cat allergy.

Water and Soil Pollution

• Ultimate sink for most chemicals: Water and soil.
• Intimate interface between soil and water: Water systems typically contain suspended soil particles, while soil contains water.
• Soil composition:
  • Inorganic constituents (silt, sand, clay)
  • Organic constituents (living and dead)

Sources of Chemicals in the Environment

• Industrial: Example: Phosphates from detergents are nutrient sources for algae and other organisms.
• Agricultural: Example: Pesticides applied to soil for insect, wood, and plant disease control can persist for years, potentially moving into water and organisms. These effects are well-documented in food chains.
• Domestic and urban: Example: Lead contamination in soil and water near highways from tetraethyllead in gasoline.
  • Example: Water fluoridation for tooth decay prevention, but excessive fluoride can cause tooth mottling and discoloration.
  • Example: Water purification using chlorination can produce potentially carcinogenic hydrocarbons.
• Naturally occurring: Example: Arsenic found naturally in copper ores can enter soil and water.

Classification of Chemical Sources

• Point source:
  • Easily identified
  • Remedies are attainable
• Nonpoint source:
  • Less dramatic effects
  • More difficult to correct

Bioaccumulation Ratio

• Measures chemical concentration in organisms compared to the environment.
• Formula:
  Bioaccumulation ratio = Conc. of chemical in organism / Conc. of chemical in medium (Environment)
• Factors contributing to high bioaccumulation ratios:
  • High partition coefficient (lipophilic): A tendency to dissolve in fats.
  • Recalcitrance towards degradation: Resistance to breakdown.

Biological Effects

• Transformation of chemicals in soil and water: Due to microorganism action involving chemical, photochemical, and biochemical reactions.
• Degradation: Leads to the disappearance of chemical molecules.
• Transport processes: Move chemicals between environmental compartments.
• Vaporization: Example: DDT

The Most Common Sources of Pollutants

• Pesticides:

  • Persistence time: The time required for 75-100% disappearance of pesticide residues.
  • Types based on persistence:
    • Persistence pesticides: Long persistence (2-5 years) like chlorinated hydrocarbon insecticides (DDT, aldrine, hexachlorohexane). They are lipid-soluble and have low water solubility. Adsorption depends on soil organic matter presence.
    • Moderately persistence pesticides: Intermediate persistence (1-18 months), like triazine herbicides. Adsorption to organic matter and clay minerals depends on pH and adsorbent surface acidity.
    • Nonpersistence pesticides: Short persistence (1-12 weeks), like organophosphate compounds, carbamates, and synthetic parathyroid. They are relatively less persistent in the environment, often applied to soil or crops for pest control.

• Non-pesticidal organic chemicals:

  • Low-molecular weight halogenated hydrocarbons: Produced through water chlorination for purification, like chloroform and bromoform.
  • Aromatic halogenated hydrocarbons: Ubiquitous contaminants of soil and water, like polychlorinated biphenyl (PCB) and tetrachlorodibenzo-p-dioxin (TCCD).
    • PCBs: Very stable, low-flammability materials used in electrical capacitors, plasticizers, and paper manufacturing.
  • Chlorophenols: Examples include pentachlorophenol (used in antibacterial products) and hexachlorophene (resistant to biotransformation, persists, and bioaccumulates).
  • Phthalate ester plasticizers: Used in construction, automotive, household products, apparel, toys, packaging, and medical products. Can be found in soil and water, examples include diethyl-hexylphthalate (DEHP) and di-butyphthalate (DBP). DEHP is carcinogenic in rats, and both DEHP and DPB can affect aquatic organism reproduction at low concentrations.

This quiz explores the various sources and types of air pollution as discussed in environmental toxicology. It covers key pollutants, their origins, and the distinction between outdoor and indoor pollution. Test your knowledge on how pollution affects wildlife and ecosystems.