1.1 Environmental Chemistry Principles and Concepts

Environmental chemistry explores how chemicals interact with our world. It examines sources, reactions, and movement of substances in air, water, and soil. Understanding these processes helps us grasp how pollutants affect ecosystems and human health.

Chemical behavior varies across environmental compartments like the atmosphere, hydrosphere, and biosphere. Speciation, or the different forms a chemical can take, influences its toxicity, mobility, and bioavailability. This knowledge is crucial for addressing environmental challenges effectively.

Fundamental Principles and Concepts of Environmental Chemistry

Principles of environmental chemistry

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• Sources of chemical species in the environment
  • Natural sources release chemicals through volcanic eruptions spew ash and gases, forest fires emit particulates and CO2, oceanic emissions produce dimethyl sulfide
  • Anthropogenic sources introduce pollutants via industrial emissions release SO2 and NOx, agricultural practices apply pesticides and fertilizers, fossil fuel combustion generates CO2 and particulate matter
• Chemical reactions in the environment
  • Photochemical reactions occur when sunlight triggers ozone formation in the troposphere
  • Acid-base reactions neutralize acidic rain in limestone-rich soils
  • Redox reactions oxidize iron in waterlogged soils turning them reddish-brown
  • Complexation reactions bind heavy metals to organic matter in soils reducing their bioavailability
• Transport mechanisms
  • Advection moves pollutants horizontally with wind or water currents (Gulf Stream)
  • Diffusion spreads chemicals from areas of high to low concentration (odors in a room)
  • Dispersion scatters pollutants in air or water due to turbulence and eddies
• Effects of chemical species
  • Bioaccumulation concentrates pollutants in organisms over time (mercury in fish)
  • Biomagnification increases contaminant levels up the food chain (DDT in birds of prey)
  • Toxicity causes harmful effects on organisms (lead poisoning in children)
• Fate of chemicals in the environment
  • Degradation processes break down chemicals
    1. Biodegradation by microorganisms decomposes organic pollutants
    2. Photodegradation by sunlight breaks down pesticides on plant surfaces
    3. Hydrolysis in water splits molecules like organophosphate pesticides
  • Partitioning between environmental compartments distributes chemicals (volatilization of PCBs from water to air)

Impact of environmental processes

• Human health impacts
  • Exposure routes introduce chemicals to the body
    • Inhalation of air pollutants (smog)
    • Ingestion of contaminated food or water (lead in drinking water)
    • Dermal contact with hazardous substances (pesticides)
  • Acute and chronic health effects range from immediate (CO poisoning) to long-term (asbestos exposure)
  • Carcinogenicity and mutagenicity cause cancer and genetic mutations (UV radiation)
• Ecosystem impacts
  • Biodiversity loss occurs due to habitat destruction and pollution (coral reef bleaching)
  • Habitat destruction fragments ecosystems (deforestation)
  • Disruption of food chains alters ecosystem balance (overfishing)
• Climate change implications
  • Greenhouse gas emissions trap heat in the atmosphere (CO2, methane)
  • Ocean acidification decreases pH affecting marine life (shellfish calcification)
• Environmental policy and regulation
  • Risk assessment evaluates potential harm from chemical exposure
  • Pollution control strategies implement technologies to reduce emissions (scrubbers)
• Sustainable development
  • Green chemistry principles design safer chemicals and processes
  • Life cycle assessment evaluates environmental impacts from cradle to grave

Environmental Compartments and Chemical Behavior

Interactions of environmental compartments

• Atmosphere
  • Troposphere contains weather phenomena and most air pollutants
  • Stratosphere houses the ozone layer protecting from UV radiation
  • Mesosphere experiences meteors burning up
  • Thermosphere absorbs X-rays and UV radiation
• Hydrosphere
  • Oceans regulate climate and absorb CO2
  • Freshwater systems provide drinking water and support aquatic ecosystems
  • Groundwater stores water in aquifers and can transport contaminants
• Geosphere
  • Lithosphere forms the Earth's crust and upper mantle
  • Pedosphere (soil) supports plant growth and filters water
• Biosphere
  • Terrestrial ecosystems include forests, grasslands, and deserts
  • Aquatic ecosystems encompass freshwater and marine environments
• Interactions between compartments
  • Water cycle moves water between atmosphere, land, and oceans
  • Carbon cycle exchanges carbon through photosynthesis, respiration, and decomposition
  • Nitrogen cycle converts nitrogen between organic and inorganic forms
  • Biogeochemical cycles circulate elements through biotic and abiotic components

Chemical speciation in environments

• Chemical speciation distribution of chemical species in different forms affects behavior (lead in soil)
• Factors affecting speciation
  • pH influences metal solubility and organic compound ionization
  • Redox conditions determine oxidation states of elements (iron in wetlands)
  • Ionic strength affects ion activity and complexation
  • Presence of complexing agents alters metal bioavailability (humic substances)
• Importance of speciation
  • Bioavailability determines uptake by organisms (selenium in plants)
  • Toxicity varies with chemical form (chromium III vs chromium VI)
  • Mobility in the environment depends on speciation (arsenic in groundwater)
• Speciation examples
  • Metal ions form different species (mercury as elemental Hg, methylmercury, Hg2+)
  • Nutrients exist in various forms (nitrogen as NH4+, NO3-, organic N)
• Analytical techniques for speciation studies
  • Chromatography separates chemical species (HPLC for pesticides)
  • Spectroscopy identifies and quantifies species (ICP-MS for metals)
• Environmental implications
  • Remediation strategies target specific chemical forms
  • Risk assessment considers bioavailable fractions
  • Fate modeling predicts transport and transformation of species