6.1 Contaminant Sources, Types, and Environmental Behavior

Water contaminants come from various sources, both point and non-point. They include inorganic, organic, and biological pollutants that can harm ecosystems and human health. Understanding their origins helps us tackle water pollution effectively.

Once in water, contaminants undergo physical, chemical, and biological processes that affect their fate and distribution. Factors like solubility, environmental conditions, and water body characteristics influence how pollutants behave and impact aquatic systems.

Sources and Behavior of Water Contaminants

Sources of water contaminants

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• Point sources directly discharge pollutants into water bodies from specific locations
  • Industrial discharges release chemicals and waste products from manufacturing processes
  • Municipal wastewater treatment plants emit treated sewage containing residual contaminants
  • Combined sewer overflows occur during heavy rainfall, releasing untreated sewage and stormwater
• Non-point sources contribute pollutants from diffuse areas over large regions
  • Agricultural runoff carries fertilizers, pesticides, and animal waste into water systems
  • Urban stormwater washes oil, grease, and debris from impervious surfaces into waterways
  • Atmospheric deposition transports airborne pollutants that settle into water bodies (acid rain)
• Categories of contaminants encompass various pollutant types affecting water quality
  • Inorganic contaminants include metals and nutrients impacting aquatic ecosystems
    • Heavy metals bioaccumulate in organisms (lead, mercury, arsenic)
    • Nutrients cause eutrophication and algal blooms (nitrogen, phosphorus)
  • Organic contaminants persist in the environment and affect living organisms
    • Pesticides harm non-target species and disrupt ecosystems
    • Polychlorinated biphenyls accumulate in fatty tissues and biomagnify in food chains
    • Pharmaceuticals and personal care products alter aquatic organism behavior and physiology
  • Pathogens cause waterborne diseases and infections
    • Bacteria lead to gastrointestinal illnesses (E. coli)
    • Viruses spread through contaminated water (hepatitis A)
    • Protozoa cause severe diarrheal diseases (Giardia)
  • Emerging contaminants pose new challenges to water quality management
    • Microplastics accumulate in aquatic environments and enter food chains
    • Per- and polyfluoroalkyl substances persist in the environment and impact human health

Fate of aquatic contaminants

• Physical processes transport and distribute contaminants in water bodies
  • Advection moves pollutants with water flow, spreading contamination downstream
  • Dispersion causes contaminants to spread due to variations in water velocity and turbulence
  • Diffusion drives the movement of contaminants from areas of high to low concentration
• Chemical processes alter contaminant properties and behavior in aquatic systems
  • Sorption attaches contaminants to particles or sediments, affecting their mobility
  • Precipitation forms solid particles from dissolved contaminants, influencing their availability
  • Redox reactions change oxidation states, impacting contaminant solubility and toxicity
• Biological processes transform and accumulate contaminants in living organisms
  • Biodegradation breaks down organic contaminants through microbial activity
  • Bioaccumulation concentrates contaminants in organisms over time
  • Biomagnification increases contaminant levels up the food chain, affecting top predators

Distribution of water pollutants

• Physical properties of contaminants influence their behavior in aquatic environments
  • Solubility determines how readily contaminants dissolve in water (polar vs non-polar compounds)
  • Volatility affects the tendency of contaminants to evaporate from water surfaces
  • Octanol-water partition coefficient ($K_{ow}$) measures hydrophobicity, predicting partitioning between water and organic phases
• Environmental conditions impact contaminant fate and transport
  • pH alters contaminant solubility and speciation, affecting bioavailability
  • Temperature influences reaction rates and solubility of gases and some compounds
  • Dissolved oxygen levels impact redox reactions and biodegradation processes
• Characteristics of the water body affect contaminant distribution and persistence
  • Residence time determines how long contaminants remain in a water system
  • Stratification creates layers with different contaminant concentrations based on temperature or density
  • Sediment composition influences sorption and desorption processes of contaminants
• Hydrological factors shape contaminant movement and concentration
  • Flow rate affects dilution and transport of contaminants in rivers and streams
  • Mixing patterns influence the distribution of contaminants in lakes and reservoirs
• Biological activity alters contaminant behavior in aquatic ecosystems
  • Presence of degrading microorganisms breaks down certain organic contaminants
  • Bioturbation mixes sediments, redistributing contaminants in bottom layers

Impacts of water contamination

• Ecological impacts disrupt aquatic ecosystems and biodiversity
  • Eutrophication causes algal blooms, depleting oxygen and creating dead zones
  • Bioaccumulation in aquatic organisms affects entire food webs
  • Endocrine disruption in wildlife alters reproductive patterns and development
  • Habitat degradation reduces suitable living spaces for aquatic species
• Human health impacts pose risks through various exposure routes
  • Acute toxicity causes immediate effects from high-dose exposure (chemical spills)
  • Chronic toxicity results in long-term effects from low-dose exposure over time
  • Carcinogenicity increases cancer risk in exposed populations
  • Reproductive and developmental effects impact fetal development and fertility
• Exposure pathways determine how contaminants reach human populations
  • Direct ingestion of contaminated water occurs through drinking or cooking
  • Consumption of contaminated fish or shellfish bioaccumulates toxins in humans
  • Dermal contact during recreational activities exposes skin to waterborne contaminants
• Vulnerable populations face higher risks from water contamination
  • Children and infants have developing organ systems more susceptible to toxins
  • Pregnant women can transfer contaminants to developing fetuses
  • Immunocompromised individuals have reduced ability to fight waterborne pathogens
• Risk assessment methods evaluate potential hazards and guide management decisions
  1. Hazard identification determines contaminant presence and potential effects
  2. Dose-response assessment establishes relationships between exposure levels and health outcomes
  3. Exposure assessment quantifies human contact with contaminants
  4. Risk characterization combines previous steps to estimate overall health risks