Glossary

2.3 Transport mechanisms in air, water, and soil

2 min read•august 7, 2024

Environmental contaminants move through air, water, and soil via various transport mechanisms. In the atmosphere, advection, diffusion, and dispersion spread pollutants, while deposition removes them. Long-range transport can carry contaminants across vast distances, impacting far-off ecosystems.

On land, contaminants move through soil by leaching, runoff, and erosion. In water bodies, pollutants travel via advection, diffusion, and dispersion in both surface water and groundwater. Understanding these processes is crucial for predicting contaminant fate and developing effective remediation strategies.

Atmospheric Transport Mechanisms

Movement of Contaminants in the Atmosphere

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  • Advection moves contaminants horizontally through the atmosphere due to wind and air currents (smoke from wildfires)
  • Diffusion spreads contaminants from areas of high concentration to areas of low concentration (perfume dispersing in a room)
    • Occurs due to random molecular motion and concentration gradients
  • Dispersion spreads contaminants vertically and horizontally due to turbulence and mixing in the atmosphere (plume from a smokestack)
    • Influenced by factors such as wind speed, temperature, and surface roughness

Deposition and Long-Range Transport of Atmospheric Contaminants

  • Atmospheric deposition is the process by which contaminants are removed from the atmosphere and deposited on Earth's surface
    • Dry deposition occurs when particles or gases settle on surfaces without precipitation (dust settling on a car)
    • Wet deposition occurs when contaminants are removed from the atmosphere by precipitation (acid rain)
  • Long-range transport allows contaminants to travel great distances from their source through atmospheric circulation patterns ( detected in Arctic regions)
    • Persistent organic pollutants (POPs) and mercury are common contaminants subject to long-range transport

Terrestrial Transport Mechanisms

Movement of Contaminants in Soil

  • Leaching is the downward movement of contaminants through soil with water (fertilizers leaching into groundwater)
    • Influenced by factors such as soil permeability, contaminant solubility, and precipitation
  • Runoff is the movement of contaminants over the soil surface with water (pesticides washing into nearby streams during heavy rainfall)
    • Occurs when precipitation or irrigation exceeds the soil's infiltration capacity
  • Erosion is the physical removal and transport of soil particles and associated contaminants by wind or water (contaminated soil eroding into rivers)
    • Can be accelerated by human activities such as deforestation and construction

Aquatic Transport Mechanisms

Movement of Contaminants in Groundwater

  • Groundwater transport is the movement of contaminants through soil and rock in aquifers (leaking underground storage tanks contaminating groundwater)
    • Influenced by factors such as aquifer permeability, groundwater flow rates, and contaminant properties
  • Advection moves contaminants in the direction of groundwater flow (plume of contamination spreading downgradient from a source)
  • Diffusion spreads contaminants from areas of high concentration to areas of low concentration in groundwater (contaminants spreading in all directions from a source)
    • Occurs due to random molecular motion and concentration gradients
  • Dispersion spreads contaminants in groundwater due to variations in flow velocity and path (contaminant plume spreading and becoming more dilute over time)
    • Caused by factors such as aquifer heterogeneity and mixing in fractures or pores

Key Terms to Review (2)

Heavy metals: Heavy metals are a group of metallic elements that have a high density and are toxic at low concentrations, including elements like lead, mercury, cadmium, and arsenic. Their persistence in the environment and potential to accumulate in living organisms makes them a significant concern in ecotoxicology, influencing various ecological and health-related outcomes.
Pesticides: Pesticides are chemical substances used to prevent, control, or eliminate pests that threaten agricultural productivity, human health, or natural ecosystems. Their use has significant implications in environmental science, as they can affect non-target organisms, disrupt ecological balances, and lead to contamination of air, water, and soil.
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