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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Water and Sediment

Fate and Transport

Fate and transport processes “link” the release of contaminants at a source with the resultant environmental concentrations to which receptors can be exposed. When a contaminant is released from a source, it is subject to transport and transformation in the environment. Compounds can also transfer from one environmental medium to another.

Migration Process Examples Relevant to Water and Sediment
Transport
  • Dispersion of a contaminant through surface water (transport within a medium)
  • Contaminants in surface water settle and accumulate in sediments or are resuspended in surface water from sediments following disturbance (transport between media)
  • Contaminants in groundwater are discharged to surface water (transport between media)
Transformation
  • Organic breakdown or biodegradation of a compound in sediment by benthic organisms (chemical change)
  • Inorganic metals that dissolve in surface water (physical change)
Transfer – Environment to Biota
  • Contaminants in sediment are taken up by benthic organisms and bioaccumulated
  • Contaminated surface water or groundwater used as a source of drinking water is ingested by animals or humans

For additional information on the uptake of contaminants from water to fish, refer to the Aquatic Biota Module of the Media Tool Set.

The characteristics of water and sediment play a large role in the transport processes of contaminants through these media. For example, if surface water is a key exposure pathway, we might want data on flow rates and water characteristics like pH, salinity, water hardness (concentrations of cations, such as calcium and magnesium), and levels of dissolved oxygen. Environmental factors such as percent organic matter can play a large role in the mobility and bioavailability of contaminants in sediment. Physicochemical characteristics—such as water solubility, octanol/water partition coefficient (Kow), and solid/water partition coefficients (Kd or Koc)—are also important in predicting fate and transport behavior of contaminants in the aqueous phase.

There are a number of sources of information related to the environmental fate and transport of contaminants in surface water and sediment.

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Models

Environmental fate and transport models can be used with monitoring data to help characterize media-specific exposure concentrations. A variety of mathematical methods or models—each with specific data needs—are available to describe the multimedia transport and fate of pollutants in the environment. There are also several resources that contain information on input parameters necessary for fate and transport models.

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