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Exposure Assessment - Tiers 2 & 3

Ecotoxicity testing protocols 

Ecotoxicity results

Contaminant mobility

Soil property data


Toxicity databases

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Problem Identification

Receptor Characterisation

Exposure Assessment

Toxicity Assessment

Risk Characterisation

Tier 2 – Exposure Assessment

A tier 2 Exposure Assessment will involve identifying and quantifying exposure-source pathways and distribution around the site. This will include:

  • preliminary quantitative descriptions of the mode and timing of contaminant releases, transport and fate
  • integration of exposure values for receptors of concern
  • undertaking a site review to determine if all considered pathways for benchmark criteria are relevant to the site
  • identification of specific human health or biological information from literature, e.g. ingestion, inhalation and dermal absorption rates
  • measurement of media properties affecting contaminant mobility and availability
  • calculation of contaminant concentration at the receptor.

At this point the exposure assessment should be able to provide a quantitative estimate of exposure for important receptors through important pathways, including estimates of uncertainty (e.g. confidence or tolerance limits).


Tier 3 – Exposure Assessment

Tier 3 Exposure Assessment principally involves the complex modelling of pathways, transport and fate, to determine:

  • present and future transport
  • transformation of contaminants (dilution, retardation, degradation)
  • environmental partitioning between media and into biota or people.

The model should be integrated with the other components of the RA and will involve the collection of further field data to refine and calibrate the model through iterations as required. 

Field data may include receptor ingestion, inhalation and absorption rates using food, air and water sampling to provide a specific exposure assessment for each human or biotic component. 

At this point the analysis of potential receptor body tissues and fluids may be appropriate. In addition, the key physical/chemical properties that determine a contaminant’s fate, as outlined in Section 4.3.1 of Environment Canada’s ERA Framework (1994), should be determined at this stage.

The model should characterise existing exposures and predict future exposures under each remediation option. A comprehensive uncertainty analysis and estimate should also be undertaken.

Finally, the default assumptions of the benchmark criteria should be modified appropriately to calculate a modified criteria specific to the site.

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Page last updated: 01 May 2007

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