Toxicity Assessment Levels

Toxicity Assessment

Tier 2 – Toxicity Assessment

At this tier, the objective is to refine your understanding of the potential effects of the contaminants of concern as identified in the RA Tier 1 assessment. This involves more than referring to generic guidance or criteria values that assume the contaminant is 100% available (to the receptor). In an RA Tier 2 you will need to conduct an extensive literature review to obtain up-to-date information regarding:

properties of the chemical
properties of the environment specific to your site
properties of the receptor organism(s)
bioaccumulation potential of the chemical
toxicity of the contaminant(s).

Note: when reviewing human health effects and ecotoxicity literature it is important to consider the quality of the data and any uncertainty factors in applying the data.

For more information on the above topics click here. For a listing of toxicity data for CCA and BTEX from the international literature click here.

Follow link for the XYZ Enterprises example at RA Tier 2.

Tier 3 – Toxicity Assessment

At this tier, the objective will be to provide site-specific toxicity estimates for the contaminants of concern. In order to achieve this, you will need to have obtained the information set out in Tier 2, i.e. properties of the chemical, environment and receptor etc.The following are some of the data that may be required to support the models being developed

measures of chronic and sub-lethal toxicity
environmental factors specific to the site that may modify the toxicity of the contaminant/s
toxicity data for chemical combinations/mixtures.

To increase the level of refinement of the model, it may be appropriate to conduct the following tests:

site specific toxicity tests, i.e. measuring the direct effects of samples of site material (i.e. water or soil) on an indicator species
soil or water-based laboratory toxicity tests.

What information does ecotoxicity test data provide? Ecotoxicity data derived from field measurements can:

determine body burdens of contaminants in various species;
identify bioaccumulation or transfer of contaminants through the food web;
be utilised to determine fate of contaminants and the extent of potential impacts;
establish necessity for site-remediation or clean-up.

Toxicity data derived from laboratory tests can:

provide quantitative assessments of contaminant bioavailability and toxicity;
characterise body-burden/effect relationships for the prediction of the level of impairment likely to be encountered in the field
determine the relative sensitivity of various species, e.g., plants, invertebrates and fish (see data derived for CCA chemicals);
identify the relative toxicological importance of various chemical contaminants;
develop appropriate site-specific guidelines for chemical contaminants;
establish necessity for site-remediation or clean-up.

Toxicity testing is a specialised field with a variety of approaches and methods from which to choose. You may wish to approach an organisation such as CENTOX or NIWA for advice.

Click on the links to read about information on toxicity testing and resources for toxicity testing protocols and to see ecotoxicity results from tests that have been undertaken in New Zealand

In addition, Environment Canada’s ERA Framework (1994) provides a particularly useful summary of the toxicity tests that might potentially be used for toxicity assessment at contaminated sites. However, it is important to remember that 'toxicity testing only serves to model the field situation and is not necessarily representative of the dynamics of populations and communities' (Environment Canada 1994). Field assessment methods serve to provide the field validation of the models developed, to ensure that the conclusions reached are representative of the actual situation at the site.

Follow link for the XYZ Enterprises example at RA Tier 3.