Receptor Characterisation

A receptor is any plant, person or animal that is potentially affected by a contaminant. There are a variety of considerations with regard to receptors, some of which are considered below:

Scale

Receptors may be identified at a variety of scales ranging from individuals, species, populations and communities, to functional groups, habitats, and ecosystems.

We envisage that most investigations would focus on species, populations, and to a lesser extent, communities due to increasing complexity of ecological systems above this scale. Except for the largest sites, or those close to habitats of particularly rare fauna, few New Zealand sites would justify an ecosystem-scale investigation as a result of site contamination.

Sensitivity

In addition to the scale on which the investigation is conducted, some consideration should be given to sensitivity of the receptor. Sensitivity refers to how readily an ecological entity is affected by a particular stressor (USEPA 1998). Sensitivity is influenced by the following factors:

Visibility

The effect of a contaminant may not be immediately visible. The stage of life history and reproductive status may mean that the adverse effect induced by exposure to a contaminant may not be visible until some other time or in some other place. This is a particular issue with regard to migrating fish and birds in New Zealand, and for long latency diseases such as cancer.

Some of the issues to be considered for ecological receptors are summarised as follows:

'Normally, the main focus of receptor characterization is on indigenous populations of living resources such as animals and plants. It is also important, though, to identify natural ecosystem processes (e.g. production, decomposition) that may be affected by the stressors, and to consider migratory species.

Natural ecosystem processes are important since changes in ecosystem structure or function may, in turn, adversely affect the ability of ecosystems to generate products of value to humans (e.g. fish, fibre) or perform vital functions (e.g. flood and erosion protection).

Migratory species, though only passing through an area for a short time, may be highly concentrated in particular habitats (e.g. bird staging areas along a migration route, fish spawning areas), which renders them potentially vulnerable to population level impacts.

Contaminant loads in migratory species cannot generally be pinpointed to a particular source, unless this source has a unique signature.

The juveniles of migratory species which are produced near the contaminated site are more comparable to an indigenous population, and their tissue concentrations are more likely to be the result of local sources. Contaminants can, however, be passed from females to their offspring through eggs, and this type of confounding influence should be considered.' (Environment Canada 1994).

It is important to remember that effects of chemical contaminants are not limited to chemical changes in the receptor (e.g. causing cancer or disrupting hormones) but may, particularly for ecological receptors, also cause significant adverse effects through behavioural changes (e.g. aversion to a site due to the presence of contaminants). This will have particularly severe effects where the species is rare and has only a limited range, where the habitat of a species is rare, and/or where habitat fragmentation is high.

Tier 1 – Receptor Characterisation tasks

At this stage, the objective is to undertake a preliminary screening to help identify the receptors most likely to be adversely affected by the potential contaminants. Receptors that are identified as being unlikely to be affected should be excluded from subsequent stages of the investigation unless new information to the contrary is obtained. Using existing data and information, and a site visit, the following information should be collected:

With regard to ecological receptors, you should consider consulting an ecologist to assist with this process to ensure that important ecological values are not overlooked. At this tier of the RA, Receptor Characterisation should require only a review of available information and a site reconnaissance. The former does not necessarily need to be an extensive investigation, but should provide basic characteristics sufficient to confirm the status as a potential receptor. The latter should include both the site itself and the surrounding area particularly downstream, downgradient and down wind of the site.