What is a
Why is it important?
What is risk management?
of risk assessment
What are RA tiers?
The objective of Receptor Characterisation is to answer the question
receptors might be affected by contamination and in what way?'.
receptor is any plant, person or animal that is potentially affected by a
are a variety of considerations with regard to receptors, some of which are
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.
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:
- the mode of action or expression of the contaminant (e.g. neuro-endocrine,
- individual and community life history characteristics (e.g. migration, reproduction,
succession; for people who spend time working at, or living on or
near a site)
- the life stage of an organism at exposure (e.g. egg-larvae-juvenile-adult, reproductive
state, moulting; for people, foetus, infant, child or pregnant woman)
- conditions that may change the effect of contaminants (e.g. pest/predator/disease
conditions, environmental conditions such as food shortages, drought; for
people, water sources, vegetable growing, % of bare land etc).
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.
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
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:
- potentially exposed people (e.g. walkers, residents, students)
- generic ecological values (e.g. river biota, riparian biota, soil
- important or sensitive species
- sensitive life stages
- potentially affected ecosystems, communities or habitats.
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
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.