Human Health Effects
The Part IIA site specific risk based approach means human
health effects need to be assessed on a site by site basis; there
are no mandatory standards defining concentrations of contaminants
in soil above which there may be an unacceptable risk to human
health. Contaminant toxicology and the extent of exposure to
contaminants, which is linked to human behaviour at a site, form an
essential part of the risk assessment process.
A practical indicator of harm is intake from the site exceeding
health criteria (tolerable daily intake for threshold substances
and index dose for non-threshold substances). Intake, expressed as
mg per kg body weight per day, is typically related to soil
concentrations, expressed as mg per kg, through an exposure
assessment. The exposure assessment considers how much of a
contaminant the critical receptor will be exposed to, as well as
for how long and how often. There are three routes of exposure
which may need to be considered depending on the site conditions:
ingestion, inhalation and skin contact. Common exposure pathways
include; ingestion of soil, consumption of contaminated food and
water, inhalation of dust and vapours and skin contact with
contaminated materials.
Various tools have been devised to assist in the risk assessment
process and to derive generic and site-specific criteria as
indicators of unacceptable risk. Whatever assessment criteria are
used, they must be appropriate to the site under consideration,
scientifically based and compatible with UK policy.
The Contaminated Land Exposure Assessment (CLEA) model has been
developed specifically to derive generic assessment criteria (soil
guideline values) for UK conditions. SEPA anticipate that CLEA soil
guideline values will be used where they are appropriate to the
site under consideration, taking into account the site conditions,
site use, the receptors under consideration and the conceptual
model for the site.
Where such circumstances do not apply, an alternative risk
assessment tool should ideally be used to derive site specific
assessment criteria. Potential tools include Risc Human, RBCA and
the "Method for deriving site-specific human health assessment
criteria for contaminants in soil" (SNIFFER project ref.LQ01):
available as free download from SNIFFER's website 