Introduction:There are various stages in an Environmental Health Impact Assessment:
Hazard Identification:The hazards are determined from a wide range of information sources relevant to what is planned - a matrix approach is to be recommended.
For example one dimension of the matrix could include the various stages and/or processes of what is proposed while the other could include the various forms of energy, hazardous chemical substances, and microbial contamination which may arise.
You might wish to access information on occupational hazard identification and risk assessment.
Exposure assessment:Note that once a hazard matrix is constructed it does not necessarily follow that a detailed assessment of all the conceivable hazards must be undertaken. Usually common sense and a preliminary review of available data by a competent professional will indicate which exposures to hazards are likely to be trivial and need be taken no further, and which ones will need a formal assessment of likely exposure. If possible it is better to measure "dose" (actually taken up by the human body) but often we have to make do with "exposure." The parameters for measuring exposure are many and varied, for example:
How can you calculate the "dose" of the agent?
What routes would you consider and what media?
e.g. could a route be ingestion by eating or drinking; skin contamination through washing, bathing, or exposure to contaminated soil; or inhalation of polluted air? Young children ingest much more soil, earth, dust and paint than adults.
Exposure/dose v response/effect
The relationship between exposure (concentration or "activity" multiplied by time in an integrated way) and harm to health expressed as response (i.e. likelihood of harm) and effect (magnitude of harm in an individual) is of fundamental importance.In other words, after assessing exposures, the exposure-response relationship is the means of translating estimates of exposure into risks to health. It will need an input of the exposure estimates. Information (so far as is already known to science) is needed about the relationship between a given exposure and the likelihood of a health effect.
Other data which may be needed includes information about the characteristics of the population likely to be exposed, and whether some are potentially more susceptible than the general population. Are we considering risk to "average" or "typical" persons or are we considering individuals for whom the risk may be higher (the very old and very young, for example).
How are we going to allow for the diversity of human responses - by looking at the most critical, or by looking at the average?
Health risk can be expressed as the frequency
with which a given level of harm may be expected from hazards associated
with a particular development. Amongst other things, we need to be clear
about the nature and severity of the harm, the number of people at risk,
and the period of time during which the specified number of new harmed
cases will arise. The health effects need to be characterised in
various ways, for example:
Latency of the health effect:
is it an acute irritant/poison (e.g. chlorine, sulphur dioxide) or a cancer risk which may be manifest only after a period of a few years (e.g. benzene) or several years (e.g. asbestos)?
Nature of the health effect:
Severity of the health effect:
is it a minor effect (e.g. acne caused by dioxins) or a very serious one (e.g. leukaemia caused by ionising radiation or benzene exposure)? Is it possible to distinguish "nuisance" symptoms from serious health effects? If the health effect appears at first to be a minor one, could it be associated with something more seious?
Reversibility of the health effect:
e.g. cancers do not usually reverse; dermatitis and asthma may do.
Is there a likelihood of harm to future generations (sometimes called "hereditary mutagenicity")?
...e.g. genetic effects caused by radiation.
To what extent could other environmental exposures (whether or not related to the environmental assessment in hand) interact to produce different/more likely/more severe health effects?
e.g. the possible interaction between various airborne irritants that may affect the respiratory tract (SO2, NOx, etc.); or a general issue - tobacco smoking.
To what extent could the proposal reduce the risk to human health, which in turn has to be balanced against possible adverse consequences? e.g.:
As with exposure assessment, but to an even greater degree, our exposure-response assessment may contain considerable uncertainty.
Worked examples, and case-studies:This website does not yet contain a worked example of an environmental impact assessement as it relates to human health, but you may wish to consult a student's assignment on the subject.
You may also wish to consult a useful document: the Canadian Handbook on Health Impact Assessment.