Environmental Engineering Reference
In-Depth Information
exposure is the first step in defining the receptor
population. However, this may not reflect the
susceptibility of different populations groups to
infection. Key population segments of interest are
the very young and old as well as those on drugs
that depress the immune system (such as those
given to transplant patients) and those with HIV
infection.
mouthing behaviour
and frequent hand-to-
mouth contact.
.
The ingestion of contaminated water supplies,
particularly where private potable supplies are
used in inundated areas, may be a significant
exposure risk (Petrie et al. 1994; Duke
et al. 1996; Fewtrell et al. 1998; DWI 2003; Kay
et al. 2007c). However, in the UK, the majority of
homes in the urban environment receive mains
water from a water utility company, where the
drinking water supply will often be a source out-
side the urban area and unaffected by flooding.
Where the infrastructure is adequate, outbreaks of
illness are unlikely to result from flooding unless
the security of the water supply is directly com-
promised (Hunter 2003). Where public drinking
water supplies are compromised, the water utility
is required to provide alternative sources of water,
as illustrated in the floods in Gloucestershire in
summer 2007 when the Mythe water treatment
works in Tewkesburywas flooded leaving 350,000
people to be supplied by bowser (Fig. 21.3) and
bottled water. The alternative source is, however,
rarely adequate for all uses, possibly leading to
compromised personal hygiene.
Vulnerable groups
There are a number of factors that make some
people more vulnerable to health impacts than
others. These may be related to age, pre-existing
disease, and behaviour, as illustrated inTable 21.2.
Quantitative Microbial Risk
Assessment (QMRA)
Data on a number of infections are routinely col-
lected; however, ascribing illness to an actual
flooding event is difficult, thus QMRA can be used
to provide an estimate of flood-related infection
risk. QMRA is a formal probabilistic process
for estimating microbial risks within defined sce-
narios. There are four steps (in which the first
three are combined in order to characterize the
estimated risk), namely: hazard characterization,
dose-response assessment, exposure assessment,
and ultimately risk characterization.
Receptors
Receptors are the people subject to the flood event
or exposed to the flood water. Clearly, physical
Fig. 21.3
Bowser supply in
Gloucester, following flooding of
Mythe water treatment works.
Photo: L. Fewtrell.
