Environmental Engineering Reference
In-Depth Information
Table 21.6
Risk characterization summary
of non-resident friends and family who may have
been present in a supportive capacity.
Cases of
illness
Hazard
Exposure Estimate
DALYs
Flood water ingestion
10 4
Campylobacteriosis Clean-up Min.
0.076
2.2
10 2
Mean
7.529
2.1
The volume of water ingested accidentally is dif-
ficult to quantify.Westrell et al. (2004) assumed an
ingestion of 1mL in children playing near a source
of reused wastewater and transferring water from
hand-to-mouth. Tanaka et al. (1998) assumed that
a golfer exposed to a course irrigated inwastewater
will ingest 1mL in a single exposure. It has been
assumed that in a clean-up situation 1mL per hour
would be ingested in both children and adults.
10 1
Max.
56.67
1.6
10 5
Cryptosporidiosis
Clean-up Min.
0.008
1.1
10 4
Mean
0.387
5.3
10 3
Max.
3.002
4.1
1.8 10 4
Viral enteritis
Clean-up Min.
0.141
4.8 10 2
Mean
38.16
1.7 10 1
Max.
139.9
6.9 10 2
Overall illness
Mean
46
It can be seen from this Table that the risk is
dominated by viral enteritis, which accounted for
38 of the estimated 46 cases of illness.
Flood water 'quality'
As outlined above under 'Flood scenario', it
has been assumed that the flood water consists of
80% river water, 10% urban surface runoff and
10%foul flow. The pathogen concentration ranges
for the riverine and foul flow components,
shown in Table 21.5, are based on a combination
of literature and experimental data (Fewtrell
et al. 2008a). The urban non-foul component was
assumed to act as a diluting component, contain-
ing negligible levels of pathogens in comparison to
the other components.
Discussion
Over 20 possible pathogens have been identified
that could present an infection hazard in either
flood water or sediment, depending upon the
composition of the flood. The majority of these
pathogens cause gastrointestinal upsets. Of the
non-gastrointestinal pathogens, many either
cause clinical infections rarely (e.g. Leptospira
spp.), are opportunistic pathogens (e.g. Pseudomo-
nas spp. and Staphylococcus spp.) or have other,
more common, means of transmission (e.g. Legio-
nella spp. and Listeria spp.).
There is relatively little published information
on actual behaviour during flooding and clean-up,
although it is safe to say that in almost all cases
some exposure is inevitable. The most frequent
routes of exposure would be expected to be
through ingestion and skin exposure. While skin
exposure to flood waters is relatively obvious,
ingestion may be less so, and is likely to occur
mainly through hand-to-mouth transfer where
complete immersion (e.g. during evacuation) does
not occur.
The exploratory QMRA of flood clean-up-relat-
ed infection suggests a relatively high number
of cases of gastrointestinal illness (46 cases from
Risk characterization
This section brings together the estimates of ex-
posure and dose-response for each of the identified
hazards to provide an overall estimation of the risk
of illness, as shown (for the mean estimates) in
Table 21.6.
Table 21.5 Pathogen concentrations in the principal
flood components
Concentration (/litre)
Pathogen
River Foul ow
Campylobacter
0 - 3300
10 - 180,000
Cryptosporidium
0 - 59
1 - 96
1 - 64 a
Virus
70
-
3200
a Based on a 50th of the sewage value.
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