3. Health risk assessment
forconsumers
In developing countries, foodborne illnesses caused by
contaminated fruits and vegetables are frequent and in some areas they cause a
large proportion of illness. However, due to lack of foodborne disease
investigation and surveillance inmost of these countries, most outbreaks go
undetected and the scientific literature reports only onvery few outbreaks(WHO,
1998). Thus, reuse of human excreta and greywater in agriculture can cause
diseases for consumers especially when theyeat those crops without cooking. In
addition, human waste may be a source of direct contamination if deposited in
farms. Alternatively, environmental contamination with pathogens from these
sources may be transferred indirectly to products via contaminated water,
insects, agents such as dust, tools and equipment (FAO and WHO, 2008).According
to FAO and WHO, 2008 fruits and vegetables can become contaminated with
microorganisms capable of causing human diseases while still on plant in fields
or orchards, or during harvesting, transport, processing distribution and
marketing, or in the house. Also, Bacteria such as Clostridium
botulinum, Bacillus cereus and Listeria monocytogenes,
all capable of causing illness, are normal inhabitants of many soils, whereas
Salmonella, Shigella, Escherichia coliand Campylobacter
reside in the intestinal tracts of animals, including humans, and are more
likely to contaminate fruits and vegetables through contact with faeces,
sewage, untreated irrigation water or surface water (WHO, 2006a);(FAO and WHO,
2008); and ----(Mara and Sleigh, 2010a). Generally, people irrigating with
wastewater have higher rates of helminth infections than those using
freshwater. In addition, skin and nail problems may occur among farmers using
wastewater -(Al-Hamaiedeh, 2010). There is substantial evidence that human
enteric pathogens which are frequently present in greywater are responsible for
low-level incidence of chronic gastroenteritis (upset stomach, vomiting, and
diarrhea) as well as other «mild illness in people»-(Al-Hamaiedeh,
2010).
To assess potential risks associated with the use of reclaimed
wastewater, the following exposure scenario is developed by -Asano et al., 1992
for spray irrigation of food crops. The following scenario is used to estimate
the risk of infection to an individual for a single or an annual or a lifetime
exposure. In this case, -Asano et al., 1992 are assumed to 10 mL reclaimed
wastewater can be left on the crops eaten raw. However, irrigation with
reclaimed wastewater is assumed to stop two weeks before harvesting. Thus,
virus die-off due to desiccation and sunlight for 14 days is included in the
calculation. Shuval et al., 1997 are corroborated the developed approach by
-Asano et al., 1992where they werecollected for 100g of long leaf lettuce, 10.8
mL for 12 days before harvesting.Based on these measurements it is possible to
estimate the amount of indicator organisms that might remain on the vegetables
if irrigated with raw wastewater and with wastewater meeting the WHO
guidelines.
In 1989, to mitigate the risks of contamination, in terms of
epidemiological and technological data available, the WHO «Health
Guidelines for the Use of Wastewater in Agriculture and Aquaculture»,
recommended the microbial guidelines for wastewater irrigation of vegetables
eaten raw of a mean of 1000 faecal coliforms (FC)/100 mL and <1 helminth
egg/L in effluent (Shuval et al., 1997).Thus, a study was carried out in Ghana
by Nana O.B. Ackerson and Esi Awuah, (2012), and which showed that, the annual
probabilities of Ascaris and E. coli infection associated
with the consumption of lettuce where farmers used the shallow well and stream
to irrigate lettuce are higher (7.51x10-2 for Ascaris and
3.63x10-1 for E. coli) than the tolerable risk
(10-6 pppy) recommended by WHO, (2006a).However, cessation of
irrigation before harvest can be adopted to minimize the risk of infection in
lettuce consumption (Nana O.B. Ackerson and Esi Awuah, 2012).
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