1.2.3. Lettuce consumption
The probabilistic values of all treatments compared with the
WHO guideline values of risk for lettuce consumption scenario are showed in the
table 11 below. Salmonella annual risk of infection in worst case from
C+TW (1.54x10^{1}) is higher than U+TW (1.30x10^{7}), C+U+GW
(5.00x10^{7}) and GW (9.42x10^{4}).
The annual risk of infection in all treatment exceeded the
tolerable risk of =10^{6} per person per year (WHO, 2006a).
Ascaris annual risks of infection C+TW and C+U+GW are equal
(4.67x10^{2}), however, this probabilistic values are higher than WHO
guideline values (2006).
Table 11: Probabilistic
values of different treatments compared with the WHO guideline values of the
risk.
Pathogens

Treatment

WHO guideline values

C+TW

U+TW

GW

C+U+GW

10^{6} pppy

Salmonella

1.54x10^{1}

1.30x10^{7}

9.42x10^{4}

5.00x10^{7}

Ascaris

2.41x10^{2}

NA

NA

2.41x10^{2}

The probabilistic values of all treatments compared with the WHO
guideline values of risk for lettuce consumption scenario are showed by figure
11 below.
Figure 11: Probabilistic
values of all treatments compared with the WHO guideline values of risk for
lettuce consumption scenario
2. Discussion
2.1. Quantitative Microbial
Risk Assessment from each treatment.
2.1.1. For compost and top water treatment (C+TW)
Annual probabilities of Salmonella and
Ascaris infection related to soil ingestion when farmers use only
compost to spread in the field and when lettuce harvest is eaten by consumers
are showed by figure 5 above.
Annual risks of Salmonella infection in scenarios
where it is assumed that farmers can ingest accidentally 10 to 100 mg of soilis
3.87x10^{3} pppy. That means there will be a risk of one infection of
Salmonella per 1000 farmers per year.Salmonella risk
infection (3.87x10^{3}) for accidental soil ingestion is relatively
high and exceeds the benchmark in this scenario by a 3 order magnitude
(10^{3}). Thus farmers may be at risk of contracting typhoid fever
(Westrell, 2004) and (Nana O.B. Ackerson and Esi Awuah, 2012).Concerning
Ascaris infection, annual risk is 4.67x10^{2}(soil ingestion
accidentally). That means there will be a risk of one infection of
Ascaris per 100 farmers when they use compost in field. The annual
infection risk is relatively high and exceeds the benchmark by a 4 order of
magnitude (10^{4}). According to Amoah et al., (2011) farmers may be
at risk of contracting ascariasis.
From lettuce consumption, Salmonella annual risks
infection is 1.54x10^{1} (i.e. one infection of Salmonella
per 10 consumers per year).Salmonella annual risk infection is
relatively high and exceeds the benchmark by a 5 order of magnitude
(10^{5}). Consumers may be at risk of contracting typhoid fever when
they eat lettuce leaves (Mara et al., 2010).Ascaris infection risk
for lettuce consumption is2.41x10^{2}i.e. one infection of
Ascaris per 100 consumers of lettuce per year.The annual infection
risk is relatively high and exceeds the benchmark by a 4 order of magnitude
(10^{4}). According to Amoah et al., (2011)consumers may be at risk of
contracting ascariasis.
Any single pathogen that is ingested can multiply and form a
clone which is capable of causing infection (Haas et al., 1993). The annual
risk of infection for all pathogens in both scenarios exceeded the tolerable
risk of =10^{6} per person per year (WHO, 2006a).
