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Health risk assessment associated with the reuse of compost, urine and greywater in agricultural field in sahelian climate.

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par Alexis Loukou BROU
Fondation 2iE - Master Environnement option Eau et Assainissement 2014
  

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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 is2.41x10-2i.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).

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