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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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1.1.4. For compost, urine, ant greywater (C+U+GW) treatment

Annual risks infection of Salmonella and Ascaris are showed by table 8 according to 3 scenarios (soil ingestion, ingestion irrigation greywater and lettuce consumption).

From soil ingestion, Salmonella annual risk infection is 1.44x10-4 (Annex xii). That is when there will be a risk of one infection of Salmonella per 10000 farmers when farmers are exposure during 20 days per year. For Ascaris infection, risk is 4.67x10-2 (Annex xiii). That means one infection of Ascaris per 100 farmers during 20 days exposure per year.

Table 8: Annual probabilities of Salmonella and Ascaris infection associated with the soil and greywater ingestion combined with compost, urine and greywater and lettuce consumption

Pathogens

Soil ingestion

Irrigation greywater

Lettuce consumption

Pinf

Pyr(n=20)

Pinf

Pyr(n=275)

Pinf

Pyr(n=52)

Salmonella

7.21x10-6

1.44x10-4

5.58x10-6

1.53x10-3

2.50x10-8

5.00x10-7

Ascaris

2.33x10-3

4.67x10-2

1,44x10-3

3.97x10-1

4.63x10-4

2.41x10-2

Fromingestion of irrigation greywater, Salmonella annual risk infection is 1.53x10-3 (Annex xiv). That means there will be a risk of one infection of Salmonella per 1000 farmers per year during 275 days of exposure. For Ascaris infection, risk is 3.97x10-1 (Annex xv). It means one infection of Ascaris per 10 farmers during 275 days of exposure per year.

From lettuce consumption, Salmonella annual risk infection is 5.00x10-7 (Annex xvi). That means there will be a risk of one infection of Salmonella per 1000000consumers of lettuce leaves per year during 52 days of exposure. For Ascaris infection, risk is 2.41x10-2 (Annex xvii). It means that one infection of Ascaris per 100 farmers during 52 days of exposure per year.

Annual infection risks of Salmonella and Ascaris which are compared with WHO guideline in red line values according to three scenarios are showed by figure 8 below.

Figure 8: Annual infection risks of Salmonella and Ascaris in function of scenarios compared with WHO guideline value.

1.2. Comparison of the probabilistic values of different treatments related with the scenarios

1.2.1. For soil ingestion scenario

The probabilistic values of all treatments compared with the WHO guideline values of risk for soil ingestion scenario are showed in the table 9 below.Salmonellaannual risk of infection in worst case from U+TW (9.55x10-1) is higher than C+TW (3.87x10-3), C+U+GW (1.44x10-4) and GW (8.89x10-6) for soil ingestion.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 in worst case from C+TW and C+U+GW are equal (4.67x10-2), however, this probabilistic values are higher than WHO guideline values (2006).

Table 9 : Probabilistic values of different treatments compared with the WHO guideline values of the risk.

Soil ingestion

WHO guidelines values

Treatment

Pathogens

10-6

Salmonella

Ascaris

C+TW

3.87x10-3

4.67x10-2

U+TW

9.55x10-1

NA

GW

8.89x10-6

NA

C+U+GW

1.44x10-4

4.67x10-2

C+TW=Compost +Top water; U+TW=Urine + Top water; GW=Greywater; C+U+GW=Compost + Urine + Greywater.

The probabilistic values of all treatments compared with the WHO guideline values in red line of risk for soil ingestion scenario are showed by figure 9 below.

Figure 9 : Probabilistic values of all treatments compared with the WHO guideline values of risk for soil ingestion scenario

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