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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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IV.RESULTS AND DISCUSSION

1. Results

1.1. Quantitative Microbial Risk Assessment from different treatments

1.1.1. From compost and top water (C+TW) treatment

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 table 5 below.Annual risks of Salmonella infection in scenarios where it is assumed that farmers can ingest accidentally soil, is 3.87x10-3 pppy (Annex iii). That is where a risk is possible for one infection of Salmonellaper 1000 farmers per year.Concerning Ascaris infection, annual risks is 4.67x10-2 (soil ingestion accidentally) (Annex v). That is where there may be a risk of one infection of Ascaris per 100 farmers when they use compost in field.

For lettuce consumption, Salmonellaannual risk infection is 1.54x10-1 (i.e. one infection of Salmonella per 10 consumers per year) (Annex iv). And Ascaris infection risk is 2.41x10-2 (Annex vi) i.e. one infection of Ascaris per 100 consumers of lettuce per year.

Table 5: Annual probabilities of Salmonella and Ascaris infection associated with the ingestion of soil combined with compost and consumption of lettuce

Pathogens

Soil Ingestion

Lettuce consumption

Pinf

Pyr(n=20)

Pinf

Pyr(n=52)

Salmonella

1.94x10-4

3.87x10-3

2.96x10-3

1.54x10-1

Ascaris

2.33x10-3

4.67x10-2

4.63x10-4

2.41x10-2

Annual infection risks of Salmonella and Ascaris which are compared with WHO guideline valuesin red line according to both scenarios are showed by figure 5 below.

Figure 5: Annual infection risks of Salmonella and Ascaris in function of scenarios compared with WHO guideline value.

1.1.2. For urine and top water (U+TW) treatment

Annual probabilities infection of Salmonella associated with the soil ingestion combined with urine and lettuce consumption are summarized in table 6 below.

Salmonella annual risk infection in a scenario which assumes that farmers can ingest accidentally soil spread with urine is9.55x10-1 (Annex vii). It means one infection of Salmonella per 10 farmers per year when they use urine to spread in field.

Table 6: Annual probabilities of Salmonella infection associated with the ingestion of soil combined with urine and consumption of lettuce

Pathogen

Soil ingestion

Lettuce consumption

Pinf

Pyr(n=20)

Pinf

Pyr(n=52)

Salmonella

4.78x10-2

9.55x10-1

2.50x10-9

1.30x10-7

For lettuce consumption, annual risk is 1.30x10-7 (Annex viii) i.e. one infection of Salmonellaper 10000000 consumers of lettuce per year.

Annual infection risks of Salmonella which are compared with WHO guideline values in red line according to both scenarios are showed by figure 6 below.

Figure 6 : Annual infection risks of Salmonella in function of scenarios compared with WHO guideline value.

1.1.3. From greywater only (GW) treatment

Annual probabilities of infection from Salmonella associated with the soil irrigated with greywater and lettuce consumption are summarized in table 7 below. Salmonella annual risksinfection in scenario which assumes that farmers ingest accidentally 10 to 100 mg of soil irrigated with greywater is8.89x10-6 (Annex ix). It means that one infection of Salmonella per 1000000 farmers per year when they are exposure 20 days per year.

From ingestion of irrigation greywater, annual risk infection is 1.02x10-4 (Annex x)i.e. one infection of Salmonellaper 10000 farmers per year for 275 days of exposure in worst case.

Table 7: Annual probabilities of Salmonella infection associated with the soil and greywater ingestion combined with greywater and lettuce consumption

Pathogen

Soil ingestion

Irrigation greywater

Lettuce consumption

Pinf

Pyr(n=20)

Pinf

Pyr(n=275)

Pinf

Pyr(n=52)

Salmonella

4.45x10-7

8.89x10-6

3.69x10-7

1.02x10-4

1.81x10-5

9.42x10-4

Concerning lettuce consumption, Salmonella risk infection is 9.42x10-4 (Annex xi).i.e. one infection of Salmonella per 10000 consumers of lettuce leaves per year when they eat it during 52 days per year.

Annual infection risks of Salmonella which are compared with WHO guideline values in red line according to three scenarios are showed by figure 7 below.

Figure 7 : Annual infection risks of Salmonella in function of scenarios compared with WHO guideline value.

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