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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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2.1.2. 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 figure 6 above.

Salmonella annual risk infection in scenario which assumes that farmers can ingest accidentally soil spread with urine is 9.55x10-1. It means one infection of Salmonella per 10 farmers per year when they use urine to spread in field.This is high and exceeds the benchmark by 5ordersof magnitude. Thus, farmers may be at risk of contracting diseases (Höglund, 2001).

For lettuce consumption, annual risk is respectively 1.20x10-7 and 1.30x10-7 for 50 and 95 percentile i.e. one infection of Salmonellaper 10000000 consumers of lettuce per year. Risk is relatively low and respects the tolerable risk recommended (10-6 pppy) by WHO guidelines (WHO, 2006b). In this scenario consumers may eat lettuce leaves without any high risk-(Carr, 2005).

2.1.3. For greywater only (GW) treatment

Annual probabilities of infection by Salmonella associated with the soil irrigated with greywater and lettuce consumption are summarized in figure 7 above.

Salmonella annual risks infection in a scenario which assumes that farmers ingest accidentally 10 to 100 mg of soil irrigated with greywater is 8.89x10-6. It means that one infection of Salmonella per 1000000 farmers per year when they is exposure of 20 days per year. This result complies with the tolerable annual risk (10-6 per person per year)recommended by WHO, (2006a). This exposure do not constitute a public health from farmers-(Zuma and Tandlich, 2010).

For irrigation with greywater (farmers can ingest 1 to 2 mL), annual risk infection is 1.02x10-4 i.e. one infection of Salmonella per 10000 farmers per year for 275 days of exposure in worst case. Theorder ofmagnitude is2. In this situation, farmers may be at risk of contracting diseases according to WHO, (2006a) guidelines.

It is concerning lettuce consumption, Salmonella risk infection is 9.42x10-4 .i.e. one infection of Salmonella per 10000 consumers of lettuce leaves per year when they eat it during 52 days per year. The magnitude is 2 orders compared to WHO recommendations (10-6 pppy). These lettuce leaves cannot eat because of high load remain on leaves when they irrigate it with greywater. However last irrigation before harvest must be considered (2 days) in evaluation of risk according to Shuval et al., (1997) and WHO, (2006a).

2.1.4. For compost, urine, and greywater (C+U+GW) treatment

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

For soil ingestion, Salmonella annual risk infection is 1.44x10-4. That means there will be a one infection of Salmonella per 10000 farmers for the worst case when farmers are exposed during 20 days per year. This is relatively high and exceeded the benchmark 2 order of magnitude compared to WHO guidelines (10-6 pppy). Farmers may be at risk of contracting salmonellosis or typhoid fever (Nana O.B. Ackerson and Esi Awuah, 2012). For Ascaris infection, risk is 4.67x10-2. It means one infection of Ascaris per 100 farmers during 20 days exposure per year.This is relatively high and exceeds the benchmark by 4 order of magnitude compared to WHO guidelines (10-6 pppy). Farmers can be infected by ascariasis.

From ingestion of irrigation greywater, Salmonella annual risk infection is 1.53x10-3. That means there will be a risk of one infection of Salmonella per 1000 farmers per year during 275 days of exposure. This is high and exceeds the benchmark in both cases by 3 orders of magnitude (10-3). Farmers may be at risk of contracting salmonellosis or typhoid fever(Höglund et al., 1998). For Ascaris infection, risk is 3.97x10-1. It means one infection of Ascaris per 10 farmers during 275 days of exposure per year. This is relatively high and exceeds the benchmark by 5 order of magnitude compared to WHO guidelines (10-6 pppy). Farmers can be infected by ascariasis(Mara and Sleigh, 2010b).

From lettuce consumption, Salmonella annual risk infection is 5.00x10-7. That means there will be a risk of one infection of Salmonella per 10000000 consumers of lettuce leaves per year during 52 days of exposure. This result complies with the tolerable annual risk (10-6 per person per year)recommended by WHO, (2006a). This exposure does not constitute a public health risk from farmers. ConcerningAscaris infection, risk is 2.41x10-2. It means one infection of Ascaris per 100 farmers during 52 days of exposure per year. This is relatively high and exceeds the benchmark by 4 order of magnitude compared to WHO guidelines (10-6 pppy). Farmers can be infected by ascariasis (Mara and Sleigh, 2010b).

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