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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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2.3. Following up indicators of pathogen on lettuce leave

Sampling consisted in taking 100 g of vegetable matter at the stage of maturity on each of the 3 repetitions, which are representing 4 samples of each treatment. The collection was carried out in the respect of the conditions of hygiene and of sterility necessary and the samples are preserved at 4 °C until the moment of the analyses which take place within the next 24 h. The analyses relate to the surface of the sheets of lettuce. A quantity of 10 g of lettuce leaves of each treatment was introduced into sterile bottles with broad collar provided with a lid. Each bottle was completed with 90 ml of a solution of NaCl with 1N, then closed and agitated during 15 minutes in horizontal position on a plate agitator.For each flushing water representing a suspension mother of 10-1, two decimal dilutions at 10-2 and 10-3 were carried out with the NaCl solution with 1N. The suspension mother and dilutions were sown by spreading out of 0.1 mL on the culture media (Chromocult Agar or Slanetz Bartley according to the required type of indicators) cast in boxes of sterile Petri 90 mm in diameter. Each dilution was the two object repetitions.

3. Quantitative Microbial Risk Analysis (QMRA) methods

3.1. Hazard identification

All pathogens that are excreted in human excreta and greywater from insanitary and unhygienic surrounding environment could potentially be found in irrigation waters and vegetables (Nana O.B. Ackerson and Esi Awuah, 2012). A selection of pathogens was made for the risk assessment, representing bacteria (Salmonella and E.coli) and helminthes (A. lumbricoides). From epidemiological reviews, helminthes and bacteria pose the greatest health risks in human excreta and greywater reuse in agriculture(WHO, 2006a); (Mara and Sleigh, 2010b). The choice of Ascaris was due to its persistence for months to years in soil under harsh conditions(Amoah et al., 2005) thus making it an ideal reference organism for QMRAs in developing country (Nana O.B. Ackerson and Esi Awuah, 2012)such as Burkina Faso.

3.2. Exposure assessment

Exposure scenarios were identified from 2 target groups of population: farmers and urban consumers.

3.2.1. For farmers

We assume that during spreading compost, urine and irrigation with greywater, farmers did not wear protective clothing and were in direct contact with the different matrix (compost urine and greywater). Furthermore compost which is used to spread in our experimental site is not totally hygienic and mature. It was spread 2 days after it was taken away from family pilot to Ziniaré.Compost is used like basic manure before plant out lettuce. It carried out 1 time per cycle of lettuce crop. Variety of lettuce crop on our site has 50 days as total cycle. Farmers can ingest 100 mg of compost accidentally when they spread it in the field(Schönning et al., 2007).In rainy season, farmers do notgrow lettuce crop now in Burkina Faso, rainy season can take 3 months per year. Thus, farmers can be exposed 5times per year.Concerning urine,we used urine which is stored during 1 week before spreading in our experimental site. For doing so,we used a small bucket for spreading. Urine is applied 3 times per cycle for lettuce crop. Farmers can ingestaccidentally 0.43mL of urine when they spread it in the field after making experimentation (Annex ii). Also farmers spread urine without wear protective clothing. Exposition frequency is15 times per year.Greywater was used to irrigate lettuce crop with watering cans. Farmers can ingest accidentally 1 to 2 mL of greywater (Nana O.B. Ackerson and Esi Awuah, 2012)during irrigation of the lettuce crop. The exposure days per year to irrigation greywater are 275 days.

Concerning soil ingestion, farmers can ingest accidentally 10 to 100 mg of soil(Haas et al., 1999)contaminated with compost, urine and greywater when they work in fields.We assume that field workers are directly in contact with soil when they are spreading compost, planting out lettuce crops, and weeding the field. Those activities can occur 4 times per cycle. Therefore, the exposure days per year for those activities are 20 days.

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