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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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3. Health risk assessment forconsumers

In developing countries, foodborne illnesses caused by contaminated fruits and vegetables are frequent and in some areas they cause a large proportion of illness. However, due to lack of foodborne disease investigation and surveillance inmost of these countries, most outbreaks go undetected and the scientific literature reports only onvery few outbreaks(WHO, 1998). Thus, reuse of human excreta and greywater in agriculture can cause diseases for consumers especially when theyeat those crops without cooking. In addition, human waste may be a source of direct contamination if deposited in farms. Alternatively, environmental contamination with pathogens from these sources may be transferred indirectly to products via contaminated water, insects, agents such as dust, tools and equipment (FAO and WHO, 2008).According to FAO and WHO, 2008 fruits and vegetables can become contaminated with microorganisms capable of causing human diseases while still on plant in fields or orchards, or during harvesting, transport, processing distribution and marketing, or in the house. Also, Bacteria such as Clostridium botulinum, Bacillus cereus and Listeria monocytogenes, all capable of causing illness, are normal inhabitants of many soils, whereas Salmonella, Shigella, Escherichia coliand Campylobacter reside in the intestinal tracts of animals, including humans, and are more likely to contaminate fruits and vegetables through contact with faeces, sewage, untreated irrigation water or surface water (WHO, 2006a);(FAO and WHO, 2008); and ----(Mara and Sleigh, 2010a). Generally, people irrigating with wastewater have higher rates of helminth infections than those using freshwater. In addition, skin and nail problems may occur among farmers using wastewater -(Al-Hamaiedeh, 2010). There is substantial evidence that human enteric pathogens which are frequently present in greywater are responsible for low-level incidence of chronic gastroenteritis (upset stomach, vomiting, and diarrhea) as well as other «mild illness in people»-(Al-Hamaiedeh, 2010).

To assess potential risks associated with the use of reclaimed wastewater, the following exposure scenario is developed by -Asano et al., 1992 for spray irrigation of food crops. The following scenario is used to estimate the risk of infection to an individual for a single or an annual or a lifetime exposure. In this case, -Asano et al., 1992 are assumed to 10 mL reclaimed wastewater can be left on the crops eaten raw. However, irrigation with reclaimed wastewater is assumed to stop two weeks before harvesting. Thus, virus die-off due to desiccation and sunlight for 14 days is included in the calculation. Shuval et al., 1997 are corroborated the developed approach by -Asano et al., 1992where they werecollected for 100g of long leaf lettuce, 10.8 mL for 12 days before harvesting.Based on these measurements it is possible to estimate the amount of indicator organisms that might remain on the vegetables if irrigated with raw wastewater and with wastewater meeting the WHO guidelines.

In 1989, to mitigate the risks of contamination, in terms of epidemiological and technological data available, the WHO «Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture», recommended the microbial guidelines for wastewater irrigation of vegetables eaten raw of a mean of 1000 faecal coliforms (FC)/100 mL and <1 helminth egg/L in effluent (Shuval et al., 1997).Thus, a study was carried out in Ghana by Nana O.B. Ackerson and Esi Awuah, (2012), and which showed that, the annual probabilities of Ascaris and E. coli infection associated with the consumption of lettuce where farmers used the shallow well and stream to irrigate lettuce are higher (7.51x10-2 for Ascaris and 3.63x10-1 for E. coli) than the tolerable risk (10-6 pppy) recommended by WHO, (2006a).However, cessation of irrigation before harvest can be adopted to minimize the risk of infection in lettuce consumption (Nana O.B. Ackerson and Esi Awuah, 2012).

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