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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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1.2. Steps of health risk assessment

Many authors have localized the health risk assessment in four steps which are mentioned below (Haas et al., 1999); (WHO, 1999);(Metcalf & Eddy, 2007):

Hazard identification, defined as the process of determining whether exposure to an agent can cause an increase in the incidence of a health condition, is the most easily recognized in the actions of regulatory agencies (Metcalf & Eddy, 2007). Also the identification of microbiology agent capable of causing adverse health effects and which may be present in a food or group of foods(WHO, 1999).

Dose-responsemay be defined as the determination of the relationship between the magnitude of exposure (dose) to a chemical, biological or physical agent and the severity and/or frequency of associated adverse health effects (response)(WHO, 1999).The dose-response assessment is the process of characterizing the relationship between the dose of an agent administered or received and the incidence of an adverse health effect in exposed populationsand then estimating the incidence of the effect as a function of human exposure to the agent(Metcalf & Eddy, 2007).

Exposure assessment is the process of measuring or estimating the intensity, frequency, and duration of human exposures to an agent currently present in the environment. For microbial risk assessment, exposure assessment describes the magnitude and/or probability of actual or anticipated human exposure to pathogenic microorganisms or microbiological toxins(Haas et al., 1999); (Metcalf & Eddy, 2007);(Fidjeland, 2010).

Risk characterization is the process of estimating the incidence of a health effect under various conditions of the human exposure described in exposure assessment. In addition, risk characterization may require compiling all the data necessary for a given model and running simulations (Haas et al., 1999); (WHO, 1999) and (Metcalf & Eddy, 2007).

1.3. Microbial risk assessment

Haas et al., (1999) were defined microbial risk assessment (MRA) as the process that is used to evaluate the likelihood of adverse human health effects that can occur following exposure to pathogenic microorganisms or to a medium in which pathogens occur.Other authors as WHO, (1999),Metcalf & Eddy, (2007) andFidjeland, (2010)explained the microbial or microbiological risk assessment process includes evaluation and consideration of quantitative information; however, qualitative information is also employed as appropriate. In other words, the microbial risk assessment should explicitly consider the dynamics of microbiological growth, survival, and death in foods and the complexity of the interaction between human and agent following consumption as well as the potential for further spread (WHO, 1999).

Quantitative Microbial Risk Assessment (QMRA) is a tool used to predict the consequences of potential or actual exposure to infectious microorganisms(Haas et al., 1999). The methodology is based on the chemical risk assessment concept for which the National Academy of Sciences published recommended definitions and main principles (Höglund, 2001).QMRA thus starts by a problem formulation where all the transmission routes and pathogens of interest are identified. It then assesses the dose of a certain pathogen to which an individual may be exposed and uses this dose in a dose-response model to calculate the probability of infection. Risks are finally characterized by taking into consideration the frequency of the exposure events for the range ofpathogens studied, to estimate a total risk (Haas et al., 1999);(Höglund, 2001).

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