II. LITERATURE REVIEW
1. Generalities on health risk
assessment
1.1. Health risk assessment
According to WHO, 2006a, the risk is the probability that
something with a negative impact may occur. The agent that causes the adverse
effect is a hazard. Risk incorporates the probability that an event will occur
with the effect that it will have on a population or the environment,
considering the sociopolitical context where it takes place (WHO, 2006a). The
WHO guideline for the safe use of wastewater, excreta and greywater (WHO,
2006a) gives recommendations on treatment and management in order to avoid
unacceptable health risk. It is based on the Stockholm framework, which is a
harmonized approach to control water-related diseases (Fidjeland, 2010).
Different exposures and diseases are compared through the Disability Adjusted
Life Years (DALY) unit, which is a measure of the years lost due to premature
death, diseases and chronic effects. The DALY unit enables cross-sectional
cost-efficiency comparison of health initiatives (WHO, 2006a); (Fidjeland,
2010). The tolerable risk which is recommended by World Health Organization is
10-6 DALY (WHO, 2006a).
Many authors have characterized the risk analysis in three
principal steps: risk assessment, risk management and risk communication(WHO,
1999);(Westrell, 2004); (Metcalf & Eddy, 2007);(Fidjeland, 2010).
According to the National Research Council of USA, risk
assessment can be defined broadly as the process of the probability of
occurrence of an event and the probable magnitude of adverse effects on safety,
health, ecology, finances over a specified time period (Metcalf & Eddy,
2007). In other words, the risk assessment is defined as the qualitative or
quantitative characterization and estimation of potential adverse health
effects associated with exposure of individuals or populations to hazards (here
microbial agents) (Westrell, 2004); (Fidjeland, 2010). Risk assessment also
includes characterization of the uncertainties inherent in the process of
inferring risk.
Risk management is the process of evaluating and, if
necessary, controlling sources of exposure and risk. Sound environmental risk
management means weighing many different attributes of a decision and
developing alternatives (Metcalf & Eddy, 2007). Risk management is
anactivity much broader than technical risk analysis alone (McDowell and Lemer,
1991).
It is the interactive exchange of information and opinions
concerning risk and risk management among risk assessors, risk managers,
consumers, and other interested parties about the nature, magnitude,
significance, or control of a risk (Metcalf & Eddy, 2007).It concerns the
health risk assessment component, is the quantitative or qualitative
characterization and estimation of potential adverse health effects associated
with exposure of individuals or populations to hazardous materials and
situations (Metcalf & Eddy, 2007). Therefore, health risk assessment can be
divided into four major steps including: hazard identification,
dose-responseassessment, exposure assessment, and risk characterization (WHO,
1999).Health risk assessment includes chemical and microbial risk assessment
(Metcalf & Eddy, 2007), and in our case of study we will focus on
microbial risk assessment.
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