Risk assessment defines as the process of estimating both the probability that an event will occur and the probable magnitude of its adverse effects. Chemical or microbial risk assessment generally follows four basic steps, that is, hazard identification, exposure assessment, dose-response assessment, and risk characterization. Risk assessment provides an effective framework for determining the relative urgency of problems and the allocation of resources to reduce risks. Using the results of risk analyses, we can target prevention, reme-diation, or control effects towards areas, sources, or situations in which the greatest risk reductions can be achieved with resources available. Risk assessment is also used to explain chemical and microbial risks as well as ecosystem impacts. Moreover, this process, which allows the quantitation and comparison of diverse risks, lets risk managers utilize the maximum amount of complex information in the decision-making process. This information can also be used to weigh the cost and benefits of control options and to develop standards or treatment options.