Animal Waste, Water Quality and Human Health

Risk management involves a balance between the most effective risk mitigationaction, based on cost or technical feasibility, and the interests and values ofstakeholders. Therefore risk managers will also seek information on costs(compared to the benefits) of risk management options. The efficacy of variousapproaches and the factors that affect it may be considered in the riskassessment to support the decisions of risk managers. The combination of riskassessment, risk management and risk communication is, in some frameworks,collectively termed ‘risk analysis’. Microbiological risk assessment frameworksrelevant to waterborne risk are discussed by Haas et al. (1999, Chapter 3);WHO (2003); Gale (2001a&b, 2003), Coffey et al. (2007) and Goss & Richards(2008).10.1.1 Key elementsComparative risk analysis 363The first step in risk assessment usually is the development of a conceptual modelor framework that combines knowledge of risk-affecting factors and how theycould interact to cause harm. In many cases this information can be expressedmathematically as a series of equations that, provided sufficient quantitative dataand knowledge exist, enable quantification of the risk or, at least, the relativerisk. In assessing the public health risk from exposure to microbial pathogens,the “risk assessment” task is often broken down into four discrete components:• Hazard Identification – which involves describing the hazard (pathogens),presenting the evidence that the hazard causes illness and that it can causeillness from the source of exposure being considered, and the type of illnesscaused.• Hazard Characterization – which presents information about characteristicsof the organism that affect its ability to cause illness, such as virulencefactors, physiological traits that affect its survival in the environment and,importantly, the severity of disease caused, including consideration ofdifferences in susceptibility of different members of the populationexposed and the probability of illness as a function of the dose ingested.In the context of water and sanitation this corresponds to considerationand characterization of elements of “pathogen virulence” and “hostsusceptibility”. This includes consideration of dose-response relationships,which is sometimes considered as a further discrete component (e.g., Haaset al. 1999).• Exposure Assessment – which attempts to estimate the exposure of theaffected population(s) to the pathogen under scrutiny. In the context ofpublic health risk from recreational/occupational exposure to water thiscould involve consideration of, for example: sources of contamination,