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Balancing Microbial and Chemical Risks • Waterborne cholera, diarrhea, and other diseases – Both developing and industrial countries • Water disinfection vs. waterborne pathogens • INFECTIOUS WATERBORNE DISEASE RISKS – (Endemic) Waterborne outbreaks: inadequate or no disinfection • Cryptoporidiosis: Crytosporidium (protozoa) • Bacteria: Shigella and enterohemorrhagic E. coli • Other microbial contaminants: Cyclospora, microsporidia, Legionella, Aeromonas, Mycobacterium, and adenoviruses • Some gastrointestinal illness: waterborne – contamination of the distribution system partly responsible for endemic gastroenteritis • MANAGING MICROBIAL AND DBP RISKS – Disinfection DBPs (chemical risk) – No disinfection waterborne disease – How to reduce to the formation of DBPs • Moving the point of disinfection • Using an alternative disinfectant • Removing DBP precursors from the water – Costs of Controlling Microbial and DBP Risks • Costs saved by the prevention of infectious disease may be as much as eight to twelve times greater than the cost of the water system • Coagulation and clarification effective removal of both pathogens and precursor materials • GAC (granular activated carbon) too expensive • CONSIDERATION OF COMPETING RISKS – Risk trade-off between exposure to DBPs and exposure to waterborne pathogens – Identification of: • The DBPs that pose the greatest health risks • How a proposed treatment strategy or technology will affect the removal (and risk) of these DBPs and microbial contaminants • The costs associated with these water technologies – Developing countries: life expectancy is too low (diarrhea) how then can we observe cancer patients? • BALANCING RISKS – THE PROBLEM STATEMENT – What specific water treatment option(s)? optimum reduction in adverse health consequencies from both DBPs and waterborne microbial contaminants – Notable imbalance between the real and perceived riks associated with disinfection of drinking water • Ex) Diarrhea and gastroenteritis perceived to be less important – How to assess risk from complex mixtures of contaminants (bacteria, viruses, protozoa, inorganic chemicals, DBPs, and other organic chemicals)?: various water quality conditions • PREVENTION-EFFECTIVE ANALYSIS – Cost-effectiveness: treatment of drinking water vs. a public health intervention (microbial risk : chemical risk) – Duration and severity of illness and the public’s perception of the degree of risk • PROPOSED APPROACH TO ASSESS RISKS FROM D/DBPs and MICROBES – Primary effects: cancer, adverse pregnancy outcomes, gastroenteritis – Secondary effects: long-term sequelae of acute disease, side effects of treatment of acute disease – Both occurrence and severity of disease should be taken into account – The mixture of DBPs and pathogens to which humans are exposed can vary with time and location within a water distribution system dose-response data for a mixture of DBPs? • PROPOSED APPROACH TO ASSESS RISKS FROM D/DBPs and MICROBES – Water Treatment Scenarios to Define Exposure • Type and characteristics of source water • Type and amount of disinfectant used and contact time with precursor material • Range of water pH and temperature • Organic material and bromide ion concentration in source water • Water treatment to remove precursor material or DBPs – Risk Estimates • Highly uncertain at present More data needed