Balancing Microbial and Chemical Risks

1. Balancing Microbial and Chemical Risks • Waterborne cholera, diarrhea, and other diseases – Both developing and industrial countries • Water disinfection vs. waterborne pathogens

2. 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

3. 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

4. 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?

5. 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

6. 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

7. 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?

8. 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