Drinking Water and Health, Volume 7 Disinfectants and Disinfectant By-Products (1987) / Chapter Skim
Currently Skimming:
5 CONCLUSIONS AND RECOMMENDATIONS
5 CONCLUSIONS AND RECOMMENDATIONS
Pages 190-200
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 190... ...
Problems also continue to occur in cases of consumption of untreated water, errors of insufficient or interrupted disinfection, failures to maintain adequate levels of residual disinfectant in potable water distribution systems, and breaches in the systems. Although chlorination continues to be the predominant method of drinking water disinfection in the United States, the use of alternative methods is increasing.
|
From page 191... ...
Without such studies, it is possible that many future drinking water treatment operations, decisions about alternative methods, and trade-offs regarding toxic by-products of chlorination may be inordinately influenced by the preponderance of existing knowledge about types of bacterial pathogens that pose less of a public health problem in the United States today than several decades ago. "Life-cycle" studies of disinfectants are also needed for comprehensive examination of the direct and indirect implications of potential widespread local conversions to alternative disinfection practices.
|
From page 192... ...
Increasing the Cl/C ratio appears to drive both types of precursors toward chloroform production and a larger fraction of identifiable products, which nevertheless represent only a small fraction of the initial organic material. It is clear from the studies described in Chapter 4 that the importance of trihalomethanes may be overestimated from experiments involving Cl/ C ratios and chlorination times that greatly exceed typical drinking water disinfection conditions.
|
From page 193... ...
~Tumor data for risk assessment calculation from drinking water animal study. eTumor data for risk assessment calculation from corn oil gavage animal study.
|
From page 194... ...
For these reasons, chloramine treatment is used to minimize by-product formation. When free chlorine is used as the primary disinfectant, an amount should be used that is sufficient to produce a slight residual of free chlorine above that required to oxidize nitrogen, followed by the addition of ammonia to form monochloramine and limit THM formation.
|
From page 195... ...
A better approach, however, is to improve specific conventional water treatment processes to remove organic compounds and to add processes such as carbon absorption and preoxidation. Initial removal of organic by-product precursors precludes the need for reducing contact time, thus improving the efficacy of the disinfection processes and minimizing formation of organic chlorine by-products.
|
From page 196... ...
Ozone is an excellent disinfectant (although it must be used in combination with a secondary disinfectant to maintain a residual in the distribution system) ; ozone is an excellent oxidant for the various needs of water treatment; it does not form chlorinated by-products; and the admittedly inadequate studies now available point to lower toxicities of ozonated water than of chlorinated water.
|
From page 197... ...
Current evidence suggests that the relative risk to human health from exposure to disinfectants is probably small in settings with effective control of treatment levels in distribution systems. Routine monitoring of disease occurrence in populations with different treatment methods may provide crude qualitative descriptions of the patterns of disease in populations using different treatment strategies.
|
From page 198... ...
Usually a prospective cohort design is not feasible, particularly if the etiologic period is many years or decades, as it may well be for the chemicals under discussion, and if the disease occurrence due to disinfection by-products is rare. The occasion of a change in water disinfection treatment is an ideal time to begin such a study.
|
From page 199... ...
Epidemiological studies undertaken to learn about effect modification require stratified analysis or a sampling approach that selects individuals according to their exposure to a particular covariate so that the distribution of exposure is balanced for efficient contrasts of the disease rates according to categories of the covariates. For example, if the interest were to study the interaction of smoking and chlorination on bladder cancer risk, then the study population should be selected expressly in terms of their smoking experience.
|
From page 200... ...
Results from epidemiological studies that are properly conceptualized and employ valid methodologies can offer important information for policymakers on disinfectant treatment strategies.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.