Water Conservation, Reuse, and Recycling Proceedings of an Iranian-American Workshop (2005) / Chapter Skim
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Pages 199-216
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199 Identifying Microbial and Chemical Contaminants for Regulatory Purposes: Lessons Learned in the United States Rebecca T Parkin SUMMARY Identification of potentially hazardous contaminants is the first step in risk management paradigms and in complying with regulatory mandates.
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200 WATER CONSERVATION, REUSE, AND RECYCLING contaminants must become more proactive so that a broader range of feasible response options can be developed. In the United States, regulation of drinking water contaminants has increased rapidly in the past decade since 1990.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 201 a list of unregulated contaminants, known as the Contaminant Candidate List (CCL) , every five years and to evaluate at least five contaminants every five years for potential regulation (SDWA, 1996)
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202 WATER CONSERVATION, REUSE, AND RECYCLING each contaminant are not feasible because of the extensive data and time required for implementation. Increasingly, regulatory programs in the United States must produce fairly rapid prioritizations of a large number of hazards, so that the greatest public health harms can be minimized and the risk reduction benefits can be achieved in a timely manner.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 203 mon ground has not become readily apparent, formal methods such as the Delphi process (reviewed in NRC, 2001) have been used to finalize the group's decisions.
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204 WATER CONSERVATION, REUSE, AND RECYCLING but none considered the impacts of the degradation byproducts of the input toxicants. All involved subjective, expert judgments, but all were less subjective than expert judgment methods.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 205 from one patient to another. The doctors may not always be able to state explicitly the specific criteria they used to make those decisions, but know that experience indicates that some treatment strategies will work more effectively with some patients as opposed to others.
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206 WATER CONSERVATION, REUSE, AND RECYCLING Expert judgment and rule-based methods suffer from the problems of developing consensus for decision criteria and processes, with the latter often getting bogged down in debates about weights and formulas for combining weights. The advantages of the prototype classification approach are that it minimizes the impacts of expert judgment, does not require a priori decision-making about the weights and formulas, produces scientifically based outcomes that are reproducible, processes all input information in a non-sequential manner so that no one factor serves as a "gate keeper," allows for more than two outcome categories, and permits processing of a very large number of substances in a limited amount of time.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 207 tions. To use neural network models the designer chooses the model's architecture; that is, determines the input variables and scoring systems to be considered, the number of neurons (or decision points)
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208 WATER CONSERVATION, REUSE, AND RECYCLING FIGURE 1 Recommended two-step process for identification of contaminants for regulatory consideration (As adapted from NRC, 2001)
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 209 FIGURE 2 Conceptual approach to identifying contaminants for inclusion in a Preliminary Contaminant Candidate List (PCCL)
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210 WATER CONSERVATION, REUSE, AND RECYCLING severity) had to be revised after the first few attempts to use it.1 Another committee member selected the modeling software (Matlab and Matlab Neural Network Toolbox of Mathworks, Inc., in Natick, Massachusetts)
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 211 FIGURE 3 Multi-layer neural network model used for contaminant classification (NRC, 2001)
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212 WATER CONSERVATION, REUSE, AND RECYCLING general attribute data appear to be sufficient to sort substances into those that merit further regulatory consideration and those that do not. An important part of developing a neural network model is examining the potential correlations and culling out highly correlated attributes so that the final set of attributes used in the model only includes those that are necessary to produce reliable outcome values.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 213 The investigators are determining the input attributes (and appropriate data sources) that will result in four distinct outcome categories: 1)
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214 WATER CONSERVATION, REUSE, AND RECYCLING contexts. The lessons learned from these efforts need to be reported in the peerreviewed literature so comparisons can be made.
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IDENTIFYING MICROBIAL AND CHEMICAL CONTAMINANTS 215 set of techniques are expected to open up opportunities for more rapid and appropriately focused public health initiatives. ACKNOWLEDGEMENTS The author acknowledges the contributions made by her colleagues on the NRC Committee on Drinking Water Contaminants that serve as the partial basis for one of her current research projects, the American Water Works Association Research Foundation Project #2776.
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216 WATER CONSERVATION, REUSE, AND RECYCLING Presidential/Congressional Commission on Risk Assessment and Management.
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