Water Reuse Potential for Expanding the Nation's Water Supply Through Reuse of Municipal Wastewater (2012) / Chapter Skim
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6 Understanding the Risks
6 Understanding the Risks
Pages 101-122
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From page 101... ...
Major research efforts have attempted to refine our There will always be a need for human-specific understanding of the human health risks of water reuse, data, and epidemiological studies will remain important particularly the risks of potable reuse, through toxico- to assessing and monitoring the occurrence of health logical and epidemiological studies (see Boxes 6-1 and impacts. However, today's decisions as to health and 6-2; NRC, 1998)
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From page 102... ...
These studies assess the incidence of acute gastrointestinal illness before and after scheduled changes in water sources or treatment processes. An example of such a study is a 1984–1987 Colorado Springs study of water reuse for public park irrigation.
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From page 103... ...
. nants that can be used to quantify health risks associ- Quantitative methods to assess potential human health ated with water reuse applications.
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From page 104... ...
aspects to the risk analysis and management process In the following sections, four core components of that are particularly germane to assessing and managing risk assessment are discussed with regard to a range of health risks from reclaimed water: water reuse applications: • Problem formulation: A t the outset, there 1. hazard identification, which includes a summary should be a problem formulation and scoping phase of chemical and microbiological agents of concern; in which the risk management question(s)
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From page 105... ...
On the other hand, death due to WATERBORNE ILLNESSES acute gastrointestinal illness, especially in the vulnerAND OUTBREAKS able young, is all too common in the developing world. As noted in Chapter 2, the early 20th century Most obvious to the public are the reported outbreaks brought significant public health improvements due of acute gastrointestinal illness largely due to pathoto the implementation of constructed water treatment gens in the water supply (Mac Kenzie et al., 1994)
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From page 106... ...
The adequacy of of water reuse, potential waterborne hazards should be the distribution system may therefore provide a limit considered in the context of the full suite of possible to the degree of risk reduction even though treatment exposure routes. becomes more stringent.
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From page 107... ...
Because of the need to disinfect wastewater, which may have comparatively higher or- Spontaneous abortiona Birth defectsa Low birth weight Preterm birth ganic content than typical drinking water sources, such treatment-related contaminants may be problematic in Target Organ Systems some reclaimed waters. Gastrointestinal organs Cardiovascular organs Multiple studies in the scientific literature have Kidney Cerebrovascular organs described associations between chemical contaminants Liver in drinking water and chronic disease such as cancer, chronic liver and kidney damage, neurotoxicity, and aMost consistently increased in epidemiological studies, adverse reproductive and developmental outcomes such especially those of trihalomethane disinfection byproducts.
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From page 108... ...
also have a high median infectious dose, sequent health risks known (NRC, 2008a; Khan, 2010; which requires ingestion of many cells for a likely esSnyder et al., 2009, 2010b)
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From page 109... ...
Accurately assessing exposure to reclaimed water is a F IGURE 6-2 C ontinuum of water quality with use and critically important aspect of assessing health risks, treatment. because the likelihood of harm from exposure distin- NOTES: (1)
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From page 110... ...
The ADD of a chemical climate, and likely other factors. Also, the concentrain reclaimed water represents the sum of the ADDs tion of contaminants in reclaimed water, which affects BOX 6-4 Cross Connections Several cross connections between nonpotable reclaimed water and potable water lines have been reported in the United States and elsewhere (e.g., Australia)
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From page 111... ...
. In terms of potential accumulation in food crops of persistent substances health risks, ingestion of reclaimed water is of greater such as perfluorinated chemicals and metals from reimportance than other reclaimed water uses because peated application of reclaimed water containing these exposure and estimation of potential health risks are substances.
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From page 112... ...
. Upon considering Dose-response relationships form the basis for the all available studies, the significant adverse biological risk assessments used for establishing drinking water effect that occurs at the lowest exposure level is idenregulatory standards.
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From page 113... ...
. induce adverse effects through a threshold mechanism, In the absence of specific mechanistic information the general approach for assessing health risks is to relating to how chemical interaction at the target site establish a health-based guidance value using animal is responsible for a physiological outcome or pathologior human data.
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From page 114... ...
Some effects may be produced at this level, but they are not considered adverse or precursors of adverse effects. LOAEL = The lowest exposure level at which there are biologically significant increases in frequency or severity of adverse effects between the exposed population and the appropriate control group.
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From page 115... ...
. The RfD, ADI, TDI, or MRTD can then be used as the basis for deriving an acceptable level of chemical contaminant in reclaimed water, using the following equation: Rfd × Body Weight × RSC Acceptable Level in Reclaimed Water Noncarcinogen/Threshold Chemical = e Drinking Water Intake where drinking water intake is assumed to equal 2 L/d, and the relative source contribution (RSC)
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From page 116... ...
= Drinking Water Intake where the acceptable risk level generally equals 10–6, and drinking water intake is assumed to be 2 L/d. Confidence interval on dose High-dose tumor Incidence (observed)
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From page 117... ...
(2008) to assess potential health risks from dioxin data on a specific contaminant, as well as chemical and dioxin-like compounds in Australian reclaimed class-based evaluation approaches in the absence of water used to augment drinking water supplies, based contaminant-specific data.
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From page 118... ...
Thresholds of Toxicological Concern Although newer than traditional risk assessments, (TTCs) which are based upon chemical-specific data, these class-based values are widely used by regulatory author For carcinogens, distributions of chronic dose rates from ities to assess health risks in the absence of complete lifetime animal cancer studies were statistically evaluated for substance-specific health effects datasets.
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From page 119... ...
tive relative risk assessments of two different water reuse projects in Southern California: the Montebello The inputs to a risk characterization may have a Forebay and Chino Basin Groundwater Recharge number of sources of uncertainty and variability, and projects. In each project, water samples from wells that therefore, the final risk characterization has inevitable contained "relatively high proportions" of reclaimed
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From page 120... ...
In contrast, when the best choice is not so clear and the consequences of a wrong choice would be serious, EPA can proceed in an CONCLUSIONS AND RECOMMENDATIONS iterative manner, making the analysis more and more sophisticated until the optimal choice is sufficiently Health risks remain difficult to fully characterize clear.
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From page 121... ...
A better understanding and a database of the Guidance and user-friendly risk assessment tools performance of treatment processes and distribution would improve the understanding and application of systems are needed to quantify the uncertainty in risk these risk assessment methods. Although risk assessassessments of potable and nonpotable water reuse ment is a useful tool to help prioritize efforts to protect projects.
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