Citation:

Regli, S., J. Chen, M. Messner, M. Elovitz, F. Letkiewicz, R. Pegram, T. Pepping, S. Richardson, AND Michael Wright. Estimating Potential Increased Bladder Cancer Risk Due to Increased Bromide Concentrations in Sources of Disinfected Drinking Waters. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 49(22):13094-13102, (2015).

Impact/Purpose:

Public water systems are increasingly facing higher bromide levels in their source waters from anthropogenic contamination. It is recognized that such increased bromide levels can cause increased formation of bromide containing disinfection byproducts (DBPs) with associated risks, potential policy decision making to address this issue has largely been constrained due to the absence of any quantified risk implication. Our paper offers an innovative approach for estimating increased potential health risks for one of the key health concerns – bladder cancer – as a function of increased bromide levels in source drinking waters. We develop a rationale from the available literature for why exposure from brominated DBPs pose a health concern and why, when the sum concentration of four trihalomethanes (three of which are brominated species) increase as a function of bromide incorporation, this can be used as a surrogate for exposure to the complex mixture to inform increased bladder cancer risk. Our analytical approach involves three steps: i) development of a risk function from epidemiological data for estimating potential bladder cancer risk as a function of the sum concentration of four THM4 occurrence levels in finished drinking waters; ii) use of THM4 formation equations to estimate increased THM4 levels in finished waters as a function of hypothetical increased bromide levels in source waters and; iii) consolidating “I” and “II” to estimate potential increase in bladder cancer risk as a function of increased bromide levels in source water on a national level. Our TOC graphic, which includes two graphs and one table taken from our paper, illustrates the integration of these three steps. Based on analysis of source water and treatment data from 201 treatment plants serving over 100 million people in the US, we predict increased plant mean THM4 concentration as a function of hypothetical increases in bromide source water concentration ranging from 10 to 100 µg/l. Our analysis indicates that if mean source water bromide concentration levels were to increase by 50 µg/L above baseline concentrations, this could result in a mean increase of between 1 to 10 µg/l THM4 in roughly 90% of the plants and, based on our risk function, would correspond to an increase of 10-4 to 10-3 potential excess lifetime bladder cancer risk among populations served. The large variation in the increased formation of THM4 for a given increase in bromide is due to the large variation in source water quality and treatment among the 201 plants evaluated. However, the implication of our analysis is that almost any plant (90%) having a mean increase of 50 µg/l of bromide in their source water could incur a significant increase in excess lifetime cancer risk (>10-4 excess lifetime) and that a small percentage of plants (5%) could incur a very significant increase in excess lifetime cancer risk (>10-3). The 10-4 excess lifetime cancer risk level is a bench mark that EPA has historically used to inform policy decisions. Given our analysis and a designated increased source water bromide concentration level of concern (e.g., 50 µg/l), we suggest that hydrodynamic modeling of in-stream dilution (not the subject of this paper) could be used to estimate point source bromide discharge levels that could lead to a bromide source water level of concern being exceeded for drinking water systems downstream of the discharge. We believe our analysis can provide a basis for supporting the development of ambient water quality to constrain bromide discharge upstream of drinking water plants. The scope of our analysis is national, and for a given drinking water system, estimates could vary widely for different disinfection treatment types and source water qualities. However, our analysis provides a potential model for assessment of additional risk due to increased bromide in source water, thus addressing a problem of increasi

Description:

Public water systems are increasingly facing higher bromide levels in their source waters from anthropogenic contamination through coal-fired power plants, conventional oil and gas extraction, and hydraulic fracturing. Climate change is likely to exacerbate this in coming years. We estimate bladder cancer risk from potential increased bromide levels in source waters of disinfecting public drinking water systems in the United States. Bladder cancer is the health endpoint used by the United States Environmental Protection Agency (EPA) in its benefits analysis for regulating disinfection byproducts in drinking water. We use estimated increases in the mass of the four regulated trihalomethanes (THM4) concentrations (due to increased bromide incorporation) as the surrogate disinfection byproduct (DBP) occurrence metric for informing potential bladder cancer risk. We estimate potential increased excess lifetime bladder cancer risk as a function of increased source water bromide levels. Results based on data from 201 drinking water treatment plants indicate that a bromide increase of 50 µg/L could result in a potential increase of between 10-3 to 10-4 excess lifetime bladder cancer risk in roughly 90% of these plants.

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