Collaborative Proposal Numbers: 1706154/1706575 PI Names: William Mitch/Michael Plewa
Increasing populations in arid regions of the US and recent droughts in Texas and California are increasing interest in purifying municipal wastewater as a local, secure supply for drinking water. A critical roadblock for potable reuse projects is lingering uncertainty among utilities, regulators, and the public regarding the human health impacts of chemicals in the purified wastewater. The National Research Council has indicated that byproducts of water and purified wastewater disinfection (disinfection byproducts or DBPs) are the predominant drivers of human health risks; however, the contribution to toxicity of DBPs as a whole and the relative importance of different DBP classes has not been quantified. In this project the PIs will quantify the contributions of different DBP classes to the toxicity of disinfected purified wastewaters to determine which classes are the most significant drivers of toxicity. Results from this project will provide critical data to enable regulators to evaluate potable reuse projects and to prioritize chemical contaminant classes (particularly DBPs) for regulatory oversight.
In this project the main hypothesis is that advanced treated municipal wastewaters exhibit lower overall toxicity than conventional drinking waters employing wastewater-impacted (i.e., de facto reuse), or even pristine source waters. To test this hypothesis, the PIs will quantitatively compare the toxicity of a series of representative conventional drinking waters using either pristine or wastewater-impacted source waters with waters associated with potable reuse operations. The comparison will employ quantitative in vitro bioassays targeting a range of relevant endpoints (cytotoxicity, genotoxicity, and oxidative stress).
To quantify the contributions of different DBP classes to the toxicity of disinfected potable reuse waters, the PIs will compare the in vitro bioassay responses of disinfected potable reuse waters to those of deionized water spiked with the concentrations of either all the DBPs measured in these waters, or all of the members of specific DBP classes. DBP research has focused on individual chemical classes (e.g., nitrosamines), with chemists and toxicologists often working separately. By integrating chemical analysis of a broad range of DBP classes with quantitative toxicology to identify the classes driving toxic responses, the PIs expect that results from this work could transform the approach to DBP research. This work will also address two long-standing questions for DBP research. First, is the toxicity associated with DBP mixtures additive or is there synergism or antagonism? This question will be answered by comparing the bioassay responses for individual DBP classes against their mixtures. Second, DBP research has focused on low molecular weight species, generally accounting for only ~30-40% of total organic halogen (TOX). To what extent do high molecular weight DBPs contribute to toxicity? With disinfectants applied upstream of reverse osmosis (RO) units, potable reuse trains are ideal for answering this question. In addition to the research opportunities afforded to graduate and undergraduate students, a high school science teacher and underrepresented high school student will assist in summer research, with an eye to incorporating this material into the high school curriculum over the following year.
