The Mitch Laboratory
RESEARCH BACK
Our Changing Water Supplies - the Importance of Nitrogen
As a result of population growth, the world is running out of pristine waters. Utilities are increasingly exploiting waters impaired by agricultural runoff or wastewater effluents. While dissolved organic matter in pristine waters is dominated by carbon-based humic substances, impaired waters exhibit nitrogen-rich organic matter due to the following:
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Direct dissolved organic nitrogen (DON) inputs from wastewater effluents. |
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Algal blooms instigated by fertilizer runoff |
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Increasing use of chloramine disinfection by utilities |
Public Health Threats from Disinfection
Disinfection is critical to prevent epidemics spread by pathogens in drinking waters, wastewaters and recreational waters. Yet epidemiology studies are linking use of disinfected drinking waters and recreational waters to bladder cancers due to the formation of carcinogenic byproducts of disinfectant reactions with dissolved organic matter. Unfortunately, recent work by our collaborator, Dr. Michael Plewa of the University of Illinois, has demonstrated that nitrogen-based byproducts are orders of magnitude more toxic than the carbon-based byproducts previously studied. Examples include (structures):
Our lab recently quantified significant concentrations of nitrosamines in recreational waters. Nitrosamines are particularly linked with bladder cancer. We seek to work with epidemiologists to exploit the differences between nitrosamine concentrations in indoor pools, outdoor pools, and hot tubs to understand the importance of this class of carcinogens for bladder cancer. Lastly, we have worked with Dr. Michael Plewa of the University of Illinois at Urbana-Champaign to evaluate the bulk toxicity genotoxicity of recreational waters disinfected by different techniques. This study sought to answer the question: Which pool disinfectants should be avoided so we can minimize poolwater toxicity? For more information, see:
Walse, S.S.; Mitch, W.A. Nitrosamine carcinogens also swim in pools. Environ. Sci. Technol., 2008, 42 (4), 1032-1037. (Full Text)
We developed a new analytical method for the bulk concentration of organic nitrosamines (TONO), comparable to TOX. Applying this to recreational waters in concert with the analysis of specific nitrosamines by EPA Method 521, we found that NDMA accounted for only ~10% of the total nitrosamine pool. Since nitrosamines of a wide range of hydrophobicity exhibit comparable cancer potencies, the additional nitrosamines should be characterized. For more information, see:
Kulshrestha, P.; McKinstry, K.C.; Fernandez, B.O.; Feelisch, M.; Mitch, W.A. Application of an optimized total N-nitrosamine (TONO) assay to pools: placing N-nitrosodimethylamine (NDMA) determinations into perspective. Environ. Sci. Technol., 2010, 44, 3369-3375. (Full Text)
This study sought to answer the question: Which pool disinfectants should be avoided so we can minimize poolwater toxicity? For more information, see:
Liviac, D.; Wagner, E.D.; Mitch, W.A.; Altonji, M.J.; Plewa, M.J. Genotoxicity of water concentrates from recreational pools after various disinfection methods. Environ. Sci. Technol., 2010, 44, 3537-3332. (Full Text)
Public Health, Engineering and Organic Chemistry Combined: Predicting Emerging Byproducts
Previous research into carbon-based byproduct formation has been plagued by the highly variable structures of humic substance precursors. Researchers could not apply known disinfectant reaction pathways to precursors to predict the most important byproducts. As a result, we have been at the mercy of analytical chemists to identify byproducts. To date, > 600 carbon-based byproducts have been identified. Which are more important? Which should regulators target?
Luckily, dissolved organic nitrogen is more uniform. We are applying the organic chemical reaction pathways we have elicidated (see below) to important organic nitrogen precursor structures (e.g., amino acids) to predict byproducts likely to form in the highest concentrations. After synthesizing these compounds, we are working closely with Dr. Michael Plewa of the University of Illinois to test their cytotoxicity and genotoxicity. The goal is to identify byproducts that are both highly toxic and form at the highest concentrations. These compounds are likely to constitute dominate the toxicity of a disinfected water, and can be used by regulators and epidemiologists as exposure markers.
Walse, S.S.; Plewa, M.J.; Mitch, W.A. Exploring amino acid side chain decomposition using enzymatic digestion and HPLC-MS: combined lysine transformations in chlorinated waters. Anal. Chem., 2009, 81 (18), 7650-7659. (Full Text)
Byproduct Formation Pathway Research
Understanding how byproducts form is of critical importance as utilities are currently redesigning disinfection systems to minimize Formation of certain of these compounds has resulted in either closure of wastewater recycling plants or the installation of extremely expensive treatment systems to remove the chemicals after formation. For recent progress:
Prevention of nitrosamine formation: Contrary to prior research implicating monochloramine, we demonstrated that nearly all nitrosamine formation could be explained by a reaction involving organic amines, dichloramine and dissolved oxygen (Figure). Understanding the reaction pathway enabled the development of alternative disinfection techniques that minimize nitrosamine formation. One of these techniques was successfully pilot-tested at a Los Angeles area wastewater recycling plant (Figure). Due to severe water shortages in Australia, Brisbane has fast-tracked the installation of 5 wastewater recycling plants. Pilot-testing of our treatment alternatives is planned in the near future.For more information see:
Schreiber, I.M.; Mitch, W.A. Enhanced nitrogenous disinfection byproduct formation near the breakpoint: implications for nitrification control. Environ. Sci. Technol., 2007, 41 (20), 7039-7046. (Full Text)
Schreiber, I.M.; Mitch, W.A. Nitrosamine
formation pathway revisited: the importance of dichloramine and
dissolved oxygen. Environ. Sci.
Technol., 2006, 40 (19), 6007-6014.
Mitch,
W.A.; Oelker, G.L.; Hawley, E.L.; Deeb, R.A.; Sedlak, D.L. Minimization of
NDMA formation during chlorine disinfection of municipal wastewater by
application of pre-formed chloramines. Environ. Eng.
Sci., 2005, 22 (6): 882-890.
Schreiber, I.M.; Mitch, W.A. Influence of the order of
reagent addition on NDMA formation during chloramination. Environ. Sci. Technol., 2005, 39 (10): 3811-3818.
Halonitroalkane, aldehyde and nitrile formation: We demonstrated that the behavior of monomethylamine, a primary amine precursor for cyanogen chloride and chloropicrin, is atypical among primary amines during chlorination and chloramination. Using another primary amine precursor as a model for more typical primary amine constituents of organic nitrogen, we demonstrated that previous research may underestimate the threat posed by these by-product families (Figure).
For more information see:
Joo, S.-H.; Mitch, W.A. Nitrile, aldehyde and halonitroalkane formation
during chlorination/chloramination of primary amines. Environ. Sci. Technol., 2007,
41 (4), 1288-1296
As for nitrosamines (see above), we determined that additional of pre-formed monochloramine minimized production of dichloroacetonitrile, a toxic N-DBP. However, for dichloroacetonitrile, formation was minimized by reducing free chlorine contact. Regardless, this relatively cheap technique holds the promise of permitting chloramine disinfection while simultaneously minimizing the formation of two highly toxic families of N-DBPs. For more information see:
Hayes-Larson, E.L.; Mitch, W.A. Influence of the method of reagent addition on dichloroacetonitrile formation during chloramination. Environ. Sci. Technol. 2010, 44 (2), 700-706. (Full Text)
Ongoing Research
UV Disinfection and Nitrogenous Byproducts: Utilities are increasingly interested in UV treatment due to it's lack of chemical treatment. However, recent research has indicated that UV treatment may enhance nitrogenous byproducts. We are examining reaction pathways responsible for this formation.