David A. Reckhow

Potential carcinogenic hazards of non-regulated disinfection by-products: Haloquinones, halo-cyclopentene and cyclohexene derivatives, N-halamines, halonitriles, and heterocyclic amines

Drinking water disinfectants react with natural organic material (NOM) present in source waters used for drinking water to produce a wide variety of by-products. Several hundred disinfections by-products (DBPs) have been identified, but none have been identified with sufficient carcinogenic potency to account for the cancer risks projected from epidemiological studies. In a search for DBPs that might fill this risk gap, the present study projected reactions of chlorine and chloramine that could occur with substructures present in NOM to produce novel by-products. A review of toxicological data on related compounds, supplemented by use of a quantitative structure toxicity relationship (QSTR) program TOPKAT®) identified chemicals with a high probability of being chronically toxic and/or carcinogenic among 489 established and novel DBPs. Classes of DBPs that were specifically examined were haloquinones (HQs), related halo-cyclopentene and cyclohexene (HCP&H) derivatives, halonitriles (HNs), organic N-chloramines (NCls), haloacetamides (HAMs), and nitrosamines (NAs). A review of toxicological data available for quinones suggested that HQs and HCP&H derivatives appeared likely to be of health concern and were predicted to have chronic lowest observed adverse effect levels (LOAELs) in the low μg/kg day range. Several HQs were predicted to be carcinogenic. Some have now been identified in drinking water. The broader class of HNs was explored by considering current toxicological data on haloacetonitriles and extending this to halopropionitriles. 2,2-dichloropropionitrile has been identified in drinking water at low concentrations, as well as the more widely recognized haloacetonitriles. The occurrence of HAMs has been previously documented. The very limited toxicological data on HAMs suggests that this class would have toxicological potencies similar to the dihaloacetic acids. Organic N-halamines are also known to be produced in drinking water treatment and have biological properties of concern, but no member has ever been characterized toxicologically beyond bacterial or in vitro studies of genotoxicity. The documented formation of several nitrosamines from secondary amines from both natural and industrial sources prompted exploration of the formation of additional nitrosamines. N-diphenylnitrosamine was identified in drinking waters. Of more interest, however, was the formation of phenazine (and subsequently N-chorophenazine) in a competing reaction. These are the first heterocyclic amines that have been identified as chlorination by-products. Consideration of the amounts detected of members of these by-product classes and their probable toxicological potency suggest a prioritization for obtaining more detailed toxicological data of HQs>HCP&H derivatives>NCls>HNs. Based upon a ubiquitous occurrence and virtual lack of in vivo toxicological data, NCls are the most difficult group to assign a priority as potential carcinogenic risks. This analysis indicates that research on the general problem of DBPs requires a more systematic approach than has been pursued in the past. Utilization of predictive chemical tools to guide further research can help bring resolution to the DBP issue by identifying likely DBPs with high toxicological potency.

Determination of free Bisphenol A (BPA) concentrations in breast milk of U.S. women using a sensitive LC/MS/MS method

Bisphenol A (BPA) is a synthetic, endocrine-disrupting compound. Free BPA has been detected in human samples indicating that humans are internally exposed to estrogenically active BPA. The purpose of this study was to develop a sensitive method to detect free BPA in human breast milk. BPA was isolated from the milk of 21 nursing mothers in the U.S. by solid-phase extraction. It was then derivatized to improve sensitivity and subsequently analyzed by ultra high performance liquid chromatography-tandem mass spectrometry. Free BPA was detected in 62% of the milk samples (≤ 0.22-10.8 ng mL(-1), median 0.68 ng mL(-1), mean 3.13 ng mL(-1)). No statistical difference in BPA concentrations was observed between women with a low or high Body Mass Index (BMI) (<30 (n=11) and>30 (n=10), respectively). However, there was a significant association between BPA concentration and race. Caucasian women had significantly higher levels of free BPA in their breast milk than non-Caucasian women (mean=4.44 (n=14) and 0.52 (n=7), respectively; p<0.05). The difference between races could be attributed to variations in exposure, lifestyle or metabolism and suggests that certain populations should take extra precautions to limit BPA exposure, particularly during pregnancy and lactation.

The ozonation of organic halide precursors: effect of bicarbonate

A laboratory study of the effect of bicarbonate on the ozonation of organic halide precursors in fulvic acid solutions and in a raw drinking water was conducted. The experimental variables were bicarbonate concentration, ozone dose and pH of chlorination. Results are expressed in terms of trihalomethane (THM), total organic halide (TOX), trichloracetic acid, dichloroacetic acid, trichloroacetone and dichloroacetonitrile precursor concentrations. Kinetic studies showed that bicarbonate slowed the decomposition of ozone in the presence of fulvic acid, and thereby, led to a greater degree of destruction of u.v.-absorbing substances. Similarly, precursor destruction increased with increasing bicarbonate concentrations in the range of 10−4spd 10−2 M. Precursor destruction was greatest when chlorination was performed at low pH. At high pHs of chlorination, some precursor enhancement was noted, especially in the absence of bicarbonate. Results are interpreted both from a mechanistic standpoint and with respect to their applicability to water treatment practice.

Correlation between SUVA and DBP formation during chlorination and chloramination of NOM fractions from different sources

Natural organic matter (NOM) is the major precursor to the formation of disinfection byproducts (DBPs) during drinking water treatment. Specific ultraviolet absorbance (SUVA) is a widely used surrogate parameter to characterize NOM and predict its DBP formation potential. The objective of this study was to determine the relationships between SUVA and different classes of DBPs formed by NOM fractions from different sources. Three natural waters with a wide SUVA range were fractionated into differing hydrophobicity and molecular weight groups using XAD-4 and XAD-8 resins and ultrafiltration membranes. Each NOM fraction was treated with chlorine and monochloramine under controlled laboratory conditions. Different classes of DBPs showed different relationships with SUVA. SUVA correlated strongly with trihaloacetic acids (THAAs) and unknown total organic halogen (UTOX) yields whereas weak correlations were observed between SUVA and trihalomethane (THM) and dihaloacetic acid (DHAA) yields during chlorination. These results reinforce the hypothesis that DHAAs and THAAs form through different precursors and reaction pathways. Strong correlation between SUVA and UTOX was also observed during chloramination. However, no significant relationship was observed between SUVA and chloramination THMs and DHAAs. Overall, SUVA is a good indicator for the formation of unknown DBPs. This indicates that UV absorbing compounds and aromatic carbon within NOM are the primary sources of precursors for unknown DBPs.

Evaluation of bromine substitution factors of DBPs during chlorination and chloramination.

Bromine substitution factor (BSF) was used to quantify the effects of disinfectant dose, reaction time, pH, and temperature on the bromine substitution of disinfection byproducts (DBPs) during chlorination and chloramination. The BSF is defined as the ratio of the bromine incorporated into a given class of DBPs to the total concentration of chlorine and bromine in that class. Four classes of DBPs were evaluated: trihalomethanes (THMs), dihaloacetonitriles (DHANs), dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs). The results showed that the BSFs of the four classes of DBPs generally decreased with increasing reaction time and temperature during chlorination at neutral pH. The BSFs peaked at a low chlorine dose (1 mg/L) and decreased when the chlorine dose further increased. The BSFs of chlorination DBPs at neutral pH are in the order of DHAN > THM & DHAA > THAA. DHAAs formed by chloramines exhibited distinctly different bromine substitution patterns compared to chlorination DHAAs. Brominated DBP formation was generally less affected by the pH change compared to chlorinated DBP formation.

Effect of pre-ozonation on the formation and speciation of DBPs.

The objective of this study was to quantitatively evaluate the effect of pre-ozonation on the formation and speciation of disinfection byproducts (DBPs) from subsequent chlorination and chloramination. Laboratory experiments were conducted on six diverse natural waters with low to medium bromide concentrations. Four groups of DBPs were investigated in this study: trihalomethanes (THMs), trihaloacetic acids (THAAs), dihaloacetic acids (DHAAs), and dihaloacetonitriles (DHANs). The results showed that the relative destructions of chlorination DBP precursors by ozone generally follow the order of DHANs > THMs & THAAs > DHAAs. Pre-ozonation substantially increased the DHAA precursors in the waters with low specific ultraviolet absorbance values. Pre-ozonation shifted the formation of DBPs to more brominated species. The bromine substitution factors (BSF) of different chlorination DBPs typically increased by 1-8 percentage points after ozonation. Pre-ozonation reduced the yields of chloramination DHAAs and THMs and increased the BSFs of chloramination DHAAs by 1-6 percentage points.

Solid phase catalytic ozonation process for the destruction of a model pollutant

Pure metal oxides, mixed metal oxides, and platinum metals were evaluated as ozonation catalysts. Batch reactor experiments were performed using deionized water at pH 7 and semi-continuous ozonation experiments were performed using a natural water. p-Chlorobenzoic acid (pCBA), a non-adsorbing model micropollutant that does not react directly with molecular ozone, was included in both solution matrixes. Titanium dioxide, cobalt oxide, nickel oxide, copper oxide, and a mixed metal oxide comprised of copper, zinc, and aluminum did not accelerate the removal pCBA in deionized water. However, cobalt oxide and the mixed metal oxide catalyst were effective at accelerating the removal of pCBA in a natural water matrix. The mixed metal oxide catalyst may have the most potential as an ozonation catalyst because it also was very stable (i.e., low solubility). A ruthenium / alumina catalyst also increased the removal of pCBA, but this metal may follow a different reaction mechanism than the metal oxide catalysts.

Effect of different solutes, natural organic matter, and particulate Fe(III) on ferrate(VI) decomposition in aqueous solutions.

This study investigated the impacts of buffer ions, natural organic matter (NOM), and particulate Fe(III) on ferrate(VI) decomposition and characterized Fe(VI) decomposition kinetics and exposure in various waters. Homogeneous and heterogeneous Fe(VI) decomposition can be described as a second- and first-order reaction with respect to Fe(VI), respectively. Fe(VI) decay was catalyzed by Fe(VI) decomposition products. Solutes capable of forming complexes with iron hydroxides retarded Fe(VI) decay. Fractionation of the resulting solutions from Fe(VI) self-decay and ferric chloride addition in borate- and phosphate-buffered waters showed that phosphate could sequester Fe(III). The nature of the iron precipitate from Fe(VI) decomposition was different from that of freshly precipitated ferric hydroxide from ferric chloride solutions. The stabilizing effects of different solutes on Fe(VI) are in the following order: phosphate > bicarbonate > borate. The constituents of colored and alkaline waters (NOM and bicarbonate) inhibited the catalytic effects of Fe(VI) decomposition products and stabilized Fe(VI) in natural waters. Because of the stabilizing effects of solutes, moderate doses of Fe(VI) added to natural waters at pH 7.5 resulted in exposures that have been shown to be effective for inactivation of target pathogens. Preformed ferric hydroxide was less effective than freshly dosed ferric chloride in accelerating Fe(VI) decomposition.

Coliform transport in a pristine reservoir : Modeling and field studies

This paper reports on field studies and model development aimed at understanding coliform fate and transport in the Quabbin Reservoir, an oligotrophic drinking water supply reservoir. An investigation of reservoir currents suggested the importance of wind driven phenomena, and that both lateral and vertical circulation patterns exist. In-situ experiments of coliform decay suggested dependence on light intensity and yielded an appropriate decay coefficient to be used in CE-QUAL-W2, a two-dimensional hydrodynamic and water quality model. Modeling confirmed the sensitivity of reservoir outlet concentration to vertical variability within the reservoir, meteorological conditions, and location of coliform source.

Kinetic Analysis of Haloacetonitrile Stability in Drinking Waters.

Haloacetonitriles (HANs) are an important class of drinking water disinfection byproducts (DBPs) that are reactive and can undergo considerable transformation on time scales relevant to system distribution (i.e., from a few hours to a week or more). The stability of seven mono-, di-, and trihaloacetonitriles was examined under a variety of conditions including different pH levels and disinfectant doses that are typical of drinking water distribution systems. Results indicated that hydroxide, hypochlorite, and their protonated forms could react with HANs via nucleophilic attack on the nitrile carbon, forming the corresponding haloacetamides (HAMs) and haloacetic acids (HAAs) as major reaction intermediates and end products. Other stable intermediate products, such as the N-chloro-haloacetamides (N-chloro-HAMs), may form during the course of HAN chlorination. A scheme of pathways for the HAN reactions was proposed, and the rate constants for individual reactions were estimated. Under slightly basic conditions, hydroxide and hypochlorite are primary reactants and their associated second-order reaction rate constants were estimated to be 6 to 9 orders of magnitude higher than those of their protonated conjugates (i.e., neutral water and hypochlorous acid), which are much weaker but more predominant nucleophiles at neutral and acidic pHs. Developed using the estimated reaction rate constants, the linear free energy relationships (LFERs) summarized the nucleophilic nature of HAN reactions and demonstrated an activating effect of the electron withdrawing halogens on nitrile reactivity, leading to decreasing HAN stability with increasing degree of halogenation of the substituents, while subsequent shift from chlorine to bromine atoms has a contrary stabilizing effect on HANs. The chemical kinetic model together with the reaction rate constants that were determined in this work can be used for quantitative predictions of HAN concentrations depending on pH and free chlorine contact times (CTs), which can be applied as an informative tool by drinking water treatment and system management engineers to better control these emerging nitrogenous DBPs, and can also be significant in making regulatory decisions.