Teng Zeng

Pesticide Photolysis in Prairie Potholes: Probing Photosensitized Processes

Prairie pothole lakes (PPLs) are glacially derived, ecologically important water bodies found in central North America and represent a unique setting in which extensive agriculture occurs within wetland ecosystems. In the Prairie Pothole Region (PPR), elevated pesticide use and increasing hydrologic connectivity have raised concerns about the impact of nonpoint source agricultural pollution on the water quality of PPLs and downstream aquatic systems. Despite containing high dissolved organic matter (DOM) levels, the photoreactivity of the PPL water and the photochemical fate of pesticides entering PPLs are largely unknown. In this study, the photodegradation of sixteen pesticides was investigated in PPL waters sampled from North Dakota, under simulated and natural sunlight. Enhanced pesticide removal rates in the irradiated PPL water relative to the control buffer pointed to the importance of indirect photolysis pathways involving photochemically produced reactive intermediates (PPRIs). The steady-state concentrations of carbonate radical, hydroxyl radical, singlet oxygen, and triplet-excited state DOM were measured and second-order rate constants for reactions of pesticides with these PPRIs were calculated. Results from this study underscore the role of DOM as photosensitizer in limiting the persistence of pesticides in prairie wetlands through photochemical reactions.

Enhanced Formation of Disinfection Byproducts in Shale Gas Wastewater-Impacted Drinking Water Supplies

The disposal and leaks of hydraulic fracturing wastewater (HFW) to the environment pose human health risks. Since HFW is typically characterized by elevated salinity, concerns have been raised whether the high bromide and iodide in HFW may promote the formation of disinfection byproducts (DBPs) and alter their speciation to more toxic brominated and iodinated analogues. This study evaluated the minimum volume percentage of two Marcellus Shale and one Fayetteville Shale HFWs diluted by fresh water collected from the Ohio and Allegheny Rivers that would generate and/or alter the formation and speciation of DBPs following chlorination, chloramination, and ozonation treatments of the blended solutions. During chlorination, dilutions as low as 0.01% HFW altered the speciation toward formation of brominated and iodinated trihalomethanes (THMs) and brominated haloacetonitriles (HANs), and dilutions as low as 0.03% increased the overall formation of both compound classes. The increase in bromide concentration associated with 0.01-0.03% contribution of Marcellus HFW (a range of 70-200 μg/L for HFW with bromide = 600 mg/L) mimics the increased bromide levels observed in western Pennsylvanian surface waters following the Marcellus Shale gas production boom. Chloramination reduced HAN and regulated THM formation; however, iodinated trihalomethane formation was observed at lower pH. For municipal wastewater-impacted river water, the presence of 0.1% HFW increased the formation of N-nitrosodimethylamine (NDMA) during chloramination, particularly for the high iodide (54 ppm) Fayetteville Shale HFW. Finally, ozonation of 0.01-0.03% HFW-impacted river water resulted in significant increases in bromate formation. The results suggest that total elimination of HFW discharge and/or installation of halide-specific removal techniques in centralized brine treatment facilities may be a better strategy to mitigate impacts on downstream drinking water treatment plants than altering disinfection strategies. The potential formation of multiple DBPs in drinking water utilities in areas of shale gas development requires comprehensive monitoring plans beyond the common regulated DBPs.

Potential for Abiotic Reduction of Pesticides in Prairie Pothole Porewaters

Prairie pothole lakes (PPLs) are critical hydrological and ecological components of central North America and represent one of the largest inland wetland systems on Earth. These lakes are located within an agricultural region, and many of them are subject to nonpoint-source pesticide pollution. Limited attention, however, has been paid to understanding the impact of PPL water chemistry on the fate and persistence of pesticides. In this study, the abiotic reductive transformation of seven dinitroaniline pesticides was investigated in PPL sediment porewaters containing naturally abundant levels of reduced sulfur species (i.e., bisulfide (HS(-)) and polysulfides (S(n)(2-))) and dissolved organic matter (DOM). Target dinitroanilines underwent rapid degradation in PPL porewaters and were transformed into corresponding amine products. While the largest fraction of the transformation could be attributed to reduced sulfur species, experimental evidence suggested that other reactive entities in PPL porewaters, such as DOM and mineral phases, might also affect the reaction rates of dinitroanilines. Results from this study highlight the importance of reductive transformation as an abiotic natural attenuation pathway for pesticides entering the PPL sedimentary environment.

Pesticide processing potential in prairie pothole porewaters.

Prairie pothole lakes (PPLs) are located within the extensively farmed Great Plains region of North America, and many are negatively impacted by nonpoint source pesticide pollution. To date, the environmental fate of pesticides in these lakes remains largely unknown. In this study, two PPLs in the Cottonwood Lake area of North Dakota were sampled, and transformations of four chloroacetanilide pesticides in sediment porewaters were examined. The reduced sulfur species in the porewaters, such as bisulfide (HS(-)) and polysulfides (S(n)(2-)), readily transformed the target pesticides into sulfur-substituted products. Although HS(-) and S(n)(2-) played a dominant role, other reactive constituents in PPL porewaters also contributed to the transformation. Results from this study revealed that abiotic reactions with reduced sulfur species could represent an important removal pathway for pesticides entering PPLs.

Modeling and mechanism of the adsorption of copper ion onto natural bamboo sawdust.

The sorption of copper ions onto natural bamboo sawdust with cellulose-lignin polymeric structure strongly depends on pH. The adsorption capacity for copper ions increases as increasing pH and copper loadings. The fitting of copper pH boundary curve by NEM surface complexation models shows that: three-sites model including the ion exchange reaction of permanent charge fits better than two-sites model. The incorporation of the hydrated ion reaction gives better fitting results. XAFS study shows that: copper ions mainly form inner complexation with sawdust, but there is no obvious evidence on the complexation of carboxylic acid groups with copper ions. EXAFS fitting result shows that: as pH rises, the spatial configuration of copper ions shifts from tetrahedron to octahedron. Meanwhile the increase in the coordination number indicates that hydrated copper ions participate in the adsorption. Both XANES and EXFAS spectrum offer a similar explanation for copper adsorption in the range of experimental and fitting errors.

Microscale Characterization of Sulfur Speciation in Lake Sediments

Prairie pothole lakes (PPLs) are naturally sulfur-enriched wetlands in the glaciated prairie region of North America. High sulfate levels and dynamic hydrogeochemistry in combination render PPLs a unique environment to explore the speciation of sedimentary sulfur (S). The goals of this research were to define and quantify the solid-phase S pools in PPL sediments and track seasonal dynamics of S speciation. A quantitative X-ray microprobe method was developed based on S 1s X-ray absorption near-edge structure (XANES) spectroscopy and multienergy X-ray fluorescence mapping. Three S pools-pyritic S, reduced organic S (organic mono- and disulfide), and oxidized S (inorganic sulfate, ester sulfate, and sulfonate)-were identified in PPL sediments. No significant seasonal variation was evident for total S, but S speciation showed a seasonal response. During the spring-summer transition, the reduced organic S decreased from 55 to 15 mol %, with a concomitant rise in the oxidized S. During the summer-fall transition, the trend reversed and the reduced organic S grew to 75 mol % at the expense of the oxidized S. The pyritic S, on the other hand, remained relatively constant (∼22 mol %) over time. The seasonal changes in S speciation have strong potential to force the cycling of elements such as mercury in prairie wetlands.

Contribution of N-Nitrosamines and Their Precursors to Domestic Sewage by Greywaters and Blackwaters

N-nitrosamines and their precursors are significant concerns for water utilities exploiting wastewater-impacted water supplies, particularly those practicing potable reuse of wastewater. Previous efforts to identify specific precursors in municipal wastewater accounting for N-nitrosamine formation have met with limited success. As an alternative, we quantified the relative importance of greywater (i.e., shower, kitchen sink, bathroom washbasin, and laundry) and blackwater (i.e., urine and feces) streams in terms of their loadings of ambient specific and total N-nitrosamines and chloramine-reactive and ozone-reactive N-nitrosamine precursors to domestic sewage. Accounting for the volume fractions of individual greywater and blackwater streams, laundry water represented the most significant source of N-nitrosamines and their precursors, followed by shower water and urine. Laundry water was particularly important for ozone-reactive N-nitrosamine precursors, accounting for ∼99% of N-nitrosodimethylamine (NDMA) precursors and ∼69% of precursors for other uncharacterized N-nitrosamines. For the other greywater streams, consumer products contributed additional N-nitrosamines and precursors, but the remarkable uniformity across different products suggested the importance of common macroconstituents. The consumption of a standard dose of the antacid ranitidine substantially increased NDMA and its chloramine-reactive precursors in urine. Nevertheless, nearly 40% of the American population would need to consume ranitidine daily to match the NDMA loadings from laundry water.

Clustering chlorine reactivity of haloacetic acid precursors in inland lakes.

Dissolved organic matter (DOM) represents the major pool of organic precursors for harmful disinfection byproducts, such as haloacetic acids (HAAs), formed during drinking water chlorination, but much of it remains molecularly uncharacterized. Knowledge of model precursors is thus a prerequisite for understanding the more complex whole water DOM. The utility of HAA formation potential data from model DOM precursors, however, is limited due to the lack of comparability to water samples. In this study, the formation kinetics of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two predominant HAA species, were delineated upon chlorination of seventeen model DOM precursors and sixty-eight inland lake water samples collected from the Upper Midwest region of the United States. Of particular interest was the finding that the DCAA and TCAA formation rate constants could be grouped into four statistically distinct clusters reflecting the core structural features of model DOM precursors (i.e., non-β-diketone aliphatics, β-diketone aliphatics, non-β-diketone phenolics, and β-diketone phenolics). A comparative approach built upon hierarchical cluster analysis was developed to gain further insight into the chlorine reactivity patterns of HAA precursors in inland lake waters as defined by the relative proximity to four model precursor clusters. This work highlights the potential for implementing an integrated kinetic-clustering approach to constrain the chlorine reactivity of DOM in source waters.

Effect of Chemical Oxidation on the Sorption Tendency of Dissolved Organic Matter to a Model Hydrophobic Surface

The application of chemical oxidants may alter the sorption properties of dissolved organic matter (DOM), such as humic and fulvic acids, proteins, polysaccharides, and lipids, affecting their fate in water treatment processes, including attachment to other organic components, activated carbon, and membranes (e.g., organic fouling). Similar reactions with chlorine (HOCl) and bromine (HOBr) produced at inflammatory sites in vivo affect the fate of biomolecules (e.g., protein aggregation). In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to evaluate changes in the noncovalent interactions of proteins, polysaccharides, fatty acids, and humic and fulvic acids with a model hydrophobic surface as a function of increasing doses of HOCl, HOBr, and ozone (O3). All three oxidants enhanced the sorption tendency of proteins to the hydrophobic surface at low doses but reduced their sorption tendency at high doses. All three oxidants reduced the sorption tendency of polysaccharides and fatty acids to the hydrophobic surface. HOCl and HOBr increased the sorption tendency of humic and fulvic acids to the hydrophobic surface with maxima at moderate doses, while O3 decreased their sorption tendency. The behavior observed with two water samples was similar to that observed with humic and fulvic acids, pointing to the importance of these constituents. For chlorination, the highest sorption tendency to the hydrophobic surface was observed within the range of doses typically applied during water treatment. These results suggest that ozone pretreatment would minimize membrane fouling by DOM, while chlorine pretreatment would promote DOM removal by activated carbon.

Impact of Nitrification on the Formation of N-Nitrosamines and Halogenated Disinfection Byproducts within Distribution System Storage Facilities.

Distribution system storage facilities are a critical, yet often overlooked, component of the urban water infrastructure. This study showed elevated concentrations of N-nitrosodimethylamine (NDMA), total N-nitrosamines (TONO), regulated trihalomethanes (THMs) and haloacetic acids (HAAs), 1,1-dichloropropanone (1,1-DCP), trichloroacetaldehyde (TCAL), haloacetonitriles (HANs), and haloacetamides (HAMs) in waters with ongoing nitrification as compared to non-nitrifying waters in storage facilities within five different chloraminated drinking water distribution systems. The concentrations of NDMA, TONO, HANs, and HAMs in the nitrifying waters further increased upon application of simulated distribution system chloramination. The addition of a nitrifying biofilm sample collected from a nitrifying facility to its non-nitrifying influent water led to increases in N-nitrosamine and halogenated DBP formation, suggesting the release of precursors from nitrifying biofilms. Periodic treatment of two nitrifying facilities with breakpoint chlorination (BPC) temporarily suppressed nitrification and reduced precursor levels for N-nitrosamines, HANs, and HAMs, as reflected by lower concentrations of these DBPs measured after re-establishment of a chloramine residual within the facilities than prior to the BPC treatment. However, BPC promoted the formation of halogenated DBPs while a free chlorine residual was maintained. Strategies that minimize application of free chlorine while preventing nitrification are needed to control DBP precursor release in storage facilities.