N-Nitrosodimethylamine in Drinking Water: Temporal Formation Potential Patterns in Source Waters and Treatability of Precursors

The seasonal (summer, fall, winter and spring) and local weather related patterns of N-nitrosodimethylamine (NDMA) formation potentials (FPs) were examined with water samples collected monthly for a two year period in 12 surface waters. This long term study allowed monitoring the patterns of NDMA FPs under dynamic weather conditions (e.g., high/low rainfall periods) covering several seasons. Anthropogenically impacted source waters (SWs) which were determined by relatively high sucralose levels (\u3e100 ng/L) had higher NDMA FPs than limited impacted SWs (\u3c100 ng/L). In some sources, NDMA FP showed more variability in spring months. However, seasonal mean values were in general relatively consistent in most sources. These results showed that watershed characteristics played an important role in NDMA FP levels. For one of the sampled surface waters, a large reservoir on a river examined in this study appeared to serve as an equalization basin for NDMA precursors. In contrast, in a river without an upstream reservoir, the NDMA FP levels were influenced by the ratio of an upstream wastewater treatment plant (WWTP) effluent discharge to the river discharge rate. The impact of WWTP effluent decreased during the high river flow periods due to rain events. Linear regression with independent variables consisting of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and sucralose yielded poor correlations with NDMA FP (R2\u3c0.27). However, multiple linear regression analysis using DOC and log (sucralose) yielded a better correlation with NDMA FP (R2=0.53). This study also examined the removal of NDMA FPs for various operational conditions (e.g., alum clarification, powdered activated carbon [PAC] application, use of polymers, pre- and post-oxidation with chlorine [Cl2] and/or chlorine dioxide [ClO2], and Ct [concentration x contact time] changes) at full-scale water treatment plants (WTPs). The impacts of different seasons and dynamic local weather conditions (e.g., high/low rainfall periods) on the removal efficiency of NDMA FP at nine WTPs were investigated for a two year period. NDMA FP removal by alum clarification process remained between 12 to 30% for different seasons and temporal weather conditions. PAC addition (\u3e4 mg/L) increased significantly the NDMA FP removal and PAC doses showed a good correlation (R2=0.71) with the NDMA FP removal. The contribution of polymers to NDMA FP depended on the polymer type used and concentration. The simultaneous application of Cl2 and ClO2 for pre-oxidation and post-oxidation were beneficial for the removal of additional NDMA FPs. The average NDMA FP removals for reverse osmosis (RO) and microfiltration (MF) units were 81% and 7%, respectively. The effect of ClO2 oxidation on the control of NDMA precursors was investigated for different background waters (e.g., low/non-impacted vs. wastewater [WW]-impacted) under various oxidation conditions (e.g., pH, oxidant dose, and Ct). The removal of NDMA FP from all water types (low/non- or WW-impacted) was ≤25% at pH 6.0 with ClO2 oxidation. However, under the similar oxidation conditions, NDMA FP removals increased up to ~80% with increasing influence (i.e., 10%, 25% and 50%) of WW effluents at pH 7.8. This indicates that the majority of WW-derived NDMA precursors can be deactivated with ClO2 oxidation at higher pH (≥7.8). This was due to the better oxidative reaction of ClO2 with amines that have lone pair electrons to be shared at higher oxidation pH conditions. Similarly, NDMA formation levels under uniform formation condition (UFC) also significantly decreased in WW-impacted waters with ClO2 oxidation at pH 7.8. Furthermore, natural attenuation simulation experiments were conducted in this study, and the results showed that ClO2 oxidation can be more effective to deactivate NDMA precursors from relatively freshly impacted waters. Finally, the effects of different oxidation scenarios (individual [ClO2 or Cl2 only] and integrated [simultaneous or sequential application of ClO2 and Cl2]) on the removal of NDMA FP from different waters (e.g., non-impacted vs. either 20% wastewater- or polymer-impacted waters) were investigated. The removal efficiency of NDMA FP in non-impacted waters for all the oxidation scenarios was ≤25%. In 20% WW-impacted waters, NDMA FP removals improved about 50% by only ClO2 oxidation at pH 7.8 (~75%) compared to pH 6.0 (≤25%). However, the increase was limited for only Cl2 oxidation case under same oxidation conditions. For integrated oxidations, NDMA FP removals increased (20-45%), especially, at pH 6.0 compared to individual application of oxidants (Cl2 or ClO2). This indicates that ClO2 and Cl2 can react with different amine precursors at lower pH (i.e., 6.0). However, increasing oxidation pH from 6.0 to 7.8 transformed amine precursors to more reactive forms for both oxidants. Furthermore, integrated use of Cl2 and ClO2 also increased (10-40%) the removal of polymer-derived (poly epichlorohydrin dimethylamine [polyamine], poly diallyldimethylammonium chloride [polyDADMAC] and polyacrylamide [Sedifloc 400C]) NDMA precursors independent of oxidation time (10 vs. 60 min) and pH (6.0 vs. 7.8)

Increased Organohalogen Diversity after Disinfection of Water from a Prescribed Burned Watershed

We evaluated impacts of prescribed burns on water quality by performing field sampling on adjacent first-order watersheds (Santee Experimental Forest, South Carolina), where one of the watersheds underwent a prescribed burn in 2016. We measured water quality parameters [dissolved organic carbon (DOC), nitrogen species, UV254 absorbance, and disinfection byproduct formation potential during chlorination and chloramination] before and after the burn. Using ultra-high-resolution mass spectrometry, we characterized dissolved organic matter features in raw water collected during the first postburn storm, as well as after chlorination and chloramination. After the burn, the median DOC to dissolved total nitrogen (DTN) ratio increased by 1.88 mg of DOC (mg of DTN)(-1) in the burned watershed. Likewise, the burned watershed showed a brief higher haloacetic acid yield after the burn [median of 95.6 mu g (mg of DOC)(-1)] compared to that of the unburned watershed. Despite similar molecular size distributions, more features were found (m/z 700-1000) for condensed aromatics and lignin-like features in the burned watershed. 'While chlorination yielded similar organohalogen diversity, chloramination yielded more halogenated molecular features in the burned watershed (m/z 300-600). The moderate impacts on DOC in this study suggest that prescribed fire likely poses a low risk to water quality

Control wildfire-induced Microcystis aeruginosa blooms by copper sulfate: Trade-offs between reducing algal organic matter and promoting disinfection byproduct formation

Elevated levels of nutrients due to wildfire ash input into stream waters will likely cause algal blooms. When source water is impeded by algae and requires immediate restoration, copper algaecides are usually applied. Previous studies indicate that Cu2+ can promote reactivity of dissolved organic matter in forming disinfection byproducts (DBPs). However, it is unclear that how DBP formation is changed after the treatment of post-fire algal bloom by copper algaecide. In this study Microcystis aeruginosa was cultured in the medium containing black and white ash water extracts (BE and WE) to study DBP concentrations before and after 4-days exposures to low and high copper sulfate (0.5 and 1.0 mg-Cu/L). Dissolved organic matter (DOM) was characterized by UV-VIS absorption and fluorescence spectroscopy and chlorination/chloramination-based DBP formation potential (FP) experiments. DOM concentrations and algal population in the treatments were lower than that in control, regardless of types of water extract. N-nitrosodimethylamine FP in the treatments were 4-6 times higher than the control (0.23-0.34 vs. 0.05-0.06 mu g/L), while haloacetonitrile FP revealed no significant difference (132-191 vs. 167-185 mu g/L). Trade-offs between reducing algal population and promoting DBP-FP were more pronounced for the solutions containing BE than WE. Low copper concentration was as effective as high concentration in inhibiting algal growth while minimizing promotion of DBP formation. The results can serve to support risk evaluations of algal population and DBP concentration when wildfire-induced algal bloom is left untreated and treated by copper algaecides. (C) 2019 Elsevier Ltd. All rights reserved

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years' post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year's initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH4+/NH3), and specific ultraviolet absorbance (SUVA(254)) were significantly higher (67 +/- 40%, 418 +/- 125%, 192 +/- 120%, and 31 +/- 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br-) concentrations (up to 8.7 mu M]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (<= 1 year). (C) 2020 Elsevier Ltd. All rights reserved

Effect of prescribed fires on the export of dissolved organic matter, precursors of disinfection by-products, and water treatability

In this study, we report for the first time the effect of prescribed fires on the export of dissolved organic matter (DOM) and precursors of disinfectant by-products (DBPs) from periodically (every 2-3 years) and seasonally (i.e., dormant and growing) burned forest fuel materials (i.e., live vegetation, woody debris, and detritus [litter and duff]) and treatability of its rainwater leachate. Periodically applied (every 2-3 years for 40 years) prescribed fires decreased total fuel load (62 10%), primarily detrital mass (75 +/- 2%). How-ever, functional groups (i.e., phenolic compounds, proteins, carbohydrates, aromatic [1-ring], polycyclic aromatic hydrocarbons [PAHs], and lipids) attached to DOM of ground solid materials did not change significantly. Outside rainwater leaching (from forest fuel materials) experiments showed that the leaching capacity of dissolved organic carbon (DOC) from burned litter samples decreased by 40 +/- 20% regardless of burning season when compared to unburned litter samples. The leaching of total dissolved nitrogen (TDN), dissolved organic nitrogen (DON), ammonium (NH4+), and reactive phosphorus (PO43-) from burned materials decreased between 40 and 70% when compared to unburned materials. Also, DOM composition was affected by prescribed fire, which partially consumed humic-like substances based on fluorescence analyses. Thus, periodically applied prescribed fires also resulted in a reduction of trihalomethane (THM) (42 +/- 23%) and haloacetic acid (HAA) (42 +/- 20%) formation potentials (FPs), while DOC normalized reactivity of THM and HAA FPs did not change significantly. Additionally, the leaching of Nnitrosodimethylamine (NDMA) precursors, bromide ion (Br-), and selected elements (K, Ca, Mg, Mn, Fe, S, Na, B, and Al) were not significantly affected by prescribed fires. Finally, coagulant (i.e., alum and ferric) dose requirements and coagulation efficiencies were similar (i.e., removal of DOC, precursors of THMs and HAAs were 52-56%, 69-70%, 78-79%, respectively) in unburned and pre-burned leachate samples. (c) 2020 Elsevier Ltd. All rights reserved

Low water treatability efficiency of wildfire-induced dissolved organic matter and disinfection by-product precursors

Wildfire could alter both the quantity and composition of terrestrial organic matter exported into source water, and water treatability of fire-impacted dissolved organic matter (DOM) could be different from its unburned counterpart. Currently, there is no standard protocol to treat wildfire-impacted source water. To identify the best treatment practices in handling post-fire runoffs, we conducted a systematic controlled study using leachates of unburned white fir (Abies concolor) and Ponderosa pine (Pinus ponderosa) and black and white ashes (collected immediately and one year after the 2013 Rim Fire, California) to evaluate coagulation and oxidation strategies for controlling disinfection byproducts (DBPs) formation. Results showed that the efficiency (%) of alum coagulation in removing dissolved organic carbon and nitrogen followed the order of litter > ash immediately after the fire > ash one year after the fire. Alum coagulation was less effectiveness in removing DOM and DBP precursors in ash leachates, compared to litter leachates. This may be attributed to the loss of side chains and the decrease of DOM molecular weight during the wildfire, thus inducing lower removal efficiency of the DOM and DBP precursors during the alum coagulation. Considering use of brominated flame retardants by firefighters, the addition of bromide (Br-) (100 mu g/L) greatly increased the formation of haloacetonitriles by chlorine, and this increase was relatively lower in ash leachates. The influence of reaction time and pH on DOM reactivity was similar among the leachates of litter and ash samples. Our results show that alum coagulation followed by chloramination at alkaline pH is an effective strategy for reducing post-fire DBP formation in drinking water. (c) 2020 Elsevier Ltd. All rights reserved

Hurricane resulted in releasing more nitrogenous than carbonaceous disinfection byproduct precursors in coastal watersheds

The frequency of Atlantic hurricanes has been predicted to increase significantly by the end of this century. Watershed disturbance initiated by hurricanes can alter dissolved organic matter (DOM) quantity and quality in source water dramatically. DOM is an important disinfection by-product (DBP) precursor, and thus hurricanes can have a significant impact on water treatability and drinking water safety. The interactions between land use and land cover (LULC) of a watershed and DBP formation potential (FP) in source water under hurricane events have rarely been evaluated. Here, we quantified the FPs of two carbonaceous (trihalomethanes [THMs] and haloacetic acids [HAA]) and two nitrogenous (haloacetonitrile [HAN] and N-nitrosodimethylamine [NDMA]) DBPs at eighteen sub-watersheds with varying LULC along the Yadkin-Pee Dee River basin across North and South Carolina during and after the flooding condition caused by the 2016 Hurricane Matthew. Using chlorine as a disinfectant. THM FP was 238% (+/- 117%) higher (p NDMA (246.4%) > THM (1152%) using chloramine as a disinfectant. Higher HAN FP and NDMA FP compared to THM IT suggested that more nitrogenous than carbonaceous DBPs precursors were released during this hurricane event. LULC analysis revealed that forested wetlands were the major contributor of THM, MA, and HAN precursors, whereas NDMA precursor was derived from developed areas. This unique study highlights the dynamic interplay between LULC and exports of carbonaceous and nitrogenous DBPs precursors during and after hurricanes. (C) 2019 Elsevier B.V. All rights reserved

Removal of wastewater and polymer derived N-nitrosodimethylamine precursors with integrated use of chlorine and chlorine dioxide

In this study, the effects of five different pre-oxidation scenarios (i.e., individual, simultaneous, and sequential applications of chlorine dioxide [ClO2] and chlorine [Cl-2]) on the removal of N-nitro-sodimethylamine (NDMA) formation potential (FP) from different water matrices (i.e., non-impacted natural waters, wastewater [WW]-impacted, and polymer-impacted waters) with subsequent chloramination were investigated. Practically relevant doses of ClO2 and Cl-2 were applied for all scenarios to avoid the formation of disinfection by-products (DBPs) at regulatory levels. The removal efficiency of NDMA FP for all the oxidation scenarios (individual or simultaneous) was <20% in non-impacted natural water samples. In 20% WW-impacted waters, pre-oxidation with ClO2 at pH 7.8 resulted in a significant reduction in NDMA FP (56-73%), whereas pre-oxidation with Cl-2 showed less removals (40-50%). For the integrated oxidation scenarios (i.e., simultaneous or sequential application), NDMA FP removals further increased (20-45%), especially, at pH 6.0 compared to individual application of oxidants in WW -impacted waters. The formation of NDMA in pre-oxidized water samples also decreased significantly under uniform formation condition (UFC). In polymer-impacted waters, integrated applications of Cl-2 and ClO2 significantly improved the deactivation of polymer-derived NDMA precursors independent of oxidation time (10 vs. 60 min) and pH (6.0 vs. 7.8) compared to individual application of these oxidants. In addition, chlorite (ClO2-) formation was low and maintained well below 1 mg/L for integrated applications of Cl-2 and ClO2, while chlorate (ClO3-) formation increased significantly as compared to application of ClO2 only. (C) 2018 Elsevier Ltd. All rights reserved

Concentration and isotopic composition of mercury in a blackwater river affected by extreme flooding events

Torrential rain and extreme flooding caused by Atlantic hurricanes mobilize a large pool of organic matter (OM) from coastal forested watersheds in the southeastern United States. However, the mobilization of toxic metals such as mercury (Hg) that are associated with this vast pool of OM are rarely measured. This study aims to assess the variations of total Hg (THg) and methylmercury (MeHg) levels and the isotopic compositions of Hg in a blackwater river (Waccamaw River, SC, U.S.A.) during two recent extreme flooding events induced by Hurricane Joaquin (October 2015) and Hurricane Matthew (October 2016). We show that extreme flooding considerably increased filtered THg and MeHg concentrations associated with aromatic dissolved organic matter. During a 2-month sampling window each year (October-November), we estimate that about 27% (2015) and 78% (2016) of the average amount of Hg deposited atmospherically during these 2 months was exported via the river. The isotopic composition of Hg in the river waters was changed only slightly by the substantial inputs of runoff from surrounding landscapes, in which mass-dependent fractionation (as delta Hg-202) decreased from -1.47 to -1.67 parts per thousand and mass-independent fractionation (as increment Hg-199) decreased from -0.15 to -0.37 parts per thousand. The slight variations in Hg isotopic composition during such extreme flooding events imply that sources of Hg in the river are nearly unchanged even under the very high wet deposition of Hg derived from the intensive rainfall. The majority of Hg exported by the river (74-85%) is estimated to have been derived from dry deposition to the watersheds. An increase in frequency and intensity of Atlantic hurricanes is expected in the next few decades due to further warming of ocean surface waters. We predict that increased hurricanes will mobilize more dry-deposited Hg and in situ produced MeHg from these coastal watersheds where MeHg can be extensively bioaccumulated and biomagnified in the downstream aquatic food webs