Thermal Decomposition of Two Gaseous Perfluorocarboxylic Acids: Products and Mechanisms.

The thermal decomposition products and mechanisms of per- and polyfluoroalkyl substances (PFASs) are poorly understood despite the use of thermal treatment to remediate PFAS-contaminated media. To identify the thermal decomposition products and mechanisms of perfluorocarboxylic acids (PFCAs), gaseous perfluoropropionic acid (PFPrA) and perfluorobutyric acid (PFBA) were decomposed in nitrogen and oxygen at temperatures from 200 to 780 °C. In nitrogen (i.e., pyrolysis), the primary products of PFPrA were CF2═CF2, CF3CF2H, and CF3COF. CF3CF═CF2 was the dominant product of PFBA. These products are produced by HF elimination (detected as low as 200 °C). CF4 and C2F6 were observed from both PFCAs, suggesting formation of perfluorocarbon radical intermediates. Pyrolysis products were highly thermally stable, resulting in poor defluorination. In oxygen (i.e., combustion), the primary product of both PFPrA and PFBA below 400 °C was COF2, but the primary product was SiF4 above 600 °C due to reactions with the quartz reactor. Oxygen facilitated thermal defluorination by reacting with PFCAs and with pyrolysis products (i.e., fluoroolefins and fluorocarbon radicals). Platinum improved combustion of PFCAs to COF2 at temperatures as low as 200 °C, while quartz promoted the combustion of PFCAs into SiF4 at higher temperatures (>600 °C), highlighting the importance of surface reactions that are not typically incorporated into computational approaches.

Critical Review of Thermal Decomposition of Per- and Polyfluoroalkyl Substances: Mechanisms and Implications for Thermal Treatment Processes.

Per- and polyfluoroalkyl substances (PFASs) are fluorinated organic chemicals that are concerning due to their environmental persistence and adverse human and ecological effects. Remediation of environmental PFAS contamination and their presence in consumer products have led to the production of solid and liquid waste streams containing high concentrations of PFASs, which require efficient and cost-effective treatment solutions. PFASs are challenging to defluorinate by conventional and advanced destructive treatment processes, and physical separation processes produce waste streams (e.g., membrane concentrate, spent activated carbon) requiring further post-treatment. Incineration and other thermal treatment processes are widely available, but their use in managing PFAS-containing wastes remains poorly understood. Under specific operating conditions, thermal treatment is expected to mineralize PFASs, but the degradation mechanisms and pathways are unknown. In this review, we critically evaluate the thermal decomposition mechanisms, pathways, and byproducts of PFASs that are crucial to the design and operation of thermal treatment processes. We highlight the analytical capabilities and challenges and identify research gaps which limit the current understanding of safely applying thermal treatment to destroy PFASs as a viable end-of-life treatment process.

Waterless Urinals Remove Select Pharmaceuticals from Urine by Phase Partitioning.

We investigated the potential for waterless urinal sealants fluids to remove pharmaceuticals from urine. 1H NMR, FTIR, and GC/MS characterization of the fluids indicated that they are mostly composed of aliphatic compounds. Removal of ethinyl estradiol was >40% for two of the three sealant fluids during simulated urination to a urinal cartridge but removal of seven other compounds with greater hydrophilicity was <30%. At equilibrium with Milli-Q water, ≥ 89% partitioning to the sealant phase was observed for three compounds with pH adjusted log Kow (log Dow) > 3.5. At equilibrium with synthetic urine, removal ranged widely from 2% to 100%. Kow was poorly correlated with removal for both matrices at equilibrium, but Dow was correlated with removal from synthetic urine for two of the three sealants, indicating that ionization and hydrophilicity control partitioning between the urine and sealant phases. To improve removal during urination, where equilibrium is not achieved, we increased the hydraulic retention time 100-fold over that of typical male urination. Removal of specific hydrophobic compounds increased, indicating that both hydrophobicity and kinetics control removal. Removal of ethinyl estradiol was ≥90% for all sealants in the increased hydraulic retention time experiment, demonstrating the potential for implementation to female urinals.

Detection and Sizing of Ti-Containing Particles in Recreational Waters Using Single Particle ICP-MS.

Single particle inductively coupled plasma mass spectrometry (spICP-MS) was used to detect Ti-containing particles in heavily-used bathing areas of a river (Salt River) and five swimming pools. Ti-containing particle concentrations in swimming pools ranged from 2.8 × 103 to 4.4 × 103 particles/mL and were an order of magnitude lower than those detected in the Salt River. Measurements from the Salt River showed an 80% increase in Ti-containing particle concentration over baseline concentration during peak recreational activity (at 16:00 h) in the river. Cloud point extraction followed by transmission electron microscopy with energy dispersive X-ray analysis confirmed presence of aggregated TiO2 particles in river samples, showing morphological similarity to particles present in an over-the-counter sunscreen product. The maximum particle mass concentration detected in a sample from the Salt River (659 ng/L) is only slightly lower than the predicted no effect concentration for TiO2 to aquatic organisms (< 1 µg/L).

Zebrafish embryo toxicity of 15 chlorinated, brominated, and iodinated disinfection by-products.

Disinfection to protect human health occurs at drinking water and wastewater facilities through application of non-selective oxidants including chlorine. Oxidants also transform organic material and form disinfection by-products (DBPs), many of which are halogenated and cyto- and genotoxic. Only a handful of assays have been used to compare DBP toxicity, and researchers are unsure which DBP(s) drive the increased cancer risk associated with drinking chlorinated water. The most extensive data set employs an in vitro model cell, Chinese hamster ovary cells. Traditionally, most DBP research focuses on the threat to human health, but the effects on aquatic species exposed to DBPs in wastewater effluents remain ill defined. We present the developmental toxicity for 15 DBPs and a chlorinated wastewater to a model aquatic vertebrate, zebrafish. Mono-halogenated DBPs followed the in vivo toxicity rank order: acetamides>acetic acids>acetonitriles~nitrosamines, which agrees well with previously published mammalian in vitro data. Di- and tri-halogenated acetonitriles were more toxic than their mono-halogenated analogues, and bromine- and iodine-substituted DBPs tended to be more toxic than chlorinated analogues. No zebrafish development effects were observed after exposure to undiluted or non-concentrated, chlorinated wastewater. We find zebrafish development to be a viable in vivo alternative or confirmatory assay to mammalian in vitro cell assays.

Novel Ion-Exchange Coagulants Remove More Low Molecular Weight Organics than Traditional Coagulants.

Low molecular weight (MW) charged organic matter is poorly removed by conventional coagulants but contributes to disinfection byproduct formation during chlorination of drinking waters. We hypothesized that CIEX, a new Al-based hybrid coagulant with ion-exchange functional groups, would be new mechanistic approach to remove low MW organic matter during coagulation and would perform better than polyaluminum chloride (PACl) or metal-salt based coagulants. We measured coagulation performance using dissolved organic carbon (DOC) in a high hardness surface water. CIEX achieved excellent turbidity removal and removed 20% to 46% more DOC than FeCl3, Al2(SO4)3, or PACl, depending on dose. The improved DOC removal was attributable to better removal of low MW organic matter (<2 kDa). We further studied removal mechanisms in a model water containing a low MW organic acid (salicylic acid (SA)). CIEX achieved high removal of organic acids (>90% of SA) independent of pH, whereas removal by metal salts was lower (<15%) and was strongly pH dependent. CIEX ion-exchange capability is facilitated by its covalently bound quaternary ammonium group, which conventional coagulants lack. Plus, unlike other cationic polymers that react with chloramines to form N-nitrosodimethylamine (NDMA), CIEX has a low molar yield (9.3 × 10(-7) mol NDMA per mol CIEX-N).

Granular Activated Carbon Treatment May Result in Higher Predicted Genotoxicity in the Presence of Bromide.

Certain unregulated disinfection byproducts (DBPs) are more of a health concern than regulated DBPs. Brominated species are typically more cytotoxic and genotoxic than their chlorinated analogs. The impact of granular activated carbon (GAC) on controlling the formation of regulated and selected unregulated DBPs following chlorine disinfection was evaluated. The predicted cyto- and genotoxicity of DBPs was calculated using published potencies based on the comet assay for Chinese hamster ovary cells (assesses the level of DNA strand breaks). Additionally, genotoxicity was measured using the SOS-Chromotest (detects DNA-damaging agents). The class sum concentrations of trihalomethanes, haloacetic acids, and unregulated DBPs, and the SOS genotoxicity followed the breakthrough of dissolved organic carbon (DOC), however the formation of brominated species did not. The bromide/DOC ratio was higher than the influent through much of the breakthrough curve (GAC does not remove bromide), which resulted in elevated brominated DBP concentrations in the effluent. Based on the potency of the haloacetonitriles and halonitromethanes, these nitrogen-containing DBPs were the driving agents of the predicted genotoxicity. GAC treatment of drinking or reclaimed waters with appreciable levels of bromide and dissolved organic nitrogen may not control the formation of unregulated DBPs with higher genotoxicity potencies.

Sorption and desorption of organic matter on solid-phase extraction media to isolate and identify N-nitrosodimethylamine precursors.

#x02010;Nitrosodimethylamine is mutagenic in rodents, a drinking water contaminant, and a byproduct of drinking water disinfection by chloramination. Nitrosodimethylamine precursor identification leads to their control and improved understanding of nitrosodimethylamine formation during chloramination. Mass balances on nitrosodimethylamine precursors were evaluated across solid-phase extraction cartridges and in eluates to select the best combination of solid-phase media and eluent that maximized recovery of nitrosodimethylamine precursors into a solvent amenable to time-of-flight mass spectrometry analysis. After reviewing literature and comparing various solid-phase cartridges and eluent combinations, a method was obtained to efficiently recover nitrosodimethylamine precursors. The approach with the greatest recoveries of nitrosodimethylamine precursors involved cation exchange resin loaded with water samples at pH 3 and eluted with 5% NH4 OH in methanol. This indicated that nitrosodimethylamine precursors are amines that protonate at low pH and deprotonate at high pH. Quaternary amines were irreversibly sorbed to the cation exchange cartridge and did not account for a large fraction of precursors. Overall, a median recovery of 82% for nitrosodimethylamine precursors was achieved from 11 surface waters and one wastewater. Applying this method allowed discovery of methadone as a new nitrosodimethylamine precursor in wastewater effluent and drinking water treatment plant intakes.

Bacterial dealkylation of benzalkonium chlorides in wastewater produces benzyldimethylamine, a potent N-nitrosodimethylamine precursor.

N-nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct that forms during chloramine disinfection of municipal wastewater effluents which are increasingly used to augment drinking water supplies due to growing water scarcity. Knowledge of wastewater NDMA precursors is limited and the known pool of NDMA precursors has not closed the mass balance between precursor loading, precursor NDMA yield, and formed NDMA. Benzalkonium chlorides (BACs) are the most prevalent quaternary ammonium surfactants and have antimicrobial properties. The extensive utilization of BACs in household, commercial and industrial products has resulted in their detection in wastewater at elevated concentrations. We report the formation of a potent NDMA precursor, benzyldimethylamine (BDMA) from the biodegradation of BACs during activated sludge treatment. BDMA formation and NDMA formation potential (FP) were functions of BAC and mixed liquor suspended solids concentration at circumneutral pH, and the microbial community source. Sustained exposure to microorganisms reduced NDMA FP through successive dealkylation of BDMA to less potent precursors. BAC alkyl chain length (C8 - C16) had little impact on NDMA FP and BDMA formation because chain cleavage occurred at the C-N bond. Wastewater effluents collected from three facilities contained BDMA from 15 to 106 ng/L, accounting for an estimated 4 to 38 % of the NDMA precursor pool.

Wildfire impact on disinfection byproduct precursor loading in mountain streams and rivers.

We investigated short (first post-fire precipitation)- and long-term (11-month) impacts of the Caldor and Mosquito Fires (2021 and 2022) on water quality, dissolved organic matter, and disinfection byproduct (DBP) precursors in burned and adjacent unburned watersheds. Both burned watersheds experienced water quality degradation compared to their paired unburned watersheds, including increases in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and DBP precursors from precipitation events. DBP precursor concentrations during storm events were greater in the Caldor Fire's burned watershed than in the unburned watershed; precursors of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) were 533 µg/L, 1,231 µg/L, 64 and 58 µg/L greater. The burned watershed of the Mosquito Fire also had greater median concentrations of THM (44 µg/L), HAA (37 µg/L), HAN (7 µg/L), and HAM (13 µg/L) precursors compared to the unburned watershed during a storm immediately following the fire. Initial flushes from both burned watersheds formed greater concentrations of more toxic DBPs, such as HANs and HAMs. The Caldor Fire burn area experienced a rain-on-snow event shortly after the fire which produced the greatest degradation of water quality of all seasons/precipitation events/watersheds studied. Over the long term, statistical analysis revealed that DOC and DON values in the burned watershed of the Caldor Fire remained higher than the unburned control (0.98 mg C/L and 0.028 mg N/L, respectively). These short and long-term findings indicate that wildfires present potential treatment challenges for public water systems outside of the two studied here.

Molecular characterization of disinfection byproduct precursors in filter backwash water from 10 drinking water treatment plants.

Organic matter reacts with chlorine forming disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetamides (HAMs), haloacetic acids (HAAs), and haloacetonitriles (HANs). Filter backwash water (FBW) is either released back to the environment or recycled to the head of the treatment plant after solids settling and the remaining dissolved organic matter is a significant pool of DBP precursors that are not well understood. We characterized dissolved organic matter in FBW from 10 treatment plants and low molecular weight (MW < 1 kDa) organic matter contributed the most to DBP formation. We demonstrated overall similarity of the molecular composition (e.g., elemental ratios, m/z, DBE) of the 10 samples of FBW by Fourier transform ion cyclotron resonance mass spectrometry. Aromatic and more highly oxidized compounds preferentially reacted with chlorine, forming DBPs. Low MW (<450 Da) aliphatic compounds, and highly unsaturated and phenolic compounds were the primary precursors of THMs, HANs, and HAMs, and the formation potentials (FPs) of these groups of DBPs were correlated with multiple individual molecular formulae. HAA FPs were correlated with low MW, highly unsaturated and phenolic compounds. These advances in the understanding of the molecular composition of DBP precursors in FBW may develop the effective strategies to control DBP formation and limit impacts on the quality of finished water, and can be expanded to understanding DBP precursors in drinking water sources.

Per- and polyfluoroalkyl substances and organofluorine in lakes and waterways of the northwestern Great Basin and Sierra Nevada.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals that occur ubiquitously in the environment and have been linked to numerous adverse health effects in humans and aquatic organisms. Although numerous environmental monitoring studies have been conducted, only one has evaluated PFAS in surface waters of the northwestern Great Basin, which features unique topography that results in dozens of endorheic basins and terminal lakes with no natural outlet, where PFAS may accumulate. To close this knowledge gap, we evaluated the occurrence of PFAS in grab samples from 15 lakes (headwater and terminal lakes) and 10 rivers in the Great Basin located in Nevada and California of the United States. PFAS and organofluorine were quantified by liquid chromatography tandem mass spectroscopy (LC-MS/MS) and combustion ion chromatography, respectively. The highest concentrations of PFAS occurred in samples taken near sites with known or suspected prior aqueous film forming foam (AFFF) application (~20 to 4754 ng/L). Samples near wastewater treatment plants and in urban areas also tended to have PFAS concentrations greater than those measured in remote, less anthropogenically influenced areas (~2 to 15 ng/L, <3 ng/L respectively). In limited snapshot sampling events PFAS appeared to accumulate in terminal lakes to some extent; in-lake concentrations were two to five times greater than those of their inflows. Fluorotelomer sulfonates were present downstream of a known AFFF application area likely to have had fluorotelomer-based foams applied to it, and the concentrations decayed in a predictable manner, suggesting they may be used as an indicator of PFAS transport away from an AFFF source. In all but two samples, organofluorine concentrations were greater than the sum of targeted PFAS (on a F basis) (median of 0.6 % of organofluorine identified via LC-MS/MS), although there was considerable variability in organofluorine measured in replicate samples.

Adsorption of N-nitrosodimethylamine precursors by powdered and granular activated carbon.

Activated carbon (AC) has been shown to remove precursors of halogenated disinfection byproducts. Granular and powdered activated carbon (GAC, PAC) were investigated for their potential to adsorb N-nitrosodimethylamine (NDMA) precursors from blends of river water and effluent from a wastewater treatment plant (WWTP). At bench scale, waters were exposed to lignite or bituminous AC, either as PAC in bottle point experiments or as GAC in rapid small-scale column tests (RSSCTs). NDMA formation potential (FP) was used as a surrogate for precursor removal. NDMA FP was reduced by 37, 59, and 91% with 3, 8, and 75 mg/L of one PAC, respectively, with a 4-h contact time. In RSSCTs and in full-scale GAC contactors, NDMA FP removal always exceeded that of the bulk dissolved organic carbon (DOC) and UV absorbance at 254 nm. For example, whereas DOC breakthrough exceeded 90% of its influent concentration after 10,000 bed volumes of operation in an RSSCT, NDMA FP was less than 40% of influent concentration after the same bed life of the GAC. At full or pilot scale, high NDMA FP reduction ranging from >60 to >90% was achieved across GAC contactors, dependent upon the GAC bed life and/or use of a preoxidant (chlorine or ozone). In all experiments, NDMA formation was not reduced to zero, which suggests that although some precursors are strongly sorbed, others are not. This is among the first studies to show that AC is capable of adsorbing NDMA precursors, but further research is needed to better understand NDMA precursor chemical properties (e.g., hydrophobicity, molecular size) and evaluate how best to incorporate this finding into full-scale designs and practice.

Modeling the fate of ionizable pharmaceutical and personal care products (iPPCPs) in soil-plant systems: pH and speciation.

A model was developed to simulate the pH-dependent speciation and fate of ionizable pharmaceutical and personal care products (iPPCPs) in soils and their plant uptake during thedt application of reclaimed wastewater to agricultural soils. The simulation showed that pH plays an important role in regulating the plant uptake of iPPCPs, i.e., ibuprofen (IBU; with a carboxylic group), triclosan (TCS; phenolic group), and fluoxetine (FXT; amine group) as model compounds. It took 89-487 days for various iPPCPs to reach the steady-state concentrations in soil and plant tissues. The simulated steady-state concentrations of iPPCPs in plant tissues at pH 9 is 2.2-2.3, 2.5-2.6, and 1.07-1.08 times that at pH 5 for IBU, TCS, and FXT, respectively. Assuming sorption only for neutral compounds led to miscalculation of iPPCPs concentrations in plant tissues by up to one and half orders magnitude. Efflux of compounds in soil, lettuce leaf, and soybean pods was primarily contributed by their degradation in soil and dilution due to plant tissue growth. Overall, the results demonstrated the importance of considering pH and speciation of iPPCPs when simulating their fate in the soil-plant system and plant uptake.

Evidence of low levels of trace organic contaminants in terminal lakes.

Endorheic lakes (or terminal lakes, TLs) have no natural outlet other than evaporation and slow infiltration. Some TLs receive reclaimed wastewater which contains poorly removed trace organic contaminants (TrOCs). To determine if TLs accumulate TrOCs we conducted a preliminary assessment of the occurrence of ten TrOCs in three TLs receiving reclaimed wastewater and one TL which does not directly receive reclaimed wastewater. Five of ten TrOCs (carbamazepine, DEET, fluoxetine, primidone, and trimethoprim) were present in all four TLs' surface waters (~0.3-1109 ng/L), six (caffeine, carbamazepine, DEET, diphenhydramine, primidone, and trimethoprim) were present in sediment samples (0.1-77 ng/gDW) and in soil samples (0.1-137 ng/gDW). Concentrations of caffeine, carbamazepine, diphenhydramine, fluoxetine and meprobamate were significantly higher in TLs receiving wastewater from a secondary treatment plant compared to those TLs which received tertiary treated wastewater. Carbamazepine, fluoxetine, sulfamethoxazole, and trimethoprim were present at concentrations greater than is typical of other U.S. freshwater lakes, but other TrOC concentrations were present at lower concentrations than in other freshwater lakes. We conclude that some TrOCs may accumulate in TLs, but to a lesser extent than would be expected based on the accumulation of dissolved constituents alone, which indicates that there are other unidentified processes in TLs that contribute to TrOC losses. Other TLs across the globe may have similar levels of TrOCs due to anthropogenic influence and treated wastewater inputs.

Quantification of pharmaceuticals in the sealant fluids of actively used waterless urinals.

Prior measurements at bench scale revealed that waterless urinal cartridges containing oily sealant fluids are capable of partitioning pharmaceuticals from urine and therefore reducing their concentration in wastewater. We sought to measure pharmaceutical removal from in-use waterless urinals. We developed a method to quantify pharmaceuticals in the sealant phase, which resulted in 79 ± 30% and 71 ± 30% recovery of eight pharmaceuticals from two sealant fluids, respectively. The method was applied to sealant samples collected over three weeks from in-use waterless urinals on a university campus. Six of eight pharmaceuticals were present in the sealant samples from 1.4 µg/L to 241 µg/L. Loads of the six pharmaceuticals detected in the sealants were removed from the receiving wastewater from 0.02 µg/day to 3.4 µg/day across the sampling period. The concentration of the pharmaceuticals were similar over time, indicating rapid saturation and washout of the sealant. We also observed relatively rapid loss of sealant at maintenance intervals consistent with the manufacturer's instructions. These findings indicate that while waterless urinals do remove some pharmaceuticals from the wastewater stream, meaningful changes to wastewater concentrations will only result if the sealant fluid and/or the urinal cartridge are significantly modified. PRACTITIONER POINTS: We developed a quantification method for pharmaceuticals in oily waterless urinal sealants. Pharmaceuticals were present at relatively low concentrations in the sealant phase of two in-use waterless urinals. We identify engineering challenges that must be overcome to meaningfully reduce pharmaceutical loads in wastewater with waterless urinals.

Modeling the fate and human health impacts of pharmaceuticals and personal care products in reclaimed wastewater irrigation for agriculture.

Wastewater reclamation and reuse for agriculture have attracted a great deal of interest, due to water stress caused by rapid increase in human population and agricultural water demand as well as climate change. However, the application of treated wastewater for irrigation can lead to the accumulation of pharmaceuticals and personal care products (PPCPs) in the agricultural crops, grazing animals, and consequently to human dietary exposure. In this study, a model was developed to simulate the fate of five PPCPs; triclosan (TCS), carbamazepine (CBZ), naproxen (NPX), gemfibrozil (GFB), and fluoxetine (FXT) during wastewater reuse for agriculture, and potential human dietary exposure and health risk. In a reclaimed wastewater-irrigated grazing farm growing alfalfa, it took 100-535 days for PPCPs to achieve the steady-state concentrations of 1.43 × 10-6, 4.73 × 10-5, 1.17 × 10-6, 1.53 × 10-5, and 7.38 × 10-6 mg/kg for TCS, CBZ, NPX, GFB, and FXT in soils, respectively. The accumulated concentration of PPCPs in the plant (alfalfa) and grazing animals (beef) ranged 2.86 × 10-7- 4.02 × 10-3 and 4.39 × 10-15- 6.27 × 10-7 mg/kg, respectively. Human dietary exposure to these compounds through beef consumption was calculated to be 1.67 × 10-18- 1.74 × 10-10 mg/kg bodyweight/d, much lower than the acceptable daily intake (ADI). Similar results were obtained for a 'typical' reclaimed wastewater irrigated farm based on the typical setup using our model. Screening analysis showed that PPCPs with relatively high LogD value and lower ratios of degradation rate (in soils) to plant uptake have a greater potential to be transferred to humans and cause potential health risks. We established a modeling method for evaluating the fate and human health effects of PPCPs in reclaimed wastewater reuse for the agricultural system and developed an index for screening PPCPs with high potential to accumulate in agricultural products. The model and findings are valuable for managing water reuse for irrigation and mitigating the harmful effects of PPCPs.

Formation and control of C- and N-DBPs during disinfection of filter backwash and sedimentation sludge water in drinking water treatment.

Drinking water treatment plants (DWTPs) produce filter backwash water (FBW) and sedimentation sludge water (SSW) that may be partially recycled to the head of DWTPs. The impacts of key disinfection conditions, water quality parameters (e.g., disinfection times, disinfectant types and doses, and pH values), and bromide concentration on controlling the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) during disinfection of FBW and SSW were investigated. Concentrations of most disinfection byproducts (DBPs) and associated calculated toxicity increased with extended chlorination for both FBW and SSW. During chlorination of both FBW and SSW, elevated chlorine doses significantly increased THM yields per unit dissolved organic carbon (DOC), but decreased HAN and HAM yields, with minimum effect on HAA yields. Chloramine disinfection effectively inhibited C-DBP formation but promoted N-DBPs yields, which increased with chloramine dose. Calculated toxicities after chloramination increased with chloramine dose, which was opposite to the trend found after free chlorine addition. An examination of pH effects demonstrated that C-DBPs were more readily generated at alkaline pH (pH=8), while acidic conditions (pH=6) favored N-DBP formation. Total DBP concentrations increased at higher pH levels, but calculated DBP toxicity deceased due to lower HAN and HAM concentrations. Addition of bromide markedly increased bromo-THM and bromo-HAN formation, which are more cytotoxic than chlorinated analogues, but had little impact on the formation of HAAs and HAMs. Bromide incorporation factors (BIFs) for THMs and HANs from both water samples all significantly increased as bromide concentrations increased. Overall, high bromide concentrations increased the calculated toxicity values in FBW and SSW after chlorination. Therefore, while currently challenging, technologies capable of removing bromide should be explored as part of a strategy towards controlling cumulative toxicity burden (i.e., hazard) while simultaneously lowering individual DBP concentrations (i.e., exposure) to manage DBP risks in drinking water.

Reclaimed wastewater as a viable water source for agricultural irrigation: A review of food crop growth inhibition and promotion in the context of environmental change.

The geographical and temporal distribution of precipitation has and is continuing to change with changing climate. Shifting precipitation will likely require adaptations to irrigation strategies, and because 35% of rainfed and 60% of irrigated agriculture is within 20 km of a wastewater treatment plant, we expect that the use of treated wastewater (e.g., reclaimed wastewater) for irrigation will increase. Treated wastewater contains various organic and inorganic substances that may have beneficial (e.g., nitrate) or deleterious (e.g., salt) effects on plants, which may cause a change in global food productivity should a large change to treated wastewater irrigation occur. We reviewed literature focused on food crop growth inhibition or promotion resulting from exposure to xenobiotics, engineered nanoparticles, nitrogen, and phosphorus, metals, and salts. Xenobiotics and engineered nanoparticles, in nearly all instances, were detrimental to crop growth, but only at concentrations much greater than would be currently expected in treated wastewater. However, future changes in wastewater flow and use of these compounds and particles may result in phytotoxicity, particularly for xenobiotics, as some are present in wastewater at concentrations within approximately an order of magnitude of concentrations which caused growth inhibition. The availability of nutrients present in treated wastewater provided the greatest overall benefit, but may be surpassed by the detrimental impact of salt in scenarios where either high concentrations of salt are directly deleterious to plant development (rare) or in scenarios where soils are poorly managed, resulting in soil salt accumulation.

Summation of disinfection by-product CHO cell relative toxicity indices: sampling bias, uncertainty, and a path forward.

The cyto- and genotoxic potencies of disinfection by-products (DBPs) have been evaluated in published literature by measuring the response of exposed Chinese hamster ovary cells. In recent publications, DBP concentrations divided by their individual toxicity indices are summed to predict the relative toxicity of a water sample. We hypothesized that the omission or inclusion of certain DBPs over others is equivalent to statistical sampling bias and may result in biased conclusions. To test this hypothesis, we removed or added actual or simulated DBP measurements to that of published studies which evaluated granular activated carbon as a treatment to reduce the relative toxicity of the effluent. In several examples, it was possible to overturn the conclusions (i.e., activated carbon is detrimental or beneficial in reducing toxicity) by preferentially including specific DBPs. In one example, removing measured haloacetaldehydes caused the predicted cytotoxicity of a treated sample to decrease by up to 47%, reversing the initial conclusion that activated carbon increased the toxicity of the water. We also discuss measurements of statistical error, which are rarely included in publications related to predicted toxicity, but strongly influence the outcomes. Finally, we discuss future research needs in the light of these and other concerns.