A comprehensive survey on the occurrence and fate of nitrosamines in sewage treatment plants and water environment

Occurrence and fate of N-nitrosamines in full-scale domestic wastewater treatment plants and their impact on receiving waters along the Lijiang River, China

Domestic wastewaters contaminated with N-nitrosamines pose a significant threat to river ecosystems worldwide, particularly in urban areas with riparian cities. Despite widespread concern, the precise impact of these contaminants on receiving river waters remains uncertain. This study investigated eight N-nitrosamines in wastewater treatment plants (WWTPs) and their adjacent receiving river, the Lijiang River in Guilin City, Southwest China. By analyzing thirty wastewater samples from five full-scale WWTPs and twenty-three river water samples from Guilin, we quantified the mass loads of N-nitrosamines discharged into the surrounding watershed via domestic effluents. The results revealed that N-nitrosodimethylamine (10-60 ng/L), N-nitrosodiethylamine (3.4-22 ng/L), and N-nitrosopyrrolidine (not detected-4.5 ng/g) were predominant in influents, effluents, and sludge, respectively, with the overall removal efficiencies ranging from 17.7 to 65.6% during wastewater treatment. Cyclic activated sludge system and ultraviolet disinfection were effective in removing N-nitrosamines (rates of 59.6% and 24.3%), while chlorine dioxide disinfection promoted their formation. A total of 30.4 g/day of N-nitrosamine mass loads were observed in the Lijiang River water, with domestic effluents contributing about 31.3% (19.4 g/day), followed by livestock breeding wastewater (34.5%, 12.0 g/day), and unknown sources (24.7%, 7.5 g/day). These findings highlight the critical role of WWTPs in transporting N-nitrosamines to watersheds and emphasize the urgent need for further investigation into other potential sources of N-nitrosamine pollution within watersheds.

Experimental and Theoretical Study of the OH-Initiated Degradation of Piperidine under Simulated Atmospheric Conditions

The OH-initiated photo-oxidation of piperidine and the photolysis of 1-nitrosopiperidine were investigated in a large atmospheric simulation chamber and in theoretical calculations based on CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ quantum chemistry results and master equation modeling of the pivotal reaction steps. The rate coefficient for the reaction of piperidine with OH radicals was determined by the relative rate method to be kOH-piperidine = (1.19 ± 0.27) × 10-10 cm3 molecule-1 s-1 at 304 ± 2 K and 1014 ± 2 hPa. Product studies show the piperidine + OH reaction to proceed via H-abstraction from both CH2 and NH groups, resulting in the formation of the corresponding imine (2,3,4,5-tetrahydropyridine) as the major product and in the nitramine (1-nitropiperidine) and nitrosamine (1-nitrosopiperidine) as minor products. Analysis of 1-nitrosopiperidine photolysis experiments under natural sunlight conditions gave the relative rates jrel = j1-nitrosoperidine/jNO2 = 0.342 ± 0.007, k3/k4a = 0.53 ± 0.05 and k2/k4a = (7.66 ± 0.18) × 10-8 that were subsequently employed in modeling the piperidine photo-oxidation experiments, from which the initial branchings between H-abstraction from the NH and CH2 groups, kN-H/ktot = 0.38 ± 0.08 and kC2-H/ktot = 0.49 ± 0.19, were derived. All photo-oxidation experiments were accompanied by particle formation that was initiated by the acid-base reaction of piperidine with nitric acid. Primary photo-oxidation products including both 1-nitrosopiperidine and 1-nitropiperidine were detected in the particles formed. Quantum chemistry calculations on the OH initiated atmospheric photo-oxidation of piperidine suggest the branching in the initial H-abstraction routes to be ∼35% N1, ∼50% C2, ∼13% C3, and ∼2% C4. The theoretical study produced an atmospheric photo-oxidation mechanism, according to which H-abstraction from the C2 position predominantly leads to 2,3,4,5-tetrahydropyridine and H-abstraction from the C3 position results in ring opening followed by a complex autoxidation, of which the first few steps are mapped in detail. H-abstraction from the C4 position is shown to result mainly in the formation of piperidin-4-one and 2,3,4,5-tetrahydropyridin-4-ol, whereas H-abstraction from N1 under atmospheric conditions primarily leads to 2,3,4,5-tetrahydropyridine and in minor amounts of 1-nitrosopiperidine and 1-nitropiperidine. The calculated rate coefficient for the piperidine + OH reaction agrees with the experimental value within 35%, and aligning the theoretical numbers to the experimental value results in k(T) = 2.46 × 10-12 × exp(486 K/T) cm3 molecule-1 s-1 (200-400 K).

Occurrence and mass loads of N-nitrosamines discharged from different anthropogenic activities in Desheng River, South China

N-nitrosamines are widespread in various bodies of water, which is of great concern due to their carcinogenic risks and harmful mutagenic effects. Livestock rearing, domestic, agricultural, and industrial wastewaters are the main sources of N-nitrosamines in environmental water. However, information on the amount of N-nitrosamines these different wastewaters contribute to environmental water is scarce. Here, we investigated eight N-nitrosamines and assessed their mass loadings in the Desheng River to quantify the contributions discharged from different anthropogenic activities. N-nitrosodimethylamine (NDMA) (< 1.6-18 ng/L), N-nitrosomethylethylamine (NMEA) (< 2.2 ng/L), N-nitrosodiethylamine (NDEA) (< 1.7-2.4 ng/L), N-nitrosopyrrolidine (NPYR) (< 1.8-18 ng/L), N-nitrosomorpholine (NMOR) (< 2.0-3.5 ng/L), N-nitrosopiperidine (NPIP) (< 2.2-2.5 ng/L), and N-nitrosodi-n-butylamine (NDBA) (< 3.3-16 ng/L) were detected. NDMA and NDBA were the dominant compounds contributing 89% and 92% to the total N-nitrosamine concentrations. The mean cumulative concentrations of N-nitrosamines in the livestock rearing area (26 ± 11 ng/L) and industrial area (24 ± 4.8 ng/L) were higher than those in the residential area (16 ± 6.3 ng/L) and farmland area (15 ± 5.1 ng/L). The mean concentration of N-nitrosamines in the tributaries (22 ng/L) was slightly higher than that in the mainstem (17 ng/L), probably due to the dilution effect of the mainstem. However, the mass loading assessment based on the river's flow and water concentrations suggested the negligible mass emission of N-nitrosamines into the mainstem from tributaries, which could be due to the small water flow of tributaries. The average mass loads of N-nitrosamines discharged into the mainstem were ranked as the livestock rearing area (742.7 g/d), industrial area (558.6 g/d), farmland area (93.9 g/d), and residential areas (83.2 g/d). In the livestock rearing, residential, and industrial area, NDMA (60.9%, 53.6%, and 46.7%) and NDBA (34.6%, 33.3%, and 44.9%) contributed the most mass loads; NDMA (23.4%), NDEA (15.8%), NPYR (10.1%), NPIP (12.8%), and NDBA (37.8%) contributed almost all the mass loads in the farmland area. Photodegradation amounts of NDMA (0.65 ~ 5.25 µg/(m³·day)), NDBA (0.37 ~ 0.91 µg/(m³·day)), and NDEA (0 ~ 0.66 µg/(m³·day)) were also calculated according to the mass loading. Quantifying the contribution of different anthropogenic activities to the river will provide important information for regional river water quality protection. Risk quotient (RQ) values showed the negligible ecological risks for fish, daphnid, and green algae.

Metabolomics-based molecular signatures reveal the toxic effect of co-exposure to nitrosamines in drinking water

Nitrosamines, a group of emerging nitrogenous pollutants, are ubiquitously found in the drinking water system. However, less is known about how systemic biological responses resist or tolerate nitrosamines, especially long-term co-exposure at low concentrations. In this study, untargeted metabolomics was used to investigate the metabolic perturbations in human esophageal epithelial Het-1A cells induced by a mixture of nine common nitrosamines in drinking water at environmentally relevant, human-internal-exposure, and genotoxic concentrations. Generally, the disrupted metabolic spectrum became complicated with nitrosamines dose increasing. Notably, two inflammation-associated pathways, namely, cysteine (Cys) and methionine (MET) metabolism, and nicotinate and nicotinamide metabolism, changed significantly under the action of nitrosamines, even at the environmentally relevant level. Furthermore, targeted metabolomics and molecular biology indicators in cells were identified in mice synchronously. For one thing, the up-regulated Cys and MET metabolism provided methyl donors for histone methylation in the context of pro-inflammatory response. For another, the down-regulated NAD⁺/NADH ratio inhibited the deacetylation of NF-кB p65 and eventually activated the NF-кB signaling pathway. Taken collectively, the metabolomics molecular signatures were important indicative markers for nitrosamines-induced inflammation. The potential crosstalk between the inflammatory cascade and metabolic regulation also requires further studies. These findings suggest that more attention should be paid to long-term co-exposure at low concentrations in the control of nitrosamines pollution in drinking water. Additionally, this study also highlights a good prospect of the combined metabolomic-molecular biology approach in environmental toxicology.

Characterization of nitrosamines and nitrosamine precursors as non-point source pollutants during heavy rainfall events in an urban water environment

N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR) and their specific precursors (N,N-dimethylformamide [DMF] for NDMA and morpholine [MOR] for NMOR) were widely identified in runoff of urban area around the southern Lake Biwa basin, Japan. It was thought that this runoff might constitute a non-point source of the four compounds in rivers and sewage treatment plants (STPs) during heavy rainfall events. We investigated the spatiotemporal patterns of NDMA, NMOR, DMF and MOR in runoff and rivers in rainy days. NDMA and NMOR were detected in concentrations of up to 295 ng/L, while DMF and MOR were detected in concentrations of up to 33.7 µg/L. Continuous sequential sampling over periods of 24 or 48 h at the largest STP in the study area revealed that the four compounds in the primary effluent (PE) each had higher mass fluxes during heavy rainfall events than on dry days. This phenomenon might be contributed to non-point sources (e.g., runoff) from infiltration/inflow related to rainwater into sanitary sewers. Moreover, the four compounds were confirmed to have higher mass fluxes in the final effluent of the STP during periods of PE bypass (1.3-1.7 times for NDMA, NMOR, and MOR; over 200 times for DMF; on average) than that on dry days because of increasing inflow during heavy rain than during periods without PE bypass in dry weather.

Quantitative analysis of source and fate of N-nitrosamines and their precursors in an urban water system in East China

The source and fate of N-nitrosamines and their precursors in terms of formation potential (FP) was investigated quantitatively in the city level for the first time. Different sources of nitrosamines and their precursors were investigated in one city in the Yangtze River delta, China. The source water located downstream of the city contained 8.4 ng/L of N-nitrosodimethyamine (NDMA) and 153 ng/L of NDMA FP. The contribution of each discharge source was evaluated based on the concentration, the river water flux, and the amount of wastewater discharges. Textile printing and dyeing wastewater, and electroplating industrial wastewater contained high concentration of nitrosamines and were important discharge sources. Taking NDMA and NDMA FP attenuation by photolysis and biodegradation into consideration, the mass load calculation showed upstream surface water brought about 13 ± 4% of NDMA and 21 ± 3% of NDMA FP to downstream source water. Local wastewater discharges contributed 30 ± 8% of NDMA and 17 ± 2% of NDMA FP to downstream source water. Endogenous formation via amino acids metabolism could contribute 36% of NDMA FP (maximum) to downstream source water. Overall, this study provides a protocol for quantitative evaluation of the nitrosamine contribution to urban water supply from different contamination sources.

Modeling in-stream attenuation of N-nitrosodimethylamine and formaldehyde during urban river transportation based on seasonal and diurnal variation

Disinfection by-products (DBPs) discharged from sewage treatment plants (STPs) could harm downstream receiving waters and drinking water resources. In-stream attenuation of photo- and non-photodegradable DBPs during river transportation is currently not well understood. Here we sought to fill this knowledge gap by meta-data-analysis for modeling in-stream attenuation of DBPs. Data were collected along a treated-wastewater-dominated 1.6-km stretch of a river channel for 3 years and incorporated seasonal and diurnal patterns. Photo-irradiation and water temperature were the main factors responsible for in-stream attenuation of photodegradable N-nitrosodimethylamine (NDMA), and water temperature for that of non-photodegradable formaldehyde (FAH). The factors were incorporated into photo-dependent and -independent models to account for temporal variations in NDMA and FAH, respectively. Estimated mass recoveries of NDMA and FAH agreed well with observed values along the stretch. The models developed here offer a novel and useful tool for estimating levels of NDMA and FAH during river transportation.

Diurnal patterns of N-nitrosodimethylamine and formaldehyde behaviors in different seasons in surface water influenced by effluent from sewage treatment plants

N-nitrosodimethylamine (NDMA) and formaldehyde (FAH) are probable carcinogenic disinfection by-products and have been found to occur in areas of the Yodo River basin that are influenced by treated wastewater. The diurnal patterns of them were examined with water samples collected over 4 years in different seasons at five outlets of four sewage treatment plants (STPs), seven main stream sites, and five tributary sites in the basin. Based on mass flux calculations, STPs were shown to be the main sources of the downstream for NDMA and FAH loads in the study area. Moreover, results revealed that photo degradable NDMA and non-photo degradable FAH showed different fates during the river transportation. For NDMA, in addition to direct photolysis, water temperature was identified as an important factor in NDMA attenuation in surface waters. NDMA attenuated significantly in the daytime and even during summer nights but persisted during winter nights, while attenuation of FAH was found to mainly be influenced by water temperature, and persisted during winter. Their behaviors were compared in an artificial river channel and whole study area, clearly demonstrating the importance of monitoring them in the water environment during periods of low UV intensity and water temperature, especially winter nights.

N-nitrosomorpholine behavior in sewage treatment plants and urban rivers

The seasonal and diurnal patterns of N-nitrosomorpholine (NMOR) and its formation potential (NMOR FP) were examined with water samples taken from five outlets of four sewage treatment plants (STPs), seven main stream sites, and five tributary sites in the Yodo River basin. STPs were shown to be the main sources of downstream NMOR load. The highest NMOR levels were found in the discharge from one STP (26.4-171 ng/L). Continuous sequential samplings over a period of 24 h at this STP revealed that NMOR flux at the influent point fluctuated in both summer (0.4-3.2 g/h) and winter (0.3-5.4 g/h), while it was steady in the effluent. In addition, levels of NMOR remained stable during the biological treatment and disinfection processes. The present research demonstrated that NMOR could be formed from morpholine (MOR) in raw sewage treated by this STP, with a possible mechanism being formaldehyde-catalyzed nitrosation of MOR by nitrites, prior to raw sewage entering the STP. This implies that the NMOR detected here might not be a disinfection byproduct per se under low-chlorine disinfection (around 1.0 mg/L), but is primarily a contaminant that is difficult to remove during sewage treatment. NMOR attenuated significantly in the rivers in the daytime with production of MOR, but persisted during nights, which demonstrated the importance of monitoring NMOR levels in the water environment during periods of low UV intensity, especially nights.

Occurrence and ecological risk assessment of disinfection byproducts from chlorination of wastewater effluents in East China

Effluents containing disinfection byproducts (DBPs) from wastewater treatment plants (WWTPs) may be discharged to the receiving water bodies or reused for irrigation, landscaping, and environmental supplies as well as a source to replenish groundwater. Thus the formation and risk of the DBPs in disinfected wastewater effluents should be concerned. In this study, the occurrence of 44 DBPs including 6 trihalomethanes (THMs), 9 haloaceticacids (HAAs), 2 haloketones (HKs), 9 halonitromethanes (HNMs), 9 haloacetonitriles (HANs) and 9 nitrosamines (NAs) was investigated in 12 chlorinated WWTP effluents from five cities of East China. The contribution of each class of DBPs to the total DBPs concentration and additive toxicity was calculated. The average concentrations of the 6 classes of DBPs were ranked as follows: HAAs (47.0 μg/L) > THMs (28.0 μg/L) > HANs (9.9 μg/L) > HNMs (2.9 μg/L) > HKs (0.79 μg/L) > NAs (0.69 μg/L). The significant positive correlations were observed between the formation of THMs and HAAs, THMs and HANs, as well as HAAs and HANs. The results showed that HAAs and THMs were the dominant DBPs on a mass concentration basis and accounted for 54% and 29%, respectively in the total measured DBPs, but they made a minor contribution to the calculated DBP-associated cytotoxicity. HANs and NAs dominated the DBP-associated cytotoxicity, accounting for 50% and 34% on an additive toxicity basis despite the minor contributions to the mass concentration with 10% and 1%, respectively. The risk quotients for three taxonomic groups (fish, daphnid, and green algae) were calculated to assess the ecological risk of DBPs, and the results demonstrated that both HAAs and HANs had high ecological risk for green algae in chlorinated wastewater effluents.

N-nitrosomorpholine in potable reuse

As potable reuse guidelines and regulations continue to develop, the presence of N-nitrosamines is a primary concern because of their associated health concerns. In this study, bench-, pilot-, and full-scale tests were conducted to focus on the occurrence and treatment of N-nitrosomorpholine (NMOR) in United States (U.S.) potable reuse systems. Out of twelve U.S. wastewater effluents collected, ambient NMOR was detected in eleven (average = 20 ± 18 ng/L); in contrast, only two of the thirteen surface water and stormwater samples had NMOR. Across all of these samples maximum formation potential by chloramination produced an average increase of 3.6 ± 1.8 ng/L. This result underscores the need to understand the sources of NMOR as it is not likely a disinfection byproduct and it is not known to be commercially produced within the U.S. At the pilot-scale, three potable reuse systems were evaluated for ambient NMOR with oxidation (i.e., chlorination and ozonation), biofiltration, and granular activated carbon (GAC). Both pre-oxidation and biofiltration were ineffective at mitigating NMOR during long-term pilot plant operation (at least eight-months). GAC adsorbers were the only pilot-scale treatment to remove NMOR; however, complete breakthrough occurred rapidly from <2000 to 10,000 bed volumes. For comparison, a full-scale reverse osmosis (RO) potable reuse system was monitored for a year and confirmed that RO effectively removes NMOR. Systematic bench-scale UV-advanced oxidation experiments were undertaken to assess the mitigation potential for NMOR. At a fluence dose of 325 ± 10 mJ/cm²_, UV alone degraded 90% of the NMOR present. The addition of 5 mg/L hydrogen peroxide did not significantly decrease the UV dose required for one-log removal. These data illustrate that efficient NMOR removal from potable reuse systems is limited to RO or UV treatment.

Antioxidant properties of Ferulago angulata and its hepatoprotective effect against N-nitrosodimethylamine-induced oxidative stress in rats

CONTEXT

Ferulago angulata (Schlecht.) Boiss. (Apiaceae) (FASB) is used to treat liver diseases and has been used both as food and therapeutics by many cultures for thousands of years because of the natural antioxidant compounds.

OBJECTIVE

This study determines antioxidant properties of FASB flowers, the levels of minerals and vitamins, and also, evaluates the hepatoprotective effect of flowers against N-nitrosodimethylamine (NDMA) induced on liver tissue by assessing antioxidant enzymes and histopathological parameters in Wistar albino rats.

MATERIALS AND METHODS

In the study, the rats were divided into six groups of ten. Control, untreated animals were given 0.9% NaCl. Rats were intraperitoneally given NDMA (10 mg/kg) for the first 7 days. FASB methanol extract (150 and 300 mg/kg) was administered orally for 21 days.

RESULTS

α-Tocopherol, retinol, ascorbic acid, total antioxidant activity, phenolic and flavonoid contents of FASB were 0.70 ± 0.13, 0.29 ± 0.03 μg/g, 139.32 ± 7.06 μg/100 g, 171.61 ± 6.05 mM ascorbic acid/g, 90.47 ± 4.11 mg GA/g and 37.39 ± 2.85 mg QE/g. DPPH and hydroxyl radical scavenging activity was obtained IC₅₀ 67.34 ± 4.14 and 64.87 ± 4.68 μg/mL, respectively.

DISCUSSION AND CONCLUSION

The results of the study indicated that FASB flowers contain high levels of vitamins, minerals, total antioxidant activity, phenolics and flavonoids. Due to the positive effect on significant changes in antioxidant enzymes of liver tissue and histopathological examination, it is thought that the plant could be used as a hepatoprotective.

Research on a soft measurement model of sewage treatment based on a case-based reasoning approach

In this paper, the measurement of biochemical oxygen demand (BOD) in a wastewater treatment process is analyzed and an intelligent integrated prediction method based on case-based reasoning (CBR) is proposed in order to overcome difficulties. Due to the fact that there are many factors that influence the accuracy of the prediction model, the radial basis function, which is a neural network with a 3 layer feedforward network, is employed to reduce the dimension of input values. Under these circumstances, a back propagation neural network combining with a nearest neighbor retrieval strategy is adopted to match case. Then, the measurement of BOD in wastewater treatment process is analyzed. Finally, the validity of the improved CBR in sewage treatment is demonstrated by using numerical results.