Fate of N-nitrosomorpholine in an anaerobic aquifer used for managed aquifer recharge: a column study

Quantum-Mechanical Approach to Predicting the Carcinogenic Potency of N-Nitroso Impurities in Pharmaceuticals

N-Nitroso contaminants in medicinal products are of concern due to their high carcinogenic potency; however, not all these compounds are created equal, and some are relatively benign chemicals. Understanding the structure-activity relationships (SARs) that drive hazards in one molecule versus another is key to both protecting human health and alleviating costly and sometimes inaccurate animal testing. Here, we report on an extension of the CADRE (computer-aided discovery and REdesign) platform, which is used broadly by the pharmaceutical and personal care industries to assess environmental and human health endpoints, to predict the carcinogenic potency of N-nitroso compounds. The model distinguishes compounds in three potency categories with 77% accuracy in external testing, which surpasses the reproducibility of rodent cancer bioassays and constraints imposed by limited (high-quality) data. The robustness of predictions for more complex pharmaceuticals is maximized by capturing key SARs using quantum mechanics, that is, by hinging the model on the underlying chemistry versus chemicals in the training set. To this end, the present approach can be leveraged in a quantitative hazard assessment and to offer qualitative guidance using electronic structure comparisons between well-studied analogues and unknown contaminants.

Probabilistic health risk assessment of nitrosamines in drinking water of Shaoxing, Zhejiang, China

Nitrosamines (NAms) are potent genotoxic and carcinogenic but widely detected in drinking water. This study aimed to investigate the occurrence of major types of NAms in drinking water in Shaoxing, China, and to conduct multi-pathway probabilistic cancer risk (CR) assessment to residents based on age-dependent adjustment Chinese exposure factors. Results showed that concentrations of NAms in water varied from not detected (ND) to dozens of nanograms per liter level. N-Nitrosodimethylamine (NDMA) was detected most frequently (93.06%), followed by N-nitrosodiethylamine (NDEA) (64.08%)-with the highest cancer risk among NAms. The CR of NAms came mainly through the oral exposure pathway. The 95th percentile of the total CR of five major NAms was 1.06 × 10^-4, exceeding the maximum acceptable lifetime CR (1 × 10^-4) recommended by US EPA. Exposure to NDEA contributed the highest to the total CR. The CR of the five NAms through ingestion was 2.5 times higher using the Chinese exposure factors than that of the Americans. The most important variables related to CRs were concentrations of NAms in drinking water, exposure duration, drinking water ingestion rate, and exposure time during bathing. Our findings suggest the urgent need to develop and enforce effective regulatory policies to control the contamination of NAms in drinking water in China. Graphical abstract.

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.

Inhibition of Biodegradation of Hydraulic Fracturing Compounds by Glutaraldehyde: Groundwater Column and Microcosm Experiments

The rapid expansion of unconventional oil and gas development has raised concerns about the potential contamination of aquifers; however, the groundwater fate and transport of hydraulic fracturing fluid compounds and mixtures remains a significant data gap. Degradation kinetics of five hydraulic fracturing compounds (2-propanol, ethylene glycol, propargyl alcohol, 2-butoxyethanol, and 2-ethylhexanol) in the absence and presence of the biocide glutaraldehyde were investigated under a range of redox conditions using sediment-groundwater microcosms and flow-through columns. Microcosms were used to elucidate biodegradation inhibition at varying glutaraldehyde concentrations. In the absence of glutaraldehyde, half-lives ranged from 13 d to >93 d. Accurate mass spectrometry indicated that a trimer was the dominant aqueous-phase glutaraldehyde species. Microbial inhibition was observed at glutaraldehyde trimer concentrations as low as 5 mg L^-1, which demonstrated that the trimer retained some biocidal activity. For most of the compounds, biodegradation rates slowed with increasing glutaraldehyde concentrations. For many of the compounds, degradation was faster in the columns than the microcosms. Four compounds (2-propanol, ethylene glycol, propargyl alcohol, and 2-butoxyethanol) were found to be both mobile and persistent in groundwater under a range of redox conditions. The glutaraldehyde trimer and 2-ethylhexanol were more rapidly degraded, particularly under oxic conditions.

Introducing sequential managed aquifer recharge technology (SMART) - From laboratory to full-scale application

Previous lab-scale studies demonstrated that stimulating the indigenous soil microbial community of groundwater recharge systems by manipulating the availability of biodegradable organic carbon (BDOC) and establishing sequential redox conditions in the subsurface resulted in enhanced removal of compounds with redox-dependent removal behavior such as trace organic chemicals. The aim of this study is to advance this concept from laboratory to full-scale application by introducing sequential managed aquifer recharge technology (SMART). To validate the concept of SMART, a full-scale managed aquifer recharge (MAR) facility in Colorado was studied for three years that featured the proposed sequential configuration: A short riverbank filtration passage followed by subsequent re-aeration and artificial recharge and recovery. Our findings demonstrate that sequential subsurface treatment zones characterized by carbon-rich (>3 mg/L BDOC) to carbon-depleted (≤1 mg/L BDOC) and predominant oxic redox conditions can be established at full-scale MAR facilities adopting the SMART concept. The sequential configuration resulted in substantially improved trace organic chemical removal (i.e. higher biodegradation rate coefficients) for moderately biodegradable compounds compared to conventional MAR systems with extended travel times in an anoxic aquifer. Furthermore, sorption batch experiments with clay materials dispersed in the subsurface implied that sorptive processes might also play a role in the attenuation and retardation of chlorinated flame retardants during MAR. Hence, understanding key factors controlling trace organic chemical removal performance during SMART allows for systems to be engineered for optimal efficiency, resulting in improved removal of constituents at shorter subsurface travel times and a potentially reduced physical footprint of MAR installations.

Fate of benzotriazole and 5-methylbenzotriazole in recycled water recharged into an anaerobic aquifer: column studies

The fate of benzotriazole (BTri) and 5-methylbenzotriazole (5-MeBT) was investigated under anaerobic conditions at nano gram per litre concentrations in large-scale laboratory columns to mimic a managed aquifer recharge replenishment strategy in Western Australia. Investigations of BTri and 5-MeBT sorption behaviour demonstrated mobility of the compounds with retardation coefficients of 2.0 and 2.2, respectively. Degradation processes over a period of 220 days indicated first order biodegradation of the BTri and 5-MeBT under anaerobic aquifer conditions after a biological lag-time of approximately 30-60 days. Biodegradation half-lives of 29 ± 2 and 26 ± 1 days for BTri and 5-MeBT were respectively observed, with no threshold effect to biodegradation observed at the 200 ng L(-1). The detection of degradation products provided further evidence of BTri and 5-MeBT biodegradation. These results suggested that if BTri and 5-MeBT were present in recycled water recharged to the Leederville aquifer, biodegradation during aquifer passage is likely given sufficient aquifer residence times or travel distances between recycled water injection and groundwater extraction.

Refinement of biodegradation tests methodologies and the proposed utility of new microbial ecology techniques

Society's reliance upon chemicals over the last few decades has led to their increased production, application and release into the environment. Determination of chemical persistence is crucial for risk assessment and management of chemicals. Current established OECD biodegradation guidelines enable testing of chemicals under laboratory conditions but with an incomplete consideration of factors that can impact on chemical persistence in the environment. The suite of OECD biodegradation tests do not characterise microbial inoculum and often provide little insight into pathways of degradation. The present review considers limitations with the current OECD biodegradation tests and highlights novel scientific approaches to chemical fate studies. We demonstrate how the incorporation of molecular microbial ecology methods (i.e., 'omics') may improve the underlying mechanistic understanding of biodegradation processes, and enable better extrapolation of data from laboratory based test systems to the relevant environment, which would potentially improve chemical risk assessment and decision making. We outline future challenges for relevant stakeholders to modernise OECD biodegradation tests and put the 'bio' back into biodegradation.

Biodegradation of three selected benzotriazoles in aquifer materials under aerobic and anaerobic conditions

We investigated the biodegradation of three selected benzotriazoles (BTs), namely benzotriazole (BT), 5-methyl-benzotriazole (5-TTri) and 5-chloro-benzotriazole (CBT), in aquifer materials. Biodegradation experiments were conducted in microcosms with fresh groundwater and aquifer sediment materials under aerobic and anaerobic (nitrate, sulfate, and Fe (III) reducing) conditions. All three BTs were degraded by microorganisms in aquifer materials under aerobic and anaerobic conditions. Under aerobic conditions, BT and 5-TTri were found to be degraded fastest with their half-lives of 43 days and 31 days, respectively, among the redox conditions used. Under anaerobic conditions, CBT was found to be degraded better with its half-life of 21 days under nitrate reducing conditions than under aerobic conditions with its half-life of 47 days. The two BT derivatives 5-TTri and CBT could be biotransformed into BT via demethylation and dechlorination reactions, respectively.

Differential microbial transformation of nitrosamines by an inducible propane monooxygenase

The toxicity of N-nitrosamines, their presence in drinking and environmental water supplies, and poorly understood recalcitrance collectively necessitate a better understanding of their potential for bioattenuation. Here, we show that the bacterial strain Rhodococcus jostii RHA1 can biotransform N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPYR), and possibly N-nitrosomorpholine (NMOR) in addition to N-nitrosodimethylamine (NDMA). Growth of cells on propane as the sole carbon source greatly enhanced degradation rates when contrasted with cells grown on complex organics. Propane-induced rates in order of fastest to slowest were NDMA > NDEA > NDPA > NPYR > NMOR at concentrations <2000 μg/L. Removal rates for linear functional groups scaled inversely with mass and cyclic nitrosamines were more recalcitrant than linear nitrosamines. Controls demonstrated significant NDEA and NDPA losses independent of biomass, suggesting abiotic processes may play a role in attenuation of these two compounds under experimental conditions tested here. In contrast to NDMA, a transition from first to zero order kinetics was not observed for the other nitrosamines included in this study over a concentration range of 20-2000 μg/L. A genetic knockout for the propane monooxygenase enzyme (PrMO) confirmed the role of this enzyme in the biotransformation of NDEA and NPYR. This study furthers our understanding of environmental nitrosamine attenuation by revealing an enzymatic mechanism for the biotransformation of multiple nitrosamines, their relative recalcitrance to transformation, and potential for abiotic loss.

Fate of N-nitrosodimethylamine in recycled water after recharge into anaerobic aquifer

Laboratory and field experiments were undertaken to assess the fate of N-nitrosodimethylamine (NDMA) in aerobic recycled water that was recharged into a deep anaerobic pyritic aquifer, as part of a managed aquifer recharge (MAR) strategy. Laboratory studies demonstrated a high mobility of NDMA in the Leederville aquifer system with a retardation coefficient of 1.1. Anaerobic degradation column and (14)C-NDMA microcosm studies showed that anaerobic conditions of the aquifer provided a suitable environment for the biodegradation of NDMA with first-order kinetics. At microgram per litre concentrations, inhibition of biodegradation was observed with degradation half-lives (260±20 days) up to an order of magnitude greater than at nanogram per litre concentrations (25-150 days), which are more typical of environmental concentrations. No threshold effects were observed at the lower ng L(-1) concentrations with NDMA concentrations reduced from 560 ng L(-1) to <6 ng L(-1) over a 42 day 14C-NDMA aerobic microcosm experiment. Aerobic (14)C-NDMA microcosm studies were also undertaken to assess potential aerobic degradation, likely to occur close to the recharge bore. These microcosm experiments showed a faster degradation rate than anaerobic microcosms, with a degradation half-life of 8±2 days, after a lag period of approximately 10 days. Results from a MAR field trial recharging the Leederville aquifer with aerobic recycled water showed that NDMA concentrations reduced from 2.5±1.0 ng L(-1) to 1.3±0.4 ng L(-1) between the recharge bore and a monitoring location 20 m down gradient (an estimated aquifer residence time of 10 days), consistent with data from the aerobic microcosm experiment. Further down gradient, in the anaerobic zone of the aquifer, NDMA degradation could not be assessed, as NDMA concentrations were too close to their analytical detection limit (<1 ng L(-1)).