Raw wastewater can contain high levels of antibiotic resistance genes (ARGs), making municipal wastewater treatment plants (WWTPs) critical for the control of the release of ARGs into the ...environment. The objective of this study was to investigate how individual treatment steps in two tertiary WWTPs affected the removal (copies/mL) and relative abundance of ARGs (copies/copies 16S rRNA genes). Nine ARG markers, representing resistance to commonly used antibiotics, as well as one integron gene (intl1) to assess ARG mobility potential, were quantified using quantitative real-time PCR (qPCR). Both WWTPs met provincial effluent regulations for removal of carbonaceous oxygen demand (CBOD5) and total suspended solids. Eight of the ten ARG markers (intl1, sul1, sul2, tet(O), ermB, blaCTX-M, blaTEM, qnrS) were detected in all samples. In contrast, mecA was detected intermittently and vanA remained below the detection limit in all samples. The total ARG marker abundances decreased by log 1.77 (p < 0.05) in the plant using an aerated lagoon (AL), and by 2.69 logs (p < 0.05) through treatment in the plant employing a biological nutrient removal (BNR) system. The BNR and secondary clarifier steps in both plants afforded the most removal of ARGs. The relative abundance of ARGs remained unchanged at the AL plant and showed a decreasing trend at the BNR plant. Levels of CBOD5, nitrate and the human Bacteroides fecal marker correlated with ARG concentrations, suggesting these variables may be useful in predicting ARG removal. In conclusion, the effluent coming from the WWTPs contained eight of the studied ARG markers in concentrations ranging from 0.01 to 3.6 log copies/mL, indicating their release into the environment, however, the relative abundance of ARGs was not enriched during treatment in the two WWTPs.
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•Tertiary wastewater treatment reduced effluent antibiotic resistance genes (ARGs) concentration.•BNR reactors and secondary clarifiers effected significant removal of ARGs.•ARG removal was modest in the aerated lagoons.•Microorganisms with ARGs were not enriched during wastewater treatment.•Removal of ARGs, nutrients and the human Bacteroides fecal indicator correlated.
Foods and related processing environments are commonly contaminated with the pathogenic Listeria monocytogenes. To investigate potential environmental reservoirs of Listeria spp. and L. ...monocytogenes, surface water and point source pollution samples from an urban and a rural municipal water supply watershed in Nova Scotia, Canada, were examined over 18 months. Presumptive Listeria spp. were cultured from 72 and 35% of rural and urban water samples, respectively, with 24% of the positive samples containing two or three different Listeria spp. The L. innocua (56%) and L. welshimeri (43%) groups were predominant in the rural and urban watersheds, respectively. Analysis by the TaqMan assay showed a significantly (P < 0.05) higher prevalence of L. monocytogenes of 62% versus 17% by the culture-based method. Both methods revealed higher prevalences in the rural watershed and during the fall and winter seasons. Elevated Escherichia coli (≥ 100 CFU/100 ml) levels were not associated with the pathogen regardless of the detection method. Isolation of Listeria spp. were associated with 70 times higher odds of isolating L. monocytogenes (odds ratio = 70; P < 0.001). Serogroup IIa was predominant (67.7%) among the 285 L. monocytogenes isolates, followed by IVb (16.1%), IIb (15.8%), and IIc (0.4%). L. monocytogenes was detected in cow feces and raw sewage but not in septic tank samples. Pulsotyping of representative water (n = 54) and local human (n = 19) isolates suggested genetic similarities among some environmental and human L. monocytogenes isolates. In conclusion, temperate surface waters contain a diverse Listeria species population and could be a potential reservoir for L. monocytogenes, especially in rural agricultural watersheds.
Domestic wastewater discharges may adversely impact arctic ecosystems and local indigenous people, who rely on being able to hunt and harvest food from their local environment. Therefore, there is a ...need to develop efficient wastewater treatment plants (WWTPs), which can be operated in remote communities under extreme climatic conditions. WWTPs have been identified as reservoirs of antibiotic resistance genes (ARGs). The objective of this work was to quantify the presence of nine different ARG markers (int1, sul1, sul2, tet(O), erm(B), mecA, blaCTX-M, blaTEM, and qnr(S)) in two passive systems (waste stabilization ponds WSPs) and one mechanical filtration plant operating in two smaller and one large community, respectively, in Nunavut, Canada. Measurement of water quality parameters (carbonaceous oxygen demand, ammonia, total suspended solids, Escherichia coli and total coliforms) showed that the WWTPs provided only primary treatment. Low levels of the ARGs (2logcopies/mL) were observed in the effluent, demonstrating that bacteria residing in three northern WWTPs harbour ARGs conferring resistance to multiple clinically-relevant classes of antibiotics. Our results indicate that long-term storage in WSPs benefitted removal of organic material and some ARGs. However, one WSP system showed evidence of the enrichment of sul1, sul2, mecA, tet(O) and qnr(S). Further research is needed to fully understand if these ARG releases pose a risk to human health, especially in the context of traditional hunting and fishing activities.
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•Antibiotic resistance genes (ARGs) in arctic wastewater treatment were investigated.•Raw wastewater, effluent discharge and immediate receiving waters contained ARGs.•Relative abundance of ARGs increased in one waste stabilization pond (WSP) system.•Long term stay in arctic WSPs may promote transfer of ARGs among microorganisms.•ARGs in the effluent highlight the need to assess human risk in arctic communities.
Abstract
Permafrost thaw leads to an increase in groundwater circulation and potential mobilization of organic carbon sequestered in deep Arctic sediments (e.g. 3–25 m below surface). Upon thaw, a ...portion of this carbon may be transported along new groundwater flow paths to surface waters or be microbially transformed or immobilized by
in-situ
biogeochemical reactions. The fate of thaw-mobilized carbon impacts surface water productivity and global climate. We developed a numerical model to investigate the effects of subsurface warming, permafrost thaw, and resultant increased groundwater flow on the mobilization and reactive transport of dissolved organic carbon (DOC). Synthetic simulations demonstrate that mobilization and groundwater-borne DOC export are determined by subsurface thermo-chemical conditions that control the interplay of DOC production (organic matter degradation), mineralization, and sorption. Results suggest that peak carbon mobilization from these depths precedes complete permafrost loss, occurring within two centuries of thaw initiation with the development of supra-permafrost groundwater flow systems. Additionally, this study highlights the lack of field data needed to constrain these new models and apply them in real-word site-specific applications, specifically the amount and spatial variability of organic carbon in deep sediments and data to constrain DOC production rates for groundwater systems in degrading permafrost. Modeling results point to key biogeochemical parameters related to organic matter and carbon bioavailability to be measured in the field to bridge the gap between models and observations. This study provides a foundation for further developing a physics-based modeling framework to incorporate the influence of groundwater flow and permafrost thaw on permafrost DOC dynamics and export, which is imperative for advancing understanding and prediction of carbon release and terrestrial-aquatic carbon exchange in warming Artic landscapes in the coming decades.
Facultative waste stabilization ponds (WSP) are a common form of wastewater treatment in cold regions. However, cold region WSPs have been found to have highly variable and inconsistent microalgae ...growth and phosphorus removal. This study investigated whether facultative WSPs can be used to provide biological phosphorus removal in cold regions by evaluating maximum specific growth rates and phosphorus removal pathways under simulated cold region summer (ice-free) conditions. A factorial experiment was conducted in order to determine the main effects and interactions of temperature (10, 15°C), photosynthetically active radiation (PAR) (100, 150μmol/m2/s) and initial phosphorus concentration (7.5, 15mg P/L) on microalgae growth and phosphorus uptake. Maximum specific growth rates varied from 0.029 to 0.058/h. PAR and temperature had a statistically significant negative and positive effect, respectively, on growth rates. Initial phosphorus concentration had no statistical effect on growth rates under the studied ranges. Growth rates were similar to those observed at temperate climates. Luxury uptake was a significant phosphorus removal mechanism as it accounted for 53±8% (g P/g P) of biomass phosphorus. Biomass phosphorus concentrations were positively affected by PAR and initial phosphorus concentration while temperature had no effect. A crossover interaction between temperature and initial phosphorus concentration was found to have a negative effect on biomass phosphorus concentration. Under cold region conditions biomass phosphorus concentrations were 45% greater than under warm climate conditions. Ultimately, it is expected that climate should not hinder microalgae production in cold region WSPs during the summer months when temperatures exceed 10°C and the surface is ice-free. Cold region conditions appear to aid in phosphorus removal by increasing biomass phosphorus concentrations.
The ability of lateral flow sand filters, used as on-site wastewater treatment systems (OWTS), to remove antibiotic resistance genes (ARGs), antibiotic resistant bacteria (ARB), and other relevant ...genetic markers (HF183, 16S rRNA, and int1) was assessed. Municipal wastewater was settled in a septic tank prior to loading into six pilot-scale lateral flow sand filters comprised of three different sand media types, at 5 and 30% slopes. The sand filters were sampled bi-weekly for: 9 ARGs and 3 other complimentary gene markers (sul1, sul2, qnrS, tetO, ermB, blaTEM, blaCTX-M, mecA, vanA, int1, HF183, 16S rRNA), and conventional microbial and water quality indicators, from July to November in 2017, and four times in the summer of 2018. The sand filters were observed to attenuate 7 of the ARGs to mostly below 2 log gene copies per mL. Log reductions ranging from 2.9 to 5.4 log were observed for the removal of absolute abundances of ARGs from septic tank effluent in 5 of the 6 sand filters. The fine-grained filter on the 5% slope did not perform as well for ARG attenuation due to hydraulic failure. The apportionment of cell-associated versus cell-free DNA was determined for the gene markers and this indicated that the genes were primarily carried intracellularly. Average log reductions of ARB with resistance to either sulfamethoxazole, erythromycin, or tetracycline were approximately 2.3 log CFU per mL within the filters compared to the septic tank effluent. This field study provides in-depth insights into the attenuation of ARB, ARGs, and their genetic compartmentalization in variably saturated sand OWTS. Overall, this type of OWTS was found to pose little risk of antimicrobial resistance contamination spread into surrounding environments when proper hydraulic function was maintained.
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•Antibiotic resistance genes were attenuated in on-site septic system sand filters.•Most of the genes were present intracellularly in the treatment train.•2 log removal of antibiotic resistant bacteria was observed across the filters.•Sand filters posed low overall risk of spread of antimicrobial resistance.
Understanding the interactions between ground freeze‐thaw, groundwater flow, and solute transport is imperative for evaluating the fate of contaminants in permafrost regions. However, predicting ...solute migration in permafrost‐affected groundwater systems is challenging due to the inherent interactions and coupling between subsurface mass and energy transport processes. To this end, we developed a numerical model that considers coupled groundwater flow, subsurface heat transfer, and solute transport, including water‐ice phase change, solute‐dependent porewater freezing, and temperature‐dependent solute reaction rates. As an illustrative example, we present simulations to investigate the potential for contamination from a municipal wastewater lagoon in the Canadian sub‐arctic. Two‐dimensional groundwater models assuming varying permafrost conditions were developed to evaluate possible contaminant migration scenarios associated with groundwater flow from the lagoon to a river, including the transport of conservative, degradable, and sorbing solutes. Model results reveal important transport mechanisms controlling the behavior of aqueous contaminants in permafrost landscapes as well as the hydrogeologic factors affecting reactive transport in cold regions. Seasonal freeze‐thaw episodically restricts connectivity of transport pathways, which attenuates both transport and reaction rates. However, elevated solute concentrations can depress the freezing temperature of porewater and produce thaw‐induced solute transport. Both thermally driven and solute‐enhanced thaw can decrease ice content in permafrost, which can have significant implications for solute migration. Therefore, thermo‐hydrogeologic process controlling reactive transport in cold‐region groundwater systems must be considered when quantitatively assessing the impact of changing environmental conditions on contaminant hydrogeology.
Plain Language Summary
Groundwater contamination associated with increased human and industrial activity is a growing risk in northern regions. However, current groundwater flow models generally do not simulate both permafrost dynamics and reactive solute transport. In this study we develop a hydrological model to simulate groundwater flow and dissolved contaminant transport for permafrost environments. The new model was applied at a site in the Canadian sub‐arctic to investigate the possibility of groundwater contamination associated with a wastewater lagoon. Results identified important mechanisms controlling the migration of contaminants in permafrost landscapes, including the effects of seasonal ground freezing and groundwater flow. Results show that the physical relationships describing the effects of contaminant levels on ground freezing characteristics and the influence of temperature on contaminant degradation properties strongly affect contamination movement. The new model will be useful for understanding how climate change and permafrost thaw will impact groundwater flow and associated subsurface migration of dissolved chemicals in cold regions.
Key Points
Subsurface aqueous contaminant transport in permafrost regions is controlled by coupled water, energy, and reactive solute transport
We developed a groundwater model to simulate reactive solute transport in permafrost landscapes
Constitutive relationships describing solute‐dependent freezing and temperature‐dependent reaction rates strongly influence contaminant migration
Coastal eutrophication poses an increasing risk to ecosystem health due to enhanced nutrient loading to the global coastline. Submarine groundwater discharge (SGD) represents a significant pathway ...for nitrate‐nitrogen (NO3‐N) transport to the coast, but diffusive SGD transport is difficult to monitor directly, given the low flux rates and expansive discharge areas. In contrast, focused SGD from intertidal springs can potentially be sampled and directly gauged, providing unique insight into SGD and associated contaminant transport. Basin Head is a coastal lagoon in Prince Edward Island, Canada that is a federally protected ecosystem. Nitrate‐nitrogen is conveyed from agricultural fields in the contributing watershed to the eutrophic lagoon via intertidal groundwater springs and groundwater‐dominated tributaries. We used several field methods to characterize groundwater discharge, nutrient loading, and in‐channel mixing associated with intertidal springs. The tributaries and intertidal springs were gauged and sampled to estimate a representative summer nitrate load to the lagoon. Our analysis revealed that NO3‐N export to the lagoon through tributaries and springs throughout summer 2023 was on average 401 kg N/month, with the combined spring loading comparable in magnitude to the combined tributary loading. We collected thermal infrared and visual imagery using drone surveys and found spatial overlap between cold‐water plumes from the spring discharge and macroalgae blooms, indicating the local thermal and ecosystem impacts of the focused SGD. We also mapped the electrical resistivity (salinity) distribution in the water column around one large spring with electromagnetic geophysics at different tidal stages to reveal the three‐dimensional spring plume dynamics. Results showed that the fresher spring water floated above the saline lagoon water with the brackish plume oriented in the direction of the tidal current. Collectively, our multi‐pronged field investigations help elucidate the hydrologic, thermal, and nutrient dynamics of intertidal springs and the cascading ecosystem impacts.
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