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The fate of six human-use drugs was assessed and predicted in mesocosms designed to mimic shallow constructed wetlands during the onset of fall and senescence. Mesocosms were monitored for 28 days after the addition of carbamazepine, clofibric acid, fluoxetine and naproxen (nominal initial concentrations of 5 µg/L each), sulfamethoxazole, and sulfapyridine (nominal initial concentrations of 150 µg/L each), with and without phosphorous (P) addition at 1.6 mg/L. We hypothesized that addition of P would stimulate primary productivity and enhance removal of pharmaceuticals from the water column. Carbamazepine, clofibric acid, fluoxetine, and naproxen had half-lives of 8.7, 11, 1.5, and 2.5, and 8.6, 11.0, 1.4, and 2.5 days in treatments with and without P amendment, respectively. Sulfamethoxazole and sulfapyridine had half-lives of 17 and 4.9 days in mesocosms with P amendment and 17 and 4.7 days without amendment. A concurrent pulse of P with pharmaceuticals did not significantly enhance the removal of these compounds. Predicted half-lives from modeling efforts were consistent with observed values, with photolysis the greatest contributor to chemical attenuation.

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Outdoor shallow wetland mesocosms, designed to simulate surface constructed wetlands to improve lagoon wastewater treatment, were used to assess the role of macrophytes in the dissipation of wastewater nutrients, selected pharmaceuticals, and antibiotic resistance genes (ARGs). Specifically, mesocosms were established with or without populations of Typha spp. (cattails), Myriophyllum sibiricum (northern water milfoil), and Utricularia vulgaris (bladderwort). Following macrophyte establishment, mesocosms were seeded with ARG-bearing organisms from a local wastewater lagoon, and treated with a single pulse of artificial municipal wastewater with or without carbamazepine, clofibric acid, fluoxetine, and naproxen (each at 7.6µg/L), as well as sulfamethoxazole and sulfapyridine (each at 150µg/L). Rates of pharmaceutical dissipation over 28d ranged from 0.073 to 3.0d(-1), corresponding to half-lives of 0.23 to 9.4d. Based on calculated rate constants, observed dissipation rates were consistent with photodegradation driving clofibric acid, naproxen, sulfamethoxazole, and sulfapyridine removal, and with sorption also contributing to carbamazepine and fluoxetine loss. Of the seven gene determinants assayed, only two genes for both beta-lactam resistance (blaCTX and blaTEM) and sulfonamide resistance (sulI and sulII) were found in sufficient quantity for monitoring. Genes disappeared relatively rapidly from the water column, with half-lives ranging from 2.1 to 99d. In contrast, detected gene levels did not change in the sediment, with the exception of sulI, which increased after 28d in pharmaceutical-treated systems. These shallow wetland mesocosms were able to dissipate wastewater contaminants rapidly. However, no significant enhancement in removal of nutrients or pharmaceuticals was observed in mesocosms with extensive aquatic plant communities. This was likely due to three factors: first, use of naïve systems with an unchallenged capacity for nutrient assimilation and contaminant removal; second, nutrient sequestration by ubiquitous filamentous algae; and third, dominance of photolytic processes in the removal of pharmaceuticals, which overshadowed putative plant-related processes.

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BACKGROUND: The discharge of complex mixtures of nutrients, organic micropollutants, and antibiotic resistance genes from treated municipal wastewater into freshwater systems are global concerns for human health and aquatic organisms. Antibiotic resistance genes (ARGs) are genes that have the ability to impart resistance to antibiotics and reduce the efficacy of antibiotics in the systems in which they are found. In the rural community of Grand Marais, Manitoba, Canada, wastewater is treated passively in a sewage lagoon prior to passage through a treatment wetland and subsequent release into surface waters. Using this facility as a model system for the Canadian Prairies, the two aims of this study were to assess: (a) the presence of nutrients, micropollutants (i.e., pesticides, pharmaceuticals), and ARGs in lagoon outputs, and (b) their potential removal by the treatment wetland prior to release to surface waters in 2012. RESULTS: As expected, concentrations of nitrogen and phosphorus species were greatest in the lagoon and declined with movement through the wetland treatment system. Pharmaceutical and agricultural chemicals were detected at concentrations in the ng/L range. Concentrations of these compounds spiked downstream of the lagoon following discharge and attenuation was observed as the effluent migrated through the wetland system. Hazard quotients calculated for micropollutants of interest indicated minimal toxicological risk to aquatic biota, and results suggest that the wetland attenuated atrazine and carbamazepine significantly. There was no significant targeted removal of ARGs in the wetland and our data suggest that the bacterial population in this system may have genes imparting antibiotic resistance. CONCLUSIONS: The results of this study indicate that while the treatment wetland may effectively attenuate excess nutrients and remove some micropollutants and bacteria, it does not specifically target ARGs for removal. Additional studies would be beneficial to determine whether upgrades to extend retention time or alter plant community structure within the wetland would optimize removal of micropollutants and ARGs to fully characterize the utility of these systems on the Canadian Prairies.

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Nutrient enrichment and loadings of pharmaceuticals and agrochemicals into freshwater systems are common concerns, especially for water bodies receiving wastewater inputs. In the rural communities of Morden and Winkler of Manitoba, Canada, sewage lagoons discharge their wastewater directly into Dead Horse Creek, a small tributary of the Red River that empties into Lake Winnipeg. This lagoon approach to managing rural wastewaters is common across the North American Prairies. Therefore, this study aimed to assess the hazards of lagoon treatment releases at this model site. This was done by characterizing the nutrients, organic micropollutants (i.e., pesticides, pharmaceuticals) and standard water quality parameters in the creek prior to and following lagoon discharge events over a number of years (2009-2011). Measured concentrations of nutrients were compared to regulatory expectations and micropollutants were assessed using hazard quotients. As expected, concentrations of nitrogen and phosphorus species were greatest in sites downstream of the sewage outfall immediately following discharge events. Pharmaceutical and agricultural chemicals were detected at concentrations between 0.5 and 90 ng/L. Detection frequencies and concentrations matched typical use patterns. Those compounds used predominately for human medicine were detected at downstream sites following discharge events, while those used in an agricultural setting were detected at relatively consistent levels over time at sites both upstream and downstream of the outfall location. Hazard quotients calculated for micropollutants of interest indicated minimal toxicological risk to aquatic biota in the creek, with only erythromycin and diazinon presenting a potential concern to aquatic algae and invertebrates. Concentrations of nutrients exceeded Canadian guideline thresholds during release, but returned to background levels once discharges ceased. Therefore, it is advisable that wastewater treatment and management strategies such as constructed wetlands and/or staggered releases be used in order to minimize the hazard posed by nutrient pulses in Dead Horse Creek and other similar systems.

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Two cultivation techniques (i-pruning and ii-nodal adventitious root encouragement) were investigated for their ability to increase PCB phytoextraction by Cucurbita pepo ssp pepo cv. Howden (pumpkin) plants in situ at a contaminated industrial site in Ontario (Aroclor 1248, mean soil [PCB] = 5.6 µg g(-1)). Pruning was implemented to increase plant biomass close to the root where PCB concentration is known to be highest. This treatment was found to have no effect on final shoot biomass or PCB concentration. However, material pruned from the plant is not included in the final shoot biomass. The encouragement of nodal adventitious roots at stem nodes did significantly increase the PCB concentration in the primary stem, while not affecting shoot biomass. Both techniques are easily applied cultivation practices that may be implemented to decrease phytoextraction treatment time.

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A greenhouse experiment was conducted to investigate polychlorinated biphenyl (PCB) uptake and translocation from soil over time in pumpkin plants (Cucurbita pepo ssp. pepo cv. Howden). Plants were grown in weathered soil collected from a former industrial site contaminated with Aroclor 1248 (mean [PCB](soil) = 6.5 mg kg(-1)). Plants were harvested five times over 42 d and analyzed for total PCB concentration in the root and shoot tissues. The concentration of PCBs in the root was not significantly different between harvests (mean [PCB](root) = 21.5 mg kg(-1)). The concentration of PCBs in the shoots was also relatively stable over time (mean [PCB](shoot) = 3.5 mg kg(-1)) despite increases in shoot biomass (fresh weight of 4.3 g at Day 12 to 59 g at Day 42). This suggests that PCBs were continuously accumulated throughout the growth period. The trends found in this study indicate the optimal time to harvest C. pepo ssp pepo plants to maximize PCB phytoextraction is when the plant shoot has reached its maximum biomass.

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