Temporal deposition of copper and zinc in the sediments of metal removal constructed wetlands

Spatiotemporal Changes in Trace Metal Bioavailability in the Sediment Pore water of a Constructed Wetland Using Passive Pore water Samplers

Sediments in aquatic systems often act as a major sink for contaminants. Diffusive gradient in thin films (DGTs) and in situ equilibrium dialysis samplers (peepers) are two major in situ pore water sampling devices that overcome the problems associated with conventional pore water sampling methods. In the present study, DGTs and peepers were used to study the spatial and seasonal effects (cool months, October-February; warm months, May-September) on metal bioavailability in the H-02 constructed wetland and the sink versus source role of the sediments by calculating the metal resupply capacity. Data showed similar seasonal trends in metal concentrations using passive samplers, peepers, and DGTs. Pooled Cu and Zn concentrations measured using DGTs were lower in warm months (1.67 ± 1.50 and 2.62 ± 0.68 μg L-1 , respectively, p < 0.001) versus in cool months (2.12 ± 0.65 and 5.58 ± 1.33 μg L-1 , respectively, p < 0.001; mean ± 95% confidence interval). Sulfate (SO4 2- ) concentrations were significantly (p = 0.0139) lower in warm months (averaged at 0.22 ± 0.05 mg L-1 ) compared to in cool months (0.16 ± 0.05 mg L-1 ). The increase in SO4 2- concentration is an indicator of the lower activity of sulfate-reducing bacteria, which need SO4 2- during anaerobic respiration, in which SO4 2- is reduced to sulfide (S2- ) that forms insoluble salts with Cu and Zn, which could partially explain the higher bioavailability of these metals in the cool season. Metal resupply capacity of the sediments was mostly <0.2 for Cu and Zn. Taken together, the H0-2 wetland sediments mostly acted as a sink to both Cu and Zn over the course of the present study. Environ Toxicol Chem 2023;42:2726-2736. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Microbial community shifts induced by plastic and zinc as substitutes of tire abrasion

Aquatic environments serve as a sink for anthropogenic discharges. A significant part of the discharge is tire wear, which is increasingly being released into the environment, causing environmental disasters due to their longevity and the large number of pollutants they contain. Main components of tires are plastic and zinc, which therefore can be used as substitutes for tire abrasion to study the effect on microbial life. We investigate environmentally realistic concentrations of plastic and zinc on a freshwater microeukaryotic community using high-throughput sequencing of the 18S V9 region over a 14-day exposure period. Apart from a generally unchanged diversity upon exposure to zinc and nanoplastics, a change in community structure due to zinc is evident, but not due to nanoplastics. Evidently, nanoplastic particles hardly affect the community, but zinc exposure results in drastic functional abundance shifts concerning the trophic mode. Phototrophic microorganisms were almost completely diminished initially, but photosynthesis recovered. However, the dominant taxa performing photosynthesis changed from bacillariophytes to chlorophytes. While phototrophic organisms are decreasing in the presence of zinc, the mixotrophic fraction initially benefitted and the heterotrophic fraction were benefitting throughout the exposure period. In contrast to lasting changes in taxon composition, the functional community composition is initially strongly imbalanced after application of zinc but returns to the original state.

Bioremediation of copper in sediments from a constructed wetland ex situ with the novel bacterium Cupriavidus basilensis SRS

The H-02 constructed wetland was designed to remove metals (primarily copper and zinc) to treat building process water and storm water runoff from multiple sources associated with the Tritium Facility at the DOE-Savannah River Site, Aiken, SC. The concentration of Cu and Zn in the sediments has increased over the lifetime of the wetland and is a concern. A bioremediation option was investigated at the laboratory scale utilizing a newly isolated bacterium of the copper metabolizing genus Cupriavidus isolated from Tim's Branch Creek, a second-order stream that eventually serves as a tributary to the Savannah River, contaminated with uranium and other metals including copper, nickel, and mercury. Cupriavidus basilensis SRS is a rod-shaped, gram-negative bacterium which has been shown to have predatory tendencies. The isolate displayed resistance to the antibiotics ofloxacin, tetracycline, ciprofloxacin, select fungi, as well as Cu²⁺ and Zn²⁺. Subsequent ribosomal sequencing demonstrated a 100% confidence for placement in the genus Cupriavidus and a 99.014% match to the C. basilensis type strain. When H-02 wetland samples were inoculated with Cupriavidus basilensis SRS samples showed significant (p < 0.05) decrease in Cu²⁺ concentrations and variability in Zn²⁺ concentrations. Over the 72-h incubation there were no significant changes in the inoculate densities (10⁶-10⁸ cells/ML) indicating Cupriavidus basilensis SRS resiliency in this environment. This research expands our understanding of the Cupriavidus genus and demonstrates the potential for Cupriavidus basilensis SRS to bioremediate sites impacted with heavy metals, most notably copper.

Evaluation of changes in the microbial community structure in the sediments of a constructed wetland over the years

This study presents the results of the long term (2007-2014) monitoring of the microbial community structure in the surface sediments of the H-02 constructed wetland system, which was built on the Savannah River Site in Aiken, SC, USA, to treat the waste water generated at the Tritium facility. Microbial community structure provides valuable information about the functioning of constructed wetlands and helps understand the biogeochemical cycling of nutrients and contaminants. Phospholipids fatty acid (PLFA) analysis and qPCR were used to identify major bacterial phyla in the sediments. The physiochemical properties of the sediments were also used to deduce potential effects on the microbial community structure over the years. Sulfate-reducing bacteria (SRB) were the most dominant bacterial groups, and their prevalence was progressively increasing throughout the years most likely on the account of methane producers. Concentrations of trace metals (copper and zinc) were negatively associated with methane producers and oxidizer while positively correlated with SRB. Overall, the H-02 wetland system was efficient in immobilizing copper and zinc through the anaerobic respiration of sulfate by SRB and minimizing methane emission through the progressive elimination of methane producers by SRB and Geobacter. The aim of this study was to monitor the changes in the microbial community structure in the surface sediments of a constructed wetland during the first 7 years of operation.

Metal fluxes at the sediment-water interface in a free water surface constructed wetland

Metal biogeochemistry in the sediment, water, and the sediment-water interface (SWI) was studied in a free water surface constructed wetland. Concentrations of labile copper (Cu), zinc (Zn), sulfate, chloride, and dissolved organic carbon (DOC) were measured with the diffusive gradients in thin film (DGT) and peeper. A good agreement between peeper- and DGT-measured metals was observed for Cu (regression r² = 0.3, 95% CI of the slopes > 0), but not for Zn (95% CI of the slopes overlapped with 0), which was attributed to the different complexed compounds between Cu and Zn in porewater. The depth profile of labile metals in sediment porewater varied with time and was consistent with the solid-phase metal deposition, showing higher concentrations in the surface layer (3 to - 3 cm) than in the bottom layer (- 4 to - 13 cm). The depth-averaged labile Cu and Zn concentrations measured by DGT were 1.0 and 3.1 µg/L, and labile sulfate, chloride, and DOC concentrations measured by peeper were 1.8, 3.6, and 2.1 mg/L, respectively. A sharp decrease in sulfate occurred in September when sulfate concentrations became the lowest among sampling months. This was caused by the seasonal sulfur cycles in the wetland, where the dominant sulfur reaction is sulfate reduction in warm seasons and sulfide oxidation in cold seasons. Different metal-removal mechanisms were observed in the two wetland cells; sulfur dynamics controlled the removal processes in the cell without frequent disturbance but failed to influence metal removal in the cell with frequent disturbance due to the interruption of anoxic layers. The flux ratios that compare labile element concentrations between the water column and the SWI (R-Cu, R-Zn, R-DOC, R-sulfate, and R-chloride) were generated to determine metal diffusive fluxes at the interface. Labile Zn was mostly transported from the water to the SWI during all seasons (R-Zn < 1 for all months except January). Labile Cu moved from the SWI to the water during the warm months (R-Cu < 1), which was explained by the bioturbation-induced transport of organic matter based on the positive correlations between R-Cu and R-DOC. In general, sediment can serve either as a sink or a source depending on the environmental conditions, metal speciation, and presence of living organisms. Metal flux at the SWI is a key component in the biogeochemical cycling of a constructed wetland.

New insights into the pollutant composition of stormwater treating wetlands

With intensified climate change and urbanisation, constructed wetland (CW) serves as an alternative to conventional wastewater treatment plants. In Australia, the primary function of CW is to reduce sediments, nutrients from runoffs and attenuate floods. However, water quality analysis after construction is limited, hence, pollutant composition in established CWs and target pollutants in many guidelines remain outdated. To refresh the understanding of pollutants in urban discharges, this study reviewed two CWs in industrialised regions of Victoria, Australia. A total number of 26 pollutants were analysed in the collected water and sediment samples from both CW. The findings highlighted excessive concentrations of Zinc, Aluminium, Iron and Copper in one wetland and less commonly found pollutants like Barium, Titanium and Strontium are also detected. While Arsenic, Zinc, Copper, Nickel and hydrocarbons' accumulations are particularly significant in the other wetland. This study also reviews the pollutants discovered in 136 stormwater wetlands and covers the sources and impacts of various metal pollutants in stormwater runoffs. Overall, it is found that the concentrations of Zinc, Aluminium and Iron are particularly high in the CWs reviewed. This study brings attention to the pollutants profile of established CWs and the impact of heavy metals on the aquatic environment. The findings from this research revealed that the existing design and management guidelines for constructed wetlands in urban catchments are lacking in reduction targets for metal pollutants, thus improvements are essential to safeguard the water quality and performance of CWs.

Sink or source? Insights into the behavior of copper and zinc in the sediment porewater of a constructed wetland by peepers

The H-02 free water surface constructed wetland has been applied to remove heavy metals, mainly copper (Cu) and zinc (Zn), from wastewater on the Savannah River Site (Aiken, SC, USA). More and more studies focus on the metal behavior between the sediment and the overlying water, which directly reflects the stability of metals after sedimentation in constructed wetlands. This study focused on the biogeochemical pathways in metal bioavailability and remobilization in the sediment after metals were removed from the overlying water. The dialysis sampling device (peeper) was used to collect porewater samples from eight depths in the sediment for the measurement of Cu, Zn, dissolved organic carbon (DOC), and major anions (sulfate and chloride). Surface water samples were also collected for the measurement of Cu, Zn, DOC, and anions. Different temporal trends were observed for dissolved Cu between the surface and bottom waters, but not for dissolved Zn. There were no obvious changes in porewater metal concentrations with increasing depths in the sediment. Sediment served as a sink for Cu as only 3% of porewater samples showed higher labile Cu concentrations than the surface water during the entire year, and these samples were collected below the sediment-water interface. However, sediment served as a source for Zn in summer and winter as 32% of porewater samples showed higher labile Zn concentrations than the surface water, and these samples were collected at all sediment depths. We think the seasonal changes in the behaviors of Cu and Zn are primarily controlled by the sulfur dynamics and the metal removal processes in the constructed wetland, as well as the different complexing chemistry between Cu and Zn. Also, our study supports that peeper is a powerful tool for studying the biogeochemistry of metals in the sediment.

Assessing annual, seasonal and spatial trends in copper sediment concentrations from a California agricultural waterbody

The objective of this study was to assess annual, seasonal and spatial trends in copper sediment concentrations in an agricultural California stream (Cache Slough) based on sampling 12 sites over two seasons (spring and fall) in 2012, 2013 and 2014. The relationship between copper sediment concentrations and precipitation was also evaluated. The results from this study showed that copper sediment concentrations from Cache Slough ranging from 19 to 63 ug/g dw were similar to concentrations reported in European agricultural streams. Copper sediment concentrations were not reported to increase over time in this agricultural waterbody where copper was used as a fungicide. However, spatial differences in copper sediment concentrations were reported among sites with the highest concentrations in the middle waterbody section. Seasonal analysis showed no significant difference in copper sediment concentrations for both spring and fall for 2012 and 2013 but 2014 spring concentrations were statistically higher than fall concentrations when precipitation was lower than the two previous years. There were no statistically significant relationships between copper sediment concentrations and precipitation for the three-year period based on an analysis by year and season.