The sulfate input and the occurrence of dryout and rewetting may promote the production of toxic methylmercury (MeHg) in a constructed wetland, Stormwater Treatment Area 2 (STA-2) in South Florida. Therefore, the aim of this study was to investigate the influences of inflow water quality, especially inflow sulfate, and the dryout and rewetting cycle on the mercury (Hg) methylation in three independent cells of STA-2 from 2000 to 2007. Because the majority of the total Hg (THg) bioaccumulated in fish is in MeHg form, THg concentration in mosquitofish was used to present the MeHg production in STA-2. Mosquitofish THg in Cells 1 and 2 (with median values of 0.101 and 0.02 mg/kg, respectively) were significantly higher than in Cell 3 and inflow (both with a median value of 0.01 mg/kg). The difference in mosquitofish THg among the three cells was likely a result of the drying and rewetting cycles occurred in Cells 1 and 2, which promoted the Hg methylation. Inflow sulfate, inorganic Hg, and chloride exhibited a significant correlation with mosquitofish THg in cells, suggesting that these inflow variables played important roles on the Hg methylation. The results indicate that inflow sulfate may likely stimulate sulfate-reducing bacteria and subsequently lead to produce MeHg in the three cells. Our findings in this study indicate that preventing the occurrence of dryout in wetland will help to decline the Hg methylation, and sulfate input is a key factor to influence the Hg methylation in wetland.

Due to the unique characteristics of subcritical water, the use of a subcritical water extraction (SCWE) process for the remediation of contaminated soil has become more attractive. Although this process has proved to be effective in lab-scale studies, the knowledge of its capability to treat distinct types of contaminants in a larger scale is still scarce. In this work, a semi-pilot scale SCWE system was used to remove petroleum hydrocarbon (diesel fuel and lubricating oil) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soils. Experiments were carried out at an extraction time ranging from 1 to 3 h and a temperature ranging from 200 to 275 °C, maintaining the minimum pressure where water remains in a liquid state (e.g., 4 MPa at 250 °C). Experimental results showed that the higher removal efficiency was obtained in static-dynamic mode than that for dynamic mode operation. With 2 h (4 cycles of static-dynamic step) of SCWE, 99 % of the diesel fuel was removed from the sand at 250 °C. At the same operating conditions, the silty loam soil showed a removal of 77 % of the diesel, and that was 92 % when the treatment time increased to 2.5 h. At 275 °C, the removal efficiency of PAHs was 91–99 % after 1 h, and that of lubricant oil was 76 % after 3 h. Although the extraction run time increased from 1 to 3 h, it seems to marginally affect the removal efficiency of lubricating oil; rather, it was observed that the effect of temperature is more pronounced.

Imidacloprid, a water-soluble neonicotinoid pesticide used globally in many applications, has been the subject of numerous studies (1) to determine its sublethal effects (5–100 ppb, LD₅₀∼200 ppb) on honeybees. This study was undertaken to determine, by ELISA assay, the presence of imidacloprid in water sources potentially frequented by honeybees in urban, suburban, and rural environments across the state of Maryland. Eighteen sites (six samples/site) were chosen which spanned diverse habitats including golf courses, nursery, livestock and crop farms, residential neighborhoods, and cityscapes. Hives were present either at or within 0.5 miles of each site. Imidacloprid was quantifiable in 8 % of the samples at sublethal levels (7–131 ppb). They were not clustered at any one type of site. Results for 13 % of the samples were at the threshold of detection; all others were below the detection limit of the assay (<0.2 ppb).

Drought conditions should magnify the effect of wastewater treatment plant (WWTP) effluent on river biogeochemistry. This study examined the impact of WWTP effluent on the Enoree River in the piedmont region of South Carolina during a period of significant drought. The Enoree River lacks impoundments, upstream agricultural runoff, and significant industrial point sources, so the single most important human influence on river chemistry is WWTP effluent. Water samples were collected from 28 locations on the Enoree River, 13 of its tributaries, and the effluent of four WWTPs. Effluent from the WWTP furthest upstream increased the salinity of the river and temporal variation and concentrations of most ions, especially nitrate, phosphate, sulfate, sodium, and chloride. The upstream WWTP set the downstream chemical composition of the river, with increasing proportions of chloride, sodium, and sulfate and decreasing proportions of dissolved silicon and bicarbonate. Downstream WWTPs had little or no impact on the chemical composition of the river. Mixing model results show that dilution was the dominant process of the downstream decrease in solute concentrations, but in-channel uptake mechanisms also contributed to declines in concentrations of nitrate, phosphate, and carbon dioxide. Despite dilution and uptake, the chemical signature of WWTP effluent was still evident 135 km downstream. These results lead to a better understanding of the effects of WWTP effluent on the biogeochemistry of rivers.

Precipitate adsorbent was produced from aluminum tanning wastewater by alkali precipitation and characterized by XPF, XRD, and FTIR. The results showed that the main components of the precipitate were Al, Ti, and Zr. The adsorption equilibrium for Cr³⁺ on the precipitate was reached within 60 min. The precipitate had better removal for Cr³⁺ from wastewater at pH 7.0. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation, and the adsorption isotherm fitted to the Langmuir model very well. Co-existed cations (Na⁺, Ca²⁺) in aqueous solution restrained Cr³⁺ adsorption on the precipitate. The adsorption of Cr³⁺ on the precipitate was mainly through the complexation and ion-exchange mechanisms, and oxide may play a major role in Cr³⁺ adsorption process.

The extracellular polymeric substance (EPS) extracted from waste-activated sludge after short-time aerobic digestion was investigated to be used as a novel biosorbent for Cd²⁺removal from water. The sorption kinetics was well fit for the pseudo-second-order model, and the maximum sorption capacity of the EPS (430.3 mg Cd²⁺/g EPS) was markedly higher than those of the reported biosorbents. Both Langmuir model and Freundlich model commendably described the sorption isotherm. The Gibbs free energy analysis of the adsorption showed that the sorption process was feasible and spontaneous. According to the results of multiple analytical techniques, the adsorption process took place via both physical and chemical sorption, but the electrostatic interaction between sorption sites with the functional groups and Cd²⁺was the major mechanism.

A simple, rapid, sensitive, and inexpensive dispersive liquid–liquid microextraction method was developed for the determination of trace amounts of copper by flame atomic absorption spectrometry (FAAS). N,N′-bis-(2-hydroxy-5-bromobenzyl)-2-hydroxy-1,3-diiminopropane was used as the chelating ligand. Several analytical parameters affecting the microextraction efficiency such as, sample pH, volume of extraction solvent (carbon tetrachloride), concentrations of the chelating ligand and NaCl, and sample volume were investigated and optimized. The effect of the interfering ions on the recovery of copper was also examined. Under the optimum conditions, the detection limit (3σ) was 0.75 μg L⁻¹for copper with a sample volume of 10 mL, and a preconcentration factor of 20 was achieved. The relative standard deviation (R.S.D) for ten independent determinations of a 10 μg L⁻¹solution of Cu(II) was 2.3 %. In order to verify the accuracy of the developed method, different certified reference materials (SLRS-5, QCS-19, Rice flour unpolished high level of Cd NIES 10c) were analyzed and the results obtained were in good agreement with the certified values. The proposed method was applied to tap water, river water, seawater, rice flour, and wheat flour samples. The percentage recovery values for spiked water samples were between 95.4 and 108.4.

This study examined the transport behavior of nano zero-valent iron (NZVI) coated with three types of stabilizers (i.e., polyacrylic acid, Tween-20, and starch) in saturated sand- and soil-packed columns under varying geochemical conditions. The cations or ionic strength and humic acid (HA) affected the transport of NZVI in varying degrees for different types of surface-modified NZVI (SM-NZVI). The effects of HA on the transport of SM-NZVI were different in sand- and soil-packed columns. In the sand-packed column, the presence of HA exerted an effect on the particle–particle interaction (i.e., aggregation), resulting in either enhanced or decreased transport of SM-NZVI. However, in the soil-packed column, the HA not only influenced the particle–particle interaction but also exerted an effect on the particle–soil grain interaction (i.e., deposition). Additionally, a significant enhancement in the transport of SM-NZVI in the soil-packed column was observed with increasing particle concentration. Moreover, the adsorption of arsenic on the surface of SM-NZVI exhibited insignificant effect on the transport of SM-NZVI. The release of arsenic from the arsenic-loaded SM-NZVI was detected when subjected to flushing with phosphate-containing groundwater. This fundamental understanding of the subsurface transport of SM-NZVI is of critical importance for the benign use and risk management of SM-NZVI.

This study assessed runoff losses following laboratory rainfall simulation on a grassland soil at two time intervals (48 and 216 h) after a single application of biosolids and meat and bone meal (MBM). The treatments were, a soil-only control, three types of biosolids (lime-stabilised (LS), thermally dried (TD) and anaerobically digested (AD)) and two types of MBM (low ash and high ash content) all applied at two rates (the maximum and double the maximum legal application rate currently permitted in Ireland). Results showed that treatment, time interval and their interactions all had significant effects on dissolved reactive P (DRP), total P (TP) and total dissolved P (TDP) concentrations. Time interval had the greatest effect for DRP and TP concentrations, while treatment was more significant for TDP. All treatments released DRP concentrations in excess of 30 μg DRP L⁻¹. Anaerobically digested biosolids released the least amount of DRP into surface runoff for both application rates at both time intervals. Low ash content MBM, applied at the maximum legal rate, released the most DRP at both time intervals, and the TD biosolids released the most DRP when applied at double the maximum rate. Lime-stabilised biosolids released the most TP in runoff at both application rates. Runoff comprised of >50 % particulate P for all treatments. Besides TD biosolids, all treatments, applied at both rates, released lower concentrations of suspended solids (SS) during the second time interval than the first. Soil-specific effects were also evident, although the soil was non-calcareous and had a low pH and high amounts of available aluminium and iron, high organic matter ensured low levels of P adsorption.

The nanoscale zero-valent iron grafted on acid-activated attapulgite (A-nZVI) was prepared by a liquid-phase reduction method and used for Cr(VI) removal from solution with enhanced efficiency. The structure of the composite A-nZVI was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface area analysis. nZVI was well-dispersed on the surface of acid-treated attapulgite, and no obvious aggregation was observed due to the support of rod-like structure of attapulgite, which is beneficial to Cr(VI) removal. Batch experiments revealed that the removal of Cr(VI) using A-nZVI was consistent with pseudo-first-order reaction kinetics, and removal efficiency was up to 98.73 % within 60 min for 100 mL 20 mg/L Cr(VI) at the initial pH 7.0 and 4.0 g/L A-nZVI. The pseudo-first-order rate constant kₒbₛwas independent of initial Cr(VI) concentration, but there was a good linearity (r² = 0.95) between kₒbₛand the A-nZVI dosage. This study demonstrates that A-nZVI has the potential to become a promising material for in situ groundwater remediation.