Seasonal Sulfur Redox Cycling in Two Constructed Wetlands with Insight on How They Age.

Long-term metal remediation in wetland treatment systems (WTSs) involves facilitating dissimilatory sulfate reduction to produce sulfide and mineralize metals in deep sediments. We evaluated seasonal sulfur cycling in two constructed wetlands (Maintained WTS constructed in 2007, and the Unmaintained WTS constructed in 2000) on the Savannah River Site in Aiken, South Carolina, USA. Significant interactions in sulfide concentration were observed between sediment depth, season, and wetland (F = 4.64, df = 11, P = 3.28 × 10 - 5). In the Maintained WTS, dissimilatory sulfate reduction dominated the surface sediments during the warm season (0-2 cm depth, t=-2.66, P = 9.70 × 10 - 3), unlike the Unmaintained system. Sulfate concentrations in pore waters increased in the warm season (F = 7.84, df = 1, P = 6.50 × 10 - 3), contrary to expectations. Sulfur limitation in the Unmaintained WTS during the warm season correlated with increased sulfur assimilation in giant bulrush. Lower sulfide concentrations in surface sediments of the Unmaintained WTS illustrated aging effects. The Maintained WTS shows potential for managing erosion, pH reduction, and sulfur limitation observed in the older Unmaintained WTS.

Use of diffusive gradients in thin films (DGT) to measure potentially bioavailable metals in southeastern USA blackwater streams.

We used diffusive gradients in thin films (DGT) to measure potentially bioavailable metals in coastal plain streams in the southeastern USA that exhibited strong to moderate blackwater characteristics. Metals were partitioned into particulate metals, DGT-inert metals (i.e., colloidal and refractory organic complexes not accumulated by DGT), and DGT-labile metals (i.e., free metal ions, small inorganic complexes, and labile organic complexes). We also examined the influence of different DGT deployment times using data collected from the field and a follow-up laboratory study. The DGT-measured fraction of dissolved metals in the streams was 15% for Cd, 21% for Zn, 33% for Cu, 37% for Pb, and 98% for Mn. Metals bound to particulates predominated only for Pb. Most of the Cd, Pb, Zn, and Cu were associated with colloids, refractory organic complexes, or particles. Relatively small amounts were in free ion or labile complexes likely to be bioavailable through respiratory surfaces. Modeled concentrations of free and inorganically bound Cu and Pb were lower than the DGT fraction indicating that DGT accumulated some organically bound Cu and Pb that might not have been bioavailable. DGT-exposure times in excess of 5 days may have contributed to the accumulation of partly labile organic-metal complexes and were associated with substantial biofouling that caused metal uptake by DGT to depart from linearity.

The Impact of Storms on Legionella pneumophila in Cooling Tower Water, Implications for Human Health.

At the U.S. Department of Energy's Savannah River Site (SRS) in Aiken, SC, cooling tower water is routinely monitored for Legionella pneumophila concentrations using a direct fluorescent antibody (DFA) technique. Historically, 25-30 operating SRS cooling towers have varying concentrations of Legionella in all seasons of the year, with patterns that are unpredictable. Legionellosis, or Legionnaires' disease (LD), is a pneumonia caused by Legionella bacteria that thrive both in man-made water distribution systems and natural surface waters including lakes, streams, and wet soil. Legionnaires' disease is typically contracted by inhaling L. pneumophila, most often in aerosolized mists that contain the bacteria. At the SRS, L. pneumophila is typically found in cooling towers ranging from non-detectable up to 108 cells/L in cooling tower water systems. Extreme weather conditions contributed to elevations in L. pneumophila to 107-108 cells/L in SRS cooling tower water systems in July-August 2017. L. pneumophila concentrations in Cooling Tower 785-A/2A located in SRS A-Area, stayed in the 108 cells/L range despite biocide addition. During this time, other SRS cooling towers did not demonstrate this L. pneumophila increase. No significant difference was observed in the mean L. pneumophila mean concentrations for the towers (p < 0.05). There was a significant variance observed in the 285-2A/A Tower L. pneumophila results (p < 0.05). Looking to see if we could find "effects" led to model development by analyzing 13 months of water chemistry and microbial data for the main factors influencing the L. pneumophila concentrations in five cooling towers for this year. It indicated chlorine and dissolved oxygen had a significant impact (p < 0.0002) on cooling tower 785A/2A. Thus, while the variation in the log count data for the A-area tower is statistically greater than that of the other four towers, the average of the log count data for the A-Area tower was in line with that of the other towers. It was also observed that the location of 785A/2A and basin resulted in more debris entering the system during storm events. Our results suggest that future analyses should evaluate the impact of environmental conditions and cooling tower design on L. pneumophila water concentrations and human health.

In situ uranium stabilization by microbial metabolites.

Microbial melanin production by autochthonous bacteria was explored in this study as a means to increase U immobilization in U contaminated soil. This article demonstrates the application of bacterial physiology and soil ecology for enhanced U immobilization in order to develop an in situ, U bio-immobilization technology. We have demonstrated microbial production of a metal chelating biopolymer, pyomelanin, in U contaminated soil from the Tims Branch area of the Department of Energy (DOE), Savannah River Site (SRS), South Carolina, as a result of tyrosine amendments. Bacterial densities of pyomelanin producers were >10(6) cells per g wet soil. Pyomelanin demonstrated U complexing and mineral binding capacities at pH 4 and 7. In laboratory studies, in the presence of goethite or illite, pyomelanin enhanced U sequestration by these minerals. Tyrosine amended soils in a field test demonstrated increased U sequestration capacity following pyomelanin production up to 13 months after tyrosine treatments.

Removal capacity and chemical speciation of groundwater iodide (I-) and iodate (IO3-) sequestered by organoclays and granular activated carbon.

Radioiodine (present mostly as 129I) is difficult to remove from waste streams or contaminated groundwater because it tends to exist as multiple anionic species (i.e., iodide (I-), iodate (IO3-) and organo-iodide) that do not bind to minerals or synthetic materials. In this work, the efficacy of organoclay OCB and OCM, and granular activated carbon (GAC) as sorbents to bind I- and IO3- from artificial groundwater (AGW) was examined. These sorbents were highly effective at removing I- and IO3- from AGW under oxic condition, with the adsorption capacity up to 30 mg I/g sorbent. Based on X-ray spectroscopy measurements, I- was bound to organic ligands in organoclays OCB and OCM, but when GAC was exposed to I- in groundwater, the sequestered I species was molecular I2. For IO3- interacting with organoclay OCB and GAC, the adsorbed I species remained being IO3-, but when organoclay OCM that contains both quaternary amine and sulfur was exposed to IO3-, the sulfur compound would reduce IO3- to I- that was then bound to organic ligands. Thus, the inexpensive and high-capacity organoclays and GAC may provide a practical solution for removing 129I contaminant from environmental systems and liquid nuclear wastes.

Aqueous (99)Tc, (129)I and (137)Cs removal from contaminated groundwater and sediments using highly effective low-cost sorbents.

Technetium-99 ((99)Tc), iodine-129 ((129)I), and cesium-137 ((137)Cs) are among the key risk-drivers for environmental cleanup. Immobilizing these radionuclides, especially TcO4(-) and I(-), has been challenging. TcO4(-) and I(-) bind very weakly to most sediments, such that distribution coefficients (Kd values; radionuclide concentration ratio of solids to liquids) are typically <2 mL/g; while Cs sorbs somewhat more strongly (Kd âˆ¼ 50 mL/g). The objective of this laboratory study was to evaluate 13 cost-effective sorbents for TcO4(-), I(-), and Cs(+) uptake from contaminated groundwater and sediments. Two organoclays sorbed large amounts of TcO4(-) (Kd > 1 × 10(5) mL/g), I(-) (Kd ≥ 1 × 10(4) mL/g), and Cs(+) (Kd > 1 × 10(3) mL/g) and also demonstrated a largely irreversible binding of the radionuclides. Activated carbon GAC 830 was effective at sorbing TcO4(-) (Kd > 1 × 10(5) mL/g) and I(-) (Kd = 6.9 × 10(3) mL/g), while a surfactant modified chabazite was effective at sorbing TcO4(-) (Kd > 2.5 × 10(4) mL/g) and Cs(+) (Kd > 6.5 × 10(3) mL/g). Several sorbents were effective for only one radionuclide, e.g., modified zeolite Y had TcO4(-)Kd > 2.3 × 10(5) mL/g, AgS had I(-) Kd = 2.5 × 10(4) mL/g, and illite, chabazite, surfactant modified clinoptilolite, and thiol-SAMMS had Cs(+)Kd > 10(3) mL/g. These low-cost and high capacity sorbents may provide a sustainable solution for environmental remediation.

Amendments for the in situ remediation of contaminated sediments: evaluation of potential environmental impacts.

Active sediment caps represent a comparatively new technology for remediating contaminated sediments. They are made by applying chemically active amendments that reduce contaminant mobility and bioavailability to the sediment surface. The objective of this study was to determine if active cap amendments including organoclay, apatite, and biopolymers have the potential to harm benthic organisms. Methods included laboratory bioassays of amendment toxicity and field evaluations of amendment impacts on organisms held in cages placed within pilot-scale active caps located in Steel Creek, a South Carolina (USA) stream. Test organisms included Hyalella azteca, Leptocheirus plumulosus, Lumbriculus variegatus, and Corbicula fluminea to represent a range of feeding modes, burrowing behaviors, and both fresh and saltwater organisms. In addition to the laboratory and field assays, chemical extractions were performed to determine if the amendments contained harmful impurities that could leach into the ambient environment. Laboratory bioassays indicated that 100% apatite had minimal effects on Hyalella in freshwater and up to 25% organoclay was nontoxic to Leptocheirus in brackish water. Field evaluations indicated that pilot-scale caps composed of up to 50% apatite and 25% organoclay did not harm Hyalella, Lumbriculus, or Corbicula. In contrast, organisms in caps containing biopolymers died because of physical entrapment and/or suffocation by the viscous biopolymers. The extractions showed that the amendments did not release harmful concentrations of metals. These studies indicated that apatite and organoclay are nontoxic at concentrations (up to 50% and 25% by weight, respectively) needed for the construction of active caps that are useful for the remediation of metals and organic contaminants in sediments.

Use of illite clay for in situ remediation of 137Cs-contaminated water bodies: field demonstration of reduced biological uptake.

We hypothesized that adding micaceous minerals to 137Cs-contaminated aquatic systems would serve as an effective in situ remediation technique by sequestering the contaminant and reducing its bioavailability. Results from several laboratory studies are presented from which an effective amendment material was chosen for a replicated field study. The field study was conducted over a 2-year period and incorporated 16 3.3-m diameter column-plots (limnocorrals) that were randomly placed in a 137Cs-contaminated pond. The limnocorrals received three rates of amendment treatments to their water surfaces. The amendment material was a commercially available mineral with high sorption (Kd > 9000 L kg(-1)) and low desorption (<20%) characteristics for cesium, even in the presence of high concentrations of the competing cation, NH4+. In the treated limnocorrals, 137Cs concentrations were reduced some 25-30-fold in the water, 4-5-fold in aquatic plants, and 2-3-fold in fish. The addition of the amendment did not adversely affect water chemistry, although increased turbidity and subsequent siltation did alter the aquatic macroinvertebrate insect community. This in situ technology provides a valuable, less-environmentally intrusive alternative to costly ex situ technologies that require the contaminated sediment to be excavated prior to treatment, or excavated and disposed of elsewhere.

Enhanced contaminant desorption induced by phosphate mineral additions to sediment.

Apatite, Ca10(PO4)6(OH,F)2, has been successfully used as a soil amendment at numerous sites to immobilize metals and radionuclides. Such sites commonly contain multiple contaminants; the impact of apatite on these contaminants is expected to vary greatly. The objective of this study was to determine the influence of apatite on nontargeted sediment contaminants. Laboratory batch experiments were conducted under oxidized (several weekly wet/dry cycles) and reduced (water-saturated) conditions with a sediment collected from a wetland contaminated with numerous metals and radionuclides. Apatite additions resulted in the significant (p < or = 0.05) reduction of porewater Cd, Co, Hg, Pb, and U concentrations. However, apatite additions also resulted in the enhanced desorption of As, Se, and Th. Increases in porewater As and Se concentrations were the result of phosphate competitive exchange and not to the release of these contaminants directly from the apatite, which contained 29 mg kg(-1) As and 0.2 mg kg(-1) Se. Apatite additions increased porewater Th and organic C concentrations under oxidized (Eh = 497 mV) but not reduced (Eh = 65 mV) conditions. In the oxidized system, the leachate from the apatite treatment had a brown coloration and contained 226 mg L(-1) organic C, as compared to 141 mg L(-1) in the unamended samples. The desorbed organic C likely contained significant quantities of Th. This conclusion was supported by (i) the observation that porewater Th partitioned to hydrophobic resins, (ii) thermodynamic calculations which predicted that essentially all porewater Th existed as organic matter complexes, and (iii) there were significant correlations (r = 0.91, n = 8, p < or = 0.01) between porewater organic C and Th concentrations. Sediment additions of zero-valent iron particles along with the apatite eliminated the enhanced desorption of As, Se, and Th observed when only apatite was added. This study underscores the importance of monitoring the influence of sediment amendments on nontarget contaminants and provides examples of how the sediment additions of apatite can effectively immobilize some contaminants while enhancing the mobility of others.