Diffusive gradient thin-films in seawater: time integrated technique for aqueous trace metal monitoring in impacted waterways

As part of an ambient monitoring program being conducted for the Puget Sound Naval Shipyard & Intermediate Maintenance Facility in Sinclair and Dyes Inlets of the Puget Sound, receiving waters of the Inlets are routinely monitored for trace metals and toxicity to assess water quality status, track progress in achieving water quality goals, and demonstrate protection of aquatic life. Recently, aqueous metal bioavailability using diffusive gradient thin-film (DGT) passive samplers has been incorporated into the monitoring program. The DGT samplers allow for the measurement of trace metal concentrations integrated over time via in situ chelation of labile metals. The DGT samplers are selective for free and weakly complexed metal species, allowing uptake to mimic diffusion limited bioavailability. This provides a monitoring solution by which episodic events are captured that provides a better representation of the potential for biological effects. A combination of laboratory performance tests and field deployed DGTs have been used to assess the reliability of the method to accurately measure labile concentrations Cu, Pb, and Zn under baseline and episodic storm events. Based on the results from DGTs deployed over different intervals spanning continuous deployments of 1-56 days and rainfall events of 0.4 – 3.2 inches/24 hr, reproducibility was affected by the presence of partially labile complexes, mass loading rate (time to equilibrium) which is proportional to free ion concentration, and variation in resin blank values. Best results were obtained for 3-7 day DGT deployments which showed high resolution of labile metal concentrations over varying spatial and temporal scales. The ability to conduct constant surveillance of metal bioavailable for a variety of freshwater and nearshore marine environments under varying environmental conditions greatly improves the assessment of potential ecological effects from exposure to metals

Ambient monitoring to inform the protection of beneficial uses and achieve water quality goals in Sinclair and Dyes Inlets, Puget Sound, WA

Currently discharge limits enforced under the Clean Water Act are focused on meeting National Pollution Discharge Elimination System (NPDES) limits at the end of the pipe and environmental performance is measured based on meeting the NPDES discharge limits; but meeting discharge limits has very little to do with achieving water quality goals for coastal and estuarine ecosystems. Therefore an effective monitoring and assessment program is needed to assess continuous process improvement, evaluate the ecological conditions, and provide metrics that can inform effective management of coastal and estuarine water quality. Here we report on an ambient monitoring program within Sinclair and Dyes Inlets, WA that was established to characterize environmental conditions, assess potential impacts, and track environmental quality trends within the Inlets. A network of water, sediment, and biota monitoring locations were selected that were co-located near suspected sources (industrial, waste water, and stormwater outfalls; marinas, stream mouths, and other sources) and locations that were representative of ambient marine and nearshore conditions for periodic sampling. Water column stations and effluents from industrial outfalls were sampled seasonally for trace metals, conventional parameters, and toxicity. Indigenous mussels have been sampled semi-annually for contaminant residues of metals and toxic organic compounds, and sediment monitoring is being conducted at five-eight year intervals. Key management questions include: (1) Are discharges from the naval shipyard protective of beneficial uses? (2) Are discharges from all sources of contamination impacting the quality of water, sediment, and biota in the Inlets? (3) What is the status and trend of water, sediment, and biota residue quality in the Inlets? Results from 2009-2016 monitoring provide metrics that are being used to evaluate ecosystem recovery and assess progress toward meeting environmental quality goals for the watershed

Assessing 21st century contaminants of concern using integrative passive sampling devices to obtain more meaningful and cost effective data on impacts from stormwater runoff

In many cases stormwater compliance monitoring is labor intensive, expensive, and largely unsuccessful in providing the data needed to support stormwater management goals. In addition, data from manual grab sampling and automated composite sampling are rarely collected in a manner that provides the information required to identify sources of contamination, evaluate the effectiveness of Best Management Practices, and inform effective decision making. Furthermore, monitoring is often driven by the need to meet low concentration benchmarks for metals and other constituents that do not take into account loading into the receiving waters, resulting in arbitrary monitoring requirements (monthly or seasonally) that are not tied to the driving forces within the watershed such as hydrology (flow regime), weather (storm events and antecedent dry periods), and upland land use and cover. To help address these issues, passive sampling devices including Diffusive Gradients in Thin films (DGT) for metals and Polar Organic Chemical Integrative Samples (POCIS) for a wide range of household, personal care, pharmaceutical, and endocrine disrupting compounds are being used to monitor stormwater runoff. In the Puget Sound a network of monitoring stations was established in Sinclair and Dyes Inlets to assess runoff from industrial areas of Naval Base Kitsap as well as commercial, residential, and rural areas within the watershed. Passive samplers were co-located with autosamplers to provide a direct comparison with grab and composite sampling. Preliminary results from multiple DGT deployments showed that time-dependent variability in stormwater impacts on ambient metal concentrations could be detected on small time scales, as well as over multiple days of rainfall. The POCIS samplers showed that a wide range of organic compounds could be reliably detected from the surveillance monitoring which should prove very useful for finger printing likely sources of contamination in stormwater runoff in the areas monitored

Temperature Dependence of Uranium and Vanadium Adsorption on Amidoxime‐Based Adsorbents in Natural Seawater

Recent advances in the development of amidoxime‐based adsorbents have made it highly promising for seawater uranium extraction. However, there is a great need to understand the influence of temperature on the uranium sequestration performance of the adsorbents in natural seawater. Here the apparent enthalpy and entropy of the sorption of uranium (VI) and vanadium (V) with amidoxime‐based adsorbents were determined in natural seawater tests at 8, 20, and 31 °C that cover a broad range of ambient seawater temperature. The sorption of U was highly endothermic, producing apparent enthalpies of 57 ± 6.0 and 59 ± 11 kJ mol−1 and apparent entropies of 314 ± 21 and 320 ± 36 J K−1 mol−1, respectively, for two adsorbent formulations. In contrast, the sorption of V showed a much smaller temperature sensitivity, producing apparent enthalpies of 6.1 ± 5.9 and −11 ± 5.7 kJ mol−1 and apparent entropies of 164 ± 20 and 103 ± 19 J K−1 mol−1, respectively. This new thermodynamic information suggests that amidoxime‐based adsorbents will deliver significantly increased U adsorption capacities and improved selectivity in warmer waters. A separate field study of seawater uranium adsorption conducted in a warm seawater site (Miami, FL, USA) confirm the observed strong temperature effect on seawater uranium mining. This strong temperature dependence demonstrates that the warmer the seawater where the amidoxime‐based adsorbents are deployed the greater the yield for seawater uranium extraction. Thermodynamic parameters of the sorption of uranium and vanadium with amidoxime‐based adsorbents in true natural seawater system were obtained. Laboratory and field data demonstrate that amidoxime‐based adsorbents exhibit greatly increased uranium adsorption capacity and selectivity in warmer seawater

Investigations into the Reusability of Amidoxime-Based Polymeric Adsorbents for Seawater Uranium Extraction

The ability to reuse amidoxime-based polymeric adsorbents is a critical component in reducing the overall cost of the technology to extract uranium from seawater. This report describes an evaluation of adsorbent reusability in multiple reuse (adsorption/stripping) cycles in real seawater exposures with potassium bicarbonate (KHCO₃) elution using several amidoxime-based polymeric adsorbents. The KHCO₃ elution technique achieved ∼100% recovery of uranium adsorption capacity in the first reuse. Subsequent reuses showed significant drops in adsorption capacity. After the fourth reuse with the ORNL AI8 adsorbent, the 56-day adsorption capacity dropped to 28% of its original capacity. FTIR spectra revealed that there was a conversion of the amidoxime ligands to carboxylate groups during extended seawater exposure, becoming more significant with longer exposure times. Ca and Mg adsorption capacities also increased with each reuse cycle supporting the hypothesis that long-term exposure resulted in converting amidoxime to carboxylate, enhancing the adsorption of Ca and Mg. Shorter seawater exposure (adsorption/stripping) cycles (28 vs 42 days) had higher adsorption capacities after reuse, but the shorter exposure cycle time did not produce an overall better performance in terms of cumulative exposure time. Recovery of uranium capacity in reuses may also vary across different adsorbent formulations. Through multiple reuses, the AI8 adsorbent can harvest 10 g uranium/kg adsorbent in ∼140 days, using a 28-day adsorption/stripping cycle, a performance much better than would be achieved with a single use of the adsorbent through a very long-term exposure (saturation capacity of 7.4 g U/kg adsorbent). A time dependent seawater exposure model to evaluate the cost associated with reusing amidoxime-based adsorbents in real seawater exposures was developed. The predicted cost to extract uranium from seawater ranged from $610/kg U to$830/kg U. Model simulation suggests that a short seawater exposure cycle (<15 days) is the optimal deployment period for lower uranium production cost in seawater uranium mining

The Uranium from Seawater Program at the Pacific Northwest National Laboratory: Overview of Marine Testing, Adsorbent Characterization, Adsorbent Durability, Adsorbent Toxicity, and Deployment Studies

The Pacific Northwest National Laboratory (PNNL) is evaluating the performance of adsorption materials to extract uranium from natural seawater. Testing consists of measurements of the adsorption of uranium and other elements from seawater as a function of time using flow-through columns and a recirculating flume to determine adsorbent capacity and adsorption kinetics. The amidoxime-based polymer adsorbent AF1, produced by Oak Ridge National Laboratory (ORNL), had a 56-day adsorption capacity of 3.9 ± 0.2 g U/kg adsorbent material, a saturation capacity of 5.4 ± 0.2 g U/kg adsorbent material, and a half-saturation time of 23 ± 2 days. The ORNL AF1 adsorbent has a very high affinity for uranium, as evidenced by a 56-day distribution coefficient between adsorbent and solution of log K_D,56day = 6.08. Calcium and magnesium account for a majority of the cations adsorbed by the ORNL amidoxime-based adsorbents (61% by mass and 74% by molar percent), uranium is the fourth most abundant element adsorbed by mass and seventh most abundant by molar percentage. Marine testing at Woods Hole Oceanographic Institution with the ORNL AF1 adsorbent produced adsorption capacities 15% and 55% higher than those observed at PNNL for column and flume testing, respectively. Variations in competing ions may be the explanation for the regional differences. Hydrodynamic modeling predicts that a farm of adsorbent materials will likely have minimal effect on ocean currents and removal of uranium and other elements from seawater when farm densities are <1800 braids/km². A decrease in uranium adsorption capacity of up to 30% was observed after 42 days of exposure because of biofouling when the ORNL braided adsorbent AI8 was exposed to raw seawater in a flume in the presence of light. No toxicity was observed with flow-through column effluents of any absorbent materials tested to date. Toxicity could be induced with some non-amidoxime based absorbents only when the ratio of solid absorbent to test media was increased to part per thousand levels. Thermodynamic modeling of the seawater−amidoxime adsorbent was performed using the geochemical modeling program PHREEQC. Modeling of the binding of Ca, Mg, Fe, Ni, Cu, U, and V reveal that when binding sites are limited (1 × 10^–8 binding sites/kg seawater), vanadium heavily outcompetes other ions for the amidoxime sites. In contrast, when binding sites are abundant, Mg and Ca dominate the total percentage of metals bound to the sorbent