Critical metal geochemistry in groundwaters influenced by dredged material.

This study investigated critical metal (CM) geochemistry including rare earth elements (REEs), Co, Ni, and Mn in groundwaters below and surrounding two dredged material placement facilities (DMPFs). Metal concentrations are elevated at both sites, spanning several orders of magnitude. The highest CM concentrations measured exceed many environments considered as aqueous resources (Co and Ni > 1 mg L-1, REEs > 3 mg L-1). Correlations between sulfur and iron, major cations, and CMs indicate that oxidation of sulfides present in the DM releases metals both directly from sulfide minerals and indirectly through acid dissolution of and/or desorption from additional minerals. REE fractionation patterns indicate that their mobility in the groundwaters may be influenced by interactions with silicate, carbonate, and phosphate minerals. Significant positive Gd and Eu anomalies were observed, which may be attributed to increased mobility of Eu2+ and anthropogenic Gd. Nanogeochemical analysis of filtered samples revealed several REE-bearing nanoparticulate (diameter < 100 nm) species, some of which co-occurred with aluminum, suggesting an (oxy)hydroxide or a clay mineral component. Further characterization of soluble and nano scale geochemical speciation is needed to fully assess the viability of CM recovery from DM-associated groundwater. CM recovery from DM-associated waters can provide a beneficial use, both offsetting costs associated with disposal, and supplementing domestic CM resources.

Integrated Assessment of Chemical and Biological Recovery After Diversion and Treatment of Acid Mine Drainage in a Rocky Mountain Stream.

Responses of stream ecosystems to gradual reductions in metal loading following remediation or restoration activities have been well documented in the literature. However, much less is known about how these systems respond to the immediate or more rapid elimination of metal inputs. Construction of a water treatment plant on the North Fork of Clear Creek (NFCC; CO, USA), a US Environmental Protection Agency Superfund site, captured, diverted, and treated the two major point-source inputs of acid mine drainage (AMD) and provided an opportunity to investigate immediate improvements in water quality. We conducted a 9-year study that included intensive within- and among-year monitoring of receiving-stream chemistry and benthic communities before and after construction of the treatment plant. Results showed a 64%-86% decrease in metal concentrations within months at the most contaminated sites. Benthic communities responded with increased abundance and diversity, but downstream stations remained impaired relative to reference conditions, with significantly lower taxonomic richness represented by a few dominant taxa (i.e., Baetis sp., Hydropsyche sp., Simulium sp., Orthocladiinae). Elevated metal concentrations from apparent residual sources, and relatively high conductivity from contributing major ions not removed during the treatment process, are likely limiting downstream recovery. Our study demonstrates that direct AMD treatment can rapidly improve water quality and benefit aquatic life, but effectiveness is limited, in part, to the extent that inputs of metals are captured and treated. Consideration should also be given to the effects of elevated major ion concentrations from the treated effluent not removed during the lime treatment process. Continued chemical and biological monitoring will be needed to quantify the NFCC recovery trajectory and to inform future remediation strategies. Environ Toxicol Chem 2023;42:512-524. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Fractionation of fulvic acid by iron and aluminum oxides--influence on copper toxicity to Ceriodaphnia dubia.

This study examines the effect on aquatic copper toxicity of the chemical fractionation of fulvic acid (FA) that results from its association with iron and aluminum oxyhydroxide precipitates. Fractionated and unfractionated FAs obtained from streamwater and suspended sediment were utilized in acute Cu toxicity tests on Ceriodaphnia dubia. Toxicity test results with equal FA concentrations (6 mg FA/L) show that the fractionated dissolved FA was 3 times less effective at reducing Cu toxicity (EC50 13 ± 0.6 µg Cu/L) than were the unfractionated dissolved FAs (EC50 39 ± 0.4 and 41 ± 1.2 µg Cu/L). The fractionation is a consequence of preferential sorption of molecules having strong metal-binding (more aromatic) moieties to precipitating Fe- and Al-rich oxyhydroxides, causing the remaining dissolved FA to be depleted in these functional groups. As a result, there is more bioavailable dissolved Cu in the water and hence greater potential for Cu toxicity to aquatic organisms. In predicting Cu toxicity, biotic ligand models (BLMs) take into account dissolved organic carbon (DOC) concentration; however, unless DOC characteristics are accounted for, model predictions can underestimate acute Cu toxicity for water containing fractionated dissolved FA. This may have implications for water-quality criteria in systems containing Fe- and Al-rich sediment, and in mined and mineralized areas in particular. Optical measurements, such as specific ultraviolet absorbance at 254 nm (SUVA254), show promise for use as spectral indicators of DOC chemical fractionation and inferred increased Cu toxicity.

Arsenic geochemistry in a biostimulated aquifer: an aqueous speciation study.

Stimulating microbial growth through the use of acetate injection wells at the former uranium mill site in Rifle, Colorado, USA, has been shown to decrease dissolved uranium (VI) concentrations through bacterial reduction to immobile uranium (IV). Bioreduction also changed the redox chemistry of site groundwater, altering the mobility of several other redox-sensitive elements present in the subsurface, including iron, sulfur, and arsenic. Following acetate amendment at the site, elevated concentrations of arsenic in the groundwater were observed. Ion chromatography-inductively coupled plasma-mass spectrometry was used to determine the aqueous arsenic speciation. Upgradient samples, unexposed to acetate, showed low levels of arsenic (≈1 µM), with greater than 90% as arsenate (As[V]) and a small amount of arsenite (As[III]). Downgradient acetate-stimulated water samples had much higher levels of arsenic (up to 8 µM), and 4 additional thioarsenic species were present under sulfate-reducing conditions. These thioarsenic species demonstrate a strong correlation between arsenic release and sulfide concentrations in groundwater, and their formation may explain the elevated total arsenic concentrations. An alternative remediation approach, enhanced flushing of uranium, was accomplished by addition of bicarbonate and did not result in highly elevated arsenic concentrations.

Radionuclides, trace elements, and radium residence in phosphogypsum of Jordan.

Voluminous stockpiles of phosphogypsum (PG) generated during the wet process production of phosphoric acid are stored at many sites around the world and pose problems for their safe storage, disposal, or utilization. A major concern is the elevated concentration of long-lived (226)Ra (half-life = 1,600 years) inherited from the processed phosphate rock. Knowledge of the abundance and mode-of-occurrence of radium (Ra) in PG is critical for accurate prediction of Ra leachability and radon (Rn) emanation, and for prediction of radiation-exposure pathways to workers and to the public. The mean (±SD) of (226)Ra concentrations in ten samples of Jordan PG is 601 ± 98 Bq/kg, which falls near the midrange of values reported for PG samples collected worldwide. Jordan PG generally shows no analytically significant enrichment (<10%) of (226)Ra in the finer (<53 µm) grain size fraction. Phosphogypsum samples collected from two industrial sites with different sources of phosphate rock feedstock show consistent differences in concentration of (226)Ra and rare earth elements, and also consistent trends of enrichment in these elements with increasing age of PG. Water-insoluble residues from Jordan PG constitute <10% of PG mass but contain 30-65% of the (226)Ra. (226)Ra correlates closely with Ba in the water-insoluble residues. Uniformly tiny (<10 µm) grains of barite (barium sulfate) observed with scanning electron microscopy have crystal morphologies that indicate their formation during the wet process. Barite is a well-documented and efficient scavenger of Ra from solution and is also very insoluble in water and mineral acids. Radium-bearing barite in PG influences the environmental mobility of radium and the radiation-exposure pathways near PG stockpiles.

Analysis of pH dependent uranium(VI) sorption to nanoparticulate hematite by flow field-flow fractionation-inductively coupled plasma mass spectrometry.

The ability to quantify the amount of metals ions that are present as macromolecular, nanoparticulate, or colloid phases is critical for understanding bioavailability and transport as well as performing risk assessments and remediation strategies. Flow field-flow fractionation-inductively coupled plasma mass spectrometry (FI FFF-ICP-MS) is a powerful separation tool that has been previously used to characterize colloidal metals in environmental samples. In this study we examine the degree to which FI FFF-ICP-MS provides quantitative data on uranium speciation by comparing the results to centrifugation followed by filtration. Sorption of uranium to nanoparticulate hematite (approximately 60 nm) was examined over the pH range of 3 to 6. Close agreement was found between the two approaches over the pH range.

Quantifying uranium complexation by groundwater dissolved organic carbon using asymmetrical flow field-flow fractionation.

The long-term mobility of actinides in groundwaters is important for siting nuclear waste facilities and managing waste-rock piles at uranium mines. Dissolved organic carbon (DOC) may influence the mobility of uranium, but few field-based studies have been undertaken to examine this in typical groundwaters. In addition, few techniques are available to isolate DOC and directly quantify the metals complexed to it. Determination of U-organic matter association constants from analysis of field-collected samples compliments laboratory measurements, and these constants are needed for accurate transport calculations. The partitioning of U to DOC in a clay-rich aquitard was investigated in 10 groundwater samples collected between 2 and 30 m depths at one test site. A positive correlation was observed between the DOC (4-132 mg/L) and U concentrations (20-603 microg/L). The association of U and DOC was examined directly using on-line coupling of Asymmetrical Flow Field-Flow Fractionation (AsFlFFF) with UV absorbance (UVA) and inductively coupled plasma-mass spectrometer (ICP-MS) detectors. This method has the advantages of utilizing very small sample volumes (20-50 microL) as well as giving molecular weight information on U-organic matter complexes. AsFlFFF-UVA results showed that 47-98% of the DOC (4-136 mg C/L) was recovered in the AsFlFFF analysis, of which 25-64% occurred in the resolvable peak. This peak corresponded to a weight-average molecular weight of about 900-1400 Daltons (Da). In all cases, AsFlFFF-ICP-MS suggested that

Characterzation of colloidal and humic-bound Ni and U in the "dissolved" fraction of contaminated sediment extracts.

The dissolved phase of environmental aqueous samples is generally defined by filtration at 0.2 microm or even 0.45 microm. However, it is also acknowledged that colloids <0.2 microm suspended in the aqueous phase can be important for determining contaminant availability and mobility. We have used flow field-flow fractionation (FI FFF) and size exclusion chromatography (SEC) coupled to UV-absorbance (UVA) and inductively coupled plasma mass spectrometry (ICP-MS) to study the dissolved organic matter (DOM) and colloidal binding of U and Ni in water extracts of sediments collected from a contaminated area of the Savannah River Site, a U.S. Department of Energy former nuclear materials production and processing facility, near Aiken, SC. High-performance SEC-UVA-ICP-MS was well-suited to the separation of DOM overthe molecular weight (MW) range of approximately 200-7000 Da. The ICP-MS element specific data indicated that a significant fraction of U was associated with DOM. Uranium exhibited a bimodal distribution and the other fraction was greater than the exclusion limit for the column and coeluted with Al. Flow FFF was used to size this fraction as colloidal with an approximate effective spherical diameter of 0.09-0.12 microm. Element specific ICP-MS data confirmed that U and Al were associated with the colloidal phase. High-field FI FFF was also applicable to sizing DOM but resolution was poorer than SEC. The results of this study suggest that "dissolved" U at this site is predominantly either complexed by DOM or bound to a colloidal fraction while Ni is predominately present as labile complexes or the free cation and, therefore, potentially bioavailable.

Application of flow field flow fractionation-ICPMS for the study of uranium binding in bacterial cell suspensions.

Field flow fractionation (FFF) is a size-based separation technique applicable to biomolecules, colloids, and bacteria in solution. When interfaced with ICPMS on-line, elemental data can be collected concurrent with size distribution. We employed hyperlayer flow FFF (Fl FFF) methodology to separate cells of Shewanella oneidensis strain MR-1 from exopolymers present in washed cell suspensions. With a channel flow of 4 mL min-1 and a cross-flow of 0.4 mL min-1 cells eluted with a retention time of 4.7 min corresponding to an approximate equivalent spherical cell diameter of 0.8 microm. Cell suspensions were amended with increasing concentrations of U to establish an adsorption isotherm and with fixed U concentrations at varying pH to establish the pH dependence of sorption. A linear sorption isotherm was determined for U solution concentrations of 0.2-16 microM, maximum U sorption occurred at pH 5. A high molecular weight compound, presumably a cell exudate, was identified by Fl FFF-ICPMS. This cell exudate complexed U, and at elevated pH, the exudate appeared to have a greater affinity for U than cell surfaces. Thus, Fl FFF interfaced with ICPMS detection is a powerful analytical technique for metal sorption studies with bacteria; analysis can be carried out on small sample volumes (25 microL) and additional speciation information can be gained because of the versatile Fl FFF separation range and multielement detection capabilities of ICPMS.