Passive Sampling-Based versus Conventional-Based Metrics for Evaluating Remediation Efficacy at Contaminated Sediment Sites: A Review.

Passive sampling devices (PSDs) are increasingly used at contaminated sites to improve the characterization of contaminant transport and assessment of ecological and human health risk at sediment sites and to evaluate the effectiveness of remedial actions. The use of PSDs after full-scale remediation remains limited, however, in favor of evaluation based on conventional metrics, such as bulk sediment concentrations or bioaccumulation. This review has three overall aims: (1) identify sites where PSDs have been used to support cleanup efforts, (2) assess how PSD-derived remedial end points compare to conventional metrics, and (3) perform broad semiquantitative and selective quantitative concurrence analyses to evaluate the magnitude of agreement between metrics. Contaminated sediment remedies evaluated included capping, in situ amendment, dredging and monitored natural recovery (MNR). We identify and discuss 102 sites globally where PSDs were used to determine remedial efficacy resulting in over 130 peer-reviewed scientific publications and numerous technical reports and conference proceedings. The most common conventional metrics assessed alongside PSDs in the peer-reviewed literature were bioaccumulation (39%), bulk sediments (40%), toxicity (14%), porewater grab samples (16%), and water column grab samples (16%), while about 25% of studies used PSDs as the sole metric. In a semiquantitative concurrence analysis, the PSD-based metrics agreed with conventional metrics in about 68% of remedy assessments. A more quantitative analysis of reductions in bioaccumulation after remediation (i.e., remediation was successful) showed that decreases in uptake into PSDs agreed with decreases in bioaccumulation (within a factor of 2) 61% of the time. Given the relatively good agreement between conventional and PSD-based metrics, we propose several practices and areas for further study to enhance the utilization of PSDs throughout the remediation of contaminated sediment sites.

Comparing Equilibrium Concentrations of Polychlorinated Biphenyls Based on Passive Sampling and Bioaccumulation in Water Column Deployments.

Biomonitoring at contaminated sites undergoing cleanup, including Superfund sites, often uses bioaccumulation of anthropogenic contaminants by field-deployed organisms as a metric of remedial effectiveness. Bioaccumulation studies are unable to assess the equilibrium status of the organisms relative to the contaminants to which they are exposed. Establishing equilibrium provides a reproducible benchmark on which scientific and management decisions can be based (e.g., comparison with human dietary consumption criteria). Unlike bioaccumulating organisms, passive samplers can be assessed for their equilibrium status. In our study, over a 3-year period, we compared the bioaccumulation of selected polychlorinated biphenyls (PCBs) by mussels in water column deployments at the New Bedford Harbor Superfund site (New Bedford, MA, USA) to codeployed passive samplers. Based on comparisons to the calculated passive sampler equilibrium concentrations, the mussels were not at equilibrium, and the subsequent analysis focused on evaluating approaches for estimating equilibrium bioaccumulation. In addition, a limited evaluation of metal bioaccumulation by the exposed mussels and a metal passive sampler was performed. In general, mussel and passive sampler accumulation of PCBs was significantly correlated; however, surprisingly, agreement on the magnitude of accumulation was optimal when bioaccumulation and passive sampler uptake were not corrected for nonequilibrium conditions. A subsequent comparison of four approaches for estimating equilibrium mussel bioaccumulation using octanol-water partition coefficients (KOW ), triolein-water partition coefficients (KTW ), and two types of polymer-lipid partition coefficients demonstrated that field-deployed mussels were not at equilibrium with many PCBs. A range of estimated equilibrium mussel bioaccumulation concentrations were calculated, with the magnitude of the KOW -based values being the smallest and the polymer-lipid partition coefficient-based values being the largest. These analyses are intended to assist environmental scientists and managers to interpret field deployment data when transitioning from biomonitoring to passive sampling. Environ Toxicol Chem 2023;42:317-332. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Probing Specific Adsorption of Electrolytes at Kaolinite-Aqueous Interfaces by Atomic Force Microscopy.

Adsorption of electrolytes (ions) at solid-liquid interfaces alters the physical and chemical properties of materials and hence plays a critical role in manufacturing and processing of nanomaterials featuring large surface or interfacial areas of desired structures and morphology. Many experiments and theoretical calculations using various electrical double layer (EDL) models have been conducted to understand how and where ions adsorb at charged surfaces in a liquid. However, conclusions from previous research remain inconclusive because of model-dependent approaches to studying ion adsorption at diverse solid-liquid interfaces. In this study, atomic force microscopy is used to image in liquids the surface lattice structure of two kaolinite basal planes in the presence and absence of monovalent and divalent cations. Distinct adsorption of ions through different mechanisms (such as electrostatic attraction and specific adsorption) is identified through atomic resolution imaging without the assumption of an EDL structure.

Unraveling Interaction Mechanisms between Molybdenite and a Dodecane Oil Droplet Using Atomic Force Microscopy.

Molybdenite (MoS2) is a mineral that has drawn great interest because of its potential application in various fields. To facilitate the flotation of molybdenite, the mineral pulp is commonly treated with nonpolar oil additives to promote hydrophobicity and to form an oil bridge between ultrafine molybdenite particles for agglomeration. In this study, dodecane was chosen as a model oil to investigate the flotation mechanisms of molybdenite with nonpolar oil. The interaction forces between a micrometer-sized dodecane droplet and the molybdenite basal plane in various electrolyte solutions were directly measured by the atomic force microscope droplet probe technique. The effects of added salts, ionic strength, and solution pH on interaction forces were evaluated by considering van der Waals, electrical double-layer (EDL), and hydrophobic forces. The experimentally measured force curves were found to agree well with the Reynolds lubrication model and the augmented Young-Laplace equation. The results show that the competition between repulsive EDL forces and attractive hydrophobic forces was directly responsible for oil-molybdenite attachment behavior. High pH and low salinity (<24 mM NaCl) led to strong repulsive EDL forces, which stabilized the interaction and prevented the attachment of oil to molybdenite. Both low pH and high salinity facilitated the attachment of oil to molybdenite through the depression of EDL force, allowing attractive hydrophobic force to dominate. The hydrophobic attraction was quantified with an exponential decay length of 1.0 ± 0.1 nm. Furthermore, calcium ions decreased the magnitude of the surface potentials of both oil and molybdenite more than that seen with the same ionic strength of sodium ions, suggesting the suppressed EDL repulsion. This study provides quantitative information about the surface forces between oil and the molybdenite basal plane and an improved understanding of the fundamental interaction mechanisms governing molybdenite recovery by mineral flotation.

Probing Anisotropic Surface Properties of Illite by Atomic Force Microscopy.

For the purpose of understanding the colloidal behaviors of illite in mineral processing, probing the surface charging property of illite is of great significance. This research explored the edge and basal surfaces of illite using an atomic force microscope (AFM). The interaction forces between Si/Si3N4 probes and illite edge/basal surfaces were measured, respectively, at different pH values in 10 mM KCl solutions. Theoretical Derjaguin-Landau-Verwey-Overbeek forces were matched up with the measured forces to derive the surface potentials of the two surfaces. On the illite basal surface, an attractive force occurred at pH 3.0, while repulsive forces dominated from pH 5.0 to 10.0. On the illite edge surface, a slight attractive force was also obtained at pH 3.0. However, the interaction changed into repulsion at pH 5.0, and this repulsive force increased gradually from pH 6.0 to 10.0. Illite basal and edge surfaces were both negatively charged, but the basal surface exhibited more negative charges than the edge surface from pH 3.0 to 10.0. Increasing solution pH from 3.0 to 10.0, there was no detection of the point of zero charge (PZC) of the illite basal surface; however, the PZC of the illite edge surface should have occurred at a pH slightly lower than 3.0. This is the first time that surface potentials of illite edge and basal surfaces were attained separately by direct force measurements. These findings provide insights into the colloidal behaviors of illite in mineral processing and oil sands extraction.