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Remedial investigations of sites contaminated with legacy pollutants like polychlorinated biphenyls (PCBs) have traditionally focused on mapping sediment contamination to develop a site conceptual model and select remedy options. Ignoring dissolved concentrations that drive transport and bioaccumulation often leads to an incomplete assessment of ongoing inputs to the water column and overestimation of potential effectiveness of sediment remediation. Here, we demonstrate the utility of codeployment of passive equilibrium samplers and freshwater mussels as dual lines of evidence to identify ongoing sources of PCBs from eight main tributaries of the Anacostia River in Washington, DC, that has been historically polluted from industrial and other human activities. The freely dissolved PCB concentrations measured using passive samplers tracked well with the accumulation in mussels and allowed predictions of biouptake within a factor of 2 for total PCBs and a factor of 4 for most congeners. One tributary was identified as the primary source of PCBs to the water column and became a focus of additional ongoing investigations. Codeployment of passive samplers and mussels provides strong lines of evidence to refine site conceptual models and identify ongoing sources critical to control to achieve river water quality standards and reduce bioaccumulation in the aquatic food web.

We evaluated the precision and accuracy of multilaboratory measurements for determining freely dissolved concentrations (C

The freely dissolved concentration of hydrophobic pollutants in sediment porewater (

Bioaccumulation of hydrophobic pollutants in an aquatic food web is governed by exposure concentrations in sediment and water phases and by complex trophic interactions among the various species. We demonstrate that biological interactions and exposure from the chemical environment can be deconvoluted for aquatic food webs to allow clearer assessments of the role of thermodynamic drivers from the sediment and surface water phases. We first demonstrate the feasibility of this deconvolution mathematically for hypothetical food webs with 3 and 4 interacting species and for more realistic real-world food webs with >10 species of aquatic organisms (i.e., the freshwater lake food web in Western Lake Erie [ON, Canada] and the marine food web in New Bedford Harbor [MA, USA]). Our results show both mathematically (for the simple food webs) and computationally (for the more complex food webs) that a deconvoluted food web model parameterized for site-specific conditions can predict the bioaccumulation of polychlorinated biphenyls in aquatic organisms same as existing complex food web models. The merit of this approach is that once the thermodynamic and biological contributions to food web bioaccumulation are computed for an ecosystem, the deconvoluted model provides a relatively simple approach for calculating concentrations of chemicals in organisms for a range of possible surface water and sedimentary concentrations. This approach is especially useful for calculating bioaccumulation of pollutants from freely dissolved concentrations measured using passive sampling devices or predicted by fate and transport models. The deconvoluted approach makes it possible to develop regulatory guidelines for a set of surface water and sediment (or porewater) concentration combinations for a water body that is able to achieve a risk-based target for fish concentration. Environ Toxicol Chem 2021;40:2145-2155. © 2021 SETAC.

Semi-volatile organic compounds like polychlorinated biphenyls (PCBs) undergo diffusive exchange flux between a water body and the overlying air. The magnitude of this exchange can be a substantial component of the overall pollutant mass balance and needs to be determined accurately to identify major pollutant sources to the water body and to plan appropriate remedies. For the PCB-impacted Anacostia River in Washington DC (USA), quantification of air-water exchange has been a major data gap. In the present study, polyethylene passive samplers were used to measure PCB concentrations in air phase at six locations in DC over a period of one year to capture spatial and seasonal variations. Concurrent water phase PCB measurements were used to quantify the direction and magnitude of air-water exchange in the Anacostia River. Two locations had nearly an order of magnitude higher air phase PCB concentrations that could be related to localized sources. Remaining four locations provided similar air phase PCB concentrations that averaged from 270 ± 44 pg/m

Biogas is considered to be one of the potential and viable renewable energy resources. However, the presence of CO2 in biogas increases the cost of its transportation. Therefore, the removal of CO2 is of utmost essential to ensure the economic viability of the bio-gas utilisation technology. Among the various routes, pressure swing adsorption (PSA) may be considered more economically viable when adsorbent selectivity is high and heat of adsorption is low. In this work, we have synthesized mesoporous cerium oxide (CeO2) and zirconium hydroxide (Zr(OH)4) which possess approximately two orders of magnitude higher selectivity for the removal of CO2 from biogas mixture compared to commercial zeolite (Na-Zeolite Y) and commercial granular activated carbon. In addition, the methane slip in CeO2 (0.16%) was five times lower than Zr(OH)4 (0.62%) and two orders of magnitude lower than activated carbon (18%). The high selectivity and low methane slip of ceria can be attributed to the large number of heterogeneous sites available for selective adsorption of CO2. Based on our results on CO2 selectivity and methane loss, we conclude that CeO2 could be a potential adsorbent for biogas purification using PSA.

The first full-scale remediation project in North America to use the direct placement of activated carbon (AC) into sediments was completed in 2013 in a 2-ha lake on the St. Jones River in ...

Polymerized apple pomace (PoAP) surface was evaluated as adsorbent for the removal of Pb+2, Cd+2, and Ni+2 ions from aqueous solution. PoAP was characterized by FTIR, SEM, EDS, XRD, and BET surface area analyzer. Furthermore, the adsorption influencing parameters such as dose, pH, time, concentration, and temperature were optimized for maximum removal of metal ions from aqueous solution. The maximum monolayer adsorption capacity of PoAP was found to be 106, 34.12, and 19.45 mg g−1, for Pb+2, Cd+2, and Ni+2 ions respectively, using the Langmuir isotherm model. The rate of adsorption was evaluated using pseudo-second order kinetics and intra-particle diffusion. The adsorption data followed pseudo-second order kinetic with the correlation coefficient (r 2) from 0.99–1 at all concentration. Thermodynamic study revealed endothermic nature of Pb+2 and Cd+2 adsorption and exothermic for Ni+2 ions. The rate of adsorption for binary and tertiary mixtures of Pb+2, Ni+2, and Cd+2 metal ion was studied using the ideal adsorbed solution theory. The regeneration study revealed that PoAP could be re-utilized up to 4 cycles for Pb+2 and 2 cycles for Cd+2 and Ni+2 ions. PoAP was successfully applied to real industrial wastewater for the removal of Pb+2, Cd+2, and Ni+2 ions.