Codeployment of Passive Samplers and Mussels Reveals Major Source of Ongoing PCB Inputs to the Anacostia River in Washington, DC.

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.

Seasonal trends of PCBs in air over Washington DC reveal localized urban sources and the influence of Anacostia River.

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/m3 (summer) to 32 ± 4.3 pg/m3 (winter). ∑PCB water-air exchange fluxes were positive across all seasons, with net PCB volatilization of 180 ± 19 g/year from the surface water. Volatilization rate was an order of magnitude lower than previously estimated from a fate and transport model. PCB load from atmospheric deposition based on previous studies in this watershed was an order of magnitude lower than the volatilization rate. Results refuted a long-standing understanding of the air phase serving as a source of PCBs to the river as per the currently approved Total Maximum Daily Load assessment. The study demonstrates the utility of passive air phase measurements in delineating local terrestrial sources of pollution as well as providing estimates for air-water exchange to complete a robust mass balance for semi-volatile pollutants in an urban river.

Equilibrium Porewater Measurement of PCBs and PAHs Using Direct Water Extraction and Comparison with Passive Sampling.

The freely dissolved concentration of hydrophobic pollutants in sediment porewater (Cpw) is a critical driver for exposure to aquatic organisms, bioaccumulation, toxicity, and flux across interfaces. In this research, we compared direct porewater extraction and passive sampling for Cpw measurements of a range of PCBs and PAHs in field-collected sediments. The direct water extraction method provided accurate quantification of Cpw for low to moderately hydrophobic PCB and PAH compounds (log Kow < 6.5) that compared well with independent measurements performed using four passive sampling methods. Direct water extraction was adequate to assess narcosis toxicity of PAHs to benthic organisms that is driven by the concentrations of low to moderately hydrophobic PAHs (naphthalene to chrysene), even for a hypothetical sediment that had a tenth of the PAH concentrations of the study sediments and was assessed to be nontoxic. Prediction of PCB bioaccumulation in benthic organisms agreed within 50% for all measurement methods, but it was apparent that for less contaminated sediments, the direct water extraction method would likely have detection limit challenges, especially for the strongly hydrophobic PCBs. To address the uncertainty of the Cpw measurement of the strongly hydrophobic compounds and naphthalene, a new extrapolation approach is demonstrated that can be applicable for both direct water extraction and passive sampling methods.

Interlaboratory Study of Polyethylene and Polydimethylsiloxane Polymeric Samplers for Ex Situ Measurement of Freely Dissolved Hydrophobic Organic Compounds in Sediment Porewater.

We evaluated the precision and accuracy of multilaboratory measurements for determining freely dissolved concentrations (Cfree ) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment porewater using polydimethylsiloxane (PDMS) and low-density polyethylene (LDPE) polymeric samplers. Four laboratories exposed performance reference compound (PRC) preloaded polymers to actively mixed and static ex situ sediment for approximately 1 month; two laboratories had longer exposures (2 and 3 months). For Cfree results, intralaboratory precision was high for single compounds (coefficient of variation 50% or less), and for most PAHs and PCBs interlaboratory variability was low (magnitude of difference was a factor of 2 or less) across polymers and exposure methods. Variability was higher for the most hydrophobic PAHs and PCBs, which were present at low concentrations and required larger PRC-based corrections, and also for naphthalene, likely due to differential volatilization losses between laboratories. Overall, intra- and interlaboratory variability between methods (PDMS vs. LDPE, actively mixed vs. static exposures) was low. The results that showed Cfree polymer equilibrium was achieved in approximately 1 month during active exposures, suggesting that the use of PRCs may be avoided for ex situ analysis using comparable active exposure; however, such ex situ testing may not reflect field conditions. Polymer-derived Cfree concentrations for most PCBs and PAHs were on average within a factor of 2 compared with concentrations in isolated porewater, which were directly measured by one laboratory; difference factors of up to 6 were observed for naphthalene and the most hydrophobic PAHs and PCBs. The Cfree results were similar for academic and private sector laboratories. The accuracy and precision that we demonstrate for determination of Cfree using polymer sampling are anticipated to increase regulatory acceptance and confidence in use of the method. Environ Toxicol Chem 2022;41:1885-1902. © 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.

Deconvoluting Thermodynamics from Biology in the Aquatic Food Web Model.

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.

Methyl acrylate modified apple pomace as promising adsorbent for the removal of divalent metal ion from industrial wastewater.

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.