Preliminary investigation of polymer-based in situ passive samplers for mercury and methylmercury

Methylmercury sorption to polyethylene terephthalate (PET) fibers and relevance to environmental exposure

Considerable amounts of polyethylene terephthalate (PET) microplastic fibers are released into the environment by the laundering of polyester clothing. Microplastic fibers can be ingested by organisms in the environment. Therefore, it has been suggested that microplastic fibers act as vectors for adsorbed contaminants, which are subsequently desorbed in the gut of the organism. We undertook sorption isotherm experiments at pH 6, 7, and 8 to quantify the sorption of methylmercury (MeHg) to PET fibers. Sorption isotherms were fit to Langmuir, Freundlich, and Brunauer-Emmett-Teller models. Sorption decreased with increasing pH, which can be explained by physisorption on the negatively charged PET surfaces and the greater presence of neutral or negatively charged MeHg species at higher pH. We used the parameters obtained by the model fits to predict the likely concentration of MeHg on PET microplastic fibers in aquatic ecosystems with environmentally realistic MeHg concentrations. We calculated MeHg concentrations on PET microplastic fibers to be four orders of magnitude lower than previously observed concentrations of MeHg in seston (suspended particles comprising algae and bacteria) at the base of the aquatic food web. The results indicate that the presence of PET microplastic fibers in the environment do not elevate the MeHg exposure to organisms that ingest fibers in the environment.

A review of peeper passive sampling approaches to measure the availability of inorganics in sediment porewater

Sediment porewater dialysis passive samplers, also known as "peepers," are inert containers with a small volume of water (usually 1-100 mL) capped with a semi-permeable membrane. When exposed to sediment over a period of days to weeks, chemicals (typically inorganics) in sediment porewater diffuse through the membrane into the water. Subsequent analysis of chemicals in the peeper water sample can provide a value that represents the concentrations of freely-dissolved chemicals in sediment, a useful measurement for understanding fate and risk. Despite more than 45 years of peeper uses in peer-reviewed research, there are no standardized methods available, which limits the application of peepers for more routine regulatory-driven decision making at sediment sites. In hopes of taking a step towards standardizing peeper methods for measuring inorganics in sediment porewater, over 85 research documents on peepers were reviewed to identify example applications, key methodological aspects, and potential uncertainties. The review found that peepers could be improved by optimizing volume and membrane geometry to decrease the necessary deployment time, decrease detection limits, and provide sufficient sample volumes needed for commercial analytical laboratories using standardized analytical methods. Several methodological uncertainties related to the potential impact of oxygen presence in peeper water prior to deployment and oxygen accumulation in peepers after retrieval from sediment were noted, especially for redox-sensitive metals. Additional areas that need further development include establishing the impact of deionized water in peeper cells when used in marine sediment and use of pre-equilibration sampling methods with reverse tracers allowing shorter deployment periods. Overall, it is expected that highlighting these technical aspects and research needs will encourage work to address critical methodological challenges, aiding in the standardization of peeper methods for measuring porewater concentrations at contaminated regulatory-driven sediment sites.

Versatile in silico modeling of XAD-air partition coefficients for POPs based on abraham descriptor and temperature

The concentration of persistent organic pollutants (POPs) makes remarkable difference to environmental fate. In the field of passive sampling, the partition coefficients between polystyrene-divinylbenzene resin (XAD) and air (i.e., K_XAD-A) are indispensable to obtain POPs concentration, and the K_XAD-A is generally thought to be governed by temperature and molecular structure of POPs. However, experimental determination of K_XAD-A is unrealistic for countless and novel chemicals. Herein, the Abraham solute descriptors of poly parameter linear free energy relationship (pp-LFER) and temperature were utilized to develop models, namely pp-LFER-T, for predicting K_XAD-A values. Two linear (MLR and LASSO) and four nonlinear (ANN, SVM, kNN and RF) machine learning algorithms were employed to develop models based on a data set of 307 sample points. For the aforementioned six models, R²_adj and Q²_ext were both beyond 0.90, indicating distinguished goodness-of-fit and robust generalization ability. By comparing the established models, the best model was observed as the RF model with R²_adj = 0.991, Q²_ext = 0.935, RMSE_tra = 0.271 and RMSE_ext = 0.868. The mechanism interpretation revealed that the temperature, size of molecules and dipole-type interactions were the predominant factors affecting K_XAD-A values. Concurrently, the developed models with the broad applicability domain provide available tools to fill the experimental data gap for untested chemicals. In addition, the developed models were helpful to preliminarily evaluate the environmental ecological risk and understand the adsorption behavior of POPs between XAD membrane and air.

Uptake Mechanisms of a Novel, Activated Carbon-Based Equilibrium Passive Sampler for Estimating Porewater Methylmercury

We describe the validation of a novel polymeric equilibrium passive sampler comprised of agarose gel with embedded activated carbon particles (ag+AC), to estimate aqueous monomethylmercury (MeHg) concentrations. Sampler behavior was tested using a combination of idealized media and realistic sediment microcosms. Isotherm bottle experiments with ag+AC polymers were conducted to constrain partitioning to these materials by various environmentally relevant species of MeHg bound to dissolved organic matter (MeHgDOM) across a range of sizes and character. Log of partitioning coefficients for passive samplers (Kps ) ranged from 1.98 ± 0.09 for MeHg bound to Suwannee River humic acid to 3.15 ± 0.05 for MeHg complexed with Upper Mississippi River natural organic matter. Reversible equilibrium exchange of environmentally relevant MeHg species was demonstrated through a series of dual isotope-labeled exchange experiments. Isotopically labeled MeHgDOM species approached equilibrium in the samplers over 14 days, while mass balance was maintained, providing strong evidence that the ag+AC polymer material is capable of equilibrium measurements of environmentally relevant MeHg species within a reasonable deployment time frame. Samplers deployed across the sediment-water interface of sediment microcosms estimated both overlying water and porewater MeHg concentrations within a factor of 2 to 4 of measured values, based on the average measured Kps values for species of MeHg bound to natural organic matter in the isotherm experiments. Taken together, our results indicate that ag+AC polymers, used as equilibrium samplers, can provide accurate MeHg estimations across many site chemistries, with a simple back-calculation based on a standardized Kps. Environ Toxicol Chem 2022;41:2052-2064. © 2022 SETAC.

Contaminated aquatic sediments

Aquatic sediments are contaminated by different anthropogenic activities and natural deposition. This review manuscript has discussed on published manuscript in 2019 based on monitoring and identification of contaminants, GIS application and isotopic evaluation for monitoring of pollutants, physicochemical and biochemical fate and transport of the pollutants as well as remediation and toxicity analysis so that environmental and ecological impacts due to pollution can be minimized.

Contaminated aquatic sediments

The remediation of contaminated aquatic sediments requires a range of expertise from assessment (investigation, risk evaluations, modeling, and remedy selection) to design and construction. Research in 2019 has added to knowledge on optimizing the use of passive samplers for assessing chemical concentrations in sediment porewater. The porewater and black carbon appear to be better predictors of contaminant bioaccumulation than total organic carbon alone. This has led to better characterization of potential risk at sediment sites. Tools to identify and model sources of chemicals have been developed and used particularly for some metals, polynuclear aromatic hydrocarbons and polychlorinated biphenyls. There is great emphasis on beneficially using dredged sediment, treating it as a resource rather than a waste. Amendments used in sediment caps continue to be refined including the use of activated carbon within the caps and by itself. A technique involving 16S rRNA has been established as a means of identifying microbiological composition that naturally degrade contaminants. © 2020 Water Environment Federation PRACTITIONER POINTS: Sediment capping technology continues to advance Sampling and testing methods continue to be refined Natural processes such as biodegradation are being better understood Beneficial use of dredged sediment continue to be emphasized.

Versatile modelling of polyoxymethylene-water partition coefficients for hydrophobic organic contaminants using linear and nonlinear approaches

Environmental fate or transport of hydrophobic organic contaminants (HOCs) depends on the partitioning properties of compounds within various environmental phases. Due to the wide application of polyoxymethylene (POM) in the passive sampling technique, several in silico models were developed to predict POM-water partition coefficients (K_POM-w) in accordance with the guidelines of the Organization for Economic Cooperation and Development (OECD). It is an attempt to combine conventional linear method (multiple linear regression, MLR) and popular nonlinear algorithm (artificial neural network, ANN) for estimating partition coefficients of HOCs. All models were performed on a dataset of 210 chemicals from 13 different classes. The polyparameter linear free energy relationship (pp-LFER) model included 5 molecular descriptors, namely, E, S, A, B and V, and predicted log K_POM-w with R²_adj of 0.825. The values of statistical parameters including R²_adj, Q²_ext, RMSE_tra and RMSE_ext for quantitative structure-property relationship (QSPR)-MLR and QSPR-ANN models with four descriptors (ALOGP, MeanDD, E1m and Mor24s) were: (0.928, 0.877, 0.498 and 0.649) and (0.943, 0.905, 0.443 and 0.571), with high similarity for both models, which confirmed the robustness, significance, and remarkable prediction accuracy of the QSPR models. Moreover, the mechanism interpretation revealed that the molecular volume and hydrophobicity had a major impact on distribution procedure of HOCs. The models developed herein, with the broad applicability domain (AD), provide suitable tools to fill the experimental data gap for untested chemicals and help researchers better understand the mechanistic basis of adsorption behavior of POM.