Analytical Chemistry
DOI: 10.1021/acs.analchem.3c01383
Bioavailability and Toxicity Models of Copper to Freshwater Life: The State of Regulatory Science
Abstract
Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness-based single-linear regression equations, water-effect ratios (WERs), biotic ligand models (BLMs), and multiple-linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness-based versus MLR-based criteria equations. The WER approach was shown to be inherently highly biased. The hardness-based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site-specific testing would be needed to determine reliable Cu criteria for such settings. The hardness-based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness-criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR-based USEPA-style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;00:1–35. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Pharmaceuticals and Personal Care Products in the Aquatic Environment: How Can Regions at Risk be Identified in the Future?
Abstract
Pharmaceuticals and personal care products (PPCPs) are an indispensable component of a healthy society. However, they are well established environmental contaminants, and many can elicit biological disruption in exposed organisms. It is now a decade since the Society of Environmental Toxicology and Chemistry (SETAC) published its landmark review of PPCPs in the environment (Boxall et al., 2012). Here we discuss key research priorities for the next 10 years with an aim on how regions where PPCPs pose the greatest risk to environmental and human health, either now or in the future, can be identified. Specifically, we discuss why this problem is of importance and review our current understanding of PPCPs in the aquatic environment. Foci include PPCP occurrence and what drives their environmental emission as well as our ability to both quantify and model their distribution. We highlight critical areas for future research including the involvement of citizen science for environmental monitoring and using modelling techniques to bridge the gap between research capacity and needs. As prioritisation of regions in need of environmental monitoring is needed to assess future/current risk, we also propose four criteria with which this may be achieved. Applying these criteria to available monitoring data we narrow the focus on where monitoring efforts for PPCPs are most urgent. Specifically, 19 cities across Africa, Central America, the Caribbean, and Asia were highlighted as priorities for future environmental monitoring and risk characterisation. Together, this informs our suggestion of four priority research questions for the next 10 years.
A toxicokinetic‐toxicodynamic modelling workflow assessing the quality of input mortality data
Abstract:
Toxicokinetic-toxicodynamic (TKTD) models simulate organismal uptake and elimination of a substance (TK) and its effects on the organism (TD). The Reduced General Unified Threshold model of Survival (GUTS-RED) is a TKTD modelling framework that is well established for aquatic risk assessment to simulate effects on survival. TKTD models are applied in three steps: parameterization based on experimental data (calibration), comparing predictions to independent data (validation) and prediction of endpoints under environmental scenarios. Despite a clear understanding of GUTS-RED predictions’ sensitivity to the model parameters, the influence of the input data on the quality of GUTS-RED calibration and validation is not systematically explored. We analyzed performance of GUTS-RED calibration and validation based on a unique, comprehensive dataset, covering different types of substances, exposure patterns and aquatic animal species taxa that are regularly used for risk assessment of plant protection products. We developed a software code to automatically calibrate and validate GUTS-RED against survival measurements from 59 toxicity tests and calculate selected model evaluation metrics. To assess whether specific survival data sets were better suited for calibration or validation, we applied a design where all possible combinations of studies for the same species-substance combination are used for calibration and validation. We found that uncertainty of calibrated parameters was lower when the full range of effects (i.e. from high survival to high mortality) was covered by input data. Increasing the number of toxicity studies used for calibration, further decreased parameter uncertainty. Including data from both acute and chronic studies as well as studies under pulsed and constant exposure in model calibrations improved model predictions on different types of validation data. Using our results we derive a workflow, including recommendations for the sequence of modelling steps from the selection of input data to a final judgement on the suitability of GUTS-RED for the dataset.
Interactive Effects of Copper‐Silver Mixtures at the Intestinal Epithelium of Rainbow Trout: an In‐Vitro Approach
ABSTRACT
While metals are present in mixture in the environment, metal toxicity studies are usually conducted on an individual metal basis. There is a paucity of data in the existing literature regarding specific metal-metal interactions and their effect on metal toxicity and bioavailability. Here, we studied interactions of silver-copper mixture at the intestinal epithelium using an intestinal cell line derived from rainbow trout (Oncorhynchus mykiss), the RTgutGC. Exposures were conducted in media containing different chloride concentrations (low chloride, 1 mM and high chloride, 146 mM) thus resulting in different metal speciation. Cytotoxicity was evaluated based on two endpoints, cell metabolic activity and cell membrane integrity. Silver-copper mixture toxicity was assessed using two designs: the independent action (IA) and concentration addition (CA). Metal mixture bioavailability was studied by exposing cells to 500 nM of Ag or Cu in single or mixture exposure (i.e., 500 nM of Cu plus 500 nM of Ag). We found an antagonistic effect in the low chloride medium and an additive/synergistic effect in the high chloride medium. We found that copper (Cu) dominates over silver (Ag) toxicity and bioavailability indicating a competitive inhibition when both metals are present as free metal ions in the exposure media which support our hypothesis. Our study also suggests different mechanisms of uptake of free metal ions and metal complexes. This study adds valuable information to our understanding of the role of metal speciation on metal mixture toxicity and bioavailability.
Bioaccumulation of Linear Siloxanes in Fish
Abstract
The bioaccumulation behavior, including the uptake, internal distribution, depuration, and biotransformation rates of three widely used linear methyl-siloxanes was investigated in Rainbow trout. Dietary uptake efficiencies of L3, L4, and L5 were 15% (3.3% SE), 8.6% (1.4% SE) and 15% (1.8% SE), respectively and for L3 and L4 were well below those of non-metabolizable reference chemicals with similar octanol-water partition coefficients, suggesting significant intestinal biotransformation of L3 and L4. Somatic biotransformation rate constants were 0.024 (0.003 SE) d-1 for L3; 0.0045 (0.0053 SE) d-1 for L4; and could not be determined for L5. Lipid-normalized biomagnification factors for L3, L4 and L5 were 0.24 (0.02 SE), 0.24 (0.01 SE) and 0.62 (0.05 SE) kg-lipid kg-lipid-1, respectively. Bioconcentration factors standardized to a 5% lipid content fish (BCF5%) for water in Canadian oligotrophic lakes with a dissolved organic carbon content of 7.1 mg L-1were 2787 (354 SE) for L3, 2689 (312 SE) for L4, and 1705 (418 SE) L kg-ww-1, respectively and 3085 (392 SE) for L3, 4227 (490 SE) for L4, and 3831 (938 SE) L kg-ww-1 in water with a dissolved organic carbon content of 2.0 mg L-1. A comparison of 238 bioaccumulation profiles for 166 different chemicals show that the bioaccumulation profiles for L3, L4 and L5 are vastly different from that of other very hydrophobic compounds found in the environment.
Substituted effects on bonding characteristics of cyclopentane‐1,3‐diyl diradicals monitored by time‐resolved infrared spectroscopy
Bonding properties of singlet and triplet cyclopentane-1,3-diyl diradicals (DRs) having C=O and C≡N groups (S-DR3 and T-DR3) were investigated by time-resolved IR spectroscopy. The C=O and C≡N wavenumber shifts observed upon the formation of S-DR3 and T-DR3 were both quite different from each other, indicating that the effects of the unpaired electrons to the C=O and C≡N bond properties in DR3 strongly depend on its spin multiplicity. The observed difference was discussed based on a resonance hybrid of DRs.
Abstract
Cyclopentane-1,3-diyl diradicals (DRs) provide excellent opportunities to study the properties of diradicals because their lifetimes can be significantly lengthened to up to milliseconds with the introduction of proper substituents. This study investigated the bonding characteristics of singlet and triplet DRs having C=O and p-cyanophenyl groups (S-DR3 and T-DR3) by monitoring the photo-induced formation of the diradicals from their precursor azo compounds using time-resolved IR (TR-IR) spectroscopy. Upon the formation of S-DR3, a C=O stretching wavenumber was upshifted by 22 cm−1, whereas a C≡N stretching one was downshifted by 12 cm−1. The observed shifts indicate that the unpaired electrons increase and decrease the C=O and C≡N bond orders, respectively. The effects of the unpaired electrons in S-DR3 were similar to those observed in our previous TR-IR studies on a singlet cyclopentane-1,3-diyl diradical having C=O but no C≡N groups (S-DR2) and on that having C≡N but no C=O groups (S-DR1), respectively. Contrastingly, upon the formation of T-DR3, the C=O wavenumber was downshifted by 16 cm−1, indicating that the unpaired electrons decrease the C=O bond order. More notably, no detectable shifts were observed in the C≡N stretching wavenumber. These observations are not clearly explained by a model suggested in the previous studies on S-DRs. Here, we discuss and propose a more elaborated resonance hybrid of DRs that can explain the directions and relative magnitudes of the observed wavenumber shifts irrespective of spin multiplicities. We expect that the findings and suggestions presented here will stimulate research in both organic and theoretical chemistry.
Role of Labile Methanol on Bio‐inspired Catalytic Activity of Zn(II) based Compound: An Experimental and Theoretical Investigation
Two Zn(II) based compounds, [Zn2L1(OAc)3(MeOH)] (1) and [Zn2L2(OAc)3]n (2) have been reported where HL1 is (E)-4-Bromo-2-methoxy-6-(((2-morpholino ethyl)imino) methyl)phenol and HL2 is (E)-4-Bromo-2-methoxy-6-(((2-(piperazine-1-yle)ethyl)imino)methyl) phenol. SCXRD analysis unveils vivid change in structural arrangements and dimensionality from 1 to 2 due to change in coordinated atom from oxygen to nitrogen of the ligands. SCXRD study shows that compound 1 is dinuclear but compound 2 has a 1-dimensional polymeric structure having helical chain. Structural diversity greatly influences the catalytic activity. Compound 1 acts as excellent catalyst for conversion of 3, 5-di-tert-butyl catechol (3, 5-DTBC) to 3, 5-di-tert-butylbenzoquinone (3, 5-DTBQ) with the turnover number (kcat) value of 34.94 sec-1. Further, compound 1 reveals phosphatase like activity for conversion of disodium salt of (4-nitrophenyl)-phosphate hexahydrate to p-nitrophenolate with the kcat value of 24.64 sec-1. Amusingly, compound 2 does not show any catalytic activity. To correlate this distinctly different catalytic behavior of two compounds, DFT calculation was carried out. The calculation reveals that detachment of coordinated methanol from coordination sphere of zinc in compound 1 is energytically favourable which creates room for substrate binding, resulting high catalytic activity. Whereas in compound 2, detachment of piperazine or Zn-O of –COOH group are energetically unfavouable, resulting no catalytic activity.
Novel Corncob‐Based Catalytic Biodiesel Production Process: Experiments, Modeling, and Simulation
A highly active corncob-based solid acid catalyst was used for the esterification of oleic acid. The study involves the design and synthesis of the new catalyst, optimization of experimental conditions, modeling of experimental data to obtain kinetic parameters, and simulation of the continuous biodiesel production process in Aspen Plus software by incorporating the obtained kinetic parameters.
Abstract
A functionalized catalyst for catalyzed biodiesel production via a heterogeneous route is a highly focused area to lower the cost of production and mitigate the drawbacks of homogeneously catalyzed reactions. Production aspects such as parameter study, kinetics modeling, and simulation of continuous process flowsheets incorporating kinetic parameters are scarce in the literature. In the current work, a sulfonic group-functionalized porous carbonaceous catalyst based on corncob was used for the esterification of oleic acid. The Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model was found to best fit to correlate the experimental data and thus applied to deduce the kinetic parameters. The obtained kinetic parameters were incorporated into the Aspen Plus simulator to simulate the continuous biodiesel production process. The catalyst showed a strong affinity for oleic acid which enhances the reaction rate.
Recent Advancements in Metal‐Organic Framework‐Based Membranes for Hydrogen Separation: A Review
Recent advancements in the development of metal-organic framework-based membranes using various fabrication strategies for hydrogen gas separation are covered in this review.
Abstract
Metal-organic frameworks (MOFs) are promising porous materials that have huge potential for gas separation when put in the membrane configuration. MOFs have huge potential due to certain salient features of the MOFs such as excellent pore size, ease of tuning the pore chemistry, higher surface area, and chemical and thermal stabilities. MOFs have been explored for various gas separation and storage applications. This review discusses various approaches for fabricating MOFs-based membranes for the separation of H2 gas from a variety of feeds having various gases CO2, CO, N2, and CH4 as impurities. The emphasis has been put on three types of membranes for H2 separation which include MOFs-based hollow fibrous/tubular/disk membranes, MOFs-based mixed matrix membranes (MMMs), and MOFs-based stand-alone membranes. In addition, various challenges such as reducing inhomogeneity between MOFs and polymeric matrices have also been discussed. Similarly, the approaches to successfully decorating MOFs on different supports in different configurations have been explained. The possible ways of improving the MOFs-based membranes for H2 have also been discussed.