Disentangling associations between pubertal development, healthy activity behaviors, and sex in adolescent social networks.

With the onset of puberty, youth begin to choose their social environments and develop health-promoting habits, making it a vital period to study social and biological factors contextually. An important question is how pubertal development and behaviors such as physical activity and sleep may be differentially linked with youths' friendships. Cross-sectional statistical network models that account for interpersonal dependence were used to estimate associations between three measures of pubertal development and youth friendships at two large US schools drawn from the National Longitudinal Study of Adolescent to Adult Health. Whole-network models suggest that friendships are more likely between youth with similar levels of pubertal development, physical activity, and sleep. Sex-stratified models suggest that girls' friendships are more likely given a similar age at menarche. Attention to similar pubertal timing within friendship groups may offer inclusive opportunities for tailored developmental puberty education in ways that reduce stigma and improve health behaviors.

Linear Free Energy Relationship for Predicting the Rate Constants of Munition Compound Reduction by the Fe(II)-Hematite and Fe(II)-Goethite Redox Couples.

Abiotic reduction by iron minerals is arguably the most important fate process for munition compounds (MCs) in subsurface environments. No model currently exists that can predict the abiotic reduction rates of structurally diverse MCs by iron (oxyhydr)oxides. We performed batch experiments to measure the rate constants for the reduction of three classes of MCs (poly-nitroaromatics, nitramines, and azoles) by hematite or goethite in the presence of aqueous Fe2+. The surface area-normalized reduction rate constant (kSA) depended on the aqueous-phase one-electron reduction potential (EH1) of the MC and the thermodynamic state (i.e., pe and pH) of the iron oxide-Feaq2+ system. A linear free energy relationship (LFER), similar to that reported previously for nitrobenzene, successfully captures all MC reduction rate constants that span 6 orders of magnitude: log(kSA)=(1.12±0.04)[0.53EH159mV-(pH+pe)]+(5.52±0.23). The finding that the rate constants of all the different classes of MCs can be described by a single LFER suggests that these structurally diverse nitro compounds are reduced by iron oxide-Feaq2+ couples through a common mechanism up to the rate-limiting step. Multiple mechanistic implications of the results are discussed. This study expands the applicability of the LFER model for predicting the reduction rates of legacy and emerging MCs and potentially other nitro compounds.

Thermodynamic Two-Site Surface Reaction Model for Predicting Munition Constituent Reduction Kinetics with Iron (Oxyhydr)oxides.

Iron (oxyhydr)oxides comprise a significant portion of the redox-active fraction of soils and are key reductants for remediation of sites contaminated with munition constituents (MCs). Previous studies of MC reduction kinetics with iron oxides have focused on the concentration of sorbed Fe(II) as a key parameter. To build a reaction kinetic model, it is necessary to predict the concentration of sorbed Fe(II) as a function of system conditions and the redox state. A thermodynamic framework is formulated that includes a generalized double-layer model that utilizes surface acidity and surface complexation reactions to predict sorbed Fe(II) concentrations that are used for fitting MC reduction kinetics. Monodentate- and bidentate Fe(II)-binding sites are used with individual oxide sorption characteristics determined through data fitting. Results with four oxides (goethite, hematite, lepidocrocite, and ferrihydrite) and four nitro compounds (NB, CN-NB, Cl-NB, and NTO) from six separate studies have shown good agreement when comparing observed and predicted surface area-normalized rate constants. While both site types are required to reproduce the experimental redox titration, only the monodentate site concentration controls the MC reaction kinetics. This model represents a significant step toward predicting the timescales of MC degradation in the subsurface.

Electron Transfer Energy and Hydrogen Atom Transfer Energy-Based Linear Free Energy Relationships for Predicting the Rate Constants of Munition Constituent Reduction by Hydroquinones.

No single linear free energy relationship (LFER) exists that can predict reduction rate constants of all munition constituents (MCs). To address this knowledge gap, we measured the reduction rates of MCs and their surrogates including nitroaromatics [NACs; 2,4,6-trinitrotoluene (TNT), 2,4-dinitroanisole (DNAN), 2-amino-4,6-dinitrotoluene (2-A-DNT), 4-amino-2,6-dinitrotoluene (4-A-DNT), and 2,4-dinitrotoluene (DNT)], nitramines [hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and nitroguanidine (NQ)], and azoles [3-nitro-1,2,4-triazol-5-one (NTO) and 3,4-dinitropyrazole (DNP)] by three dithionite-reduced quinones (lawsone, AQDS, and AQS). All MCs/NACs were reduced by the hydroquinones except NQ. Hydroquinone and MC speciations were varied by controlling pH, permitting the application of a speciation model to determine second-order rate constants (k) from observed pseudo-first-order rate constants. The intrinsic reactivity of MCs (oxidants) decreased upon deprotonation, while the opposite was true for hydroquinones (reductants). The rate constants spanned ∼6 orders of magnitude in the order NTO ≈ TNT > DNP > DNT ≈ DNAN ≈ 2-A-DNT > DNP- > 4-A-DNT > NTO- > RDX. LFERs developed using density functional theory-calculated electron transfer and hydrogen atom transfer energies and reported one-electron reduction potentials successfully predicted k, suggesting that these structurally diverse MCs/NACs are all reduced by hydroquinones through the same mechanism and rate-limiting step. These results increase the applicability of LFER models for predicting the fate and half-lives of MCs and related nitro compounds in reducing environments.

Antecedents to COVID-19 vaccine uptake among patients and employees in the Veterans Health Administration.

The present study sought to understand the antecedents to COVID-19 vaccination among those reporting a change in vaccine intention in order to improve COVID-19 vaccine uptake in the United States. We employed semi-structured interviews and one focus group discussion with vaccinated and unvaccinated Veterans Health Administration (VHA) employees and Veterans at three Veterans' Affairs medical centers between January and June 2021. A subset of these participants (n=21) self-reported a change in COVID-19 vaccine intention and were selected for additional analysis. We combined thematic analysis using the 5C scale (confidence, collective responsibility, complacency, calculation, constraints) as our theoretical framework with a constant comparative method from codes based on the SAGE Working Group on Vaccine Hesitancy. We generated 13 themes distributed across the 5C constructs that appeared to be associated with a change in COVID-19 vaccine intention. Themes included a trusted family member, friend or colleague in a healthcare field, a trusted healthcare professional, distrust of government or politics (confidence); duty to family and protection of others (collective responsibility); perceived health status and normative beliefs (complacency); perceived vaccine safety, perceived risk-benefit, and orientation towards deliberation (calculation); and ease of process (constraints). Key factors in promoting vaccine uptake included a desire to protect family; and conversations with as key factors in promoting vaccine uptake. Constructs from the 5C scale are useful in understanding intrapersonal changes in vaccine intentions over time, which may help public health practitioners improve future vaccine uptake.

In this study of the Veteran and VA employee population, we aimed to understand what factors led to a decision to receive a COVID-19 vaccine. As part of a quality improvement project, we interviewed individuals at three Veterans' Affairs sites in the first six months of 2021. We then used a smaller sample of 21 participants who reported a change in their intentions to receive a COVID-19 vaccine to analyze for this study. This analysis utilizes constructs from the 5C scale, which was developed to understand the conditions required for an individual to decide to receive a vaccine (confidence, collective responsibility, complacency, calculation, constraints). The coding process revealed a number of recurring themes across the interviews falling under each of the five constructs, but concepts relating to vaccine confidence (i.e., level of trust in those developing and disseminating the vaccine) were most common, and constraints (i.e., psychological and structural barriers that stand in the way of vaccination) appeared least frequently in our interviews. We found that significant motivators to receive the vaccine included a desire to protect family and conversations with trusted clinicians, particularly mental healthcare providers. Our study was unique in using the 5Cs to understand changes in vaccine changes over time. Findings show that change in vaccine attitudes is possible even in the presence of concerns and shed light on approaches that public health providers could use to improve vaccine and booster rates.

Ferrocyanide enhanced evaporative flux to remediate soils contaminated with produced water brine.

Accidental releases of highly saline produced water (PW) to land can impact soil quality. The release of associated salts can clog soil pores, disperse soil clays, and inhibit plants and other soil biota. This study explores a novel remediation technique using ferrocyanide to enhance the evaporative flux of soil porewater to transport dissolved salts to the soil surface, where crystallization then occurs. The addition of ferrocyanide modifies crystal growth that enhances salt transport, allowing salt efflorescence on the soil surface and physical removal. Release sites were simulated through beaker sand column experiments using two PWs collected from the Permian Basin. PW composition altered efflorescence, with up to ten times as much ferrocyanide required in PWs than comparable concentrations of pure NaCl solutions. The addition of EDTA reduced dissolved cation competition for the ferrocyanide ion, improving PW salt recovery at the soil surface. The speciation model, PHREEQC, was used to predict the onset of salt precipitation as a function of evaporative water loss and model the effect of aqueous ferrocyanide and EDTA speciation on efflorescence. The results highlight the utility of predictive modeling for optimizing additive dosages for a given release of PW.

Modeling the Reduction Kinetics of Munition Compounds by Humic Acids.

Dissolved organic matter (DOM) comprises a sizeable portion of the redox-active constituents in the environment and is an important reductant for the abiotic transformation of nitroaromatic compounds and munition constituents (NACs/MCs). Building a predictive kinetic model for these reactions would require the energies associated with both the reduction of the NACs/MCs and the oxidation of the DOM. The heterogeneous and unknown structure of DOM, however, has prohibited reliable determination of its oxidation energies. To overcome this limitation, humic acids (HAs) were used as model DOM, and their redox moieties were modeled as a collection of quinones of different redox potentials. The reduction and oxidation energies of the NACs/MCs and hydroquinones, respectively, via hydrogen atom transfer (HAT) reactions were then calculated quantum chemically. HAT energies have been used successfully in a linear free energy relationship (LFER) to predict second-order rate constants for NAC reduction by hydroquinones. Furthermore, a linear relationship between the HAT energies and the reduction potentials of quinones was established, which allows estimation of hydroquinone reactivity (i.e., rate constants) from HA redox titration data. A training set of three HAs and two NACs/MCs was used to generate a mean HA redox profile that successfully predicted reduction kinetics in multiple HA/MC systems.

System avoidance and social isolation: Mechanisms connecting police contact and deleterious health outcomes.

A growing body of literature suggests even routine or low-level contact with the criminal justice system impacts health outcomes. In this paper, I examine two mechanisms by which police contact contributes to deleterious health outcomes: system avoidance and social isolation. I use data from 12,016 respondents from the National Longitudinal Study of Adolescent to Adult Health, a longitudinal and nationally representative sample. Findings suggest system avoidance may be an important mechanism by which police stops shape health outcomes. Whether social isolation serves as a mechanism varies based on how it is measured. Results suggest police stops are associated with subjective feelings of loneliness, which in turn explained some of the association between police stops and health outcomes. Notably, women were more likely to exhibit system avoidance and poor health following police contact compared to men.

Attitudes and Intentions of US Veterans Regarding COVID-19 Vaccination.

Importance: Compared with the general population, veterans are at high risk for COVID-19 and have a complex relationship with the government. This potentially affects their attitudes toward receiving COVID-19 vaccines. Objective: To assess veterans' attitudes toward and intentions to receive COVID-19 vaccines. Design, Setting, and Participants: This cross-sectional web-based survey study used data from the Department of Veterans Affairs (VA) Survey of Healthcare Experiences of Patients' Veterans Insight Panel, fielded between March 12 and 28, 2021. Of 3420 veterans who were sent a link to complete a 58-item web-based survey, 1178 veterans (34%) completed the survey. Data were analyzed from April 1 to August 25, 2021. Exposures: Veterans eligible for COVID-19 vaccines. Main Outcomes and Measures: The outcomes of interest were veterans' experiences with COVID-19, vaccination status and intention groups, reasons for receiving or not receiving a vaccine, self-reported health status, and trusted and preferred sources of information about COVID-19 vaccines. Reasons for not getting vaccinated were classified into categories of vaccine deliberation, dissent, distrust, indifference, skepticism, and policy and processes. Results: Among 1178 respondents, 974 (83%) were men, 130 (11%) were women, and 141 (12%) were transgender or nonbinary; 58 respondents (5%) were Black, 54 veterans (5%) were Hispanic or Latino, and 987 veterans (84%) were non-Hispanic White. The mean (SD) age of respondents was 66.7 (10.1) years. A total of 817 respondents (71%) self-reported being vaccinated against COVID-19. Of 339 respondents (29%) who were not vaccinated, those unsure of getting vaccinated were more likely to report fair or poor overall health (32 respondents [43%]) and mental health (33 respondents [44%]) than other nonvaccinated groups (overall health: range, 20%-32%; mental health: range, 18%-40%). Top reasons for not being vaccinated were skepticism (120 respondents [36%] were concerned about side effects; 65 respondents [20%] preferred using few medications; 63 respondents [19%] preferred gaining natural immunity), deliberation (74 respondents [22%] preferred to wait because vaccine is new), and distrust (61 respondents [18%] did not trust the health care system). Among respondents who were vaccinated, preventing oneself from getting sick (462 respondents [57%]) and contributing to the end of the COVID-19 pandemic (453 respondents [56%]) were top reasons for getting vaccinated. All veterans reported the VA as 1 of their top trusted sources of information. The proportion of respondents trusting their VA health care practitioner as a source of vaccine information was higher among those unsure about vaccination compared with those who indicated they would definitely not or probably not get vaccinated (18 respondents [26%] vs 15 respondents [15%]). There were no significant associations between vaccine intention groups and age (χ24 = 5.90; P = .21) or gender (χ22 = 3.99; P = .14). Conclusions and Relevance: These findings provide information needed to develop trusted messages used in conversations between VA health care practitioners and veterans addressing specific vaccine hesitancy reasons, as well as those in worse health. Conversations need to emphasize societal reasons for getting vaccinated and benefits to one's own health.

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS).

3-Nitro-1,2,4-triazol-5-one (NTO) is a major and the most water-soluble constituent in the insensitive munition formulations IMX-101 and IMX-104. While NTO is known to undergo redox reactions in soils, its reaction with soil humic acid has not been evaluated. We studied NTO reduction by anthraquinone-2,6-disulfonate (AQDS) and Leonardite humic acid (LHA) reduced with dithionite. Both LHA and AQDS reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO), stoichiometrically at alkaline pH and partially (50-60%) at pH ≤ 6.5. Due to NTO and hydroquinone speciation, the pseudo-first-order rate constants (kObs) varied by 3 orders of magnitude from pH 1.5 to 12.5 but remained constant from pH 4 to 10. This distinct pH dependency of kObs suggests that NTO reactivity decreases upon deprotonation and offsets the increasing AQDS reactivity with pH. The reduction of NTO by LHA deviated continuously from first-order behavior for >600 h. The extent of reduction increased with pH and LHA electron content, likely due to greater reactivity of and/or accessibility to hydroquinone groups. Only a fraction of the electrons stored in LHA was utilized for NTO reduction. Electron balance analysis and LHA redox potential profile suggest that the physical conformation of LHA kinetically limited NTO access to hydroquinone groups. This study demonstrates the importance of carbonaceous materials in controlling the environmental fate of NTO.

Vaccine hesitancy as an opportunity for engagement: A rapid qualitative study of patients and employees in the U.S. Veterans Affairs healthcare system.

Although COVID-19 vaccines have been available to many U.S. Veterans Affairs (VA) healthcare system employees and Veteran patients since early 2021, vaccine receipt data indicates some groups are not receiving them. Our objective was to conduct a rapid qualitative assessment of Veterans' and VA employees' views on COVID-19 vaccination to inform clinical leaders' ongoing efforts to increase vaccine uptake across the VA. We employed semi-structured interviews and a focus group involving employees and Veterans as part of a quality improvement project between January and June 2021 at three VA medical centers. Thirty-one employees and 27 Veterans participated in semi-structured interviews; 5 Veterans from a national stakeholder organization participated in a focus group. Data were analyzed using directed content analysis, involving an a priori coding framework comprised of four domains with subcodes under each: contextual influences, barriers and facilitators, vaccine-specific issues, and VA/military experiences. We then classified initial codes into five categories of hesitancy: vaccine deliberation, dissent, distrust, indifference and skepticism. A subset of Veterans (n = 14) and employees (n = 8) identified as vaccine hesitant. Vaccine hesitancy categories were represented by subcodes of religion, culture, gender or socio-economic factors, perceptions of politics and policies, role of healthcare providers, and historical influences; (contextual influences); knowledge or awareness of vaccines, perceived susceptibility to COVID-19, and beliefs and attitudes about health and illness (barriers and facilitators); vaccine development process (vaccine-specific issues) and military experiences (VA/military factors). Facilitators involved talking with trusted others, ease of vaccine access, and perceptions of family and societal benefits of vaccines. Vaccine hesitancy is multi-faceted and likely requires multiple strategies for engaging in conversations to address Veteran and VA employee concerns. Messages should involve patient-centered communication strategies delivered by trusted healthcare providers and peers and should focus on addressing expected benefits for family, friends, and society.

A Unified Linear Free Energy Relationship for Abiotic Reduction Rate of Nitroaromatics and Hydroquinones Using Quantum Chemically Estimated Energies.

Determining the fate of nitroaromatic compounds (NACs) in the environment requires the use of predictive models for compounds and conditions for which experimental data are insufficient. Previous studies have developed linear free energy relationships (LFERs) that relate the thermodynamic energy of NAC reduction to its corresponding rate constant. We present a comprehensive LFER that incorporates both the reduction and oxidation half-reactions through quantum chemically calculated energies. Environ Toxicol Chem 2020;39:2389-2395. © 2020 SETAC.

Reduction of 3-Nitro-1,2,4-Triazol-5-One (NTO) by the Hematite-Aqueous Fe(II) Redox Couple.

3-Nitro-1,2,4-triazol-5-one (NTO) is an insensitive munition compound (MC) that has replaced legacy MC. NTO can be highly mobile in soil and groundwater due to its high solubility and anionic nature, yet little is known about the processes that control its environmental fate. We studied NTO reduction by the hematite-Fe2+ redox couple to assess the importance of this process for the attenuation and remediation of NTO. Fe2+(aq) was either added (type I) or formed through hematite reduction by dithionite (type II). In the presence of both hematite and Fe2+(aq), NTO was quantitatively reduced to 3-amino-1,2,4-triazol-5-one following first-order kinetics. The surface area-normalized rate constant (kSA) showed a strong pH dependency between 5.5 and 7.0 and followed a linear free energy relationship (LFER) proposed in a previous study for nitrobenzene reduction by iron oxide-Fe2+ couples, i.e., log kSA = -(pe + pH) + constant. Sulfite, a major dithionite oxidation product, lowered kSA in type II system by ∼10-fold via at least two mechanisms: by complexing Fe2+ and thereby raising pe, and by making hematite more negatively charged and hence impeding NTO adsorption. This study demonstrates the importance of iron oxide-Fe2+ in controlling NTO transformation, presents an LFER for predicting NTO reduction rate, and illustrates how solutes can shift the LFER by interacting with either iron species.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis.

A linear free energy model is presented that predicts the second-order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). Previously presented models use the one-electron reduction potential EH1(ArNO2) of the NAC reaction ArNO2+e-→ArNO2•- . If EH1(ArNO2) is not available, it has been proposed that EH1(ArNO2) be computed directly or estimated from the gas-phase electron affinity (EA). The model proposed uses the Gibbs free energy of the hydrogen atom transfer (HAT) reaction ArNO2+H•→ArNOOH• as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic energies. The available and proposed models are compared using experimentally determined second-order rate constants from 5 investigations from the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the HAT energy model and the experimental one-electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed EA has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed HAT reaction free energy produces a more reliable prediction of the NAC abiotic reduction second-order rate constant than previously available methods. The advantages of the proposed HAT energy model and its mechanistic implications are discussed as well. Environ Toxicol Chem 2020;39:1678-1684. © 2020 SETAC.

Childhood Polyvictimization and the Life Course: Associations With Depression and Crime.

Exposure to multiple forms of victimization has been shown to have increasingly negative outcomes, but their unique trajectory-setting effects have been largely unexplored. Using a life course approach, this article examines the life trajectories of child polyvictims. I use a nationwide sample including 3,652 respondents after cleaning and preparation. Seemingly unrelated regressions were used to predict depression and criminal behavior in childhood and adulthood. Results suggest that children who experience multiple forms of parental abuse tend to have life trajectories which grow increasingly worse through the life course. However, life trajectories of children experiencing violence outside the home have less persistent negative outcomes. Researchers and interventions should take differing life trajectories into account when attempting to aid different types of polyvictims.

Weight-of-Evidence Approach for Assessing Removal of Metals from the Water Column for Chronic Environmental Hazard Classification.

The United Nations and the European Union have developed guidelines for the assessment of long-term (chronic) chemical environmental hazards. This approach recognizes that these hazards are often related to spillage of chemicals into freshwater environments. The goal of the present study was to examine the concept of metal ion removal from the water column in the context of hazard assessment and classification. We propose a weight-of-evidence approach that assesses several aspects of metals including the intrinsic properties of metals, the rate at which metals bind to particles in the water column and settle, the transformation of metals to nonavailable and nontoxic forms, and the potential for remobilization of metals from sediment. We developed a test method to quantify metal removal in aqueous systems: the extended transformation/dissolution protocol (T/DP-E). The method is based on that of the Organisation for Economic Co-operation and Development (OECD). The key element of the protocol extension is the addition of substrate particles (as found in nature), allowing the removal processes to occur. The present study focused on extending this test to support the assessment of metal removal from aqueous systems, equivalent to the concept of "degradability" for organic chemicals. Although the technical aspects of our proposed method are different from the OECD method for organics, its use for hazard classification is equivalent. Models were developed providing mechanistic insight into processes occurring during the T/DP-E method. Some metals, such as copper, rapidly decreased (within 96 h) under the 70% threshold criterion, whereas others, such as strontium, did not. A variety of method variables were evaluated and optimized to allow for a reproducible, realistic hazard classification method that mimics reasonable worst-case scenarios. We propose that this method be standardized for OECD hazard classification via round robin (ring) testing to ascertain its intra- and interlaboratory variability. Environ Toxicol Chem 2019;38:1839-1849. © 2019 SETAC.

Method Development for Determining the Removal of Metals from the Water Column under Transformation/Dissolution Conditions for Chronic Hazard Classification.

An extension of the transformation/dissolution protocol (T/DP) was developed and evaluated as a tool to measure the removal of metals from the water column for chronic aquatic hazard classification. The T/DP extension (T/DP-E) consists of 2 parts: T/DP-E part 1, to measure metal removal from the water column via binding of metals to a substrate and subsequent settling, and T/DP-E part 2, to assess the potential for remobilization of metals following resuspension. The T/DP-E methodology (672-h [28-d] removal period, 1-h resuspension event, and 96-h resettling period) was tested using Cu, Co, and Sr solutions in the presence of a substrate. The metal removal rates varied from rapid removal for Cu to slower rates of removal for Co and Sr. The resuspension event did not trigger any increase in dissolved Cu, Co, or Sr. Additional 96-h experiments were conducted using dissolved Ni, Pb, Zn, and Ag and supported the conclusion that the T/DP-E is sufficiently robust to distinguish removal rates between metals with a wide range of reactivities. The proposed method provides a means to quantify the rate of metal removal from the water column and evaluate remobilization potential in a standardized and reliable way. Environ Toxicol Chem 2019;38:2032-2042. © 2019 SETAC.

Experimental Validation of Hydrogen Atom Transfer Gibbs Free Energy as a Predictor of Nitroaromatic Reduction Rate Constants.

Nitroaromatic compounds (NACs) are a class of prevalent contaminants. Abiotic reduction is an important fate process that initiates NAC degradation in the environment. Many linear free energy relationship (LFER) models have been developed to predict NAC reduction rates. Almost all LFERs to date utilize experimental aqueous-phase one-electron reduction potential ( EH1) of NAC as a predictor, and thus, their utility is limited by the availability of EH1 data. A promising new approach that utilizes computed hydrogen atom transfer (HAT) Gibbs free energy instead of EH1 as a predictor was recently proposed. In this study, we evaluated the feasibility of HAT energy for predicting NAC reduction rate constants. Using dithionite-reduced quinones, we measured the second-order rate constants for the reduction of seven NACs by three hydroquinones of different protonation states. We computed the gas-phase energies for HAT and electron affinity (EA) of NACs and established HAT- and EA-based LFERs for six hydroquinone species. The results suggest that HAT energy is a reliable predictor of NAC reduction rate constants and is superior to EA. This is the first independent, experimental validation of HAT-based LFER, a new approach that enables rate prediction for a broad range of structurally diverse NACs based solely on molecular structures.

The Fate of Copper Added to Surface Water: Field, Laboratory, and Modeling Studies.

The fate and effects of copper in the environment are governed by a complex set of environmental processes that include binding to inorganic and organic ligands in water, soil, and sediments. In natural waters, these interactions can limit copper bioavailability and result in copper transport from the water column to the sediment. In the present study, data on the fate of copper added to lakes, microcosms, and mesocosms were compiled and analyzed to determine copper removal rates from the water column. Studies on copper behavior in sediment were also reviewed to assess the potential for remobilization. A previously developed, screening-level fate and transport model (tableau input coupled kinetic equilibrium transport-unit world model [TICKET-UWM]) was parameterized and applied to quantify copper removal rates and remobilization in a standardized lake setting. Field and modeling results were reconciled within a framework that links copper removal rates to lake depths and solids fluxes. The results of these analyses provide converging evidence that, on a large scale, copper is removed relatively quickly from natural waters. For the majority of studies examined, more than 70% of the added copper was removed from the water column within 16 d of dosing. This information may be useful in the context of environmental hazard and risk assessment of copper. Environ Toxicol Chem 2019;38:1386-1399. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Modeling the Fate of Metal Concentrates in Surface Water.

Metals present in concentrates are in a solid form and are not bioavailable, but they can dissolve or potentially transform to more soluble forms. Transformation/dissolution laboratory protocols have been developed to assess the importance of dissolution of sparingly soluble metal substances in the context of hazard classification; however, these tests represent worst-case scenarios for metal bioavailability because attenuation mechanisms such as complexation, sorption, and transport to the sediment are not considered. A unit world model (UWM) for metals in lakes, tableau input coupled kinetics equilibrium transport (TICKET)-UWM, has been developed that considers key processes affecting metal transport, fate, and toxicity including complexation by aqueous inorganic and ligands, partitioning to dissolved organic carbon (DOC) and particulate organic carbon (POC), precipitation, and transport of dissolved metals and solids between the water column and sediment. The TICKET-UWM model was used to assess the fate of a metal concentrate and dissolved metal ions released from the concentrate following an instantaneous input to a generalized lake. Concentrate dissolution rates in the water column were parameterized using results from batch transformation/dissolution tests for 2 specific concentrates containing lead (Pb), copper (Cu), and cobalt (Co). The TICKET-UWM results for a generalized lake environment showed that water column concentrations of metals in the lake environment after 28 d were several orders of magnitude lower than the 28-d concentration from the transformation/dissolution tests because Pb, Cu, and Co partitioned to POC in the water column and were subsequently removed due to settling. Resuspension of sediment served to increase total metal in the water column, but the resulting concentrations were still much lower than the 28-d concentrations from the transformation/dissolution tests. Information from TICKET-UWM could be used to refine the environmental hazard profiles of metals. Environ Toxicol Chem 2019;38:1256-1272. © 2019 SETAC.