Reduction of benzo[a]pyrene with acid-activated magnesium metal in ethanol: a possible application for environmental remediation

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 μM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

Impact of benzo[a]pyrene with other pollutants induce the molecular alternation in the biological system: Existence, detection, and remediation methods

The exposure of benzo [a]pyrene (BaP) in recent times is rather unavoidable than ever before. BaP emissions are sourced majorly from anthropogenic rather than natural provenance from wildfires and volcanic eruptions. A major under-looked source is via the consumption of foods that are deep-fried, grilled, and charcoal smoked foods (meats in particular). BaP being a component of poly aromatic hydrocarbons has been classified as a Group I carcinogenic agent, which has been shown to cause both systemic and localized effects in animal models as well as in humans; has been known to cause various forms of cancer, accelerate neurological disorders, invoke DNA and cellular damage due to the generation of reactive oxygen species and involve in multi-generational phenotypic and genotypic defects. BaP's short and accumulated exposure has been shown in disrupting the fertility of gamete cells. In this review, we have discussed an in-depth and capacious run-through of the various origins of BaP, its economic distribution and its impact as well as toxicological effects on the environment and human health. It also deals with a mechanism as a single compound and its ability to synergize with other chemicals/materials, novel sensitive detection methods, and remediation approaches held in the environment.

Trichloroethylene dechlorination rates, pathways, and efficiencies of ZVMg/C in aqueous solution

The removal mechanism from the reductive dechlorination of trichloroethylene (TCE) by zero valent magnesium (ZVMg) in aqueous solution is systematically studied. Following the preparation and characterization of ball-milled micro ZVMg with graphite (ZVMg/C) particles, this paper evaluated the TCE reaction rates, pathways, utilization rates and aging effects of ZVMg/C particles in aqueous solution under uncontrolled pH conditions. Overall, 38 μM of TCE was transformed by 10 g/L of ZVMg/C to methane (62.51%) and n-hexane (11.86%) and ethane (7.40%) and other alkene and alkyne products through the catalytic hydrogenation pathway. The measured surface area normalized pseudo-first order rate constants (K_SA) were up to 9.31 × 10^-2 L/m²/h and the utilization rate of Mg⁰ accounted for around 60%. The K_SA were decreased to 1.90 × 10^-2 L/m²/h in case of ZVMg/C being exposed in the atmosphere for 6 days due to 7.3% reduction in the utilization rate of Mg⁰ from the initial 85.2%, and 5.11 × 10^-2 L/m² h in case of ZVMg/C aged in water for one day. The removal efficiencies of approximately 56%, 58% and 87% by 10 g/L of ZVMg/C were achieved in the contaminated groundwater comprising 38 μM of TCE, 43 μM of 1,2-dichlorobenzene and 8.12 μM of trichlormethane. Therefore, it is concluded that ZVMg/C is viewed as a potential and effective remediation reagent for the groundwater remediation.

Epigenome-wide DNA methylation signature of benzo[a]pyrene exposure and their mediation roles in benzo[a]pyrene-associated lung cancer development

Benzo[a]pyrene (B[a]P) is a typical carcinogen associated with increased lung cancer risk, but the underlying mechanisms remain unclear. This study aimed to investigate epigenome-wide DNA methylation associated with B[a]P exposure and their mediation effects on B[a]P-lung cancer association in two lung cancer case-control studies of 462 subjects. Their plasma levels of benzo[a]pyrene diol epoxide-albumin (BPDE-Alb) adducts and genome-wide DNA methylations were separately detected in peripheral blood by using enzyme-linked immunosorbent assay (ELISA) and genome-wide methylation arrays. The epigenome-wide meta-analysis was performed to analyze the associations between BPDE-Alb adducts and DNA methylations. Mediation analysis was applied to assess effect of DNA methylation on the B[a]P-lung cancer association. We identified 15 CpGs associated with BPDE-Alb adducts (P_-meta < 1.0 × 10^-5), among which the methylation levels at five loci (cg06245338, cg24256211, cg15107887, cg02211741, and cg04354393 annotated to UBE2O, SAMD4A, ACBD6, DGKZ, and SLFN13, respectively) mediated a separate 38.5%, 29.2%, 41.5%, 47.7%, 56.5%, and a joint 58.2% of the association between BPDE-Alb adducts and lung cancer risk. Compared to the traditional factors [area under the curve (AUC) = 0.788], addition of these CpGs exerted improved discriminations for lung cancer, with AUC ranging 0.828-0.861. Our results highlight DNA methylation alterations as potential mediators in lung tumorigenesis induced by B[a]P exposure.

Degradation kinetics of hexachlorobenzene over zero-valent magnesium/graphite in protic solvent system and modeling of degradation pathways using density functional theory

Hexachlorobenzene (HCB), like many chlorinated organic compounds, has accumulated in the environment from agricultural and industrial activity. Because of its health risks and adverse impact on various ecosystems, remediation of this contaminant is of vital concern. The objective of this study is to evaluate the proficiency of activated magnesium metal in a protic solvent system to accomplish reductive dechlorination of HCB. Experimental results were compared with those predicted by quantum chemical calculations based on Density Functional Theory (DFT). Multivariate analysis detected complete degradation of HCB within 30 min at room temperature, the reaction having a rate constant of 0.222 min^-1. Dechlorination was hypothesized to proceed via an ionic mechanism; the main dechlorination pathways of HCB in 1:1 ethanol:ethyl lactate were HCB → PCBz → 1,2,4,5-TCB; 1,2,3,5-TCB → 1,2,4-TriCB; 1,3,5-TriCB → 1,4-DiCB; 1,3-DiCB. The direct relationship between the decreasing number of Cl substituents and dechlorination reaction kinetics agrees with the ΔG values predicted by the computational model. This methodology shows promise for the development of a practical and sustainable field application for the remediation of other chlorinated aromatic compounds.

Optimizing Reductive Degradation of PAHs Using Anhydrous Ethanol with Magnesium Catalyzed by Glacial Acetic Acid

Targeted degradation of individual polycyclic aromatic hydrocarbon (PAH) constituents like anthracene, may offer cost effective and efficient cleaning of coal tar-contaminated sites. Thus, a reductive degradation procedure of anthracene using activated magnesium with anhydrous ethanol at room temperature was developed and optimized. To determine the optimum conditions for anthracene, such as effective magnesium concentrations, glacial acetic acid volumes, and exposure time for the anthracene reduction, the experiments were designed using the response surface methodology based on the central composite design. The design also minimized the number of experiments. The main product from anthracene reduction is 9,10-dihyrdoanthracene. Optimum conditions for 98% degradation capacity of anthracene (2.80 × 10^-3 mmol) were 30 mg of Mg powder (1.20 mmol), 60 μL of glacial acetic acid (1.05 mmol), and 30 min exposure time. When the optimized method was tested on the coal tar specimen, twice as many reagents (i.e., Mg and glacial acetic acid) were required to obtain a 90% degradation of anthracene and fluoranthene from the coal tar. This method of using activated Mg and anhydrous ethanol selectively reduces PAHs in coal tar; in particular anthracene and fluoranthene are most efficiently removed.

Comparative study for the removal and destruction of pentachlorophenol using activated magnesium treatment systems

Chlorophenols are highly toxic, environmentally-persistent compounds which have been classified as probable human carcinogens by the United States Environmental Protection Agency. Due to the high toxicity of these compounds, it is necessary to treat water and soils with concentrations of chlorophenols above the detection limit set by regulatory agencies. The aim of this work is to demonstrate the capabilities of using ball-milled magnesium for the dechlorination of PCP. Comparison of dechlorination processes were performed in an attempt to determine the most effective system for degradation of PCP to phenol. Three systems with powerful capabilities of treatment were studied: ball-milled zero-valent magnesium (ZVMg), ball-milled zero-valent magnesium carbon (ZVMg/C), and ball-milled zero-valent magnesium with palladium (ZVMg/Pd). In addition to measuring PCP disappearance, all byproducts were identified and quantified for each degradation system. The results of these studies indicate that all three of the systems degrade PCP within 30 min. The most rapid and complete PCP dechlorination is achieved using ball-milled Mg/Pd and a matrix consisting of at least 0.02 g Mg0/mL ethanol, and 10 μL acetic acid/mL ethanol, in which case 20 ng/μL of PCP was dechlorinated to chlorophenols in approximately 15 min with complete dechlorination achieved in six days. Carbon mass balances of 90.16% for Mg, 94.76% (Mg/C) and 97.05% (Mg/Pd) verify dechlorination was responsible for declining concentrations of PCP. The reactions of PCP degradation and phenol formation were found to follow pseudo-first order kinetics for all systems. Further work will consist of optimization and development of field-scale applications.

Effective parameters on selective catalytic hydrodeoxygenation of phenolic compounds of pyrolysis bio-oil to high-value hydrocarbons

Selective hydrodeoxygenation of phenolic compounds present in pyrolysis bio-oil (phenol, cresol, guaiacol and anisole) to high-value hydrocarbons is a great function of catalyst properties and operating conditions.

Laboratory evaluation of a prospective remediation method for PCB-contaminated paint

BACKGROUND

Paint laden with polychlorinated biphenyls (PCBs) often acts as a point source for environmental contamination. It is advantageous to address contaminated paint before the PCBs transport to surrounding media; however, current disposal methods of painted material introduce a variety of complications. Previous work demonstrates that PCBs can be broken down at ambient temperatures and pressures through a degradation process involving magnesium metal and acidified ethanol. This report is an extension of that work by describing the development of a delivery system for said reaction in preparation for a field test. Two treatment options including the Activated Metal Treatment System (AMTS) and the Non-Metal Treatment System (NMTS) remove and degrade PCBs from painted surfaces.

FINDINGS

AMTS decreased the Aroclor® concentration of a solution by more than 97% within 120 minutes and the Aroclor® concentration of industrial paint chips by up to 98% over three weeks. After removing up to 76% of PCBs on a painted surface after seven days, NMTS also removed trace amounts of PCBs in the paint's concrete substrate. The evaporation rate of the solvent (ethanol) from the treatment system was reduced when the application area was increased. The solvent system's ability to remove more than 90% of PCBs was maintained after losing 36% of its mass to solvent evaporation.

CONCLUSIONS

The delivery systems, AMTS and NMTS, are able to support the hydrodechlorination reaction necessary for PCB degradation and are therefore attractive options for further studies regarding the remediation of contaminated painted surfaces.

Reductive degradation of oxygenated polycyclic aromatic hydrocarbons using an activated magnesium/co-solvent system

This study evaluates the capability of zero-valent magnesium and a protic co-solvent to promote the degradation of oxygenated polycyclic aromatic hydrocarbons compounds, specifically 9-fluorenone, 9,10-anthraquinone, 7,12-benz(a)anthraquionone, and 7H-benz(de)anthracene-7-one. At room temperature conditions, greater than 86% degradation efficiency is observed after 24h of reaction time for a mixture containing 0.05 g of magnesium and four selected oxygenated aromatic hydrocarbons with 250 mg L(-1) concentrations. It is noted that glacial acetic acid is needed as an activator for the degradation reaction to proceed. It is also presumed that the acid removes oxide and hydroxide species from the magnesium surface. With the GC-MS analysis of the reaction products, possible reductive pathways are suggested. Furthermore, this study is the first report on the degradation of these emerging contaminants and it is proposed that the magnesium-powder/protic-solvent system is a promising low-cost reagent and may allow for the future development of an economic and environmentally-friendly remediation application.

Multivariate evaluation and optimization of an activated-magnesium/co-solvent system for the reductive degradation of polycyclic aromatic hydrocarbons

The present study evaluates the capability of an activated-magnesium metal and protic co-solvents to promote the reductive degradation of three different polycyclic aromatic hydrocarbons, specifically pyrene, benzo[k]fluoranthene and benzo[g,h,i]perylene. Multivariate analyses demonstrated that the kinetics of degradation was affected by several experimental factors such as magnesium loading, acid addition and solubility of the compounds. It was determined that an acid activator is needed for the degradation reaction to proceed and it is also noted that the use of a 1:1 ethanol/ethyl lactate co-solvent is ideal for the complete dissolution of all three compounds with concentrations varying from 200 to 275mgL(-1). The experimental results also indicate that, at room temperature conditions, only 0.05-0.1g of magnesium is required in order to achieve greater than 93% degradation efficiency after 24h of reaction. This methodology is attractive and may allow for the development of an economic and environmentally friendly field application for the remediation of other polycyclic aromatic hydrocarbons.