Effect of ozonation on polychlorinated biphenyl degradation and on soil physico-chemical properties

Strategies for mitigation of pesticides from the environment through alternative approaches: A review of recent developments and future prospects

Chemical-based peticides are having negative impacts on both the healths of human beings and plants as well. The World Health Organisation (WHO), reported that each year, >25 million individuals in poor nations are having acute pesticide poisoning cases along with 20,000 fatal injuries at global level. Normally, only ∼0.1% of the pesticide reaches to the intended targets, and rest amount is expected to come into the food chain/environment for a longer period of time. Therefore, it is crucial to reduce the amounts of pesticides present in the soil. Physical or chemical treatments are either expensive or incapable to do so. Hence, pesticide detoxification can be achieved through bioremediation/biotechnologies, including nano-based methodologies, integrated approaches etc. These are relatively affordable, efficient and environmentally sound methods. Therefore, alternate strategies like as advanced biotechnological tools like as CRISPR Cas system, RNAi and genetic engineering for development of insects and pest resistant plants which are directly involved in the development of disease- and pest-resistant plants and indirectly reduce the use of pesticides. Omics tools and multi omics approaches like metagenomics, genomics, transcriptomics, proteomics, and metabolomics for the efficient functional gene mining and their validation for bioremediation of pesticides also discussed from the literatures. Overall, the review focuses on the most recent advancements in bioremediation methods to lessen the effects of pesticides along with the role of microorganisms in pesticides elimination. Further, pesticide detection is also a big challenge which can be done by using HPLC, GC, SERS, and LSPR ELISA etc. which have also been described in this review.

Contaminant containment for sustainable remediation of persistent contaminants in soil and groundwater

Contaminant containment measures are often necessary to prevent or minimize offsite movement of contaminated materials for disposal or other purposes when they can be buried or left in place due to extensive subsurface contamination. These measures can include physical, chemical, and biological technologies such as impermeable and permeable barriers, stabilization and solidification, and phytostabilization. Contaminant containment is advantageous because it can stop contaminant plumes from migrating further and allow for pollutant reduction at sites where the source is inaccessible or cannot be removed. Moreover, unlike other options, contaminant containment measures do not require the excavation of contaminated substrates. However, contaminant containment measures require regular inspections to monitor for contaminant mobilization and migration. This review critically evaluates the sources of persistent contaminants, the different approaches to contaminant remediation, and the various physical-chemical-biological processes of contaminant containment. Additionally, the review provides case studies of contaminant containment operations under real or simulated field conditions. In summary, contaminant containment measures are essential for preventing further contamination and reducing risks to public health and the environment. While periodic monitoring is necessary, the benefits of contaminant containment make it a valuable remediation option when other methods are not feasible.

Remediation of pesticides in commercial farm soils by solarization and ozonation techniques

Soil contamination by pesticides is a growing environmental problem. Even though nowadays numerous soil remediation technologies are available, most of them have not been tested at field scale. This study attempts to demonstrate the efficiency of solarization-ozonation techniques for the removal of twelve pesticides at full scale. Initial solarization and ozonation trials were conducted in plots located in a greenhouse using freshly and aged contaminated soils under controlled pilot conditions. The combination of solarization and ozonation treatment was efficient for all the studied pesticides both in freshly and in aged contaminated soils, being the lower degradation values found for the second type. This low removal suggests that the increase of pesticides' adsorption on soil resulting from ageing decreases their availability. Once the essays were carried out at pilot scale, the solarization-ozonation applicability was evaluated in a commercial farm soil. This trial was carried out in a greenhouse whose soil had previously been contaminated with some of the pesticides studied. A significant degradation (53.8%) was observed after 40 days of treatment. Pesticides' main metabolites were identified during the different remediation experiments. In addition, the cost of the combined solarization and ozonation technology was evaluated. Finally, our results suggest that this combination of techniques could be considered a promising technology to degrade pesticides in soil.

Remediation of triazole, anilinopyrimidine, strobilurin and neonicotinoid pesticides in polluted soil using ozonation and solarization

This study aimed to investigate the effectiveness of ozonation and solarization techniques for the removal of different types of pesticides from soil during the summer season. The effect of two experimental parameters (temperature and ozone application mode) on the pesticide degradation was evaluated. The results showed that solarization (S), solarization with surface ozonation (SOS), and solarization with deep ozonation (SOD) enhanced pesticide degradation rates in comparison with the control (untreated soil, C). The triazole, anilinopyrimidine, strobilurin and neonicotinoid pesticides showed similar behaviour under S and SOS conditions. The highest decrease was found in SOD, indicating the significant effect of temperature and ozone application mode on the efficiency of the ozonation treatment. Thus, a higher soil temperature and a longer accumulated time at high temperature in treatments S, SOS and SOD were observed due to solarization process. In addition, the removal efficiency was enhanced with exposure time. Finally, the main 15 transformation products were identified during SOD treatment. The results suggest that solarization combined with ozonation techniques allows decontamination of soil containing pesticide residues.

Advances and perspective in bioremediation of polychlorinated biphenyl-contaminated soils

In recent years, microbial degradation and bioremediation approaches of polychlorinated biphenyls (PCBs) have been studied extensively considering their toxicity, carcinogenicity and persistency potential in the environment. In this direction, different catabolic enzymes have been identified and reported for biodegradation of different PCB congeners along with optimization of biological processes. A genome analysis of PCB-degrading bacteria has led in an improved understanding of their metabolic potential and adaptation to stressful conditions. However, many stones in this area are left unturned. For example, the role and diversity of uncultivable microbes in PCB degradation are still not fully understood. Improved knowledge and understanding on this front will open up new avenues for improved bioremediation technologies which will bring economic, environmental and societal benefits. This article highlights on recent advances in bioremediation of PCBs in soil. It is demonstrated that bioremediation is the most effective and innovative technology which includes biostimulation, bioaugmentation, phytoremediation and rhizoremediation and acts as a model solution for pollution abatement. More recently, transgenic plants and genetically modified microorganisms have proved to be revolutionary in the bioremediation of PCBs. Additionally, other important aspects such as pretreatment using chemical/physical agents for enhanced biodegradation are also addressed. Efforts have been made to identify challenges, research gaps and necessary approaches which in future, can be harnessed for successful use of bioremediation under field conditions. Emphases have been given on the quality/efficiency of bioremediation technology and its related cost which determines its ultimate acceptability.

Impacts of moisture content during ozonation of soils containing residual petroleum

We tested the effect of soil moisture content on the efficiency of gas-phase ozonation for two types of soils containing residual petroleum. For the first soil (BM2), having a total petroleum hydrocarbons (TPH) concentration of 18,000mg/kg soil, a moisture content of 5% benefited oxidation, giving the highest efficiency of ozonation for TPH removal and for producing soluble and biodegradable products. In contrast, higher moisture content hindered O₃ from oxidizing reactive materials in the second soil (BM3), which had a higher TPH concentration, 33,000mg/kg soil. This trend was documented by less TPH removal, less generation of soluble and biodegradable organic products, and a carbon balance that showed retarded carbon oxidation. An unexpected phenomenon was smoldering during ozonation of air-dried (<1% moisture) BM3, which did not occur with the same moisture conditions for BM2. BM3 smoldered was due to its higher TPH content, low heat buffering, and more release of volatiles with low self-ignition points. Smoldering did not occur for ≥ 5% water content, as it suppressed the temperature increase needed to volatilize the organics that initiated smoldering. The findings underscore the importance of controlling water content during ozonation to optimize the effectiveness of ozonation and prevent smoldering.

Phenanthrene degradation in soil by ozonation: Effect of morphological and physicochemical properties

The aim of this study was to characterize the ozone reaction with phenanthrene adsorbed in two types of soils (sand and agricultural). The effect of soil physicochemical properties (texture, bulk density, particle density, porosity, elemental composition, permeability, surface area and pore volume) on the phenanthrene decomposition was evaluated. Commercial sand has a uniform morphology (spherical) with a particle size range between 0.178 and 0.150 mm in diameter, regular elemental composition SiO₂, specific density of 1701.38 kg/m³, a true density of 2492.50 kg/m³, with an effective porosity of 31%. On the other hand, the agricultural soil had heterogeneous morphology, particle size between 0.1779 and 0.05 mm in diameter, elemental composition was montmorrillonite silicon oxide, apparent density of 999.52 kg/m³, a true density of 2673.55 kg/m³, surface area of 34.92 m²/g and porosity of 57%. The percentage of phenanthrene decomposition in the sand was 79% after 2 h of treatment. On the other hand, the phenanthrene degradation in the agricultural soil was 95% during the same reaction time. The pore volume of soil limited the crystal size of phenanthrene and increased the contact surface with ozone confirming the direct impact of physicochemical properties of soils on the decomposition kinetics of phenanthrene. In the case of agricultural soil, the effect of organic matter on phenanthrene decomposition efficiency was also investigated. A faster decomposition of initial contaminant and byproducts formed in ozonation was obtained in natural agricultural soil compared to the sand. The partial identification of intermediates and final accumulated products produced by phenanthrene decomposition in ozonation was developed. Among others, phenanthroquinone, hydroquinone, phenanthrol, catechol as well as phthalic, diphenic, maleic and oxalic acids were identified.

Removal of polychlorinated biphenyl congeners in mixture Delor 103 from wastewater by ozonation vs/and biological method

Polychlorinated biphenyls (PCBs) produced in Slovakia as a commercial mixture Delor 103 cause the main contamination of sediment, water and fish in the eastern part of Slovakia. Delor 103 is a mixture of 40% PCB congeners, nine of them: PCB 8 (2,4'-dichlorobiphenyl), PCB 28 (2,4,4'-trichlorobiphenyl), PCB 52 (2,2',5,5'-tetrachlorobiphenyl), PCB 101 (2,2',4,5,5'-pentachlorobiphenyl), PCB 118 (2,3',4,4',5-pentachlorobiphenyl), PCB 138 (2,2',3,4,4',5'-hexachlorobiphenyl), PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl), PCB 180 (2,2',3,4,4',5,5'-heptachlorobiphenyl), and PCB 203 (2,2',3,4,4',5,5',6-octachlorobiphenyl), were monitored for their removal by ozonation and biodegradation using Achromobacter xylosoxidans. Ozonation improved the removal of PCB 52, 118, 153, 138, 180, and 203 using biological method with A. xylosoxidans. Degradation of 55% of the total amount of nine selected PCB congeners was achieved by the biological method with A. xylosoxidans, while 86% of the total amount of the nine selected PCB congeners were removed by the ozonation method; using a combination of biological and chemical methods, ozonation and A. xylosoxidans, showed a 94% removal efficiency of the selected PCB congeners present in mixture Delor 103.

Interpreting Interactions between Ozone and Residual Petroleum Hydrocarbons in Soil

We evaluated how gas-phase O₃ interacts with residual petroleum hydrocarbons in soil. Total petroleum hydrocarbons (TPH) were 18 ± 0.6 g/kg soil, and TPH carbon constituted ∼40% of the dichloromethane-extractable carbon (DeOC) in the soil. At the benchmark dose of 3.4 kg O₃/kg initial TPH, TPH carbon was reduced by nearly 6 gC/kg soil (40%), which was accompanied by an increase of about 4 gC/kg soil in dissolved organic carbon (DOC) and a 4-fold increase in 5-day biochemical oxygen demand (BOD₅). Disrupting gas channeling in the soil improved mass transport of O₃ to TPH bound to soil and increased TPH removal. Ozonation resulted in two measurable alterations of the composition of the organic carbon. First, part of DeOC was converted to DOC (∼4.1 gC/kg soil), 75% of which was not extractable by dichloromethane. Second, the DeOC containing saturates, aromatics, resins, and asphaltenes (SARA), was partially oxidized, resulting in a decline in saturates and aromatics, but increases in resins and asphaltenes. Ozone attack on resins, asphaltenes, and soil organic matter led to the production of NO₃^-, SO₄^2-, and PO₄^3-. The results illuminate the mechanisms by which ozone gas interacted with the weathered petroleum residuals in soil to generate soluble and biodegradable products.

DFT Studies of SN2 Dechlorination of Polychlorinated Biphenyls

Nucleophilic dechlorination of all 209 PCBs congeners by ethylene glycol anion has been studied theoretically at the DFT level. The obtained Gibbs free energies of activation are in the range 7-22 kcal/mol. The reaction Gibbs free energies indicate that all reactions are virtually irreversible. Due to geometric constrains these reactions undergo rather untypical attack with attacking oxygen atom being nearly perpendicular to the attacked C-Cl bond. The most prone to substitution are chlorine atoms that occupy ortho- (2, 2', 6, 6') positions. These results provide extensive information on the PEG/KOH dependent PCBs degradation. They can also be used in further developments of reaction class transition state theory (RC-TST) for description of complex reactive systems encountered for example in combustion processes.

Kinetics and products of PCB28 degradation through a goethite-catalyzed Fenton-like reaction

Efficiencies of 2,4,4'-trichlorobiphenyl (PCB28) degradation in a goethite-catalyzed Fenton-like system under various conditions were investigated. Up to 99% of PCB28 was degraded in the Fenton-like system after 48 h. The hydroxyl radical was responsible for the degradation of PCB28 at pH 3-7. Degradation of PCB28 and H2O2 followed pseudo-first-order kinetics. The rate of PCB28 degradation decreased when the pH increased from 3 to 7, but increased with increasing concentration of goethite and H2O2. The rate of H2O2 decomposition increased at higher pH and goethite concentration, and decreased at lower H2O2 concentration. The half-lives of 4-chlorobiphenyl, 4,4'-dichlorobiphenyl, 2,4,4'-trichlorobiphenyl, and 2,2',4,4'-tetrachlorobiphenyl were 1.8, 3.5, 4.1, and 11h, respectively; therefore, the number of chlorine atoms in the biphenyl molecule determined the chemical reactivity of PCBs. By gas chromatography-mass spectrometry, one monochlorobiphenyl, three dichlorobiphenyl, and two hydroxytrichlorobiphenyl derivatives were identified as major products of PCB28 degradation. The decrease in pH of the reaction mixture after 48h reaction revealed that acidic products might be formed during degradation.

Transformation of polychlorinated biphenyls by persulfate at ambient temperature

Increasing attention has been paid to persulfate due to its high efficiency in degrading organic pollutants. This paper investigated the transformation of a selected polychlorinated biphenyl (PCB) by sodium persulfate without activators at near ambient temperature (10-40°C). The results showed that 2,4,4'-CB was completely decomposed by persulfate at 30°C in 8 h. The products were identified by gas chromatography-mass spectrometry (GC-MS), and transformation pathways could be divided into two steps as dechlorination and hydroxylation. Electron paramagnetic resonance (EPR) technique was used to identify the generated radical species at different pH values at ambient temperature. The results showed that sulfate radicals (SO(4)(•-)) were predominant under acidic condition and hydroxyl radicals ((•)OH) were predominant under basic condition. This behavior was also confirmed by the quenching studies and kinetic model. Decreasing the solution pH resulted in increasing the degradation efficiency of 2,4,4'-CB. Moreover, the degradation of other PCBs such as 2-CB, 4-CB, 2,4-CB, 2,4'-CB, and 2,4,6-CB with persulfate was examined. The findings of this study can provide guidance in the remediation of PCBs contaminated soil and water with persulfate.

Visual observations and Raman spectroscopic studies of supercritical water oxidation of chlorobenzene in an anticorrosive fused-silica capillary reactor

Supercritical water oxidation of chlorobenzene (CB) was studied using an anticorrosive fused-silica capillary reactor (FSCR) combined with a polarization microscope recorder system for visual observations and a Raman spectroscopic system for qualitative and quantitative analyses of the gaseous products. The effects of operating parameters, including the stoichiometric amount of oxidizer, temperature, and reaction time, on oxidation behavior were investigated. Our results show that a 100% conversion yield of CB and 100% CO(2) yield were achieved with a 150% stoichiometric amount of H(2)O(2) at 450 °C within 8 and 10 min, respectively. The conversion yield and the CO(2) yield both depend strongly on temperature, and the CO(2) yield is always less than the CB conversion yield under the same experimental conditions, suggesting that some carbon exists in intermediate products of incomplete oxidation, as confirmed by gas chromatography-mass spectrometry. Global kinetics analysis based on the complete conversion of CB to CO(2) showed that the reaction was first order. CB phase-changes in sub- and supercritical H(2)O-H(2)O(2) system in the FSCR were observed and recorded; CB eventually dissolved completely to form a homogeneous liquid solution above 326.1 °C. This method has great potential for use in the theoretical study of fluids and chemical reactions under elevated pressure-temperature conditions.

Degradation of polychlorinated biphenyls in the rhizosphere of rape, Brassica napus L

The objective of this study was to investigate the rhizosphere effect of rape plants on polychlorinated biphenyls (PCB) dissipation in soils spiked with seven indicator congeners. Depletion of PCB in the rhizosphere was significantly higher in the soil with lower organic matter content. While in the Chernozem soil, 87% of PCB related to bulk soil were found in the 1st mm from roots, only 62%-69% were found in the Fluvisol soil with no significant influence of increased initial PCB concentration. Further from the roots, the concentration of lower chlorinated congeners decreased, which indicates their greater biodegradation in comparison with more chlorinated ones.