Reduction Of Polychlorinated Biphenyls Research Articles

Effectiveness of Charcoal Adsorbent in Flue Gas Filters for PCB Reduction in Smoke from Hospital Incinerators

The release of gas-phase polychlorinated biphenyls (PCBs) as one of the persistent organic pollutants (POPs) is an unfortunate result of combustion, especially from medical waste incinerators. This tends to make incinerators unpopular. The idea of a cheaply available air pollution control device fitted to incinerator chimneys can justify the continued use of incinerators. A gas filter unit, consisting of 3 filter beds with activated charcoal as an adsorbent, was designed, constructed, and fitted onto an existing incinerator at a university hospital in Ghana. Flue gas from the incinerator was sampled before and after the filter beds, using cylindrically-shaped mini-polyurethane foam (mini-PUF) samplers, and the analytes in the samples were then Soxhlet-extracted, purified, and analyzed for certain PCBs using the gas chromatography-mass spectrometer (GC-MS) technique. Twelve of the 14 indicators PCBs analyzed in the smoke samples were present, and 11 of them saw mean reductions ranging from 3.67% to 54.9% by the charcoal filter beds. These were PCB 18, PCB 28, PCB 31, PCB 44, PCB 101, PCB 118, PCB 138, PCB149, PCB 153, PCB 170, and PCB180. The gaseous concentrations of PCBs before filtration ranged from 0.0000788 ng/m3 for PCB 180 to 0.00129 ng/m3 for PCB 153. After the filtration by the charcoal adsorbent, they ranged from 0.00003734 ng/m3 for PCB 170 to 0.00112016 ng/m3 for PCB 153. The highest mean reduction of 54.9% came from the homologue, PCB 180, whilst the homologue with a dioxin-like character (PCB 118) saw a 22.44% reduction. This suggests that dioxins and other dioxin-like compounds are most likely adsorbed by the charcoal adsorbent. This gas filter unit should further be investigated for its effectiveness at removing other dioxin-like PCBs, dioxins, and furanes and for testing the effectiveness of thermophilic bacterial strains that can further metabolize these POPs into less harmful products.

Long-Term Monitoring of an In Situ Activated Carbon Treatment to Reduce Polychlorinated Biphenyl Availability in an Active Harbor.

Activated carbon-based amendments have been demonstrated as a means of sequestering sediment-associated organic compounds such as polychlorinated biphenyls (PCBs). In a 2012 effort, an activated carbon amendment was placed at a 0.5-acre amendment area adjacent to and underneath Pier 7 at the Puget Sound Naval Shipyard and Intermediate Maintenance Facility, Bremerton, Washington, USA to reduce PCB availability. Multiple postplacement monitoring events over a 3-year period showed an 80%-90% reduction in PCBs, stability of activated carbon, and no significant negative impacts to the benthic community. To further evaluate the long-term performance, a follow-on to the approximately 7-year (82-month) postplacement monitoring event was conducted in 2019. The results of in situ porewater and bioaccumulation evaluations were consistent with previous observations, indicating overall PCB availability reductions of approximately 80%-90% from preamendment conditions. Multiple measurement approaches for quantifying activated carbon and amendment presence indicated that the amendment was present and stable in the amendment area and that the activated carbon content was similar to levels observed previously. As in the previous investigation, benthic invertebrate community metrics indicated that the amendment did not significantly impair benthic health. An application of carbon petrography to quantify activated carbon content in surface sediments was also explored. The results were found to correspond within a factor of 1.3 (on average) with those of data for the black carbon content via a black carbon chemical oxidation method, an approach that quantifies all forms of black carbon (including activated carbon). The results suggest that at sites with low soot-derived black carbon content in sediment (relative to the targeted activated carbon dose), the black carbon chemical oxidation method would be a reasonable method for measurement of activated carbon dosage in sediment at sites amended with activated carbon. Environ Toxicol Chem 2022;41:1568-1574. © 2022 SETAC.

Epidemiologically-informed cumulative risk hypertension models simulating the impact of changes in metal, organochlorine, and non-chemical exposures in an environmental justice community

Blood pressure is a leading risk factor for cardiovascular disease, influenced by chemical and non-chemical stressors. Exposure reduction strategies can potentially improve public health, but there are analytical challenges in developing quantitative models of health benefits, including the need for detailed multi-stressor exposure models, corresponding health evidence, and methods to simulate changes in exposure and resultant health benefits. These challenges are pronounced in low-income urban communities, where residents are often simultaneously exposed to numerous chemical and non-chemical stressors. For New Bedford (Massachusetts, USA), a low-income community near a Superfund site, we simulated geographically-resolved individual data, and applied previously published structural equation models developed from National Health and Nutrition Examination Survey (NHANES) data. These models simultaneously predict exposures to multiple chemicals (e.g., lead (Pb), cadmium (Cd), and polychlorinated biphenyls (PCBs)) and non-chemical factors (e.g., socioeconomic status), and determine their combined effects on blood pressure. We then modeled counterfactual scenarios reducing exposures and estimated the resulting changes in blood pressure distribution in the community. Results indicated small shifts in mean blood pressure and percentage of normotensive individuals with a reduction of Pb and/or PCB exposure. For example, a reduction in PCB to the lowest 10th percentile exposure in the NHANES resulted in a 2.4 mm Hg shift in systolic blood pressure (SBP), corresponding with 3% fewer individuals with SBP in the Stage 2 hypertension category [SBP ≥140]. Our model also emphasized the importance of the multi-stressor framework by simulating benefits of reductions in smoking rates, given positive associations with Pb and Cd but inverse associations with body mass index and blood pressure. This research demonstrates the ability to jointly consider chemical and non-chemical exposures and their impact on cardiovascular health, using approaches generalizable to other cumulative risk assessment applications.

Rhizoremediation of weathered PCBs in a heavily contaminated agricultural soil: Results of a biostimulation trial in semi field conditions

This paper describes the results of a rhizoremediation greenhouse experiment planned to select the best plant species and soil management for the bioremediation of weathered polychlorinated biphenyls (PCBs). We evaluated the ability of different plant species to stimulate activity and diversity of the soil microbial community leading to the reduction of PCB concentrations in a heavily contaminated soil (at mg kg-1 dw level), of the national priority site for remediation (SIN) “Brescia-Caffaro” in Italy. Biostimulation was determined in large size (6kg) pots, to reflect semi-field conditions with a soil/root volume ratio larger than in most rhizoremediation experiments present in the literature. In total, 10 treatments were tested in triplicates comparing 7 plant species (grass and trees) and 5 soil/cultivation conditions (i.e., only one plant species, plant consociation, redox cycle, compost or ammonium thiosulfate addition) with the appropriate unplanted controls. After 18months of biostimulation the overall reduction of total PCBs varied between 14 and 20%. Microbial analysis revealed a shift in the microbial community structure over time and showed that all the planted treatments significantly enhanced microbial hydrolytic activity and the abundance of bacterial populations, including potential PCB degraders, in the soil surrounding plant roots. The plant species most effective in reducing the contaminant concentrations were Festuca arundinacea cultivated adding compost or in consociation with Cucurbita pepo ssp. pepo and Medicago sativa cultivated with Rhizobium spp. and mycorrhizal fungi; they reduced total PCB concentrations of about 20% and showed the significant depletion of a high number of PCB congeners (29, 37 and 23, respectively, out of the 79 measured). Our results suggest that these plant species are particularly efficient in increasing soil PCB bioavailability and in stimulating microbial degradation. They could be used in field rhizoremediation strategies to enhance the natural attenuation process and reduce PCB levels in historically contaminated sites.

Effects of Ferric Oxyhydroxide on Anaerobic Microbial Dechlorination of Polychlorinated Biphenyls in Hudson and Grasse River Sediment Microcosms: Dechlorination Extent, Preferences, Ortho Removal, and Its Enhancement.

Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) has been observed in many PCB-impacted sediments. However, this biodegradation is relatively site-specific and can be affected by PCB compositions and sediment geochemical conditions. To better understand the influence of a common competing electron acceptor, ferric oxyhydroxide (FeOOH), on dechlorination, two sediments (Hudson River and Grasse River sediments), and two PCB mixtures (PCB 5/12, 64/71, 105/114, and 149/153/170 in Mixture 1 and PCB 5/12, 64/71, 82/97/99, 144/170 in Mixture 2) were used for this microcosm study. The addition of 40 mmole/kg FeOOH completely inhibited PCB dechlorination in the Hudson sediment, but only moderately inhibited PCB dechlorination in the Grasse sediment with a 3-week longer lag time. The inhibitory effect in the Grasse sediment was mainly due to the loss of unflanked para dechlorination activity. Fe(II) analysis showed that dechlorination started prior to the consumption of Fe(III), which indicates PCB reduction and Fe(III) reduction were able to take place concurrently. Dehalococcoides 16S rRNA genes increased with the commencement of dechlorination in the Grasse sediment, but not in the completely inhibited Hudson sediment. Rare ortho dechlorination pathways were identified in FeOOH-amended Grasse sediment microcosms, dominated by transformations of PCB 25(24-3-CB) to PCB 13(3-4-CB) and PCB 28(24-4-CB) to PCB 15(4-4-CB). The addition of carbon sources (acetate or a fatty acid mixture with acetate, propionate, and butyrate) after 27 weeks of incubation reinitiated dechlorination in FeOOH-amended Hudson sediment microcosms. Also, the addition of carbon sources greatly enhanced ortho dechlorination in FeOOH-amended Grasse microcosms, indicating the utilization of acetate and/or the fatty acid mixture for ortho dechlorination-related microorganisms. A dechlorination pathway analysis approach revealed that para-flanked meta dechlorination was primarily preferred followed by ortho-/double-flanked meta dechlorination and single-/double-flanked para dechlorination in the Grasse sediment.

Time-dependent bacterial community and electrochemical characterizations of cathodic biofilms in the surfactant-amended sediment-based bioelectrochemical reactor with enhanced 2,3,4,5-tetrachlorobiphenyl dechlorination.

Applying an electric field to stimulate the microbial reductive dechlorination of polychlorinated biphenyls (PCBs) represents a promising approach for bioremediation of PCB-contaminated sites. This study aimed to demonstrate the biocathodic film-facilitated reduction of PCB 61 in a sediment-based bioelectrochemical reactor (BER) and, more importantly, the characterizations of electrode-microbe interaction from microbial and electrochemical perspectives particularly in a time-dependent manner. The application of a cathodic potential (-0.45 V vs. SHE) significantly improved the rate and extent of PCB 61 dechlorination compared to the open-circuit scenario (without electrical stimulation), and the addition of an external surfactant further increased the dechlorination, with Tween 80 exerting more pronounced effects than rhamnolipid. The bacterial composition of the biofilms and the bioelectrochemical kinetics of the BERs were found to be time-dependent and to vary considerably with the incubation time and slightly with the coexistence of an external surfactant. Excellent correlations were observed between the dechlorination rate and the relative abundance of Dehalogenimonas, Dechloromonas, and Geobacter, the dechlorination rate and the cathodic current density recorded from the chronoamperometry tests, and the dechlorination rate and the charge transfer resistance derived from the electrochemical impedance tests, with respect to the 120 day-operation. After day 120, PCB 61 was resistant to further appreciable reduction, but substantial hydrogen production was detected, and the bacterial community and electrochemical parameters observed on day 180 were not distinctly different from those on day 120.

Method for polychlorinated biphenyls removal from mussels and its photocatalytic dechlorination

A simple method has been proposed for the removal and degradation of polychlorinated biphenyls (PCBs) from catches using low cost and environmental friendly way. The removal of PCBs from lipid layer to aqueous layer was done by utilizing polyethylene glycol (PEG) as phase transfer agent and photocatalysis technology for its degradation. Experimental involving various types of PEG and concentrations were performed to obtain the highest percentage of removal. The highest total amount of PCBs removal was attained using PEG 400 with concentration of 0.2M. In order to determine the suitable photocatalyst to use for the degradation study, the physicochemical properties of WO3/SnO2/TiO2 prepared from mechanical mixed and sol-immobilization were compared. In situ and ex situ techniques were explored to determine its influence on removal and degradation of PCBs. Substantial degradation of removed PCBs in ex situ method was achieved in the presence of heterostructured WO3/SnO2/TiO2 photocatalyst prepared by mechanical mixing under visible light. Meanwhile significant total amount of PCBs reduction in mussels was observed under in situ method (with PEG 400, 0.2M and photocatalyst) compared to control run. Thus, this study displayed conformity of the method with high degradation.

Microbial polychlorinated biphenyl dechlorination in sediments by electrical stimulation: The effect of adding acetate and nonionic surfactant

The necessity for developing an efficient and cost-effective in situ bioremediation technology for sediments contaminated with polychlorinated biphenyls (PCBs) has prompted the application of low-voltage electrical fields to anaerobic digestion systems. Here we show that the use of a sediment-based bio-electrochemical reactor (BER) poised at a potential of -0.50V (vs. a standard calomel electrode, SCE) substantially enhanced the reduction of 2,3,4,5-tetrachlorobiphenyl (PCB 61) when acetate was added as a carbon source. The addition of surfactant Tween 80 to the BER further accelerated the PCB 61 transformation. The comparative study of closed- and open-circuit reactors demonstrated the enrichment conditions affecting the bacterial community structure, the dominant dechlorination metabolisms, and thus the extent, the rate and the products of the reduction of PCBs. The dominant bacterial dechlorinators detected in the BERs in the presence of acetate and Tween 80 are Dehalogenimonas, Dehalobacter, Sulfuricurvum, Dechloromonas and Geobacter, which should be responsible for PCB dechlorination. This study improves understanding of the key factors influencing dechlorination activity in sediment-based BERs polarized at a low potential, as well as the metabolic mechanisms dominating in the PCB dechlorination process.

Temporal trends of polychlorinated biphenyls serum levels in subjects living in a highly polluted area in Italy from 2003 to 2015: a population-based cohort study.

Introduction A chemical factory located in Brescia, an industrialized town in North Italy, produced polychlorinated biphenyls since the 1930s to the 1980s, determining a relevant pollution of soil, food and people. Since 2001, after a survey carried out in the general population living in the town, the individuals with serum levels of polychlorinated biphenyls higher than the reference entered a follow-up study for evaluating the temporal trend of their polychlorinated biphenyls serum levels. Methods We performed a prospective cohort study including subjects with at least three polychlorinated biphenyls measures during the period 2003-2015. We evaluated the temporal trends of total polychlorinated biphenyls serum levels using mixed models with a cubic-spline for time. We also stratified the analysis for the most commonly found congeners (IUPAC codes 138,153, 170, 180, 194 and 209) and subjects’ age. Results A total of 128 subjects were enrolled (mean age 57.7 years). The mean of polychlorinated biphenyls decreased from 58.35 ng/ml at the beginning (0-3 years) to 40.62 ng/ml at the end (9-12 years) of the follow-up. Polychlorinated biphenyls reduction over time was confirmed when using multivariate mixed models adjusted for age, and when analysing the major congeners separately. Finally, we evaluated the temporal trend according to age tertiles using mixed models with cubic splines terms for polychlorinated biphenyls. From baseline to twelve years, mean values of polychlorinated biphenyls levels increased with age and decreased over time, for each age category: from 43.05 ng/ml to 26.57 ng/ml, from 54.95 ng/ml to 31.30 ng/ml and from 75.36 ng/ml to 49.42 ng/ml for ages ≤55 years, 56-65 and ≥66 years, respectively. Conclusions A significant decrease of the serum concentrations of polychlorinated biphenyls was observed in subjects with high values of these chemicals at enrolment, over a 12 year period. The decrease was evident for each congener and age group.

Polychlorinated biphenyls (PCBs) in sediments from the western Adriatic Sea: Sources, historical trends and inventories

Sources, historical trends and inventories of polychlorinated biphenyls (PCBs) were investigated in sediments collected in five transects along the north-south axis of the western Adriatic Sea. The concentration of total PCBs (∑28 PCBs) ranged from <LOD (limit of detection) to 9.0ngg−1 in the sediment cores and between 0.1 and 2.2ngg−1 in recent sediments. Chronological records of PCB concentrations displayed a common pattern with historical PCB production and use, with the maximum peak values detected between the 1960s and the 1980s. Sediments deposited within the last two decades presented a ~40% to ~80% PCB reduction in comparison to the peak levels, reflecting the ban on PCB production and use since the late 1970s. PCB levels along with the presence of high-chlorinated congeners decreased southwards, indicating the Po River as the major source of PCBs in the western Adriatic Sea. This is further corroborated by the estimated inventories of PCBs, which were ~4–7 times higher in the Po River prodelta (256ngcm−2) in comparison to the middle and southern Adriatic, respectively, and about 100 times higher than the in the deep Adriatic Sea.

Enhanced dechlorination of 2,2′,4,4′,5,5′-hexachlorobiphenyl in water-sediment mixture by adding anthraquinone-2,6-disulfonic acid

Dechlorination of polychlorinated biphenyls (PCBs) in aquatic sediments and anaerobic bioreactors has been widely observed, and mechanisms have also been studied. However, the role of humic acid in the biotic dechlorination of PCBs has not been studied. The present study investigated the role of humic acid as the redox mediator in the anaerobic biotransformation of PCBs in water and sediment mixture. Degradation of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) in water and sediment mixture was studied by adding different concentrations of anthraquinone-2,6-disulfonic acid (AQDS), which was a model substance for quinone moieties in humic acid. Chemical reduction of PCB 153 by sterile AH2QDS was performed to investigate the mechanisms involved. Decrease of PCB 153 was enhanced significantly by adding AQDS. The loss percentage of PCB 153 after 15 days of incubation was increased from 9.03 ± 2.73 % to 38.3 ± 3.27 % (P = 95 %) by adding 1 mM AQDS, while it was increased to 46.8 ± 4.41 % (P = 95 %) by adding 5 mM sodium acetate and 1 mM AQDS. Less chlorinated congeners PCB 101 and PCB 52 were identified as the products through the dechlorination of PCB 153 mainly in para positions. The results suggested that the quinone moieties in humic acid may play an important role in the dechlorination of PCBs in nature. This finding will help us to understand the natural attenuation of PCBs better and also provide a method to enhance the removal of higher chlorinated PCBs in waste treatment process.

Reduction of the body burden of PCBs and DDE by dietary intervention in a randomized trial

Serum polychlorinated biphenyls (PCBs) in Anniston, AL, residents have been associated with hypertension and diabetes. There have been no systematic interventions to reduce PCB body burdens in Anniston or other populations. Our objective was to determine the efficacy of 15 g/day of dietary olestra to reduce PCBs in Anniston residents. Blood PCBs and 1,1-bis-(4-chlorophenyl)-2,2-dichloroethene were measured at baseline and 4-month intervals in a double-blind, placebo-controlled, 1-year trial. Participants with elevated serum PCBs were randomized into two groups of 14 and received potato crisps made with olestra or vegetable oil (VO). Elimination rates during the study period were compared with 5-year prestudy rates. Eleven participants in the olestra group and 12 in the VO group completed the study. Except for one participant in the VO group, reasons for dropout were unrelated to treatments. The elimination rate of 37 non-coplanar PCB congeners during the 1-year trial was faster during olestra consumption compared to the pretrial period (−0.0829±0.0357 and −0.00864±0.0116 year−1, respectively; P=.04), but not during VO consumption (−0.0413±0.0408 and −0.0283±0.0096 year−1, respectively; P=.27). The concentration of PCBs in two olestra group participants decreased by 27% and 25% during the trial. There was no significant time by group interaction in change from baseline. However, group main effects for total PCBs and PCB 153 were of borderline significance. This pilot study has demonstrated that olestra can safely reduce body burdens of PCBs and supports a larger intervention trial that may also determine whether reduction in PCBs will reduce the risk of hypertension and diabetes.

The effect of PCB-contaminated sewage sludge and sediment on metabolism of cucumber plants (Cucumis sativus L.)

Increasing amounts of sewage sludge are produced nowadays, which need to be disposed of in a safe and responsible manner. Likewise, bottom sediments from small urban water bodies undergo periodical dredging and need to be utilized. These deposits often contain Persistant Organic Pollutants (POPs) and other toxic substances. Plants can be used to reduce these pollutants during or before disposal to land (phytoremediation). Cucurbitaceae are known to accumulate high levels of POPs, including polychlorinated biphenyls (PCB), compared with other plant species but such accumulation may lead to secondary oxidative stress that may limit their value. This study examined the impact of sewage sludge and urban lake sediment on soil toxicity, measured as PCB concentration, and changes in the antioxidative system of cucumber plants grown in the soils.There was an average reduction of PCB by 38.63% and 27.38% in soil amended with sewage sludge and sediment, respectively after 5 weeks of cucumber plant cultivation. In the case of plants grown with sewage sludge, guaiacol peroxidase (POx) activity significantly decreased to 49% of the control at the highest dose given, while that of glutathione S-transferase (GST) increased to 172% of the control value in the same treatment. α-Tocopherol concentration was higher in the plants grown in the sewage sludge amended soil.

Reductive dechlorination of polychlorinated biphenyls (PCBs) by ultrasound-assisted chemical process (UACP)

The dechlorination of aqueous polychlorinated biphenyls (PCBs) using the ultrasound-assisted chemical process (UACP), which is a combination of ultrasonic irradiation and radical generations using di-tert-butyl peroxide as a radical initiator and ferrous ion as a catalyst at moderate temperature in alkaline 2-propanol, was demonstrated with a high reduction of PCBs. A commercial PCB-containing compound, Aroclor 1260, was also decomposed with the removal efficiency of 97 % achieved within 3 h of UACP. The gas chromatograph was used as a quantitative method to measure the decomposition rate of PCBs. The competitive elimination among the ortho (2-position), meta (3-position), and para (4-position) chlorine atoms of PCB was also identified.

Dechlorination of polychlorinated biphenyls in transformer oil using UV and visible light

A study on dechlorination of PCB138 in transformer oil (TO) and 2-propanol (IPA) using 254 nm ultraviolet (UV) light as well as dye sensitized visible light has been conducted. Studies on dechlorination of polychlorinated biphenyls (PCBs) in TO using visible light in the presence of methylene blue (MB) and triethylamine (TEA) (providing a ‘photocatalytic’ cycle) in both deaerated and aerated conditions have been conducted to determine effects of TO, MB and TEA on reaction rates. The results show that photolytic methods are effective in treating PCBs in TO, and that the oil plays a limited adverse role. Under UV irradiation, PCB 138 can be >99% dechlorinated in the presence 0.06% (w/w) TO in IPA within 1 h with a rate constant of 0.0853 min−1, while 47% of PCB138 can be dechlorinated in 92.1% (w/w) TO in IPA within 2 h with a rate constant of 0.0051 min−1. In the ‘photocatalytic’ system, 94% reduction of PCB 138 was achieved within 30 min with a rate constant of 0.0968 min−1 when the solvent was 60.70% (w/w) TO in IPA, while 71% dechlorination of PCB138 was achieved within 30 min with a rate constant of 0.0382 min−1 when 81.62% (w/w) TO was present. In treatment of 30–73 ppm PCBs in TO, the optimal concentration of MB and TEA were found to be 0.5 g/L and 58.08 g/L respectively. Because of quenching by oxygen, deaeration of the solution is necessary for an efficient reaction. The photocatalytic system is especially adapted for treating lower concentration of PCBs in TO.

PCBs stimulate laccase production and activity in Pleurotus ostreatus thus promoting their removal

Pleurotus ostreatus degrades polychlorinated biphenyls (PCBs) with an increase of laccase activity. Laccases are well known for their detoxifying activity. We show, using reverse transcription polymerase chain reaction and a biochemical assay, that reduction in PCBs (di, tri, tetra, and penta) levels are correlated with an increase in laccase activity. P. ostreatus cultures were obtained from 0 to 30 days in the presence or absence of 7,100 mg/L PCBs (from transformer oil) and a surfactant. After each selected time cultures were withdrawn and remaining PCBs were determined, a maximal removal percentage of PCBs was obtained at 20 (63.5 ± 2.0) and 30 days (63.8 ± 4.6) post-induction. Also, the activity of the enzyme was analyzed and it was found to increase at 10 (6.9-fold) and 20 (6.77-fold) days post-induction in the presence of PCBs, as determined by its activity. Taken together, these data suggest that PCBs induce laccase expression and that laccase catalyzes PCBs removal.

Reply to comment on “Reductive dechlorination of γ-hexachlorocyclohexane using Fe–Pd bimetallic nanoparticles”, by C. Noubactep

A simple method has been proposed for the removal and degradation of polychlorinated biphenyls (PCBs) from catches using low cost and environmental friendly way. The removal of PCBs from lipid layer to aqueous layer was done by utilizing polyethylene glycol (PEG) as phase transfer agent and photocatalysis technology for its degradation. Experimental involving various types of PEG and concentrations were performed to obtain the highest percentage of removal. The highest total amount of PCBs removal was attained using PEG 400 with concentration of 0.2 M. In order to determine the suitable photocatalyst to use for the degradation study, the physicochemical properties of WO3/SnO2/TiO2 prepared from mechanical mixed and sol-immobilization were compared. In situ and ex situ techniques were explored to determine its influence on removal and degradation of PCBs. Substantial degradation of removed PCBs in ex situ method was achieved in the presence of heterostructured WO3/SnO2/TiO2 photocatalyst prepared by mechanical mixing under visible light. Meanwhile significant total amount of PCBs reduction in mussels was observed under in situ method (with PEG 400, 0.2 M and photocatalyst) compared to control run. Thus, this study displayed conformity of the method with high degradation.

Electrochemical Removal of Chloride from Polychlorinated Biphenyls in an Oil/n-Butanol/HCl and an n-Propanol/HCl System

We present an exploratory study that seeks to identify new routes for the treatment of transformer dielectric oils contaminated with polychlorinated biphenyls (PCBs), through the usage of direct reduction electrochemical methods, using Pb/PbO2 electrodes. It is known to be possible to prepare a PCB emulsion using tensoactive agents and perform the direct PCB reduction effectively (1). Nevertheless, this procedure has drawbacks. We are orienting this study towards identifying media capable of dissolving the contaminated oil and conferring enough conductivity to make the direct reduction of the PCBs or to make an extraction of the PCBs of the contaminated oil before the electrolysis. To reach this goal, n-butanol as a solubilization agent and n-propanol as an extraction agent in HCl environment were selected. The high electrical resistance of the environment avoided the direct reduction, while selective electrolysis of the PCBs, once extracted in Pb/PbO2 electrodes, could take place.

Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones

This study pilot-tested carboxymethyl cellulose (CMC) stabilized zero-valent iron (ZVI) nanoparticles (with a trace amount of Pd catalyst) for in situ destruction of chlorinated ethenes such as perchloroethylene (PCE) and trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) that had been in groundwater for decades. The test site was located in a well-characterized secondary source zone of PCBs and chlorinated ethenes. Four test wells were installed along the groundwater flow direction (spaced 5 ft apart), including one injection well (IW), one up-gradient monitoring well (MW-3) and two down-gradient monitoring wells (MW-1 and MW-2). Stabilized nanoparticle suspension was prepared on-site and injected into the 50-ft deep, unconfined aquifer. Approximately 150 gallons of 0.2 g/L Fe–Pd (CMC = 0.1 wt%, Pd/Fe = 0.1 wt%) was gravity-fed through IW-1 over a 4-h period (Injection #1). One month later, another 150 gallons of 1.0 g/L Fe–Pd (CMC = 0.6 wt%, Pd/Fe = 0.1 wt%) was injected into IW-1 at an injection pressure <5 psi (Injection #2). When benchmarked against the tracer, approximately 37.4% and 70.0% of the injected Fe was detected in MW-1 during injection #1 and #2, respectively, confirming the soil mobility of the nanoparticles through the aquifer, and higher mobility of the particles was observed when the injection was performed under higher pressure. Rapid degradation of PCE and TCE was observed in both MW-1 and MW-2 following each injection, with the maximum degradation being observed during the first week of the injections. The chlorinated ethenes concentrations gradually returned to their pre-injection levels after ∼2 weeks, indicating exhaustion of the ZVI's reducing power. However, the injection of CMC-stabilized nanoparticle and the abiotic reductive dechlorination process appeared to have boosted a long-term in situ biological dechlorination thereafter, which was evidenced by the fact that PCE and TCE concentrations showed further reduction after two weeks. After 596 days from the first injection, the total chlorinated ethenes concentration decreased by about 40% and 61% in MW-1 and MW-2, respectively. No significant long-term reduction of PCB 1242 was observed in MW-1, but a reduction of 87% was evident in MW-2. During the 596 days of testing, the total concentrations of cis-DCE (dichloroethylene) and VC (vinyl chloride) decreased by 20% and 38% in MW-1 and MW-2, respectively. However, the combined fraction of cis-DCE and VC in the total chlorinated ethenes (PCE, TCE, cis-DCE and VC) increased from 73% to 98% and from 62% to 98%, respectively, which supports the notion that biological dechlorination of PCE and TCE was active. It is proposed that CMC-stabilized ZVI-Pd nanoparticles facilitated the early stage rapid abiotic degradation. Over the long run, the existing biological degradation process was boosted with CMC as the carbon source and hydrogen from the abiotic/biotic processes as the electron donor, resulting in the sustained enhanced destruction of the chlorinated organic chlorinated ethenes in the subsurface.

Contaminated site investigation and remediation of chlorinated aromatic compounds

The high degree of public concern and anxiety about chlorinated aromatic compounds persisting in the environment mandate that effective clean-up methods be found to eliminate their hazard. The factors that lead to the implementation of such techniques are found to vary significantly according to economic factors, site locations, and community perceptions. The disposal of chlorinated aromatic compounds has become a major environmental and social problem. Due to their chemical stability and resistance to degradation, their presence in the environment poses a potential health hazard to humans and other organisms. This investigation reviews the methods currently in use for the remediation of chlorinated aromatic compounds in soils and sediments and examines the factors that lead to the implementation of each technique under specific conditions. An experimental program has also been conducted to investigate the effectiveness of low temperature dechlorination of PCB contaminated soil. From the bench-scale experiments performed, it could be determined that the potential exists for scale-up to accommodate larger quantities of soils and sediments. Destruction and removal efficiency (DRE) exceeding 99% show that by manipulation of controlled conditions, further improvements in the degradation of polychlorinated biphenyls (PCBs) from soils can be attained. Preliminary studies using a novel process have shown that low temperatures and controlled conditions can achieve reduction of PCBs in soils and sediments from 1000 to below 10 ppm. The augmentation of an alkaline source and saturated steam diffusing across the fixed bed was found to contribute substantially to the dechlorination process. In experiments conducted to date, altering conditions in a tube furnace have determined how dechlorination can best be promoted. This has entailed optimising reaction times, temperatures and the augmentation of additives.