Sustainable decontamination of an actual-site aged PCB-polluted soil through a biosurfactant-based washing followed by a photocatalytic treatment

A two phases process consisting of a soya lecithin (SL)-based soil washing process followed by the photocatalytic treatment of resulting effluents was developed and applied at the laboratory scale in the remediation of an actual-site soil historically contaminated by 0.65 g/kg of polychlorinated biphenyls (PCBs). Triton X-100 (TX) was employed in the same process as a control surfactant. SL and TX, both applied as 2.25 g/L aqueous solutions, displayed a comparable ability to remove PCBs from the soil. However, SL solution displayed a lower ecotoxicity, a lower ability to mobilize soil constituents and a higher soil detoxification capacity with respect to the TX one. The photocatalytic treatment resulted in marked depletions (from 50% to 70%) of total organic carbon (TOC) and PCBs initially occurring in the SL and TX contaminated effluents. Despite the ability of SL to adversely affect the rate of TOC and PCB photodegradation, higher PCB depletion and dechlorination yields along with lower increases of ecotoxicity were observed in SL-containing effluents with respect to the TX ones at the end of 15 days of treatment. The two phases process developed and tested for the first time in this study seems to have the required features to become, after a proper optimization and scale up, a challenging procedure for the sustainable remediation of actual site, poorly biotreatable PCB-contaminated soils.     

Biomass-supported palladium catalysts on Desulfovibrio desulfuricans and Rhodobacter sphaeroides

A Rhodobacter sphaeroides-supported dried, ground palladium catalyst ("Rs-Pd(0)") was compared with a Desulfovibrio desulfuricans-supported catalyst ("Dd-Pd(0)") and with unsupported palladium metal particles made by reduction under H2 ("Chem-Pd(0)"). Cell surface-located clusters of Pd(0) nanoparticles were detected on both D. desulfuricans and R. sphaeroides but the size and location of deposits differed among comparably loaded preparations. These differences may underlie the observation of different activities of Dd-Pd(0) and Rs-Pd(0) when compared with respect to their ability to promote hydrogen release from hypophosphite and to catalyze chloride release from chlorinated aromatic compounds. Dd-Pd(0) was more effective in the reductive dehalogenation of polychlorinated biphenyls (PCBs), whereas Rs-Pd(0) was more effective in the initial dehalogenation of pentachlorophenol (PCP) although the rate of chloride release from PCP was comparable with both preparations after 2 h.     

Molecular assessment of the potential for in situ bioremediation of PCBs from aquatic sediments

Polychlorinated biphenyls (PCBs) are a family of xenobiotic compounds that are ubiquitous and oftentimes persistent environmental pollutants. As such, PCBs are a common target of sediment remediation efforts. Microbial degradation of sediment pollutants such as PCBs offers an environmentally sound and economically favorable alternative to conventional means of remediation such as dredging. This project describes the development of a PCR-based assay to determine the potential for PCB bioremediation by the resident microbial consortium in contaminated sediments. Using PCR and RT-PCR of DNA and RNA, respectively, extracted from aquatic sediments collected from the western basin of Lake Erie and one of its tributaries, we were able to amplify the bphA1 gene that encodes the large subunit of biphenyl dioxygenase. Since other studies have determined that the BphA1 gene product dictates PCB congener specificity, this assay may prove to be a useful screen for endemic catabolic activities for PCB mixtures in aquatic sediments.     

Remediation of PCBs in soil by surfactant washing and biodegradation in the wash by Pseudomonas sp. LB400

Solutions from the washing of polychlorinated biphenyl (PCB)-contaminated soil with a variety of commercial nonionic or anionic surfactants were incubated with Pseudomonas sp. LB400 in an attempt to remediate the soil and destroy the PCBs. Nonionic surfactants washed more PCBs from the soil (up to 89%) but inhibited their biodegradation. Anionic surfactants washed less PCBs from the soil but were more effective in biodegradation tests, removing up to 67% of total PCBs.     

Molecular characterization of polychlorinated biphenyl-dechlorinating populations in contaminated sediments

Polychlorinated biphenyl (PCB)-dechlorinating microorganisms were characterized in PCB-contaminated sediments using amplified ribosomal DNA restriction analysis (ARDRA). The sediments were prepared by spiking Aroclor 1248 into PCB-free sediments, and were inoculated with microorganisms eluted from St. Lawrence River sediments. PCB-free sediments inoculated with the same inoculum served as the control. Four restriction fragment length polymorphism (RFLP) groups in the eubacterial and two in the archaeal domain were found exclusively in PCB-spiked sediment clone libraries. Sequence analysis of the four eubacterial clones showed homology to Escherichia coli, Lactosphaera pasteurii, Clostridium thermocellum, and Dehalobacter restrictus. The predominant archaeal sequence in the PCB-spiked sediment clone library was closely related to Methanosarcina barkeri, which appear to support earlier findings that methanogens are involved in PCB dechlorination. When the dot-blot hybridization was performed between the sediment DNA extract and the probes designed with eubacterial RFLP groups, the intensity of two of eubacterial RFLP groups, which showed high sequence homology to C. pascui and D. restrictus, was highly correlated with the number of dechlorinating microorganisms suggesting these two members intend to contribute to PCB dechlorination.     

Degradation of polychlorinated biphenyls by extracellular enzymes of Phanerochaete chrysosporium produced in a perforated plate bioreactor

The white rot fungus Phanerochaete chrysosporium was cultivated in a perforated plate bioreactor and the expression of activities of manganese-dependent peroxidase (MnP) and lignin peroxidase (LiP) was measured. Peak activities of the two enzymes were reached close to day 11 and therefore the cultivation was terminated on that day. Extracellular proteins were concentrated and both peroxidases separated by isoelectric focusing. Degradation of technical PCB mixtures containing low and highly chlorinated congeners (Delor 103 and Delor 106 as equivalents of Aroclor 1242 and Aroclor 1260, respectively) was performed using intact mycelium, crude extracellular liquid and enriched MnP and LiP. A decrease in PCB concentration caused by a 44-h treatment with mycelium (74% w/w for Delor 103 and 73% for Delor 106) or crude extracellular liquid (62% for Delor 103 and 58% for Delor 106) was observed. The degradation was not substrate-specific, because no significant differences between the respective degradation rates were observed with di-, tri-, tetra-, penta-, hexa-, hepta-, and octachlorinated congeners. In contrast, MnP and LiP isolated from the above-mentioned extracellular liquid did not catalyse any degradation.     

Colonization and growth of dehalorespiring biofilms on carbonaceous sorptive amendments

Removal of polychlorinated biphenyls (PCBs) from contaminated sediments is a priority due to accumulation in the food chain. Recent success with reduction of PCB bioavailability due to adsorption onto activated carbon led to the recognition of in situ treatment as a remediation approach. In this study, reduced bioavailability and subsequent break-down of PCBs in dehalorespiring biofilms was investigated using Dehalobium chlorocoercia DF1. DF1 formed a patchy biofilm ranging in thickness from 3.9 to 6.7?µm (average 4.6?±?0.87?µm), while the biofilm coverage varied from 5.5% (sand) to 20.2% (activated carbon), indicating a preference for sorptive materials. Quantification of DF1 biofilm bacteria showed 1.2–15.3?×?10⁹ bacteria per gram of material. After 22?days, coal activated carbon, bone biochar, polyoxymethylene, and sand microcosms had dechlorinated 73%, 93%, 100%, and 83%, respectively. These results show that a biofilm-based inoculum for bioaugmentation of PCBs in sediment can be an efficient approach.     

Gene regulation in the marine diatom Thalassiosira pseudonana upon exposure to polycyclic aromatic hydrocarbons (PAHs)

Diatoms are eukaryotic algae, which can be found worldwide in oceans and freshwaters. These organisms are ecologically relevant due to their key role in the global carbon cycle, contributing to about 25% to the global primary production [Falciatore, A., Bowler, C., 2002. Revealing the molecular secrets of marine diatoms. Annu. Rev. Plant Biol. 53, 109-130]. We investigated the effects of three polycyclic aromatic hydrocarbons (PAHs, pyrene, fluoranthene, and benzo[a]pyrene), either as single compound or as mixture, at molecular level. Dose-response curves for growth inhibition were determined and four concentrations eliciting from "no effect" up to a severe growth inhibition were chosen for further investigation to detect alterations at gene expression level by Real-Time PCR. Among the eight selected genes, two were strongly influenced by the PAH treatment. lacsA, which is involved in the fatty acid metabolism, was found to be strongly up-regulated by all single PAHs, as well as by the mixture. sil3, involved in the formation of the silica shell, was repressed by a factor up to three even at low PAH concentrations not eliciting any growth inhibition. For other genes, involved e.g. in photosynthesis, a slight down-regulation was detected. Based on the effects at gene expression level it can be assumed that PAHs impair the fatty acid metabolism and silica shell formation.