Plant terpenes and lignin as natural cosubstrates in biodegradation of polyclorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs)

Myco- and phyco-remediation of polychlorinated biphenyls in the environment: a review

Polychlorinated biphenyls (PCBs) are toxic organic compounds and pose serious threats to environment and public health. PCBs still exist in different environments such as air, water, soil, and sediments even on ban. This review summarizes the phyco- and myco-remediation technologies developed to detoxify the PCB-polluted sites. It was found that algae mostly use bioaccumulation to biodegradation strategies to reclaim the environment. As bio-accumulator, Ulva rigida C. Agardh has been best at 25 ng/g dry wt to remove PCBs. Evidently, Anabaena PD-1 is the only known PCB degrading alga and efficiently degrade Aroclor 1254 and dioxin-like PCBs up to 84.4% and 37.4% to 68.4%, respectively. The review suggested that factors such as choice of algal strains, response of microalgae, biomass, the rate of growth, and cost-effective cultivation conditions significantly influence the remediation of PCBs. Furthermore, the Anabaena sp. linA gene of Pseudomonas paucimobilis Holmes UT26 showed enhanced efficiency. Pleurotus ostreatus (Jacq.) P. Kumm is the most efficient PCB degrading fungus, degrading up to 98.4% and 99.6% of PCB in complex and mineral media, respectively. Combine metabolic activities of bacteria and yeast led to the higher detoxification of PCBs. Fungi-algae consortia would be a promising approach in remediation of PCBs. A critical analysis on potentials and limits of PCB treatment through fungal and algal biosystems have been reviewed, and thus, new insights have emerged for possible bioremediation, bioaccumulation, and biodegradation of PCBs.

Submillimetre mechanistic designs of termite-built structures

Termites inhabit complex underground mounds of intricate stigmergic labyrinthine designs with multiple functions as nursery, food storage and refuge, while maintaining a homeostatic microclimate. Past research studied termite building activities rather than the actual material structure. Yet, prior to understanding how multi-functionality shaped termite building, a thorough grasp of submillimetre mechanistic architecture of mounds is required. Here, we identify for Nasutitermes exitiosus via granulometry and Fourier transform infrared spectroscopy analysis, preferential particle sizes related to coarse silts and unknown mixtures of organic/inorganic components. High-resolution micro-computed X-ray tomography and microindentation tests reveal wall patterns of filigree laminated layers and sub-millimetre porosity wrapped around a coarse-grained inner scaffold. The scaffold geometry, which is designed of a lignin-based composite and densely biocementitious stercoral mortar, resembles that of trabecula cancellous bones. Fractal dimension estimates indicate multi-scaled porosity, important for enhanced evaporative cooling and structural stability. The indentation moduli increase from the outer to the inner wall parts to values higher than those found in loose clays and which exceed locally the properties of anthropogenic cementitious materials. Termites engineer intricately layered biocementitious composites of high elasticity. The multiple-scales and porosity of the structure indicate a potential to pioneer bio-architected lightweight and high-strength materials.

Bentonite addition to a PCB-contaminated sandy soil improved the growth and phytoremediation efficiency of Zea mays L. and Alternanthera sessilis L

In this study, the removal of 17 selected PCB_i congeners was assessed in a transformer oil-contaminated soil amended with bentonite clay powder applied at the three levels of 0, 2, and 4% and cultivated by Zea mays L. or Alternanthera sessilis L. in a pot experiment. Results showed that Z. mays and A. sessilis were able to reduce the residual concentrations of the PCB_i congeners in the contaminated soil significantly (p < 0.05). The average reductions in the ƩPCB_i due to Z. mays or A. sessilis cultivations were 34.3 and 21.4%, respectively, depending on initial soil ƩPCB_i loading and plant growth period. Moreover, addition of bentonite led to significant (p < 0.05) enhancements in plant growth and dissipation of residual soil PCB_i congeners under Z. mays and A. sessilis cultivations. Addition of 4% bentonite to the soil was found to have the greatest positive impact on PCB_i removal so that average PCB_i dissipations in the soil were 56.1 and 51.8% after growing Z. mays and A. sessilis, respectively. It might be concluded that the combined phytoremediation and bentonite addition is an effective technique for removing PCB_i and remediating transformer oil-contaminated coarse-textured soils.

Coupling of bioaugmentation and phytoremediation to improve PCBs removal from a transformer oil-contaminated soil

This study was carried out to assess the dissipation of 17 selected polychlorinated biphenyl (PCB_i) congeners in a transformer oil-contaminated soil using bioaugmentation with 2 PCB-degrading bacterial strains, i.e., Pseudomonas spp. S5 and Alcaligenes faecalis, assisted or not by the maize (Zea mays L.) plantation. After 5 and 10 weeks of treatment, the remaining concentrations of the target PCB_i congeners in the soil were extracted and measured using GC-MS. Results showed that the bacterial augmentation treatments with Pseudomonas spp. S5 and A. faecalis led to 21.4% and 20.4% reduction in the total concentration of the target PCBs (ΣPCB_i), respectively, compared to non-bioaugmented unplanted control soil. The ΣPCB_i decreased by 35.8% in the non-bioaugmented planted soil compared with the control. The greatest degradation of the PCB congeners was observed over a 10-week period in the soil inoculated with Pseudomonas spp. S5 and cultivated with maize. Under this treatment, the ΣPCB_i decreased from 357 to 119 ng g^-1 (66.7% lower) and from 1091 to 520 ng g^-1 (52.3% lower). Overall, the results suggested that the combined application of phytoremediation and bioaugmentation was an effective technique to remove PCBs and remediate transformer oil-contaminated soils.

Plant-bacteria partnerships for the remediation of persistent organic pollutants

High toxicity, bioaccumulation factor and widespread dispersal of persistent organic pollutants (POPs) cause environmental and human health hazards. The combined use of plants and bacteria is a promising approach for the remediation of soil and water contaminated with POPs. Plants provide residency and nutrients to their associated rhizosphere and endophytic bacteria. In return, the bacteria support plant growth by the degradation and detoxification of POPs. Moreover, they improve plant growth and health due to their innate plant growth-promoting mechanisms. This review provides a critical view of factors that affect absorption and translocation of POPs in plants and the limitations that plant have to deal with during the remediation of POPs. Moreover, the synergistic effects of plant-bacteria interactions in the phytoremediation of organic pollutants with special reference to POPs are discussed.

Phytoremediation and bioremediation of polychlorinated biphenyls (PCBs): state of knowledge and research perspectives

This review summarizes the bioremediation and phytoremediation technologies proposed so far to detoxify PCB-contaminated sites. A critical analysis about the potential and limits of the PCB pollution treatment strategies by means of plants, fungi and bacteria are elucidated, including the new insights emerged from recent studies on the rhizosphere potential and on the implementation of simultaneous aerobic and anaerobic biodegradation processes. The review describes the biodegradation and phytoremediation processes and elaborates on the environmental variables affecting contaminant degradation rates, summarizing the amendments recommended to enhance PCB degradation. Additionally, issues connected with PCB toxicology, actual field remediation strategies and economical evaluation are discussed.

[Advance in bioremediation of polychlorinated biphenyls]

As one of the persistent organic pollutants, polychlorinated biphenyls are harmful to the environment and humans. Biodegradation is the most potential way to remove PCBs. Biodegradation can mainly be divided into microbial degradation, phytoremediation, plant and microbial combined remediation. Here, we introduced isolation of the PCBs-degrading strains, cloning and modification of the related degradation genes. Additionally, on the other hand, the natural remediation of plant, plant and microbial combined remediation, plant transgenic remediation were described.