Potential for phytoremediation of polychlorinated biphenyl-(PCB-)contaminated soil

Ectopic expression of an Old Yellow Enzyme (OYE3) gene from Saccharomyces cerevisiae increases the tolerance and phytoremediation of 2-nitroaniline in rice

2-nitroaniline (2-NA) is an environmental pollutant and has been extensively used as intermediates in organic synthesis. The presence of 2-NA in the environment is not only harmful for aquatic life but also mutagenic for human beings. In this study, we constructed transgenic rice expressing an Old Yellow Enzyme gene, ScOYE3, from Saccharomyces cerevisiae. The ScOYE3 transgenic plants were comprehensively investigated for their biochemical responses to 2-NA treatment and their 2-NA phytoremediation capabilities. Our results showed that the rice seedlings exposed to 2-NA stress, showed growth inhibition and biomass reduction. However, the transgenic plants exhibited strong tolerance to 2-NA stress compared to wild-type plants. Ectopic expression of ScOYE3 could effectively protect transgenic plants against 2-NA damage, which resulted in less reactive oxygen species accumulation in transgenic plants than that in wild-type plants. Our phytoremediation assay revealed that transgenic plants could eliminate more 2-NA from the medium than wild-type plants. Moreover, omics analysis was performed in order to get a deeper insight into the mechanism of ScOYE3-mediated 2-NA transformation in rice. Altogether, the function of ScOYE3 during 2-NA detoxification was characterized for the first time, which serves as strong theoretical support for the phytoremediation potential of 2-NA by Old Yellow Enzyme genes.

The Effect of Granulometry of Carbonaceous Materials and Application Rates on the Availability of Soil-Bound Dichlorodiphenyltrichloroethane (DDT) and Its Metabolites

Biochars (BCs) and activated carbons (ACs) are well-known carbon-rich materials that are being increasingly studied in environmental sciences for water treatment applications to remediate pollutant sequestration in soil. This study aimed to assess the impact of Sargasso BC particle size and amendment rate on the environmental availability of DDT and DDT metabolites in two distinct Kazakh soils. These two soils were collected in the vicinity of storehouse facilities in Kyzylkairat and Beskainar that store banned pesticides. They presented very distinct concentration levels of DDT and DDT metabolites. Three different types of carbonaceous matrices were tested: Sargasso BC and two commercial ACs (ORBOTM and DARCO©). For the granulometry effect, Sargasso BC was ground, and two particle sizes were tested (<150 µm, >150 µm) and compared to an unground material. Four distinct application rates were tested (0.25, 0.5, 1, and 2% (w/w)). After a three-month maturation period, environmental availability was assessed using an ISO/DIS 16751, part B-modified methodology. Interestingly, the best reductions in DDT environmental availability were obtained with the finest particle size (both ACs and Sargasso BC < 150 µm). More specifically, the effectiveness of the strategy seemed to depend on many factors. Firstly, a clear soil effect was demonstrated, suggesting that the more contaminated the soil, the more efficient this strategy may be. Secondly, the results showed that an increase in the amendment rate improves the immobilization of DDT and DDT metabolites. The sequestration material demonstrated different efficiency values (up to 58 ± 4% for Sargasso BC < 150 µm and 85 ± 4% for DARCO at a 2% application rate). Finally, a clear molecule effect was displayed, demonstrating the following immobilization order: p,p'-DDE > p,p'-DDD > p,p'-DDT > o,p'-DDT.

ElNFS1, a nitroreductase gene from Enterobacter ludwigii, confers enhanced detoxification and phytoremediation of 4-nitrobenzaldehyde in rice

4-nitrobenzaldehyde (4-NBA) is a widely used chemical intermediate for industrial application and an important photodegradation product of chloramphenicol. This compound represents a substantial threat to human health and ecosystem due to its genotoxic and mutagenic effect. In this study, the 4-NBA detoxification by transgenic rice overexpressing a bacterial nitroreductase gene, ElNFS1, from Enterobacter ludwigii were investigated. The cytosol-targeted ElNFS1 transgenic plants were selected to comprehensively examine their physio-biochemical responses and phytoremediation potential to 4-NBA. Our results showed that the transgenic plants exhibited strong tolerance to 4-NBA. Overexpression of ElNFS1 could significantly alleviate 4-NBA-induced damages of photosynthetic apparatus and reactive oxygen species overproduction in transgenic plants. The phytoremediation assay revealed that transgenic plants could remove more 4-NBA from the medium than wild-type plants. HPLC and LC-MS assays showed that 4-aminobenzaldehyde was found in the reductive products of 4-NBA. Altogether, the function of ElNFS1 during 4-NBA detoxification was characterized for the first time, which provides a strong theoretical support for the application potential of ElNFS1 transgenic plants on the phytoremediation of 4-NBA.

Environmental health and risk assessment metrics with special mention to biotransfer, bioaccumulation and biomagnification of environmental pollutants

The environment pollutants, which are landed up in environment because of human activities like urbanization, mining and industrializations, affects human health, plants and animals. The living organisms present in environment are constantly affected by the toxic pollutants through direct contact or bioaccumulation of chemicals from the environment. The toxic and hazardous pollutants are easily transferred to different environmental matrices like land, air and water bodies such as surface and ground waters. This comprehensive review deeply discusses the routes and causes of different environmental pollutants along with their toxicity, impact, occurrences and fate in the environment. Environment health and risk assessment tools that are used to evaluate the harmfulness, exposure of living organisms to pollutants and the amount of pollutant accumulated are explained with help of bio-kinetic models. Biotransfer, toxicity factor, biomagnification and bioaccumulation of different pollutants in the air, water and marine ecosystems are critically addressed. Thus, the presented survey would be collection of correlations those addresses the factors involved in assessing the environmental health and risk impacts of distinct environmental pollutants.

Assessment of an NDL-PCBs Sequestration Strategy in Soil Using Contrasted Carbonaceous Materials through In Vitro and Cucurbita pepo Assays

The present study aims to assess the respective efficiency of Biochars (BCs) and activated carbons (ACs) to limit PCB 101, 138, 153 and 180 transfer to plants. A set of 6 high carbon materials comprising 3 BCs and 3 ACs was tested and used to amend a soil at 2% rate. Then, the two most efficient carbonaceous materials were used as an amendment of an historically contaminated soil sampled in the St Cyprien vicinity (Loire, France). An environmental availability assessment was performed using the ISO/DIS 16751 Part A assay (n = 3). For the in vivo part, Cucurbita pepo were grown for 12 weeks. Significant decreases of transfer were found for both assays notably for powdered ACs (up to 98%). By contrast, significantly lower levels of transfer reduction were observed when BCs amendments were performed, ranging from 27 to 80% for environmental availability assessment and 0 to 36% for C. pepo. Reduction factors above 90% for the 2 selected materials were found from amended historically contaminated soils. Present results led to consider such a sequestering strategy as valuable to ensure plant production on non-dioxin-like polychlorobiphenyls (NDL-PCBs) contaminated soils.

Risk assessment of PBDEs and PCBs in dust from an e-waste recycling area of China

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are widely used in outdated electronic and electrical products. In the present study, dust samples from houses, kindergartens, and roads were collected in Guiyu, where informal e-waste recycling activities have been sustained since the 1980s. Haojiang was chosen as a reference site without e-waste pollution. A total of 20 PBDE congeners and 18 PCB congeners was measured. Concentrations of total PBDEs and PCBs in dust samples from Guiyu were significantly higher than those from Haojiang. In Guiyu, kindergarten dust had the highest concentration of PCBs in these three typical environments, whereas the concentration of PBDEs showed no significant difference. Concentrations of PBDEs in Haojiang house dust were found significantly higher than other two environmental dusts. According to the questionnaires, we found that factors such as shoe cabinets, electrical products, and potted plants might affect PBDE and PCB concentrations in house dust. Daily intake of PBDEs and PCBs via dust ingestion was estimated after correction by their house, kindergarten, and road dust concentrations. The mean estimated daily intake (EDI) of PBDEs for Guiyu children was far lower than the oral reference dose recommended by the environmental protection agency (EPA). The Guiyu children seem to have a higher trend of daily intakes of PCBs although their EDIs not being calculated accurately due to the low detection rate. Child exposure to PBDEs via dust ingestion in Guiyu was 36 times higher than those in Haojiang. This indicates that children from e-waste-polluted areas stay in surroundings with heavy burdens of PBDEs, even PCBs. The risk to their health from contaminants is a severe concern.

Uptake and translocation of polybrominated diphenyl ethers in the rhizosphere soil-crop-atmosphere system in e-waste dismantling areas in Taizhou, China

Air, crop, and rhizosphere soil samples were collected from e-waste dismantling areas in Taizhou City (Zhejiang Province, China). The mean PBDEs (Polybrominated diphenyl ethers) concentrations in air in the Fengjiang and Binhai areas were 27.8 and 25.1 pg m^-3, respectively (no significant difference, P > 0.05). The mean PBDE concentrations in rhizosphere soil from Fengjiang and Binhai were 9.19 × 10⁴ and 1.34 × 10³ pg g^-1 dry weight, respectively (no significant difference, P > 0.05). The mean PBDE concentrations in the crop samples from Fengjiang and Binhai were 1.38 × 10³ and 6.64 × 10² pg g^-1 dry weight, respectively (no significant difference, P > 0.05). PBDEs with≥6 bromine atoms (BDEs-153, -154, -183, and -190) were not translocated from the crop roots to other tissues. PBDEs were taken up by crops selectively. The root epidermis effectively prevented PBDEs from entering edible crop parts and kept the PBDE concentrations in edible roots low. PBDEs with≤5 bromine atoms (BDEs-15, -28, -47, -66, -85, -99, and -100) were selectively enriched from the rhizosphere soil into crop roots, but PBDEs with more bromine substituents were not transferred from the rhizosphere soil to the crop roots. PBDEs with≥6 bromine atoms were selectively enriched from the atmosphere into crop leaves. Crop roots and leaves took up PBDEs with ortho bromine substituents more readily than PBDEs with meta bromine substituents because the octanol-water partition coefficients are lower for ortho-brominated than meta-brominated PBDEs.

Bioremediation strategies with biochar for polychlorinated biphenyls (PCBs)-contaminated soils: A review

Polychlorinated biphenyls (PCBs) are hazardous organic contaminants threatening human health and environmental safety due to their toxicity and carcinogenicity. Biochar (BC) is an eco-friendly carbonaceous material that can extensively be utilized for the remediation of PCBs-contaminated soils. In the last decade, many studies reported that BC is beneficial for soil quality enhancement and agricultural productivity based on its physicochemical characteristics. In this review, the potential of BC application in PCBs-contaminated soils is elaborated as biological strategies (e.g., bioremediation and phytoremediation) and specific mechanisms are also comprehensively demonstrated. Further, the synergy effects of BC application on PCBs-contaminated soils are discussed, in view of eco-friendly, beneficial, and productive aspects.

Phytotoxicity of tris-(1-chloro-2-propyl) phosphate in soil and its uptake and accumulation by pakchoi (Brassica chinensis L. cv. SuZhou)

This study investigated physiological and biochemical changes in pakchoi at different growth stages (25 and 50 d) under different tris-(1-chloro-2-propyl) phosphate (TCIPP) treatments (10, 100, 500, and 1000 μg kg^-1). The uptake and accumulation of TCIPP by pakchoi and variation of TCIPP speciation in soil were also determined. TCIPP decreased the length and fresh weight of pakchoi root compared with those in blank controls, and this effect was significant when the concentration of TCIPP was higher than 100 μg kg^-1. The fresh weight of pakchoi stems and leaves, the chlorophyll content, and the activities of superoxide dismutase, peroxidase, and catalase in the leaves first increased and then decreased with increasing TCIPP concentration. The inflection point of the variation in these indices was 100 μg kg^-1 TCIPP in soil. The contents of proline and malondialdehyde increased continuously with increasing TCIPP concentration. The uptake of TCIPP by pakchoi increased linearly with increasing TCIPP concentration, and the highest TCIPP concentrations in the roots, stems, and leaves were 275.9, 80.0, and 2126.3 μg kg^-1, respectively. TCIPP was easily transferred from the roots to leaves of pakchoi, with translocation factor of up to 12.6. The content of bioavailable TCIPP in soil was high, accounting for 46.5%. Planting pakchoi could significantly reduce the content of bioavailable TCIPP, with removal rate of 39.9%-54.1%. After 50 d of planting pakchoi, the removal rate of TCIPP in soil (10.4%-18.6%) was significantly higher than that in the control without plant, but the contribution of phytoextraction was small, accounting for 2.62%-26.6%.

'Cry-for-help' in contaminated soil: a dialogue among plants and soil microbiome to survive in hostile conditions

An open question in environmental ecology regards the mechanisms triggered by root chemistry to drive the assembly and functionality of a beneficial microbiome to rapidly adapt to stress conditions. This phenomenon, originally described in plant defence against pathogens and predators, is encompassed in the ‘cry‐for‐help’ hypothesis. Evidence suggests that this mechanism may be part of the adaptation strategy to ensure the holobiont fitness in polluted environments. Polychlorinated biphenyls (PCBs) were considered as model pollutants due to their toxicity, recalcitrance and poor phyto‐extraction potential, which lead to a plethora of phytotoxic effects and rise environmental safety concerns. Plants have inefficient detoxification processes to catabolize PCBs, even leading to by‐products with a higher toxicity. We propose that the ‘cry‐for‐help’ mechanism could drive the exudation‐mediated recruitment and sustainment of the microbial services for PCBs removal, exerted by an array of anaerobic and aerobic microbial degrading populations working in a complex metabolic network. Through this synergistic interaction, the holobiont copes with the soil contamination, releasing the plant from the pollutant stress by the ecological services provided by the boosted metabolism of PCBs microbial degraders. Improving knowledge of root chemistry under PCBs stress is, therefore, advocated to design rhizoremediation strategies based on plant microbiome engineering.

Phytoremediation potential of Miscanthus sinensis And. in organochlorine pesticides contaminated soil amended by Tween 20 and Activated carbon

The organochlorine pesticides (OCPs) have raised concerns about being persistent and toxic to the environment. Phytoremediation techniques show promise for the revitalization of polluted soils. The current study focused on optimizing the phytoremediation potential of Miscanthus sinensis And. (M. sinensis), second-generation energy crop, by exploring two soil amendments: Tween 20 and activated carbon (AC). The results showed that when M. sinensis grew in OCP-polluted soil without amendments to it, the wide range of compounds, i.e., α-HCH, β-HCH, γ-HCH, 2.4-DDD, 4.4-DDE, 4.4-DDD, 4.4-DDT, aldrin, dieldrin, and endrin, was accumulated by the plant. The introduction of soil amendments improved the growth parameters of M. sinensis. The adding of Tween 20 enhanced the absorption and transmigration to aboveground biomass for some OCPs; i.e., for γ-HCH, the increase was by 1.2, for 4.4-DDE by 8.7 times; this effect was due to the reduction of the hydrophobicity which made pesticides more bioavailable for the plant. The adding of AC reduced OCPs absorption by plants, consequently, for γ-HCH by 2.1 times, 4.4-DDD by 20.5 times, 4.4-DDE by 1.4 times, 4.4-DDT by 8 times, α-HCH was not adsorbed at all, and decreased the translocation to the aboveground biomass: for 4.4-DDD by 31 times, 4.4-DDE by 2.8 times, and γ-HCH by 2 times; this effect was due to the decrease in the bioavailability of pesticides. Overall, the amendment of OCP-polluted soil by Tween 20 speeds the remediation process, and incorporation of AC permitted to produce the relatively clean biomass for energy.

Understanding the effect of oil on phytoremediation of PCB co-contamination in transformer oil using Chromolaena odorata

Greenhouse assessment of the effect of oil on Chromolaena odorata ability to remove PCB from soil treated with transformer oil co-contaminated with Aroclor 1260 was done. Plants were transplanted into one kilogram of soil contained in 1 L pots differently containing 100, 200, and 500 ml of transformer oil (T/O), co-contaminated with 100 ppm of Aroclor. Treatments were done in two microcosms; direct contamination and soil cultured method. Measured plant growth parameters showed that C. odorata growth was affected by the different concentrations of oil. Inhibition of plant growth by oil increased with concentrations. At the end of six weeks, plant growth was affected in T/O amended soil. Plants size was increased by 1.4, 0.46 and -1.0% in direct treatment and 17.01, 6.09 and 1.08% in soil culture at the 100, 200 and 500 ppm respectively. Untreated control showed a 43.07% increase. Slight PCB recovery was observed in root tissues of C. odorata but soil PCB was reduced by 66.6, 53.2, 41.5% and 77.3, 74.7, 58.8% at both treatments in their respective concentrations of oil. However, unplanted control was reduced by 21.4 and 16.7% in the two treatments at 66,000 ppm of oil. This study has shown that with improved agronomic practices, there is a possibility of phytoremediation of soil PCB from PCB contained transformer oil contaminated soil using Chromolaena odorata, hence it should be optimized in the field.

Optimization of microbial assisted phytoremediation of soils contaminated with pesticides

580 microbial strains were isolated from the rhizosphere of the plants Cucurbita pepo L. and Xanthium strumarium grown on soil contaminated with dichlorodiphenyltrichloroethane (DDT) and its metabolites. During the cultivation, two bacterial strains were selected because of their ability to grow on media containing 0.5-5.0 mg L^-1 of dichlorodiphenyldichloroethylene (DDE) as the sole carbon source. They were identified as Bacillus vallismortis and Bacillus aryabhattai. Both of these species were shown to have a high capacity for the utilization of DDE - more than 90% of which was consumed after 21 days of cultivation. Laboratory experiments were carried out then to assess the possibility of using these strains for the decontamination of organochlorine pesticides (OCPs) contaminated soils. Inoculation of C. pepo and X. strumarium with our isolates B. vallismortis and B. aryabhattai resulted in a reduction of the pollutant stress to the plants as shown by an increase both in aboveground and in root biomass. The microorganisms enhanced the uptake and phytostabilization potential of C. pepo and X. strumarium and can be applied for the treatment of DDE contaminated soils.

Evaluation of biphenyl- and polychlorinated-biphenyl (PCB) degrading Rhodococcus sp. MAPN-1 on growth of Morus alba by pot study

This study focused on isolation of bacteria with biphenyl/polychlorinated biphenyl (PCB) degrading ability from the rhizosphere of Morus alba (mulberry plant). Repetitive enrichment of rhizospheric soil samples with biphenyl resulted in the isolation of Rhodococcus sp. MAPN-1, identified by 16S rRNA gene sequence analysis. The bacterium showed growth on five different aromatic compounds (naphthalene, salicylic acid, benzoic acid, dibenzofuran and anthracene). Benzoic acid was detected as the major metabolite during biphenyl degradation using high-performance thin-layer chromatography (HPTLC) with R_f 0.42 at 254 nm. Further GC-MS/MS study showed 95% and 15% degradation of biphenyl and dichlorobiphenyl, respectively. A pot study was conducted to evaluate the effect of presence of biphenyl on M. alba and the role of biphenyl degrader Rhodococcus sp. MAPN-1 in relation to phytoremediation. Morus alba twigs in biphenyl spiked soil (100 mg/kg and 300 mg/kg) inoculated with Rhodococcus sp. MAPN-1 showed growth, whereas, growth of plants (control) was adversely affected in biphenyl-spiked uninoculated soil. It is the first report of isolation of Rhodococcus sp. MAPN-1 from the rhizosphere of Morus alba, its capability to degrade biphenyl, thereby showing a positive effect on the plant growth grown in biphenyl spiked soil.

Polychlorinated biphenyls in the soil-crop-atmosphere system in e-waste dismantling areas in Taizhou: Concentrations, congener profiles, uptake, and translocation

Samples of soil, air, and locally grown crops from around an old e-waste dismantling area (Fengjiang) and a new e-waste dismantling area (Binhai) in Taizhou were analyzed to investigate the behavior of polychlorinated biphenyls (PCBs) released during e-waste dismantling in the soil-crop-atmosphere system. The results indicated that PCB pollution is still widespread in the study area. The PCB concentrations were clearly higher in soil from FJ than in soil from BH, and the concentrations in the functional zones decreased strongly in the order industry park > residential area > farmland. Historical and current emissions during e-waste dismantling processes are probably the main sources of PCBs to soil because PCB production and use are banned. The long half-lives of PCBs have caused the target congener concentrations in soil not to decrease markedly over 10 years. The "halo effect" may have caused PCBs in soil in the heavily polluted FJ area to diffuse into the surrounding area. Soil-air exchange of PCBs in heavily contaminated FJ area may supply PCBs to air because the temperatures in Taizhou are often high. PCBs can accumulate in crops through various pathways. Less-chlorinated PCBs (mainly including Tri-PCBs) can enter crops by root uptake and translocated to the aerial tissues, and more-chlorinated PCBs (including Penta-PCBs and Hexa-PCBs) at high concentrations in soil can enter underground crop tissues through passive transport. More-chlorinated PCBs in underground tissues cannot be transferred to aboveground tissues of tall crops but may be transferred to aboveground tissues of short crops through the root-to-stem pathway and through soil dust being transferred to aboveground external surfaces.

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.

Phytoremediation of soil contaminated with PCBs using different plants and their associated microbial communities

In this work, we evaluate the abilities of the plants Brassica juncea, Avena sativa, Brachiaria decumbens, and Medicago sativa to uptake polychlorinated biphenyls (PCBs) and induce degradation of soil microorganisms from contaminated soil. Removal of PCBs 44, 66, 118, 153, 170, and 180 was evaluated in both rhizospheric and nonrhizospheric soils. Microbial and bphA1 gene quantifications were performed by real-time PCR. The PCB concentrations in plant tissues and soil were determined, and a fluorescein diacetate (FDA) hydrolysis assay was used to measure microbial activity in soil. The removal percentages for all PCB congeners in planted soil versus unplanted control soil were statistically significant and varied between 45% and 63%. PCBs 118, 153, 138, and 170 were detected in Brachiaria decumbens roots at different concentrations. In planted soil, an increase in the concentration of bacteria was observed compared to the initial concentration and the concentration in unplanted control soil; however, no significant differences were identified between plants. The number of copies of the bphA1 gene was higher in rhizospheric versus non- rhizospheric soil for all plants at the end of the experiment. However, alfalfa and oat rhizospheric soil showed significant differences in the copy number of the bphA1 gene. In general, the concentration of fluorescein in the rhizospheric soil was greater than that in the nonrhizospheric soil. Although the plants had a positive effect on PCB removal, this effect varied depending on the type of PCB, the plant, and the soil.

Arbuscular mycorrhizal inoculum sources influence bacterial, archaeal, and fungal communities' structures of historically dioxin/furan-contaminated soil but not the pollutant dissipation rate

Little is known about the influence of arbuscular mycorrhizal fungi (AMF) inoculum sources on phytoremediation efficiency. Therefore, the aim of this study was to compare the effects of two mycorrhizal inocula (indigenous and commercial inocula) in association with alfalfa and tall fescue on the plant growth, the bacterial, fungal, and archaeal communities, and on the removal of dioxin/furan (PCDD/F) from a historically polluted soil after 24 weeks of culture in microcosms. Our results showed that both mycorrhizal indigenous and commercial inocula were able to colonize plant roots, and the growth response depends on the AMF inoculum. Nevertheless, the improvement of root dry weight in inoculated alfalfa with indigenous inoculum and in inoculated tall fescue with commercial inoculum was clearly correlated with the highest mycorrhizal colonization of the roots in both plant species. The highest shoot dry weight was obtained in inoculated alfalfa and tall fescue with the commercial inoculum. AMF inoculation differently affected the number of bacterial and archaeal OTUs and bacterial diversity, with elevated bacterial and archaeal OTUs and bacterial diversity observed with indigenous inoculum. Mycorrhizal inoculation increases the abundance of bacterial OTUs (in particular with indigenous inoculum) and microbial richness but it does not improve PCDD/F dissipation. Vegetation had no effect on the abundance of microbial OTUs nor on richness but stimulated specific communities (Planctomycetia and Gammaproteobacteria) likely to be involved in the dissipation of PCDD/F. The reduction of toxic equivalency PCDD/F concentration also could be explained by the stimulation of soil microbial activities estimated with dehydrogenase and fluorescein diacetate hydrolase.

Phytoremediation of sewage sludge contaminated by trace elements and organic compounds

Phytoremediation is a green technique being increasingly used worldwide for various purposes including the treatment of municipal sewage sludge (MSS). Most plants proposed for this technique have high nutrient demands, and fertilization is often required to maintain soil fertility and nutrient balance while remediating the substrate. In this context, MSS could be a valuable source of nutrients (especially N and P) and water for plant growth. The aim of this study was to determine the capacity willow (Salix matsudana, cv Levante), poplar (Populus deltoides × Populus nigra, cv Orion), eucalyptus (Eucalyptus camaldulensis) and sunflower (Helianthus annuus) to clean MSS, which is slightly contaminated by trace elements (TEs) and organic pollutants, and to assess their physiological response to this medium. In particular, we aimed to evaluate the TE accumulation by different species as well as the decrease of TEs and organic pollutants in the sludge after one cropping cycle and the effect of MSS on plant growth and physiology. Since MSS did not show any detrimental effect on the biomass yield of any of the species tested, it was found to be a suitable growing medium for these species. TE phytoextraction rates depended on the species, with eucalyptus showing the highest accumulation for Cr, whereas sunflower exhibited the best performance for As, Cu and Zn. At the end of the trial, some TEs (i.e. Cr, Pb and Zn), n-alkanes and PCBs showed a significant concentration decrease in the sludge for all tested species. The highest Cr decrease was observed in pots with eucalyptus (57.4%) and sunflower (53.4%), whereas sunflower showed the highest Cu decrease (44.2%), followed by eucalyptus (41.2%), poplar (16.2%) and willow (14%). A significant decrease (41.1%) of Pb in the eucalyptus was observed. Zn showed a high decrease rate with sunflower (59.5%) and poplar (52%) and to a lesser degree with willow (35.3%) and eucalyptus (25.4%). The highest decrease in n-alkanes concentration in the sludge was found in willow (98.3%) and sunflower (97.3%), whereas eucalyptus has the lowest PCBs concentration (91.8%) in the sludge compared to the beginning of the trial. These results suggest new strategies (e.g. crop rotation and intercropping) to be adopted for a better management of this phytotechnology.

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.

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.

Rhizoremediation of a dioxin-like PCB polluted soil by alfalfa: Dynamic characterization at temporal and spatial scale

This study investigates the temporal and spacial dissipation dynamics of a dioxin-like polychlorinated biphenyl (PCB 77) in the rhizosphere of alfalfa. A three-chamber rhizobox was designed to compare the PCB 77 dissipation efficiency in the rhizosphere, near-rhizosphere, and far-rhizosphere zones. Culture-independent techniques, including quantitative PCR (qPCR), Biolog-ECO plate, and denatured gradient gel electrophoresis (DGGE) were employed to investigate the variation of bacterial quantity, metabolic diversity and community structure in the alfalfa-rhizobium symbiosis rhizosphere at different rhizoremediation stages. PCB dissipation rates in different rhizosphere zones were in the order: rhizosphere (90.9%) > near-rhizosphere (80.5%) > far-rhizosphere (31.7%). The number of the bacterial 16S rRNA gene copies in the rhizosphere zone in the polluted treatment reached the highest value of all the treatments. Microbial metabolic diversity, as indicated by average well color development (AWCD) in both rhizosphere and near-rhizosphere zones, had recovered from the PCB 77 pollution. The soil bacterial community diversity improved greatly in the rhizosphere of alfalfa, with some new species appeared in the rhizosphere and near-rhizosphere zones. In conclusion, the dissipation of PCB 77, the quantity of total soil bacteria, soil microbial metabolic diversity, and soil microbial community structure were significantly improved in rhizosphere and near-rhizosphere zones of alfalfa.

Polychlorinated biphenyls in alfalfa: Accumulation, sorption and speciation in different plant parts

The accumulation, chemical speciation and distribution of polychlorinated biphenyls (PCBs) were investigated in various parts of alfalfa. Moreover, the adsorption characteristics for PCB 28 by alfalfa and the influencing factors of the adsorption characteristics were studied. There were different degrees of PCB accumulation in alfalfa roots, root nodules and shoots. The decreasing order of the accumulation of PCBs in plant tissues was root nodules > roots > shoots, and the decreasing order of the total PCB contents was roots > shoots > root nodules, indicating that the roots were the main sink for PCB accumulation. There were three modes of PCB speciation in alfalfa roots and root nodules, comprising strong sorption (78%) and weak sorption (19%) on tissue surfaces and absorption within tissues (2%). The adsorption isotherms of PCB 28 indicate that the adsorption capacities of root nodules and shoots were both significantly higher than that of the roots. Both lipids and carbohydrates, and especially lipids, affected the PCB adsorption capacities of the tissues. These results may help in the elucidation of the mechanisms of sorption and accumulation of PCBs in the plants and their main influencing factors and thus contribute to the development of phytoremediation technologies for PCB-contaminated soils.

Effects of Polychlorinated Biphenyls (PCBs) and Their Hydroxylated Metabolites (OH-PCBs) on Arabidopsis thaliana

Plants metabolize polychlorinated biphenyls (PCBs) into hydroxylated derivatives (OH-PCBs), which are sometimes more toxic than the parent PCBs. The objective of this research was to compare the toxicity of a suite of PCBs and OH-PCBs toward the model plant, Arabidopsis thaliana. While parent PCBs and higher-chlorinated OH-PCBs exhibited a low or nondetectable toxicity, lower-chlorinated OH-PCBs significantly inhibited the germination rate and plant growth, with inhibition concentration 50% (IC₅₀) ranging from 1.6 to 12.0 mg L^-1. The transcriptomic response of A. thaliana to 2,5-dichlorobiphenyl (2,5-DCB), and its OH metabolite, 4'-OH-2,5-DCB, was then examined using whole-genome expression microarrays (Affymetrix). Exposure to 2,5-DCB and 4'-OH-2,5-DCB resulted in different expression patterns, with the former leading to enrichment of genes involved in response to toxic stress and detoxification functions. Exposure to 2,5-DCB induced multiple xenobiotic response genes, such as cytochrome P-450 and glutathione S-transferases, potentially involved in the PCB metabolism. On the contrary, exposure to both compounds resulted in the down-regulation of genes involved in stresses not directly related to toxicity. Unlike its OH derivative, 2,5-DCB was shown to induce a transcriptomic profile similar to plant safeners, which are nontoxic chemicals stimulating detoxification pathways in plants. The differentiated induction of detoxification enzymes by 2,5-DCB may explain its lower phytotoxicity compared to 4'-OH-2,5-DCB.

Opinion: Taking phytoremediation from proven technology to accepted practice

Phytoremediation is the use of plants to extract, immobilize, contain and/or degrade contaminants from soil, water or air. It can be an effective strategy for on site and/or in situ removal of various contaminants from soils, including petroleum hydrocarbons (PHC), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), solvents (e.g., trichloroethylene [TCE]), munitions waste (e.g., 2,4,6-trinitrotoluene [TNT]), metal(loid)s, salt (NaCl) and radioisotopes. Commercial phytoremediation technologies appear to be underutilized globally. The primary objective of this opinion piece is to discuss how to take phytoremediation from a proven technology to an accepted practice. An overview of phytoremediation of soil is provided, with the focus on field applications, to provide a frame of reference for the subsequent discussion on better utilization of phytoremediation. We consider reasons why phytoremediation is underutilized, despite clear evidence that, under many conditions, it can be applied quite successfully in the field. We offer suggestions on how to gain greater acceptance for phytoremediation by industry and government. A new paradigm of phytomanagement, with a specific focus on using phytoremediation as a "gentle remediation option" (GRO) within a broader, long-term management strategy, is also discussed.

Plant-assisted bioremediation of a historically PCB and heavy metal-contaminated area in Southern Italy

A plant-assisted bioremediation strategy was applied in an area located in Southern Italy, close to the city of Taranto, historically contaminated by polychlorinated biphenyls (PCBs) and heavy metals. A specific poplar clone (Monviso) was selected for its ability to promote organic pollutant degradation in the rhizosphere, as demonstrated elsewhere. Chemical and microbiological analyses were performed at the time of poplar planting in selected plots at different distances from the trunk (0.25-1m) and at different soil depths (0-20 and 20-40cm), at day 420. A significant decrease in PCB congeners and a reduction in all heavy metals was observed where the poplar trees were present. No evidence of PCB and heavy metal reduction was observed in the non poplar-vegetated soil. Microbial analyses (dehydrogenase activity, cell viability, microbial abundance) of the autochthonous microbial community showed an improvement in soil quality. In particular, microbial activity generally increased in the poplar-rhizosphere and a positive effect was observed in some cases at up to 1m distance from the trunk and up to 40cm depth. The Monviso clone was effective in promoting both a general decrease in contaminant occurrence and an increase in microbial activity in the chronically polluted area a little more than one year after planting.

Isolation of the PCB-degrading bacteria Mesorhizobium sp. ZY1 and its combined remediation with Astragalus sinicus L. for contaminated soil

A bacterial strain ZY1 capable of utilizing PCBs as its carbon source was isolated from the root nodules of Chinese milk vetch (Astragalus sinicus L.). The strain was identified as Mesorhizobium sp. according to its physiological-biochemical properties and the analysis of its 16S rRNA gene sequence. When the initial OD600 was 0.15, 62.7% of 15 mg L(-1) 3,3',4,4'-TCB in a liquid culture was degraded by Mesorhizobium sp. ZY1 within 10 days. Mesorhizobium sp. ZY1 also greatly increased the biotransformation of soil PCBs. Pot experiments indicated that the soil PCB concentrations of a single incubation of strain ZY1 (R) and a single planting of A. sinicus (P) decreased by 20.5% and 23.0%, respectively, and the concentration of PCBs in soil treated with A. sinicus and strain ZY1 decreased by 53.1%. We also observed that A. sinicus-Mesorhizobium sp. ZY1 treatment (PR) improved plant biomass and the concentration of PCBs in plants compared with a single A. sinicus planting treatment (P). The results suggest that the synergistic association between A. sinicus and PCBs-degrading Mesorhizobium sp. ZY1 can stimulate the phytoextraction of PCBs and the rhizosphere microflora to degrade PCBs, and might be a promising bioremediation strategy for PCB-contaminated soil.

Harnessing microbial gene pools to remediate persistent organic pollutants using genetically modified plants--a viable technology?

It has been 14 years since the international community came together to legislate the Stockholm Convention on Persistent Organic Pollutants (POPs), restricting the production and use of specific chemicals that were found to be environmentally stable, often bioaccumulating, with long-term toxic effects. Efforts are continuing to remove these pollutants from the environment. While incineration and chemical treatment can be successful, these methods require the removal of tonnes of soil, at high cost, and are damaging to soil structure and microbial communities. The engineering of plants for in situ POP remediation has had highly promising results, and could be a more environmentally-friendly alternative. This review discusses the characterization of POP-degrading bacterial pathways, and how the genes responsible have been harnessed using genetic modification (GM) to introduce these same abilities into plants. Recent advances in multi-gene cloning, genome editing technologies and expression in monocot species are accelerating progress with remediation-applicable species. Examples include plants developed to degrade 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), trichloroethylene (TCE), and polychlorinated biphenyls (PCBs). However, the costs and timescales needed to gain regulatory approval, along with continued public opposition, are considerable. The benefits and challenges in this rapidly developing and promising field are discussed.

Bioaccumulation and translocation of polyhalogenated compounds in rice (Oryza sativa L.) planted in paddy soil collected from an electronic waste recycling site, South China

The bioaccumulation and translocation of polyhalogenated compounds (PHCs) in rice planted in the paddy soils of an electronic waste (e-waste) recycling site were investigated, along with the effect of contaminated soils on rice growth. The PHCs included polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), and dechlorane plus (DPs). The morphological development and all measured physiological parameters of rice plants except for peroxidase were significantly inhibited by e-waste contaminated soils. Specifically, soil-root bioaccumulation factors (RCFs) increased with increasing logarithm of octanol-water partition coefficient (logKow) for PCBs, but decreased for PBDEs. During translocation from root to stem, translocation factors (TFs) and logKow were positively correlated. However, the accumulation mechanism in the leaf was concentration-dependent. In the high concentration exposure group, translocation play more important role in determination PHCs burden in leaf than atmospheric uptake, with logTF (from stem to leaf) being positively correlated with logKow. In contrast, in the low exposure and control groups, logTF (from stem to leaf) was negatively correlated with logKow. In addition, Syn-DP was selectively accumulated in plant tissues. In conclusion, this study demonstrates that e-waste contaminated soils affect rice growth, revealed the rule of the bioaccumulation and translocation of PHCs in rice plants.

Differential tissue accumulation of 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin in Arabidopsis thaliana affects plant chronology, lipid metabolism and seed yield

BACKGROUND

Dioxins are one of the most toxic groups of persistent organic pollutants. Their biotransmission through the food chain constitutes a potential risk for human health. Plants as principal actors in the food chain can play a determinant role in removing dioxins from the environment. Due to the lack of data on dioxin/plant research, this study sets out to determine few responsive reactions adopted by Arabidopsis plant towards 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins.

RESULTS

Using a high resolution gas chromatography/mass spectrometry, we demonstrated that Arabidopsis plant uptakes TCDD by the roots and accumulates it in the vegetative parts in a tissue-specific manner. TCDD mainly accumulated in rosette leaves and mature seeds and less in stem, flowers and immature siliques. Moreover, we observed that plants exposed to high doses of TCDD exhibited a delay in flowering and yielded fewer seeds of a reduced oil content with a low vitality. A particular focus on the plant fatty acid metabolism showed that TCDD caused a significant reduction in C18-unsaturated fatty acid level in plant tissues. Simultaneously, TCDD induced the expression of 9-LOX and 13-LOX genes and the formation of their corresponding hydroperoxides, 9- and 13-HPOD as well as 9- or 13-HPOT, derived from linoleic and linolenic acids, respectively.

CONCLUSIONS

The current work highlights a side of toxicological effects resulting in the administration of 2,3,7,8-TCDD on the Arabidopsis plant. Similarly to animals, it seems that plants may accumulate TCDD in their lipids by involving few of the FA-metabolizing enzymes for sculpting a specific oxylipins "signature" typified to plant TCDD-tolerance. Together, our results uncover novel responses of Arabidopsis to dioxin, possibly emerging to overcome its toxicity.

Phytoextraction of DDT-Contaminated Soil at Point Pelee National Park, Leamington, ON, Using Cultivar Howden and Native Grass Species

A field investigation was conducted at three dichlorodiphenyltrichloroethane (DDT)-contaminated areas in Point Pelee National Park (PPNP), Leamington, ON. cultivar Howden and three native grass species, (Michx.) Nash (little bluestem), L. (switchgrass), and (Torr.) A. Gray (sand dropseed) were grown at three different sites in the PPNP having low (291 ng/g), moderate (5083 ng/g), and high (10,192 ng/g) soil DDT contamination levels. A threshold soil DDT concentration was identified at ∼5000 ng/g where the DDT uptake into was maximized, resulting in plant shoot and root DDT concentrations of 16,600 and 45,000 ng/g, respectively. Two native grass species ( and ) were identified as potential phytoextractors, with higher shoot extraction capabilities than that of the known phytoextractor when optimal planting density was taken into account.

Enhanced tolerance and remediation to mixed contaminates of PCBs and 2,4-DCP by transgenic alfalfa plants expressing the 2,3-dihydroxybiphenyl-1,2-dioxygenase

Polychlorinated biphenyls (PCBs) and 2,4-dichlorophenol (2,4-DCP) generally led to mixed contamination of soils as a result of commercial and agricultural activities. Their accumulation in the environment poses great risks to human and animal health. Therefore, the effective strategies for disposal of these pollutants are urgently needed. In this study, genetic engineering to enhance PCBs/2,4-DCP phytoremediation is a focus. We cloned the 2,3-dihydroxybiphenyl-1,2-dioxygenase (BphC.B) from a soil metagenomic library, which is the key enzyme of aerobic catabolism of a variety of aromatic compounds, and then it was expressed in alfalfa driven by CaMV 35S promoter using Agrobacterium-mediated transformation. Transgenic line BB11 was selected out through PCR, Western blot analysis and enzyme activity assays. Its disposal and tolerance to both PCBs and 2,4-DCP were examined. The tolerance capability of transgenic line BB11 towards complex contaminants of PCBs/2,4-DCP significantly increased compared with non-transgenic plants. Strong dissipation of PCBs and high removal efficiency of 2,4-DCP were exhibited in a short time. It was confirmed expressing BphC.B would be a feasible strategy to help achieving phytoremediation in mixed contaminated soils with PCBs and 2,4-DCP.

Uptake, translocation, and elimination in sediment-rooted macrophytes: a model-supported analysis of whole sediment test data

Understanding bioaccumulation in sediment-rooted macrophytes is crucial for the development of sediment toxicity tests using macrophytes. Here, we explore bioaccumulation in sediment-rooted macrophytes by tracking and modeling chemical flows of chlorpyrifos, linuron, and six PCBs in water-sediment-macrophyte systems. Chemical fluxes across the interfaces between pore water, overlying water, shoots, and roots were modeled using a novel multicompartment model. The modeling yielded the first mass-transfer parameter set reported for bioaccumulation by sediment-rooted macrophytes, with satisfactory narrow confidence limits for more than half of the estimated parameters. Exposure via the water column led to rapid uptake by Elodea canadensis and Myriophyllum spicatum shoots, followed by transport to the roots within 1-3 days, after which tissue concentrations gradually declined. Translocation played an important role in the exchange between shoots and roots. Exposure via spiked sediment led to gradual uptake by the roots, but subsequent transport to the shoots and overlying water remained limited for the chemicals studied. These contrasting patterns show that exposure is sensitive to test set up, chemical properties, and species traits. Although field-concentrations in water and sediment will differ from those in the tests, the model parameters can be assumed applicable for modeling exposure to macrophytes in the field.

Application of lipid extracts from Solidago canadensis to phytomonitoring of PCB126 in transgenic Arabidopsis plants

The aim of this study is to elucidate the effect of lipid extracts from Solidago canadensis for phytomonitoring of polychlorinated biphenyl (PCB) 126 in the transgenic Arabidopsis plant XgD2V11-6 carrying the recombinant guinea pig (g) aryl hydrocarbon receptor (AhR)-mediated β-glucuronidase (GUS) reporter gene expression system. A lipid extract was prepared from S. canadensis and separated into simple lipid, glycolipid, and phospholipid fractions by silica gel column chromatography. Sterylglucoside (SG), monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and glucosyl ceramide were found in the glycolipid fraction. When the transgenic Arabidopsis plants were treated with the glycolipid fraction together with PCB126, PCB126-induced GUS activity significantly increased in the whole plant. Moreover, S. canadensis-derived SG, MGDG, and DGDG also significantly increased PCB126-induced GUS activity. These results indicated that glycolipids in S. canadensis enhanced the sensitivity of this monitoring assay.

Remediation of polychlorinated biphenyl-contaminated soil by using a combination of ryegrass, arbuscular mycorrhizal fungi and earthworms

In this work, a laboratory experiment was performed to investigate the influences of inoculation with the arbuscular mycorrhizal fungus (AMF) Glomus caledoniun L. and/or epigeic earthworms (Eisenia foetida) on phytoremediation of a PCB-contaminated soil by ryegrass grown for 180d. Planting ryegrass, ryegrass inoculated with earthworms, ryegrass inoculated with AMF, and ryegrass co-inoculated with AMF and earthworms decreased significantly initial soil PCB contents by 58.4%, 62.6%, 74.3%, and 79.5%, respectively. Inoculation with AMF and/or earthworms increased the yield of plants, and the accumulation of PCBs in ryegrass. However, PCB uptake by ryegrass accounted for a negligible portion of soil PCB removal. The number of soil PCB-degrading populations increased when ryegrass was inoculated with AMF and/or earthworms. The data show that fungal inoculation may significantly increase the remedial potential of ryegrass for soil contaminated with PCBs.

Hydroxylated polychlorinated biphenyls in the environment: sources, fate, and toxicities

Hydroxylated polychlorinated biphenyls (OH-PCBs) are produced in the environment by the oxidation of PCBs through a variety of mechanisms, including metabolic transformation in living organisms and abiotic reactions with hydroxyl radicals. As a consequence, OH-PCBs have been detected in a wide range of environmental samples, including animal tissues, water, and sediments. OH-PCBs have recently raised serious environmental concerns because they exert a variety of toxic effects at lower doses than the parent PCBs and they are disruptors of the endocrine system. Although evidence about the widespread dispersion of OH-PCBs in various compartments of the ecosystem has accumulated, little is currently known about their biodegradation and behavior in the environment. OH-PCBs are, today, increasingly considered as a new class of environmental contaminants that possess specific chemical, physical, and biological properties not shared with the parent PCBs. This article reviews recent findings regarding the sources, fate, and toxicities of OH-PCBs in the environment.

Distribution of PCDD/Fs and dioxin-like PCBs in sediment and plants from a contaminated salt marsh (Tejo estuary, Portugal)

Concentrations and profiles of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) were investigated in sediment and plants collected from a salt marsh in the Tejo estuary, Portugal. The highest PCDD/F and dl-PCB concentrations were detected in uncolonized sediments, averaging 325.25 ± 57.55 pg g(-1) dry weight (dw) and 8,146.33 ± 2,142.14 pg g(-1) dw, respectively. The plants Sarcocornia perennis and Halimione portulacoides growing in PCDD/F and dl-PCB contaminated sediments accumulated contaminants in roots, stems, and leaves. It was observed that PCDD/F and dl-PCB concentrations in roots were significantly lower in comparison with stems and leaves. In general, concentration of ΣPCDD/Fs and Σdl-PCBs in H. portulacoides tissues were found to be twofold higher than those in S. perennis, indicating a difference in the accumulation capability of both species. Furthermore, congener profiles changed between sediments and plant tissues, reflecting a selective accumulation of low chlorinated PCDD/Fs and non-ortho dl-PCBs in plants.

Cucurbita spp. and Cucumis sativus enhance the dissipation of polychlorinated biphenyl congeners by stimulating soil microbial community development

A number of Cucurbita species have the potential to extract polychlorinated biphenyls (PCBs) from soil, but their impact on the soil microbial communities responsible for PCB degradation remains unclear. A greenhouse experiment was conducted to investigate the effect of three Cucurbita and one Cucumis species on PCB dissipation and soil microbial community structure. Compared to the unplanted control, enhanced losses of PCBs (19.5%-42.7%) were observed in all planted soils. Cucurbita pepo and Cucurbita moschata treatments were more efficient in PCB dissipation, and have similar patterns of soil phospholipid fatty acids (PLFAs) and PCB congener profiles. Cucurbita treatments tend to have higher soil microbial biomass than Cucumis. Gram-negative (G(-)) bacteria were significantly correlated with PCB degradation rates (R(2) = 0.719, p < 0.001), while fungi and G(-) bacteria were correlated with dissipation of the penta homologue group (R(2) = 0.590, p < 0.01). Therefore, Cucurbita related soil microorganisms could play an important role in remediation of PCB contaminated soils.

In situ application of activated carbon and biochar to PCB-contaminated soil and the effects of mixing regime

The in situ use of carbon amendments such as activated carbon (AC) and biochar to minimize the bioavailability of organic contaminants is gaining in popularity. In the first in situ experiment conducted at a Canadian PCB-contaminated Brownfield site, GAC and two types of biochar were statistically equal at reducing PCB uptake into plants. PCB concentrations in Cucurbita pepo root tissue were reduced by 74%, 72% and 64%, with the addition of 2.8% GAC, Burt's biochar and BlueLeaf biochar, respectively. A complementary greenhouse study which included a bioaccumulation study of Eisenia fetida (earthworm), found mechanically mixing carbon amendments with PCB-contaminated soil (i.e. 24 h at 30 rpm) resulted in shoot, root and worm PCB concentrations 66%, 59% and 39% lower than in the manually mixed treatments (i.e. with a spade and bucket). Therefore, studies which mechanically mix carbon amendments with contaminated soil may over-estimate the short-term potential to reduce PCB bioavailability.

Terrestrial ecosystem recovery following removal of a PCB point source at a former pole vault line radar station in Northern Labrador

Saglek Bay (LAB-2), located on the northeast coast of Labrador is a former Polevault station that was operated by the U.S. Air Force from 1953 to 1971 when it was abandoned. An environmental assessment carried out in 1996 determined that the site was contaminated with polychlorinated biphenyls (PCBs) with concentrations in soils far exceeding the Canadian Environmental Protection Agency (CEPA) regulation of 50 μg/g in three areas of the site (Beach, Site Summit, Antenna Hill). This led to remediation work carried out between 1999 and 2004 to remove and/or isolate all PCB-contaminated soil exceeding 50 μg/g and to further remediate parts of the site to <5 μg/g PCBs. In this study, spatial and temporal trends of PCB concentrations in soil, vegetation (Betula glandulosa and Salix spp.), and deer mice (Peromyscus maniculatus) were investigated over a period of fourteen (1997-2011) years in an effort to track ecosystem recovery following the removal of the PCB point sources. The data collected shows that PCB levels in vegetation samples are approximately four times lower in 2011 than pre-remediation in 1997. Similarly, PCB concentrations in deer mice in 2011 are approximately three times lower than those measured in 1997/98. Spatial trends in vegetation and deer mice continue to demonstrate that areas close to the former point sources of PCBs have higher PCB concentrations than those further away (and higher than background levels) and these residual PCB levels are not likely to decrease in the foreseeable future given the persistent nature of PCBs in general in the environment, and in particular in cold climates.

Dechlorination of PCBs in the rhizosphere of switchgrass and poplar

Polychlorinated biphenyl (PCB) congeners (PCB 52, 77, and 153) singly and in mixture were spiked and aged in soil microcosms and subsequently planted with switchgrass (Panicum virgatum) or poplar (Populus deltoids x nigra DN34). The planted reactors showed significantly greater reductions in PCB parent compounds when compared to unplanted systems after 32 weeks. There was evidence of reductive dechlorination in both planted and unplanted systems, but the planted microcosms with fully developed roots and rhizospheres showed greater biotransformation than the unplanted reactors. These dechlorination products accounted for approximately all of the molar mass of parent compound lost. Based on the transformation products, reductive dechlorination pathways are proposed for rhizospheric biotransformation of PCB 52, 77, and 153. This is the first report of rhizosphere biotransformation pathways for reductive dechlorination in marginally aerobic, intermittently flooded soil as evidenced by a mass balance on transformation products.

Reducing the bioavailability of PCBs in soil to plant by biochars assessed with triolein-embedded cellulose acetate membrane technique

Coupling with triolein-embedded cellulose acetate membrane (TECAM) technique, hydroxypropyl β-cyclodextrins (HPCD) extraction method, and the greenhouse pot experiments, the influences of biochars on polychlorinated biphenyls (PCBs) bioavailability in soil to plant (Brassica chinensis L. and Daucus carota) were investigated. Addition of 2% biochars to soils significantly reduced the uptake of PCBs in plant, especially for di-, tri- and tetra-chlorobiphenyls. PCBs concentrations in the roots of B. chinensis and D. carota were reduced for 61.5-93.7%, and 12.7-62.4%, respectively in the presence of biochars. The kinetic study showed that in the soils amended with/without biochars, PCBs concentrations accumulated in TECAM, as well as in the HPCD extraction solution, followed significant linear relationships with those in plant roots. Application of biochars to soil is a potentially promising method to reduce PCBs bioavailability whereas TECAM technique can be a useful tool to predict the bioavailability of PCBs in soil.

Deciduous vegetation (Betula glandulosa) as a biomonitor of airborne PCB contamination from a local source in the Arctic

Concentrations of polychlorinated biphenyls (PCBs) were measured in the new-year growth of dwarf birch (Betula glandulosa) before (2001-2002), during (2003-2004), and for six years after (2005-2010) the screening and containerization of PCB-contaminated soils (>50 μg/g PCBs) at a remote Arctic radar site. During the remediation activities, ambient air PCB concentrations were measured using active air samplers for comparison to the passive samplers (dwarf birch). PCB concentrations measured by the active samplers reached a maximum of 0.037 μg/m(3) which was below the project criteria of 0.15 μg/m(3) indicating minimal source emissions. During the same time period, PCB concentrations in the dwarf birch (passive samplers) showed significant increases of 2-14 fold compared to the baseline data from previous years. The birch data also showed significant changes between monitoring events within the 2003 and 2004 sampling seasons (June to September) and decreases when ambient air concentrations were low, indicating the sensitivity of new-year growth to reflect net accumulation and ambient conditions at a temporal scale of approximately two weeks. The dwarf birch PCB concentrations remained elevated compared to baseline levels for two years after the remediation was completed. In the third year following remediation, concentrations decreased to below baseline levels reflecting the overall remediation and source removal at the site. Spatial variations observed in dwarf birch PCB concentrations are likely due to the influence of wind direction on contaminant dispersal and deposition.

Overview of in situ and ex situ remediation technologies for PCB-contaminated soils and sediments and obstacles for full-scale application

Polychlorinated biphenyls (PCB) are persistent organic pollutants used worldwide between the 1930s and 1980s. Although their use has been heavily restricted, PCB can be found in contaminated soils and sediments. The most frequent remediation solutions adopted are "dig and dump" and "dig and incinerate", but there are currently new methods that could be more sustainable alternatives. This paper takes a look into the remediation options available for PCB-contaminated soils and sediments, differentiating between biological, chemical, physical and thermal methods. The use of combined technologies was also reviewed. Most of them are still in an initial development stage and further research in different implementation issues is needed. There is no single technology that is the solution for PCB contamination problem. The successful remediation of a site will depend on proper selection, design and adjustment of the technology or combined technologies to the site characteristics.

Legume-grass intercropping phytoremediation of phthalic acid esters in soil near an electronic waste recycling site: a field study

A field experiment was conducted to study the phytoremediation of phthalic acid esters (PAEs) by legume (alfalfa, Medicago sativa L.)-grass (perennial ryegrass, Lolium perenne L. and tall fescue, Festuca arundinacea) intercropping in contaminated agricultural soil at one of the largest e-waste recycling sites in China. Two compounds, DEHP and DnBP, were present in the soil and in the shoots of the test plants at much higher concentrations than the other target PAEs studied. Over 80% of 'total' (i.e., all six) PAEs were removed from the soil across all treatments by the end of the experiment. Alfalfa in monoculture removed over 90% of PAEs and alfalfa in the intercrop of the three plant species contained the highest shoot concentration of total PAEs of about 4.7 mg kg(-1) DW (dry weight). Calculation of phytoextraction efficiency indicated that the most effective plant combinations in eliminating soil PAEs were the three-species intercrop (1.78%) and the alfalfa monocrop (1.41%). Phytoremediation with alfalfa was effective in both monoculture and intercropping. High bioconcentration factors (BCFs) indicated the occurrence of significant extraction of PAEs by plants from soil, suggesting that phytoremediation may have potential for the removal of PAEs from contaminated soils.

Phytoaccumulation of antimicrobials by hydroponic Cucurbita pepo

Consumer use of antimicrobial-containing products continuously introduces triclocarban and triclosan into the environment. Triclocarban and triclosan adversely affect plants and animals and have the potential to affect human health. Research examined the phytoaccumulation of triclocarban and triclosan by pumpkin (Cucurbita pepo cultivar Howden) and zucchini (Cucurbita pepo cultivar Gold Rush) grown hydroponically. Pumpkin and zucchini were grown in nutrient solution spiked with 0.315 microg/mL triclocarban and 0.289 microg/mL triclosan for two months. Concentrations of triclocarban and triclosan in nutrient solutions were monitored weekly. At the end of the trial, roots and shoots were analyzed for triclocarban and triclosan. Research demonstrated that pumpkin and zucchini accumulated triclocarban and triclosan. Root accumulation factors were 1.78 and 0.64 and translocation factors were 0.001 and 0.082 for triclocarban and triclosan, respectively. The results of this experiment were compared with a previous soil column study that represented environmentally relevant exposure of antimicrobials from biosolids and had similar root mass. Plants were not as efficient in removing triclocarban and triclosan in hydroponic systems as in soil systems. Shoot concentrations of antimicrobials were the same or lower in hydroponic systems than in soil columns, indicating that hydroponic system does not overpredict the concentrations of antimicrobials.

The use of biochar to reduce soil PCB bioavailability to Cucurbita pepo and Eisenia fetida

Biochar is a carbon rich by-product produced from the thermal decomposition of organic matter under low oxygen concentrations. Currently many researchers are studying the ability of biochar to improve soil quality and function in agricultural soils while sustainably sequestering carbon. This paper focuses on a novel but complimentary application of biochar - the reduced bioavailability and phytoavailability of organic contaminants in soil, specifically polychlorinated biphenyls (PCBs). In this greenhouse experiment, the addition of 2.8% (by weight) biochar to soil contaminated with 136 and 3.1 μg/g PCBs, reduced PCB root concentration in the known phytoextractor Cucurbita pepo ssp. pepo by 77% and 58%, respectively. At 11.1% biochar, even greater reductions of 89% and 83% were recorded, while shoot reductions of 22% and 54% were observed. PCB concentrations in Eisenia fetida tissue were reduced by 52% and 88% at 2.8% and 11.1% biochar, respectively. In addition, biochar amended to industrial PCB-contaminated soil increased both aboveground plant biomass, and worm survival rates. Thus, biochar has significant potential to serve as a mechanism to decrease the bioavailability of organic contaminants (e.g. PCBs) in soil, reducing the risk these chemicals pose to environmental and human health, and at the same time improve soil quality and decrease CO(2) emissions.

Accumulation of weathered p,p'-DDTs in grafted watermelon

The grafting of melon plants onto cucurbit rootstocks is a common commercial practice in many parts of the world. However, certain cucurbits have been shown to accumulate large quantities of weathered persistent organic pollutants from the soil, and the potential contamination of grafted produce has not been thoroughly evaluated. Large pot and field experiments were conducted to assess the effect of grafting on accumulation of weathered DDX (the sum of p,p'-DDT, p,p'-DDD, and p,p'-DDE) from soils. Intact squash (Cucurbita maxima × moschata) and watermelon (Citrullus lanatus), their homografts, and compatible heterografts were grown in pots containing soil with weathered DDX at 1480-1760 ng/g soil or under field conditions in soil at 150-300 ng/g DDX. Movement of DDX through the soil-plant system was investigated by determining contaminant levels in the bulk soil and in the xylem sap, roots, stems, leaves, and fruit of the grafted and nongrafted plants. In all plants, the highest DDX concentrations were detected in the roots, followed by decreasing amounts in the stems, leaves, and fruit. Dry weight concentrations of DDX in the roots ranged from 7900 ng/g (intact watermelon) to 30100 ng/g (heterografted watermelon) in the pot study and from 650 ng/g (intact watermelon) to 2430 ng/g (homografted squash) in the field experiment. Grafting watermelon onto squash rootstock significantly increased contaminant uptake into the melon shoot system. In the pot and field studies, the highest stem DDX content was measured in heterografted watermelon at 1220 and 244 ng/g, respectively; these values are 140 and 19 times greater than contaminant concentrations in the intact watermelon, respectively. The xylem sap DDX concentrations of pot-grown plants were greatest in the heterografted watermelon (6.10 μg/L). The DDX contents of the leaves and fruit of watermelon heterografts were 3-12 and 0.53-8.25 ng/g, respectively, indicating that although the heterografted watermelon accumulated greater pollutant levels, the resulting contamination is not likely a food safety concern.

Effect of pumpkin root exudates on ex situ polychlorinated biphenyl (PCB) phytoextraction by pumpkin and weed species

INTRODUCTION

A greenhouse experiment was conducted to determine if Cucurbita pepo ssp. pepo (pumpkin) root exudates could increase the uptake of polychlorinated biphenyls (PCBs) into plants. Contaminated soil was pre-treated with pumpkin root exudates by first growing pumpkins in the soil. Plants (pumpkins and weeds) were grown in the pre-treated (root exudate group) and non-treated (control group) contaminated soils. Seeds from five weed species collected from two contaminated sites were germinated in sufficient quantities (n ≥ 6) for three seedlings to be planted in two groups.

DISCUSSION

Plants from both the control group and the root exudate group extracted a combined total of ∼1.2% PCBs from soil. Differences in root concentrations between groups were observed for Bidens cernua (beggar's tick) and in total PCBs extracted into the roots for pumpkins. This is the first report of significant changes in the PCB phytoextraction ability of multiple plant species due to the presence of root exudates. In addition, slight differences were also observed for root and shoot concentrations and extractions by several other species, though these were not statistically different at α = 0.05. While the mechanism of phytoextraction is still unknown, this study indicates that the root exudates of C. pepo ssp. pepo can affect the uptake and transport of contaminants within specific plant species.

Phytoextraction and uptake patterns of weathered polychlorinated biphenyl-contaminated soils using three perennial weed species

Three promising phytoextracting perennial weed species [ L. (ox-eye daisy), L. (curly dock), and L. (Canada goldenrod)] were planted in monoculture plots at two polychlorinated biphenyl (PCB)-contaminated sites in southern Ontario and followed over 2 yr to investigate the effects of plant age, contaminant characteristics, and species-specific properties on PCB uptake and accumulation patterns in plant tissues. Results from this study indicate that, for each of these weed species, shoot contaminant concentrations and total biomass are dependent on plant age and life cycle (vegetative and reproductive stages), which affects the total amount of PCBs phytoextracted on a per-plant basis. Even at suboptimal planting densities of 3 to 5 plants m, all three weed species extracted a greater quantity of PCBs per unit area (4800-10,000 μg m) than the known PCB-accumulator L. ssp (cv Howden pumpkins) (1500-2100 μg m) at one of the two sites. Calculated PCB extractions based on theoretical optimal planting densities were significantly higher at both sites and illustrate the potential of these weeds for site remediation. This study also demonstrates that plants may accumulate PCBs along the stem length in a similar manner as plants.