Influence of citric acid amendments on the availability of weathered PCBs to plant and earthworm species

A series of small and large pot trials were conducted to assess the phytoextraction potential of several plant species for weathered polychlorinated biphenyls (PCBs) in soil (105 microg/g Arochlor 1268). In addition, the effect of citric acid on PCB bioavailability to both plants and earthworms was assessed. Under small pot conditions (one plant, 400 g soil), three cucurbits (Cucurbita pepo ssp pepo [zucchini] and ssp ovifera [nonzucchini summer squash], Cucumis sativus, cucumber) accumulated up to 270 microg PCB/g in the roots and 14 microg/g in the stems, resulting in 0.10% contaminant removal from soil. Periodic 1 mM subsurface amendments of citric acid increased the stem and leaf PCB concentration by 330 and 600%, respectively, and resulted in up to a 65% increase in the total amount of contaminant removed from soil. Although citric acid at 10 mM more than doubled the amount of PCB desorbed in abiotic batch slurries, contaminant accumulation by two earthworm species (Eisenia foetida and Lumbricus terrestris) was unaffected by citric acid at 1 and 10 mM and ranged from 11-15 microg/g. Two large pot trials were conducted in which cucurbits (C. pepo ssp pepo and ssp ovifera, C. sativus) and white lupin (Lupinus albus) were grown in 70 kg of PCB-contaminated soil White lupin was the poorest accumulator of PCBs, with approximately 20 microg/g in the roots and 1 microg/g in the stems. Both C. pepo ssp ovifera (summer squash) and C. sativus (cucumber) accumulated approximately 65-100 microg/g in the roots and 6-10 microg/g in the stems. C. pepo ssp pepo (zucchini) accumulated significantly greater levels of PCB than all other species, with 430 microg/g in the roots and 22 microg/g in the stems. The mechanism by which C. pepo spp pepo extracts and translocates weathered PCBs is unknown, but confirms earlier findings on the phytoextraction of other weathered persistent organic pollutants such as chlordane, p,p'-DDE, and polycyclic aromatic hydrocarbons.     

Technical note monitoring native vegetation on a dumpsite of PCB-contaminated soil

Composition of native vegetation on a polychlorinated biphenyls (PCB)-contaminated soil dumpsite at Lhenice, South Bohemia (Czech Republic), was determined and species variability in the accumulation of PCBs in plant biomass was investigated. Soil stripping contaminated by PCBs originated at a factory producing electrical transformers that mostly used the commercial PCB mixture Delor 103 and 106. The PCB content of soil in the most contaminated part of the dumpsite reached 153 mg kg(-1) dry soil. Low diversity of plant species was found on the dumpsite. Results showed three grass species, Festuca arundinacea Schreb., Phalaroides arundinacea (L.) Rauschert., and Calamagrostis epigeios (L.) Roth., to be the major components of the vegetation and confirmed their high tolerance toward PCB contamination. The highest content of PCB in plant biomass--813.2 microg kg(-1) dry biomass--was determined in Festuca aboveground biomass. For phytoextraction purposes especially, Festuca can be recommended due to its high biomass yield, but its bioconcentration factor was very low (0.006). Tripleurospermum maritimum (L.) Sch. Bip. and Cirsium arvense (L.) Scop. grew mainly at the margins of the most contaminated part of the dumpsite. The PCB content determined in their aboveground biomass-278.7 and 289.5 microg kg(-1) dry biomass, respectively--was nonsignificantly lower compared to grass species Phalaroides and Calamagrostis. Salix (Salix viminalis L. and Salix caprea L.) was monitored among plant species composition at this site as a representative of woody species.     

红树植物秋茄对PCBs污染沉积物的修复

通过盆栽试验,研究了红树植物秋茄(Kandelia candel)对污染沉积物中系列浓度的PCB47(2,2′,4,4′-tetrachlorobiphenyl)和PCB155( 2,2′,4,4′,6,6′, -hexachlorophenyl)的修复作用与累积机理.结果表明:(1)经过180d处理,栽种了秋茄的沉积物中PCB47的残留浓度为53.99～528.37μg·kg-1,PCB155的残留浓度为68.25～682.90μg·kg-1,分别比对照1(加二氯化汞)低10.40%～15.46% 和6.10%～11.94%;比对照2(无二氯化汞)低7.70%～12.85% 和5.28%～8.27%;(2)秋茄对沉积物中PCB47和PCB155均具有较强的吸收积累作用,并随沉积物中PCB47和PCB155含量的增加而增大,不同种类PCBs在秋茄体内不同部位的积累趋势相同,不论是PCB47还是PCB155的累积量均是根> 叶> 茎.秋茄叶片中多氯联苯来自根部传输和空气吸收两部分,较低浓度的处理中,主要来自空气吸收,较高浓度的处理中,主要来自根部传输;(3)秋茄根对PCBs的生物富集系数(BCFs) 随着沉积物中PCB47和PCB155含量的增加而减小.不同种类PCBs 以及植物不同部位间BCFs 差异较大, PCB47的生物富集系数大于PCB155, 秋茄不同部位对PCBs生物富集系数大小不同,无论是PCB47还是PCB155,生物富集系数均是根＞叶＞茎.总体看来,秋茄能积累与去除污染沉积物中的PCB47和PCB155,表明用红树植物秋茄修复PCBs污染沉积物是一种有效、可行的方法.     

Phytoremediation of polycyclic aromatic hydrocarbons in soil: part I. Dissipation of target contaminants

Phytoremediation has been demonstrated to be a viable cleanup alternative for soils contaminated with petroleum products. This study evaluated the application of phytoremediation to soil from a manufactured gas plant (MGP) site with high concentrations of recalcitrant, polycyclic aromatic hydrocarbons (PAHs). Two greenhouse studies investigated the potential dissipation and plant translocation of PAHs by fescue (Festuca arundinacea) and switchgrass (Panicum virgatum) in the first experiment and zucchini (Curcubita pepo Raven) in the second. The MGP soil was highly hydrophobic and initially inhibited plant growth. Two unplanted controls were established with and without fertilization. In the first experiment, concentrations of PAHs decreased significantly in all treatments after 12 mo. Plant biomass and microbial numbers were statistically equivalent among plant species. PAH concentrations in plant biomass were negligible for fescue and switchgrass. In the second experiment, zucchini enhanced the dissipation of several PAHs after 90 d of treatment when compared to the unvegetated soil. Plant tissue concentrations of PAHs were not elevated in the zucchini roots and shoots, and PAHs were not detectable in the fruit.     

Effect of a polycyclic aromatic hydrocarbon on the phytoremediation of zinc by two plant species (Brassica juncea and Festuca arundinacea)

The redevelopment of contaminated land is becoming increasingly necessary under sustainable- development legislation; however, many of the contaminated sites are "orphan" sites and therefore require a low-cost remediation technology. These sites often contain a cocktail of pollutants including organics and inorganics. Phytoremediation provides a possible solution, but there is little information available on the tolerance of plant species to multiple pollutants and their ability to remediate in mixed-contaminant soils. The effect of a polycyclic aromatic hydrocarbon (pyrene) in soil upon the remediation of zinc by Brassica juncea and Festuca arundinacea was investigated under normal climatic conditions in the United Kingdom. Zinc was effectively removed from mixed-contaminant soils in the presence of both species, in comparison to a control treatment. Both species accumulated zinc in plant tissues in the presence of pyrene, but the growth of B. juncea was significantly reduced when zinc and pyrene were supplied in combination. Zinc was predominantly associated with root tissues for F. arundinacea, whereas B. juncea contained higher concentrations in shoot tissues. F. arundinacea provides a possible species to be used for the phytoremediation of brownfield sites, but further research is required to determine a range of species that may be used and their applicability to different contaminants.     

Soil hydraulic manipulation and organic amendment for the enhancement of selenium volatilization in a soil–pickleweed system

Biological volatilization of selenium (Se) in contaminated areas represents an environmentally friendly phytoremediation approach. Implementation of phytovolatilization technology for the remediation of Se-contaminated soils or sediments is oftentimes limited by its low remediation efficiency under field conditions. This greenhouse study determined the feasibility of manipulating soil organic content and hydraulic conditions in a soil–pickleweed (Salicornia bigelovii) system for the enhancement of Se volatilization. Based on annual shoot biomass production rate under field conditions (approximately 1.5 kg m⁻²), the addition of pickleweed shoot tissues to the soil surface resulted in 2.2-fold more biogenic volatile Se than the control, up to 251.6 ± 140.5 μg m⁻² d⁻¹. Selenium volatilization was significantly reduced at a soil water potential of −25 kPa, but substantially increased after re-irrigation to 0 kPa. In a 42-day experiment, the rate of Se volatilization was significantly correlated with soil water potential (P < 0.0001). Findings from this study demonstrate that Se volatilization be substantially enhanced by amending soil with pickleweed residues and by creating wetting and drying cycles that can be monitored with soil water potential probes in the field.     

Isolation and characterisation of polychlorinated biphenyl (PCB) degrading fungi from a historically contaminated soil

Background  

Polychlorinated biphenyls (PCBs) are widespread toxic pollutants. Bioremediation might be an effective, cost competitive and environment-friendly solution for remediating environmental matrices contaminated by PCBs but it is still unsatisfactory, mostly for the limited biodegradation potential of bacteria involved in the processes. Very little is known about mitosporic fungi potential in PCB bioremediation and their occurrence in actual site historically contaminated soils. In the present study, we characterised the native mycoflora of an aged dump site soil contaminated by about 0.9 g kg^-1 of Aroclor 1260 PCBs and its changing after aerobic biotreatment with a commercial complex source of bacteria and fungi. Fungi isolated from the soil resulting from 120 days of treatment were screened for their ability to adsorb or metabolise 3 target PCBs.     

Methyl-beta-cyclodextrin-enhanced solubilization and aerobic biodegradation of polychlorinated biphenyls in two aged-contaminated soils

The bioremediation of aged polychlorinated biphenyl (PCB)-contaminated soils is adversely affected by the low bioavailability of the pollutants. Randomly methylated-beta-cyclodextrins (RAMEB) were tested as a potential PCB-bioavailability-enhancing agent in the aerobic treatment of two aged-contaminated soils. The soils, contaminated by about 890 and 8500 mg/kg of Aroclor 1260 PCBs, were amended with biphenyl (4 g/kg), inorganic nutrients (to adjust their C:N ratio to 20:1), and variable amounts of RAMEB (0%, 0.5%, or 1.0% [w/w]) and treated in both aerobic 3-L solid-phase reactors and 1.5-L packed-bed loop reactors for 6 months. Notably, significant enhancement of the PCB biodegradation and dechlorination, along with a detectable depletion of the initial soil ecotoxicity, were generally observed in the RAMEB-treated reactors of both soils. RAMEB effects were different in the two soils, depending upon the treatment conditions employed, and generally increased proportionally with the concentration at which RAMEB was applied. RAMEB, which was slowly metabolized by the soil's aerobic microorganisms, was found to markedly enhance the occurrence of the indigenous aerobic, cultivable biphenyl-growing bacteria harboring genes homologous to those of two highly specialized PCB degraders (i.e., bphABC genes of Pseudomonas pseudoalcaligenes KF707 and bphA1A2A3A4BC1 genes of Rhodococcus globerulus P6) and chlorobenzoic acid-degrading bacteria as well as the occurrence of PCBs in the water phase of the soil reactors. These findings indicate that RAMEB enhanced the aerobic bioremediation of the two soils by increasing the bioavailability of PCBs and the occurrence of specialized bacteria in the soil reactors.     

Phytoremediation of soil contaminated with cadmium, copper and polychlorinated biphenyls

A pot experiment and afield trial were conducted to study the remediation of an aged field soil contaminated with cadmium, copper and polychlorinated biphenyls (PCBs) (7.67 +/- 0.51 mg kg(-1) Cd, 369 +/- 1 mg kg(-1) Cu in pot experiment; 8.46 +/- 0.31 mg kg(-1) Cd, 468 +/- 7 mg kg(-1) Cu, 323 +/- 12 microg kg(-1) PCBs for field experiment) under different cropping patterns. In the pot experiment Sedum plumbizincicola showed pronounced Cd phytoextraction. After two periods (14 months) of cropping the Cd removal rates in these two treatments were 52.2 +/- 12.0 and 56.1 +/- 9.1%, respectively. Total soil PCBs in unplanted control pots decreased from 323 +/- 11 to 49.3 +/- 6.6 microg kg(-1), but with no significant difference between treatments. The field microcosm experiment intercropping of three plant species reduced the yield of S. plumbizincicola, with a consequent decrease in soil Cd removal. S. plumbizincicola intercropped with E. splendens had the highest shoot Cd uptake (18.5 +/- 1.8 mg pot(-1)) after 6 months planting followed by intercropping with M. sativa (15.9 +/- 1.9 mg pot(-1)). Liming with S. plumbizincicola intercropped with M. sativa significantly promoted soil PCB degradation by 25.2%. Thus, adjustment of soil pH to 5.56 combined with intercropping with S. plumbizincicola and M. sativagave high removal rates of Cd, Cu, and PCBs.     

Capability of selected crop plants for shoot mercury accumulation from polluted soils: phytoremediation perspectives

High-biomass crops can be considered as an alternative to hyperaccumulator plants to phytoremediate soils contaminated by heavy metals. In order to assess their practical capability for the absorption and accumulation of Hg in shoots, barley, white lupine, lentil, and chickpea were tested in pot experiments using several growth substrates. In the first experimental series, plants were grown in a mixture of vermiculite and perlite spiked with 8.35 microg g(-1) d.w. of soluble Hg. The mercury concentration of the plants' aerial tissues ranged from 1.51 to 5.13 microg g(-1) d.w. with lentil and lupine showing the highest values. In a second experiment carried out using a Hg-polluted soil (32.16 microg g(-1) d.w.) collected from a historical mining area (Almadén, Spain), the crop plants tested only reached shoot Hg concentration up to 1.13 microg g(-1) d.w. In the third experimental series, the Almadén soil was spiked with 1 microg g(-1) d.w. of soluble Hg; as a result, mercury concentrations in the plant shoots increased approximately 6 times for lupine, 5 times for chickpea, and 3.5 times for barley and lentil, with respect to those obtained with the original soil without Hg added. This marked difference was attributed to the low availability of Hg in the original Almadin soil and its subsequent increase in the Hg-spiked soil. The low mercury accumulation yields obtained for all plants do not make a successful decontamination of the Almadén soils possible byphytoremediation using crop plants. However, since the crops tested can effectively decrease the plant-available Hg level in this soil, their use could, to some extent, reduce the environmental risk of Hg pollution in the area.     

Differences on Pb accumulation among plant tissues of 25 varieties of maize (Zea mays)

Pollution of agricultural land by heavy metals has imposed an increasingly serious risk to environmental and human health in recent years.Heavy metal pollutants may enter the human food chain through agricultural products and groundwater from the polluted soils.Progress has been made in the past decade on phytoremediation,a safe and inexpensive approach to remove contaminants from soil and water using plants.However,in most cases,agricultural land in China cannot afford to grow phytoremediator plants instead of growing crops due to food supply for the great population.Therefore,new and effective methods to decrease the risk of heavy metal pollution in crops and to clean the contaminated soils are urgently needed.If we can find crop germplasms (including species and varieties) that accumulate heavy metals in their edible parts,such as the leaves of vegetables or grains of cereals,at a level low enough for safe consumption,then we can grow these selected species or varieties in the lands contaminated or potentially contaminated by heavy metals.If we can find crop germplasms that take in low concentrations of heavy metals in their edible parts and high content of the metals in their inedible parts,then we can use these selected species or varieties for soil remediation.In this study,the feasibility of the method is assessed by analyzing Pb concentrations in edible and inedible parts of 25 varieties of maize (Zea mays) grown in Pb-contaminated soils.The soil concentrations of Pb were 595.55 mg/kg in the high Pb exposed treatment and 195.55 mg/kg in the control.The results showed that the Pb concentrations in different tissues were in the order of root ＞ shoot ≌ leaf＞ grain.Compared with the control,the Pb concentrations in root,shoot and leaf were greatly increased under the high Pb exposed condition,while the increments of Pb concentration in grain were relatively lower.Under the high Pb exposure,the grain Pb concentrations of 12 varieties exceeded the maximal Pb limitation of the National Food Hygiene Standard of China (NFHSC) and were inedible.This indicates that there is a high Pb pollution risk for maize grown on Pb polluted sites.Although 22 of the 25 tested varieties had harvest loss under the highly Pb stressed condition,ranging from 0.86%-38.7% of the grain biomass acquired at the control,the average harvest loss of all the tested varieties was only 12.6%,which is usually imperceptible in normal farming practices.Therefore the risk of Pb pollution in maize products cannot be promptly noticed and prevented based only on the outcome of the harvest.However,we did find that 13 of the 25 tested varieties had grain Pb concentrations lower than the limitation of the NFHSC.It is,therefore,possible to reduce the pollution risk if these favorable varieties are used for maize production in Pb-contaminated or potentially contaminated agricultural lands.Pb concentrations in vegetative tissues (root,stem and leaf) were significantly correlated with each other,while Pb concentrations of each vegetative tissue were not significantly correlated with that of grain.Among the 25 tested varieties,some varieties had Pb concentrations in grain lower than (No.1-3 and No.6) or slightly above (No.4) the limitation of the NFHSC,while their Pb concentrations in the vegetative tissues were among the highest.When excluding these varieties,correlations between the Pb concentrations of grain and those of vegetative tissues of the rest of the tested varieties became highly significant.In addition,variety No.1 had the lowest harvest loss under high Pb exposed,and the highest Pb accumulation in vegetative tissues (51.69 mg/plant,12 times as much as in the control).Similar features were also observed in varieties No.2,No.3 and No.6,which absorbed Pb for 36-42 mg/plant under high Pb exposed.We recommend these varieties of maize to be used for bioremediation of Pb contaminated soil and crop production at the same time.     

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.     

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.     

Polychlorinated biphenyls in vegetable soils from Changchun,Northeast China: Concentrations,distribution, sources and human health risks

To investigate the occurrences of polychlorinated biphenyls (PCBs) in suburban vegetable soils of Changchun area, Northeast China, 106 urban vegetable soil samples were collected from Changchun City, Nongan County, Dehui City, Yushu City, Jiutai City, Shuangyang District. We analyzed the concentrations, compositions and sources of 7 PCBs in top soils of Changchun area, and evaluated the non-carcinogenic and carcinogenic risk of PCBs pollution to exposed population. The total concentrations of 7 PCBs ranged from 1.31 to 148 ng/g dry weight (dw) with a mean value of 42.0 ng/g and dominated by Hepta-CBs and Penta-CBs. Principal component analysis (PCA) revealed that PCB pollution in soils of Changchun area mainly related to transportation, vehicle emissions, paints and other industries. Human health risk assessment showed that the cumulative non-carcinogenic and the cumulative carcinogenic risk in children and adults in the industrial land and residential land were acceptable, considering only 7 PCBs homologues were analyzed in this study, the actual risk could be higher.     

The uptake of persistent organic pollutants by plants

In a field experiment, the transfer of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soil to maize (Zea mays L.), sunflower (Helianthus annuus), poplar (Populus nigra × P. maximowiczii) and willow (Salix × smithiana) and the distribution of PCB congeners in maize and sunflower was investigated. The former waste incinerator in Hradec Králové (Czech Republic) was chosen for the experiment. Results of plot screening showed heterogenous contamination by PCBs and PAHs. PCB soil contamination was evidently caused by Delor 106 or Aroclor 1260 stocking and PAH contamination by chemicals containing fluoranthene, benzo/b/fluoranthene, phenanthrene and pyrene. Tested plants were planted on a contaminated field site, in soil contaminated with 1530 μg/kg of total PCBs and 0.138 and 3.42 mg/kg of total PAHs. The results show that maize and sunflower roots accumulated the most PCBs from soil. These plants accumulated hexa- and heptachlorobiphenyl congeners more than tri-, tetra-, and pentachlorobiphenyl congeners. Total concentrations of PAHs in tested plants ranged from 0.096 to 1.34 mg/kg. The highest phenanthrene concentration was found in aboveground biomass of sunflower and the highest concentration of pyrene, in maize roots.     

Genetically modified Pseudomonas biosensing biodegraders to detect PCB and chlorobenzoate bioavailability and biodegradation in contaminated soils

Whole cell microbial biosensors offer excellent possibilities for assaying the complex nature of the bioavailable and bioaccessible fraction of pollutants in contaminated soils, which currently cannot be easily addressed. This paper describes the application and evaluation of three microbial biosensor strains designed to detect the bioavailability and biodegradation of PCBs (and end-products) in contaminated soils and sediments. Polychlorinated biphenyls (PCBs) are considered to be one of the most wide spread, hazardous and persistent pollutants. Herein we describe that there was a positive correlation between the PCB levels within the samples and the percentage of biosensor cells that were expressing their reporter gene; gfp. Immobilisation of the biosensors in calcium alginate beads allowed easy and accurate detection of the biosensor strains in contaminated soil and sludge samples. The biosensors also showed that PCB degradation activity was occurring at a much greater level in Pea inoculated planted soil compared to inoculated unplanted soil indicating rhizoremediation (the removal of pollutants by plant root associated microbes) shows considerable promise as a solution for removing organic xenobiotics from the environment.     

Effects of humic substances on the bioavailability and aerobic biodegradation of polychlorinated biphenyls in a model soil.

The very high hydrophobicity of polychlorinated biphenyls (PCBs) strongly reduces their bioavailability in aged contaminated soils, thus limiting their bioremediation. The biodegradability of PCBs in heavily contaminated soils can be significantly enhanced by soil treatment with surface-active agents. In this work, the effects of naturally occurring surfactants such as humic substances (HS) on the aerobic biodegradation of PCBs in a model soil were studied. The soil was amended with biphenyl (4 g/kg), Fenclor 42 (1,000 mg/kg), the aerobic PCB-biodegrading bacterial co-culture ECO3 (inoculum: 10(8)CFU/mL), and treated in aerobic batch slurry-phase conditions (17.5% w/v) with and without the addition of HS at the rates of 1.5 and 3.0% (w/w). Low PCBs biodegradation and dechlorination yields were observed in the HS-free microcosms, probably as a result of the rapid disappearance of inoculated bacteria. The presence of HS influenced significantly the activity of the specialized biomass and the biodegradation of PCBs in the microcosms. The microcosms that received HS at the 1.5% rate showed a higher persistence of the specialized bacteria and yields of PCB biodegradation and dechlorination about 150 and 100%, respectively, larger than those found for the HS-free microcosms. Lower stimulating effects were observed in the microcosms added with the HS at 3.0% rate. These effects were attributed to an increased solubilization of PCBs in the hydrophobic domains of the humic supramolecular associations and to a different accessibility of PCBs by the specialized bacteria at the different rates of HS addition. Although the slurry-phase treatment generally showed a decrease of the original soil ecotoxicity, the addition of the originally non-toxic HS decreased soil ecotoxicity for the Collembola animal biomarker and increased that towards the Lepidium sativum vegetal biomarker.     

Accumulation of weathered pp'-DDE in xylem sap of grafted watermelon

Movement of weathered p,p'-dichlorodiphenyldichloroethane (p,p'-DDE) from contaminated soil to the rhizosphere pore water to the xylem sap of grafted watermelon was studied under green house conditions. p,p'-DDE concentrations in pore water and xylem sap was compared in intact plants, homografted, and compatible heterografts of Cucurbita pepo spp. pepo and Citrullus lanatus plants. An average p,p'-DDE concentrations in pore water of contaminated soil ranged from 0.36 microg/L to 0.55 microg/L and there were no statistically significant among the cultivars. Conversely, the xylem sap p,p'-DDE concentration of heterografted watermelon having a zucchini rootstock and watermelon scion was 71 microg/L and it was greater than intact watermelon plants (0.49 microg/L) but less than that of intact plants of zucchini (141 microg/L). Homografting showed no effect on xylem sap p,p'-DDE concentrations of the identical cultivars. The bio-concentration factors (BCFs) which is an average p,p'-DDE concentration in xylem sap over average p,p'-DDE in pore water were 344, 325, 197, 1.28, and 0.89 for intact plant of zucchini, homografted zucchini, heterografted watermelon, homografted watermelon, and intact plant of watermelon, respectively. Xylem sap p,p'-DDE concentrations of the heterografted watermelon plants were clearly influenced by plant phylogeny and enhanced by the zucchini rootstock compared to intact watermelon plants.     

玉米各器官积累Pb能力的品种间差异

为了研究不同玉米(Zea mays)品种及不同器官对Pb积累能力的差异,在土壤Pb含量为595.55 mg·kg^-1 的高Pb胁迫和含量为195.55 mg·kg^-1的低Pb胁迫(对照)条件下,采用盆栽试验结合火焰原子吸收等方法,测定了25个玉米品种各器官Pb的含量。结果表明:Pb胁迫下供试玉米品种各器官含Pb量表现为根>茎≌叶>籽实;与对照相比,根、茎、叶Pb含量均大幅度提高,籽实含量的提高幅度相对较小;Pb胁迫条件下,有近半数的供试玉米品种的籽实Pb含量超过了国家规定的卫生标准,显示了在受重金属污染农田生产的玉米产品存在着较高的受Pb污染的风险。有22个品种平均籽实生物量在较强Pb胁迫下有所下降,降幅为0.9%~38.7%,但平均降幅仅为12.6%,显示玉米在Pb胁迫下的减产不易察觉,从而增加了在受污染农田中玉米产品受Pb污染的风险。但研究也表明,在较高Pb胁迫下尚有52%的品种籽实Pb含量未超过国家卫生标准最高限量值,因此可以利用这些品种在受Pb污染农田中进行玉米生产,以降低Pb经玉米产品进入人类食物链的风险。研究结果还发现供试玉米品种各营养器官间Pb含量均呈极显著正相关,但营养器官与籽实Pb含量间无显著相关。其中在较强的胁迫条件下营养器官Pb含量特别高的品种No.1的籽实中Pb含量(0.19 mg·kg^-1)比较低,未超过国家卫生标准;品种No.2、No.3和品种No.6也有类似的特点。除上述品种以及品种No.4外,其余品种籽实Pb含量遵循与营养器官Pb含量成正比的一般规律。根中Pb含量特别高的品种No.1,籽实产量在Pb胁迫下略有下降,但下降幅度最小。胁迫条件下,品种No.1的营养器官Pb总量最高(51.69 mg·plant^-1),是对照的近12倍;籽实Pb含量符合国家标准的品种No.2,No.3和No.6的营养器官Pb总量也较高,在36~42 mg·plant^-1之间。由此可见,存在着在受Pb污染农田利用这些品种进行玉米生产同时修复受污染土壤的可能。     

Biodegradation of PCBs in two-phase partitioning bioreactors following solid extraction from soil

This article demonstrates the feasibility of a novel process concept for the remediation of PCB contaminated soil. The proposed process consists of PCB extraction from soil using solid polymer beads, followed by biodegradation of the extracted PCBs in a solid-liquid two-phase partitioning bioreactor (TPPB), where PCBs are delivered from the polymer beads to the degrading organisms. The commercially available thermoplastic polymer Hytrel was used to extract Aroclor 1242 from contaminated artificial soil in bench scale experiments. Initial PCB contamination levels of 100 and 1,000 mg kg(-1) could be reduced to 32% +/- 1 to 41% +/- 7 of the initial value after 48 h mixing in the presence of a mobilizing agent at polymer-to-soil ratios of 1% (w/w) and 10% (w/w). The decrease of detectable PCBs in the soil was consistent with an increase of PCBs in the polymer beads. It was further shown that Aroclor 1242 could be delivered to the PCB degrading organism Burkholderia xenovorans LB400 in a solid-liquid TPPB via Hytrel beads. A total of 70 mg Aroclor 1242 could be degraded in a 1 L solid-liquid TPPB within 80 h of operation.