Natural and induced cadmium-accumulation in poplar and willow: Implications for phytoremediation

Potentially poplars and willows may be used for the in situ decontamination of soils polluted with Cd, such as pasturelands fertilised with Cd-rich superphosphate fertiliser. Poplar (Kawa and Argyle) and willow (Tangoio) clones were grown in soils containing a range (0.6–60.6 μg g⁻¹ dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μg g⁻¹ dry matter) than the two poplar clones (6–75 μg g⁻¹), which themselves were not significantly different. Poplar trees (Beaupré) sampled in situ from a contaminated site near the town of Auby, Northern France, were also found to accumulate significant quantities (up to 209 μg g⁻¹) of Cd. The addition of chelating agents (0.5 and 2 g kg⁻¹ EDTA, 0.5 g kg⁻¹ DTPA and 0.5 g kg⁻¹NTA) to poplar (Kawa) clones caused a temporary increase in uptake of Cd. However, two of the chelating agents (2 g kg⁻¹ EDTA and 0.5 g kg⁻¹ NTA) also resulted in a significant reduction in growth, as well as abscission of leaves. If the results obtained in these pot experiments can be realised in the field, then a single crop of willows could remove over 100 years worth of fertiliser-induced Cd contamination from pasturelands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sheep prefer clean forage over forage contaminated with military explosives TNT, RDX and HMX

The common military explosives 2-methyl-1,3,5-trinitrobenzene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) are distributed in many military training areas, and are thus encountered by grazing animals. The aim of this study was to examine small ruminant's intake of forage contaminated with explosives. An indoor, experimental setup was used to determine if contamination of forage by these compounds affected intake by sheep. The results clearly demonstrate that contamination by any of the three explosives reduced forage intake in sheep; in order of increasing avoidance: RDX < TNT < HMX. The results are discussed in a risk assessment context.     

Plant uptake and leaching of copper during EDTA-enhanced phytoremediation of repacked and undisturbed soil

EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 g g^–1 of Na₂H₂ EDTA in solution was added to repacked soil columns, and intact cores of a sandy loam of volcanic origin, that was growing Agrostis tenuis. The soil contained up to 400 g g^–1 of copper due to a history of fungicide spraying. EDTA application increased the herbage copper concentration of the grass growing in repacked soil from 30 to 300 g g^–1, but the same application to an intact core only brought about an increase from 10 to 60 g g^–1. More copper accumulated in the herbage when the EDTA was applied in numerous small doses than in just one or two larger amounts. Calculation of the concentration of copper in the water taken up by the grass revealed this to be two orders of magnitude lower than that in the soil solution. As a result of the EDTA applications, about 100 times more copper was leached than was taken up by the herbage. This means that a strategy for managing leaching losses needs to be part of any plan for EDTA-enhanced phytoremediation.     

Heavy metal uptake by arbuscular mycorrhizas of Elsholtzia splendens and the potential for phytoremediation of contaminated soil

A pot culture experiment and a field experiment were carried out separately to study heavy metal (HM) uptake from soil contaminated with Cu, Zn, Pb and Cd by Elsholtzia splendens Nakai ex F. Maekawa inoculated with arbuscular mycorrhizal (AM) fungi and the potential for phytoremediation. The HM-contaminated soil in the pot experiment was collected from the field experiment site. Two AM fungal inocula, MI containing only one AM fungal strain, Glomus caledonium 90036, and M II consisting of Gigaspora margarita ZJ37, Gigaspora decipens ZJ38, Scutellospora gilmori ZJ39, Acaulospora spp. andGlomus spp., were applied to the soil under unsterilized conditions. In the pot experiment, the plants were harvested after 24 weeks of growth. Mycorrhizal colonization rate, plant dry weight (DW) and P, Cu, Zn, Pb, Cd concentrations were determined. MI-treated plants had higher mycorrhizal colonization rates than MII-treated plants. Both MI and MII increased shoot and root DW, and MII was more effective than MI. In shoots, the highest P, Cu, Zn and Pb concentrations were all observed in the plants treated with MII, while MI decreased Zn and Pb concentrations and increased P but did not alter Cu, and Cd concentrations were not affected by either of two inocula. In roots, MII increased P, Zn, Pb concentrations but did not alter Cu and Cd, and MI did not affect P, Cu, Zn, Pb, Cd concentrations. Cu, Zn, Pb, Cd uptake into shoots and roots all increased in MII-treated plants, while in MI-treated plants, Cu and Zn uptake into shoots and Cu, Zn, Pb, Cd into roots increased but Pb and Cd uptake into shoots decreased. In general, MII was more effective than MI in promoting plant growth and HM uptake. The field experiment following the pot experiment was carried out to investigate the effects of MII under field conditions. The 45-day-old nonmycorrhizal and MII-colonized seedlings of E. splendens were transplanted to HM-contaminated plots and harvested after 5 months. MII-inoculation increased shoot DW and shoot P, Cu, Zn, Pb concentrations significantly but did not alter shoot Cd concentrations, which led to higher uptake of Cu, Zn, Pb, Cd by E. splendens shoots. These results indicate that the AM fungal consortium represented by MII can benefit phytoextraction of HMs and therefore play a role in phytoremediation of HM-contaminated soils.     

Mechanism of aerobic transformation of carbon tetrachloride by poplar cells

The biochemical mechanism of carbon tetrachloride transformation by poplarcells was investigated using an axenic poplar cell culture.After one-day incubations of poplar cells under aerobic conditions, about 1.5% of dosedcarbon tetrachloride was transformed to carbon dioxide, about 0.001% to chloroform andabout 3% of the carbon was bound to insoluble poplar cellular materials. The productionof carbon dioxide increased under aerobic conditions while the formation of chloroformand cell binding of carbon tetrachloride-carbon was enhanced under anaerobic conditions.Both carbon dioxide production and cell binding were significantly inhibitedby a general inhibitor of cytochrome P-450 activity (carbon monoxide) and by specific P-450 2E1 inhibitors(chlorzoxazone, isoniazid, 4-methylpyrazole and 1-phenylimidazole). However, no inhibitory effects were observed when the cells were incubated in thepresence of lignin peroxidase inhibitors (NaVO₃ and 3-amino-1,2,4-triazole). These resultssuggest that an enzyme similar to mammalian cytochrome P450-2E1 is involved inthe metabolism of carbon tetrachloride by poplar cells. This study demonstratesan environmental biodegradative process for carbon tetrachloridethat operates under aerobic conditions.     

Role of earthworm-straw interactions on phytoremediation of Cu contaminated soil by ryegrass

It is well known that the earthworm's activities can increase the availability of soil nutrients, improve soil structure, and enhance the biomass of plants in uncontaminated soil. Recently, many researchers found that some metal-tolerant earthworms can survive and even change the fractional distribution of heavy metals in contaminated soil. Furthermore, it has been revealed that earthworms are able to increase metal availability, and therefore, accumulate more metals in plants through their burrowing and casting activity. It is clear that the influence of soil animals is an important factor for phyto-remedation that must be taken into account. ~In this article, the authors studied some effects of addition of earthworms (Metaphire guillelmi), corn straw, and in combinations of earthworms and corn straw on the growth and Cu uptake by ryegrass in Cu contaminated pot soils. The experiment consisted of four levels of Cu addition (0, 100, 200, 400 mg·kg?1) and four treatments. The treatments were 1. control (CK); 2.straw mulching only (M); 3. earthworm additions to soil only (E); and 4.straw mulching plus earthworm additions (ME). Each treatment had three replicates. 10 seeds of ryegrass (Lolium multiflorum) were sowed in each pot and harvested after 30 days. After 30 days of incubation, all earthworms were found to be alive and the pot soils were burrowed through by earthworms. Results showed that the biomass of earthworm declined with the increase of the dosage of Cu additions. The biomass of earthworm increased significantly in treatment 4 (ME) as compared with treatment 3 (E). Not only the earthworms could get more food from the straw, but also could counteract some negative effects of Cu on the earthworms. The rates of straw decomposition in ME treatment increased by about 58.11% ?77.32%. The earthworm activities increased root biomass of ryegrass significantly, but did not show the effect on plant root growth. On the contrary, straw enhanced roots biomass significantly instead of shoots biomass. It was also found that the concentration of Cu in the plant shoot and the plant root, as well as plant Cu uptake were enhanced by earthworm's activities and straw mulching. The increased amount by straw mulching was lower than that of earthworms (E). The treatment of the earthworm–straw mulching combinations enhanced plant Cu concentration, and the amount increased by it was lower than that of the earthworm treatment (E) but higher than that of straw mulching treatment (M). The accumulation factors of copper in the shoots of ryegrass were increased by 31.22% ?121.07%, 2.12% ?61.28% and 25.56% ?132.64%, respectively, in treatment 3(E), 2(M), and 4(ME), respectively. In conclusion, the earthworm activities, straw-mulching and their interactions may have potential roles in elevating phyto-extraction efficiency in low to medium level Cu contaminated soil.     

蚯蚓-秸秆及其交互作用对黑麦草修复Cu污染土壤的影响

以高沙土为供试土壤,加入Cu^2＋以模拟成：0,100,200,400mg／kgCu^2＋的Cu污染土壤,设置接种蚯蚓（E）、表施秸秆（M）,同时加入蚯蚓和秸秆（ME）及不加蚯蚓和秸秆的对照（CK）4个处理,并种植黑麦草。研究蚯蚓、秸秆相互作用对黑麦草吸收、富集铜的影响。结果表明：加入秸秆显著提高了蚯蚓的生物量,一定程度上缓解了重金属对蚯蚓的毒害,同时蚯蚓显著提高了秸秆的分解率,较无蚯蚓对照提高了58．11％～77．32％。接种蚯蚓（E,ME）还提高了土壤有效态重金属（DTPA-Cu）含量,秸秆处理（M）则降低了土壤有效态重金属含量。研究还发现,E处理促进了黑麦草地上部生长,而M和ME处理均显著提高了黑麦草地下部的生物量。E和ME处理同时提高了植物地上部和地下部的Cu浓度及Cu吸收量,M处理则只对植物的地下部Cu浓度和Cu吸收量有显著促进作用。总体来看,E处理、M处理及ME处理分别使黑麦草地上部Cu富集系数提高了31．22％～121．07％．2．12％～61．28％和25．56％～132．64％。     

Role of earthworm-straw interactions on phytoremediation of Cu contaminated soil by ryegrass

It is well known that the earthworm's activities can increase the availability of soil nutrients, improve soil structure, and enhance the biomass of plants in uncontaminated soil. Recently, many researchers found that some metal-tolerant earthworms can survive and even change the fractional distribution of heavy metals in contaminated soil. Furthermore, it has been revealed that earthworms are able to increase metal availability, and therefore, accumulate more metals in plants through their burrowing and casting activity. It is clear that the influence of soil animals is an important factor for phyto-remedation that must be taken into account. ~In this article, the authors studied some effects of addition of earthworms (Metaphire guillelmi), corn straw, and in combinations of earthworms and corn straw on the growth and Cu uptake by ryegrass in Cu contaminated pot soils. The experiment consisted of four levels of Cu addition (0, 100, 200, 400 mg·kg?1) and four treatments. The treatments were 1. control (CK); 2.straw mulching only (M); 3. earthworm additions to soil only (E); and 4.straw mulching plus earthworm additions (ME). Each treatment had three replicates. 10 seeds of ryegrass (Lolium multiflorum) were sowed in each pot and harvested after 30 days. After 30 days of incubation, all earthworms were found to be alive and the pot soils were burrowed through by earthworms. Results showed that the biomass of earthworm declined with the increase of the dosage of Cu additions. The biomass of earthworm increased significantly in treatment 4 (ME) as compared with treatment 3 (E). Not only the earthworms could get more food from the straw, but also could counteract some negative effects of Cu on the earthworms. The rates of straw decomposition in ME treatment increased by about 58.11% ?77.32%. The earthworm activities increased root biomass of ryegrass significantly, but did not show the effect on plant root growth. On the contrary, straw enhanced roots biomass significantly instead of shoots biomass. It was also found that the concentration of Cu in the plant shoot and the plant root, as well as plant Cu uptake were enhanced by earthworm's activities and straw mulching. The increased amount by straw mulching was lower than that of earthworms (E). The treatment of the earthworm–straw mulching combinations enhanced plant Cu concentration, and the amount increased by it was lower than that of the earthworm treatment (E) but higher than that of straw mulching treatment (M). The accumulation factors of copper in the shoots of ryegrass were increased by 31.22% ?121.07%, 2.12% ?61.28% and 25.56% ?132.64%, respectively, in treatment 3(E), 2(M), and 4(ME), respectively. In conclusion, the earthworm activities, straw-mulching and their interactions may have potential roles in elevating phyto-extraction efficiency in low to medium level Cu contaminated soil.     

A Transient Study of Formation of Conjugates during TNT Metabolism by Plant Tissues

The formation of TNT-derived conjugates was investigated in hairy root tissue cultures of Catharanthus roseus and in aquatic plant systems of Myriophyllum aquaticum. The temporal profiles of four TNT-derived conjugates, TNT-1, 2A-1, TNT-2 and 4A-1, were determined over 3 to 16-day exposure durations. When axenic C. roseus roots were exposed separately to 2,4,6 trinitrotoluene, 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene, the array and levels of conjugates varied. Exposure of axenic roots to either 4-amino-2,6-dinitrotoluene or 2-amino-4,6-dinitrotoluene resulted in the formation of only 4A-1 and 2A-1, respectively, and not TNT-1 and TNT-2. However, amendment of previously unexposed roots with TNT produced all four conjugates. The conjugates were preferentially accumulated within the biomass phase of root cultures. Significantly, conjugates TNT-1 and TNT-2 were observed in the biomass phase of intact M. aquaticum plants exposed to TNT. The results clearly indicate the presence of common TNT transformation products in two diverse plants species and tissue type. The distribution of conjugates formed via monoamine derivatives of TNT, however, may be a function of several factors, including the starting xenobiotic type and/or level. Initial bulk rate constants for disappearance of 2,4,6 trinitrotoluene, 2-amino-4,6-dinitrotoluene, and 4-amino-2,6-dinitrotoluene were also determined. Their magnitude followed the order: TNT >> 4-A-2,6-DNT > 2-A-4,6-DNT.     

环境重金属污染的植物修复及基因工程在其中的应用

随着工业技术的发展,重金属在土壤和水体中的含量越来越高,重金属污染已日益成为威胁人类健康和人类生活质量的严重的社会问题和环境问题。植物修复可部分解决这一问题且正引起人们的普遍关注。但现在发现许多用于修复的超量积累植物生长缓慢、植株矮小、地上部生物量小,成了实际应用中的最大限制。利用基因工程手段改变植物对重金属吸收、转运、积累和忍耐的机制,从而提高植物对重金属的富集能力,将成为今后植物修复领域研究的一个重要方向。     

A Peat Moss-Based Technology for Mitigating Residues of the Explosives TNT,RDX, and HMX in Soil

There is increased interest in how to balance military preparedness and environmental protection at Department of Defense (DoD) facilities. This research evaluated a peat moss-based technology to enhance the adsorption and biodegradation of explosive residues at military testing and training ranges. The evaluation was performed using 30-cm-long soil columns operated under unsaturated flow conditions. The treatment materials were placed at the soil surface, and soil contaminated with 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was spread over the surface. Simulated rainfall initiated dissolution and leaching of the explosive compounds, which was monitored at several depths within the columns. Peat moss plus soybean oil reduced the soluble concentrations of TNT, RDX and HMX detected at 10 cm depth by 100%, 60%, and 40%, respectively, compared to the no-treatment control column. Peat moss alone reduced TNT and HMX concentrations at 10 cm depth relative to the control, but exhibited higher soluble RDX concentrations by the end of the experiment. Concentrations of HMX and RDX were also reduced at 30 cm depth by the peat moss plus soybean oil treatments relative to those observed in the control column. These preliminary results demonstrate proof-of-concept of a low cost technology for reducing the contamination of groundwater with explosives at military test and training ranges.     

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.     

重金属污染土壤植物修复基本原理及强化措施探讨

阐述了植物修复的基本概念及主要作用方式 ,并从土壤中重金属存在形态 ,植物对重金属吸收、排泄和积累以及植物生物学特性与植物修复的关系等方面讨论了重金属污染土壤植物修复的基本原理及局限性和限制性因素 ,从超富集植物性能强化和技术强化两方面探讨了植物修复的强化措施 ,并指出与现代化农业技术相结合是植物修复重金属污染土壤大规模商业应用的一条捷径     

Pretreatment of hybrid poplar by aqueous ammonia

Enzymatic hydrolysis of hybrid poplar treated by ammonia recycle percolation (ARP) was studied applying cellulase enzyme supplemented with additional xylanase or pectinase. The effect of xylanase addition was much more significant than pectinase addition. Conversion of ARP‐treated hybrid poplar to ethanol was carried out by simultaneous saccharification and fermentation (SSF) and SS and cofermentation (SSCF). The maximum ethanol yield observed from the SSCF experiment was 78% of theoretical maximum based on the total carbohydrate (glucan + xylan). The same feedstock was also treated by soaking in aqueous ammonia (SAA), a batch pretreatment process with lower severity than ARP. The test results indicated that relatively high severity is required to attain acceptable level of digestibility of hybrid poplar. In order to lower the severity of the pretreatment, addition of H₂O₂ was attempted in the SAA. Addition of H₂O₂ significantly enhanced delignification of hybrid poplar due to its oxidative degradation of lignin. Several different H₂O₂ feeding schemes and different temperature profiles were attempted in operation of the SAA to investigate the effects of H₂O₂ on degradation of lignin and carbohydrates in hybrid poplar. More than 60% of lignin in hybrid poplar was removed with stepwise‐increase of temperature (60–120°C after 4h of reaction). Increase of carbohydrate degradation was also observed under this condition. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Effectiveness of arbuscular mycorrhizal fungi in phytoremediation of lead- contaminated soil by vetiver grass

A greenhouse experiment was conducted to evaluate the effectiveness of arbuscular mycorrhizal (AM) fungi in phytoremediation of lead (Pb)-contaminated soil by vetiver grass. Experiment was a factorial arranged in a completely randomized design. Factors included four Pb levels (50, 200, 400, and 800 mg kg^?1) as Pb (NO₃)₂, AM fungi at three levels (non mycorrhizal (NM) control, Rhizophagus intraradices, Glomus versiforme). Shoot and root dry weights (SDW and RDW) decreased as Pb levels increased. Mycorrhizal inoculation increased SDW and RDW compared to NM control. With mycorrhizal inoculation and increasing Pb levels, Pb uptake of shoot and root increased compared to those of NM control. Root colonization increased with mycorrhizal inoculation but decreased as Pb levels increased. Phosphorus concentration and uptake in shoot of plants inoculated with AM fungi was significantly higher than NM control at 200 and 800 mg Pb kg^?1. The Fe concentration, Fe and Mn uptake of shoot in plants inoculated with Rhizophagus intraradices in all levels of Pb were significantly higher than NM control. Mycorrhizal inoculation increased Pb extraction, uptake and translocation efficiencies. Lead translocation factor decreased as Pb levels increased; however inoculation with AM fungi increased Pb translocation.     

重金属污染土壤植物修复中细胞分裂素的作用与机制

植物修复因投资成本低、环境扰动少、二次污染易控制、美化环境等优点成为重金属污染土壤修复重要的治理技术。植物内源细胞分裂素调控植物生理活动,外源细胞分裂素对植物生理生态特征产生显著影响,且在植物修复中逐渐受到研究人员的关注。细胞分裂素能够调控植物根茎发育、叶片衰老、激素传递等过程,同时在重金属胁迫下也参与蒸腾、光合、抗性、解毒等系统的运转。以细胞分裂素对植物生理活动的调控作用研究为基础,阐述了细胞分裂素在植物修复中的作用机制。主要包括：增强光合作用,延缓叶片衰老,提升植物抗性能力;调控根茎叶发育,增加植物生物量,强化植物富集效果;增强转运蛋白表达,提高叶面蒸腾作用,促进重金属吸收转运;参与解毒过程,降低重金属毒性,调控重金属体内转化。最后提出了细胞分裂素在重金属污染土壤植物修复中的研究方向,这对促进细胞分裂素在植物修复中的实际应用具有重要意义。