Growth response and phytoextraction of copper at different levels in soils by Elsholtzia splendens

Phytoremediation is a promising approach for cleaning up soils contaminated with heavy metals. Information is needed to understand growth response and uptake mechanisms of heavy metals by some plant species with exceptional capability in absorbing and superaccumulating metals from soils. Greenhouse study, field trial, and old mined area survey were conducted to evaluate growth response and Cu phytoextraction of Elsholtzia splendens in contaminated soils, which has been recently identified to be tolerant to high Cu concentration and have great potential in remediating contaminated soils. The results from this study indicate that the plant exhibited high tolerance to Cu toxicity in the soils, and normal growth was attained up to 80 mg kg(-1) available soil Cu (the NH4OAc extractable Cu) or 1000 mg kg(-1) total Cu. Under the field conditions, a biomass yield of 9 ton ha(-1) was recorded at the soil available Cu level of 77 mg kg(-1), as estimated by the NH4OAc extraction method. Concentration-dependent uptake of Cu by the plant occurred mainly at the early growth stage, and at the late stage, there is no difference in shoot Cu concentrations grown at different extractable soil Cu levels. The extractability of Cu from the highly polluted soil is much greater by the roots than that by the shoots. The NH4OAc extractable Cu level in the polluted soil was reduced from 78 to 55 mg kg(-1) in the soil after phytoextraction and removal of Cu by the plant species for one growth season. The depletion of extractable Cu level in the rhizosphere was noted grown in the mined area, even at high Cu levels, the NH4OAc extractable Cu in the rhizosphere was 30% lower than that in the bulk soil. These results indicate that phytoextraction of E. splendens can effectively reduce the plant-available Cu level in the polluted soils.     

The use of maize and poplar in chelant-enhanced phytoextraction of lead from contaminated agricultural soils

Chelant-enhanced phytoextraction of heavy metals is an emerging technological approach for a non-destructive remediation of contaminated soils. The main objectives of this study were (i) to assess the extraction efficiency of two different synthetic chelating agents (ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS)) for desorbing Pb from two contaminated agricultural soils originating from a mining and smelting district and (ii) to assess the phytoextraction efficiency of maize (Zea mays) and poplar (Populus sp.) after EDTA application. EDTA was more efficient than EDDS in desorbing and complexing Pb from both soils, removing as much as 60% of Pb. Maize exhibited better results than poplar when extracting Pb from the more acidic (pH approximately 4) and more contaminated (up to 1360 mg Pb kg(-1)) agricultural soil originating from the smelting area. On the other hand, poplars proved to be more efficient when grown on the near-neutral (pH approximately 6) and less contaminated (up to 200 mg Pb kg(-1)) agricultural soil originating from the mining area. Furthermore, the addition of EDTA led to a significant increase of Pb content especially in poplar leaves, proving a strong translocation rate within the poplar plants.     

Enhanced uptake of As, Zn, and Cu by Vetiveria zizanioides and Zea mays using chelating agents

Vetiveria zizaniodes (vetiver) is commonly known for its effectiveness in soil and sediment erosion control. It can tolerate to extreme soil conditions and produce a high biomass even growing in contaminated areas. Zea mays (maize) can also produce a very high biomass with a fast growth rate and possesses some degree of metal tolerance. A greenhouse study was conducted to investigate the feasibility of using vetiver and maize for remediation of arsenic (As)-, zinc (Zn-), and copper (Cu)-amended soils and evaluate the effects of chelating agents on metal uptake by these plants. Vetiver had a better growth (dry weight yield of root and shoot) than maize under different treatment conditions. The effects of different chelating agents on As, Zn, and Cu extraction from soil to soil solution were studied. Among the nine chelating agents used, it was noted that 20 mmol NTA could maximize As and Zn bioavailability, while 20 mmol HEIDA could maximize Cu bioavailability in the soil solution. The surge time in maximizing metal uptake ranged from 16 to 20 days which indicated that timing on plant harvest was an important factor in enhanced metal accumulation. In general, vetiver was a more suitable plant species than maize in terms of phytoextraction of metals from metal-contaminated soil. Application of NTA in As-amended soil and HEIDA in Cu-amended soil at the rate of 20 mmol kg(-1) increased 3-4-fold of As and Cu in shoot of both plants, whereas application of NTA (20 mmol kg(-1)) increased 37- and 1.5-fold of Zn accumulation in shoot of vetiver and maize, respectively. The potential environmental risk of metal mobility caused by chelating agents used for phytoextraction should not be overlooked.     

Copper bioavailability in the rhizosphere of maize (Zea mays L.) grown in two Italian soils

In this study, potentially bioavailable copper was estimated in two soils (a fungicide polluted and a natural soil) using a passive sampling technique, DGT. As plants can alter copper mobility and bioavailability in the soil, the rhizosphere properties of Zea mays L. were investigated using rhizoboxes.

Compared to the total concentration, the soluble and the potentially bioavailable copper concentration in the bulk soils were generally low (less than 0.20% and 0.06% respectively), with a sixfold increase in the rhizosphere of the polluted soil. Our results suggest that maize cultivation in a polluted vineyard soil could increase the potentially available fraction of copper. DGTs showed a good sensitivity to soil properties and to root-induced changes in the rhizosphere, but the potentially bioavailable copper could not be related to the copper concentration in the above ground parts of maize. The results suggest that DGT may be used to predict some effects of the cultivation of polluted soils, for example, metal mobility and increased availability, but they cannot mimic the uptake of a tolerant plant.

For both soils, dissolved organic carbon (DOC) concentrations were threefold higher in the rhizosphere than in the bulk soil, whilst bioaccumulation in leaves and roots was not significant. DOC production, usually effective in ion mobilization and assimilation, may help also in the reduction of Cu uptake at toxic concentrations. The sequestration of available Cu in soil and soil solution by DOC seems to contribute to maize tolerance.     

Evaluation of copper availability to plants in copper-contaminated vineyard soils

The repeated use of copper (Cu) fungicides to control vine downy mildew has led to long-term accumulation of Cu in vineyard soils which now raises the issue of the potential bioavailability of Cu for various living organisms including plant species. The bioavailable Cu can be defined as the portion of soil Cu that can be taken up by roots, for a given plant species. In order to evaluate the bioavailability of Cu to plants, a pot experiment was conducted in glasshouse conditions with a crop species (maize) and 12 soils sampled in the upper horizon of 10 vineyard plots (total Cu ranging from 38 to 251 mg kg-1) and two woodland plots (control soils that had not received any Cu application; total Cu amounting to 20-26 mg kg-1). These soils were selected for their diverse physical (large range of particle size distribution) and chemical (from acid to calcareous soils) properties. After 35 days of growth, plant shoots were harvested for analysis. The roots were separated from soil particles for further analysis. The concentrations of Cu in the roots and aerial parts of the maize were then compared with the amounts of Cu extracted from the soil by a range of conventional extractants. Observed Cu concentrations in maize roots which have grown in contaminated vineyard soils were very high (between 90 and 600 mg kg-1), whereas Cu concentrations in the aerial parts varied only slightly and remained low (< 18 mg kg-1). Root Cu concentrations observed for maize increased with increasing total Cu content in the soil and with decreasing soil CEC. Cu accumulation in maize roots may be as high in calcareous soils as in acid soils, suggesting that soil pH had little influence. In the case of the vineyard soils studied, the lack of correlation found for maize between Cu concentrations in roots and in the aerial parts, suggests that an analysis of the aerial parts would not be a good indicator of plant Cu uptake, as it provides no insight into the real amount of Cu transferred from the soil to the plant. For maize, our results show that extraction with organic complexing agents (EDTA, DTPA) and extraction with ammonium acetate seem to provide a reasonably good estimate of root Cu concentration.     

An uptake and elimination kinetics approach to assess the bioavailability of chromium,copper, and arsenic to earthworms (Eisenia andrei) in contaminated field soils

The aim of this study was to determine the bioavailability of metals in field soils contaminated with chromated copper arsenate (CCA) mixtures. The uptake and elimination kinetics of chromium, copper, and arsenic were assessed in the earthworm Eisenia andrei exposed to soils from a gradient of CCA wood preservative contamination near Hartola, Finland. In soils contaminated with 1480–1590 mg Cr/kg dry soil, 642–791 mg Cu/kg dry soil, and 850–2810 mg Ag/kg dry soil, uptake and elimination kinetics patterns were similar for Cr and Cu. Both metals were rapidly taken up and rapidly excreted by Eisenia andrei with equilibrium reached within 1 day. The metalloid As, however, showed very slow uptake and elimination in the earthworms and body concentrations did not reach equilibrium within 21 days. Bioaccumulation factors (BAF) were low for Cu and Cr (< 0.1), but high for As at 0.54–1.8. The potential risk of CCA exposure for the terrestrial ecosystem therefore is mainly due to As.

     

The evaluation of heavy metal accumulation and application of a comprehensive bio-concentration index for woody species on contaminated sites in Hunan,China

Fast-growing metal-accumulating woody plants are considered potential candidates for phytoextraction of metals. Shuikoushan mining, one of the biggest Pb and Zn production bases in China, presents an important source of the pollution of environment during the last 100 years. Over 150 km² of fertile soil have been contaminated by the dust, slag, and tailings from this mining. The goal of the present work has been to determine the content of Pb, Zn, Cd, and Cu in wild woody plants (18 species) naturally growing in this area. Two hundred five plant and soil samples from 11 contaminated sites were collected and analyzed. In addition, to assess the ability of multi-metal accumulation of these trees, we proposed a predictive comprehensive bio-concentration index (CBCI) based on fuzzy synthetic assessment. Our data suggest some adult trees could also accumulate a large amount of metals. Pb concentrations in leaves of Paulownia fortunei (Seem.) Hemsl. (1,179 mg/kg) exceeded the hyperaccumulation threshold (1,000 mg/kg). Elevated Pb concentrations (973.38 mg/kg) were also found in the leaves of Broussonetia papyrifera (L.) Vent., with a Pb bio-concentration factor of up to 0.701. Endemic species, Zenia insignis Chun exhibited huge potential for Zn and Cd phytoextraction, with the highest concentrations of Zn (1,968 mg/kg) and Cd (44.40 mg/kg), characteristic root nodules, and fast growth rates in poor soils. As for multi-metal accumulation ability, native species B. papyrifera was calculated to have the most exceptional ability to accumulate various metals simultaneously (CBCI 2.93), followed by Amorpha fruticosa L. (CBCI 2.72) and Lagerstroemia indica L. (CBCI 2.53). A trend of increasing metal from trunks to leaves (trunks?<?branches?<?leaves) and towards fine roots has been shown by metal partitioning between tissues. The proposed CBCI would allow for the selection of suitable trees for phytoremediation in the future.     

Copper uptake and translocation in a submerged aquatic plant Hydrilla verticillata (L.f.) Royle

A comprehensive understanding of the uptake, tolerance and transport of heavy metals in the wetland system through aquatic plants will be essential for the development of phytoremediation technologies. Copper accumulation and translocation of a submersed macrophyte Hydrilla verticillata (L.f.) Royle were investigated. Plant shoots showed a significant accumulation of Cu with a maximum of 30830 mg Cu kg?1 dry weight after exposed to 4000 μg L?1 Cu for 4d. Both roots and shoots can directly take up Cu from solution and Cu mainly accumulated in cell wall fractions. Moreover, H. verticillata predominantly accumulated Cu through shoots from the aqueous solutions because of the higher weights and bioaccumulation factors of shoots than those of roots. Acropetal translocation of Cu in the plant is higher than the basipetal translocation, which implies that upward translocation of Cu is mainly via the xylem and downward translocation is mainly through the phloem. These findings contribute to the application of submerged aquatic plants to copper removal from moderately contaminated waters.     

Linking plant tissue concentrations and soil copper pools in urban contaminated soils

Copper tissue concentrations of radish (Raphanus sativa cv. Cherry Belle), lettuce (Lactuca sativa cv. Buttercrunch) and ryegrass (Lolium perenne cv. Barmultra) grown in a greenhouse in urban contaminated soils are compared to total, soluble and free ion copper pools. The tissue concentrations of copper vary between 8.1 and 82.6 mg Cu kg(-1) dry tissue and the total soil copper content varies between 32 and 640 mg Cu kg(-1) dry soil. The linear regressions with cupric ion activity and total soil copper are both significant (p < 0.01), but cupric ion activity yields a higher level of statistical significance in every case. The results support the hypothesis that free metal in the soil solution is a better indicator of plant metal bioavailability than either total or soluble metal.     

Metal contamination of vineyard soils in wet subtropics (southern Brazil)

The vine-growing areas in Brazil are the dampest in the world. Copper maximum value registered in this study was as much as 3200 mg kg(-1), which is several times higher than reported for vineyard soils in temperate climates. Other pesticide-derived metals accumulate in the topsoil layer, surpassing in the old vineyards the background value several times for Zn, Pb, Cr and Cd. Copper is transported to deeper soils' horizons and can potentially contaminate groundwater. The soils from basaltic volcanic rocks reveal the highest values of Cu extracted with CaCl(2), demonstrating a high capacity of copper transference into plants. When evaluating the risks of copper's toxic effects in subtropics, the soils from rhyolitic volcanic rocks are more worrisome, as the Cu extracted with ammonium acetate 1M surpasses the toxic threshold as much as 4-6 times.     

Effect of plant growth on copper solubility and speciation in soil solution samples

The effect of plant growth on copper solubility and speciation was studied in a 10-week pot experiment. A copper-tolerant grass variety (Agrostis capillaris L. var. Parys Mountain) was grown in pots that contained either clean (copper-total approx. 30 mg kg(-1)) or copper contaminated soil (copper-total approx. 170 mg kg(-1)) at two pH levels (4.7 and 5.5). Also, similar pots without vegetation were included in the study. Due to the addition of NH(4)NO(3) fertilizer and subsequent nitrification of ammonia to nitrate, soil pH decreased from 4.7 to 3.5 and from 5.5 to 4, respectively. In the planted pots, soil pH recovered faster after depletion of NH(4)(+). This resulted in a decrease in the calcium solution concentrations and an increase in the dissolved organic carbon (DOC) concentrations in the planted pots. However, this was only observed in the clean soil; in the contaminated soil no difference in DOC levels between bare and planted pots was observed. Copper solubility in the contaminated soil was lower in the presence of plants; in the clean soil no differences were observed between the bare and planted pots. In the planted pots, copper activities in solution in both clean and contaminated soils were two orders of magnitude lower than in the bare pots. Copper activities in the non-planted contaminated soil reached potentially toxic levels ([Cu]+/-10(-5) to 10(-6) M) in contrast to the lower levels in the planted pots ([Cu]+/-10(-7) to 10(-10) M). Data and model results show that plant growth improves pH, DOC and calcium in solution to such an extent that both the total dissolved copper concentration and the free metal activity in soils can be reduced. This stresses the potential beneficial role of plants for the immobilization and detoxification of metals in contaminated soils.     

Diuron mobility through vineyard soils contaminated with copper

The herbicide diuron is frequently applied to vineyard soils in Burgundy, along with repeated treatments with Bordeaux mixture (a blend of copper sulfate and calcium hydroxide) that result in elevated copper concentrations. Cu could in principle affect the fate and transport of diuron or its metabolites in the soil either directly by complexation or indirectly by altering the populations or activity of microbes involved in their degradation. To assess the effect of high Cu concentrations on diuron transport, an experiment was designed with ten undisturbed columns of calcareous and acidic soils contaminated with 17--509 mg kg(-1) total Cu (field-applied). Grass was planted on three columns. Diuron was applied to the soils in early May and in-ground lysimeters were exposed to outdoor conditions until November. Less than 1.2% of the diuron applied was found in the leachates as diuron or its metabolites. Higher concentrations were found in the effluents from the grass-covered columns (0.1--0.45%) than from the bare-soil columns (0.02--0.14%), and they were correlated with increases in dissolved organic carbon. The highest amounts of herbicide were measured in acidic-soil column leachates (0.98--1.14%) due to the low clay and organic matter contents of these soils. Cu also leached more readily through the acidic soils (32.8--1042 microg) than in the calcareous soils (9.5--63.4 microg). Unlike in the leachates, the amount of diuron remaining in the soils at the end of the experiment was weakly related to the Cu concentrations in the soils.     

The use of poplar during a two-year induced phytoextraction of metals from contaminated agricultural soils

The efficiency of poplar (Populus nigra L.xPopulus maximowiczii Henry.) was assessed during a two-year chemically enhanced phytoextraction of metals from contaminated soils. The tested metal mobilizing agents were EDTA (ethylenediaminetetraacetic acid) and NH4Cl. EDTA was more efficient than chlorides in solubilizing metals (especially Pb) from the soil matrix. The application of chlorides only increased the solubility of Cd and Zn. However, the increased uptake of metals after the application of higher concentrations of mobilizing agents was associated with low biomass yields of the poplar plants and the extraction efficiencies after the two vegetation periods were thus comparable to the untreated plants. Additionally, the application of mobilizing agents led to phytotoxicity effects and increased mobility of metals. Higher phytoextraction efficiencies were observed for Cd and Zn compared to Pb and Cu. Poplars are therefore not suitable for chemically enhanced phytoextraction of metals from severely contaminated agricultural soils.     

Phytoextraction potential of two Rumex acetosa L. accessions collected from metalliferous and non-metalliferous sites: effect of fertilization

Metal tolerance and phytoextraction potential of two common sorrel (Rumex acetosa L.) accessions, collected from a Pb/Zn contaminated site (CS, Lanestosa) and an uncontaminated site (UCS, Larrauri), were studied in fertilized and non-fertilized pots prepared by combining soil samples from both sites in different proportions (i.e., 0%, 33%, 66% and 100% of Lanestosa contaminated soil). The original metalliferous mine soil contained 20480, 4950 and 14 mg kg(-1) of Zn, Pb and Cd, respectively. The microcosm experiment was carried out for two months under greenhouse controlled conditions. It was found that fertilization increased mean plant biomass of both accessions as well as their tolerance. However, only the CS accession survived all treatments even though its biomass decreased proportionally according to the percentage of contaminated mine soil present in the pots. This metallicolous accession would be useful for the revegetation and phytostabilization of mine soils. Due to its high concentration and bioavailability in the contaminated soil, the highest values of metal phytoextracted corresponded to Zn. The CS accession was capable of efficiently phytoextracting metal from the 100% mine soil, indeed reaching very promising phytoextraction rates in the fertilized pots (6.8 mg plant(-1) month(-1)), similar to the ones obtained with hyperaccumulator plants. It was concluded that fertilization is certainly worth being considered for phytoextraction and revegetation with native plants from metalliferous soils.     

Trichoderma atroviride F6 improves phytoextraction efficiency of mustard (Brassica juncea (L.) Coss. var. foliosa Bailey) in Cd, Ni contaminated soils

Trichoderma atroviride F6, isolated from decaying feather and resistant to 100 mg l(-1) Cd2+ and 250 mg l(-1) Ni2+, was applied for rhizoremediation of Cd, Ni and Cd-Ni combination contaminated soils through association with Brassica juncea (L.) Coss. var. foliosa. The strain significantly alleviated the cellular toxicity of cadmium and nickel to plants. Inoculation of B. juncea (L.) Coss. var. foliosa with T. atroviride F6 resulted a 110%, 40% and 170% increase in fresh weight in Cd, Ni and Cd-Ni contaminated soils, respectively (P<0.05). The translocation factors and metal bioconcentration factors calculated for the inoculated plant were increased compared to the noninoculated plants. The results indicated that the efficiency of phytoextraction for B. juncea (L.) Coss. var. foliosa enhanced after inoculating with T. atroviride F6. The fungal treated plants grown in Cd-Ni combination contaminated soils showed higher phytoextraction efficiency than those in Cd or Ni contaminated soils. Thus, it is suggested that the fungus T. atroviride F6 endowed with organic-degrading capabilities could be exploited for fungi-assisted phytoremediation of mixed organic-metal contaminated soils.     

Copper uptake by Elsholtzia splendens and Silene vulgaris and assessment of copper phytoavailability in contaminated soils

Tolerance and metal uptake are two essential characteristics required for phytoextraction of metals from contaminated soils. We compared tolerance and Cu uptake of Elsholtzia splendens (reported previously to be a Cu hyperaccumulator) with Silene vulgaris (the Imsbach population, a well-known Cu-tolerant excluder species), using 30 soils varying widely in total Cu concentration (19-8645 mg kg(-1)). We further investigated the effectiveness of different soil testing methods for predicting plant metal uptake. The results showed that both Elsholtzia splendens and Silene vulgaris were tolerant to Cu, especially Silene vulgaris. However, Elsholtzia splendens did not hyperaccumulate Cu, but behaved as a typical Cu excluder like Silene vulgaris. The concentrations of Cu in both plants correlated more closely with 1 M NH4NO3 extractable Cu, soil solution Cu, or effective Cu concentration determined using DGT, than with soil total Cu, EDTA extractable Cu or free Cu2+ activity. The relationships between soil solution properties and root Cu concentrations were further investigated using multiple regression. The results showed that increasing soil solution pH increased root Cu concentration when free Cu2+ activity was held constant, suggesting a higher phytoavailability of free Cu2+ at a higher pH. Soil solution DOC appeared to play two contrasting roles on the phytoavailability of Cu: (1) reducing Cu availability by complexing Cu; and (2) increasing Cu availability at the same level of free Cu2+ activity by providing a strong buffer for free Cu2+. The results are consistent with the intensity/capacity concept for phytoavailability of metals in soils.     

The effect of nitrogen form on rhizosphere soil pH and zinc phytoextraction by Thlaspi caerulescens

The phytoextraction of Zn may be improved by applying N fertilizers to increase the biomass and Zn content of shoots. Rhizosphere-pH change from uptake of different N forms will affect Zn phyto-availability in the rhizosphere and Zn phytoextraction. This glasshouse study examined the effect of N form on Zn phytoextraction by Thlaspi caerulescens (Prayon). The plants were grown in a Zn-contaminated soil (total Zn 250 mg kg-1 soil; pHwater 5.7) and supplied with (NH4)2SO4, Ca(NO3)2 or urea [(NH2)2CO]. The form was maintained by applying the nitrification inhibitor dicyandiamide. A biodegradable chelator ethylenediaminedisuccinic acid (EDDS) was included for comparison. The addition of N doubled the shoot biomass. The highest shoot Zn content occurred in the Ca(NO3)2 treatment and was associated with the highest rhizosphere pH. The lowest shoot dry weight occurred in the EDDS treatment. The Zn concentration in the shoots increased as the rhizosphere pH increased. A significant correlation occurred between Ca and Zn concentrations in the shoots. This study demonstrated that Ca(NO3)2 is a more effective treatment than , urea or EDDS for enhancing Zn phytoextraction in a mildly acidic soil.     

Pedological characteristics of Mn mine tailings and metal accumulation by native plants

In southern China revegetation and ecological restoration of many abandoned Mn tailings has become a major concern. To determine the major constraints for plant establishment and evaluate the feasibility of remediation, a comparative study was conducted on Mn tailings and rhizosphere soils at the boundary of the tailings pond. Both tailings and rhizosphere soils had neutral to slightly alkaline pH and normal electrical conductivity. They were both enriched with organic matter (6.8-9.2%), total N (1.77-5.94 g kg(-1)), available P (41.78-73.83 mg kg(-1)) and K (146.7-906.9 mg kg(-1)), suggesting the tailings were a nutrient rich substrate for revegetation. Mn tailings were clay textured, while rhizosphere soils were silty loam or clay loam. The compaction and anoxic nature of Mn tailings were considered to be the major constraints for plant establishment. Total Mn (31903 mg kg(-1)), Cd (119 mg kg(-1)), Cu (126 mg kg(-1)) and Zn (2490 mg kg(-1)) in tailings were all at phytotoxic levels, but did not differ significantly from those in rhizosphere soils. In both tailings and rhizosphere soils, percentages of water- and DTPA-extractable metals were less than 1% and 2% of the total metal pools, respectively. Sequential extraction revealed that the majority of Mn, Cu and Zn were associated with the residual fraction, while the majority of Cd occurred as Fe-Mn oxides. The natural succession of plants around Mn tailings formed a distinctive metal-tolerant plant community, mainly comprising nine species such as Cynodon dactylon and Humulus scandens and so on. All species studied could be good candidates for revegetation of Mn tailings.     

Effects of copper fungicide residues on the microbial function of vineyard soils

The use of copper-based fungicides leads to an accumulation of copper (Cu) in vineyard soils, potentially causing adverse effects to the microbial function and fertility of the soil. This study used a soil microcosm approach to assess the effects of Cu accumulation on microbial function in vineyard soils. Surface soil samples were collected from 10 vineyards and a number of un-impacted reference sites in each of three different viticultural regions of Australia. The field-collected soils were transferred to microcosms and maintained for up to 93 days in the laboratory at 20–22 °C and 60 % of their maximum water-holding capacity. The microbial function of the soils was indicated by measuring phosphomonoesterase, arylsulfatase, urease, and phenol oxidase activities. In general, the vineyard soils had greater concentrations of Cu and lower enzyme activities than in the reference soils, although a weak negative relationship between Cu and enzyme activity could only be found for phosphomonoesterase activity. The results show that soil physical–chemical properties (i.e., organic carbon, pH) are greater determinants of soil enzyme activity than increased soil Cu concentration at the Cu concentrations present in vineyard soils.     

Evaluation of the effect of small organic acids on phytoextraction of Cu and Pb from soil with tobacco Nicotiana tabacum

Phytoremediation, the use of plants to extract contaminants from soils and groundwater, is a promising approach for cleaning up soils contaminated with heavy metals. However its use is limited by the time required for plant growth, the nutrient supply and, moreover, by the limited metal uptake capacity. Synthetic chelators have shown positive effects in enhancing heavy metal extraction, but they have also revealed several negative side-effects. The objective of this study was to investigate the use of three natural low molecular weight organic acids (NLMWOA) (citric, oxalic, and tartaric acid) as an alternative to synthetic chelators. Slurry-, column-, toxicity- and phytoextraction experiments were performed. For the phytoextraction experiment the three NLMWOA were applied to a copper- and a lead-contaminated soil respectively. A significant increase in copper uptake was visible only in the citric acid treatment (67 mg kg-1) in comparison to the EDTA treatment (42 mg kg-1). The NLMWOA application showed no enhanced effect concerning the lead phytoextraction. A possible explanation for this lack of significance could be the rate of the degradation of NLMWOA. This rate might well be too high for these heavy metals with low mobility and bioavailability such as lead. The amounts of NLMWOA applied to the soil were very high (62.5 mmol kg-1 of soil) and the effect was too little. In this respect EDTA, which was applied in very small amounts (0.125 mmol kg-1) was more efficient. Thus making NLMWOA unsuitable to enhance phytoextraction of heavy metals from soil.