The effects of cadmium and zinc interactions on the accumulation and tissue distribution of zinc and cadmium in lettuce and spinach

The interactions between Zn and Cd on the concentration and tissue distribution of these metals in lettuce and spinach were studied at levels corresponding to background and Zn-Cd contaminated sites. Plants were grown in nutrient solutions containing 0.398-8.91 microM Zn and 0.010-0.316 microM Cd. Cadmium accumulated more in old than in young leaves of both crops at any solution Cd level, whereas Zn followed that pattern only at Zn levels > or = 3.16 microM. Increasing solution Cd increased Zn concentrations in young leaves of lettuce but not of spinach, regardless of Zn levels. Cadmium concentrations in young leaves of both crops decreased exponentially with increasing solution Zn at low (0.0316 microM) but not at high (0.316 microM) solution Cd. The Zn: Cd concentration ratios in young leaves of lettuce and spinach grown at 0.316 microM Cd became greater as the solution Zn increased. Cadmium and Zn concentrations in young leaves were related more closely to the relative concentrations of Zn and Cd in solution than were the concentrations in old leaves, especially in lettuce. Studies of Zn-Cd interactions and Cd bioavailability should differentiate between basal and upper leaves of lettuce and spinach. Compared to Cd-only pollution, Zn-Cd combined pollution may not decrease Cd concentrations in lettuce and spinach edible tissues, but because it increases their Zn concentrations it lowers plant Cd bioavailability.     

Sensitivity of Mediterranean woody seedlings to copper, nickel and zinc

The restoration of heavy metal contaminated areas requires information on the response of native plant species to these contaminants. The sensitivity of most Mediterranean woody species to heavy metals has not been established, and little is known about phytotoxic thresholds and environmental risks. We have evaluated the response of four plant species commonly used in ecological restoration, Pinus halepensis, Pistacia lentiscus, Juniperus oxycedrus, and Rhamnus alaternus, grown in nutrient solutions containing a range of copper, nickel and zinc concentrations. Seedlings of these species were exposed to 0.048, 1 and 4 microM of Cu; 0, 25 and 50 microM of Ni; and 0.073, 25 and 100 microM of Zn in a hydroponic silica sand culture for 12 weeks. For all four species, the heavy metal concentration increased in plants as the solution concentration increased and was always higher in roots than in shoots. Pinus halepensis and P. lentiscus showed a higher capacity to accumulate metals in roots than J. oxycedrus and R. alaternus, while the allocation to shoots was considerably higher in the latter two. Intermediate heavy-metal doses enhanced biomass accumulation, whereas the highest doses resulted in reductions in biomass. Decreases in shoot biomass occurred at internal concentrations ranging from 25 to 128 microg g-1 of Zn, and 1.7 to 4.1 microg g( -1) of Cu. Nickel phytoxicity could not be established within the range of doses used. Rhamnus alaternus and J. oxycedrus showed higher sensitivity to Cu and Zn than P. halepensis and, especially, P. lentiscus. Contrasted responses to heavy metals must be taken into account when using Mediterranean woody species for the restoration of heavy metal contaminated sites.     

Arbuscular mycorrhizae enhance metal lead uptake and growth of host plants under a sand culture experiment

A sand culture experiment was conducted to investigate whether mycorrhizal colonization and mycorrhizal fungal vesicular numbers were influenced by metal lead, and whether mycorrhizae enhance host plants tolerance to metal lead. Metal lead was applied as Pb(NO3)2 in solution at three levels (0, 300 and 600 mg kg(-1) sand). Five mycorrhizal host plant species, Kummerowia striata (Thunb.) Schindl, Ixeris denticulate L., Lolium perenne L., Trifolium repens L. and Echinochloa crusgalli var. mitis were used to examine Pb-mycorrhizal interactions. The arbuscular mycorrhizal inoculum consisted of mixed spores of mycorrhizal fungal species directly isolated from orchard soil. Compared to the untreated control, both Pb concentrations reduced mycorrhizal colonization by 3.8-70.4%. Numbers of AM fungal vesicles increased by 13.2-51.5% in 300 mg Pb kg(-1) sand but decreased by 9.4-50.9% in 600 mg Pb kg(-1) sand. Mycorrhizae significantly enhanced Pb accumulation both in shoot by 10.2-85.5% and in root by 9.3-118.4%. Mycorrhizae also enhanced shoot biomass and shoot P concentration under both Pb concentrations. Root/shoot ratios of Pb concentration were higher in highly mycorrhizal plant species (K.striata, I. denticulate, and E. crusgalli var. mitis) than that in poorly mycorrhizal ones (L. perenne and T. repens,). Mycorrhizal inoculation increased the root/shoot ratio of Pb concentration of highly mycorrhizal plant species by 7.6-57.2% but did not affect the poorly mycorrhizal ones. In the treatments with 300 Pb mg kg(-1) sand, plant species with higher vesicular numbers tended to show higher root/shoot ratios of the Pb concentration. We suggest that under an elevated Pb condition, mycorrhizae could promote plant growth by increasing P uptake and mitigate Pb toxicity by sequestrating more Pb in roots.     

Effect of transpiration on Pb uptake by lettuce and on water soluble low molecular weight organic acids in rhizosphere

The effect of transpiration (high and low) on Pb uptake by leaf lettuce and on water soluble low molecular weight organic acids (LMWOAs) in rhizosphere has been studied. After two weeks of growth the plants were cultured in greenhouse for more four weeks and two days. Pb(NO(3))(2) solutions of different concentrations (100, 200, and 300 mg l(-1) of Pb) were then added to the quartz sand pots of different plants and studies were initiated. Blank experiments (without treating the quartz sand pots with Pb(NO(3))(2) solutions) were also run in parallel. No significant differences in the growth of the plants with the concentrations of added Pb(NO(3))(2) solutions were observed by both low and high transpirations at the end of the 0, 3rd, and 10th days of studies. The total evaporation of the volatiles during 10 days did not depend on the concentration of Pb(2+) but with high transpiration the rate of evaporation was significantly higher than with low transpiration. Uptake of Pb by shoots and roots of the plants was found to be proportional to the concentration of various Pb(NO(3))(2) solutions added and more accumulation was observed in roots than in shoots at the end of 3rd and 10th days. High transpiration created more Pb uptake than low transpiration did. One volatile acid, propionic acid and nine non-volatile acids, lactic, glycolic, oxalic, succinic, fumaric, oxalacetic, D-tartaric, trans-aconitic, and citric acids in rhizosphere quartz sands were identified and quantified by gas chromatography (GC) analysis. D-Tartaric and citric acids were major among the non-volatile acids. The amount of LMWOAs in rhizosphere quartz sands increased with the higher amount of Pb uptake and also with the duration of studies. The total quantities of the LMWOAs in the rhizosphere quartz sands were significantly higher under high transpiration with 300 mg l(-1) Pb solution addition at the end of 10th day. The present study shows prominent correlation between transpiration and uptake of heavy metal and interesting correlation between Pb contaminated level and quantity of water soluble LMWOAs in rhizosphere quartz sands. The latter thus deserves of further studies.     

Toxic effects of Pb2+ on growth of cowpea (Vigna unguiculata)

A concentration as low as 1 microM lead (Pb) is highly toxic to plants, but previous studies have typically related plant growth to the total amount of Pb added to a solution. In the present experiment, the relative fresh mass of cowpea (Vigna unguiculata) was reduced by 10% at a Pb2+ activity of 0.2 microM for the shoots and at a Pb2+ activity of 0.06 microM for the roots. The primary site of Pb2+ toxicity was the root, causing severe reductions in root growth, loss of apical dominance (shown by an increase in branching per unit root length), the formation of localized swellings behind the root tips (due to the initiation of lateral roots), and the bending of some root tips. In the root, Pb was found to accumulate primarily within the cell walls and intercellular spaces.     

Ca(2+) -dependent plant response to Pb(2+) is regulated by LCT1

Tobacco plants transformed with TaLCT1 were cultured on Knop's medium with modified calcium concentrations (0.01-3 mM) in the presence of Pb(2+), and in soil contaminated by lead. A 4-5 microM Pb(2+) administered in the presence of 1 mM Ca(2+) inhibited the root growth of transgenic plants to much lesser degree than of control plants, whereas in the presence of 3mM Ca(2+) no differences were found between the studied lines. The reduction of Pb(2+) toxicity in the presence of 1 mM Ca(2+) was not accompanied by a change in the lead tissue concentration. However, when Ca(2+) level in the medium was lowered to 0.01 mM, several fold higher root/shoot Pb ratio in transgenic plants was observed, twofold increase in the total amount of metal accumulated, and lower concentration of Pb in the xylem sap. Results suggest the involvement of TaLCT1 in the regulation of Ca-dependent Pb-detoxification, and under conditions of low calcium in lead uptake and distribution.     

A comparison of stable caesium uptake by six grass species of contrasting growth strategy

Six plant species in the family Gramineae were used to investigate the relationship between Cs uptake, nutrient regime and plant growth strategy sensu Grime (1979: Plant Growth Strategies and Vegetation Processes, John Wiley). The roots of 66 day old Elymus repens (L.) Gould., Bromus sterilis L., Agrostis stolonifera L., Anthoxanthum odoratum L., Festuca ovina L. and Nardus stricta L. plants grown in acid-washed sand at high and low nutrient levels were exposed to a 96 h pulse of stable Cs at 0.05 mM, 0.15 mM, 0.3 mM, 1.0 mM and 3.0 mM concentrations. Different nutrient regimes induced large differences in dry wt in E. repens, B. sterilis and A. stolonifera plants but only small differences in N. stricta and F. ovina plants. At high nutrient concentrations, A. stolonifera, A. odoratum, F. ovina and N. stricta shoots showed significantly greater increases in internal Cs concentration with rising external Cs concentrations than did E. repens and B. sterilis shoots. The relationship between increases in shoot and external Cs concentrations was statistically indistinguishable between species in plants grown at the low nutrient concentration. These patterns of Cs uptake ensured that with long-term high K concentrations the more competitive plants (E. repens and B. sterilis) accumulated higher concentrations of Cs from low external concentrations than did non-competitive plants or competitive plants grown at low nutrient levels. It is suggested that the relationship between plant growth strategy sensu Grime (1979) and Cs accumulation patterns may help to explain the different concentrations to which species accumulate radiocaesium from the soil.     

Nutrient status and plant growth effects of forest soils in the Basin of Mexico

The nutrient status of forest soils in the Mexico City Air Basin was evaluated by observing plant growth responses to fertilization with N, P or both nutrients combined. P deficiency was the most frequent condition for soil from two high pollution sites and N deficiency was greatest at a low N deposition site. Concentrations of Pb and Ni, and to a lesser extent Zn and Co, were higher at the high pollution sites. However, positive plant growth responses to P and sometimes to N, and results of wheat root elongation bioassays, suggest that heavy metal concentrations were not directly phytotoxic. Further studies are needed to determine if heavy metal toxicity to mycorrhizal symbionts of eucalyptus (Eucalyptus camaldulensis Dehnh.) from high pollution sites may explain the P deficiency and stunted growth. P deficiency is expected to limit the capacity for biotic N retention in N saturated forested watersheds in the Basin of Mexico dominated by Andisols.     

Influence of Lead on Atrazine Uptake by Rice (Oryza sativa L.) Seedlings from Nutrient Solution (7 pp)

Background Atrazine is a widely used herbicide, and its persistence in soil and water causes environmental concerns. In the past, plat uptake processes are mainly investigated for single contaminants. However, in many cases, contaminants co-exist in environmental matrix, such as soil, and plant uptake of one contaminant may be influenced by its co-existing ones.Methods The uptake of atrazine by rice seedlings (Oryza sativa L.) from nutrient solution through the roots was investigated in a solution culture, over an exposure period of 4 weeks. Atrazine accumulation in plant tissues was determined by gas chromatography, and lead was determined using atomic absorption spectrometry.Results and Discussion With different ratios of atrazine and Pb2+ concentrations in solution, the observed atrazine concentrations in shoots and roots varied significantly. In atrazine-Pb2+ mixture systems, the added Pb2+ either increased or decreased the concentrations or BCFs of atrazine in seedlings (relative to those without Pb2+), depending on the atrazine-Pb2+ ratio in nutrient solution. The enhanced atrazine uptake results presumably from atrazine-Pb2+ complex formation. The reduced atrazine uptake, which occurred mainly at high atrazine concentrations, is attributed to atrazine toxicity that inhibited seedling growth and transpiration. Conclusion The formation of atrazine-Pb2+ complex both in the solution and within plant tissues may affect the accumulation of both contaminants by rice plants.     

Reciprocal effects of platinum and lead on the water household of poplar cuttings

In order to study the accumulation rates and effects of platinum as influenced by lead, experiments were performed with poplar cuttings in a growth chamber. The heavy metals were added at a final concentration of 34.8 ppb each to nutrient solutions as PtCl₄ and Pb(NO₃)₂. The variants were 1) control; 2) permanent Pt treatment for 6 weeks; 3) pretreatment with Pt plus subsequent treatment with Pb (three weeks each), and 4) heavy metal application in inverse order to variant 3. The experiments revealed that platinum accumulates in the roots of poplar cuttings to a higher degree than lead. It is translocated from the roots to other plant parts to an extremely low degree. Lead is displaced from the roots by subsequent Pt treatment. Insoluble platinum was found to be associated especially on the cell walls of the rhizodermis and exodermis of the root tips. Accumulation of platinum in the roots leads to a gradual depletion of the plants’ water supply. The disturbance of the water household causes a reduction of the transpirational surface, lowered transpiration rates and enhanced root growth. All these alterations are induced as a means of coping water stress. From the results of this experiment, the conclusion can be drawn that, under the chosen experimental conditions, platinum manifests a higher toxicity than lead in plant roots because of its higher accumulation rates.     

Growth and metal accumulation in vetiver and two Sesbania species on lead/zinc mine tailings

The lead (Pb)/zinc (Zn) tailings contained high concentrations of heavy metals (total Pb, Zn, Cu and Cd concentrations 4164, 4377, 35 and 32 mg kg(-1), respectively), and low contents of major nutrient elements (N, P, and K) and organic matter. A field trial was conducted to compare growth performance, metal accumulation of Vetiver (Vetiveria zizanioides) and two legume species (Sesbania rostrata and Sesbania sesban) grown on the tailings amended with domestic refuse and/or fertilizer. It was revealed that domestic refuse alone and the combination of domestic refuse and artificial fertilizer significantly improved the survival rates and growth of V. zizanioides and two Sesbania species, especially the combination. However, artificial fertilizer alone did not improve both the survival rate and growth performance of the plants grown on tailings. Roots of these species accumulated similar levels of heavy metals, but the shoots of two Sesbania species accumulated higher (3-4 folds) concentrations of Pb, Zn, Cu and Cd than shoots of V. zizanioides. Most of the heavy metals in V. zizanioides were accumulated in roots, and the translocation of metals from roots to shoots was restricted. Intercropping of V. zizanioides and S. rostrata did not show any beneficial effect on individual plant species, in terms of height, biomass, survival rate, and metal accumulation, possibly due to the rather short experimental period of 5 months.     

Uptake and translocation of plutonium in two plant species using hydroponics

This study presents determinations of the uptake and translocation of Pu in Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) from Pu contaminated solution media. The initial activity levels of Pu were 18.50 and 37.00 Bq ml(-1), for Pu-nitrate [239Pu(NO3)4] and for Pu-citrate [239Pu(C6H5O7)+] in nutrient solution. Plutonium-diethylenetriaminepentaacetic acid (DTPA: [239Pu-C14H23O10N3] solution was prepared by adding 0, 5, 10, and 50 microg of DTPA ml(-1) with 239Pu(NO3)4 in nutrient solution. Concentration ratios (CR, Pu concentration in dry plant material/Pu concentration in nutrient solution) and transport indices (Tl, Pu content in the shoot/Pu content in the whole plant) were calculated to evaluate Pu uptake and translocation. All experiments were conducted in hydroponic solution in an environmental growth chamber. Plutonium concentration in the plant tissue was increased with increased Pu contamination. Plant tissue Pu concentration for Pu-nitrate and Pu-citrate application was not correlated and may be dependent on plant species. For plants receiving Pu-DTPA, the Pu concentration was increased in the shoots but decreased in the roots resulting in a negative correlation between the Pu concentrations in the plant shoots and roots. The Pu concentration in shoots of Indian mustard was increased for application rates up to 10 microg DTPA ml(-1) and up to 5 microg DTPA ml(-1) for sunflower. Similar trends were observed for the CR of plants compared to the Pu concentration in the shoots and roots, whereas the Tl was increased with increasing DTPA concentration. Plutonium in shoots of Indian mustard was up to 10 times higher than that in shoots of sunflower. The Pu concentration in the apparent free space (AFS) of plant root tissue of sunflower was more affected by concentration of DTPA than that of Indian mustard.     

Uptake and accumulation of cadmium, lead and zinc by Siam weed [Chromolaena odorata (L.) King & Robinson

The Siam weed, Chromolaena odorata (L.) King & Robinson, Family Asteraceae, was found to be a new Pb hyperaccumulator by means of field surveys on Pb soil and hydroponic studies. Plants from field collection accumulated 1377 and 4236mgkg(-1) Pb in their shoots and roots, respectively, and could tolerate soil Pb concentrations up to 100000 mgkg(-1) with a translocation factor of 7.62. Very low concentrations of Cd and Zn were found in plants collected from the field. Under nutrient solution culture condition, C. odorata from the contaminated site (CS) and from non-contaminated site (NCS) grew normally with all three metals (Pb, Cd, Zn) supplied. However, the relative growth rates of all treated plants decreased with increased metal concentrations. The percentage uptakes of Pb, Cd, and Zn by C. odorata increased with increasing metal concentrations. Pb concentration in shoots and roots reached its highest values (1772.3 and 60655.7mgkg(-1), respectively) at a Pb supply level of 10mgl(-1). While the maximum concentrations of Cd (0.5mgl(-1)) in shoots and roots of C. odorata were 102.3 and 1440.9mgkg(-1), and the highest concentrations of Zn (20mgl(-1)) were 1876.0 and 7011.8mgkg(-1), respectively. The bioaccumulation coefficients of Pb and Cd were greater than 1000. These results confirm that C. odorata is a hyperaccumulator which grows rapidly, has substantial biomass, wide distribution and has a potential for the phytoremediation of metal contaminated soils.     

Interactive effects of nitrogen and phosphorus loadings on nutrient removal from simulated wastewater using Schoenoplectus validus in wetland microcosms

The concentrations of nutrients (N and P) in the wastewater and loading rate to the constructed wetlands may influence the nutrient removal from the secondary-treated municipal wastewater using wetland plants. Three loading rates of N (low 5.7, medium 34.3 and high 103 mg N d(-1)) and two of P (low 3.4 and high 17.1 mg P d(-1)) were studied in simulated secondary-treated municipal wastewater using Schoenoplectus validus (Vahl) A. L?ve & D. L?ve in the vertical free surface-flow wetland microcosms. After 70-d growth, there were significant interactive effects of N and P on the total, above-ground and root biomass. The below-ground biomass (rhizome and root) was negatively affected by the high N treatment. The tissue concentrations of N increased with an increase in N additions and decreased with an increase in P applications, whereas the tissue concentrations of P increased with an increase in P additions and decreased with an increase in N applications at the low P treatment, but increased at the high P treatment. Significant interactive effects of N and P loadings were found for the removal efficiencies of NH(4) and P, but not that of NO(x). The plant uptake, substrate storage and other losses (e.g. denitrification and formation of organic film) had similar contribution to N removal when N loading was relatively low. The P storage by substrate was the main contribution to P removal when P loading was high, but plant uptake was the major factor responsible for P removal when P loading was low and N loading was high. The high nutrient availability and optimum ratio of N:P are required to stimulate growth of S. validus, resulting in preferential allocation of resources to the above-ground tissues and enhancing the nutrient removal efficiencies, but the high N concentration in wastewater may hamper the growth of S. validus in constructed wetlands.     

Copper and lead concentrations in salt marsh plants on the Suir Estuary,Ireland

Concentrations of Cu and Pb were determined in the roots and shoots of six salt marsh plant species, and in sediment taken from between the roots of the plants, sampled from the lower salt marsh zone at four sites along the Suir Estuary in autumn 1997. Cu was mainly accumulated in the roots of monocotyledonous and dicotyledonous species. Pb was mainly accumulated in the roots of monocotyledons, while dicotyledons tended to accumulate Pb in the shoots. In the case of Aster tripolium there was a clear differentiation in the partitioning of Pb within the plant, between low and high salinity sites. At the low salinity sites, Pb accumulated only in the roots while at the high salinity sites there was a marked translocation to the shoots. The increase in Pb concentrations in roots and shoots of A. tripolium was accompanied by a concomitant decrease in sediment concentrations of Pb. This inverse correlation between sediment and plant concentrations of Pb was also recorded for Spartina spp. and Schoenoplectus tabernaemontani but in the case of these species the roots contained higher concentrations of Pb regardless of salinity levels. These differences in accumulation of Cu and Pb in various salt marsh species, and the influence of salinity on the translocation of Pb in A. tripolium in particular, should be taken into account when using these plants for biomonitoring purposes.     

Accumulation of nutrients and heavy metals in Phragmites australis (Cav.) Trin. ex Steudel and Bolboschoenus maritimus (L.) Palla in a constructed wetland of the Venice lagoon watershed

A recently constructed wetland, located in the Venice lagoon watershed, was monitored to investigate growth dynamics, nutrient and heavy metal shoot accumulation of the two dominating macrophytes: Phragmites australis and Bolboschoenus maritimus. Investigations were conducted over a vegetative season at three locations with different distance to the inlet point to assess effects on vegetation. The distance from the inlet did not affect either shoot biomass or nutrients (N, P, K and Na) and heavy metals (Cr, Ni, Cu and Zn) shoot content. With the exception of Na, nutrient and heavy metal concentrations were higher in shoots of P. australis than in B. maritimus. Heavy metal concentration in the incoming water and in the soil was not correlated to the plant content of either species. Shoot heavy metal concentrations were similar to those reported in the current literature, but accumulation generally increased towards the end of the growing season.     

Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils

Soil washing is considered a useful technique for remediating metal-contaminated soils. This study examined the release edges of Cd, Zn, Ni, Cr, Cu or Pb in two contaminated rice soils from central Taiwan. The concentrations exceeding the trigger levels established by the regulatory agency of Taiwan were Cu, Zn, Ni and Cr for the Ho-Mei soil and Pb for the Nan-Tou soil. Successive extractions with HCl ranging from 0 to 0.2 M showed increased release of the heavy metals with declining pH, and the threshold pH value below which a sharp increase in the releases of the heavy metals was highest for Cd, Zn, and Ni (pH 4.6 to 4.9), intermediate for Pb and Cu (3.1 to 3.8) and lowest for Fe (2.1), Al (2.2) and Cr (1.7) for the soils. The low response slope of Ni and Cr particularly for the rice soils make soil washing with the acid up to the highest concentration used ineffective to reduce their concentrations to below trigger levels. Although soil washing with 0.1 M HCl was moderately effective in reducing Cu, Pb, Zn and Cd, which brought pH of the soils to 1.1+/-0.1 (S.D.), the concurrent release of large quantities of Fe and Al make this remediation technique undesirable for the rice soils containing high clay. Successive washings with 0.01 M HCl could be considered an alternative as the dissolution of Fe and Al was minimal, and between 46 to 64% of Cd, Zn, and Cu for the Ho-Mei soil and 45% of Pb in the Na-Tou soil were extracted after four successive extractions with this dilute acid solution. The efficacy of Cd extraction improved if CaCl2 was added to the acid solution. The correlation analysis revealed that Cr extracted was highly correlated (P < 0.001) with Fe extracted, whereas the Cu, Ni, Zn, Cd or Pb extracted was better correlated (P < 0.001) with Al than with Fe extracted. It is possible that the past seasonal soil flooding and drainage in the soils for rice production was conducive to incorporating Cr within the structure of Fe oxide, thereby making them extremely insoluble even in 0.2 M HCl solution. The formation of solid solution of Ni with Al oxide was also possible, making it far less extractable than Cd, Zn, Cu, or Pb with the acid concentrations used.     

Pteris umbrosa R. Br. as an arsenic hyperaccumulator: accumulation, partitioning and comparison with the established As hyperaccumulator Pteris vittata

The capacity of the Australian native fern Pteris umbrosa to function as an arsenic (As) hyperaccumulator (shoot:soil As concentration >1) was examined by growing plants under glasshouse conditions in an inert medium supplemented with As. Arsenic preferentially accumulated in the fronds, a trait of a hyperaccumulator. The As concentration of fronds decreased with age, being particularly high in the croziers and low in the senesced fronds. Below ground, rhizomes accumulated more As than adventitious roots. Uptake from a range of solution concentrations followed Michaelis Menten kinetics up to a soil solution As concentration of 400mgl(-1). The K(m) for As uptake by roots suggested the operation of a low-affinity carrier. The predicted Nernst membrane potential indicated that uptake was against the electrochemical gradient of As. At 600mgl(-1), the rate of As uptake increased and phytotoxic effects were indicated by a significant decline in biomass. Arsenic uptake and translocation in P. umbrosa and Pteris vittata were similar at low exposure to As. At higher exposure, As uptake and translocation by P. vittata increased more than in P. umbrosa. The growth rate of both ferns was similar, whereas the biomass distribution was not, with P. vittata having a much larger root mass. This suggests that As uptake by P. umbrosa roots was very efficient and may be improved by stimulating root growth to enhance its potential.     

Enhancement of lead uptake by alfalfa (Medicago sativa) using EDTA and a plant growth promoter

Phytoremediation is a novel cleanup technology for the removal of contaminants from polluted waters and soils. In phytoremediation, the plant uptake capability and the availability of the pollutant in the media are important. Here we show the results of a study on the combined effects of ethylenediaminetetraacetic acid (EDTA) and the phytohormone indole-3-acetic acid (IAA) on Pb uptake by Medicago sativa (alfalfa). Plants were grown in hydroponics media containing a nutrient solution amended with Pb at 0.2mM and different combinations of EDTA, and IAA. After 10d of treatment, the Pb content in plant tissues was quantified using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP/OES). The results showed that the combination of 100 microM IAA/0.2 mM EDTA increased the Pb accumulation in leaves by about 2800% and by about 600%, as compared to Pb content in leaves of plants exposed to Pb alone and those cultivated with Pb/EDTA, respectively. These results indicate that non-metal hyperaccumulator plants could increase their hyperaccumulating potential without genetic manipulation.     

Concentrations of two organic contaminants in precipitation, soils and plants in the Essex region of Southern Ontario

Recent research has indicated that the atmosphere is an important pathway by which pollutants enter terrestrial and aquatic ecosystems. We report here concentrations of PCBs and octachlorostyrene (OCS) in precipitation, soils and plants in Essex County, Ontario. The average PCB concentration in urban precipitation (23 ng litre(-1)) was lower than that previously reported for urban areas in the Great Lakes basin. Differences between sites and with varying wind directions were not significant. OCS concentrations in precipitation averaged 1.6 ng litre(-1). Concentrations of PCBs in soils were 2-3 orders of magnitude greater than in precipitation. Concentrations of these pollutants in city soils and plant roots were consistently higher than those from suburban and rural sites. Ratios of urban to suburban concentrations in soils and precipitation were approximately 5:1 for PCBs. However, concentrations of OCS were similar in urban and suburban samples of precipitation, soils and plant tissues. These comparisons suggest an urban source for PCBs, but not OCS. Concentrations of all contaminants in plant leaves, unlike those in precipitation, roots and soils, were relatively similar in urban and suburban areas. That similarity suggests that direct foliar uptake is not an important pathway for pollutant uptake in plants.