Responses of non-protein thiols to Cd exposure in Cd hyperaccumulator Arabis paniculata Franch

We investigated the responses of phytochelatins (PCs), glutathione (GSH) and other non-protein thiols in Cd hyperaccumulator Arabis paniculata after Cd exposure. Applying γ-glutamylcysteine synthetase (γ-ECS) inhibitor, l-buthionine-sulfoximine (BSO), the roles of PCs in Cd tolerance and Cd accumulation in A. paniculata were evaluated. Plants were exposed to four Cd concentrations (0, 50, 100 and 250 μM) for different times (2w or 3w) with and without BSO. Overall, Cd exposure had little impact on plant biomass after 2w or 3w of growth except at the highest Cd level. A. paniculata tolerated ≤100 μM Cd with up to 1127 mg kg^?1 Cd in the shoots and 5624 mg kg^?1 Cd in the roots after 3w of Cd exposure. Cd exposure induced formation of PCs and three unknown thiols in the roots, but none were detected in the shoots. BSO had no significant effect on Cd sensitivity in plants though it reduced Cd accumulation in the roots. In addition, the molar ratio of PCs:Cd, which ranged from 0.7 to 1.3 after exposing to 50–100 μM Cd without BSO in the roots, was close to the value expected for PC-mediated Cd sequestration in plants. Those data indicate that GSH and PCs did not contribute to Cd tolerance in the shoots and Cd transport from the root to shoot in A. paniculata, but they may play an important role in Cd accumulation and Cd complexation in the roots of A. paniculata.     

Response of native grasses and Cicer arietinum to soil polluted with mining wastes: Implications for the management of land adjacent to mine sites

Mine tailings are an environmental problem in Southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew two grasses, Lygeum spartum and Piptatherum miliaceum, and the crop species Cicer arietinum (chickpea) under controlled conditions in pots containing a mine tailings mixed into non-polluted soil to give treatments of 0%, 25%, 50%, 75% and 100% mine tailings. We tested a neutral (pH 7.4) mine tailings which contained high concentrations of Cd, Cu, Pb and Zn. Water-extractable metal concentrations increased in proportion to the amount of tailings added. The biomass of the two grasses decreased in proportion to the rate of neutral mine-tailing addition, while the biomass of C. arietinum only decreased in relation to the control treatment. Neutron radiography revealed that root development of C. arietinum was perturbed in soil amended with the neutral tailings compared to those of the control treatment, despite a lack of toxicity symptoms in the shoots. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoots. The highest concentrations occurred in the roots of P. miliaceum (2500 mg kg^?1 Pb, 146 mg kg^?1 Cd, 185 mg kg^?1 Cu, 2700 mg kg^?1 Zn). C. arietinum seeds had normal concentrations of Zn (70–90 mg kg^?1) and Cu (6–9 mg kg^?1). However, the Cd concentration in this species was ～1 mg kg^?1 in the seeds and 14.5 mg kg^?1 in shoots. Consumption of these plant species by cattle and wild fauna may present a risk of toxic metals entering the food chain.     

Tolerance,accumulation and distribution of zinc and cadmium in hyperaccumulator Potentilla griffithii

In this study, zinc (Zn) and cadmium (Cd) tolerance, accumulation and distribution was conducted in Potentilla griffithii H., which has been identified as a new Zn hyperaccumulator found in China. Plants were grown hydroponically with different levels of Zn²⁺ (20, 40, 80 and 160 mg L^?1) and Cd²⁺ (5, 10, 20 and 40 mg L^?1) for 60 days. All plants grew healthy and attained more biomass than the control, except 40 mg L^?1 Cd treatment. Zn or Cd concentration in plants increased steadily with the increasing addition of Zn or Cd in solution. The maximum metal concentrations in roots, petioles and leaves were 14,060, 19,600 and 11,400 mg kg^?1 Zn dry weight (DW) at 160 mg L^?1 Zn treatment, and 9098, 3077 and 852 mg kg^?1 Cd DW at 40 mg L^?1 Cd treatment, respectively. These results suggest that P. griffithii has a high ability to tolerate and accumulate Cd and Zn, and it can be considered not only as Zn but also as a potential cadmium hyperaccumulator. Light microscope (LM) with histochemical method, scanning electron microscope combined with energy dispersive spectrometry (SEM-EDS) and transmission electron microscope (TEM) were used to determine the distribution of Zn and Cd in P. griffithii at tissue and cellular levels. In roots, SEM-EDS confirmed that the highest Zn concentration was found in xylem parenchyma cells and epidermal cells, while for Cd, a gradient was observed with the highest Cd concentration in rhizodermal and cortex cells, followed by central cylinder. LM results showed that Zn and Cd distributed mainly along the walls of epidermis, cortex, endodermis and some xylem parenchyma. In leaves, Zn and Cd shared the similar distribution pattern, and both were mostly accumulated in epidermis and bundle sheath. However, in leaves of 40 mg L^?1 Cd treatment, which caused the phytotoxicity, Cd was also found in the mesophyll cells. The major storage site for Zn and Cd in leaves of P. griffithii was vacuoles, to a lesser extent cell wall or cytosol. The present study demonstrates that the predominant sequestration of Zn and Cd in cell walls of roots and in vacuoles of epidermis and bundle sheath of leaves may play a major role in strong tolerance and hyperaccumulation of Zn and Cd in P. griffithii.     

Cadmium tolerance in Thlaspi caerulescens: I. Growth parameters,metal accumulation and phytochelatin synthesis in response to cadmium

A population of the metallophyte, Thlaspi caerulescens, originating from a Cd–Pb–Zn old mining and smelter site at Plombières (Belgium) was studied. T. caerulescens was cultivated hydroponically to investigate Cd uptake and tolerance. Cd was added to Hoagland’s medium at concentration range from 5 to 500 μM. The plants could tolerate 500 μM Cd in the solution showing only minor visible symptoms of toxicity but with a 32% decrease in fresh weight. After 14 days at 500 μM, Cd content in roots and shoots was 707 and 602 mg kg⁻¹ of dry weight (d.w.), respectively. Application of Cd to hydroponically cultivated T. caerulescens induced the accumulation of PCs in plant roots and shoots. Buthionine sulfoximine (BSO) application almost completely reduced (by 98–100%) the accumulation of PCs without simultaneous increase in plants sensitivity to Cd. These results suggest a minor if any role of PCs in tolerance to Cd of the studied population of T. caerulescens in hydroponics. On the other hand, no PC accumulation was detected either in T. caerulescens plants growing in their natural environment at Plombierès or in plants growing in their native soil in a greenhouse. These results suggest that naturally selected tolerance in T. caerulescens population from Plombières is not associated with enhanced PCs synthesis.     

Brachythecium rutabulum and Betula pendula as bioindicators of heavy metal pollution around a chlor-alkali plant in Poland

Chlor-alkali plants are known to be major sources of Hg emissions into the air. Therefore level of this metal in their surrounding must be carefully controlled. The aim of this work was to study the impact of the chlor-alkali industry in Brzeg Dolny (SW Poland) on the length of the vegetative short shoots of the pollution tolerant Betula pendula using the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in the ubiquitous, terrestrial moss Brachythecium rutabulum as the pollution indicator of the environment. This investigation showed up to 14 mg kg⁻¹ elevated concentrations of Hg in mosses from sites the most close (0–500 m) to the chlor-alkali factory. This concentration decreased with increasing distance from the factory. Two and half km away from the factory the Hg concentration falls to values of 0.1–0.2 mg kg⁻¹ being still higher than background concentrations of 0.03–0.04 mg kg⁻¹. Decreasing concentrations of Co, Cr, Fe and Ni were also correlated with increasing distance from the plant. The results indicate that B. rutabulum may be a suitable ecological indicator of metal pollution by chlor-alkali industry. Higher concentration of accumulated metals by this moss corresponds with longer vegetative short shoots of B. pendula. Vegetative short shoots may be used as bioindicators of metal pollution where mosses are absent. This study demonstrates the importance of controlling the emissions of chlor-alkali industry especially if situated in the midst of densely populated areas with potential risks to the inhabitants.     

Bioavailability and extraction of heavy metals from contaminated soil by Atriplex halimus

Pot experiments were performed to evaluate the phytoremediation capacity of plants of Atriplex halimus grown in contaminated mine soils and to investigate the effects of organic amendments on the metal bioavailability and uptake of these metals by plants. Soil samples collected from abandoned mine sites north of Madrid (Spain) were mixed with 0, 30 and 60 Mg ha⁻¹ of two organic amendments, with different pH and nutrients content: pine-bark compost and horse- and sheep-manure compost. The increasing soil organic matter content and pH by the application of manure amendment reduced metal bioavailability in soil stabilising them. The proportion of Cu in the most bioavailable fractions (sum of the water-soluble, exchangeable, acid-soluble and Fe–Mn oxides fractions) decreased with the addition of 60 Mg ha⁻¹ of manure from 62% to 52% in one of the soils studied and from 50% to 30% in the other. This amendment also reduced Zn proportion in water-soluble and exchangeable fractions from 17% to 13% in one of the soils. Manure decreased metal concentrations in shoots of A. halimus, from 97 to 35 mg kg⁻¹ of Cu, from 211 to 98 mg kg⁻¹ of Zn and from 1.4 to 0.6 mg kg⁻¹ of Cd. In these treatments there was a higher plant growth due to the lower metal toxicity and the improvement of nutrients content in soil. This higher growth resulted in a higher total metal accumulation in plant biomass and therefore in a greater amount of metals removed from soil, so manure could be useful for phytoextraction purposes. This amendment increased metal accumulation in shoots from 37 to 138 mg pot⁻¹ of Cu, from 299 to 445 mg pot⁻¹ of Zn and from 1.8 to 3.7 mg pot⁻¹ of Cd. Pine bark amendment did not significantly alter metal availability and its uptake by plants. Plants of A. halimus managed to reduce total Zn concentration in one of the soils from 146 to 130 mg kg⁻¹, but its phytoextraction capacity was insufficient to remediate contaminated soils in the short-to-medium term. However, A. halimus could be, in combination with manure amendment, appropriate for the phytostabilization of metals in mine soils.     

Accumulation of zinc and cadmium and localization of zinc in Picris divaricata Vant.

Picris divaricata Vant., a plant species native to subtropical China, was recently identified as the first Cd/Zn hyperaccumulator from Asteraceae. P. divaricata was grown from wild collected seed for 4 months in a series of pH adjusted test soils with added Zn levels 0–7000 mg kg⁻¹ and Cd levels 0–150 mg kg⁻¹. Plants did not hyperaccumulate Zn (threshold >3000 μg g⁻¹) and weakly hyperaccumulated Cd with little or no dose–response.P. divaricata has multicellular simple trichomes concentrated on the leaf margins and midrib. X-ray analysis showed that Zn was concentrated in larger trichomes and epidermal cells adjacent to the trichome but virtually absent in other leaf tissues. Within the trichomes, Zn was localized in ovate spots around the tips of individual cells. These tips and other locations in the trichome cell contained black electron dense material when examined with transmission electron microscopy, some of which was identified as SiO₂. Silicon and Mn were concentrated in the same areas as Zn. Si has been previously associated with alleviating Zn, Mn and Cd toxicity. Our results support this observation and further investigation is warranted.Calcium and P were concentrated in the distal tips of trichomes, similar to patterns previously observed for calcicole plants grown in elevated Ca soils. Overall, nonsecretory trichomes from many plant families may have a common origin as tissues adapted to handle a variety of environmental metals.     

Changes in proline accumulation and antioxidative enzyme activities in Groenlandia densa under cadmium stress

In this study an experiment was carried out to study the process of stress adaptation in Groenlandia densa (opposite-leaved pondweed) grown under cadmium stress (0–20 mg L^?1 Cd). The results showed that Cd concentrations in plants increased with increasing Cd supply levels and reached a maximum of 0.43 mg kg^?1 DW at 0.5 mg L^?1 Cd concentrations. The level of photosynthetic pigments and soluble proteins decreased only upon exposure to high Cd concentrations. At the same time, the level of malondialdehyde (MDA) increased with increasing Cd concentration. These results suggested an alleviation of stress that was presumably the result of by antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione S-transferase (GST) as well as ascorbate peroxidase (APX), which increased linearly with increasing Cd levels. Cellular antioxidants levels showed a decline suggesting a defensive mechanism to protect against oxidative stress caused by Cd. In addition, the proline content in G. densa increased with increasing cadmium levels. These findings suggest that G. densa is equipped with an efficient antioxidant mechanism against Cd-induced oxidative stress which protects the plant's photosynthetic machinery from damage.Our present work concluded that G. densa has a high level of Cd tolerance and accumulation. We also found that moderate Cd treatment (0.05–5 mg L^?1 Cd) alleviated oxidative stress in plants, while the addition of higher amounts of Cd (10–20 mg L^?1) could cause an increasing generation of ROS, which was effectively scavenged by the antioxidative system.     

The phytoremediation potential for strontium of indigenous plants growing in a mining area

This study investigated the distribution and accumulation of strontium (Sr) in the shoots and roots of Euphorbia macroclada (EU), Verbascum cheiranthifolium (VR), and Astragalus gummifer (AS), with respect to their potential use in phytoremediation. Plant samples and their associated soils were collected from the arid and semi-arid Keban mining area and were analyzed inductively by ICP-MS for Sr. Mean Sr values in the shoots, roots and soil were, respectively, 453, 243 and 398 mg kg^?1 for E. macroclada; 149, 106 and 398 mg kg^?1 for V. cheiranthifolium; and 278, 223 and 469 mg kg^?1 for A. gummifer. The enrichment factors for root (ECR) and shoot (ECS) of these plants were lower than 1 or close to 1, except for the shoot of E. macroclada. The mean translocation factors (TLF) of these plants were higher than 1 and 2.08 for E. macroclada, 1.47 for V. cheiranthifolium, 1.18 for A. gummifer. It thus appeared that the shoots of these plants can be an efficient bioaccumulator plant for Sr and it can be used in cleaning or rehabilitating of the contaminated soil and areas by Sr because of their high translocation factors.     

Physiological mechanism of hypertolerance of cadmium in Kentucky bluegrass and tall fescue: Chemical forms and tissue distribution

Kentucky bluegrass (Poa pratensis) and tall fescue (Festuca arundinacea) are hypertolerant grasses to soil cadmium contamination. Little information is available on their tolerance mechanism. A sand culture and a hydroponic culture experiment were designed to investigate the Cd chemical form changes and its translocation in different tissues. The results showed that Kentucky bluegrass and tall fescue can tolerate 50–200 mg kg⁻¹ of soil Cd stresses and accumulate as high as 4275 and 2559 mg Cd kg⁻¹ DW, respectively, in their shoots without the loss of shoot biomass. Their Cd hypertolerance was correlated with an increase of the undissolved Cd phosphates in the leaves in both grass species, as determined by sequential solvent extraction procedures. The superior Cd tolerance of tall fescue to Kentucky bluegrass was associated with less Cd translocation into the stele of roots and less Cd transported to leaves. The pectate- and protein-integrated Cd forms may be involved in the symplastic translocation of Cd from cortex into stele, and this may lead the higher Cd concentrations in the stele of roots and then above ground leaves via long-distance transport in Kentucky bluegrass.     

Influence of environmental related concentrations of heavy metals on motility parameters and antioxidant responses in sturgeon sperm

The effects of heavy metals (Cd, Cr and Cd + Cr) on the motility parameters and oxidative stress of sterlet (Acipenser ruthenus) sperm were investigated in vitro. Sturgeon sperm were exposed for 2 h to heavy metals at environmental related concentrations (0.1 mg L^?1 Cr, 0.001 mg L^?1 Cd, 0.1 mg L^?1 Cr + 0.001 mg L^?1 Cd) and higher concentrations (5.0 mg L^?1 Cr, 0.05 mg L^?1 Cd, 5.0 mg L^?1 Cr + 0.05 mg L^?1 Cd). Results revealed that environmental concentrations of heavy metals had no significant influence on motility parameters and antioxidant responses indices in sturgeon sperm, except for LPO level and SOD activity. But higher concentrations of these metals induced oxidative tress in sturgeon sperm in vitro, associated with sperm motility parameters inhibition. Our results suggest that using of sperm in vitro assays may provide a novel and efficiently means for evaluating the effects of residual heavy metals in aquatic environment on sturgeon.     

Recycling of agro-industrial sludge through vermitechnology

This work illustrates the feasibility of vermitechnology to stabilize sludge from an agro-industry. To achieve the goal, industrial sludge (IS) was mixed with three different bulky agents, i.e. cow dung (CD), biogas plant slurry (BGS) and wheat straw (WS), in different ratios to produce nine different feed mixtures for earthworm Eisenia fetida. Vermicomposting bedding material was analyzed for its different physic-chemical parameters after 15 weeks of experimentations. In all waste mixtures, a decrease in pH, organic C and C:N ratio, but increase in total N, available P, exchangeable K, exchangeable Ca and trace elements (Mg, Fe and Zn) was recorded. IS (40%) + CD (60%) and IS (40%) + BGS (60%) vermibeds showed the highest mineralization rate and earthworm growth patterns during vermicomposting process. Vermicompost contains (dry weight basis) a considerable range of plant available forms of P (17.5–28.9 g kg^?1), K (13.8–21.4 g kg^?1), Ca (41.1–63.4 g kg^?1), Mg (262.4–348.3 mg kg^?1), Fe (559.8–513.0 mg kg^?1) and Zn (363.1–253.6 mg kg^?1). Earthworm growth parameters, i.e. biomass gain, total cocoon production, individual growth rate (mg wt. worm^?1 day^?1), natality rate, total fecundity were optimum in bedding containing 20–40% industrial sludge. C:N ratio of worm-processed material was within the agronomic acceptable or favorable limit (<15–20). The results clearly suggested that vermitechnology can be a potential technology to convert industrial sludges into vermifertilizer for sustainable land restoration practices.     

Arsenic reduced scale-insect infestation on arsenic hyperaccumulator Pteris vittata L.

Arsenic hyperaccumulation by Pteris vittata L. (Chinese brake fern) may serve as a defense mechanism against herbivore attack. This study examined the effects of arsenic exposure (0, 5, 15 and 30 mg kg^?1) on scale insect (Saissetia neglecta) infestation of P. vittata. Scale insects were counted as a percentage fallen from the plant to the total number of insects after 1 week of As-treatment. The arsenic concentrations in the fronds ranged from 5.40 to 812 mg kg^?1. Greater arsenic concentrations resulted in higher percentage of fallen-scale insects (17.2–55.0%). Lower arsenic concentrations (≤5 mg kg^?1) showed significantly lower effect on the population compared to 15–30 mg kg^?1 (p < 0.05). Arsenic content in the fallen-scale insects was as high as 194 mg kg^?1, which indicated that arsenic has been ingested by the scale insects via plant sap. This study is consistent with the hypothesis that arsenic may help P. vittata defend against herbivore's attack.     

Biodegradation of Tapis blended crude oil in marine sediment by a consortium of symbiotic bacteria

Biodegradation rate and the high molecular weight hydrocarbons are among the important concerns for bioremediation of crude oil. Inoculation of a non-oil-degrading bacterium as supplementary bacteria increased oil biodegradation from 57.1% to 63.0% after 10 days of incubation. Both the oil-degrading bacteria and the non-oil-degrading bacteria were isolated from Malaysian marine environment. Based on the 16S rDNA sequences, the oil-degrading bacteria was identified as Pseudomonas pseudoalcaligenes (99% similarity) while the non-oil-degrading bacterium was Erythrobacter citreus (99% similarity). E. citreus does not grow on crude oil enriched medium under present experimental condition but it withstands 5000 mg kg^?1 Tapis blended crude oil in sediment. Under optimal condition, the oil-degrading bacterium; P. pseudoalcaligenes, alone utilized 583.3 ± 3.8 mg kg^?1 (57.1%) at the rate of 3.97 × 10^?10 mg kg^?1 cell^?1 day^?1 Tapis blended crude oil from 1000 mg kg^?1 oil-contaminated sediment. Inoculation of E. citreus as the supplementary bacteria to P. pseudoalcaligenes enhanced biodegradation. The bacterial consortium degraded 675.8 ± 18.5 mg kg^?1 (63.0%) Tapis blended crude oil from the 1000 mg kg^?1 oil-contaminated sediment. Biodegradation rate of the bacterial consortium increased significantly to 4.59 × 10^?10 mg kg^?1 cell^?1 day^?1 (p = 0.02). Improvement of the oil degradation by the bacterial consortium was due to the synergetic reaction among the bacterial inoculants. There are two implications: (1) E. citreus may have a role in removing self-growth-inhibiting compounds of P. pseudoalcaligens. (2) P. pseudoalcaligenes degraded Tapis blended crude oil while E. citreus competes for the partially degraded hydrocarbons by P. pseudoalcaligenes. P. pseudoalcaligenes forced to breakdown more hydrocarbons to sustain its metabolic requirement. The bacterial consortium degraded 78.7% of (C₁₂–C₃₄) total aliphatic hydrocarbons (TAHs) and 74.1% of the 16 USEPA prioritized polycyclic aromatic hydrocarbons.     

Trace amounts of nickel in belowground rhizomes of Vaccinium myrtillus L. decrease anthocyanin concentrations in aerial shoots without water stress

Nickel (Ni) may impair plant water balance through detrimental effects on the belowground level. Bilberry (Vaccinium myrtillus L.) plants were grown in a mesic heath forest-type soil and subjected to Ni sulphate (NiSO₄·6H₂O) concentrations of 0, 10, 50, 100 and 500 mg m⁻² during an entire growing season in northern Finland (65°N). Biomass of belowground rhizomes, and tissue water content (TWC) and anthocyanin concentrations of aerial shoots were determined from mature plants in order to study rhizospheric Ni stress, and its possible long-distance effects on aerial shoots. As the major proportion of biomass of bilberry is invested in belowground parts, it was hypothesised that Ni-induced rhizospheric disturbance causes water stress in aerial shoots and increases their anthocyanin concentrations for osmotic regulation. Uptake of Ni from the soil to the rhizome and aerial shoots was measured with X-ray fluorescence spectrometry. Ni concentrations in the soil and rhizome exhibited a dose–response relationship, but the concentrations in the rhizome were about 10-fold lower (<3 mg Ni kg⁻¹) than those in the soil (<30 mg Ni kg⁻¹). Translocation of Ni from the rhizome to aerial shoots did not occur, as Ni concentrations in shoots remained at 1 mg Ni kg⁻¹. Although Ni concentrations in the rhizome were below the threshold values of Ni toxicity (i.e. 10–50 mg Ni kg⁻¹), Ni decreased the rhizome biomass. Anthocyanins decreased in aerial shoots along with the Ni accumulation in the rhizome, while TWC was unaffected. The result suggests that anthocyanins are not involved in osmotic regulation under Ni stress, since anthocyanins in aerial shoots responded to the Ni concentrations in the rhizome despite the lack of water stress.     

The collembola Lobella sokamensis juvenile as a new soil quality indicator of heavy metal pollution

We propose Lobella sokamensis Deharveng and Weiner, 1984 juvenile as a new soil quality indicator to assess heavy metal polluted soils. L. sokamensis is a collembola commonly found with earthworms, and it plays a key role in decomposing dead earthworms. The soil quality assessment of cadmium (Cd), copper (Cu), antimony (Sb), and zinc (Zn) on the survival of L. sokamensis adults were performed in artificial soil. The LC50 values for L. sokamensis adults exposed to Cd, Cu, Sb and Zn for 5 days were calculated to be 4729, 4472, 4702, and 2521 mg kg⁻¹, respectively. L. sokamensis juveniles (10–12 days) were also exposed to Cd, Cu, Sb, and Zn, and 5 days-LC50 values for Cd, Cu, Sb, and Zn were 282, 229, 447, and 163 mg kg⁻¹, respectively. Both adult and juvenile survivals of L. sokamensis in metal spiked soil were inhibited. We found that the soil quality assessment using L. sokamensis juveniles were sensitive enough to evaluate soil pollution, compared to conventional Folsomia candida assay which is widely used. In addition, L. sokamensis has advantage for easy detection in soil due to the big and orange-colored body. The 5 days-soil quality assessment using L. sokamensis juveniles appears to be rapid protocols for the collembola assay. This is the first report on the collembola assay of heavy metal contaminated soils using the L. sokamensis as a soil indicator.     

Beef cattle pasture to wetland reconversion: Impact on soil organic carbon and phosphorus dynamics

There is a major need to understand the historical condition and chemical/biological functions of the ecosystems following a conversion of wetlands to agricultural functions. To better understand the dynamics of soil total organic carbon (TOC) and phosphorus (P) during beef cattle pastures to wetland reconversion, soil core samples were collected from the beef cattle pasture and from the natural wetland at Plant City, FL, during five summer seasons (2002–2007). The levels of TOC and soil P were significantly affected by changing land use and hydrology. Draining natural wetlands to grazed pastures resulted in very pronounced reduction of TOC from 180.1 to 5.4 g g^?1. Cumulative concentrations of total phosphorus (TP) in soils (1134 mg kg^?1) under drained condition are two to three times lower than those in soils (2752 mg kg^?1) under flooded condition over the periods of land use reconversion. There was a declining trend (r = 0.82**; p ≤ 0.01) in total soil P from natural wetland (763 mg kg^?1) to altered pastures (340 mg kg^?1), largely as organic-bound P (natural wetland, 48%; grazed pastures, 44%; altered pastures, 29%). These results are important in establishing baseline information on soil properties in pasture and wetland prior to restoring and reconverting pasture back to wetland conditions. The results further suggest that changes in soil properties due to changing land use and hydrologic conditions (drying and re-wetting) could be long lasting.     

Subcellular distribution and chemical forms of cadmium in Bechmeria nivea (L.) Gaud.

Bechmeria nivea (L.) Gaud. (Ramie) is a promising species for Cd phytoextraction with large biomass and fast growth rate. Nevertheless, little information is available on its tolerance mechanisms towards Cd. Determination of Cd distribution and chemical speciation in ramie is essential for understanding the mechanisms involved in Cd accumulation, transportation and detoxification. In the present study, ramie plants were grown in hydroponics with increasing Cd concentrations (0, 1, 3, 7 mg l^?1). The subcellular distribution and chemical forms of Cd in different tissues were determined after 20 days exposure to this metal. To assess the effect of Cd uptake on plant performance, nitrate reductase activity in leaves and root activity were analyzed during the entire experimental period. Increased Cd level in the medium caused a proportional increase in Cd uptake, and the highest Cd concentration occurred in roots, followed by stems and leaves. Subcellular fractionation of Cd-containing tissues indicated that about 48.2–61.9% of the element was localized in cell walls and 30.2–38.1% in soluble fraction, and the lowest in cellular organelles. Cd taken up by ramie rapidly equilibrated among different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 1 M NaCl and 2% HAC, and the least in residues in all test tissues. In roots, the subdominant amount of Cd was extracted by d-H₂O and 80% ethanol, followed by 0.6 M HCl. While in stems and leaves, the amount of 0.6 M HCl-extractable Cd was comparable with that extracted by 80% ethanol or d-H₂O. 1 mg l^?1 Cd stimulated nitrate reductase activity in leaves and root activity, while a concentration-dependent inhibitory effect was observed with increasing Cd concentration, particularly at 7 mg l^?1 Cd. It could be suggested that the protective mechanisms evolved by ramie play an important role in Cd detoxification at relatively low Cd concentrations (below 3 mg l^?1 Cd) but become restricted to maintain internal homeostasis with higher Cd stress.     

Toxic and essential elements in children's blood (<6 years) from Kinshasa,DRC (the Democratic Republic of Congo)

In this study we determined the concentration of 9 trace elements (As, Cd, Cu, Hg, Mn, Mo, Pb, Se and Zn) in whole blood of children (n = 100, 64 girls, 36 boys and median age: 36 months) using inductively coupled plasma mass spectrometry (ICP-MS). The proportion of children potentially deficient in essential elements or poisoned by toxic elements was evaluated. The aging effects on the concentration of these elements were also investigated. The median values were 3.17 μg/L (As), 0.15 μg/L (Cd), 1.1 mg/L (Cu), 2.1 μg/L (Hg), 10.4 μg/L (Mn), 17.7 μg/L (Mo), 8.7 μg/dL (Pb), 10.7 μg/L (Se) and 5.0 mg/L (Zn). The concentration of many elements (As, Cd, Hg, Mn, Pb and Zn) showed significant age variations but not sex influence. Regarding levels of the essential elements (Cu, Mn, Mo, Se and Zn), B-Cu, B-Mn, B-Se and B-Zn were in the normal range, whereas exceeded levels were observed for B-Mo. None of these children was deficient in essential elements. Except B-Cd, all toxic elements showed exceeded blood levels. The proportion of children potentially poisoned by toxic elements varies from 10% (n = 10) to 95% (n = 95) and depends on toxic element: 95% for As, 10% for Hg and 35% for Pb. The main health concerns emerging from this study are the high As, Hg and Pb exposures of the Kinshasan children requiring further documentation, corrective actions and the implementation of appropriate regulations.     

Long-term effects of exogenous silicon on cadmium translocation and toxicity in rice (Oryza sativa L.)

Most nutrient solution studies on the interactions between silicon (Si) and cadmium (Cd) are short term. Here we reported a long-term experiment in which rice (Oryza sativa L.) was cultured for 105 days and harvested at four different growth stages to measure biomass accumulation and Cd uptake and distribution in shoots and roots. Exogenous Si increased shoot biomass by 61–238% and root biomass by 48–173% when the culture solution was free of Cd. When 2 μmol L^?1 Cd was added, Si supply increased shoot and root biomass by 125–171% and by 100–106% compared to the zero-Si treatment. Increasing the Cd concentration to 4 μmol L^?1 decreased the beneficial effects of Si on root and shoot biomass. Silicon supply decreased shoot Cd concentrations by 30–50% and Cd distribution ratio in shoot by 25.3–46%, compared to the treatment without Si supply. Additionally, lower Si supply or more serious Cd stress would lead to roots with bigger biomass and higher Si concentration. Energy-dispersive X-ray microanalysis showed that both Si and Cd accumulated synchronously in the border and middle of phytoliths of the shoots. We conclude that Si enhances plant growth and decreases Cd accumulation in shoots and thereby helps to lower the potential risks of food contamination.