Zhenguo Shen

Chemical forms of Pb, Zn and Cu in the sediment profiles of the Pearl River Estuary.

The chemical forms of heavy metals (Pb, Zn and Cu) in sediment cores of the Pearl River Estuary were studied using a sequential chemical extraction method. The isotope ratios of 206Pb/207Pb in various chemical fractions were also measured to assess the potential Pb sources. Zinc and Cu were mainly associated with the residual fraction. The Fe-Mn oxide and organic/sulphide fractions were the next important phases for Zn and Cu, respectively. For Pb, different chemical partitioning patterns were found among different sediment cores. Most Pb was associated with the residual fraction in the sediments. In some sediment profiles, the major phase of Pb in the top layers was the Fe-Mn oxide fraction. The proportion of Pb in the Fe-Mn oxide fraction decreased significantly with increasing depth. Among the different depths, the 206Pb/207Pb isotope ratios in the residual fraction remained fairly stable, with a mean value of 1.202, which may represent the natural background value. The 206Pb/207Pb ratios in the exchangeable fraction were the lowest among the five fractions, particularly in top sediments, showing the anthropogenic inputs of heavy metals from recent rapid industrial development in the surrounding region. For the other three non-residual fractions, there was a similar trend of increasing 206Pb/207Pb ratios down the profile. Results from this study are useful in assessing both the chemical changes for heavy metals in marine sediments and the potential of heavy metal release into the water environment of an estuary area.

Effects of silicon on salinity tolerance of two barley cultivars

Abstract Added silicon (Si) could significantly enhance dry matter yields of both salt‐sensitive (Hordeum vulgare L. Kepin No. 7) and salt‐tolerant (Hordeum vulgare L. Jian 4) barley cultivars under salt‐stressed condition. The dry matter yield of Kepin No.7 grown in the solution containing high Si (1.0 mM Si/L) and high salt (120 mM NaCl/L) was 18.0% greater than that of the plants treated with 120 mM NaCl/L alone. The dry matter yield of Jian 4 treated with low Si (0.5 mM Si/L) and high salt (120 mM NaCl/L) was found to increase by 15.2% compared with that of plants treated with 120 mM NaCl/L only. Silicon added could increase net photosynthetic rate of two barley cultivars grown in the solution containing 120 mM NaCl/L. The electrolytic leakage percentage was significantly lower in the leaves of two barley cultivars treated with 120 mM NaCl/L and 1.0 mM Si/L than in the leaves treated with 120 mM NaCl/L alone, which indicated that added Si resulted in a reduction of membrane permeability of salt‐stress...

Bioaccumulation of heavy metals by the aquatic plants Potamogeton pectinatus L. and Potamogeton malaianus Miq. and their potential use for contamination indicators and in wastewater treatment.

The concentrations of heavy metals in the leaves of two aquatic plants Potamogeton pectinatus L. and Potamogeton malaianus Miq., and the corresponding water and sediment samples from the Donghe River in Jishou City of Hunan Province, China were studied to investigate metal contamination from the intensive industrial activities in the surrounding area. Results showed that the concentrations of heavy metals in the sediments, especially Cd, Mn and Pb, were much higher than the eco-toxic threshold values developed by the U. S. Environmental Protection Agency. Between the two plant species, P. pectinatus showed the higher capacity in metal accumulation. The highest concentrations of Cd, Pb, Cu, Zn and Mn were found in the leaves of P. pectinatus, reaching 596, 318, 62.4, 6590 and 16,000 mg kg(-1) (DW), respectively. Significantly positive relationships were observed among the concentrations of Zn, Cu and Mn in the leaves of both aquatic plants and those in water, indicating the potential use of the two plants for pollution monitoring of these metals. In addition, a laboratory experiment was conducted to investigate the ability of P. pectinatus and P. malaianus to remove heavy metals from contaminated river water. The average removal efficiencies by P. pectinatus and P. malaianus for Cd, Pb, Mn, Zn and Cu from the spiked Donghe River water were 92%, 79%, 86%, 67% and 70%, respectively. The results indicated that P. pectinatus and P. malaianus had high capabilities to remove heavy metals directly from the contaminated water. The potential use of these plants in wastewater treatment is worth further exploration.

Cadmium accumulation and distribution in populations of Phytolacca americana L. and the role of transpiration.

The concentrations of heavy metals in Phytolacca americana L. and corresponding soil samples from three contaminated sites and an uncontaminated site were studied. Hydroponic experiments were also conducted to investigate the Cd uptake ability and mechanism of P. americana. The field results showed that the average Cd concentration was 42 mg kg(-1) in P. americana leaves, with the highest concentration of 402 mg kg(-1) found at Datianwan. A significant relationship was observed between the concentrations of Cd in leaves and those of corresponding soils on a logarithmic scale. Under laboratory hydroponic conditions, the maximum Cd concentration in aerial tissues of P. americana was 637 mg kg(-1), under treatment with 100 microM Cd. The population from the uncontaminated site (Zijinshan) also had a remarkable ability to accumulate Cd in shoots to concentrations well in excess of 100 microM in the hydroponic experiment, similar to the population from contaminated site, suggesting that Cd accumulation is a constitutive trait of P. americana. In the presence of 100 microM Cd, the addition of polyethylene glycol decreased leaf transpiration, the shoot Cd concentration, and the shoot/root Cd concentration ratio. There was a significantly positive relationship between the shoot Cd concentration and the leaf transpiration of P. americana. A similar significant positive correlation was also obtained between the shoot/root Cd concentration and leaf transpiration. Moreover, pretreatment with 5 microM abscisic acid or 5 microM HgCl(2) significantly decreased the Cd concentration in P. americana shoots. These results suggest that transpiration has an important role in Cd accumulation in shoots of P. americana.

Chemical partitioning of heavy metal contaminants in sediments of the Pearl River Estuary.

Abstract Sequential extraction was used to study the operationally determined chemical forms of four heavy metals (Zn, Cu, Ni and Co) and their spatial distribution in the sediments of the Pearl River Estuary. It was found that the residual fraction was the most important phase for the four metals in these sediments. Among non-residual fractions, Zn, Ni and Co were mainly associated with the Fe–Mn oxide fraction while Cu was associated with the organic fraction. The Zn bound to the Fe–Mn oxide fraction had significant relationships with reducible Mn and reducible Fe concentrations (Fe–Mn oxides), suggesting that Fe–Mn oxides may be the main carriers of Zn from the fluvial environment to the marine body. There was a significant relationship between Cu bound to the organic fraction and sediment organic contents. The Zn bound to the Fe–Mn oxide fraction and Cu bound to the organic fraction showed general distinctive decrease from the west side to the east side of the estuary, and from upstream in the north to the sea in the south. This was in the same trend with the total Zn and Cu concentrations in these sediments. The results may reflect the anthropogenic inputs of heavy metals to the top sediments from recent rapid industrial development and urbanisation in the surrounding area.

Proteomic identification of small, copper-responsive proteins in germinating embryos of Oryza sativa

BACKGROUND AND AIMS Although copper (Cu) is an essential micronutrient for plants and algae, excess Cu is toxic to most plants and can cause a wide range of deleterious effects. To investigate the response of rice (Oryza sativa) to Cu stress, a proteomic approach was used to analyse Cu stress-induced changes in the expression of low molecular-weight proteins in germinating rice seed embryos. METHODS Rice seeds were germinated in the presence or absence of 200 microm Cu for 6 d, and embryos, including newly formed shoots and radicles, were isolated. After proteins were extracted from the germinating embryos and separated by two-dimensional PAGE, 16 proteins in the 6- to 25-kDa range were identified using MALDI-TOF mass spectrometry. KEY RESULTS AND CONCLUSIONS Thirteen of the proteins identified, including metallothionein-like protein, membrane-associated protein-like protein, putative wall-associated protein kinase, pathogenesis-related proteins and the putative small GTP-binding protein Rab2, were up-regulated by Cu stress. Three proteins, a putative small cytochrome P450 (CYP90D2), a putative thioredoxin and a putative GTPase, were down-regulated by Cu stress. As far as is known, this study provides the first proteomic evidence that metallothionein and CYP90D2 are Cu-responsive proteins in plants. These findings may lead to a better understanding of plant molecular responses to toxic metal exposure.

Cadmium-induced accumulation of hydrogen peroxide in the leaf apoplast of Phaseolus aureus and Vicia sativa and the roles of different antioxidant enzymes

The effects of cadmium (Cd) on the accumulation of hydrogen peroxide (H(2)O(2)) and superoxide anion (O(2)(-)) in leaves of Phaseolus aureus and Vicia sativa were investigated. Cadmium at 100 microM significantly increased the production of O(2)(-) and H(2)O(2), as well as the activities of plasma membrane-bound nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and the symplastic and apoplastic activities of superoxide dismutase and ascorbate peroxidase in the leaves of both species. Apoplastic guaiacol peroxidase activity was significantly induced in the leaves of both species, particularly in P. aureus exposed to 100 microM Cd. Experiments with diphenylene iodonium as an inhibitor of NADPH oxidase and NaN(3) as an inhibitor of peroxidase showed that the majority of Cd-induced reactive oxygen species production in the leaves of both species may involve plasma membrane-bound NADPH oxidase and apoplastic peroxidase. Compared to V. sativa, increases in Cd-induced production of O(2)(-) and H(2)O(2) and activities of NADPH oxidase and apoplastic peroxidase were more pronounced in P. aureus. In contrast, V. sativa had higher leaf symplastic superoxide dismutase and ascorbate peroxidase activities than P. aureus. The results indicated that V. sativa was more tolerant to Cd than P. aureus.

Vegetation Composition and Heavy Metal Uptake by Wild Plants at Three Contaminated Sites in Xiangxi Area, China

The plant species composition and their ability to accumulate heavy metals were investigated at three contaminated sites in Xiangxi area, Southern China. The concentrations of Cd, Pb, Zn, and Cu in more than 363 samples of 125 plant species were analyzed in the present study. The average concentrations of Cd, Pb, Zn, and Cu in the plants were 19, 81, 637, and 8 mg kg−1, respectively. The highest concentration of Cd in above-ground plant tissues was found to be 287 mg kg−1 in the leaves of Lobelia chinensis Lour, at the Datianwan site, followed by Solamim nigrum L. with 99 mg kg−1 Cd in the leaves. They might be potential Cd hyperaccumulators. At the three contaminated sites, some dominant and relative dominant species with high accumulation potential of metals, such as Kalimeris indice (L.) Sch.-Bip. and Solanum nigrum L., might be suitable for use in the phytoextraction of contaminated soils. The dominant and relative dominant species with low accumulation of metals and dense fibrous root systems, such as Imperata cylindrical (L.) Beauv. var. major C. E. and Miscanthus floridulus (Labill.) Warb., might be suitable for stabilizing such metal contaminated sites.

Response of Antioxidative Enzymes in Cucumber Chloroplasts to Cadmium Toxicity

Abstract Solution culture experiments were conducted to investigate the effects of cadmium (Cd) toxicity on growth of cucumber seedlings, chlorophyll content, and net photosynthetic rate in leaves, activities of antioxidant enzymes, and contents of glutathione (GSH) and ascorbic acid (ASA) in purified intact chloroplasts. Results showed that lengths of main root and hypocotyl, weights of shoot and root, the root/shoot ratio, chlorophyll content, and net photosynthetic rate decreased significantly with increasing Cd level from 0 to 100 µmol L−1 in nutrient solution. Levels of malondialdehyde (MDA), H2O2, and O2 ·− in chloroplasts increased with increasing Cd concentration in solution. In the antioxidant defense system of chloroplasts, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and the contents of GSH and ASA decreased with increasing Cd concentration in the nutrient solution. The results suggest that Cd interferes with the growth of cucumber seedlings by destroying chloroplast membrane integrity and decreasing chlorophyll content and net photosynthetic rate in leaves.

Metal leaching along soil profiles after the EDDS application – A field study

One concern about the chelant-enhanced phytoextraction is the potential metal leaching associated with chelant application. A field study was carried out and the metal leaching along the 60-cm depth soil profiles were evaluated within 36 days after the biodegradable chelant EDDS was applied. Results showed EDDS significantly increased soluble Cu in the top 5 cm soil layer 1 day after the application, and the increase of soluble metals was generally limited in the top 20 cm soil. Metal speciation analysis indicated all Cu and Zn were in forms of Cu-EDDS and Zn-EDDS complexes in soil solution, and Ca was the major competitor with trace metals to EDDS. The soluble metals decreased quickly with time, and no significant difference was observed in the extractable Cu between EDDS treatments and the controls 22 days after the EDDS addition. The potential leaching associated with biodegradable EDDS addition may be controlled under field conditions.