[Effects of Exogenous Melatonin Treatment on the Growth and Antioxidant System of Rice Seedlings Under Antimony Stress].

To investigate the effect of exogenous application of melatonin (MT) on rice seedlings under antimony (Sb) stress, hydroponic experiments were carried out with rice seedlings (Huarun No.2). The fluorescent probe localization technology was used to locate the reactive oxygen species (ROS) in the root tips of rice seedlings, and the root viability, malondialdehyde (MDA) content, ROS (H2O2 and O2-·) content, antioxidant enzyme (SOD, POD, CAT, and APX) activities, and antioxidant (GSH, GSSG, AsA, and DHA) contents in the roots of rice seedlings were analyzed. The results showed that exogenous addition of MT could alleviate the adverse effects of Sb stress on the growth and increase the biomass of rice seedlings. Compared with the Sb treatment, the application of 100 µmol·L-1 MT increased rice root viability and total root length by 44.1% and 34.7% and reduced the content of MDA, H2O2, and O2-· by 30.0%, 32.7%, and 40.5%, respectively. Further, the MT treatment increased the activities of POD and CAT by 54.1% and 21.8%, respectively, and also regulated the AsA-GSH cycle. This research indicated that exogenous application of 100 µmol·L-1MT can promote the growth and antioxidant ability of rice seedlings and alleviate the damage of lipid peroxidation by Sb stress, thus improving the resistance of rice seedlings under Sb stress.

[Effects of Exogenous Jasmonic Acid on Arsenic Accumulation and Response to Stress in Roots of Rice Seedlings].

Arsenic (As) pollution has a toxic effect on crop growth, leading to reduced crop quality and yield. Therefore, it is urgent to explore safe and effective strategies to reduce its toxicity. In this experiment, hydroponics, fluorescent probe locating technology, differential centrifugation, and Fourier infrared spectroscopy (FTIR) analysis were used to research the effect of exogenous jasmonic acid (JA) on the accumulation and stress resistance of rice seedlings. The results showed that JA application reduced the As content in the roots and shoots of rice by 31.4% and 51.4%, respectively, and significantly reduced As content in the cell wall and soluble fractions of rice roots. JA changed the distribution ratio of As in the subcellular components. The distribution ratio of As in the cell wall increased by 16.4%, and the distribution ratio of soluble fractions decreased by 17.3%. JA enhanced the fixation of As by the cell wall and reduced the As content in the soluble fraction. Furthermore, JA increased the levels of SOD, CAT, GSH, and PEPC in root cells and reduced the contents of H2O2 and MDA, indicating that JA reduced lipid peroxidation damage, regulated carbon and nitrogen metabolism, and alleviated As toxicity. This research provides a new approach for the prevention and control of rice As pollution.

[Effect of Chelating Agents and Organic Acids on Remediation of Cadmium and Arsenic Complex Contaminated Soil Using Xanthium sibiricum].

In order to improve the phytoextraction efficiency of Xanthium sibiricum on farmland soil that had been contaminated by Cd and As, this study explored the effects of chelating agents and organic acids (EDTA, SAP, CA, and MA) on the extraction of Cd and As heavy metals using X. sibiricum. The results showed that the four different chelating agents and organic acids had little effect on the biomass of the roots, stems, and leaves of X. sibiricum. However, they had different effects on the concentrations and accumulation of Cd and As in various organs of X. sibiricum. Compared with the those in the CK treatment, EDTA, SAP, CA, and MA significantly increased the Cd concentrations in the leaves of X. sibiricum by 44.1%, 32.4%, 41.2%, and 38.2% and the As concentrations in the roots of X. sibiricum by 89.6%, 7.4%, 94.8%, and 61.5%, respectively. The four treatments (EDTA, SAP, CA, and MA) improved the total Cd accumulation of X. sibiricum, with increasing ranges, respectively, of 70.2%, 29.4%, 28.9%, and 33.1%, and the As accumulation increased by 67.0%, 19.6%, 81.9%, and 40.8%, respectively, compared with that of the CK treatment. The four chelating agents and organic acids had different effects on the Cd and As bioconcentration factor and transfer factor of various organs of X. sibiricum. Treatments with EDTA, SAP, CA, and MA resulted in a decrease of 32.7%-38.2% in soil Cd concentrations and a decrease of 14.6%-20.5% in soil As concentrations. These four chelating agents can be used for enhancing the efficiency of extraction Cd and As heavy metals by X. sibiricum.

[Isolation and Identification of the Plant Endophyte R-13 and Its Effect on Cadmium Accumulation in Solanum nigrum L.]

The combination of endophytes and hyperaccumulator plants can significantly improve the efficiency of heavy metal phytoremediation in contaminated soil. A plant endophyte named Herbaspirillum R-13 was isolated from rice roots in a cadmium (Cd) contaminated paddy field. This strain exhibited a strong tolerance to Cd2+ and could grow on a solid medium with a Cd2+ concentration of 300 mg·kg-1. The R-13 strain was able to produce siderophores and Indole acetic acid (IAA), through color reactions. In addition, Pikovskaya's and Ashby's solid medium tests showed that the R-13 strain had a lower capacity for dissolving phosphorus but a higher capacity for fixing nitrogen. In the pot experiment, high-throughput sequencing technology was used to track the colonization of the R-13 strain in Solanum nigrum L. roots. Three days after inoculation, the relative abundance of Herbaspirillum in the root of Solanum nigrum L. had increased by 201.88% compared to the blank control (CK) and after two inoculations, the relative abundance of Herbaspirillum in the root of Solanum nigrum L. had increased by 1182.44% compared to CK. The relative abundance of Herbaspirillum in the root of Solanum nigrum L. began to decrease significantly from 5 days after inoculation. Inoculation with 20 mL·pot-1 of R-13 fermentation broth resulted in no significant effects on the Cd content of roots, stems, leaves, or fruits of S. nigrum L. With 40 mL·pot-1 of fermentation broth, the Cd content of vegetative organs and fruits was significantly increased. When it reached 200 mL·pot-1, the Cd content of vegetative organs was the highest, with Cd concentrations in the roots, stems, leaves, and fruits increasing by 84.42%, 43.67%, 64.06%, and 20.29%, respectively. In conclusion, root inoculation with endophytic Herbaspirillum R-13 can significantly increase the relative content of Herbaspirillum in the root system and enhance Cd absorption of S. nigrum L. Therefore, this strain has excellent prospects for application in the phytoremediation of soil contaminated with Cd.

[Mechanism of S-allyl-L-cysteine Alleviating Cadmium Stress in Seedling Roots and Buds of Rice Seedlings].

Cd has toxic effects on rice seed germination and plant growth, which may eventually lead to decreased yield and excessive Cd content in rice grains. The potential mechanism of S-allyl-L-cysteine (SAC), a natural sulfur compound derived from garlic extract, in alleviating Cd2+ stress in young roots and buds of rice seedlings was studied by a seed germination experiment. "Zhong zao 35", one of the main rice varieties in Southern China, was selected as the test material. Firstly, the alleviating effect of SAC on Cd2+ stress in rice seedling roots and buds was studied. Following this, the physiological mechanism of Cd2+ stress alleviation by SAC was examined based on the expression of the Cd transporter coding gene using real-time fluorescent quantitative PCR. The results showed that when the Cd2+ stress concentration reached 50 µmol·L-1, the young roots and buds of rice seedlings were significantly inhibited, and when the SAC concentration reached 200 µmol·L-1, Cd2+ stress was significantly alleviated. Compared to a Cd2+ stress treatment group, the total root length, surface area, and volume of young roots was increased by 173.5%, 65.52%, and 37.04%, respectively; CAT and SOD activity in young roots and buds was increased by 212.42% and 110.76%, and 31.41% and 47.31%, respectively; MDA and GSH content was decreased by 43.09% and 34.12%, and 33.97% and 35.74%, respectively; and Cd content was decreased by 35.91% and 28.86%, respectively. The results of quantitative real-time PCR showed that the relative expression levels of OsNramp5 and OsHMA2 were significantly reduced by 33.38% and 34.99% compared with the Cd2+ stress group, respectively. However, the relative expression level of OsHMA3 was significantly increased by 33.96%. From the above experimental results, the main mechanism by which SAC reduces Cd2+ stress in the young roots and buds of rice is via the regulation of Cd transporter-encoding genes, reducing Cd2+ transport to young roots and buds, and increasing transport to vacuoles.

[Effects of Different Exogenous Plant Hormones on the Antioxidant System and Cd Absorption and Accumulation of Rice Seedlings Under Cd Stress].

In order to explore the effects of the exogenous addition of plant hormones on the antioxidant system and Cd absorption and accumulation of rice seedlings under Cd stress, the transportation and accumulation of Cd was reduced in plants to alleviate the stress of Cd on the rice. With the rice seedlings of Zhongjiazao 17 as the research object, a hydroponic experiment was carried out with three Cd concentration treatments (0, 5, and 25 µmol·L-1), and four exogenous plant hormone treatments:no plant hormones, 100 µmol·L-1 melatonin (MT), 0.2 µmol·L-1 2,4-epibrassinolide (EBL), and 0.2 µmol·L-1 jasmonic acid (JA), for a total of 12 treatments, each treatment repeated three times. The contents of Cd in the rice seedlings were analyzed, as well as the content of MDA, POD, CAT, and reduced GSH in the shoots and roots of the rice seedlings. The results indicated that under the stress of 5 µmol·L-1 and 25 µmol·L-1 Cd, the addition of MT, EBL, and JA significantly reduced the MDA content of the shoots by 11%-24%, and the roots and shoots were healthy. On the contrary, the addition of the three exogenous substances all caused an increase in the MDA content in the root system, but the effects of MT and EBL were obvious. Under the 5 µmol·L-1 Cd stress, compared with CK, the MDA contents increased by 45.5% and 20.0% respectively; under 25 µmol·L-1 Cd stress, they increased by 46.2% and 19.8%. The exogenous addition of plant hormones can significantly increase the activity of POD and CAT in the shoots and underground parts of the rice seedlings and reduce the contents of GSH and Cd. Under the 5 µmol·L-1 Cd stress, the Cd content in the shoots of rice plants decreased by 39.4%, 40.1%, and 51.6%, the roots were reduced by 38.9%, 40.2%, and 7.0%. Under the 25 µmol·L-1 Cd stress, the aboveground Cd content was reduced by 18.9%, 14.5%, and 35.6%, and the roots were reduced by 85.3%, 81.1%, and 56.5%. By exogenously adding low-concentration plant hormones MT, EBL, and JA, the stress of Cd on the rice can be alleviated, and the toxic effect of Cd on rice can be reduced.

[Effects of Exogenous Spermidine on Seed Germination and As Uptake and Accumulation of Rice Under As5+ Stress].

As pollution in farmland has a toxic effect on the growth of crops, which reduces their yield and quality. The effects of exogenous spermidine (Spd) on rice seed germination and seedling growth under As5+ stress were studied. The results showed that exogenous Spd could promote the germination of rice seeds under As5+ stress, improve the germination potential and germination rate of seeds, and promote the growth of seedling roots. The addition of Spd could increase the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) of rice seedlings and roots under As5+ stress, and reduce the content of malondialdehyde (MDA) in rice buds and roots. When As5+ concentration was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, MDA content in rice roots was decreased by 12.3% and 31.3% and CAT activity of rice shoots was increased by 105.1% and 101.4%, and CAT activity of rice roots was increased by 29.9% and 57.1%, respectively. The addition of Spd also affected the uptake and accumulation of As in rice. When the concentration of As5+ was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, the concentration of As in rice shoots decreased by 69.4% and 75.1%, and As concentration in rice roots decreased by 7.6% and 24.4%, respectively. Spd could therefore effectively alleviate the toxic effect of As5+ on rice.

[Effects of Foliar Spraying of 2,3-dimercaptosuccinic Acid on Cadmium Uptake, Transport, and Antioxidant System in Rice Seedlings].

Rice contaminated by Cd has aroused widespread public concern. It is of great importance to find effective ways to reduce Cd translocation from roots to shoots and alleviate Cd stress in rice to ensuring food quality and safety. In this study, 2,3-dimercaptosuccinic acid (DMSA) was sprayed onto the leaves of rice seedlings to evaluate the feasibility of DMSA reducing Cd translocation to rice shoots and alleviating Cd stress. Therefore, seedlings of Zhongzao 35, one of the main rice cultivars in southern China, were used to study the effects of different concentrations of DMSA on the uptake and transport of Cd in rice seedlings by hydroponics. The effects of DMSA on MDA and GSH content, and activities of antioxidant enzymes such as CAT and SOD in rice seedlings, were also investigated. The results showed that after four iterations of foliar application of DMSA at concentrations of 0.2, 0.4, and 1.0 mmol·L-1, the Cd concentration in the rice seedling shoots decreased significantly with increasing DMSA spraying concentration. Compared with the control, the Cd concentration in shoots decreased by 22.1%, 39.7%, and 43.5%, respectively, but had no significant effect on the root Cd concentration. There was no significant effect on the concentrations of K, Ca, Mg, Fe, Zn, or Mn in the shoot or root. The content of MDA and GSH in the shoots of rice seedlings decreased significantly after four spraying times of DMSA and the activity of CAT and SOD increased significantly, which shows that spraying DMSA alleviated the stress effect of Cd on rice seedlings. Foliar application of DMSA can significantly reduce the accumulation of Cd in rice shoots but has no significant effect on the content of six common mineral elements, and can effectively relieve the oxidative damage caused by Cd stress. DMSA has the potential to develop a foliar modulator for reducing rice grain Cd content.

[Effects of Rice Straw Addition on Methanogenic Archaea and Bacteria in Two Paddy Soils].

Rice straw (RS) returning has an important effect on CH4 emission in rice paddy soil. In the present study, two paddy soil types from Jiangxi (JX) and Guangdong (GD), respectively, with different amounts of added RS were incubated through microcosmic anaerobic incubation experiments to investigate the responses of methanogenic archaea and bacteria communities after relatively long-term incubation. The different amounts of added RS affected methanogenic archaea community structures in the JX soil to some extent but did not affect the GD soil. The mcrA gene copy number increased with an increase in RS amount in both soils. Under the same amount of RS, the copy number of this gene in the JX soil was greater than that in the GD soil. In addition, significant positive correlations were shown between the RS amount and the copy number of the mcrA gene, and the response of the copy number was more sensitive to the RS amount in the JX soil. Obvious differences in methanogenic archaea community structures were shown between two soils. Methanosarcinaceae, Methanocellaceae, Methanomicrobiaceae, Methanobacteriaceae, and unknown microorganism (494 bp) were detected in the JX soil, and Methanobacteriaceae, Methanosarcinaceae, and Methanocellaceae were observed in the GD soil. The bacterial communities exhibited obvious differences between the two soil types after 180 days of incubation. The bacterial diversity in the GD soil was higher than that in the JX soil, although the amounts of dominant bacteria in the JX soil, including Bacillus, Desulfovirgula, Thermosporothrix, Acidobacteria/Gp1, Acidobacteria/Gp3, and Ktedonobacter, were higher than those of the GD soil, including Longilinea, Acidobacteria/Gp6, Bellilinea, and Thermosporothrix. RS application promoted the growth of methanogenic archaea as important substrates. Moreover, different structures of methanogens and bacteria were shown between the two soil types after relatively long-term incubation.

[Alleviation Effects of Exogenous Melatonin on Ni Toxicity in Rice Seedings].

The alleviation effect of exogenous melatonin (MT) on Ni toxicity in rice seedings was investigated. The results showed that low concentration of Ni stress (10, 50 µmol·L-1) had little effect on the growth of root of rice seedings, while higher concentration of Ni stress (100-1000 µmol·L-1) significantly inhibited the growth of rice root. Compared with the control treatment, the addition of 100 and 1000 µmol·L-1 Ni would decrease the total length and surface area of root by 63.3%-98.0% and 56.9%-96.3%, respectively. The results showed that addition of exogenous melatonin had a positive effect on the growth of rice seedings under Ni stress. This kind of positive effect was even more obvious in the root of rice seedings. The total length of rice root decreased by 58.4%-83.8% at Ni concentration of 100 µmol·L-1, whereas it decreased by only 8.7%-29.1% when 100 µmol·L-1 Ni and 10 µmol·L-1 MT were added, compared with the control treatment. The addition of exogenous melatonin had significant alleviation effects on oxidative stress in rice seedings caused by Ni. Compared with the 100 µmol·L-1Ni treatment, addition of 10 µmol·L-1 exogenous MT could significantly decrease the production rate of O2-· by 43.2%-50.2% and the relative electrolytic leakage by 25.7%-31.6%, whereas increase the activities of CAT by 21.9%-33.7% and the soluble protein content by 82.6%-84.6%. The results suggested that application of exogenous melatonin could effectively alleviate the toxic effects of Ni on rice seedings.

[Effects of exogenous melatonin on accumulation and chemical form of Cd in rice]. / è¤ªé»‘ç´ å¯¹æ°´ç¨»é•‰ç§¯ç´¯åŠå ¶åŒ–å­¦ç»“åˆå½¢æ€çš„å½±å“.

Effects of exogenous melatonin on accumulation and chemical form of Cd in rice seedlings were investigated. The results showed that Cd stress significantly decreased the biomass of shoots and roots, and the chlorophyll content in rice leaves. The addition of exogenous melatonin could remarkably increase the biomass of rice and significantly decreased Cd content in the shoots and roots. At Cd concentration of 5 Μmol·L-1, addition of 20 Μmol·L-1 exogenous melatonin could decrease Cd content in rice shoots and roots by 48.4% and 16.9% respectively, compared with the control. When the concentration of exogenous melatonin rose to 100 Μmol·L-1, Cd content in rice shoots and roots decreased by 67.5% and 47.9% respectively. Furthermore, the addition of exogenous melatonin obviously decreased the Cd-translocation efficiency of rice seedlings. When the Cd concentration was 20 Μmol·L-1, addition of 20 and 100 Μmol·L-1 exogenous melatonin could decrease the Cd-translocation efficiency by 24.4% and 46.8% respectively. The chemical form of Cd in rice seedlings was analyzed by using sequential extraction. The results showed that exogenous melatonin addition increased the proportion of NaCl-extractable Cd, while decreased the proportion of ethanol-extractable Cd and water-extractable Cd in rice seedlings. It was suggested that the addition of exogenous melatonin could promote the transfer of Cd from strong to weak mobility form, thereby reducing the uptake and transport of Cd in rice seedlings.

[Effect of Boron-antimony Interaction on the Uptake and Accumulation of Antimony and Boron by Rice Seedling].

Effect of interactions between boron (B) and antimony on the uptake and accumulation by rice (Oryza sativa L.) seedling was investigated in solution culture. The results showed that Sb(III) and Sb(V) could inhibit rice growth and Sb(III) was more toxic than Sb(V). Concentrations of B in rice roots and shoots were significantly affected by the addition of Sb(III) and Sb(V). The addition of 30 µmol x L(-1) Sb(III) could significantly decrease B of rice shoots and roots by 57.6% and 75.6%, and 30 µmol x L(-1) Sb(V) could decrease B of rice roots by 16.0%, compared with the control treatment, when the B concentration was 0.5 mg x L(-1). Equally, adding B also significantly affected the concentrations of Sb in rice roots and shoots. The addition of 2.0 mg x L(-1) B could decrease the concentrations of Sb in rice roots and shoots,by 39.1% and 9.2%, respectively, compared with 0.5 mg x L(-1) B, when the Sb(III) concentration was 10 µmol x L(-1). Adding 2.0 mg x L(-1) B could decreasd Sb concentrations in rice roots by 13.9%, compared with 0.5 mg x L(-1) B, when the Sb(V) concentration was 10 µmol x L(-1). Furthermore, adding B had significant effect on bioaccumulation factor and distribution ratio of Sb in rice roots and shoots. The results of the study demonstrated that Sb pollution in farmland could be alleviated by adding B fertilizer, thus protecting human health from Sb pollution.

[Rare earth elements content in farmland soils and crops of the surrounding copper mining and smelting plant in Jiangxi province and evaluation of its ecological risk].

Rare earth elements content in farmland soils and crops of the surrounding copper mining and smelting plant in Jiangxi province was studied. The results showed that copper mining and smelting could increase the content of rare earth elements in soils and crops. Rare earth elements content in farmland soils of the surrounding Yinshan Lead Zinc Copper Mine and Guixi Smelting Plant varied from 112.42 to 397.02 mg x kg(-1) and 48.81 to 250.06 mg x kg(-1), and the average content was 254.84 mg x kg(-1) and 144.21 mg x kg(-1), respectively. The average contents of rare earth elements in soils in these two areas were 1.21 times and 0.68 times of the background value in Jiangxi province, 1.36 times and 0.77 times of the domestic background value, 3.59 times and 2.03 times of the control samples, respectively. Rare earth elements content in 10 crops of the surrounding Guixi Smelting Plant varied from 0.35 to 2.87 mg x kg(-1). The contents of rare earth elements in the leaves of crops were higher than those in stem and root. The contents of rare earth elements in Tomato, lettuce leaves and radish leaves were respectively 2.87 mg x kg(-1), 1.58 mg x kg(-1) and 0.80 mg x kg(-1), which were well above the hygienic standard limit of rare earth elements in vegetables and fruits (0.70 mg x kg(-1)). According to the health risk assessment method recommended by America Environmental Protection Bureau (USEPA), we found that the residents' lifelong average daily intake of rare earth elements was 17.72 mg x (kg x d)(-1), lower than the critical value of rare earth elements damage to human health. The results suggested that people must pay attention to the impact of rare earth elements on the surrounding environment when they mine and smelt copper ore in Jiangxi.

Interactive effects of different inorganic As and Se species on their uptake and translocation by rice (Oryza sativa L.) seedlings.

There is a lack of information on the interactive relationship of absorption and transformation between two inorganic arsenic (As) species and two inorganic selenium (Se) species in rice grown under hydroponic condition. Interactive effects of inorganic As (As(III)) and (As(V)) and Se (Se(IV)and Se(VI)) species on their uptake, accumulation, and translocation in rice (Oryza sativa L.) seedlings were investigated in hydroponic culture. The results clearly showed the interactive effects of inorganic As and Se on their uptake by rice. The presence of Se reduced the sum of As species in the rice shoots regardless of Se speciation. If Se is present as Se(IV), then is it is accompanied by a corresponding increase of the sum of As species, but if Se is present as Se(VI), then there is no change in the sum of As species in rice roots. These effects are observed regardless of initial As speciation. When the rice plants are exposed to Se(IV), the presence of As increases the sum of Se species in the roots, and decreases the sum of Se species in the corresponding shoots. This effect is more pronounced for As(III) than for As(V). There is no effect on Se during exposure to Se(VI). Co-existence of As also increased SeMet in rice roots.

[Effect of selenium on the uptake and translocation of manganese, iron, phosphorus and selenium in rice (Oryza sativa L.)].

A pot experiment was conducted to clarify the effect of selenium on the uptake and translocation of manganese (Mn), iron (Fe) , phosphorus (P) and selenium (Se) in rice ( Oryza sativa L.). The results showed that addition of Se led to the significant increase of Se concentration in iron plaque on the root surface, root, shoot, husk and brown rice, and significant decrease of Mn concentration in shoot, husk and brown rice. At the Se concentrations of 0.5 and 1.0 mg.kg-1 in soil, Mn concentrations in rice shoot decreased by 32. 2% and 35.0% respectively, in husk 22.0% and 42.6% , in brown rice 27.5% and 28.5% , compared with the Se-free treatment. There was no significant effect of Se on the P and Fe concentrations in every parts of rice, except for Fe concentrations in husk. The translocation of P and Fe from iron plaque, root, shoot and husk to brown rice was not significantly affected by Se addition, but Mn translocation from iron plaque and root to brown rice was significantly inhibited by Se addition. Addition of 1.0 mg.kg-1. Se resulted in the decrease of translocation factor from iron plaque and root to brown rice by 38.9% and 37.9%, respectively, compared with the control treatment. The distribution ratios of Mn, Fe, P and Se in iron plaque, root, shoot, husk and brown rice were also affected by Se addition. The results indicated that Mn uptake, accumulation and translocation in rice could be decreased by the addition of Se in soil, therefore, Se addition could reduce the Mn harm to human health through food chain.

The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings.

A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (C(pw)) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8-5.7 and 1.4-2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the C(pw) of Cd and Zn, increasing the C(pw) of As, and increasing the iron plaque blocking capacity for Cd and Pb.

[Soil contamination and assessment of heavy metals of Xiangjiang River Basin].

The contents of heavy metals (As, Cd, Cu, Zn, Ni and Pb) in soils from Xiangjiang River Basin, Hunan Province, China, were analyzed by toxicity characteristic leaching procedure (TCLP) and Nemrow method. Results showed that the total contents of As, Cd, Cu, Zn, Ni and Pb were 4.25-549.67, 0.13-76.84, 11.49-281.69, 7.75-7234.81, 5.50-56.65 and 8.60-2084.81 mg x kg(-1), respectively, and the available contents of As, Cd, Cu, Zn, Ni and Pb extracted by TCLP were 0.02-10.97, 0.06-28.41, 0.04-72.29, 0.59-1 152.32, 0.07-10. 65 and 0.17-1 165.58 mg x kg(-1). The contents of available heavy metals extracted by TCLP correlated with total contents of heavy metals. Moreover, the pollution index Nemrow method showed that 72 samples at safety level, alert level, light pollution level, medium pollution level and heavy pollution level ratios were 60.52%, 11.33%, 5.65%, 4.22% and 18.38% separately, illustrating that pollution of heavy metals in soil samples of Xiangjiang River Basin is serious.

Copper toxicity thresholds in Chinese soils based on substrate-induced nitrification assay.

Copper toxicity in 17 Chinese soils was screened using a substrate-induced nitrification assay to generate information for the development of a terrestrial biotic ligand model (tBLM). The leaching effect on the Cu toxicity thresholds was investigated. Both the total Cu-based median effective concentration (EC50) values (46.9-2726 mg/kg) and the solution Cu-based EC50 values (0.04-2.91 mg/L) in unleached soils varied substantially among the soils in the present study. For unleached soils, linear stepwise multiple regression analysis showed that total Ca and soil pH were the best predictors for total Cu-based EC50, while electrical conductivity (EC) and soil pH were the best predictors for solution Cu-based EC50. The variation in solution Cu-based EC50 was largely (R(2) = 0.75) explained by Mg but not Ca and H(+) concentration in soil solution at EC50, suggesting a protective effect of Mg(2+) against Cu toxicity in the test soils. Leaching impacted Cu toxicity differently among the soils and apparently reduced the variations of both the total Cu-based and the solution Cu-based EC50. The predictability of the Cu EC50 by empirical models was decreased after leaching. The leaching effect on Cu toxicity, indicated by a leaching factor, was not predicted by any soil properties. There is a need to investigate quantitatively the mechanisms for the leaching effect on Cu toxicity in soils.

Characterization of PAHs contamination in soils from metropolitan region of Northern China.

The present study characterized the distribution, sources as well as carcinogenic potency of PAHs in surface soil from metropolitan region of northern China. The total PAHs in topsoil ranged from 322.6 to 23244.7 microg kg(-1). The mean and median concentrations of 16 PAHs were 1040.8 and 626.7 microg kg(-1), respectively. Source analysis revealed that pyrogenic sources played a major role at the locations and pyrogenic PAHs were mainly from incomplete combustion of coal, biomass and petroleum. The calculated mean BaP-equivalent values for individual carcinogenic PAHs were 148.4 microg kg(-1).

[Adverse health effects of cadmium and related factors].

Cd is a very toxic chemical to animal and human beings. Cd contamination has been ubiquitous because of industry and the human activities. Cd not only affects adversely the growth, yield and quality of crops but also effects on the health of animal and human being. The damage of Cd on bone, kidney, liver, immune and procreation systems as well possible factors that influence Cd absorption, accumulation and damage in the body are summarized in this paper.