[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 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.

[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.

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.