[Effects of Chelate GLDA on the Remediation of Cadmium Contaminated Farmland by Pennisetum purpureum Schum].

In order to clarify the effects of chelate tetrasodium glutamate diacetate (GLDA) on the remediation of cadmium (Cd) contaminated farmland by Pennisetum purpureum Schum, GLDA was applied in different methods within 60 days:total application doses of 585, 1170, and 2340 kg·hm-2 were equally divided into 1-4 applications, respectively, and the time intervals of 2-4 applications were 30, 20, and 15 days, respectively. The biomass, Cd content, and amount of Cd extracted from aboveground parts of Pennisetum purpureum Schum, in addition to the pH, dissolved organic carbon (DOC) mass concentration, and other indicators in soil were analyzed. The results showed that the biomass and Cd content of the aboveground parts of Pennisetum purpureum Schum increased significantly when GLDA was applied many times at a low application dose. The number of applications and the total dose were the key factors influencing the biomass and Cd content, respectively. The highest amount of Cd extracted was 16.78 g·hm-2 at 585 kg·hm-2 (applied four times), which was 275.39% higher than the CK treatment (i.e., no GLDA was applied). There was significant positive correlations between the pH, mass concentration of DOC, and content of DTPA-Cd, and the total dose and number of applications. The mass concentration of DOC was the main factor affecting the DTPA-Cd content. The total Cd content in the soil (after at 585 kg·hm-2 was applied four times) decreased by 3.23% compared with that of the soil before planting Pennisetum purpureum Schum. Therefore, the application of GLDA is of great significance for the remediation of Cd contaminated farmland by Pennisetum purpureum Schum, and the application method should be selected reasonably.

Cadmium and arsenic accumulation during the rice growth period under in situ remediation.

Rice (Oryza sativa L.) planted in cadmium (Cd)- and arsenic (As)-contaminated soil is considered the main source of dietary Cd and As intake for humans in Southeast Asia and thereby poses a threat to human health. Minimizing the transfer of these pollutants to rice grain is an urgent task for environmental researchers. The main objective of this study was to investigate the effects and the mechanisms of a combined amendment (hydroxyapatite + zeolite + biochar, HZB) on decreasing Cd and As accumulation in rice. In situ remediation and aqueous solution adsorption experiments were conducted. The results showed that after application of HZB, Cd and As concentrations of the exchangeable fraction and TCLP extraction in soil decreased with the growth of rice plants. Cd concentrations in rice tissues were decreased at the tillering, filling and maturing stages after in situ remediation, while As concentrations in rice tissues were decreased only at the maturing stage. When 8 kg·plot-1 (9000 kg ha-1) HZB was applied, concentrations of Cd and inorganic As in brown rice were decreased to 0.18 and 0.16 mg kg-1, respectively, lower than the levels permissible for grain in China, i.e., 0.2 mg kg-1. Application of HZB reduced Cd accumulation in rice tissues, and the suppression of Cd accumulation was significantly greater than that of As. Furthermore, HZB significantly increased rice grain yield. An aqueous solution adsorption experiment demonstrated that HZB could adsorb and covalently bind Cd and As (V) via -OH, -COOH, -Si-O-Si and CO32- groups to produce carboxylates, silicates and carbonates, thereby promoting in situ immobilization of Cd and As in soil solution.

[Effects of a Tribasic Amendment on Cadmium and Arsenic Accumulation and Translocation in Rice in a Field Experiment].

An in-situ paddy field experiment was carried out to study the influence of a tribasic amendment (QFJ, hydroxyapatite+zeolite+biochar) on Cd and As accumulation and translocation in rice grown in soil contaminated with cadmium and arsenic, with the concentrations of soil Cd and As being 3.58 mg·kg-1 and 124.79 mg·kg-1, respectively. The results showed that, after application of QFJ, the pH, CEC, and OM contents of the rice rhizosphere soil tended to increase. The exchangeable concentrations of Cd and As were reduced from 0.37 mg·kg-1 and 0.07 mg·kg-1 to 0.12 mg·kg-1 and 0.04 mg·kg-1, respectively. The concentrations of Cd and As in rice tissues decreased after in-situ restoration. When 9.00 t·hm-2 of QFJ was applied, the Cd concentration in brown rice was reduced from 0.46 to 0.18 mg·kg-1, and that of inorganic As was reduced from 0.25 to 0.16 mg·kg-1, both lower than 0.2 mg·kg-1, meeting the requirement set by the National Food Standards (GB 2762-2012). QFJ application decreased the Cd and As bioaccumulation capacity of the roots and decreased the rice plant's capacity of Cd translocation quantity from the underground parts to the aerial parts; at same time, the Cd transferring capacity of the roots and the As transferring capacity in straw and husk were also decreased.

Cadmium uptake, accumulation, and remobilization in iron plaque and rice tissues at different growth stages.

Rice consumption is considered the main source of human dietary Cd intake in Southeast Asia. This study aimed to investigate Cd uptake, accumulation, and remobilization in iron plaque and rice (Oryza sativa L. cv. 'Xiangwanxian 12') tissues at different growth stages. A pot experiment was performed in two Cd-contaminated paddy soils. Cd concentrations in iron plaque and rice tissues at five different growth stages (tillering, booting, milky, dough, and maturing) were measured. Cd concentrations in iron plaque and rice tissues (roots, stems, leaves, spikelet, husks, and brown rice) varied with growth stage. Cd accumulation in rice plants increased with extending growth in both soils, reaching 15.3 and 35.4µg/pot, respectively, at the maturing stage. The amounts of Cd in brown rice increased from the milky to maturing stages, with the greatest percentage uptake during the maturing stage. Cd amount in iron plaque significantly affected the uptake and accumulation of Cd in roots and aerial parts of rice plants. Accumulated Cd in leaves was remobilized and transported during the booting to maturing stages, and the contributions of Cd transportation from leaves to brown rice were 30.0% and 22.5% in the two soils, respectively. A large amount of Cd accumulated in brown rice during the maturing stage. The transportation of remobilized Cd from leaves was also important for the accumulation of Cd in brown rice.

[Correlations Between Different Extractable Cadmium Levels in Typical Soils and Cadmium Accumulation in Rice].

Pot experiments were used to study the correlations between different extractable cadmium levels in typical soil and cadmium accumulation in rice. To analyze the pH, Cd in soil solution(SSE-Cd), TCLP extractable Cd level(TCLP-Cd), and Cd accumulation in rice at different growth stages of rice, we conducted pot experiments which selected the reddish clayey soil(developed from quaternary red clay parent materials) and purple paddy field(developed from purple sandy shale parent materials), meanwhile added with exogenous Cd with the gradients of 0, 0.5, 1, 2, 5, 10 mg·kg-1. The results showed that, during the rice growth period, the content of SSE-Cd in reddish clayey soil was in the range of 0 and 2.5 µg·L-1, and the average content was 0.57 µg·L-1; TCLP-Cd was in the range of 0 and 0.25 µg·L-1 with the average content of 0.10 mg·kg-1;The content of SSE-Cd in purple paddy field was in the range of 0 and 1.6 µg·L-1 with the average content of 0.48 µg·L-1; TCLP-Cd was in the range of 0 and 0.2 mg·kg-1, and the average content was 0.07 mg·kg-1. It showed that the cadmium concentrations in soil solution and the TCLP extractable Cd levels were both significantly reduced in two types of soil with the extension of rice growth period, and the content in reddish clayey soil was higher than that in purple paddy. The TCLP extractable Cd level was significantly positively correlated with Cd concentration in soil solution. The total Cd accumulation in rice plants gradually increased with increasing exogenous Cd concentration. There were significant positive correlations between Cd concentration in soil solution and Cd concentration in rice, Cd concentration in soil extracted by TCLP method and Cd concentration in rice and total Cd accumulation in rice plant. The soil environmental capacities of the two different parent materials varied greatly,and the safety threshold of Cd in purple paddy field was 2.06 times of that of reddish clayey soil. There were significant differences in Cd uptake and accumulation in different soils, so different measures may be needed to control Cd pollution in different parent materials. TCLP extractable Cd was more relevant with total Cd accumulation in rice, and had more extraction amount. Therefore, the TCLP method can more accurately evaluate the biological availability of soil Cd.

[Provoking Effects of Exogenous Zn on Cadmium Accumulation in Rice].

Pot experiments were carried out to study the influences of different concentrations of exogenous Zn on accumulation of Cd in various rice organs of low Cd accumulation cultivar Xiang-Wanxian 12 (XWX12) and high Cd accumulation cultivar Wei-You 46 (WY 46) exposed to soil with medium and serious Cd pollution. The results showed that:In the soil with medium Cd pollution, Cd contents in various rice organs of two rice varieties were increased by exogenous Zn, and the Cd contents in brown rice of XWX12 and WY46 were increased by 125.0% -275.0% and 6.6% -91.2%, respectively, but still lower than 0.2 mg·kg-1. In the soil with serious Cd pollution, Cd accumulation in various rice organs were reduced by exogenous Zn. Cd contents in brown rice of XWX12 and WY46 were reduced by 16.6%-63.5%, and 15.6%-74.4%, respectively, and Cd contents in brown rice of WY 46 were gradually decreased with increasing exogenous Zn application, resulting in lower than 0.2 mg·kg-1 of Cd in brown rice. The correlations of Cd contents in brown rice and exchangeable contents of Cd and Zn in soil were different depending on the Cd pollution levels and the rice varieties. In the soil with medium Cd pollution, Cd content in brown rice of XWX12 was linearly positively related to exchangeable Zn content in soil, and Cd content in brown rice of WY46 was linearly positively related to exchangeable Cd or Zn contents in soil. In the soil with serious pollution, however, the correlation of Cd contents in brown rice of WY46 and the contents of exchangeable Cd or Zn in soil was linear negative correlation. Therefore, for improvement of the rice quality, under the condition that total Zn content in soil was lower than the pollution level, applying a certain amount of Zn to reduce Cd contents in brown rice was feasible in the soil with serious pollution.