Cd Concentration In Rice Grains Research Articles

Contrasting effects of alkaline amendments on the bioavailability and uptake of Cd in rice plants in a Cd-contaminated acid paddy soil.

Reducing cadmium (Cd) concentrations in rice grains is important for food safety, particularly in acid paddy fields in South China where the soils have been previously contaminated with Cd. A field experiment was conducted to evaluate the effects of four alkaline amendments, i.e., lime, compost, biochar, and carbide slag on soil bioavailability and uptake of Cd in plants of two rice cultivars (Oryza sativa L.) in a Cd-contaminated acid paddy soil. The addition of these amendments significantly decreased the concentrations of CaCl2-extractable Cd by 13-41%. Cd in the acid-soluble fraction was decreased in these amended soils while it increased in the residual fraction. The amendments also decreased the uptake of Cd in the plants at the tillering and mature growth stages. The concentrations of Cd in plant tissues at maturity were in the order: root > shoot > bran > polished rice > husk. The amendment of carbide slag decreased Cd concentration in rice grains the most, followed by lime, biochar, and compost. The increases in soil pH and the decreases in the acid-soluble fraction of Cd (F1-Cd) indicated that these amendments can directly transform the highly availability fraction of Cd to a more stable fraction (residual Cd fraction) in soils. Furthermore, the Cd concentrations in polished rice grains of the two rice cultivars used were reduced by 66-67% by treatment with carbide slag. Our study suggests that carbide slag has a great potential to reduce the bioavailability and uptake of Cd in rice plants in Cd-contaminated acid paddy field soils.

Reduction of cadmium uptake in rice endophytically colonized with the cadmium-tolerant bacterium Cupriavidus taiwanensis KKU2500-3.

The effects of the cadmium (Cd)-tolerant bacterium Cupriavidus taiwanensis KKU2500-3 on the growth, yield, and Cd concentration in rice grains were investigated in the rice variety Phitsanulok 2 (PL2), which was cultivated in a hydroponic greenhouse. The numbers of Cd-tolerant bacteria isolated from the roots and shoots of plants under the RB (rice with bacteria) and RBC (rice with bacteria and Cd) treatments ranged from 2.60 to 9.03 and from 3.99 to 9.60 log cfu·g-1 of PL2, respectively. This KKU2500-3 strain was successfully colonized in rice, indicating that it was not only nontoxic to the plants but also became distributed and reproduced throughout the plants. Scanning electron microscopy analysis revealed attachment of the bacterium to the root surface, whereas the internally colonized bacteria were located in the vascular tissue, cell wall, and intercellular space. Although the Cd contents found in PL2 were very high (189.10 and 79.49 mg·kg-1 in the RC (rice with Cd) and RBC roots, respectively), the Cd accumulated inside the rice seeds at densities of only 3.10 and 1.31 mg·kg-1, respectively; thus, the bacteria reduced the Cd content to 57.74% of the control content. Therefore, the colonizing bacteria likely acted as an inhibitor of Cd translocation in PL2.

Effects of Soil Amendments Application on Growth of Rice Cultivated in Soils Polluted with Heavy Metal(loid) and on the As and Cd Content in Brown Rice

Heavy metal(loid) contamination of rice is the main issue in abandoned metal mine area with regard to food safety. A field study was conducted in mine area to see if soil amendments treatment including calcium superphosphate, sulfur, steel slag and S-containing fertilizer could reduce As and/or Cd content in rice grain and increase the growth of rice. The As content in brown rice reduced to 60% compared to the control only in <TEX>$7.0Mg\;ha^{-1}$</TEX> of steel slag treatment. Cd reduction in rice was thought to be not the effect of amendments but the result from the difference in growth and development of rice plant and this could be ascribed to low soil Cd availability to rice plant. Compared with control, increased rice yield of cultivar Hwanggeumnuri was 1.3~2.2 and <TEX>$1.5Mg\;ha^{-1}$</TEX> in calcium super phosphate and S-containing fertilizer treatment, respectively and the trend was also observed in cultivar Ungwang. However, steel slag treatment reduced the Ungwang yield by <TEX>$0.4{\sim}0.9Mg\;ha^{-1}$</TEX>. Future work will be needed to establish the agricultural measure with which secure the safety and yield of rice simultaneously.

Application of Aspergillus aculeatus to rice roots reduces Cd concentration in grain

Background and aims ‘Cd toxicity in rice’ events have resulted in vast public concern and uncertainty. Effective bioremediation could be accomplished via applying microbes that are capable of alleviating Cd content in rice grains.

Using Data Mining to Predict the Concentration of Cadmium in Khuzestan Paddies, Iran

Background: Rice is the second highly consumed foodstuff among Iranian people. However, high levels of cadmium (Cd) are reported in some paddy fields in Khuzestan province, Iran. Objectives: The current study aimed at investigating the Cd concentration in rice grains by the decision tree using J48 algorithm. The current study also used WEKA software to implement the algorithm. Methods: A total of 630 samples (9 attributes in 70 sampling areas) were taken from each paddy field (5 regions); hence, seed and soil samples were analyzed according to the standard laboratory procedures and finally, the data mining technique was used for the classification of trees by J48 algorithm to predict the concentration of Cd in rice seed. Results: The results showed that the average concentrations of Cd in rice seed and soil were 81.4 and 273.6 μg/kg, respectively; it was also shown that J48 gives 95.71% accuracy, 0.899 Kappa coefficient, and less error (RMSE = 0.179), which make a good predictive model. A significant correlation was observed between soil characteristics and the concentration of Cd in rice seeds. Conclusions: The data mining technology can be used to predicate Cd concentration in rice seeds, and also J48 algorithm is a simple designer to construct a decision tree; nevertheless, offers good results in experiments.

Cadmium Accumulation Risk in Vegetables and Rice in Southern China: Insights from Solid-Solution Partitioning and Plant Uptake Factor.

Solid-solution partitioning coefficient (Kd) and plant uptake factor (PUF) largely determine the solubility and mobility of soil Cd to food crops. A four-year regional investigation was conducted in contaminated vegetable and paddy fields of southern China to quantify the variability in Kd and PUF. The distributions of Kd and PUF characterizing transfers of Cd from soil to vegetable and rice are probabilistic in nature. Dynamics in soil pH and soil Zn greatly affected the variations of Kd. In addition to soil pH, soil organic matter had a major influence on PUF variations in vegetables. Heavy leaching of soil Mn caused a higher Cd accumulation in rice grain. Dietary ingestion of 85.5% of the locally produced vegetable and rice would have adverse health risks, with rice consumption contributing 97.2% of the risk. A probabilistic risk analysis based on derived transfer function reveals the amorphous Mn oxide content exerts a major influence on Cd accumulation in rice in pH conditions below 5.5. Risk estimation and field experiments show that to limit the Cd concentration in rice grains, soil management strategies should include improving the pH and soil Mn concentration to around 6.0 and 345 mg kg-1, respectively. Our work illustrates that re-establishing a balance in trace elements in soils' labile pool provides an effective risk-based approach for safer crop practices.

Effects of growing seasons and genotypes on the accumulation of cadmium and mineral nutrients in rice grown in cadmium contaminated soil.

Heavy metals naturally occur in soil but their concentrations may be changed by seasonal rainfall under double-rice cropping system. The field trials at three sites, which represent low, medium and high cadmium (Cd) content in soil, revealed significant genotypic and environmental variations in grain Cd concentrations. Most cultivars in late rice at three sites produced grains with Cd content over the maximum permissible concentration (MPC) 0.20mgkg-1. However, grain Cd content in early rice was over MPC only at high Cd site. When planted at same site, late rice showed remarkably higher content of Cd as well as K, Mg, Fe and Mn than that in early rice in both grains and rachises. Content of Ni, Pb and Cr was generally in the safe range and it was determined by the interactions between genotypes and environmental factors. Element concentrations in rachises were about 2-10 times higher than those in grains, depending on element species, cultivars, locations and seasons. Low-Cd-accumulation cultivars generally displayed both lower Cd content in rachis and lower Cd transportation ratio from rachises to grains than those of high-Cd-accumulation cultivars. There was a significant and positive correlation between Cd and Mn concentrations in grains. The most important factor that causes great variation in Cd accumulation in rachises and grains between early and later rice is water contents and levels in paddy soils mainly caused by different rainfall amount. Inhibiting Cd accumulation in rachises and Cd transportation from rachises to grains could efficiently decrease Cd content in rice grains produced in contaminated soil.

Root application of selenite can simultaneously reduce arsenic and cadmium accumulation and maintain grain yields, but show negative effects on the grain quality of paddy rice

Most current technologies can hardly simultaneously reduce the accumulation of arsenic (As) and cadmium (Cd) in crops. In this study, root application of selenite [Se (IV)] and selenate [Se (VI)] was used to assess their abilities to reduce the accumulation of As and Cd, and maintain the yields and quality of rice grains. The results show that Se (IV) showed a weaker ability than Se (VI) to maintain the grain contents of many essential elements, but a stronger ability to decrease As and Cd contents in rice grains, and maintain the yields, photosynthesis rate and stomatal conductance, and increase the grain contents of several amino acids (AAs), total Se, selenomethionine (SeMet) and selenocysteine (SeCys). The best outcomes resulted at a relatively high application of 5 mg kg−1 Se (IV), reflecting in the highest total Se, SeCys and SeMet content (14.95, 118.70 and 864.73 μg kg−1, respectively) in the grains, highest grain yield, and lowest grain As and Cd content (0.36 and 0.07 mg kg−1, respectively). In addition, the application of 1–5 mg kg−1 Se (IV) seemed to facilitate the formation of SeMet in the grains, but most inorganic Se in the grains were transformed into SeCys and SeMet under Se (VI) treatments. This study provides a new idea to resolve the problems of high accumulation of As and Cd in rice grains and insufficiency of Se intake in China.

Cadmium Accumulation Characteristic in a Soil-rice System in Zhejiang Province, China

Cadmium (Cd) pollution of rice grain or soil is of increasing concern. This study investigates the concentrations of Cd in soil-rice system in parts area of Zhejiang province and analysis the effects of soil pH and organic matter content on the available Cd concentration in soil and the Cd accumulation of rice grain. The results showed that Cd concentrations in 90 rice grain samples range from 0.01 to 0.31 mg/kg, with an average of 0.1 mg/kg. There is high Cd accumulation in soil that 40% of soil samples were polluted by Cd. The available Cd concentrations in soils had a range of 0.01-0.25 mg/kg, with an average of 0.10 mg/kg. The total Cd concentrations in soil were not the uniquely determined factor for the Cd accumulation of rice grain, Cd concentrations in rice grain were also significantly positive correlated with the available Cd concentrations in soil. The soil pH value and SOM also negatively correlated with available Cd concentrations in soils and Cd concentration in corresponding rice grain. The results indicated the variations of Cd concentration in rice grain were related to Cd concentrations in corresponding soils. Also, soil pH and organic matter content influence the Cd concentrations in soils and affected Cd absorption in rice.

Impacts of rapeseed dregs on Cd availability in contaminated acid soil and Cd translocation and accumulation in rice plants.

The objective of the present study was to investigate the effects of rapeseed dregs (RSD, a commonly organic fertilizer in rural China) at application rates of 0, 0.75, 1.5, and 3.0% on Cd availability in soil and its accumulation in rice plants (Oryza sativa L., Xiangwanxian 12#, and Weiyou 46#) by means of a pot experiment. The results showed that application of RSD resulted in a sharp decrease in the soil TCLP-extractable Cd content. However, the soil TCLP-extractable Cd content in amended soil gradually increased during the rice growing period. Application of RSD significantly increased Cd transport from root to shoot and the amount of Cd accumulated in the aerial part. RSD was an effective organic additive for increasing rice grain yield, but total Cd content in rice grain was also increased. At an application rate of 1.5-3.0% RSD, the total Cd content in Weiyou 46# brown rice was 0.27-0.31mgkg-1, which exceeded the standard safe limit (0.2mgkg-1) and was also higher than that of Xiangwanxian 12# (0.04-0.14mgkg-1). Therefore, Weiyou 46# had a higher dietary risk than Xiangwanxian 12# with RSD application. We do not recommend planting Weiyou 46# and applying more than 0.75% RSD in Cd-contaminated paddy fields.

Modest amendment of sewage sludge biochar to reduce the accumulation of cadmium into rice(Oryza sativa L.): A field study

Much research has considered the influence of biochars on the availability and phytoaccumulation of potentially toxic elements (PTEs) from soil. However, the vast majority of these studies use, what are arguably, unrealistic and unpractical amounts of biochar (10, 50 and even up to 100 t/ha). To offer a more realistic insight into the influence of biochar on PTE partitioning and phytoaccumulation, a field study, using modest rates of biochar application (1.5, 3.0 t/ha), was undertaken. Specifically, the research investigated the influence of sewage sludge biochar (SSBC) on the accumulation of Cd into rice (Oryza sativa L.) grown in Cd contaminated (0.82 ± 0.07 mg/kg) paddy soil. Results indicated, Cd concentrations in rice grains to significantly (p < 0.05) decrease from 1.35 ± 0.09 mg/kg in the control to 0.82 ± 0.07 mg/kg and 0.80 ± 0.21 mg/kg in the 1.5 t/ha and 3.0 t/ha treatments, respectively. Accordingly, the hazardous quotient (HQ) indices for Cd, associated with rice grain consumption, were also reduced by ∼40%. SSBC amendment significantly (p < 0.05) increased grain yields from 1.90 ± 0.08 g/plant in the control to 2.17 ± 0.30 g/plant and 3.40 ± 0.27 g/plant in the 1.5 t/ha and 3.0 t/ha treatments, respectively. Thus, the amendment of SSBC to contaminated paddy soils, even at low application rates, could be an effective approach to mitigate Cd accumulation into rice plants, to improve rice grain yields, and to thereby improve food security and protect public health.

Temporal variability in trace metal solubility in a paddy soil not reflected in uptake by rice (Oryza sativa L.).

Alternating flooding and drainage conditions have a strong influence on redox chemistry and the solubility of trace metals in paddy soils. However, current knowledge of how the effects of water management on trace metal solubility are linked to trace metal uptake by rice plants over time is still limited. Here, a field-contaminated paddy soil was subjected to two flooding and drainage cycles in a pot experiment with two rice plant cultivars, exhibiting either high or low Cd accumulation characteristics. Flooding led to a strong vertical gradient in the redox potential (Eh). The pH and Mn, Fe, and dissolved organic carbon concentrations increased with decreasing Eh and vice versa. During flooding, trace metal solubility decreased markedly, probably due to sulfide mineral precipitation. Despite its low solubility, the Cd content in rice grains exceeded the food quality standards for both cultivars. Trace metal contents in different rice plant tissues (roots, stem, and leaves) increased at a constant rate during the first flooding and drainage cycle but decreased after reaching a maximum during the second cycle. As such, the high temporal variability in trace metal solubility was not reflected in trace metal uptake by rice plants over time. This might be due to the presence of aerobic conditions and a consequent higher trace metal solubility near the root surface, even during flooding. Trace metal solubility in the rhizosphere should be considered when linking water management to trace metal uptake by rice over time.

Subcellular Distribution of Cadmium in Two Paddy Rice Varieties with Different Cooking Methods

Cadmium (Cd) is a non-essential element that is highly mobile within organisms where, following plant uptake, subcellular distribution plays an important role in plant tolerance and detoxification. Cd uptake and subcellular distribution were studied in two paddy rice varieties (Japonica and Indica) hydroponically cultivated in Cd-containing solutions. Japonica rice grains containing Cd were also collected from a Cd-contaminated site and subjected to various cooking treatments (boiled, stir-fried, steamed, and control) to determine the influence of cooking method on the subcellular distribution of Cd. Cd treatment inhibited both shoot height and root length, especially in Japonica, where for the same Cd treatment, Japonica accumulated more Cd in roots and shoots than Indica. Most of the accumulated Cd (92% - 99%) was bound to the cell wall and vacuoles, and decreased in the order: soluble fraction (Fs) > cell wall fraction (Fcw) > organelle fraction (Fco). Subcellular Cd concentrations in rice grains were significantly affected by cooking treatment. The proportion of trophically available Cd decreased with increase in cooking duration and temperature, indicating that consuming steamed and stir-fried rice had a lower Cd exposure risk than consuming boiled rice.

不同生长调节物质对水稻生长及镉积累的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同生长调节物质对水稻生长及镉积累的影响 DOI: 10.5846/stxb201504270861 作者: 作者单位: 广西大学农学院,广西大学农学院,广西大学农学院,广西大学,广西大学,广西大学农学院,广西大学 作者简介: 通讯作者: 中图分类号: 基金项目: 农业部专项资助项目（2014-2016）；广西土壤污染与生态修复人才小高地项目；国家自然科学基金金资助项目（31560122） Effects of four plant growth regulators on growth and cadmium accumulation in rice Author: Affiliation: College of Agriculture, Guangxi University,College of Agriculture, Guangxi University,College of Agriculture, Guangxi University,,,College of Agriculture, Guangxi University,College of Agriculture, Guangxi University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:比较脱落酸（ABA）、乙烯利（ETH）、水杨酸（SA）和茉莉酸甲酯（MeJA）4种植物生长调节物质（PGR）对水稻生长及籽粒镉（Cd）积累的影响差异。试验采用重金属污染土种植水稻，于分蘖期、灌浆期各进行1次PGR叶面喷施处理，分析灌浆期叶片光合指标，丙二醛（MDA）含量以及收获期各部位生物量和Cd含量。结果表明：（1）低浓度ABA（5mg/L）可维持水稻正常产量；高浓度ABA（15mg/L）则导致产量下降。ETH对水稻地上部生长和单株产量有显著抑制作用，SA和MeJA（0.56mg/L）均可保证地上部正常生长，维持正常产量。（2）外施4种PGR均抑制灌浆期叶片气孔开放，降低蒸腾速率和光合速率，抑制效果最明显的是高浓度MeJA（0.56mg/L）。（3）在供试浓度范围内SA、低浓度ABA（5mg/L）以及高浓度MeJA均可降低灌浆期叶片MDA含量，减少质膜过氧化水平。（4）4种PGR均可降低水稻籽粒Cd含量，其中低浓度ABA（5mg/L）抑制籽粒Cd积累的效应最佳。相关性分析结果表明，PGR抑制籽粒积累Cd的效应与地上部向籽粒转运Cd的调控机制有关，与蒸腾速率无显著相关关系。（5）综上所述，低浓度ABA（5mg/L）处理对水稻产量无影响，且籽粒Cd含量降低程度最大。适当浓度的PGR可降低水稻籽粒Cd含量，在中低度重金属污染农田生态修复实践中具有一定的应用前景，但必须精确控制PGR的处理时间和处理浓度，避免出现抑制生长和降低产量的负效应。 Abstract:Cadmium (Cd) pollution has become a serious problem following rapid industrial development. The increasing amounts of Cd in farmlands are the result of increased discharge of industrial waste, abuse of chemical fertilizers, and other man-made sources. Cd likely causes damage to crop physiology when its concentration in soil exceeds the maximum tolerable limit, resulting in growth inhibition and grain yield reduction. Continuous intake of Cd causes human health problems. Therefore, reducing Cd concentration in rice grain, a staple food for half of the world's population, is extremely important and urgent. Plant growth regulators (PGRs) are chemicals-plant endogenous hormones and artificially synthetic growth regulators-that affect and regulate plant growth and/or development at trace levels. Some PGRs play important roles in inducing plant tolerance to drought, salt, low temperature, high temperature, and heavy metals. In this study, the roles of four PGRs, abscisic acid (ABA), ethylene (ETH), salicylic acid (SA), and methyl jasmonate (MeJA), were investigated during stress responses to Cd treatments in rice. Rice seedlings, grown in heavy metal-contaminated soil, were sprayed with the four PGRs on leaves twice, one time each during tillering and filling stages. On the second day after the PGR treatments during the filling stage, the photosynthesis indices and malondialdehyde (MDA) contents of the upper leaves were analyzed. After harvesting, the roots, shoots, and grains were collected to investigate Cd content, biomass, and yield. The results were as follows: (1) The ABA treatment at 5 mg/L maintained normal rice growth and yield, while the ABA treatment at 15 mg/L showed the opposite effects. Treatment with two different levels of ETH significantly decreased the grain yield compared to that of the control. However, SA and MeJA high-level treatments maintained normal yields. (2) The exogenous application of the four PGRs inhibited stomatal opening and reduced the transpiration and photosynthetic rates. Interestingly, the most obvious inhibitory action was observed following the treatment with 0.56 mg/L MeJA. (3) Both the SA treatments, 5 mg/L ABA and 0.56 mg/L MeJA treatments, reduced MDA production and prevented plasma membrane peroxidation of leaves at the tillering stage. (4) Decreases in the Cd concentrations were observed in rice grain treated with the four PGRs at their appropriate levels, and the ABA treatment at 5 mg/L showed the strongest inhibitory effect. The grain Cd content showed positive and highly significant (P<0.01) correlation with the Cd translocation factor from shoot to grain, but it did not show a significant correlation with the transpiration rate. PGRs may inhibit the accumulation of Cd in the grain by regulating Cd transport from shoots to grain. (5) In summary, ABA treatment at 5 mg/L had no effect on grain yield but induced the maximum decline in grain Cd content compared to the treatments with other PGRs. Proper application of PGRs can reduce the Cd content in rice grain and can be used in bioremediation of heavy metal polluted farmland. For a practical application of PGRs, appropriate timing, and accurate concentrations are the critical factors to avoid negative effects of inhibited growth and reduced rice yields. 参考文献 相似文献 引证文献

Cadmium availability in rice paddy fields from a mining area: The effects of soil properties highlighting iron fractions and pH value

Cadmium (Cd) availability can be significantly affected by soil properties. The effect of pH value on Cd availability has been confirmed. Paddy soils in South China generally contain high contents of iron (Fe). Thus, it is hypothesized that Fe fractions, in addition to pH value, may play an important role in the Cd bioavailability in paddy soil and this requires further investigation. In this study, 73 paired soil and rice plant samples were collected from paddy fields those were contaminated by acid mine drainage containing Cd. The contents of Fe in the amorphous and DCB-extractable Fe oxides were significantly and negatively correlated with the Cd content in rice grain or straw (excluding DCB-extractable Fe vs Cd in straw). In addition, the concentration of HCl-extractable Fe(II) derived from Fe(III) reduction was positively correlated with the Cd content in rice grain or straw. These results suggest that soil Fe redox could affect the availability of Cd in rice plant. Contribution assessment of soil properties to Cd accumulation in rice grain based on random forest (RF) and stochastic gradient boosting (SGB) showed that pH value should be the most important factor and the content of Fe in the amorphous Fe oxides should be the second most important factor in affecting Cd content in rice grain. Overall, compared with the studies from temperate regions, such as Europe and northern China, Fe oxide exhibited its unique role in the bioavailability of Cd in the reddish paddy soil from our study area. The exploration of practical remediation strategies for Cd from the perspective of Fe oxide may be promising.

Mitigation of cadmium and arsenic in rice grain by applying different silicon fertilizers in contaminated fields.

A field experiment was established to support the hypothesis that application of different silicon (Si) fertilizers can simultaneously reduce cadmium (Cd) and arsenic (As) concentration in rice grain. The "semi-finished product of Si-potash fertilizer" treatment at the high application of 9000 kg/ha (NP+S-KSi9000) significantly reduced the As concentration in rice grain by up to 20.1%, compared with the control. Si fertilization reduces the Cd concentration in rice considerably more than the As concentration. All Si fertilizers apart from sodium metasilicate (Na2SiO3) exhibited a high ability to reduce Cd concentration in rice grain. The Si-calcium (CaSi) fertilizer is the most effective in the mitigation of Cd concentration in rice grain. The CaSi fertilizer applied at 9000 kg/ha (NPK+CaSi9000) and 900 kg/ha (NPK+CaSi900) reduced the Cd concentration in rice grain about 71.5 and 48.0%, respectively, while the Si-potash fertilizer at 900 kg/ha (NP+KSi900), the semi-finished product of Si-potash fertilizer at both 900 kg/ha (NP+S-KSi900) and 9000 kg/ha (NP+S-KSi9000), and the rice straw (NPK+RS) treatments reduced the Cd concentration in rice grain about 42, 26.5, 40.7, and 23.1%, respectively. The results of this investigation demonstrated the potential effects of Si fertilizers in reducing Cd and As concentrations in rice grain.

Direct and residual effect of sewage sludge on yield, heavy metals content and soil fertility under rice–wheat system

Soil application of sewage sludge in crop production offers an alternative technique for its disposal and management. The present study was taken up to evaluate the effect of sewage sludge on yield of rice, soil fertility and heavy metals accumulation in grain and straw in a glass house. The residual effect of sludge application was evaluated in subsequent wheat crop in the sequence. Five doses of sludge i.e., 0, 10, 20, 30 and 40tha−1 were applied to rice and their effects were compared with the recommended dose of fertilizers i.e., 120, 60 and 60kgN, P2O5 and K2Oha−1, respectively. There was significant increase in straw and grain yields of both the crops with application of sludge. The grain yield of rice increased 45% at 40tha−1 sludge application over no sludge. The residual effect on wheat yield was more pronounced. Soil pH in post harvest rice soil increased with the application of sludge, however, it decreased in post harvest wheat soil at higher levels of sludge application. Increase in available nutrients content of soil was also recorded with increasing levels of sludge application after harvest of rice and wheat crops. Application of sludge also increased the heavy metals contents in soil and plant. The Cd content in rice grain was above the Indian safe limit at 20tha−1 or higher levels of sludge application. There was a significant build up of P, S, Zn, Fe, and Mn in post harvest wheat soil at 40tha−1 sludge application.

Current situation of cadmium-polluted paddy soil, rice and soybean in the Mae Sot District, Tak Province, Thailand

Since 2002, a joint research team from the International Water Management Institute and the Department of Agriculture, Thai Government, has reported that there are cadmium (Cd)-contaminated paddy fields in northern Thailand. We evaluated the current situation of the Cd-polluted paddy fields in this report. Home-consumed rice grains were collected from all 23 households in the village of Pha Te, Mae Sot District of Tak Province, Thailand. The Cd concentration in unhusked rice (Oryza sativa L.) grains ranged from 0.04 to 1.75 mg Cd kg−1, and the rice of more than half of the households contained Cd levels higher than the critical level of 0.4 mg Cd kg−1 polished rice, which is CODEX standard. Among the paddy fields, we selected one plot (1.2 ha) and analyzed Cd concentrations of the soil, and rice and soybean (Glycine max L.) grains. In this area, a rotation cropping system of wet-season rice and dry-season soybean is common practice. The soil Cd concentration ranged from 0.31 to 13.9 mg Cd kg−1 (total Cd) and 0.030 to 13.3 mg Cd kg−1 [extracted with 0.1 M hydrochloric acid (HCl)], the Cd concentration in the rice grains ranged from 0.12 to 1.27 mg Cd kg−1, and that in the soybean grains ranged from 0.07 to 0.80 mg Cd kg−1. The soil extractable Cd concentration was well reflected in the soybean grain Cd levels (r2 = 0.581), but not in the rice grain levels (r2 = 0.015), suggesting that rice grain Cd levels are influenced not only by the soil Cd concentration, but by other factors as well, such as soil water regime and soil pH. However, a significant difference in the grain-Cd concentration was found; that is, lower Cd in the cultivar “Khao’ Khaeng” and higher in the “Khao Dawk Mali 105”, which suggests a possibility of selecting a rice cultivar having low-grain Cd.

The OsHMA2 transporter is involved in root‐to‐shoot translocation of Zn and Cd in rice

Zinc (Zn) is an essential micronutrient for plants and humans. Cadmium (Cd) is a Zn analog and one of the most toxic heavy metals to humans. Here we investigated the role of the Zn/Cd transporter OsHMA2. OsHMA2:GFP fusion protein localized to the plasma membrane in onion epidermal cells. The yeast expressing OsHMA2 was able to reverse the growth defect in the presence of excess Zn. The expression of OsHMA2 in rice was observed mainly in the roots where OsHMA2 transcripts were abundant in vascular bundles. Furthermore, Zn and Cd concentrations of OsHMA2-suppressed rice decreased in the leaves, while the Zn concentration increased in the roots compared with the wild type (WT). These results suggest that OsHMA2 plays a role in Zn and Cd loading to the xylem and participates in root-to-shoot translocation of these metals in rice. Furthermore, the Cd concentration in the grains of OsHMA2-overexpressing rice as well as in OsSUT1-promoter OsHMA2 rice decreased to about half that of the WT, although the other metal concentrations were the same as in the WT. A phenotype that reduces only the Cd concentration in rice grains will be very useful for transgenic approaches to food safety.

Effect of application of molasses to paddy soil on the concentration of cadmium and arsenic in rice grain

Molasses, a liquefied by-product of sugar production from sugarcane, is one of the most easily decomposable organic substances. We investigated the effect of the application of diluted molasses in paddy rice (Oryza sativa L.) fields on cadmium (Cd) and arsenic (As) absorption in rice grains as a measure of the shortage of irrigation water or rainfall. The application of diluted molasses on to the top of the soil surface at one week before or after heading led to a decrease in the redox potential of the soil. The Cd concentration in the rice grains was significantly decreased with the application of molasses (2000 kg ha−1) at heading or one week after heading. However, early application of molasses (one week before heading) did not decrease the Cd concentration in the rice grains with downsizing of grain particle size. Meanwhile, As concentration in the rice grains did not change with early application at one week before heading, while it increased with application of molasses at heading or one week after heading. This method is useful especially for decreasing Cd concentration in rice grains in a region under lack of irrigation due to drought.