Cd Concentration In Rice Research Articles

Effects of Different Water Managements and Soil Eh on Migration and Accumulation of Cd in Rice

A pot experiment was conducted to study the effects of four modes of water managements on soil Eh values,bioavailability of soil Cd,migration and accumulation of Cd in rice.These four modes of water managements were moistening throughout the entire period of rice growth (M),moistening before filling stage and flooding after filling stage (M-F),flooding before filling stage and moistening after filling stage (F-M),and flooding throughout the entire period of rice growth (F).The results indicated that the exchangeable contents of Cd increased firstly and then declined with the soil Eh values changing from negative to positive.Compared with M,the other three modes (M-F,F-M,and F) significantly reduced the contents of Cd in all rice tissues,including roots,stems,husks and brown rice.Meanwhile,Cd contents in brown rice due to the treatments of M-F and F were 0.19 mg·kg-1 and 0.10 mg·kg-1,respectively.These Cd contents were lower than the limits of 0.2 mg·kg-1 in national food safety standard (GB 2762-2012).Compared with M,the other three modes significantly decreased Cd accumulation amounts in the aboveground parts of rice and also decreased Cd translocation factors in rice.There were significant positive exponential relations between soil Eh values and Cd accumulation amounts in the aboveground parts of rice,Cd translocation factors in rice,or Cd contents in brown rice.The rice biomass due to M-F treatment reached the maximum among the four modes.It was worthy to be mentioned that although Weiyou 46 was considered a variety rice with high Cd accumulation,Cd content in rice brown of Weiyou 46 could be lower than 0.2 mg·kg-1 in the 5 mg·kg-1 of Cd contaminated soil through proper water managements.In summary,M-F treatment ensured high rice yield with low Cd contents in brown rice and could be recommended as the irrigation mode in rice production.Simultaneously,maintaining soil Eh value between -160--130 mV was also important after the filling stage.

Effects of a Combined Amendment on Pb, Cd, and As Availability and Accumulation in Rice Planted in Contaminated Paddy Soil

ABSTRACTThe objectives of the present study were to investigate the mitigation of lead (Pb), cadmium (Cd), and arsenic (As) in a multi-metal contaminated soil and their accumulation in rice plants (Oryza sativa L., cv II You 93) using a combined amendment (CMF, calcium carbonate + metakaolin + fused calcium–magnesium phosphate fertilizer). The results showed that application of CMF was effective in reducing the acid-extractable concentrations of soil Pb and Cd. The exchangeable concentrations of soil As showed an initial decrease followed by a gradual increase. The application of 0.2% CMF notably reduced the concentrations of Pb, Cd, and As in brown rice by 46.5%, 43.6%, and 32.0%, respectively. The concentration of As in brown rice was 0.179 mg kg−1 at 0.2% CMF, which met the maximum levels of contaminants in foods of China (MLs) (the ML of Pb, Cd, and As is 0.2 mg kg−1 according to the China national standard GB 2762-2012). At 1.6% CMF, the concentrations of Pb and Cd in brown rice were 0.002 and 0.185 mg kg−1, respectively, i.e., reductions of 99.6% and 74.1%, and these values also fell within the MLs.

2015年珠三角地区市售大米和蔬菜中重金属含量及健康风险评价

为了更好地了解和评价珠江三角洲地区市售农产品中As、Cd、Hg和Pb含量及其对人体的健康影响，本研究对珠江三角洲地区9个城市(广州市、佛山市等)市售大米和蔬菜中重金属含量进行分析，并对人体的健康风险进行评价。结果表明，大米中总砷含量均值为126 µg/kg；大米镉含量均值为113 µg/kg，大米中总汞含量均值为15.1 µg/kg，大米铅含量均值为85 µg/kg；广州市、佛山市、肇庆市和东莞市等城市共有13个样品中镉超过标准规定；佛山市和肇庆市的部分大米样品中总汞超过标准规定。所采集的6种蔬菜302份样品中的Cd和Pb含量均未见超标。仅通过食用大米，珠三角地区居民As、Cd、Hg、Pb的平均最高摄入量分别为0.67 (珠海)、0.81 (广州)、0.14 (佛山)、0.53 (佛山) µg/kg/d；而通过食用蔬菜，Cd、Pb的平均最高摄入量分别为0.20 (佛山)和0.15 (东莞) µg/kg/d。珠三角地区市售大米对人体存在一定的健康风险，蔬菜中铅、镉的含量及人群摄入量总体处于安全水平。 A systematic survey of heavy metals concentrations in market rice and vegetables from 9 cities in Pearl Delta River area was carried out for assessing health risk to local inhabitants. The average concentrations of As, Cd, Hg and Pb in market rice were 126, 113, 15.1 and 85 µg/kg, respectively. The concentrations of Cd and Hg in partly market rice samples from Guangzhou, Foshan and Zhaoqing cities exceeded the maximum allowable limits. The average concentrations of As, Cd, Hg and Pb in 6 species of vegetables (302 samples) were all far below the maximum allowable limits. The Target Hazard Quotient (THQ) method is used to assess the possible health risks to local population through consumption of rice and vegetables. Via consumption of market rice, daily intakes of As, Cd, Hg and Pb were 0.67 (Zhuhai), 0.81 (Guangzhou), 0.14 (Foshan), 0.53 (Foshan) µg/kg/d；and daily intakes of Cd and Pb were 0.20 (Foshan) and 0.15 (Dongguan) µg/kg/d from consumption of market vegetables. The potential health risk for local residents is seriously due to the combined heavy metal from rice.

Cd inhibition and pH improvement via a nano-submicron mineral-based soil conditioner.

Cd contamination of rice in recent years has aroused a nationwide concern on the potential health risk to people in China. A significant increase of soil acidification in major Chinese croplands improves available Cd content by crops, and this further pushes a heavier burden on controlling Cd contamination. Therefore, it is urgent to find a workable and green way to control Cd contamination, i.e., decrease Cd content in rice, for people's health in China, as other countries in the world. From chemical and economic points, stabilizing/solidifying Cd may be a feasible way except in-situ ways such as removing it by the absorption of special plants and ex-situ ones such as removing the contaminated soil and treating it by special equipment. Then, it is very important how to choose a green solidifying agent. By simulating a rock-weathering process, a nano-submicron mineral-based soil conditioner (NSC) was prepared through environmentally friendly hydrothermal reaction. The application of NSC not only decreased Cd content in rice, i.e., inhibited Cd absorption, and increased pH of the soil, but also improved the content of healthy nutrients such as organic matter, available Ca, available K, available P, and available Si in the soil. The mechanism why NSC showed such good performance was also discussed in this study.

Comprehensive Risk Evaluation of Cadmium in Soil-rice System Based on Uncertainty Analysis

Cadmium (Cd) can cause adverse health effects and is a subject of concern in rice consumption. The uncertainty analysis helps improve the accuracy in the risk assessment for Cd in soil-rice system. A regional investigation on Youxian prefecture, southern China, was conducted to analyze the Cd concentration in rice. Based on the species sensitivity distribution model (SSD), health risk assessment model, and Monte Carlo simulation, the accumulation characteristic of Cd in soil-rice system, accumulation risk of Cd in soil, and health risk of Cd concentration in rice were determined. The results showed that the plant uptake factor (PUF) of Cd of rice was well fitted by the SSD model. The mean level of PUF was 1.86, with a significant spatial heterogeneity. The rice produced in WL county tended to accumulate a high level of Cd. There was no significant relationship between concentrations of Cd in soil and rice, suggesting that of rice renders the Cd risk management very difficult. The pollution load index of Cd in soil was 2.4, which belonged to a moderate contamination level. Under current accumulation condition of Cd in soil, there would be a 90.4% probability for soil Cd concentration to be higher than the national soil quality standard after 10 years. Health risk assessment showed that the average daily dose (ADD) was 2.9 μg·(kg·d)-1, 3.5 fold higher than the WHO limit. About 93.9% of the adult populations consuming rice cropping in affected areas had the risk that the daily Cd intake was above the WHO limit. The health risk index (HRI) was around 2.1 to 4.7. The probability for health risk index (HRI) higher than 5 was 21.5%, suggesting a high health risk. When the soil pH was lower than 5.5, the probability for HRI higher than 1 was 95.3%, and when the soil pH was higher than 6, the probability for HRI higher than 1 reduced to 68.1%. An improved management of soil pH values would be needed for a better and safer rice production. The combination of uncertainty analysis, species sensitivity model and health risk assessment model was validated to be feasible and reliable in the risk analysis.

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.

A three-season field study on the in-situ remediation of Cd-contaminated paddy soil using lime, two industrial by-products, and a low-Cd-accumulation rice cultivar

To mitigate the serious problem of Cd-contaminated paddy soil, we investigated the remediation potential of combining in-situ immobilization with a low-Cd-accumulation rice cultivar. A three-season field experiment compared the soil pH, available Cd and absorption of Cd by three rice cultivars with different Cd accumulation abilities grown in Cd-contaminated paddy soil amended with lime (L), slag (S), and bagasse (B) alone or in combination. The three amendments applied alone and in combination significantly increased soil pH, reduced available Cd and absorption of Cd by rice with no effect on grain yield. Among these, the LS and LSB treatments reduced the brown rice Cd content by 38.3–69.1% and 58.3–70.9%, respectively, during the three seasons. Combined with planting of a low-Cd-accumulation rice cultivar (Xiang Zaoxian 32) resulted in a Cd content in brown rice that met the contaminant limit (≤0.2mgkg−1). However, the grain yield of the low-Cd-accumulation rice cultivar was approximately 30% lower than the other two rice cultivars. Applying LS or LSB as amendments combined with planting a low-Cd-accumulation rice cultivar is recommended for the remediation of Cd-contaminated paddy soil. The selection and breeding of low-Cd-accumulation rice cultivars with high grain production requires further research.

Risk assessment of cadmium in rice in Xiangtan, Hunan, China based on Bayesian method

In this study, a total of 73 groups of paddy soil and rice samples were collected from 3 counties of Xiangtan City, Hunan Province, which were Xiangtan, Yuhu, and Xiangxiang, respectively. The total content of Cd in soil and rice samples was determined, the available Cd in soil samples also was measured, and the correlation analysis was conducted among them, respectively. According to the prior probability and data feature, we proposed to use the Bayesian method to eva-luate the risk of Cd content exceeding criterion in rice and construct the risk assessment model. The results indicated that, the average soil Cd content, soil available Cd content and the rice Cd content in the study area were (0.891±0.638) mg·kg-1, (0.791±0.582) mg·kg-1 and (0.376±0.395) mg·kg-1, respectively, and the exceeding standard rate of Cd content in soil and rice reached 89.0% and 52.1%. The rice Cd content was significantly correlated with the available Cd content and total Cd content in soil in Xiangtan and Yuhu. A better correlation was presented between the soil available Cd content and rice Cd content. The rice Cd content in Xiangxiang had no correlation with total Cd content and available Cd content in soil. When the total Cd content and available Cd content were selected as the variables of Bayesian model, the deviations between the predicted exceeding probability of Cd in rice and the true exceeding standard rate were 6.6% and 3.9%, respectively, which proved the Bayesian risk assessment model was reliable. Selecting the available Cd content as the model variable, the predicted result was closer to the true value.

Effects of alkaline and bioorganic amendments on cadmium, lead, zinc, and nutrient accumulation in brown rice and grain yield in acidic paddy fields contaminated with a mixture of heavy metals.

Paddy soils and rice (Oryza sativa L.) contaminated by mixed heavy metals have given rise to great concern. Field experiments were conducted over two cultivation seasons to study the effects of steel slag (SS), fly ash (FA), limestone (LS), bioorganic fertilizer (BF), and the combination of SS and BF (SSBF) on rice grain yield, Cd, Pb, and Zn and nutrient accumulation in brown rice, bioavailability of Cd, Pb, and Zn in soil as well as soil properties (pH and catalase), at two acidic paddy fields contaminated with mixed heavy metals (Cd, Pb, and Zn). Compared to the controls, SS, LS, and SSBF at both low and high additions significantly elevated soil pH over both cultivation seasons. The high treatments of SS and SSBF markedly increased grain yields, the accumulation of P and Ca in brown rice and soil catalase activities in the first cultivation season. The most striking result was from SS application (4.0tha-1) that consistently and significantly reduced the soil bioavailability of Cd, Pb, and Zn by 38.5-91.2% and the concentrations of Cd and Pb in brown rice by 20.9-50.9% in the two soils over both cultivation seasons. LS addition (4.0tha-1) also markedly reduced the bioavailable Cd, Pb, and Zn in soil and the Cd concentrations in brown rice. BF remobilized soil Cd and Pb leading to more accumulation of these metals in brown rice. The results showed that steel slag was most effective in the remediation of acidic paddy soils contaminated with mixed heavy metals.

Iron plaque decreases cadmium accumulation in Oryza sativa L. and serves as a source of iron.

Cadmium (Cd) contamination occurs in paddy soils; hence it is necessary to reduce Cd content of rice. Application and mode of action of ferrous sulphate in minimizing Cd in rice was monitored in the present study. Pot culture with Indian rice variety Swarna (MTU 7029) was maintained in Cd-spiked soil containing ferrous sulphates, which is expected to reduce Cd accumulation in rice. Responses in rhizosphere pH, root surface, metal accumulation in plant and molecular physiological processes were monitored. Iron plaque was induced on root surfaces after FeSO4 application and the amount of Fe in plaque reduced with increases in Cd in the soil. Rhizosphere pH decreased during plaque formation and became more acidic due to secretion of organic acids from the roots under Cd treatment. Moreover, iron chelate reductase activity increased with Cd treatment, but in the absence of Cd, activity of this enzyme increased in plaque-induced plants. Cd treatment caused expression of OsYSL18, whereas OsYSL15 was expressed only in roots without iron plaque. Fe content of plants increased during plaque formation, which protected plants from Cd-induced Fe deficiency and metal toxicity. This was corroborated with increased biomass, chlorophyll content and quantum efficiency of photo-synthesis among plaque-induced plants. We conclude that ferrous sulphate-induced iron plaque prevents Cd accumulation and Fe deficiency in rice. Iron released from plaque via organic acid mediated dissolution during Cd stress.

Simultaneous decrease of arsenic and cadmium in rice (Oryza sativa L.) plants cultivated under submerged field conditions by the application of iron-bearing materials

ABSTRACTThe Codex Alimentarius Commission has recently adopted maximum levels for inorganic arsenic (As; in 2014) and total cadmium (Cd; in 2006) in polished rice grains to maintain food safety and to decrease the risk to human health. As rice is a staple crop in Japan and monsoon Asian countries, reducing concentrations of As and Cd in rice is an urgent matter. In flooded conditions, Cd concentration in soil solution decreases whereas As concentration increases. Therefore, we aimed to evaluate the efficiency of iron-bearing materials to decrease As concentration in soil solution and rice (Oryza sativa L.) grain under submerged cultivation, while also considering Cd concentration. In experiments conducted in paddy fields in six regions, As concentrations in the soil solution during the cultivation period decreased in the following order: control (REF) > steel converter furnace slag (SCS) > non-crystalline iron hydroxide (FH) > zero-valent iron (ZVI). The concentrations of As in brown rice were in the same order, with ZVI achieving particularly strong reduction. Cadmium concentrations were low, probably owing to submerged cultivation conditions. Application of iron-bearing materials slightly and insignificantly reduced the yields of brown rice and straw. Application of these materials did not have a significant negative impact on the quality of rice. Our data indicate that the application of iron-bearing materials effectively reduces As concentrations in soil solution and rice grains without negative effects on yield and quality, with a particularly powerful effect of ZVI which is possibly explained by arsenic sulfide formation.

Effect of silicon on grain yield of rice under cadmium-stress

Many publications indicated various beneficial effects of the addition of silicon (Si) in soil on the physiology of rice plants. The gene responsible for the Si-uptake in rice, low Si-influx 1 (Lsi1), was identified and cloned for this study. The photosynthetic rate (Pn), grain yield, and resistance to Cadmium (Cd)-stress of the wild-type (WT) and Lsi1-transgenic Lemont rice lines under Cd-stress were examined in an attempt to better understand the mechanism associated with the Si-addition, Cd-stress, and rice physiology. Si-fertilization significantly reduced the Cd-content in rice under Cd-stress. The effect was most significant in the Lsi1-overexpression transgenic Lemont rice (Lsi1-OE line) under high Cd-stress. Conversely, Cd in soil lowered the Si-uptake of the plants indicating a significant interaction between the two elements. During the grain-filling period, Cd-stress greatly reduced the chlorophyll content and Pn of the rice resulting in a diminished grain output. However, Lsi1-OE line with a higher chlorophyll content and Pn than either WT or Lsi1-RNAi transgenic Lemont rice (Lsi1-RNAi line) maintained a high photo-assimilate transportation for high yield potential. At harvest, Lsi1-OE line contained more Si and less Cd than WT, whereas the Lsi1-RNAi line showed an opposite result. In general, Cd-stress reduced, while Si-fertilization significantly increased, the grain yield on rice. However, no significant difference on the grain yields existed between WT and Lsi1-RNAi line. This might be due to a compensation effect generated by Lsi1-RNAi line. It appeared that Si in the soil, as well as the enhancing or inhibiting Lsi1 expression and the resistance to Cd-toxicity of the plants, could significantly affect the rice yield making alternations on these factors a plausible approach for production improvement.

Itai-itai disease: Renal tubular osteomalacia induced by environmental exposure to cadmium—historical review and perspectives

ABSTRACTCadmium (Cd) is one of the most toxic elements encountered in industry and contaminated environments. In Japan, environmental exposure to Cd and its effects on human health have been significant issues since the first outbreak of itai-itai disease, which is the most severe stage of chronic Cd poisoning, in the Cd-polluted Jinzu River basin of Toyama. In this region, the soil replacement of polluted rice paddy fields, which was an intervention program, was continuously conducted from 1980 until it was completed in 2012. As a result, the Cd content in rice has markedly decreased. However, Cd nephropathy is still prevalent, progressive and irreversible among the inhabitants of the Jinzu River basin, and new occurrences of itai-itai disease are found even today.

Functional effects of manganese and iron oxides on the dynamics of trace elements in soils with a special focus on arsenic and cadmium: A review

The dynamics and availability of arsenic (As), cadmium (Cd), and other trace elements in soils are of great concern to soil scientists. Owing to the human toxicity of As and Cd, the Codex Alimentarius Commission set maximum permissible concentrations of these elements in foodstuffs, including rice which is a major source of human intake of As and Cd, especially in Asia. Therefore, attenuation of As and Cd concentrations in crops, especially rice, is important for both human health and agroindustry.Manganese (Mn) and iron (Fe) oxides have great capacity to sorb trace elements. Adsorption of cationic elements increases with increasing pH, whereas adsorption of arsenate [As(V)] shows the opposite trend. Adsorption of cationic elements by Mn oxides is generally much greater than adsorption by Fe oxides, whereas Fe oxides have a much higher adsorption capacity for As than Mn oxides do. Trace elements can co-precipitate with Mn/Fe oxides and are subsequently released from or incorporated into solid phases with aging depending on the natures of elements and on the surrounding conditions. Moreover, Mn/Fe oxides, especially Mn oxides, oxidize arsenite [As(III)] to As(V), which is less soluble. Sorbed elements solubilize under reducing conditions through reductive dissolution of Mn/Fe oxides. In addition to the transformation of As from As(V) to As(III), the release of As from Fe oxides is responsible for the increase in dissolved As concentration that accompanies flooding. In contrast, Cd precipitates as barely soluble sulfides under strong reducing conditions. This difference may explain why the concentrations of As and Cd in rice grown with different water management show opposite trends. Iron plaque, an Fe oxide precipitate that forms on rice roots, may attenuate As concentrations in rice tissues by fixing and sequestering As, although some studies have questioned this possibility.There have been many attempts to use Mn/Fe oxides (or materials containing them) to attenuate the soil solubility of trace elements and/or reduce their uptake by crops. Application of Mn/Fe oxides has useful effects in most cases; in particular, application of Fe oxides or Fe oxide-containing materials immobilizes As in soils. Therefore, application of Mn/Fe oxides combined with flooded cultivation may attenuate the concentrations of both As and Cd in rice. However, additional studies are required because only a few studies have focused on the effects of application of Mn/Fe oxides on As mobility in anaerobic soils and consequent uptake by rice plants.

Comparison of Dietary Cadmium Exposure among the General Population from Two Cadmium-polluted Regions in China

Background: In China, Dayu County is famous for tungsten, lead–zinc mines that are abundant in Hezhang County. Cadmium (Cd) is a concomitant pollutant with tungsten and lead–zinc mining. The most severe Cd pollution occurred from the 1970s until 2006. Large-scale mining stopped after 2006 in the two counties; however, the longterm mining led to soil Cd pollution in these areas. Aim: The study aimed to investigate Cd concentration in crops and dietary exposure among the general population in two Cd-polluted regions. Methods: Local self-seeded grain and vegetable samples were collected and analyzed for Cd content with atomic absorption spectrometry. A three-day dietary interview was carried out among local residents to estimate diet Cd intake. Results: In total, 957 and 281 crop samples were collected. Three-day diet surveys were conducted among 546 residents and 262 residents, respectively from Hezhang and Dayu Counties. Higher Cd content of rice (0.536 mg/kg) and a ratio of rice to Cd content (71.69%) over the standard limit were found in Dayu, whereas a higher Cd content was found in leafy vegetables (0.386 mg/kg) and ratio of leafy vegetables to Cd content (51.40%) over the standard limit in Hezhang. Rice is the main food consumed and it is a major source of dietary Cd intake for local residents in Dayu; however, maize is the main food consumed and leafy vegetables are the major source of dietary Cd intake for local residents in Hezhang. For the two counties, both average daily Cd intake and cumulative Cd intake of residents in the polluted areas exceeded the limitation of Cd from food, and the consumption is higher in Dayu. Conclusion: Cd exposure through food is very high among the general population in the two regions. Different measures should be taken in different regions. Also, close attention should be paid to the health of the local residents.

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.

Do soil Fe transformation and secretion of low-molecular-weight organic acids affect the availability of Cd to rice?

The bioavailability of cadmium (Cd) to rice may be complicated by chemical and biological factors in the rhizosphere. The aim of this work is to investigate how soil iron (Fe) redox transformations and low-molecular-weight organic acid (LMWOA) exudation from root affect Cd accumulation in rice. Two soils (a paddy soil and a saline soil) with different physicochemical properties were used in this study. Soil redox conditions were changed by flooding and addition of organic matter (OM). Two days after the soil treatments, rice seedlings were transplanted in a vermiculite-soil system and grown for 10 days. We measured pH and Eh, LMWOA, Fe and Cd contents in rice, and their fractions in the soils and vermiculite. Cadmium accumulation in rice declined in both soils upon the flooding and OM treatment. Iron dissolution in the paddy soil and its deposition in the rhizosphere significantly increased upon the OM addition, but the concentration of Fe plaque on the rice root significantly declined. Conversely, although Fe transformed into less active fractions in the saline soil, Fe accumulation on the surface and in the tissue of root was considerably enhanced. The secretion of LMWOA was remarkably induced when the OM was amended in the saline soil, but the same effect was not observed in the paddy soil. Reduction of Cd uptake by rice could be attributed to different factors in the two soils. For the paddy soil, the lowered Cd bioavailability was likely due to the competition of Fe and Cd for the binding sites on the vermiculite surface. For the saline soil, however, rice responded to the low Fe mobility through more LMWOA exudation and Fe plaque formation, and their increases could explain the decrease of rice Cd.

Additional Burden of Diseases Associated with Cadmium Exposure: A Case Study of Cadmium Contaminated Rice Fields in Mae Sot District, Tak Province, Thailand.

The cadmium (Cd) contaminated rice fields in Mae Sot District, Tak Province, Thailand has been one of the major environmental problems in Thailand for the last 10 years. We used disability adjusted life years (DALYs) to estimate the burden of disease attributable to Cd in terms of additional DALYs of Mae Sot residents. Cd exposure data included Cd and β2–microglobulin (β2-MG) in urine (as an internal exposure dose) and estimated cadmium daily intake (as an external exposure dose). Compared to the general Thai population, Mae Sot residents gained 10%–86% DALYs from nephrosis/nephritis, heart diseases, osteoporosis and cancer depending on their Cd exposure type and exposure level. The results for urinary Cd and dietary Cd intake varied according to the studies used for risk estimation. The ceiling effect was observed in results using dietary Cd intake because of the high Cd content in rice grown in the Mae Sot area. The results from β2-MG were more robust with additional DALYs ranging from 36%–86% for heart failure, cerebral infarction, and nephrosis/nephritis. Additional DALYs is a useful approach for assessing the magnitude of environmental Cd exposure. The Mae Sot population lost more healthy life compared to populations living in a non- or less Cd polluted area. This method should be applicable to various types of environmental contamination problems if exposure assessment information is available.

Uptake of cadmium by rice grown on contaminated soils and its bioavailability/toxicity in human cell lines (Caco-2/HL-7702).

Cadmium (Cd) enters the food chain from polluted soils via contaminated cereals and vegetables; therefore, an understanding of Cd bioaccessibility, bioavailability, and toxicity in humans through rice grain is needed. This study assessed the Cd bioaccessibility, bioavailability, and toxicity to humans from rice grown on Cd-contaminated soils using an in vitro digestion method combined with a Caco-2/HL-7702 cell model. Cadmium bioaccessibility (18.45-30.41%) and bioavailability (4.04-8.62%) were found to be significantly higher in yellow soil (YS) rice than calcareous soil (CS) rice with the corresponding values of 6.89-11.43 and 1.77-2.25%, respectively. Toxicity assays showed an initial toxicity in YS rice at 6 mg kg(-1) Cd, whereas CS rice did not show any significant change due to low Cd concentrations. The acidic soils of Cd-contaminated areas can contribute to a higher dietary intake of Cd. Therefore, it is imperative to monitor Cd concentration in rice to minimize human health risk.

Heavy metal pollution and potential health risk assessment of white rice around mine areas in Hunan Province, China

To assess the pollution situation and human health risks, the concentrations of heavy metals Pb, Cd, Cu, and Zn in paddy soils and white rice around seven mining-affected areas in Hunan Province were analyzed. The ranges of concentrations of Pb (23.9–1595.8 mg kg−1), Cd (0.3–9.5 mg kg−1), Cu (31.2–321.5 mg kg−1) and Zn (56.1–3478.9 mg kg−1) in all paddy soils were significantly higher than Hunan background values and even exceeded the maximum permissible concentrations for paddy soil quality recommended by the Ministry of Environmental Protection of China. The geoaccumulation index (I- geo ) showed that Cd (1.42–6.33) was the predominant pollutant in all paddy soils, while Zn was the least important element. The concentrations of Pb, Cd, Cu, and Zn in white rice ranged from 0.18 to 0.72 mg kg−1, 0.10 to 1.32 mg kg−1, 3.83 to 5.95 mg kg−1, and 8.64 to 18.18 mg kg−1, respectively. Human health risk, associated with these heavy metals, was assessed based on hazard quotients (HQ) and hazard indexes (HI) for adults through consumption of white rice. HQ values of heavy metals (except for Cd) in most of mining-affected areas were below 1.0, while the HI of all heavy metals in all mine areas was higher than 1.0, the maximum acceptable level, suggesting that consumption of such contaminated white rice was a health risk. Except for the Leng Shui-Jiang mine area, Cd was the major contributor to the risk in the mine areas through white rice consumption, amounting to over 67 % of the HI, while Zn was a minimal contributor compared to the other metals.