Cd In Brown Rice Research Articles

Cadmium accumulation characteristics of low-cadmium rice (Oryza sativa L.) line and F1 hybrids grown in cadmium-contaminated soils.

Cadmium (Cd) pollution has threatened severely to food safety and human health. A pot experiment and a field experiment were conducted to investigate the difference of Cd accumulation between rice (Oryza sativa L.) lines and F1 hybrids in Cd-contaminated soils. The adverse effect on biomass of rice lines was greater than that of F1 hybrids under Cd treatments in the pot experiment. The variations of Cd concentration among rice cultivars in different organs were smaller in stem and leaf, but larger in root and ear. Average proportion of Cd in root of F1 hybrids was 1.39, 1.39, and 1.16 times higher than those of rice lines at the treatment of 1, 2, and 4mg Cdkg-1 soil, respectively. Cd concentrations in ear of F1 hybrids were significantly lower than rice lines with the reduction from 29.24 to 50.59%. Cd concentrations in brown rice of all F1 hybrids were less than 0.2mgkg-1 at 1mg Cdkg-1 soil, in which Lu98A/YaHui2816, 5406A/YaHui2816, and C268A/YaHui2816 could be screened out as cadmium-safe cultivars (CSCs) for being safe even at 2mg Cdkg-1 soil. C268A/YaHui2816 showed the lowest Cd concentration in root among F1 hybrids, while Lu98A/YaHui2816 and 5406A/YaHui2816 showed lower capability of Cd translocation from root to shoot under Cd exposure, which eventually caused the lower Cd accumulation in brown rice. The lower level of Cd translocation contributed to reducing the accumulation of Cd in brown rice had been validated by the field experiment. Thus, Lu98A/YaHui2816, 5406A/YaHui2816, and C268A/YaHui2816 could be considered as potential CSCs to cultivate in Cd-contaminated soils (<2mg Cdkg-1 soil).

Determination of Bioconcentration Factor of Heavy Metal (loid)s in Rice Grown on Soils Vulnerable to Heavy Metal (loid)s Contamination

There is an increasing concern over heavy metal (loid) contamination of soil in agricultural areas including paddy soils. This study was conducted to determine the bioconcentration factor (BCF) for heavy metal (loid)s to brown rice grown in paddy soils vulnerable to heavy metal (loid)s contamination, for the quantitative health risk assessment to the residents living nearby the metal contaminated regions. The samples were collected from 98 sites nationwide in the year 2015. The mean and range BCF values of As, Cd, Cu, Ni, Pb, and Zn in brown rice were 0.027 (0.001 ~ 0.224), 0.143 (0.001 ~ 2.434), 0.165 (0.039 ~ 0.819), 0.028 (0.005 ~ 0.187), 0.006 (0.001 ~ 0.048), and 0.355 (0.113 ~ 1.263), respectively, with Zn showing the highest. Even though the relationship between heavy metal (loid) contents in the vulnerable soils and metal contents in brown rice collected at the same fields was not significantly correlated, the relationship between log contents of heavy metal(loid)s in the vulnerable soils and BCF of brown rice wes significantly correlated with As, Cd, Cu, and Zn in rice. In conclusion, soil environmental risk assessment for crop uptake should consider the bioconcentration factor calculated using both the initial and vulnerable heavy metal (loid) contents in the required soil and the crop cultivated in the same fields.Correlation coefficients between log contents of As (A) and Cd (B) in the vulnerable paddy fields by arsenic contamination and bioconcentration factors of brown rice collected at the same fields.

Genotypic and Environmental Variations in Grain Cadmium and Arsenic Concentrations Among a Panel of High Yielding Rice Cultivars

BackgroundRice is a major dietary source of cadmium (Cd) and arsenic (As) for populations consuming rice as the staple food. Excessive Cd and As accumulation in rice grain is of great concern worldwide, especially in South China where soil contamination with heavy metals and metalloids is widespread. It is important to reduce Cd and As accumulation in rice grain through selection and breeding of cultivars accumulating low levels of Cd or As.ResultsTo assess the genetic and environmental variations in the concentrations of Cd and As in rice grains, 471 locally adapted high-yielding rice cultivars were grown at three moderately contaminated sites in South China for two years. Cadmium and As concentrations in brown rice varied by 10 – 32 and 2.5 – 4 fold, respectively. Genotype (G), environment (E) and G x E interactions were highly significant factors explaining the variations. Brown rice Cd concentration was found to correlate positively with the heading date among different cultivars, whereas As concentration and heading date correlated negatively. There was a significant and negative correlation between grain Cd and As concentrations.ConclusionsEight and 6 rice cultivars were identified as stable low accumulators of Cd and As, respectively, based on the multiple site and season trials. These cultivars are likely to be compliant with the grain Cd or As limits of the Chinese Food Safety Standards when grown in moderately contaminated paddy soils in South China.

Use of clay to remediate cadmium contaminated soil under different water management regimes

We examined in situ remediation of sepiolite on cadmium-polluted soils with diverse water regimes, and several variables including brown rice Cd, exchangeable Cd, pH, and available Fe/P. pH, available Fe/P in soils increased gradually during continuous flooding, which contributed to Cd absorption on colloids. In control group (untreated soils), compared to conventional irrigation, brown rice Cd in continuous flooding reduced by 37.9%, and that in wetting irrigation increased by 31.0% (p<0.05). In contrast to corresponding controls, brown rice Cd in sepiolite treated soils reduced by 44.4%, 34.5% and 36.8% under continuous flooding, conventional irrigation and wetting irrigation (p<0.05), and exchangeable Cd in amended soils reduced by 27.5–49.0%, 14.3–40.5%, and 24.9–32.8% under three water management regimes (p<0.05). Compared to corresponding controls, decreasing amplitudes of exchangeable Cd and brown rice Cd in sepiolite treated soils were higher in continuous flooding than in conventional irrigation and wetting irrigation. Continuous flooding management promoted soil Cd immobilization by sepiolite.

Immobilization remediation of Cd-polluted soil with different water condition

To demonstrate effects of water management on soil Cd immobilization using palygorskite, the investigation evaluated impacts of palygorskite on uptake of Cd present in soils with different water condition by rice plant. Pot experiment results showed that, pH, available Fe and P in untreated soils were higher in continuous flooding than in traditional irrigation and wetting irrigation, which were reasons for lower soil exchangeable Cd and plant Cd in continuous flooding. In control group (untreated soils), compared to traditional irrigation, continuous flooding reduced brown rice Cd by 37.9%, that in wetting irrigation increased by 31.0%. At palygorskite concentrations of 5 g kg−1, 10 g kg−1 and 15 g kg−1, brown rice Cd reduced by 16.7%, 44.4% and 55.6% under continuous flooding, 13.8%, 34.5% and 44.8% under traditional irrigation, 13.1%, 36.8% and 47.3% under wetting irrigation (p < 0.05). At the same palygorskite addition, decreasing amplitude of brown rice Cd was higher in continuous flooding than in traditional irrigation and wetting irrigation. Competition for adsorption sites in root coating between Cd2+ and Fe2+ was another factor governing plant Cd. In control group, compared to traditional irrigation, root coating Fe(II) increased by 124.5% and root coating Cd reduced by 17.6% upon continuous flooding (p < 0.05). In conclusion, palygorskite addition combined with continuous flooding was an efficacious technique to stabilize Cd in paddy soils.

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.

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.

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.

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.

In Situ Field-Scale Remediation of Low Cd-Contaminated Paddy Soil Using Soil Amendments

At present, the remediation of heavy-metal-polluted cropland soil is a considerable problem. In this study, in situ immobilization field experiment was conducted by planting rice (Oryza sativa L.) in low Cd-contaminated paddy soil to determine the optimal soil amendment that would reduce the accumulation of Cd in brown rice. GL (main component is alkaline residue), FG (main components are Si and Ca), and SH (main component is lime) were utilized as amendments. The remediation effects of the amendments on the soil and rice were investigated, and the potential mechanisms of reducing Cd availability to rice were analyzed. Amendment application significantly increased the soil pH value, reduced the DTPA-extractable Cd concentrations, and shifted Cd species from the exchangeable Cd fractions to the carbonate-bound, Fe-Mn oxides and residual fractions in paddy soil. For the plant, amendment application apparently increased the concentrations of Ca in rice plants, which could compete with Cd in root uptake. Besides, amendment application also effectively restricted the translocation of Cd from roots to shoots and consequently led to a notable decrease of Cd concentration in brown rice. These results demonstrated that the FG ameliorant could be effective in reducing Cd bioavailability and accumulation in rice grown on low Cd-contaminated paddy soils.

Heavy Metal(loid) Levels in Paddy Soils and Brown Rice in Korea

There is an increasing concern over heavy metal(loid) contamination of soil in agricultural areas including paddy soils. This study was conducted to monitor the background levels of heavy metal(loid)s, arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn) in major rice growing soils and its accumulation in brown rice in Korea. The samples were collected from 82 sites nationwide in the year 2012. The mean and range values of As, Cd, Cu, Hg, Ni, Pb, and Zn in paddy soils were 4.41 (0.16-18.9), 0.25(0.04-0.82), 13.24 (3.46-27.8), 0.047 (0.01-0.20), 13.60 (3.78-35.0), 21.31 (8.47-36.7), and 54.10 (19.19-103.0) mg kg-1, respectively. This result indicated that the heavy metal(loid) levels in all sampled paddy soils are within the permissible limits of the Korean Soil Environment Conservation Act. The mean and range values of As, Cd, Cu, Hg, Ni, Pb, and Zn in brown rice were 0.146 (0.04-0.38), 0.024 (0.003-0.141), 4.27(1.26-16.98), 0.0024 (0.001-0.008), 0.345 (0.04-2.77), 0.113 (0.04-0.197), and 22.64 (14.1-35.1) mg kg -1 , respectively. The mean and range BCF (bioconcentration factor) values of As, Cd, Cu, Hg, Ni, Pb, and Zn in brown rice were 0.101 (0.01-0.91), 0.121 (0.01-0.70), 0.399 (0.05-2.60), 0.061 (0.016-0.180), 0.033 (0.004-0.44), 0.005 (0.003-0.013), and 0.473 (0.19-1.07), respectively, with Zn showing the highest. The results show that the levels of all metal(loid)s in all sampled brown rice are generally within the acceptable limit for human consumption.

Transfer Characteristics of Cd in Paddy Soil-Rice System under Field Condition

It is important to control Cadmium (Cd) content in rice and ensure the grain security. The transfer characteristics of Cd in paddy soil-rice system between different soil types (red soil and purple soil) under field condition were researched to provide a theoretical basis for Cd environmental management in paddy. In this study, many rice plant samples and corresponding paddy soil samples were collected from fields around the industrial and mining area in central Hunan province in 2011 and 2012. The Cd concentration of samples was analyzed, and the degree of Cd contamination was evaluated. Moreover, the differences of enrichment factor and influencing factors in paddy soil-rice system between red soil and purple soil were discussed. The results revealed that paddy soils and brown rice in the survey area were serious contaminated by Cd. The Cd content and enrichment factor were arranged in the order of root&gt; straw &gt;chaff &gt;brown rice. The Cd content and enrichment factor were in the order of red soil &gt;purple soil. In addition, multivariate linear regression was analyzed and predictions models of Cd concentration of brown rice are based on different types of soil were worked out. It showed that total Cd of soil, organic matter and clay were the main factors that affecting the content of Cd in brown rice. In conclusion, the contamination characteristics, transfer disciplinarian and influencing factors of Cd in the soil-rice system are different between red soil and purple soil. So it needs to pay more attention to the characteristics of different soil parent material when making environmental management related to Cd contamination in soil-rice system.

Cadmium Exposure in General Populations in Japan: a Review

Cadmium (Cd) intake via diet (Cd-D) has been a long-standing focus of administrative as well as public concern in Japan after the endemic of Itai-itai disease (chronic cadmium poisoning). The aim of this report was to review cadmium exposure in Japan by introducing publications from our study group and related articles. Literature survey disclosed that Cd-D was high (up to 100 µg/day) in 1960s even in non-polluted areas. Such high Cd-D levels were followed by gradual decreases in 1970s-1980s to current level of well below 20 µg/day. Once, a very high Cd-D (600 µg/day) was reported for a Cd-polluted area. Replacement of Cd-polluted rice paddy soil with clean soil resulted in substantial reduction in rice-associated Cd-D. In large-scale surveys in 10 prefectures all over Japan conducted early in 2000s, the geometric mean (GM) of Cd-Ucr (Cd in urine as corrected for creatinine concentration) was 1.26 µg/g cr, but was higher in one north-west sea coast prefecture in Honshu Island (>3 µg/g cr). Supplemental survey in 6 neighboring prefectures on the sea coast disclosed that Cd-Ucr in some prefectures were higher as compared with the national average. It was reported that Cd in brown rice was also high. However no clear-cut indication was detected to suggest renal tubular dysfunctions. Surveys in major cities in East and South-East Asia in 1980s-1990s made it clear that Cd-D was substantially lower there than in Japanese cities; Cd exposure of general populations was almost exclusively from foods. Statistical analysis revealed that tubular dysfunction markers increased sharply when Cd-Ucr exceeded 10–12 µg/g cr. The Cd-Ucr level of 11 µg/g cr corresponded to Cd-D level of 59 µg/day. This level was in agreement with the tolerable weekly intake of 7 µg/kg body weight/week, the value recommended by the Food Safety Commission of Japan.

Immobilization of Cd in paddy soil using moisture management and amendment.

To offer scientific data support for remediation of Cd-contaminated paddy soils under reasonable water condition, pot experiment was conducted to study the effects of moisture management and amendments on Cd immobilization in a paddy soil. Application of biochar combined with organic fertilizer reduced the exchangeable Cd by 20.4, 15.7, and 13.0% and brown rice Cd by 43.8, 35.5, and 42.1% under continuous flooding, conventional irrigation, and wetting irrigation, respectively, compared to the controls. Under no amendments, the content of Fe(II) in root coating in the continuous flooding treatment was 2.3 and 3.6 times of that in the conventional and wetting irrigation treatments, but Cd in root coating in the continuous flooding treatment was only 82.6 and 73.8% of that in the conventional and wetting irrigation treatments. Applying amendments increased the Fe(II) in root coating by 27.3, 59.1, and 65.0% but reduced the Cd in root coating by 33.6, 26.5, and 25.1% under continuous flooding, conventional irrigation, and wetting irrigation, respectively. The lower bioavailability of Cd in paddy soil and the competition for adsorption sites in root coating of rice plant between Cd(2+) and Fe(2+) reduced from bivalent ions jointly caused the lower brown rice Cd in amended soils.

Influence of Rapeseed Cake on Heavy Metal Uptake by a Subsequent Rice Crop After Phytoextraction Using Sedum plumbizincicola

A glasshouse pot experiment was conducted to study the effects of phytoextraction by Sedum plumbizincicola and application of rapeseed cake (RSC) on heavy metal accumulation by a subsequent rice (Oryza sativa L.) crop in a contaminated paddy soil collected from east China. After phytoextraction by S. plumbizincicola the soil and brown rice Cd concentrations effectively declined. After phytoextraction, RSC application reduced brown rice Cd concentrations in the subsequent rice crop to 0.23–0.28 mg kg−1, almost down to the standard limit (0.2 mg kg−1). After phytoextraction and then application of RSC, the soil solution pH, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations increased during early stages of rice growth resulting directly and indirectly in lowering the bioavailability of the heavy metals. Thus the grain yield of the subsequent rice crop increased and the heavy metals in the brown rice declined significantly. In this contaminated acid soil, growing the hyperaccumulator S. plumbizincicola and rice in rotation together with RSC application may therefore be regarded as a viable strategy for safe grain production and bioremediation.

In situ field-scale remediation of Cd polluted paddy soil using sepiolite and palygorskite

At present, the remediation of heavy-metal polluted soil is a considerable problem. In this study, in situ immobilization field experiments were conducted by planting rice (Oryza sativa L.) in Cd contaminated paddy soil to determine the optimal remediation mode that would reduce the accumulation of Cd in brown grain. Sepiolite and palygorskite were utilized as amendments, while ordinary and low Cd-accumulating rice cultivars were selected as model plants. The remediation effects of the amendments on the soil and rice were investigated and the potential immobilization mechanisms were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy. The application of sepiolite and palygorskite was found to increase the pH value of the paddy soil, by varying amounts, and significantly reduce the HCl, TCLP, CaCl2, and NH4OAc-extractable Cd concentrations resulting in a notable decrease in the Cd concentration in brown rice. Both sepiolite and palygorskite were found to reduce exchangeable Cd concentrations and increase the carbonate-bound and residual fractions in paddy soil. Precipitation of Cd as carbonates or hydroxides and surface complexation were the main immobilization mechanisms for sepiolite and palygorskite. The concentration of Cd in brown rice of the low Cd-accumulating cultivar from the control plot was 0.72mg·kg−1. Sepiolite treatment reduced the value to 0.18mg·kg−1 below the maximum levels reported by Codex Stan 193-1995 and the national standard of China. It was concluded that chemical immobilization combined with crop cultivar selection could be a suitable proposal for crop safety regulation and sustainable agriculture.

Effects of combined amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on contaminated paddy soil

Stabilization of heavy metals in situ was investigated. Two combined amendments (LS, limestone+sepiolite; HZ, hydroxyhistidine+zeolite) were applied at ratios of 0.2%, 0.4%, and 0.8% (w/w) to paddy soil with multi-metal (Pb, Cd, Cu, and Zn) contamination. The effects of these two combined amendments on heavy metal bioavailability in soil, and on uptake and accumulation of heavy metals in rice plants were investigated. Application of LS and HZ significantly increased soil pH values and cation exchange capacity contents, and resulted in a reduction in exchangeable fraction of metals and in extract metal concentrations of amended soils through toxicity characteristic leaching procedure (TCLP). LS and HZ obviously inhibited uptake and accumulation of Pb, Cd, Cu, and Zn in rice plants. Compared with the control soil, concentrations of Pb, Cd, Cu, and Zn in brown rice were decreased by 10.6–31.8%, 16.7–25.5%, 11.5–22.1%, and 11.7–16.3%, respectively, as a result of 0.2% to 0.8% addition of LS, and decreased by 5.1–40.8%, 16.7–20.0%, 8.1–16.2%, and 13.3–21.7%, respectively, as a result of 0.2–0.8% addition of HZ. Significant positive linear correlations were found between heavy metal concentrations in TCLP extracts and those in rice tissues except for Pb. Extracting heavy metals with TCLP was a more suitable method for estimating heavy metal bioavailability concentrations of amended soil than exchangeable fraction of heavy metals, because the latter underestimated heavy metal bioavailability. These results demonstrate that LS and HZ could be effective in reducing heavy metal bioavailability and accumulation in rice grown on multi-metal-contaminated soils.

Water management affects arsenic and cadmium accumulation in different rice cultivars

Paddy rice (Oryza sativa L.) is a staple food and one of the major sources of dietary arsenic (As) and cadmium (Cd) in Asia. A field experiment was conducted to investigate the effects of four water management regimes (aerobic, intermittent irrigation, conventional irrigation and flooding) on As and Cd accumulation in seven major rice cultivars grown in Zhejiang province, east China. With increasing irrigation from aerobic to flooded conditions, the soil HCl-extractable As concentrations increased significantly and the HCl-extractable Cd concentrations decreased significantly. These trends were consistent with the As and Cd concentrations in the straw, husk and brown rice. Water management both before and after the full tillering stage affected As and Cd accumulation in the grains. The intermittent and conventional treatments produced higher grain yields than the aerobic and flooded treatments. Cd concentrations in brown rice varied 13.1-40.8 times and As varied 1.75-8.80 times among the four water management regimes. Cd and As accumulation in brown rice varied among the rice cultivars, with Guodao 6 (GD6) was a low Cd but high-As-accumulating cultivar while Indonesia (IR) and Yongyou 9 (YY9) were low As but high-Cd-accumulating cultivars. Brown rice Cd and As concentrations in the 7 cultivars were significantly negatively correlated. The results indicate that As and Cd accumulated in rice grains with opposite trends that were influenced by both water management and rice cultivar. Production of 'safe' rice with respect to As and Cd might be possible by balancing water management and rice cultivar according to the severity of soil pollution.

Effect of water management on cadmium and arsenic accumulation by rice (Oryza sativa L.) with different metal accumulation capacities

Water management affects the bioavailability of cadmium (Cd) and arsenic (As) in the soil and hence their accumulation in rice grains and grain yields. However, Cd and As show opposite responses to soil water content, but information, particularly on irrigation, is missing on a field scale. The purpose of the present study was therefore to find a water management regime that can lower accumulation of both Cd and As in grain without yield loss. Two rice (Oryza sativa L.) cultivars, A16 and A159, with different grain Cd accumulation capacities were employed in field plot experiments with four water management regimes comprising aerobic, intermittent, conventional practice and flooded. The dynamics of Cd and As bioavailability in the soil and Cd and As concentrations in roots, straw and grains were determined at the early tillering, full tillering, panicle initiation, filling and maturity stages of crop growth. The lower water content regimes (aerobic and intermittent) mostly led to higher soil HCl-extractable Cd than the higher soil water content regimes (conventional and flooded). HCl-extractable As in contrast was favoured by the higher soil water content treatments. Conventional and flooded irrigation accordingly gave higher plant As concentrations but lower Cd compared to aerobic and intermittent irrigation. Cd concentrations in roots and straw of both varieties increased with growth stage, especially in aerobic and intermittent regimes, while As concentrations in plants showed little change or a slight decrease. As the water irrigation volume increased from aerobic to flooded, brown rice Cd decreased from 1.15 to 0.02 mg kg(-1) in cultivar A16 and from 1.60 to 0.05 mg kg(-1) in cultivar A159, whereas brown rice As increased. Aerobic and flooded treatments produced approximately 10-20 % lower grain yields than intermittent and conventional treatments. Cultivars with low Cd accumulation capacity show higher brown rice grain As than those with high Cd uptake capacity. Of the four water management regimes, the conventional irrigation method (flooding maintained until full tillering followed by intermittent irrigation) ensured high yield with low Cd and As in the brown rice and so remains the recommended irrigation regime.

Identification of rice cultivars with low brown rice mixed cadmium and lead contents and their interactions with the micronutrients iron, zinc, nickel and manganese

Paddy fields in mining areas are usually co-contaminated by a cocktail of mixed toxic heavy metals (e.g., Cd and Pb in Pb/Zn mines). However, previous studies on rice cultivars screened for effective metal exclusion have mostly focused on individual metals, and have been conducted under pot-trial or hydroponic solution conditions. This study identified rice cultivars with both low Cd and Pb accumulation under Cd- and Pb-contaminated field conditions, and the interactions of the toxic elements Cd and Pb with the micronutrient elements Fe, Zn, Mn and Ni were also studied. Among 32 rice cultivars tested, there were significant differences in Cd (0.06–0.59 mg/kg) and Pb (0.25–3.15 mg/kg) levels in their brown rice, and similar results were also found for the micronutrient elements. Significant decreases in concentrations of Fe and Mn were detected with increasing Cd concentrations and a significant elevation in Fe, Mn and Ni with increasing Pb concentrations. A similar result was also shown by Cd and Ni. Three cultivars were identified with a combination of low brown rice Cd and Pb, high micronutrient and grain yield (Wufengyou 2168, Tianyou 196 and Guinongzhan). Present results suggest that it is possible to breed rice cultivars with low mixed toxic element (Cd, Pb) and high micronutrient contents along with high grain yields, thus ensuring food safety and quality.