Cd In Brown Rice Research Articles

Residual effects of sulfur application prior to oilseed rape cultivation on cadmium accumulation in brown rice under an oilseed rape–rice rotation pot experiment

We aimed to investigate how sulfur (S) application prior to oilseed rape cultivation influences the uptake of cadmium (Cd) by rice grown in low- and high-Cd soils. A pot experiment involving four S levels (0, 30, 60, 120 mg S kg−1) combined with two Cd rates (low and high—0.35 and 10.35 mg Cd kg−1, respectively) was conducted. Soil pore water during rice growth and plant tissues at maturity were analyzed. The soil pore water results indicated that S application decreased Cd solubility under submergence due to the S-induced increase of soil pH and the enhancement of sulfide formation in soil micropores. When S was applied at rates of 30, 60 and 120 mg S kg−1, brown rice Cd concentrations decreased by 18%, 18%, and 55% (p < 0.05) in the low-Cd soil but increased by 20%, 40%, and 40% in the high-Cd soil compared with those in the non-S treatment. The different effects of S on Cd accumulation in brown rice were related to Cd-induced oxidative stress in the rice plants. In low-Cd soils, a S-induced increase in phytochelatins in rice roots restricted and inhibited Cd translocation in brown rice. In high-Cd soils, the Cd-induced oxidative stress in rice plants weakened the protective effects of S, while highlighted the promotion of Cd uptake by S. Overall, S fertilizer is recommended for oilseed rape–rice rotations in low-Cd paddy fields. In high Cd-contaminated fields, oilseed rape–rice rotations are suitable for the simultaneous remediation by oilseed rape and production of rice without S fertilization.

Reducing cadmium in rice using metallothionein surface-engineered bacteria WH16-1-MT

Cadmium (Cd) accumulation in rice grains poses a health risk for humans. In this study, a bacterium, Alishewanella sp. WH16-1-MT, was engineered to express metallothionein on the cell surface. Compared with the parental WH16-1 strain, Cd2+ adsorption efficiency of WH16-1-MT in medium was increased from 1.2 to 2.6 mg/kg dry weight. The WH16-1-MT strain was then incubated with rice in moderately Cd-contaminated paddy soil. Compared with WH16-1, inoculation with WH16-1-MT increased plant height, panicle length and thousand-kernel weight, and decreased the levels of ascorbic acid and glutathione and the activity of peroxidase. Compared with WH16-1, WH16-1-MT inoculation significantly reduced the concentrations of Cd in brown rice, husks, roots and shoots by 44.0 %, 45.5 %, 36.1 % and 47.2 %, respectively. Moreover, inoculation with WH16-1-MT reduced the bioavailability of Cd in soil, with the total Cd proportion in oxidizable and residual states increased from 29 % to 32 %. Microbiome analysis demonstrated that the addition of WH16-1-MT did not significantly alter the original bacterial abundance and community structure in soil. These results indicate that WH16-1-MT can be used as a novel microbial treatment approach to reduce Cd in rice grown in moderately Cd-contaminated paddy soil.

Effects of Organic Fertilizers on Cd Activity in Soil and Cd Accumulation in Rice in Three Paddy Soils from Guizhou Province.

A greenhouse pot experiment was conducted to investigate the effects of organic fertilizer application on Cd activity in soil and Cd accumulation in rice in paddy soils with different levels of contamination from varying Cd sources in Guizhou Province (the soil types are NJ, which is a soil with a high geological background of Cd; and QX and JZ, which are anthropogenic Cd-polluted soils). The application of organic fertilizer increased the content of organic matter in the soil and reduced the concentration of acetic acid-extractable Cd in QX and JZ paddy soils. Organic fertilizer increased rice yields and significantly decreased the Cd concentration in brown rice. In the QX and JZ soils, however, the concentration of Cd in brown rice exceeded the allowable maximum levels (MLs) of Cd in China. In contrast, the concentration of Cd in brown rice in NJ soil met the MLs of Cd. Additionally, the average daily dose and the health risk index of Cd in NJ soil were much lower than those in QX and JZ soils. The results indicate that organic fertilizer application is a promising and economic means to control Cd pollution in paddy soil. Moreover, risk assessment shows that the risk of exposure to Cd in the high geological background soil (NJ) was much lower than that in anthropogenically polluted soils (QX and JZ).

Effects of sulfur application on cadmium accumulation in brown rice under wheat-rice rotation

We investigated how sulfur (S) application prior to wheat cultivation under wheat-rice rotation influences the uptake of cadmium (Cd) in rice grown in low- and high-Cd soils. A pot experiment was conducted with four S levels (0, 30, 60, 120 mg S kg−1) and two Cd rates (low and high, 0.35 and 10.35 mg Cd kg−1) supplied to wheat. Part of the wheat straw was returned to the soil before planting rice, which was cultivated for 132 days. To explore the key mechanisms by which S application controlled Cd accumulation in brown rice, (1) soil pore water at the key growth stages was sampled, and dissolved Cd and S species concentrations were determined; (2) rice plant tissues (including iron plaque on the root surface) were sampled at maturity for Cd and S analysis. With increasing S level, Cd accumulation in brown rice peaked at 60 mg S kg−1, irrespective of soil Cd levels. For high-Cd soils, concentrations of Cd in brown rice increased by 57%, 228%, and 100% at 30, 60, and 120 mg S kg−1, respectively, compared with no S treatment. The increase in brown rice Cd by low S levels (0–60 mg kg−1) could be attributed to (1) the S-induced increase in soil pore water sulfate increasing the Cd influx into rice roots and (2) the S-induced increase in leaf S promoting Cd translocation into brown rice. However, brown rice Cd decreased at 120 mg S kg−1 due to (1) low Cd solubility at 120 mg S kg−1 and (2) root and leaf S uptake, which inhibited Cd uptake. Sulfur application to wheat crop increased the risk of Cd accumulation in brown rice. Thus, applying S-containing fertilizers to Cd-contaminated paddy soils is not recommended.

Divergent patterns of heavy metal accumulation in paddy fields affect the dietary safety of rice: a case study in Maoming City, China.

The objective of this work was to study the impact of large petrochemical plants and mining operations on the accumulation of heavy metals in farmland and rice, as well as assess their potential risks on human health. The contents of seven heavy metals, Cd, Pb, Cr, Ni, Co, Cu, and Mn, were monitored in a typical polluted paddy soil-rice system near a petrochemical plant and mining area in Maoming, China. The results showed that the content of Cd in the soil exceeds the standard rate by 100%, and the single factor pollution index of Cd was 5.12, which is considered heavy pollution. Excessive heavy metals can inhibit and poison the growth of rice plants. Rice plants can maintain a certain level of heavy metal content by reducing the absorption or interception in the root cells, leading to great differences in the distribution of different heavy metals in plant tissues. Cadmium, Cu, Co, and Mn are easily absorbed from the soil by rice roots, while other heavy metals are relatively difficult to absorb by rice roots. Cuprum, Cd, Co, Pb, and Cr were mainly accumulated in the root of rice, but Mn and Ni migrate to the above ground plant tissues quickly. The brown rice produced in the paddy fields in the study area was seriously polluted. The concentration of Cd, Pb, and Ni in brown rice exceeded the standard by 100%, and Cr in brown rice also exceeded the standard by 80%. If residents consume rice from the study area, their daily intake of Cr and Cd will be 1.02 and 3.24 times higher, respectively, than the standard limit recommended by the FAO/WHO. The irrigation streams were polluted due to the discharge of petrochemical plants and mining wastewater, causing the serious pollution of heavy metals in the surrounding paddy fields. The rice produced in this area poses a serious risk to consumers, and so this problem of pollution should be addressed.

Effects of Water Management on Cadmium Accumulation by Rice (Oryza sativa L.) Growing in Typical Paddy Soil

In order to explore the effects of water management on the Cd accumulation of rice in paddy soils with different parent materials, a pot experiment with three paddy soils with different parent materials from Hunan Province (granite sandy soil, plate shale soil, and purple sandy shale soil) with different water management treatments ［flooding and alternate wetting and drying (AWD)］ was performed. The soil pH, DTPA-Cd, Fe plaque in the rice roots, and heavy metal concentration in the rice were determined. The results showed that the soil pH of the three paddy soils under the flooding treatment was increased by 0.17-1.33 units. During the filling and maturity periods, compared with that under AWD, the DTPA-Cd concentration in the three paddy soils was reduced by 14.39%-36.56% under the flooding treatment, but the DTPA-Fe concentration was increased by 35.35%-347.25%. In the three growth stages, the Cd and Mn concentrations in the Fe plaque (except for DCB-Fe) were in the order of tillering stage < filling stage < mature stage. Compared with that under AWD, the brown rice Cd concentration in the three soils was reduced by 57.84%-93.79% under flooding treatment. The Cd accumulation in rice was reduced under flooding treatment by reducing the DTPA-Cd via increasing the soil pH and DTPA-Fe and by decreasing the formation of Fe plaque. According to the results of the correlation and SEM analysis, the soil pH and DCB-Cd were the main factors affecting the Cd accumulation in rice grains, although the changes in the DTPA-Cd and DTPA-Fe also impacted the Cd in rice grains. In summary, our study demonstrated that water management had a significant impact on the Cd content in rice, and there were significant differences among the three paddy soils with different parent materials. In conclusion, the Cd content in rice grains was affected by the soil parent material, soil physicochemical properties, and Fe plaque on the surface of the rice roots. The granite sandy soil and plate shale soil with different water management treatments had significant impacts on the contents of heavy metals in rice. Continuous flooding is a valuable strategy for improving soil acidity and alkalinity and minimizing soil available Cd, but the soil parent materials must be considered.

Combined use of lime, bentonite, and biochar for immobilization of Cd and mobilization of Se in paddy soil.

Remediation of soil contaminated with cadmium (Cd) that can produce rice enriched with selenium (Se) is highly significant for improving the public health in China. A key issue needing resolution in this regard is the simultaneous immobilization of Cd and mobilization of Se. To explore a potential promising method to remediate median-high Se soil that is contaminated by Cd, a potted experiment was conducted, and seven combined amendments (0.03-0.12% lime, 0.03-0.18% bentonite, and 0.3-1.2% biochar of the dry soil weight) were used to immobilize Cd in three paddy soils, in which the concentrations of Cd and Se are 0.46 and 0.45 mg/kg, 1.12 and 0.33 mg/kg, and 2.96 and 0.31 mg/kg, respectively. The soil pH increased by 1.5-2 units after the application of the amendments, and the soil organic carbon (SOC) concentration increased notably with the addition of large quantities of biochar. As the pH and SOC concentration increased, the concentrations of the available Cd in the soil decreased by 35-50%, and the FTIR spectrum showed that O-containing groups and Si-O facilitated the Cd immobilization. The concentration of Cd in brown rice decreased with a decrease in the available Cd. There was no apparent correlation between the Se concentration in the brown rice and the concentration of the available Se in the soil, although the available Se increased by 40-80% after the application of amendments. The accumulation of Se in rice grains was regulated by interactions among the lime, bentonite, biochar, and the soil. An SEM-EDS analysis showed that the biochar particles were covered with bentonite and other soil minerals that could postpone biochar aging and contribute to the longevity of the combined amendments in the soil.

Mediation effects of different sulfur forms on solubility, uptake and accumulation of Cd in soil-paddy rice system induced by organic carbon and liming.

Liming is a safe and effective remediation practice for Cd contaminated acid paddy soil. The fate of Cd can also be strongly influenced by redox chemistry of sulfur. But it is unclear if, to what extent and how the combination of liming and sulfur mediation could further control Cd uptake by paddy rice. A rice cultivation pot experiment was conducted to evaluate the impact of different sulfur forms (S0 and SO42- in K2SO4) on the solubility, uptake and accumulation of Cd in the soil-paddy rice system and how liming and reducing organic carbon mediate the process. Results showed that under neutral soil circumstances achieved by liming, co-application of K2SO4 and glucose significantly reduced brown rice Cd by 33%, compared to liming alone. They made it more readily for Cd2+ to be precipitated into CdS/CdS2 or co-precipitate with newly formed FeS/FeS2/iron oxides. The higher pH balancing capability of K2SO4 as well as liming kept the newly formed sulfide or iron containing minerals negatively charged to be more prone to adsorb Cd2+, that kept the porewater Cd2+ the lowest among all the treatments. Individual K2SO4 showed significant promoting effect on soil Cd solubility due to SO42- chelation effect. Furthermore, K2SO4 had much weaker inhibiting effect on Cd translocation from root to grain, it showed no significant attenuating effect on brown rice Cd. S0 containing treatments displayed weaker or no attenuating effect on brown rice Cd due to its strong soil acidification effect. On the basis of liming, organic carbon induced sulfur (K2SO4) mediation showed great application potential for safe production on large areas of acid paddy soil contaminated by Cd.

Polymer-coated manganese fertilizer and its combination with lime reduces cadmium accumulation in brown rice (Oryza sativa L.)

Manganese (Mn) has the potential to reduce cadmium (Cd) uptake by rice; however, the efficiency depends on its soil availability. Therefore, this study designed a slow-release Mn fertilizer by employing a polyacrylate coating. Pot trials were conducted to study the effects of coated-Mn and uncoated-Mn alone or in combination with lime on the dynamics of soil dissolved-Mn and available Cd, and the transportation of Mn and Cd within rice. The results showed that coated-Mn declined the release of Mn until the 7th day of application; however, it consistently supplied more dissolved-Mn than uncoated-Mn. As a result, coated-Mn induced a greater Cd reduction (45.8%) in brown rice than uncoated-Mn (9.7%). The total Cd of rice and its proportion in brown rice were greatly reduced by coated-Mn, indicating the inhibition of root uptake and interior transport of Cd. Additionally, lime addition prominently increased the soil pH and decreased the CaCl2-extractable Cd (90.1–93.9%). However, since lime reduced the soil dissolved-Mn, downregulated the OsHMA3 expression and upregulated the OsNramp5 expression, brown rice Cd was reduced by only 43.0%. The combined addition of lime and coated-Mn alleviated the liming effect on soil Mn and gene expression in roots, thereby reducing brown rice Cd by 71.5%.

Effects of Exogenous Phosphorus on Rice Growth and Cadmium Accumulation and Transportation Under Cadmium Stress

In this study, we investigated the effects of exogenous phosphorus on the accumulation and transportation of cadmium in rice plants through a hydroponic experiment. In the experiment, the rice variety was Huanghuazhan, P solution concentrations were 10.0-45.0 mg ·L-1 that was made using NaH2PO4, and Cd solution concentrations were 0.1 mg ·L-1 and 0.2 mg ·L-1. The results showed that: ① the biomass in all parts of rice plants and contents of photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoid) increased gradually with an increase in exogenous P. ② Content of Cd in rice stems, leaves, husk, and brown rice increased gradually with an increase in the amounts of exogenous P. The content of Cd in brown rice increased by 2.8%-22.8% and 40.9%-61.8% when treated with Cd concentrations of 0.1 mg ·L-1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ③ Cd accumulation in rice plants was accelerated due to the application of exogenous P. Cd accumulating amounts increased from 395.1 μg ·plant-1 to 542.6 μg ·plant-1 and 639.6 μg ·plant-1 to 1082.0 μg ·plant-1 when treated with Cd concentrations of 0.1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ④ With an increase in the applied amounts of exogenous P, the P/Cd quality ratio in rice roots increased, while those in rice stems, leaves, husks, and brown rice decreased; meanwhile, the Cd transfer coefficients from root to stem (TFroot-stem) and stem to leaf (TFstem-leaf) increased. This showed that there was a certain synergistic effect between P and Cd in the rice parts. Finally, the application of exogenous P promoted the transfer of Cd from the rice root to other rice tissues, resulting in a synergistic effect on Cd accumulation and transportation in various rice tissues and increased Cd contents in brown rice.

The critical role of the shoot base in inhibiting cadmium transport from root to shoot in a cadmium-safe rice line (Oryza sativa L.)

Cadmium (Cd) is harmful to rice and human, thus screening and understanding the mechanism of Cd-safe rice lines, which accumulate little Cd in brown rice, is necessary. D62B was screened as a Cd-safe rice line with low Cd translocation from roots to shoots, and there must be a switch restricting Cd transport from roots to shoots. Here we found that shoot base played the role as switch. Cd concentration in the shoot base of D62B was 1.57 times higher compared with a high Cd-accumulating rice line (Wujin4B) and lower Cd translocation under Cd stress. Glutathione (GSH) and phytochelatins (PCs) were important in this process. GSH and PCs concentrations in the shoot bases of D62B were 1.01– 1.83 times higher than Wujin4B as well as the glutathione S-transferase (GST) and phytochelatin synthase (PCS) concentrations, keeping in consistent with up-regulation of the genes OsGST and OsPCS1. PCs synthesis was further promoted by exogenous GSH. Our results prove the role of shoot bases as switch for restricting Cd transport in D62B due to its great potential for GSH and PCs biosynthesis, and thereby Cd chelation. This could be considered a key mechanism for low Cd accumulation in brown rice of the Cd-safe rice line.

Remediation of Cd, Pb and as Co-contaminated Paddy Soil by Applying Different Amendments.

The current study investigated the efficiency of sepiolite (SE), sodium humate (HS), microbial fertilizer (JF) and SE combined with JF/HS in a ratio of 2:1 (w/w) (JF-2SE and HS-2SE) on Cd, Pb and As bioavailability in field trials with rice (Oryza sativa L.). The results showed that all the amendments remarkably decreased (p < 0.05) the contents of available Cd and available Pb in soil. Only JF-2SE treatment reduced available As concentration in soil. All the amendments were found to effectively reduce (p < 0.05) the contents of As in brown rice. Both JF-2SE and HS-2SE co-applications reduced the concentrations of Cd in brown rice to 0.108 and 0.135mg kg-1, and that of Pb reduced to 0.2 and 0.175mg kg-1, which met the national standard limit of China. Thus, the co-application of JF/HS-2SE can be a promising remediation strategy in Cd, Pb and As co-contaminated paddy soil.

Watering techniques and zero-valent iron biochar pH effects on As and Cd concentrations in rice rhizosphere soils, tissues and yield

Zero-valent iron amended biochar (ZVIB) has been proposed as a promising material in immobilizing heavy metals in paddy fields. In this study, the impacts of pH of ZVIB (pH 6.3 and pH 9.7) and watering management techniques (watering amount in the order of CON (control, 5/72)>3/72>1–3/72>3/100>1/72, with 5/72, for example, representing irrigation given to 5 cm above soil surface in 72 hr regular interval) on As and Cd bioavailability for rice and its grain yield (YieldBR) were investigated in a pot experiment. Brown rice As (AsBR) content was irrelative to the watering treatments, while significantly decreased (>50%) with the addition of both ZVIB materials. The diminutions of brown rice Cd (CdBR) content as well as the YieldBR were highly dependent on both the soil amendment materials’ pH and watering amount. Among all the watering treatments, 3/72 treatment (15% less irrigation water than the CON) with ZVIB 6.3 amendment was the optimum fit for simultaneous reduction of AsBR (50%) and CdBR contents (19%) as well as for significant increment (12%) of the YieldBR. Although high pH (9.7) ZVIB application could also efficiently decrease As and Cd contents in brown rice, it might risk grain yield lost if appropriate (e.g. 3/72 in our study) watering management technique was not chosen. Therefore, ZVIB would be an environmentally friendly option as an amendment material with proper selection of watering management technique to utilize As and Cd co-contaminated arable soils safely for paddy cultivation.

Mitigation of Cd accumulation in rice with water management and calcium-magnesium phosphate fertilizer in field environment.

Pollution of Cd has seriously threatened environmental safety and human health. The field experiment was conducted to investigate the effects of calcium-magnesium phosphate fertilizer and water management on bioavailability of Cd in soils and its accumulation in rice. The results revealed that continuous flooding has enhanced soil pH from 5.10 to 5.72 and reduced soil redox potential (Eh) from 164 to - 60mV. Application of calcium-magnesium phosphate fertilizer has significantly raised soil pH from 5.10 to 6.45 (P < 0.05). The treatment of calcium-magnesium phosphate fertilizer and continuous flooding has reduced available content of Cd in soils by 28.57%. The content of Cd in brown rice was significantly diminished by 51.36% (P < 0.05). The continuous flooding has promoted formation of residual Cd in soil with application of calcium-magnesium phosphate fertilizer. The biomass and grain production of rice was not significantly decreased compared with control.

Combining biochar and zerovalent iron (BZVI) as a paddy field soil amendment for heavy cadmium (Cd) contamination decreases Cd but increases zinc and iron concentrations in rice grains: a field-scale evaluation

Consuming rice grown in contaminated soil that has an elevated level of cadmium (Cd) is a health risk. This study revealed that using a combination of biochar and zerovalent iron (BZVI) reduces the concentration of Cd and enhances that of the essential elements zinc (Zn) and iron (Fe) in rice. The Cd concentration in brown rice grain cultivated in an untreated paddy was 0.84 ± 0.20 mg kg−1, double the acceptable level (0.4 mg kg−1). Soil amendment with BZVI successfully decreased Cd in brown rice by 83 % compared to the untreated field presumably due to the Cd sorption on biochar (BC) and enhanced ZVI corrosion by-products while ZVI and BC alone achieved only 40 % and 74 % reduction, respectively. Moreover, while using ZVI or BC alone decreased Fe in rice grain by 8–14 %, BZVI enhanced the Fe concentrations in rice grain by 11 % because of Fe2+/Fe3+ release from BC-enhanced ZVI corrosion. Similarly, the presence of BC in BZVI enhanced Zn accumulation in rice grain by 8% due to competitive sorption of Cd2+ on BZVI, which may desorb Zn2+, promoting Zn translocation to rice. Using ZVI alone decreased Zn in rice by 19 %.

Reduction of Soil Cadmium Activity and Rice Cadmium Content by 4-year-consecutive Application of Organic Fertilizer

Because commercial organic fertilizers may contain cadmium (Cd) and may cause the dual effect of "inhibition" and "activation" on Cd availability in paddy soil with organic fertilizer input, the reduction of rice Cd following organic fertilizer application is still uncertain. Herewith, typical purple mud paddy fields were selected in the eastern Hunan Province. The effect of commercial organic fertilizer input on Cd reduction of double-rice paddy ecosystem was monitored for four consecutive years. The relationships between brown rice Cd content, soil available Cd, and soil factors (pH, soil labile organic carbon fractions, and iron oxide) at different growth stages in double-rice paddy fields were investigated. Results showed that the input of organic fertilizer reduced the Cd content in brown rice by 28%-56%. Meanwhile, the decrease of Cd content in brown rice of late rice (43%-56%) was higher than that of early rice (28%-45%), and the inter-annual fluctuation of the decrease was relatively small. On the one hand, soil available Cd content decreased by 6%-7% during several growth stages of double-rice (from tillering peak stage to full heading stage) with organic fertilizer input. Additionally, the content of soil exchangeable Cd was decreased by 11%, whereas the content of organic bound Cd was increased by 14%. This directly reflects the decrease of soil Cd availability. On the other hand, the soil pH value was steadily increased by 0.1-0.3 units following organic fertilizer input, which promoted the development of soil from acidity to slight acidity. Besides, the content of soil active organic carbon (light fraction organic carbon, coarse particulate organic carbon, and fine particulate organic carbon) was increased significantly (53%, 77%, and 107%, respectively). This indirectly reflects the decrease in soil Cd availability. This study implies that the decrease of soil Cd availability may be the primary driving force for the reduction of rice Cd content with consecutive organic fertilizer input in purple mud paddy fields.

Health risk assessment of Cd pollution in irrigated paddy field system: A field investigation in Hunan Province, China

Paddy crops cadmium (Cd) pollution has received widespread attention. Here, we assessed levels of Cd and organic matter fractions in sediments and paddy system of 19 paddy fields that were located 20 km away from an irrigation water source in central Hunan Province, China, to determine pollution risks of Cd to human health. With the exception of a single study site, levels of Cd in irrigation water met national irrigation water quality standards (GB5084-2005). In contrast, average Cd content in paddy soil and brown rice (0.625 and 0.567 mg kg−1, respectively) was 1.6 and 2.8 times higher than levels permitted by national standards for soils (GB15618-2018) and food safety (GB2762-2017), respectively. Dominant speciated Cd in sediments included extractable, oxidizable, and reducible Cd that accounted for 84.96% of total sediment Cd content. The average carbon content of humus was 18.906 g kg−1. Fulvic acid content of humus was positively correlated with reducible and oxidizable Cd content. Cd pollution in paddy fields was great and risks of Cd in brown rice to human health were high. Risk assessment can provide reasonable suggestions for human diets and provide new ideas for the prevention and control of soil Cd pollution.

Foliage application of selenium and silicon nanoparticles alleviates Cd and Pb toxicity in rice (Oryza sativa L.)

Direct discharge of untreated industrial waste water in water bodies and then irrigation from these sources has increased trace metals contamination in paddy fields of southern China. Among trace metals, cadmium (Cd) and lead (Pb) are classified as most harmful contaminants in farmland to many organisms including plants, animals and humans. Rice is a staple food which is consumed by half population of the world; due to longer growth period it can easily absorb and accumulate the trace metals from soil. The objective of study was to check the efficacy of Se and Si NPs (nanoparticles) alone or in combination on metals accumulation and Se-fortified rice (Oryzasativa L.) production as their efficiency remained untested. Alone as well as combined application of Se- and Si-NPs (5, 10 and 20 mg L−1) was achieved along with CK. All the treatments significantly reduced the Cd and Pb contents in brown rice, except CK, Se3, Si1 and Se1Si3. Combined application of Se and Si (Se3Si2) was more effective in reducing the Cd and Pb contents by 62 and 52%, respectively. In addition, foliar application of both NPs improved the rice growth and quality by increasing the grain yield, rice biomass, and Se contents in brown rice. Highest concentration of Se (1.35 mg kg−1) in brown rice was observed with combined application of Se- and Si-Nps (Se3Si2). Selenium speciation revealed the presence of organic species (74%) in brown rice. The combinations of different doses of Se- and Si-Nps are the main determining factor for total concentration of metals in grains. These results demonstrate that foliage supplementation of Se and Si-Nps alleviate the Cd and Pb toxicity by reducing the metals' concentration in brown rice. Additionally foliage supplementation improved the nutritional quality by reducing the phytic acid contents in rice grains.

Prediction models for rice cadmium accumulation in Chinese paddy fields and the implications in deducing soil thresholds based on food safety standards

Deducing soil cadmium (Cd) safety thresholds should be different for rice cultivars with different capacities to accumulate Cd to guarantee safe rice production in China. This study developed prediction models based on soil properties and deduced soil safety thresholds for Cd translocation from thirty-three paddy soils by two contrasting rice cultivars, Yelicanghua (high Cd accumulator, HCd) and Longhuamaohu (low Cd accumulator, LCd). A total of 330 paired field validation samples were used to examine the accuracy of prediction models and soil safety thresholds. The average soil Cd concentration was 0.26 (range 0.057–0.72) mg kg−1. The average brown rice Cd concentrations were 0.14 (0.043–0.55) mg kg−1 in HCd and 0.024 (0.007–0.15) mg kg−1 in LCd in 2017, with corresponding values of 0.16 (0.016–0.66) and 0.027 (0.009–0.10) mg kg−1 in 2018. Soil total Cd and pH were the two most important variables exhibiting direct effects on Cd concentrations in HCd, explaining 66% of the variance across the 33 soils. Soil total Cd, pH and organic carbon (OC) were the three most important variables in LCd, explaining 75% of the variance. Soil safety thresholds ranged from 0.27 to 1.00 mg kg−1 for HCd and from 4.52 to 46.9 mg kg−1 for LCd with pH ranging from 4.5 to 8.0. The validation results suggest ∼60% for HCd or the current soil quality standard (SQS) and 88% for LCd of the validation samples were suitable to meet the food quality standard (FQS), with 6.4% and 12%, respectively, of the validation soils unsuitable for rice cultivation. The current Chinese SQS is too strict for LCd which may be grown safely in moderately polluted soils and the derivation of soil thresholds should therefore consider the abilities of different cultivars to accumulate Cd.

Effect of RM-based-passivator for the remediation of two kinds of Cd polluted paddy soils and mechanism of Cd(II) adsorption

ABSTRACT This study aimed to investigate the effects of red mud-based-passivator (RM-based-passivator) on rice yield, cadmium (Cd) in brown rice, pH and available Cd in Cd-polluted soil by pot experiments, and to explore the adsorption mechanism of the passivator by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis. The results showed that this passivator obviously improved the pH, reduced the available Cd in soil and the Cd content in brown rice in Changsha Cd polluted soil (CS soil), while had little effect on Hengyang Cd polluted soil (HY soil). Compared with the control, the soil pH increased in the range from 0.31 to 1.37, the available Cd in soil decreased in the range from 13.25% to 52.34%, and the total Cd in brown rice decreased in the range from 46.44% to 84.98% in CS soil. Considering the impacts of RM-based-passivator on the growth of rice, the Cd content in brown rice, and the pH and available Cd in soil, 0.10–0.30% (w/w) of the passivator is recommended to apply in CS soil but not in HY soil. Based on the analysis of SEM, EDX, FTIR and XRD, the mechanism of Cd(II) adsorption by RM-based-passivator included physical adsorption, surface complexation and ion exchange. The present results indicated that the appropriate addition of RM-based-passivator could be an effective strategy for the remediation of acidic Cd-polluted soils.