Heavy Metal Accumulation In Rice Research Articles

Soil Heavy Metal Absorption Potential of Azolla pinnata and Lemna gibba with Arbuscular Mycorrhizal Fungi in Rice (Oryza sativa L.) Farming

This study assessed the potential uptake of soil-contaminated heavy metals by Azolla pinnata and Lemna gibba in combination with and without arbuscular mycorrhizal fungi (AMF) in traditional and improved rice varieties. Total levels of cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As) in soil, rice roots, shoots, grains, A. pinnata, and L. gibba were estimated using ICP-MS. The percentage colonization in AMF-inoculated and AMF-uninoculated rice varied from 1.13–30.67% and 1.33–5.42%, respectively. These findings suggested that AMF provide protection to rice plants against the combined toxicity of Cd, As, Pb, and Hg in rice field soil. The combined interaction of AMF, organic fertilizer, and A. pinnata decreased heavy metal accumulation in rice roots, shoots, and grains in both tested varieties. The intake and subsequent accumulation of Cd, As, Pb, and Hg in the rice grains differed significantly (p < 0.05) between the two rice varieties. Furthermore, it was revealed that the AMF-inoculated rice plants reduced the translocation of heavy metals from root to shoot. Therefore, it can be concluded that heavy metal absorption and accumulation in rice can be reduced by the application of AMF, organic fertilizer, and A. pinnata together in rice farming.

Heavy Metal Accumulation in Rice and Aquatic Plants Used as Human Food: A General Review.

Aquatic ecosystems are contaminated with heavy metals by natural and anthropogenic sources. Whilst some heavy metals are necessary for plants as micronutrients, others can be toxic to plants and humans even in trace concentrations. Among heavy metals, cadmium (Cd), arsenic (As), chromium (Cr), lead (Pb), and mercury (Hg) cause significant damage to aquatic ecosystems and can invariably affect human health. Rice, a staple diet of many nations, and other aquatic plants used as vegetables in many countries, can bioaccumulate heavy metals when they grow in contaminated aquatic environments. These metals can enter the human body through food chains, and the presence of heavy metals in food can lead to numerous human health consequences. Heavy metals in aquatic plants can affect plant physicochemical functions, growth, and crop yield. Various mitigation strategies are being continuously explored to avoid heavy metals entering aquatic ecosystems. Understanding the levels of heavy metals in rice and aquatic plants grown for food in contaminated aquatic environments is important. Further, it is imperative to adopt sustainable management approaches and mitigation mechanisms. Although narrowly focused reviews exist, this article provides novel information for improving our understanding about heavy metal accumulation in rice and aquatic plants, addressing the gaps in literature.

Alternate wetting and drying irrigation and phosphorus rates affect grain yield and quality and heavy metal accumulation in rice

Alternate wetting and drying (AWD) irrigation was reported to increase rice root activity and element bioavailability, which results in enhanced heavy metal (HM) absorption and this HM ends up in rice grains. HM uptake was also affected by the levels of phosphorus (P) fertilizer application. HMs enter food chain via consumption of rice grains and cause health problems. In this study, we compared the differences in grain yield, grain quality, water use efficiency (WUE), partial factor productivity of applied P (PFPp), HM contents in different tissues and transfer coefficient (TC) of HMs under a combination of treatments involving two irrigation regimes (continuous flooding (CF) and AWD irrigation) and three P fertilizer application levels (0.4 g P2O5/kg soil, HP; 0.2 g P2O5/kg soil, MP; 0 g P2O5/kg soil, LP). Compared to CF, AWD irrigation increased grain yield (without reducing grain quality), decreased irrigation water use and the number of irrigation events needed and improved WUE and PFPp at all three P fertilizer application levels, while the accumulation of HMs in grains increased when more P was applied. This accumulation of HMs in grains thus requires immediate attention to the level of P fertilizer application and its optimization in water-saving AWD irrigation to minimize grain HM content.

Analysis of influencing factors of heavy metals pollution in farmland-rice system around a uranium tailings dam

Due to the limitation of special regions, few studies have combined the environmental pollution around uranium tailings dams and heavy metal pollution in farmland. The study aimed to analyze the pollution status and causes of U, Cd, Cr, Pb, Cu, Zn, As, and Hg in the farmland-rice system around a uranium tailings dam. It was found that Cr, Pb, Cu, and Zn exceeded the standards. The principal component analysis method was used to determine that there were three sources of heavy metals in the region: road transportation, human intervention, and natural background. The results of chemical speciation analysis showed that the pollution of Pb, Cu, and Zn needed to be vigilant. pH and SOM had a greater impact on them. A regression model was established to investigate the cause of heavy metal accumulation in rice, and it was found that various parts of rice were greatly affected by pH. The main reason for the current status of the study area was not the pollution input of the uranium tailings dam itself, but human activities. Improving the local soil acidity was of great significance for controlling local pollution problems and protecting residents' health.

Mitigation effects of the microbial fuel cells on heavy metal accumulation in rice (Oryza sativa L.)

The increase in toxic heavy metal pollutants in rice paddies threatens food safety. There is an urgent need for lnow-cost remediation technology for immobilizing these trace metals. In this study, we showed that the application of the soil microbial fuel cell (sMFC) can greatly reduce the accumulation of Cd, Cu, Cr, and Ni in the rice plant tissue. In the sMFC treatment, the accumulation of Cd, Cu, Cr, and Ni in rice grains was 35.1%, 32.8%, 56.9% and 21.3% lower than the control, respectively. The reduction of these elements in the rice grain was due to their limited mobility in the soil porewater of soils employing the sMFC. The restriction in Cd, Cu, Cr, and Ni bioavailability was ascribed to the sMFC ability to immobilize trace metals through both biotic and abiotic means. The results suggest that the sMFC may be used as a promising technique to limit toxic trace metal bioavailability and translocation in the rice plants.

Variations in iron plaque, root morphology and metal bioavailability response to seedling establishment methods and their impacts on Cd and Pb accumulation and translocation in rice (Oryza sativa L.)

Global rice production is undergoing a shift from traditional seedling transplanting to direct seeding. There are also serious global challenges caused by heavy metal pollution in grain. To evaluate heavy metal accumulation in rice under different seedling establishment methods, we conducted field experiments with manual transplanting (MT), seedling throwing (ST) and direct seeding (DS). Data revealed that DS method enhances cadmium (Cd) and lead (Pb) accumulation in roots, straw, and brown rice. In particular, the Cd concentration in DS brown rice was 35.4% and 22.5% higher than in MT and ST methods, respectively; the concentration of Pb in DS brown rice was 1.97 times higher than in MT. The reasons for these observations are that DS rice root systems have finer diameters, larger specific surface areas, larger specific root lengths, more root tips, and reducing Fe plaque formation on root surface while DS rice roots formed in the upper soil layer and exhibited higher Cd and Pb bioactivity within the rhizosphere soil. Collectively, here we show for the first time that the shift in seedling establishment methods from transplanting to direct seeding also have played a partial contribution in the observed increased severity of heavy metal pollution in rice levels.

Germination and seedling growth of rice (Oryza sativa L.) as affected by varying concentrations of loom-dye effluent

Indiscriminate discharge of industrial effluent has become a serious problem for the agro-ecological environment in most of the areas of Bangladesh. The effects of loom-dye effluents on seed germination and early seedling growth of rice (Oryza sativa L.) were investigated by conducting an experiment in the laboratory of the Department of Agricultural Chemistry of Bangladesh Agricultural University, Mymensingh. Three types of loom-dye effluents were applied in sterilized petridishes at different loading ratios. Seven treatments (i.e., T0, T1, T2, T3, T4, T5 and T6 with 0, 5, 10, 25, 50, 75 and 100% effluent, respectively) of each effluent were used following completely randomized design (CRD) and replicated three times. Subsequently, Pb, Fe, Zn, Mn and Cr accumulation were also investigated in the harvested rice seedlings. Rice seed showed a significant difference in germination percentage with varying levels of effluent application at different days after setting of germination. The decreased seed germination rate and seedling growth of rice were observed with increased concentration of loom-dye effluents. The highest germination speed (97.8%) was obtained from control whereas the lowest germination speeds were obtained from T5 of black, and T6 of both black and violet effluents. Phytotoxic effects of loom-dye effluents on germination and radical length were extreme at 100% effluent concentration having the order of black > violet > pink. The maximum radical length (6.4 cm) and plumule length (7.5 cm) were observed with T1 of pink dye effluent whereas the minimum length of radical and plumule were obtained from T6 treatment of the effluents. The highest fresh weight (39.8 mg petridish–1), dry weight (5.7 mg petridish–1) and seedling vigor index (746.7%) were also observed from T1 of pink dye effluent. The maximum uptake of Pb, Fe, Mn and Zn was 0.48, 3.81, 0.79 and 0.13 μg g−1, respectively. The uptake of Cr was below the detectable limit. Total heavy metal accumulation in rice was in the following order: Fe>Mn>Pb>Zn>Cr. Results showed that the higher concentration of loom-dye effluent showed the higher toxic effects on different parameters of germination and early seedling growth compared with the lower effluent concentrations.
 J. Bangladesh Agril. Univ. 17(2): 153–160, June 2019

Water managements limit heavy metal accumulation in rice: Dual effects of iron-plaque formation and microbial communities

Understanding the mechanisms on how water management can minimize the concentrations of heavy metals in rice grains is important. Two water managements were concerned in our studies, including continuously flooding and alternate wetting and drying (AWD). Compared to AWD, a continuously flooded culture reduces the concentration of cadmium and other metals in the rice grains by reducing the root-to-shoot translocation and the availability of metals in rhizosphere. In a flooded environment, the rice rhizosphere was characterized by an increased soil pH, reduced fluorescein diacetate (FDA) activity, and lower metal bioavailability. In addition, flooding significantly decreased the iron plaque on the root surface and reduced the affinity for metals in rhizosphere. Water managements significantly changed soil microbial diversity, especially the proportion of anaerobic bacteria, including the iron-reducing bacteria Latescibacteria, Desulfuromonadales, and Geobacteraceae. Interestingly, these bacteria exhibited a significant correlation with cadmium that was adsorbed on the root. This study revealed that continuously flooded culture is a valuable strategy for minimizing heavy metal accumulation in rice grains. By increasing the abundance of unique bacterial community, iron plaque formation and the affinity of metals in rhizosphere were reduced, and the uptake and accumulation of heavy metals in rice plants was finally mitigated.

Assessment and genetic analysis of heavy metal content in rice grain using an Oryza sativa × O. rufipogon backcross inbred line population.

Heavy metal accumulation in rice is a growing concern for public health. Backcross inbred lines derived from an interspecific cross of Oryza sativa × O. rufipogon were grown in two distinct ecological locations (Hangzhou and Lingshui, China). The objective of this study was to characterise the contents of heavy metal in rice grains, and to identify quantitative trait loci (QTLs) for heavy metal contents. The contents of Ni, As, Pb, Cr and Hg in milled rice showed a significant decline as compared with those in brown rice, whereas the content of Cd showed little change. The concentration of heavy metal in rice grain varied greatly between the two environments. A total of 24 QTLs responsible for heavy metal contents were detected, including two for both the brown and milled rice, 13 for brown rice only, and nine for milled rice only. All the QTLs except two had the enhancing alleles derived from O. rufipogon. Sixteen QTLs were clustered in six chromosomal regions. Environmental variation plays an important role in the heavy metal contents in rice grain. QTLs detected in this study might be useful for breeding rice varieties with low heavy metal content. © 2017 Society of Chemical Industry.

The influence of bioavailable heavy metals and microbial parameters of soil on the metal accumulation in rice grain

A field-based study was undertaken to analyze the effects of soil bioavailable heavy metals determined by a sequential extraction procedure, and soil microbial parameters on the heavy metal accumulation in rice grain. The results showed that Cd, Cr, Cu, Ni, Pb and Zn concentrations in rice grain decreases by 65.9%, 78.9%, 32.6%, 80.5%, 61.0% and 15.7%, respectively in the sites 3 (far-away), compared with those in sites 1 (close-to). Redundancy analysis (RDA) indicated that soil catalase activity, the MBC/MBN ratio, along with bioavailable Cd, Cr and Ni could explain 68.9% of the total eigenvalue, indicating that these parameters have a great impact on the heavy metal accumulation in rice grain. The soil bioavailable heavy metals have a dominant impact on their accumulation in rice grain, with a variance contribution of 60.1%, while the MBC/MBN has a regulatory effect, with a variance contribution of 4.1%. Stepwise regression analysis showed that the MBC/MBN, urease and catalase activities are the key microbial parameters that affect the heavy metal accumulation in rice by influencing the soil bioavailable heavy metals or the translocation of heavy metals in rice. RDA showed an interactive effect between Cu, Pb and Zn in rice grain and the soil bioavailable Cd, Cr and Ni. The heavy metals in rice grain, with the exception of Pb, could be predicted by their respective soil bioavailable heavy metals. The results suggested that Pb accumulation in rice grain was mainly influenced by the multi-metal interactive effects, and less affected by soil bioavailable Pb.

Heavy metal accumulation in rice (Oryza sativa) near electronic waste dumps and related human health risk assessment

ABSTRACTThis research was conducted to assess heavy metal contamination in the environment and within Oryza sativa. The translocation factors (TFs) and bioaccumulation factors (BAFs) for heavy metals in O. sativa and estimated daily intake (EDI) and health risk index (HRI) were measured. The samples were analyzed for heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES). Pb and Cr concentrations in water samples within and near the electronic-waste dumping area exceeded water quality standards for surface water sources from the Pollution Control Department in the Ministry of Natural Resources and Environment of Thailand (PCD). The Pb concentration in soil samples within the area also exceeded soil quality standards for habitat and agriculture from PCD. Most of the metals were highly concentrated in roots, except for Mn which has the highest concentration in leaves. Pb concentrations in rice grains exceeded the FAO/WHO standard (0.2 mg/kg). The average TF values for heavy metals from the soil to roots, roots to stems, stems to leaves, and stems to grains were Mn > Pb > Ni > Cr, Mn > Cr > Ni > Pb, Ni > Pb > Mn > Cr, and Pb > Ni > Cr > Mn, respectively. The average BAF values in O. sativa were Mn > Ni > Pb > Cr. The EDI for Cr, Pb, Mn, and Ni via O. sativa consumption were 6.19, 6.02, 370.57, and 3.80 µg/kg/day, respectively. The HRI for Cr, Pb, Mn, and Ni via O. sativa consumption were 0.30, 1.50, 2.60, and 0.002, respectively.

Genotypic-dependent effects of N fertilizer, glutathione, silicon, zinc, and selenium on proteomic profiles, amino acid contents, and quality of rice genotypes with contrasting grain Cd accumulation.

Soil heavy metal (HM) contamination has posed a serious problem for safe food production. For restricting the translocation of HM into grain, many proteins were regulated to involve in the process. To identify these proteins, 2D-based proteomic analysis was carried out using different rice genotypes with distinct Cd accumulation in grains and as affected by an alleviating regulator (AR) in field experiments. AR application improved grain quality, with increased contents in Glu, Cys, His, Pro, and protein. Twenty-six low-grain HM accumulation-associated protein species were identified and categorized as physiological functions via two-dimensional gel electrophoresis (2DE) and mass spectrometry. Among these proteins, 8, 9, and 9 proteins exhibited higher accumulation, lower accumulation, and unchanged accumulation, respectively, in Xiushui817 (low accumulator) vs R8097 (high accumulator) under control conditions but showed differential accumulation patterns after AR application. These proteins included sucrose synthase 3, alanine aminotransferase, glutelin, cupin family protein, and zinc finger CCCH domain-containing protein 32. The differential expression of these protein species might contribute to decreased HM accumulation in grain via decreasing the protein accumulation which had high affinity to HM or regulating energy metabolism and signal transduction. Our findings provide valuable insights into the mechanisms of low-grain HM accumulation in rice and possible utilization of candidate protein species in developing low-grain HM accumulation genotypes.

Heavy Metal Accumulation in Different Rice Cultivars as Influenced by Foliar Application of Nano-silicon

Silicon (Si) is one of beneficial elements for rice and is considered to enhance plant resistance to toxic metals. Nanofertilizers generally have a smaller particle size and specific characters and behaviors in soil and plants. Thus, nano-Si fertilizers may putatively have an advantage over traditional fertilizers in reducing heavy metal accumulation in rice straws and grains, but their effects still require investigation. Here, using a greenhouse pot culture experiment, we studied the effects of foliar application with organic or inorganic nano-Si on growth and yields, and heavy metal accumulation in six rice cultivars grown in soil artificially polluted with Cd, Pb, Cu, and Zn. Generally, hybrid cultivars had higher biomass and yields than conventional cultivars (P < 0.001), and nano-Si showed positive effects on at least four cultivars (P < 0.001). The average spike weight of six cultivars increased to 25.3 and 24.8 %, respectively, by inorganic and organic nano-Si. Hybrid cultivars generally had higher Cd concentrations in roots, shoots, and grains than conventional cultivars. In most cases, both organic and inorganic nano-Si reduced concentrations (P < 0.01) and bio-concentration factor (BCF) of the heavy metals in grains and decreased the translocation factor (TF) of heavy metals from roots to shoots and/or from shoots to grains, and the most pronounced effects were found on Cd. The average grain Cd concentration decreased to 27.1 and 23.8 %, respectively, by inorganic and organic nano-Si. In general, inorganic nano-Si had more pronounced effect than organic nano-Si on both rice growth and heavy metal accumulation. This present study firstly showed that nano-Si had positive effects on the growth and yields of rice grown in multi-metal-polluted soil and potentially reduced heavy metal accumulation in rice, especially the toxic Cd in grains. However, both rice cultivar and chemical form of Si fertilizers should be taken into account to develop efficient nano-Si fertilizers for preventing heavy metal-contaminated rice grains.

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated. Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg−1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS. Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg−1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively. The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.

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.

Mitigation effects of silicon rich amendments on heavy metal accumulation in rice ( Oryza sativa L.) planted on multi-metal contaminated acidic soil

The mechanisms of stabilization by silicon-rich amendments of cadmium, zinc, copper and lead in a multi-metal contaminated acidic soil and the mitigation of metal accumulation in rice were investigated in this study. The results from a pot experiment indicated that the application of fly ash (20 and 40 g kg −1) and steel slag (3 and 6 g kg −1) increased soil pH from 4.0 to 5.0–6.4, decreased the phytoavailability of heavy metals by at least 60%, and further suppressed metal uptake by rice. Diffusion gradient in thin-film measurement showed the heavy metal diffusion fluxes from soil to solution decreased by greater than 84% after remediation. X-ray diffraction analysis indicated the mobile metals were mainly deposited as their silicates, phosphates and hydroxides in amended treatments. Moreover, it was found metal translocation from stem to leaf was dramatically restrained by adding amendments, which might be due to the increase of silicon concentration and co-precipitation with heavy metals in stem. Finally, a field experiment showed the trace element concentrations in polished rice treated with amendments complied with the food safety standards of China. These results demonstrated fly ash and steel slag could be effective in mitigating heavy metal accumulation in rice grown on multi-metal contaminated acidic soils.

E-Junk explosion.

e-Junk explosion.