Metals In Rice Grains Research Articles

Evaluation of the potentials of rice varieties and water management practices for reducing human health risks associated with polluted river water irrigated rice in Bangladesh

The consumption of arsenic and trace-metal-contaminated rice is a human health concern worldwide, particularly in Bangladesh. In this study, the effects of rice varieties and water management practices on the concentrations of arsenic and trace metals in rice grains were investigated to reduce human health risks related to rice consumption. In addition, the performance of risk reduction using the optimum combination of rice variety and water management practices was quantitatively assessed using Monte Carlo simulation, in which non-carcinogenic and carcinogenic risk distributions under the status quo and the optimum combination were compared. The experimental results revealed that Dular and BRRI dhan45 (rice varieties) cultivated under alternate wetting and drying (AWD) and continuous flooding (CF) conditions showed the lowest hazard quotient (HQ) values for copper, cadmium, and arsenic and the lowest target cancer risk (TR) for arsenic. In Dular and BRRI dhan45 (AWD and CF) varieties, the proportion of the population for which HQs exceeded 1.0 (the reference value) tended to decrease (except for arsenic), compared with populations for which the rice varieties and water management practices were not specified. These results suggest that the use of optimum combinations of rice varieties and water management practices could reduce non-carcinogenic and carcinogenic risks associated with arsenic and trace metals uptake via rice grain consumption by the Bangladeshi people.

Absorption, accumulation, and distribution of atmospheric metals in rice (Oryza sativa L.)

Crop metal contamination caused by atmospheric metal pollution has been increasingly reported. To investigate the absorption, accumulation, and distribution of atmospheric metals in rice (Oryza sativa L.), a field experiment was conducted with rice grown at an atmospheric metal pollution site and a background site. The concentrations of Pb, Cd, Cu, Mn, and Zn in the atmospheric deposition at the pollution site were significantly higher than those at the background site. Consequently, the rice tillering number decreased by 56–64% and the yield decreased by 53–69% at the pollution site compared to the background site. Particularly, Pb isotope analysis found that 76% of the Pb in the rice grain at the pollution site was attributed to atmospheric Pb. Furthermore, observations by transmission electron microscopy found penetration through the leaf cuticle seems to be the primary pathway for the absorption of atmospheric metals. Using laser ablation inductively coupled plasma-mass spectrometry, it was found that the distribution of metals in rice grains at the two sites was similar, with Pb, Cr, Fe, Mn, Cu, and Ca mainly in the bran layer while Cd and Zn uniformly distributed throughout the entire grains. Possible solutions to address atmospheric metal pollution in crops are discussed.

Spatial and variety distributions, risk assessment, and prediction model for heavy metals in rice grains in China.

In this study, 6229 brown rice grains from three major rice-producing regions were collected to investigate the spatial and variety distributions of heavy metals in rice grains in China. The potential sources of heavy metals in rice grains were identified using the Pearson correlation matrix and principal component analysis, and the health risks of dietary exposure to heavy metals via rice consumption were assessed using the hazard index (HI) and total carcinogenic risk (TCR) method, respectively. Moreover, 48 paired soil and rice samples from 11 cities were collected to construct a predicting model for Cd accumulation in rice grains using the multiple linear stepwise regression analysis. The results indicated that Cd and Ni were the main heavy metal pollutants in rice grains in China, with approximately 10% of samples exceeding their corresponding maximum allowable limits. The Yangtze River basin had heavier pollution of heavy metals than the Southeast Coastal Region and Northeast Plain, and the indica rice varieties had higher heavy metal accumulation abilities compared with the japonica rice. The Cu, Pb, and Cd mainly originated from anthropogenic sources, while As, Hg, Cr, and Ni originated from both natural and anthropogenic sources. The mean HI and TCR values of dietary exposure to heavy metals via rice consumption ranged from 2.92 to 4.31 and 9.74 × 10-3 to 1.44 × 10-2, respectively, much higher than the acceptable range, and As and Ni were the main contributor to the HI and TCR for Chinese adults and children, respectively. The available Si (ASi), total Cd (TCd), available Mo (AMo), and available S (AS) were the main soil factors determining grain Cd accumulation. A multiple linear stepwise regression model was constructed based on ASi, TCd, AMo, and AS in soils with good accuracy and precision, which could be applied to predict Cd accumulation in rice grains and guide safe rice production in contaminated paddy fields.

Effect of Biochar Application on Heavy Metal accumulation in Different Parts of Paddy Plant

Heavy metal contamination in agricultural field is a challenging aspect globally. Various methods are employed to address the issue; biochar among the most cost-effective and promising one. Our study encompasses biochar preparation from Parthenium, a noxious weed of agricultural field, and its subsequent modification using ferric chloride and orthophosphoric acid. Results revealed that more than 20% reduction of Pb, Cd and Ni in Rice roots under 5 and 7.5 t ha-1 biochar treatments. Moreover, greater than 30% reduction of abovementioned heavy metals in rice grains is also noted in 10 t ha-1 biochar application rates. So, it can be concluded from our study that biochar application to a metal contaminated soil can be a promising approach to reduce metal accumulation in different parts of rice and subsequently addressing the adverse effect of it in human body.

Agronomic performance and remote sensing assessment of organic and mineral fertilization in rice fields.

Rice heavily relies on nitrogen fertilizers, posing environmental, resource, and geopolitical challenges. This study explores sustainable alternatives like animal manure and remote sensing for resource-efficient rice cultivation. It aims to assess the long-term impact of organic fertilization and remote sensing monitoring on agronomic traits, yield, and nutrition. A six-year experiment in rice fields evaluated fertilization strategies, including pig slurry (PS) and chicken manure (CM) with mineral fertilizers (MIN), MIN-only, and zero-fertilization. Traits, yield, spectral responses, and nutrient content were measured. Sentinel-2 remote sensing tracked crop development. Cost-effective organic fertilizers (PS and CM) caused a 13% and 15% yield reduction but still doubled zero-fertilization yield. PS reduced nitrogen leaching. Heavy metals in rice grains were present at safe amounts. Organic-fertilized crops showed nitrogen deficiency at the late vegetative stages, affecting yield. Sentinel-2 detected nutrient deficiencies through NDVI. Organic fertilizers, especially PS, reduce nitrogen loss, benefiting the environment. However, they come with yield trade-offs and nutrient management challenges that can be managed and balanced with reduced additional mineral applications. Sentinel-2 remote sensing helps manage nutrient deficiencies. In summary, this research favors cost-effective organic fertilizers with improved nutrient management for sustainable rice production.

Characterisation of a low methane emission rice cultivar suitable for cultivation in high latitude light and temperature conditions

Rice cultivation on paddy soil is commonly associated with emissions of methane, a greenhouse gas, but rice varieties may differ in their actual level of emissions. This study analysed methane emissions associated with 22 distinct rice genotypes, using gas chromatography, and identified the cultivar Heijing 5 from northern China as a potential low-methane rice variety. To confirm this and to examine whether Heijing 5 can perform similarly at higher latitudes, Heijing 5 was cultivated in field trials in China (lat. 32° N) and Sweden (lat. 59° N) where (i) methane emissions were measured, (ii) methanogen abundance in the rhizosphere was determined using quantitative PCR, and (iii) the concentrations of nutrients in water and of heavy metals in rice grain and paddy soil were analysed. The results demonstrated that the low-methane rice cultivar Heijing 5 can successfully complete an entire growth period at high-latitude locations such as central Sweden. Massively parallel sequencing of mRNAs identified candidate genes involved in day length and cold acclimatisation. Cultivation of Heijing 5 in central Sweden was also associated with relatively low heavy metal accumulation in rice grains and lowered nutrient losses to neighbouring water bodies.

Risk Assessment of Selected Heavy Metals Contamination In Rice Grains in the Rajshahi City of Bangladesh

The concentrations of four heavy metals in rice grains and the health risk assessments of the metals were studied. Sixteen rice samples were gathered from Rajshahi, Bangladesh. Average lead, chromium, manganese, and cadmium concentrations measured in rice samples were 6.87, 0.43, 44.58, and 1.13 mg/kg, respectively. The concentration level found in most rice samples is greater than the acceptable limit as set by WHO. The risk assessment was done by using the intended hazard ratio and target carcinogenic risk where the values for the lead, manganese, and cadmium quotient were greater than 1. The target cancer-causing risk values for a maximum number of samples are lower than 10-4, which is considered safe. However, target carcinogenic risk values for cadmium are higher than 10-4, which is considered a carcinogenic risk. The results of the current investigations suggest that appropriate measures should be taken to determine the cause and origin of this heavy metal contamination. Journal of Engineering Science 14(1), 2023, 29-41

Trace Metals in Rice Grains and Their Associated Health Risks from Conventional and Non-Conventional Rice Growing Areas in Punjab-Pakistan

Rice (Oryza sativa L.) is cultivated and consumed worldwide, but the contamination of rice grains with trace metals (TMs) could cause adverse impacts on human health. The aims of this study were to determine the concentrations of TMs in different rice varieties available for sale in local markets and to determine whether consumers are likely to be at risk via the consumption of these rice cultivars. For this purpose, samples of rice grains were collected from 12 rice growing districts (administrative units) in Punjab, Pakistan. These districts were further classified based on rice growing methods due to specific soil type. In conventional districts, the puddling method was used, while direct seeding was used for rice cultivation in non-conventional districts. The samples were collected and analyzed for the determination of essential (Cu, Fe, Zn, and Mn) and non-essential (Cd, Ni, and Pb) TMs using an atomic absorption spectrophotometer (AAS). The results showed that the maximum respective concentrations of Cd, Ni, and Pb (0.54, 0.05, 1.10 mg kg−1) were found in rice grains in conventional areas, whereas values of 0.47, 0.20, and 1.20 mg kg−1 were found in non-conventional rice growing areas. The maximum concentrations of essential TMs (Cu, Fe, Mn, and Zn) were 4.54, 66.01, 4.82, and 21.51 mg kg−1 in conventional areas and 3.76, 74.11, 5.66, 19.63 mg kg−1 in non-conventional areas. In the conventional rice growing areas, Fe and Zn concentrations exceeded the permissible limits in the 27 and 7% samples, respectively. In the non-conventional rice areas, the concentrations of Cu, Fe, and Mn exceeded the permissible limits in the 15, 26, and 3% samples, respectively, while its Zn concentration was found within the permissible limits. The estimated weekly intake (EWI) and maximum tolerable dietary intake (MTDI) values for all studied metals were found within the permissible values set by WHO, except for Fe, in both sampled areas. It was concluded that no health risks were associated by utilizing the rice grains. However, the mean values of TMs were found considerably higher in collected rice samples from non-conventional areas than the conventional areas. Therefore, the concentrations of TMs should be monitored properly.

Spatial distribution of heavy metals in rice grains and human health risk assessment in Hunan Province, China.

Rice is the main food in China, and its pollution by heavy metals has attracted widespread attention. In this study, rice grain samples were collected from 14 prefecture-level cities in Hunan Province, China. The contents of 9 heavy metals (i.e., As, Cr, Co, Ni, Cu, Zn, Cd, Pb, and Sb) were measured using graphite digestion-inductively coupled plasma mass spectrometry (ICP-MS). Pearson correlation analysis and principal component analysis were performed to evaluate the correlation among these heavy metals. In addition, ordinary kriging interpolation were applied to investigate the spatial distribution pattern of the heavy metals. Results showed that the average concentrations of these heavy metals were 0.48 (As), 1.28 (Cr), 0.03 (Co), 0.84 (Ni), 2.39 (Cu), 15.73 (Zn), 0.28 (Cd), 0.66 (Pb), and 0.0043 (Sb) mg/kg, respectively. The single-factor pollution index (SFPI) contamination assessment showed that As, Pb, Cr, Ni, and Cd accumulated significantly in the rice grain, with over-standard rates of 100%, 100%, 64.70%, 47.05%, and 44.12%, respectively. The Sb concentrations at the sampling sites were low, and there was no obvious pollution. Health risk assessment showed that the target hazard quotient followed the order of As> Cr> Cd> Pb> 1.0> Co> Cu> Zn> Ni> Sb, and the carcinogenic risk value was in the order of Cd> Ni> As> Cr> 1.0×10-4> Pb. In particular, quick actions should be taken to regulate As, Cr, and Cd contents in rice because they posed greater non-carcinogenic and carcinogenic health risks than the others to the local residents.

Effects of two different selenium fertilizers on accumulation of selenium and heavy metals in rice grains in field trials

Selenium (Se) is a nutritionally important micronutrient for humans. The use of Se fertilizers is often the most feasible approach to precisely increase Se contents in rice grains, but the effects of common commercial Se fertilizers on producing Se-rich rice remain to be investigated. In this study, we compared the effects of liquid and granular Se fertilizers on the accumulation of Se and heavy metals in rice grains of four different varieties in field. Results showed that Se accumulation in rice grains was affected by the form of fertilizers, applied concentrations of Se fertilizers, and rice varieties. Liquid fertilizer displayed significantly higher Se transfer efficiency than granular fertilizer, whereas the granular fertilizer had a slightly higher effect on organic Se accumulation. More than 95.5% Se in grains were organic Se, with selenomethionine (SeMet) being the dominant one. The proportion of organic selenocysteine (SeCys2) in grains was significantly higher in treatments with liquid fertilizer. Both forms of fertilizers significantly reduced the accumulation of cadmium, lead, and arsenic. Collectively, our study provides a reference for producing Se-rich rice in a more competitive manner in practice.

Ecological and human health risk evaluation of potential toxic metals in paddy soil, rice plants, and rice grains (Oryza sativa) of Omor Rice Field, Nigeria.

Potential toxic metals from natural and anthropogenic sources accumulate in soil and plants, and represent important environmental contamination challenges. The ecological and human health risks of the potential toxic metals in rice grain, paddy soil, and rice plants of Omor rice field were assessed. The total metal concentration from the four sampling sections (mg/kg) were soil-Zn (29.51 ± 2.23), Mn (55.27 ± 8.10), Cd (5.49 ± 2.24), Cu (2.94 ± 1.47), Pb (14.35 ± 6.54), and Cr (27.06 ± 8.31); rice grain-Zn (21.70 ± 5.44), Mn (3.30 ± 0.21), Cd (00.14 ± 0.11), Cu (2.80 ± 0.34), Pb (11.98 ± 0.58), and Cr (15.86 ± 2.79); and for rice plant-Zn (5.24 ± 1.93), Mn (4.68 ± 1.91), Cd (0.21 ± 0.11), Cu (4.88 ± 0.61), Pb (15.24 ± 6.16), and Cr (46.5 ± 6.05). The estimated daily intakes for adult showed that Cd and Pb exceeded the safe limit by 1% and 93%, respectively. The metal hazard quotients (Zn-0.0007, Mn-0.00019, Cd-0.16, Cu-0.19, and Cr-0.0000077) were less than 1 indicating no probable health risk originating from their exposure. The total hazard index (0.35) also suggests no probable health risk connected with the rice consumption. The metals' ecological risk indices of the soil showed low-risk (< 40), except Cd in some sections of the rice field which indicated moderate potential ecological risk (40-80).

Rice cultivation in former rubber land without soil remediation contribute toxicity risk of heritable heavy metals contamination

The rubber-based intercropping management system (RBIS) land management using chemical fertilizer and herbicides cause heavy metal accumulation in soil. Rice is a good heavy metal bioindicator to monitor soil quality and often integrated with RBIS while rubber trees are young as subsistence farming. Heavy metal accumulation in soil and hill paddy grown on former rubber land and specialized paddy field (control) had been assessed to determine whether harvested rice grain poses toxicity risk. Grain harvested from specialized paddy land was safer to consume as none of the selected heavy metal concentrations in rice grain had exceeded the permissible limit of Malaysia Food Regulation 1985 (MFR 1985). Meanwhile, hill paddy grown intercropping with young rubber trees on former rubber land had accumulated a high amount of heavy metals in rice grain whereby nonessential heavy metals like arsenic, cadmium and lead had exceeded the permissible limit of MFR 1985. Commonly, indigenous hill paddy belongs to tall paddy variety group can grow more than 120 cm tall. All harvested hill paddy landraces grown on specialized paddy field surpassed 120 cm. Nevertheless, all hill paddy landraces that were cultivated in former rubber land were below 100 cm tall indicated that heavy metal phytotoxicity occurred in plants. Rice grain produced in former rubber land poses toxicity risk to consumers due to unsustainable conventional agricultural management practice. Soil degradation needs to be prevented as it can impact food safety and food security. Further soil remediation requirement must be determined to ensure high productivity and safety.

A Field Evidence of Cd, Zn and Cu Accumulation in Soil and Rice Grains after Long-Term (27 Years) Application of Swine and Green Manures in a Paddy Soil

Although inorganic and organic manures with high concentrations of heavy metals can lead to accumulation or contamination of heavy metals in soils, there are few reports on the effects of long-term application of swine and green manures on the accumulation of heavy metals in rice grains in paddy soils. A long-term field experiment, which was established in 1990 in paddy soil in Hangzhou, China, was used to investigate the effects of inorganic and organic manures on the availability and accumulation of heavy metals in soil and uptake by rice plant. The results showed that long-term application of nitrogen, phosphorus and potash (NPK) plus green manure or swine manure, and swine manure only increased 202%, 146%, and 100% for total Cd, and 5.5%, 7.6%, and 6.6% for total Cu in rice grains, respectively compared to the control without fertilization. Total Zn in rice grain was significantly increased by 13.9% for the treatment of NPK plus green manure. The accumulation of Cd, Zn, and Cu in rice grains after long-term application of swine and green manures is due to the combined effects of the increased concentrations of total and EDTA extractable Cd, Zn, and Cu in soil and the changes of soil properties. Furthermore, the highest bioconcentration factor for Cd was found in the treatment of NPK plus green manure while for Zn and Cu it was observed in NPK treatment. Thus, it may be concluded that green manure and manure with increased Cd, Zn, and Cu in rice grain results in a potential risk of metal accumulation in paddy soils.

Spatial distribution of heavy metals in rice grains, rice husk, and arable soil, their bioaccumulation and associated health risks in Haryana, India

In this study rice grain, rice husk, and arable soil samples collected from Panipat district, Haryana, India were analyzed for Cd, Pb, Cr, Fe, Zn, Co, Cu, and Ni content using Atomic absorption spectrophotometer. The bioaccumulation of heavy metals in rice husk was found to be more than rice grains. Soil pH and Total organic carbon significantly influenced the uptake of metals by the rice plants. Chronic daily dose (CDD) of Fe, Pb, and Cu marginally exceeded the permissible dose at 30–50% locations. Further, it is recommended that such studies should be conducted periodically to avoid health risks to the population.

Potential health risk assessment for inhabitants posed by heavy metals in rice in Zijiang River basin, Hunan Province, China.

The contents of total arsenic (tAs), inorganic arsenic (iAs), Cd, Cr, Cu, Mn, Ni, Pb, Sb, and Zn in 135 rice grain samples from Zijiang River basin were determined, and the probabilistic distribution of noncarcinogenic and carcinogenic risks associated with ingesting locally produced rice was determined by Monte Carlo simulation. Further, multivariate statistical analysis was used to analyze the potential sources of the heavy metals in rice grains. The average concentrations of the heavy metals in rice grains were ranked as follows: Mn (17.314mg/kg) > Zn (16.043mg/kg) > Cu (2.013mg/kg) > Ni (1.332mg/kg) > Cr (0.571mg/kg) > Cd (0.283mg/kg) > tAs (0.241mg/kg) > Pb (0.145mg/kg) > Sb (0.027mg/kg). These heavy metals were significantly enriched in some rice grain samples. The analysis of potential sources indicated that As, Pb, Sb, and Zn were mainly derived from mining and smelting and agricultural activities; Cd, Cu, Mn, and Ni were mainly derived from the agricultural activities; Cr were mainly derived from the natural source. The results of Monte Carlo simulation indicated that ingestion of rice grown in the area may pose health risks for children, adult males, and adult females. The noncarcinogenic risks were mainly from As, Cd, Mn, Ni, and Sb, and the carcinogenic risk was mainly from As, Cd, and Ni. This study could provide basic information for land management and rice intake in the study area.

Simultaneous removal of Cd(II) and As(III) by graphene-like biochar-supported zero-valent iron from irrigation waters under aerobic conditions: Synergistic effects and mechanisms

Irrigation water is commonly contaminated with cadmium and arsenic near mining regions, which significantly contributes to excessive heavy metals in rice grains. Herein, we have developed a novel graphene-like biochar (GB)-supported nanoscale zero-valent iron (nZVI) and the underlying mechanisms of synergistic effects between GB and nZVI for the simultaneous removal of Cd(II) and As(III) under aerobic conditions. The results show that GB/nZVI has a high removal capacity of 363 mg/g (nZVI) for As(III) at pH 4 and 92.8 mg/g (nZVI) for Cd(II) at pH 7. These values are significantly higher than GB and nZVI (1.7 times for Cd(II); 1.4 times for As(III)) alone, suggesting strong synergistic effects between GB and nZVI. GB promotes nZVI oxidation to form iron oxyhydroxides and causing 35 % of As(III) converting to As(V). Importantly, As(III) significantly enhance Cd(II) removal by GB/nZVI (i.e., 131.8 mg/g as nZVI). Coexisting ions such as phosphate and humic acid have a stronger inhibitory effect on the simultaneous removal of Cd(II) and As(III). Our results indicate that oxidation and surface complexation are the dominant mechanisms and electrostatic binding exists for As(III) removal, while surface complexation predominates for Cd(II) removal. These findings provide insight into developing an effective solution for removing Cd(II)/As(III) from irrigation waters.

Presence of toxic metals in rice with human health hazards in Tangail district of Bangladesh

ABSTRACT Rice is the staple food of Bangladeshi people and is consumed at least twice a day. Thus, the presence of toxic metals in rice grains has become a major public health concern in Bangladesh. The present research was conducted to investigate the concentrations of toxic metals in rice grains and their possible human health risks in the Tangail district of Bangladesh. Toxic metals were measured by using an inductively coupled plasma mass spectrometer (ICP-MS), and the mean concentrations of toxic metals in rice samples were found in order of Cr > Pb > Ni > As > Cu > Cd. The concentrations of Cr, Pb, As, and Cd in the studied rice grain samples exceeded the FAO/WHO standard values for food samples by 100%, whereas the Ni concentrations by 10%. The principal component analysis (PCA) revealed significant anthropogenic contributions of Cr, Ni, As, and Pb concentrations in rice grains. The metal concentrations in rice grain samples showed strong significant correlations by forming primary clusters with each other. The estimated daily intake (EDI) values of Cr, Ni, As, Cd, and Pb from all samples were higher than the maximum tolerable daily intake (MTDI) allowed. The total targeted hazard quotient (TTHQ) values of Cu, Ni, As, Cd, and Pb also exceeded the threshold value of 1.00, indicating a potential non-carcinogenic risk. The estimated target carcinogenic risk of As was higher than the USEPA threshold level 10−4 (0.0001) indicating increased risk of cancer for adults and children in the study area.

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.

Risk assessment of heavy metal contamination of paddy soil and rice (Oryza sativa) from Abakaliki, Nigeria.

The study assessed the concentration and bioavailability of Pb, Cd, Zn, Cr and Fe metals in soil from rice fields in Abakaliki, Nigeria. The concentrations of these heavy metals in rice grains were also determined, with a view to assessing their human health risk on consumers. Heavy metal concentrations in soil and rice were determined using FAAS after digestion with 5:1 HNO3:HClO4 while Tessier's sequential extraction method was used to obtain the fractionated soil digests. The mean concentrations (μg/g) of the total heavy metal ranged from 1.036 ± 1.86 (Cd) to 6900.537 ± 734.82 (Fe) in soil while that of rice grains ranged from 0.024 ± 0.07 (Cd) to 101.446 ± 75.26 (Fe).The concentrations of Fe and Cd in most of the soil samples and Pb in rice grains exceeded some Nigerian and International standards. The heavy metal sequential extractions of soil samples showed that lead and zinc were less mobile in the soil and are bioavailable for plant uptake. The estimated daily intake of the metals was below the tolerable daily intake. The hazard quotient and the total hazard index were less than one showing that at present, there is no possible adverse health effect on rice consumers.

Heavy Metals Bioavailability under Aerobic and Anaerobic Condition in Soil and Bubut Rice Plant Cultivated at Crocker Range, Borneo (Malaysia)

Bioaccumulation of heavy metals in rice that can pose health risk is a grave concern as more than half of world populations are rice consumers. Bioaccumulation of heavy metals in rice grain depends on the heavy metal bioavailability in the medium that provide nutrient sources to plant. Throughout paddy life-cycle from seed germination to development of mature seeds, paddy plants cultivated in flooded field are exposed to alternating anaerobic condition and aerobic condition. The aim of this study is to assess whether these two different paddy field conditions influence heavy metal bioavailability in soil and heavy metal accumulation in Bubut paddy plants cultivated at highland of West Coast Sabah, Malaysia. Heavy metal uptake characteristic of Bubut paddy in different part (root, straw and grain) were also determined for baseline data that can be used for selective breeding or Phyto mining. Bubut paddy plants were uprooted together with soil that were collected randomly at 3 months old age (reducing (anaerobic) condition) and harvest season (oxidizing (aerobic) condition) for heavy metal analysis by inductively coupled plasma optical emission spectrometry (ICP-OES). Higher bioavailability of heavy metal at oxidizing condition in soil and Bubut paddy plant were observed compared to reducing condition. Bubut paddy was found to be a potential candidate for Cr, Ni and Zn phytoextraction. Heavy metal concentration in Bubut rice grain is below the maximum permissible limit of Malaysia Food Regulation 1985 (MFR 1985). A comprehensive water irrigation management plan is required to strategically develop at West Coast Sabah to reduce bioavailability of toxic heavy metals and reduce heavy metals toxicity risk in rice consumption.