Screen for low-arsenic-risk rice varieties based on environment-genotype interactions by using GGE analysis.

Arsenic (As) accumulation in rice is a global health concern that has received increased attention in recent years. In this study, 12 rice genotypes were cultivated at four As-contaminated paddy sites in Taiwan. According to the different crop seasons and As levels in the soil, the sites were further divided into 18 environmental conditions. For As in soils, results showed that 67% of the studied environments were likely to represent As contamination. For As in rice, the mean total As concentration in brown rice grains ranged from 0.17 to 0.45 mg kg-1. The analysis of variance for the environment effect indicated that grain As concentration was mainly affected by the environmental conditions, suggesting that there was a remarkable degree of variation across the trial environments. According to the combination of the GGE biplot and cumulative distribution function of order statistics (CDFOS) analysis, five genotypes-TCS17, TCS10, TT30, KH139, and TC192-were regarded as stable, low-risk genotypes because the probability of grain As concentration exceeding the maximum permissible concentration (MPC) was lower for these genotypes across all environmental conditions. Particularly, TCS17 was recommended to be the safest rice genotype. Thus, grain As levels in the selected genotypes were applied to assess the health risk to Taiwanese residents associated with As exposure through rice consumption. Results showed that the upper 75th percentile values of the hazard quotient were all less than unity. This suggested that the health risk associated with consuming the selected rice genotypes was acceptable for most of the residents. The methodology developed here would be applicable to screen for stable, low-As-risk rice genotypes across multiple field environments in other regions or countries.

Cadmium in rice grains from a field trial in relation to model parameters of Cd-toxicity and -absorption in rice seedlings.

Selecting rice varieties that absorb less Cd from soil will reduce human health risks posed by Cd through rice consumption. Nine rice cultivars that are commonly grown in Taiwan were used for investigating genotypic differences in Cd tolerance and absorption. Hydroponic testing with Cd treatments of 5, 10, and 50 µM CdCl2 for 7-day exposure was conducted for the cultivars. The reductions in plant growth by Cd treatments were fitted to a dose-response curve; the modeling parameters, that is, the effective Cd concentration resulting in 50% reduction (EC50), were obtained. The Cd concentrations in plant were expressed by a Michaelis-Menten kinetic model and the uptake rate parameters (M/k) were obtained. A field experiment was also conducted in farmland with Cd ~0.2 mg kg-1 in soil. For the rice cultivars used in hydroponics, Cd distributions and physiological traits (CAT, H2O2, and MDA) in seedlings were related to their tolerances to Cd toxicity. Modeling parameters, EC50 and M/k, correspond to the Cd concentrations in rice plant. In the field experiment, the Cd concentrations in brown rice of the indica cultivars (i.e., TCS10, TCS17, and TNGS22) were 0.6 mg kg-1; these were significantly higher than those of the japonica cultivars (i.e. TY3, TK9, TNG71, KH145, TKW1, and TKW3). By contrast, the three cultivars, KH145, TKW1, and TKW3, whose Cd concentrations in brown rice were lower than 0.3 mg kg-1 were considered safe relative to the permissible level of 0.4 mg kg-1. In addition, for the used cultivars, Cd concentrations in brown rice were well expressed (i.e., r2 = 0.95) as a function of EC50, M/k, and MDA by using multiple regression. Newly bred cultivars could be screened rapidly with hydroponic testing to predict their Cd concentrations in brown rice when grown in the field.

The growth and uptake of Ga and In of rice (Oryza sative L.) seedlings as affected by Ga and In concentrations in hydroponic cultures.

Limited information is available on the effects of gallium (Ga) and indium (In) on the growth of paddy rice. The Ga and In are emerging contaminants and widely used in high-tech industries nowadays. Understanding the toxicity and accumulation of Ga and In by rice plants is important for reducing the effect on rice production and exposure risk to human by rice consumption. Therefore, this study investigates the effect of Ga and In on the growth of rice seedlings and examines the accumulation and distribution of those elements in plant tissues. Hydroponic cultures were conducted in phytotron glasshouse with controlled temperature and relative humidity conditions, and the rice seedlings were treated with different levels of Ga and In in the nutrient solutions. The growth index and the concentrations of Ga and In in roots and shoots of rice seedlings were measured after harvesting. A significant increase in growth index with increasing Ga concentrations in culture solutions (<10mgGaL-1) was observed. In addition, the uptake of N, K, Mg, Ca, Mn by rice plants was also enhanced by Ga. However, the growth inhibition were observed while the In concentrations higher than 0.08mgL-1, and the nutrients accumulated in rice plants were also significant decreased after In treatments. Based on the dose-response curve, we observed that the EC10 (effective concentration resulting in 10% growth inhibition) value for In treatment was 0.17mgL-1. The results of plant analysis indicated that the roots were the dominant sink of Ga and In in rice seedlings, and it was also found that the capability of translocation of Ga from roots to shoots were higher than In. In addition, it was also found that the PT10 (threshold concentration of phytotoxicity resulting in 10% growth retardation) values based on shoot height and total biomass for In were 15.4 and 10.6µgplant-1, respectively. The beneficial effects on the plant growth of rice seedlings were found by the addition of Ga in culture solutions. In contrast, the In treatments led to growth inhibition of rice seedlings. There were differences in the phytotoxicity, uptake, and translocation of the two emerging contaminants in rice seedlings.

Coupling phytotoxicity and human health risk assessment to refine the soil quality standard for As in farmlands.

In the present study, a field experiment was conducted to investigate arsenic (As) concentrations in soils and in grains of 15 rice varieties in a contaminated site in Taiwan. The studied site was divided into two experimental units, namely plot A and plot B. The results showed that mean total As concentrations were 70.94 and 61.80 mg kg-1 in plot A and plot B, respectively, and thus greater than or approximate to the soil quality standard for total As in Taiwan (60 mg kg-1). The As levels in rhizosphere soil in plot A (19.71-32.33 mg kg-1) were much higher than in plot B (6.41-8.60 mg kg-1); however, As accumulation in brown rice did not significantly differ between the plots. These results implied that a significant variation in the bioconcentration factor (BCF) value of As existed among different rice genotypes, and a negative correlation was observed between BCF value and rhizosphere As level in the soil. In phytotoxicity, the median values of the ecological risk indicator were 104.85 and 103.89 in plot A and plot B, respectively, indicating considerable risk. In human health risk assessment, the median and 97.5%-tile values for cancer risk for both male and female residents were markedly higher than the acceptable risk (1 × 10-4). Furthermore, non-cancer and cancer risks were higher for males than females, mainly due to the greater rice ingestion rate of males. Sensitivity analysis showed that total As concentration in soil was the main factor affecting health risks, suggesting that priority should be given to the reduction of soil As levels. To better manage the phytotoxicity of As on rice, as well as the health risk to residents resulting from exposure to As-contaminated soils, the soil quality standard for As in farmland soils should be set between 5 and 10 mg kg-1. The methodology developed in this study could also be applied to provide the basis for refining and revising the soil quality standard for heavy metals in farmland in other regions and countries.

Field experiments for evaluating the effects of water management and phosphate application on inorganic arsenic accumulation in water spinach (Ipomoea aquatica Forssk.).

Water spinach (Ipomoea aquatica Forssk.) is a commonly planted vegetable in the Southeast Asia; it is a semi-aquatic leafy vegetable with high inorganic arsenic (As) accumulation capability and can be planted under both upland and flooding cultivation conditions. To date, a limited number of field studies have investigated the effect of soil management on As phytotoxicity and accumulation of water spinach. Therefore, in this study, a field experiment was conducted to investigate the effects of water management and phosphate (P) application on the As phytotoxicity and accumulation of water spinach grown in As-contaminated fields (121 mg As kg-1). Water spinach was planted in the study field with two water management (flooding and upland cultivation) and two P application rates (90 and 180 kg P2O5 ha-1), and continuously harvested three times. Results reveal that the concentration and estimated daily intake (EDI) of inorganic As in the edible parts of water spinach under flooding cultivation were approximately twofold higher than those under upland cultivation. It was also found that the accumulation of As in the shoot of water spinach was strongly related to the As concentrations, rather than P/As molar ratio in pore water due to that P application rates were lower than the maximum capacity for P retention of the tested soil. Moreover, the As phytotoxicity and accumulation of water spinach were reduced at the third harvest relative to the first two harvests because of the increase in iron plaque formation on the root surface and the decrease in the growing temperature during the experimental period. Our results suggest that upland cultivation is the better practice than flooding cultivation for reducing inorganic As accumulation in the edible parts of water spinach grown in As-contaminated soils. Further, ratooning may be a feasible cultivation approach to reducing inorganic As accumulation in water spinach.

Uncovering the Genetic of Cadmium Accumulation in the Rice 3K Panel.

Because Cadmium (Cd) is harmful to humans, and most non-smokers are exposed to Cd mainly through rice consumption, low-Cd rice breeding is urgently needed. It might not be possible to apply variation created using gene editing technology to breeding directly, so it is important to explore genetic variation in this trait in a natural population. In this study, variation in 4 genes was identified among 3024 accessions from the International Rice Research Institute 3000 Rice Genome Project (IRRI 3K-RGP) and 71 other important varieties, and the relationships between the variants and plant Cd accumulation were validated with hydroponic and pot experiments. Variants in OsNRAMP1, OsNRAMP5, OsLCD, and OsHMA3 were grouped into two, four, three, and two haplotypes, respectively. Fourteen combinations of these haplotypes, which were referred to as Cd-mobile types, were found in the collection. Of these, type 14 was shown to have the greatest potential for low-Cd accumulation, and functional markers for this type were designed. The results of this study provide an important resource for low-Cd rice breeding and highlight an effective strategy for pre-breeding programs.

The growth and uptake of gallium (Ga) and indium (In) of wheat seedlings in Ga- and In-contaminated soils.

The emerging contaminants gallium (Ga) and indium (In) are extensively used in advanced industries and are considered as toxic to humans. Limited information is available on the dynamics of Ga and In in soil-upland crop systems. Therefore, this study aimed to investigate the effects of Ga and In on the growth and uptake of Ga and In by wheat plants grown in Ga- and In-contaminated soils. The wheat seedlings were planted in soils of different properties spiked with various Ga and In concentrations (50, 100, 200, and 400 mg kg-1). The plant-available Ga, In, and Al in the soils were extracted by 0.02 M CaCl2, and their concentrations in plant tissues of wheat seedlings and plant biomass were determined after harvesting. The results indicated that the Al toxicity of wheat seedlings increased with Ga and In concentrations in acidic soils. Indium phytotoxicity was found in both neutral and acidic soils. Plant analysis results indicated that the concentration of Ga and In in roots was approximately one order of magnitude higher than that in the shoots of wheat seedlings, and the capability for Ga translocation from roots to shoots was higher than for In. The results of this study suggest that the dynamics of Ga and In in soil-upland crop systems is strongly dependent on the soil properties, such as pH and Al availability.

Comparison of As accumulation and speciation in water spinach (Ipomoea aquatica Forssk.) grown in As-elevated soils under flooding versus upland conditions.

Water spinach (Ipomoea aquatica Forssk.) is a popular semi-aquatic vegetable with high arsenic (As) accumulation capability in tropical and subtropical areas, and it can grow under both flooding and upland conditions. Because only few studies addressed the dietary As risk of vegetable consumption, this study investigated the accumulation and speciation of As in the water spinach, and the human health risk of consuming this crop grown in different water managements. Pot experiments were conducted in two soils with different As levels under both flooded and upland conditions. The results showed that As concentrations, mainly inorganic As, in soil pore water and shoots under flooded conditions increased 2.05- to 5.11-fold and 1.30- to 2.55-fold respectively as compared with upland conditions. Even though Fe plaque formation on the root surface was higher under flooded conditions than under upland conditions, it still cannot act as an effective barrier to sequester As released from flooded soils into plant tissue. The dietary risk of consuming inorganic As through water spinach planted in flooded soils was higher than in upland soils, especially in high-As-level soils. This suggests that in As-elevated soils, water spinach should be planted in upland conditions rather than in flooding conditions.

Assessing human health risk of arsenic for rice consumption by an iron plaque based partition ratio model.

A field experiment was conducted to study the transport and uptake of arsenic (As) from soil to rice roots and the subsequent translocation from roots to shoots and grains. Twelve rice cultivars were used in the field experiment. The amount of As accumulated in rice grains and sequestered by root iron plaque and rhizosphere soil, were determined to establish the relationship between As concentrations in brown rice and As sequestration by iron oxides. Human health risk was then assessed for Taiwan's population exposed to As through rice consumption. The result of this study showed that the mean total As concentrations in the experimental site and in brown rice were 93.02 mg/kg and 0.158 mg/kg, respectively. The As sequestration by iron oxides on root plaque (3.48-9.51) was higher than that of the rhizosphere soil (1.86-4.09) for all tested rice cultivars. Therefore, the partition ratio (PR) representing the relative tendency of As sequestration by rhizosphere soil to that in root iron plaque was all less than 1. In addition, there was a significant negative linear relationship between inorganic As concentration (iAs) in brown rice and PR value (r2 = 0.38, p < 0.05). Based on the iAs in brown rice, the median value of hazard quotient (HQ) and target cancer risk (TR) was 1.13 and 5.10 × 10-4, respectively, indicating potential cancer and non-cancer risk for Taiwan residents exposed to As through the consumption of rice grown on the studied site. Various PR values were then successfully used for estimating risk, implying that screening the PR of the rice plant before harvest could serve as an early warning signal for protecting consumers' health. However, more experiments with different rice cultivars for the paddy soils were suggested in the future to establish a comprehensive relationship between iAs in brown rice and PR value.

Effect of applying calcium peroxide on the accumulation of arsenic in rice plants grown in arsenic-elevated paddy soils.

Water management such as drainage for creating aerobic conditions is considered to be an adequate method for reducing the accumulation of arsenic (As) in rice grains; however, it is difficult to conduct drainage operations in some areas that experience a lengthy rainy season as well as in soils with poor drainage. In this regard, application of oxygen-releasing compounds (ORCs) may be an alternative method for maintaining aerobic conditions even under flooding in paddy soils. Therefore, a pot experiment was conducted to investigate the effects of application of an ORC, calcium peroxide (CaO2), on the growth and accumulation of As in rice plants grown in As-contaminated paddy soils. The rice plants were grown in two soils with different characteristics and As levels, and all of the tested soils were treated with 0, 5, 10, and 20 g CaO2 kg-1. Results revealed that the concentration of As and the distribution of arsenite in the pore water of all tested soils was reduced by CaO2 application. In addition, the grain yields increased and the concentration of inorganic As in brown rice decreased by 25-45% upon CaO2 treatment of low-As-level soils (<16 mg kg-1). However, the effect of CaO2 application on the accumulation of inorganic As in brown rice in As-enriched soils (>78 mg kg-1) could not found in this study, due to the rice plant suffered from serious As phytotoxicity. It suggests that CaO2 amendment may be suitable for reducing the As concentration of rice grains grown in low-As-level paddy soils, but for As-enriched soils, the proposed CaO2 application method is not feasible.

Aspects of cultivar variation in physiological traits related to Cd distribution in rice plants with a short-term stress.

BACKGROUND: Genotypic variations are seen in cadmium (Cd) tolerance and accumulation in rice plants. Cultivars that show low Cd translocation from the root into shoot can be selected to reduce Cd contamination in rice grains. This study aims to clarify the physiological regulation related to Cd absorption by rice plants for screening out the cultivars, which have relatively low Cd accumulation in grains. Eight Taiwan mega cultivars of paddy rice: japonica (TY3, TK9, TNG71, and KH145 cultivars), indica (TCS10 and TCS17 cultivars), and glutinous (TKW1 and TKW3 cultivars), which are qualified with the criteria for rice grain quality by the Council of Agriculture, Taiwan, were used for illustration. An experiment in hydroponics was conducted for the rice seedlings with a treatment of 50 µM CdCl2 for 7 days. RESULTS AND DISCUSSION: After the Cd treatment, the reductions in shoot growth were more significant than those in root growth; however, Cd absorbed in the rice plant was sequestered much more in the root. The malondialdehyde (MDA) was preferentially accumulated in rice root but the hydrogen peroxide (H2O2) was increased more significantly in the shoot; the antioxidative enzymes, superoxide dismutase (SOD) and ascorbate peroxidase (APX), were pronounced more in rice shoot. CONCLUSIONS: The rice cultivars preferentially accumulated Cd in the root rather than the shoot with the Cd treatment, which resulted in significant enhancements of MDA and growth reductions in the root. However, H2O2 accumulation was toward the shoot to retard shoot growth suddenly and then the root could keep a gradual growth. Also, the rice cultivars, which preferentially accumulate Cd in the root, would have the regulation tendency of SOD toward the shoot. Due to that SOD is responsible for H2O2 production, H2O2 accumulation would be thus toward the shoot. Moreover, the cultivars, which have a less regulation tendency of APX toward the shoot, would present higher translocation of Cd into the shoot.

Accumulation of gallium (Ga) and indium (In) in rice grains in Ga- and In-contaminated paddy soils.

To understand the risk of two emerging contaminants, gallium (Ga) and indium (In) to humans via rice consumption, effects of soil properties and concentrations of spiked Ga/In on the accumulation of Ga and In in rice grains were investigated. A pot experiment was conducted, and paddy rice was grown in three soils with different pH values and Al availabilities (i.e., Pc, TWz and Cf), which were spiked with various Ga and In concentrations. The growth index and concentrations of Ga, In, and Al in plant tissues and soil pore water were measured. Results revealed that the concentrations of Ga and In in soil pore water increase with the spiking of Ga or In in all of the tested soils, but the biomass of roots and shoots does not significantly decrease. The accumulation of Ga in shoots and brown rice was significantly reduced in high available Al acidic soils (Pc soils), but this accumulation was significantly increased in low available Al acidic soils (TWz soils), which can be explained by the competitive uptake between Ga and Al by rice plants. The extent of competitive effects between In and Al was less than that between Ga and Al because of the lower solubility and translocation capability of In than those of Ga in soil-rice systems. However, significant differences in the concentrations of Ga and In in brown rice in neutral soils (Cf soils) among the Ga or In treatment were not observed. In addition, the iron plaque formed on the root surface can serve as a barrier to reduce the accumulation of Ga in rice plants. This study suggested that the risk of accumulation of Ga and In in rice grains should be of concern when paddy rice is grown in acidic Ga- or In-contaminated soils with low Al availability.

Growth inhibition of rice (Oryza sativa L.) seedlings in Ga- and In-contaminated acidic soils is respectively caused by Al and Al+In toxicity.

Limited information exists on the effects of emerging contaminants gallium (Ga) and indium (In) on rice plant growth. This study investigated the effects on growth and uptake of Ga and In by rice plants grown in soils with different properties. Pot experiment was conducted and the rice seedlings were grown in two soils of different pH (Pc and Cf) spiked with various Ga and In concentrations. The results showed concentrations of Ga, In, and Al in soil pore water increased with Ga- or In-spiking in acidic Pc soils, significantly decreasing growth indices. According to the dose-response curve, we observed that the EC50 value for Ga and In treatments were 271 and 390mgkg-1 in Pc soils, respectively. The context of previous hydroponic studies suggests that growth inhibition of rice seedlings in Ga-spiked Pc soils is mainly due to Al toxicity resulting from enhanced Al release through competitive adsorption of Ga, rather than from Ga toxicity. In-spiked Pc soils, both In and Al toxicity resulted in growth inhibition, while no such effect was found in Cf soils due to the low availability of Ga, In and Al under neutral pH conditions.

Field experiment for determining lead accumulation in rice grains of different genotypes and correlation with iron oxides deposited on rhizosphere soil.

Paddy rice (Oryza sativa L.) is a major staple crop in Asia. However, heavy metal accumulation in paddy soil poses a health risk for rice consumption. Although plant uptake of Pb is usually low, Pb concentrations in rice plants have been increasing with Pb contamination in paddy fields. It is known that iron oxide deposits in the rhizosphere influence the absorption of soil Pb by rice plants. In this study, 14 rice cultivars bred in Taiwan, including ten japonica cultivars (HL21, KH145, TC192, TK9, TK14, TK16, TN11, TNG71, TNG84, and TY3) and four indica cultivars (TCS10, TCS17, TCSW2, and TNGS22), were used in a field experiment. We investigated the genotypic variation in rice plant Pb in relation to iron oxides deposited in the rhizosphere, as seen in a suspiciously contaminated site in central Taiwan. The results showed that the cultivars TCSW2, TN11, TNG71, and TNG84 accumulated brown rice Pb exceeding the tolerable level of 0.2mgkg-1. In contrast, the cultivars TNGS22, TK9, TK14, and TY3 accumulated much lower brown rice Pb (<0.1mgkg-1); therefore, they should be prioritized as safe cultivars for sites with potential contamination. Moreover, the iron oxides deposited on the rhizosphere soil show stronger affinity to soil-available Pb than those on the root surface to form iron plaque. The relative tendency of Pb sequestration toward rhizosphere soil was negatively correlated with the Pb concentrations in brown rice. The iron oxides deposited on the rhizosphere soil but not on the root surface to form iron plaque dominate Pb sequestration in the rhizosphere. Therefore, the enhancement of iron oxide deposits on the rhizosphere soil could serve as a barrier preventing soil Pb on the root surface and result in reduced Pb accumulation in brown rice.

Adsorption of tetracycline on Fe (hydr)oxides: effects of pH and metal cation (Cu2+, Zn2+ and Al3+) addition in various molar ratios.

Iron (Fe) (hydr)oxides control the mobility and bioavailability of tetracycline (TC) in waters and soils. Adsorption of TC on Fe (hydr)oxides is greatly affected by polyvalent metals; however, impacts of molar metal/TC ratios on TC adsorptive behaviours on Fe (hydr)oxides remain unclear. Results showed that maximum TC adsorption on ferrihydrite and goethite occurred at pH 5-6. Such TC adsorption was generally promoted by the addition of Cu2+, Zn2+ and Al3+. The greatest increase in TC adsorption was found in the system with molar Cu/TC ratio of 3 due to the formation of Fe hydr(oxide)-Cu-TC ternary complexes. Functional groups on TC that were responsible for the complexation with Cu2+shifted from phenolic diketone groups at Cu/TC molar ratio < 1 to amide groups at Cu/TC molar ratio ≥ 1. For the addition of Al3+, the complexation only took place with phenolic diketone groups, resulting in the enhanced TC adsorption at a molar Al/TC ratio of 1. However, TC adsorption decreased for Al/TC molar ratio > 1 as excess Al3+ led to the competitive adsorption with Al/TC complexes. For the Zn2+ addition, no significant correlation was found between TC adsorption capacity and molar Zn/TC ratios.

Arsenic accumulation and speciation in rice grains influenced by arsenic phytotoxicity and rice genotypes grown in arsenic-elevated paddy soils.

Rice consumption is a major route of As exposure to human for the population of worldwide. This study investigates the effect of phytotoxicity and rice genotypes on the content and speciation of As in rice grains grown in different levels of As-elevated paddy soils from Taiwan. Three levels of As-elevated soils and six rice genotypes commonly planted in Taiwan were used for this study. The results indicate that As contents in grains of rice is not proportional to soil As concentrations and they were equal or higher in indica genotypes than japonica genotypes used in this study. It was also found that the As phytotoxicity not only reducing the grain yields but also the As concentrations in grain of rice. The predominant As species found in rice grains were dimethylarsinic acid (DMA) and arsenite. The concentrations of DMA increased with total As concentrations, wherggeas the arsenite remained in a narrow range from 0.1 to 0.3 mg kg(-1). Because of the lower toxicity of DMA than inorganic As species, the health risks may not be increased through consumption of rice even when total As content in the grains is increased.

Increase of As release and phytotoxicity to rice seedlings in As-contaminated paddy soils by Si fertilizer application.

Silicon (Si) was shown to be able to reduce arsenic (As) uptake by rice in hydroponic culture or in low As soils using high Si application rates. However, the effect of Si application on As uptake of rice grown in As-contaminated soils using Si fertilizer recommendation rate has not been investigated. In this study, the effect of Si application using Si fertilizer recommendation rate on As release and phytotoxicity in soils with different properties and contents of As was examined. The results show that the concentrations of As in soil solutions increased after Si applications due to competitive adsorption between As and Si on soil solids and the Si concentrations in soil solutions were also elevated to beneficial levels for rice growth. The rice seedlings accumulated more As and its growth was inhibited by Si application in As contaminated/spiked soils. The results indicate that there is an initial aggravation in As toxicity before the beneficial effects of Si fertilizing to rice were revealed when Si application based on fertilizer recommendation rate to As-contaminated paddy soils. Therefore, for As-contaminated paddy soils with high levels of As, the application of Si fertilizer could result in increasing As phytotoxicity and uptake by rice.