Chien-Hui Syu

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.

Arsenic sequestration in iron plaque and its effect on As uptake by rice plants grown in paddy soils with high contents of As, iron oxides, and organic matter

Abstract The aim of this study is to investigate the effects of the rice (Oryza sativa L.) roots iron (Fe) plaques on arsenic (As) uptake by rice plants grown in As-contaminated soil with high contents of iron oxides and organic matter, from the Guandu Plain of northern Taiwan. The results of the soil incubation study show that both As and Fe concentrations in the soil solutions increased with flooding time due to reductive dissolution of iron oxides induced by the soils high contents of organic matter. Large Fe plaques were deposited on rice roots and substantial amounts of As were sequestrated in these Fe plaques. About 73.8 to 90.4 % of the total As released from soils was distributed in the iron plaques and only a small proportion was distributed in the rice plants. This study provides evidence that iron plaques are the main controlling factor in limiting the uptake of As into the rice plants grown in the tested soils, and that iron plaque formation enhancement could be used to reduce As uptake by paddy rice grown in As-contaminated soils, thus reducing As toxicity.

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.

Effects of foliar and soil application of sodium silicate on arsenic toxicity and accumulation in rice (Oryza sativa L.) seedlings grown in As-contaminated paddy soils

ABSTRACT Silicon (Si) and arsenite (iAsIII) share the same pathway of uptake and translocation in rice (Oryza sativa L.), and it has been reported that Si can decrease arsenic (As) uptake by rice in hydroponic culture. Due to the competitive sorption between Si and As for the soil minerals, different extents of effects on As toxicity and uptake by rice as influenced by soil Si application were found. In order to avoid the competitive sorption between Si and As for the soil minerals, foliar applications of Si might be a more efficient alternative to reduce As uptake by rice. Therefore, the aim of this study was to investigate the effects of Si foliar and soil applications on the growth and As accumulation in rice seedlings. In this study, three application rates of Si (as sodium silicate) were applied to (1) the foliage and (2) the soil, of rice grown in two soils with different Si retention capacities and As contents. The results showed that there were no significant differences in Si concentrations in shoots among different Si foliar applications, and it had no significant effect on the growth and As accumulation in rice seedlings. In contrast, soil applications of Si caused a decrease in As accumulation in shoots grown in the tested soils, resulting from a high Si/As ratio in the soil pore water allowing enough Si to out-compete the As for uptake by roots. These results were further supported by the significant negative correlation found between Si and As in the shoots. However, a growth inhibition of rice plants was also observed due to As toxicity from the addition of excessive treatments of Si into As-contaminated soils. Therefore, the results of this study suggest that foliar applications of Si are not able to decrease As accumulation in rice seedlings, but that the application of moderate amounts of Si into As-contaminated soils could effectively reduce As uptake by rice seedlings.

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.

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.