Introduction

Arsenic (As) is a widespread environmental pollutant and a Group I human carcinogen (Bradham et al. 2018; Martinez et al. 2011). The main sources of As in the soil are weathering of As-containing rocks, coal combustion, As-based pesticides and herbicides, chromated copper arsenate for wood preservation, and mining (Kumar et al. 2016). Arsenate (As(V)) and arsenite (As(III)) are the dominant inorganic forms of As in the environment. Arsenate is mostly present in aerated soils and arsenite is prevalent in paddy soils (Takahashi et al. 2004). The transformation of As(V) to As(III) can result in retention of the element in plants, mostly in the roots, and its subsequent compartmentalization in the root vacuoles as arsenite-phytochelatins (Li et al. 2016). Silicon (Si) transporters are able to load As(III) into the xylem or exude As(III) outside of the roots (Zhao et al. 2010). The competition between As(III) and silicic acid inhibits As(III) uptake (Fleck et al. 2013).

The Shimen realgar mine (29°38′11″–29°38′42″N, 111°2′06″–111°2′22″E) is located in Shimen County, Hunan Province. This mine is the largest deposit of realgar in Asia, with a mining history of more than 1500 years, until it closed in 2011 (Yang et al. 2018). The mining there has resulted in As pollution of a large area including agricultural land e, with soils containing up to 5240 mg kg−1 of As (Tang et al. 2016). The former mining and transport of As and disposal of mine tailings, wastewater, and waste residuals caused severe As pollution in both the nearby Huangshui River and the Xieshui River, which is only a few kilometers further away from the mine (Chi et al. 2017; Zheng et al. 2012). Water from these rivers is used to irrigation the rice paddies.

Rice (Oryza sativa L.) is a staple crop in a large part of the world, especially in East Asia. Rice accumulates high quantities of As in grains, compared to other cereals such as wheat and barley (Su et al. 2010). In rice paddy soils, total As content typically ranges between 4 and 8 mg kg−1, but it can reach up to 83 mg kg−1 in areas where the land has been irrigated with As-contaminated water (Williams et al. 2007). Arsenic(III) is a dominant form of As under paddy conditions, but monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenate are also present in flooded soils (Abedin et al. 2002). Arsenic toxicity causes inhibition of adenosine triphosphate (ATP) formation, which adversely impacts yield (Panaullah et al. 2009). Toxicity symptoms such as retarded development, brown spots, and scorched spots were observed on plants in soils containing > 60 mg kg−1 of As (Choudhury et al. 2011; Khan et al. 2010). Arsenic(III) reacts with sulphydryl groups of enzymes and proteins and disturbs cellular functions. At the metabolic level, As triggers the generation of reactive oxygen species (ROS), thus leading to oxidative stress (Shrivastava et al. 2015).

Silicon is considered to be a quasi-essential element for plants (Luyckx et al. 2017), which absorb Si as monosilicic acid [Si(OH)4]. Rice is recognized as a Si accumulator and plant tissue can contain more than 10% Si (dry weight; Yamamoto et al. 2012). Silicon protects plants against numerous biotic and abiotic stresses through: (1) a physical or mechanical protection; (2) physiological reinforcement of the cell and inter-cell organelles and membranes, including chlorophylls and mitochondria; (3) chemical precipitation of inorganic pollutants, and (4) a biochemical response triggering metabolic changes (Meharg and Meharg 2015; Vaculik et al. 2015). Over the last 5–10 years, many authors have reported that Si-rich substances alleviate the negative influence of As on various plants (Fleck et al. 2013; Gupta and Khan 2015; Sanglard et al. 2016; Seyfferth et al. 2018; Silva et al. 2015). For example, it has been shown that Si reduces plant uptake and translocation of As by competition for transport (Fleck et al. 2013; Gupta and Khan 2015; Sanglard et al. 2016; Seyfferth et al. 2018; Tripathi et al. 2013). Improved Si nutrition was also reported to mediate photosynthetic performance and enhance antioxidant enzyme activity in As-exposed plants (Gupta and Khan 2015; Sanglard et al. 2016; Silva et al. 2015; Tripathi et al. 2013). While most studies focus on the plant mechanisms responsible for the Si-induced alleviation of As stress, it is also important to consider the soil–plant system. The effect of Si-rich materials applied to soil on As adsorption, precipitation, and complexation is poorly studied. Some authors observed an increase in As mobility through replacement of As anion by silicic acid (Seyfferth et al. 2018). Our previous study evidenced higher As adsorption by sand and different Si minerals with increasing amounts of monosilicic acid (Ji et al. 2017). The main aim of this investigation was to determine the effect of applying potassium silicate (K2SiO3) to soil on As mobility in soil and its translocation to rice.

Materials and Methods

Two paddy soils differing in total As (30.6 and 66.9 mg kg−1 in moderately and highly polluted soil) were selected. Soil samples were collected near the realgar (arsenic sulfide mineral) mining area. The coordinates of the first site were E111°3′30.2″, N29°39′46.3″ and of the second site—E111°2′51.1″, N29°39′44.3″. Rice has been grown in both fields for more than 50 years. Soils were sampled from a 0–10 cm depth, air-dried at room temperature (25–28 °C), ground, and passed through a 2-mm sieve. The basic soil properties were analyzed using standard procedures (Sparks et al. 1996). The data obtained is presented in Table 1.

Table 1 Selected chemical properties of the paddy soils
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Rice (O. sativa L. cv. Yuzhenxiang) seeds were obtained from the Institute of Rice (Hunan Province). Seeds were soaked in 10% H2O2 for 10 min, rinsed in double-distilled water, and germinated in autoclave-sterilized water. After 6 days of germination, plants were transferred to aerated nutrient solution. The solution was prepared according to Kukier and Chaney (2002) using deionized water, as follows: 126 mg L−1 KNO3, 33 mg L−1 CaCl2, 60 mg L−1 MgSO4, 68 mg L−1 KH2PO4, 66 mg L−1 (NH4)2SO4, 7.6 mg L−1 Fe–EDTA, 0.002 mg L−1 Na2MoO4, 0.12 mg L−1 H3BO3, 0.12 mg L−1 MnCl2, 0.32 mg L−1 CuSO4, 0.32 mg L−1 ZnSO4. The final pH was adjusted to 5.5 with 1 N NaOH or 1 N HNO3 and monitored throughout the experimental period. Growth solution was changed every 5 days for 30 days. Six seedlings were put into a pot at the 3-leaf stage (5 kg of soil, 25 cm diameter, and 20 cm height). Nitrogen as urea at 200 mg kg−1, P as CaH2PO4 at 150 mg kg−1, and K as KCl at 200 mg kg−1, were applied to the soil before planting the rice. Silicon was then added as K2SiO3 (PS) as follows: soil 1, no Si (T1SiCK); soil 1, 150 mg kg−1 Si (T1Si1); soil 1, 300 mg kg−1 Si (T1Si2); soil 2, no Si (T2SiCK); soil 2, 150 mg kg−1 Si (T2Si1); soil 2, 300 mg kg−1 Si (T2Si2). The rice was grown under waterlogged conditions with 2–3 cm of water above the soil surface. Deionized water was added every 2 days to maintain the same approximate level of flooding. The temperature regime was 26 ± 2 °C during the day and 24 ± 2 °C at night. The light and night periods were each 12 h, with a light intensity of 950 mmol photons m−2 s−1. The air humidity was 75 ± 5% during the day and 70 ± 5% at night.

Plants were harvested after maturity (105 days after transplanting) and the biomass of the roots, shoots, and grains were measured. The collected plant tissues were dried at + 65 °C for 24 h and weighed. Soils were sampled with harvesting, air-dried at room temperature, ground, and passed through a 1 mm sieve.

Plant Analysis

The total As in the roots, shoots and grain was analyzed by the following method. Dried, milled and passed through a 0.2-mm sieve plant sample (0.5 g) was put into a conical flask with 5 mL of concentrated nitric acid (HNO3) The prepared solution was kept overnight at room temperature and then heated using a hot block at 12 °C until the extracts became clear. The digested solution was made up to a volume of 20 mL using deionized water and analyzed for As by atomic fluorescence spectrometry (AFS-7300).

The method of evaluating As speciation [As(V), As(III), and DMA] has been described by Shi et al. (2013). A milled sample of grain (1.0 ± 0.01 g) was put into a 50 mL centrifuge tube and extracted with 20 mL of 1% HNO3 at 95 °C for 1.5 h. Then samples were cooled to room temperature and centrifuged at 5000 rpm for 10 min. The supernatant solution was filtered through a 0.22 μm filter. Arsenic was analyzed by HPLC-HG-AFS (Shimadzu LC-15C Suzhou Instruments Co., China; HG-AFS, AFS8230, Beijing Jitian Instruments Co., China).

To analyze total Si in plant tissue, a dried and ground plant sample of 0.20 ± 0.01 g was placed into a Teflon tube, then 4 mL of 50% NaOH was added. After standing overnight, 2 mL of 30% H2O2 was added, then the tubes were kept for 30 min, capped and placed into the microwave (CEM MARS 6 MS5181) for 30 min. Silicon in the obtained solution was analyzed by the Mullin and Riley method (1955).

Soil Analysis

The plant-available Si in the soil was determined by a 3.6 g L−1 HCl extract, according to the following procedure: Ten (10.0 ± 0.01) g of an air-dried soil sample was placed in a 100 mL polyethylene cup; 50.0 mL of 3.6 g L−1 HCl was added to each cup and the mixture was agitated at 200 rpm for 0.5 h. Then, after standing overnight, the mixture was agitated again for 0.5 h, and then the supernatant was centrifuged at 7000 rpm for 15 min (Matichenkov and Ammosova 1996; NIAES 1987). The Si was analyzed in a centrifuged solution using the Mullin and Riley method (1955). Soil As speciation was evaluated by sequential extraction (Herreweghe et al. 2003), as presented in Table 2.

Table 2 Different As fractions of sequential extraction
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Statistical Analysis

All data was entered into Microsoft Excel (2007). Analysis of variance was determined using SPSS 17.0. Figures were created by origin 8.0. The absorption factor (AF) was calculated as follows: AF = As concentration in roots/initial As concentration in soil. The arsenic translocation factors (TFs) were calculated as follows (Liu et al. 2014; Ye et al. 2012): TF1 of As from root to shoot = As concentration in roots/As concentration in shoots; TF2 of As from shoot to grain (maturity) = As concentration in grain/As concentration in shoots.

Results

The biomass of roots, shoots, and grains are shown in Table 3. The weight of roots, shoots, and grains in Soil 2 was 37.5, 9.7, and 18.8% less, respectively, than that in Soil 1. Application of PS significantly increased the biomass of plants. PS at a low rate increased biomass of the roots by 18.3 and 16.9%, biomass of the shoots by 12.3 and 12.6%, and grain yield by 20.1 and 14.8% in Soils 1 and 2, respectively. The higher rate of PS increased the rice biomass by 26.0–38.4% (Fig. 1).

Table 3 Dry weight of roots, shoots and grain (g plant−1)
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Fig. 1
figure 1

Soil concentration of acid-extractable Si after experiment, mg kg−1

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In our study, the 0.1 M HCl extraction method was used to assess soil Si available for plant uptake. Numerous methods have been suggested for determining the plant-available Si in the soil (Bocharnikova and Matichenkov 2012; Miles et al. 2014). The literature indicates that the 0.1 M HCl-extractable Si in the soil correlates better with total plant Si than other Si extraction methods (Bocharnikova and Matichenkov 2012; Matichenkov and Ammosova 1996). The correlation coefficients between 0.1 M HCl-extractable soil Si and plant Si was 0.89–0.95 (Bocharnikova and Matichenkov 2012; Matichenkov 2007), while it did not exceed 0.77 for the CaCl2 extraction method, one of the most commonly used methods of evaluating mobile Si in soil (Georgiadis et al. 2014; Miles et al. 2014). The concentration of plant-available Si in both untreated soils was 43.2 mg kg of Si (Table 4). The K2SiO3 addition increased this by 40.6–46.9 and 64.4–67.8%, according to the application rate.

Table 4 Plant-available Si in soil, pH of soil and total Si in the roots and shoots of rice
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The total content of Si in the roots and shoots differed depending on the level of As soil contamination. Without Si treatment, the root Si was 0.81% of Si in Soil 1 and only 0.56% of Si in Soil 2. The shoot (stem + leaf) Si amounted to 1.68 and 1.16% in Soil 1 and Soil 2, accordingly. Application of PS increased that up to 0.91 and 0.97% of the root Si in Soil 1, but reduced it to 0.52 and 0.50% in Soil 2. The shoot Si was significantly affected by Si added at a low rate (2.24 and 1.49% of Si in Soils 1 and 2), whereas a higher Si rate had little effect (Fig. 2).

Fig. 2
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Concentration of total Si in shoots and roots, %

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The original soils were slightly acid with a pH of 5.43 (Soil 1) and 5.46 (Soil 2). Application of PS increased the pH to 6.06 and 6.17, and to 6.59 and 6.58, in Soils 1 and 2, respectively.

The total As concentrations in the rice plants are presented in Table 5. The most As (90.37 mg kg−1) was observed in the roots of the rice in Soil 2. The shoot As was 89.5% less than in the roots in Soil 1 and 84.3% less in Soil 2. The minimum As was detected in the rice grains (0.46 and 0.81 mg kg−1 of As, accordingly in Soils 1 and 2).

Table 5 Arsenic concentration in shoots, roots and grain of rice under different treatments, mg kg−1 As
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The PS significantly decreased the total As in all of the plant parts. The As reductions were greater in the roots and grains (by 43.3 and 32.0%, respectively) in Soil 1 at the higher PS application rate. The shoot As decreased more (by 40.4%) in Soil 2 at the higher PS application rate.

In the rice grains, As was mostly present as As(III) (Table 6). As As increased in the soil, all of the tested forms of As in the grain increased: As(III)—by 79.2%, As(V)—by 7,6%, and DMA—by 187.8%. While the Si application did not significantly affect the As(V) content, it significantly reduced As(III) content in the rice grains by 41.2 and 30.6%, when applied at a low rate, and by 51.0 and 42.0% at a high rate, in Soils 1 and 2.

Table 6 Content of As(III), As(V) and DMA in rice grain
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The As content in the different soil fractions is presented in Table 7. In the original Soil 1, the maximum As was observed in fraction 3 (3.68 ± 0.07 mg kg−1 As), while the maximum As content in the original Soil 2 was detected in fraction 5 (9.89 ± 0.71 mg kg−1 As). Five fractions in total comprised about 33% of the soil As. Application of PS reduced As mobility in the soil. The amount of As in the first two fractions was decreased in both soils and at both Si rates. The NaOH-extractable As was increased in Soil 1 at a higher Si rate and in Soil 2 at both Si rates. The H2SO4-extractable As was insignificantly reduced by Si in Soil 1 and significantly increased in Soil 2. Silicon added at both rates increased the residual As in both soils (Fig. 3).

Fig. 3
figure 3

Effect of applied PS on the soil pH

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Table 7 Content of As in sequential extraction fractions in the soil
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Discussion

The test soil was collected near Asia’s biggest realgar mine. The As concentrations in the Xianyang River range from 0.01 to 28 mg L−1 (Chi et al. 2017). Periodic aeration of the soil during rice harvesting initiates As oxidation and transformation into less mobile forms (Geng et al. 2017). Then additional As enters the soil with irrigation.

As(V) is the dominant form of the element in aerobic soils. Because of adsorption to iron (Fe), aluminum (Al), and manganese (Mn) oxides and hydroxides, soluble forms of As are low (Inskeep et al. 2002). In flooded fields, Fe3+ is reduced to Fe2+ and As is released into the soil solution. In addition, As(V) is reduced to As(III), which is more mobile than arsenate (Takahashi et al. 2004). However, continuous changes in the redox state for many years have led to strong As fixation in Soil 2. As a result, the more soluble forms of As (fraction 1) were similar in Soils 1 and 2. But the more contaminated Soil 2 had a greater content of the less soluble forms of As (fractions 3–5) than Soil 1. This can be attributed to the process of As chemical fixation, which proceeds more actively in the more contaminated Soil 2.

Although the soluble forms of As were similar in the two soils, there was significantly more biomass in Soil 1 (by 16.4% for whole plants and 37.5% for roots) than in Soil 2. This suggests that even soil-bound As might have a deleterious effect on plant growth and that it could be partially transformed into plant-available As during the growing season. The AF for the control plants in Soil 1 was twice as high as that in Soil 2 (Table 8). In our study, a large difference in the AF values between two soils is attributed mostly to the difference in the total soil As, whereas plant-available forms in both soils as well as the root content of As did not differ much.

Table 8 Adsorption and translocation factors of As
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It is important that the control plants in Soil 1 had a much lower TF1 than Soil 2. Therefore, natural plant mechanisms responsible for restricting root to shoot As translocation were more efficient in the less contaminated soil. The TF2 was the same for the control plants in both soils. According to Gupta et al. (2011), retention can be mediated through As compartmentation in vacuoles, complexation by glutathione and peptides, transformation into non-toxic organic forms, and volatilization into the atmosphere.

Soil-applied PS significantly reduced AF values in both soils, and the effect was increased at a greater PS rate. As in the control plants, TF1 was less in the less contaminated Soil 1 than in Soil 2, but a direct correlation between PS application and TF1 was not observed. The TF2 values differed insignificantly in both PS-treated soils. Apparently, the PS mostly impacted the transfer of As from soil to root.

The PS application significantly decreased the mobility of As in the soil and its accumulation by the rice. At the same time, the amount of strongly adsorbed As are increased. Therefore PS application stabilized the As in the soil–plant system. Several mechanisms could be suggested to explain the PS effect on As behavior.

The first mechanism is based on a PS-mediated increase in soil sorption capacity. Our previous experiments on As sorption showed that the sorption capacity of Si-rich minerals rises with increasing monosilicic acid concentration (Ji et al. 2017; Peng et al. 2017). The dissolution of PS and the formation of monosilicic acid could be responsible for enhanced As sorption to the soil. In the scientific literature on As adsorption, many studies focus on the role of Fe-based minerals in As immobilization. Monosilicic acid was reported to compete with As for adsorption on different Fe minerals, thus decreasing the metalloid retention (Möller and Sylvester 2008). However, this data was not obtained for soil, but for chemically pure Fe-based minerals and at high pH levels. In our work, the soils were characterized by pH of about 5.6 and a predominance of silicates in mineral composition. There was only 23.1–23.3 mg kg−1 of total Fe in the soil, so the role of Fe minerals in As fixation was low. We suspect that monosilicic acid, a product of PS dissolution, is initially adsorbed on Si-based minerals due to their chemical affinity, thus forming additional As-adsorbing sites (Ji et al. 2017; Peng et al. 2017).

Another possible PS-mediated mechanism is related to the observed increased pH in the tested soil, which would slightly decrease the sorption of As(V) and DMA, but increase sorption of As(III) (Smith et al. 1998). Considering that As(V) is reduced to As(III) under flooded conditions, total As adsorption could be enhanced.

During the first 30 days of the current study, all rice plants were grown at a low level of Si, mostly the Si available in grain husks (about 1 mg of Si grain−1). However, this period is characterized by enhanced vegetative growth and consequent high Si uptake (Ma and Takahashi 2002). After this period, the biomass production rate decreases and the demand for Si diminishes as well. After replanting, the plant’s Si absorption was not intensive and as a result, the total Si in the control and Si-treated mature plants differed insignificantly.

The application of PS significantly reduced the total As in all of the analyzed parts of the rice plant. This data is consistent with other studies (Fleck et al. 2013; Gupta and Khan 2015; Sanglard et al. 2016; Seyfferth et al. 2018; Silva et al. 2015). PS was selected as a common source of monosilicic acid in soil-rice system research (Buck et al. 2008; Raj and Pannu 2017). This substance totally dissolves, forming monosilicic acid, the only Si form that is taken up by plants (Ma and Takahashi 2002). Therefore, it is possible to state that there was a monosilicic acid-induced effect on As transport in rice plants. There are a lot of Si-rich materials that can serve as a source of monosilicic acid: diatomites, zeolites, amorphous silica, some Si-based industrial by-products (Bakhat et al. 2018; Ji et al. 2017; Wei et al. 2018). In this study, we used chemically pure PS to eliminate the influence of solid particles on the As behavior in soil. Our previous investigations and other reports, conducted with diatomite, calcium silicate slag, and amorphous silica have shown that improved plant Si nutrition reduced the root to leaf transport of inorganic pollutants via apoplast and symplast in rice plants (Ji et al. 2017; Wei et al. 2018). We have also shown that added Si reduced the stem to leaf As transport in rice more intensively than the root to stem transport (Wei et al. 2018).

In the grain, the PS application reduced the concentration of As(III), while its influence on As(V) was insignificant. According to Ma et al. (2007, 2008), arsenite is taken up by the rice roots via Lsi1 and/or Lsi2. The same transporters facilitate Si accumulation by rice. The competition between Si and As(III) transport could be responsible for: less Si accumulation in rice in the more contaminated Soil 2, and less As accumulation in both soils with the PS application.

Conclusion

The current study demonstrates that PS applied to As-contaminated paddy soil had a combined impact on the As behavior via soil and plant mechanisms. It contributed to: (a) reduced As bioavailability by altering As speciation in the soil, with increasing fixation in the residual fraction; (b) decreased As uptake by and translocation within rice plants; and (c) mitigation of biotoxicity through transformation of the highly toxic As(III) into the less toxic organic As. The PS application resulted in an increase in the root, leaf, and grain biomass of the rice plants by 12–36%, while the As content in the rice grains decreased by 14–32%, due to less As(III); the As(V) content did not change and the organic As increased.

German Translation of:Manuscript number: MWEN-D-18-00117R3Translated TitleWirkung von Si auf As-Speziationen und Verteilung in Reispflanzen in der Umgebung der Shimen-Realgar-MineZusammenfassungTranslated abstract:Der Schutz von natürlichen Wasserressourcen und von Kulturpflanzen vor Kontaminationen ist in vielen bergbaubeeinflussten Gebieten ein Problem. Bergbauabfälle und -abwässer aus der Shimen-Realgar-Mine in der chinesischen Provinz Hunan weisen ein hohes toxisches Risikopotenzial bzgl. Arsen (As) auf. In dieser Studie wurden die durch Kaliumsilicat (PS) unterstützten Mechanismen der As-Mobilität und Akkumulationsreduktion in einem Nassreis-Kulturpflanzen-System untersucht. In Vegetationsexperimenten wurde Reis auf mäßig sowie stark As-belastetem Boden (entsprechend 30,6 und 66,9 mg kg-1 As) mit und ohne PS angebaut. Die gesamte As- und Silizium- (Si) Verteilung in Wurzeln, Sprossen und Körnern sowie die As-Speziation in den Körnern wurde analysiert. Eine sequentielle Extraktion von As im Boden zeigte, dass PS die Mobilität von As im Boden und die Anreicherung in der Reispflanze signifikant verringerte. Verschiedene PS-induzierte Mechanismen sind vermutlich dafür verantwortlich: (1) Die Auflösung von PS-Monokieselsäure erhöht die Sorptionskapazität von Si-haltigen Mineralien für As; (2) Erhöhte pH-Werte in der Bodenlösung bedingen eine höhere As-Sorption im Boden; (3) Eine Si-induzierte kompetitive Hemmung des durch Lsi1 und Lsi2 ausgelösten As (III) -Transports. Die Ergebnisse zeigen das Potenzial von löslichem Si zur Verringerung der As-Mobilität und der Biotoxizität an Standorten mit hohen As-Gehalten in Bergbauabwässern, Tailings und Abfallrückständen.Spanish Translation of:Manuscript number: MWEN-D-18-00117R3Translated Title: Efecto del Si en la especiación y distribución de As en el arroz cerca de la mina de rejalgar ShimenResumen La protección del agua natural y los cultivos de la contaminación en las áreas afectadas por la minería es un problema en muchas regiones. Las aguas residuales y los residuos de la mina de rejalgar Shimen, en la provincia de Hunan, China, representan un alto riesgo de envenenamiento por arsénico (As). Se investigaron los mecanismos asistidos por el silicato de potasio (PS) de la movilidad del As y la reducción de la acumulación en un sistema de suelo-planta de arroz. En un experimento de vegetación, el arroz se cultivó en un suelo moderadamente y altamente contaminado con As (30,6 y 66,9 mg kg-1 de As, respectivamente) con y sin PS. Se analizaron el As total y el silicio (Si) en raíces, brotes y granos y las formas químicas de As en los granos. La extracción secuencial del As en el suelo mostró que el PS redujo significativamente la movilidad del As en el suelo y su acumulación por el arroz. Se discutieron varios mecanismos mediados por PS: (1) la disolución del ácido monosilícico PS aumenta la capacidad de sorción de los minerales a base de Si para As; (2) el aumento del pH en la solución del suelo proporciona una mayor sorción de As por el suelo; (3) inhibición competitiva inducida por Si del transporte de As (III) iniciado por Lsi1 y Lsi2. Los resultados indican el potencial del uso de Si soluble para reducir la movilidad y biotoxicidad de As en sitios con altos niveles de As en aguas residuales, relaves y residuos.Effect of Si on As Speciation and Distribution in Rice near the Shimen Realgar MineProtection of natural water and cultivated crops from contamination in mining-affected areas is a problem in many regions. Wastewater and waste residuals from the Shimen realgar mine in Hunan Province, China, pose a high risk of arsenic (As) poisoning. The potassium silicate (PS)-assisted mechanisms of As mobility and accumulation reduction in a paddy soil-plant system were investigated. In a vegetation experiment, rice was grown in moderately and highly As-polluted soil (30.6 and 66.9 mg kg-1 of As, correspondingly) with and without PS. Total As and silicon (Si) in roots, shoots, and grains and the forms of As in the grains were analyzed. Sequential extraction of the As in the soil showed that the PS significantly reduced the mobility of As in the soil and its accumulation by rice. Several PS-mediated mechanisms were discussed: (1) dissolution of PS monosilicic acid enhances the sorption capacity of Si-based minerals for As; (2) increased pH in the soil solution provides higher As sorption by soil; (3) Si-induced competitive inhibition of As(III) transport initiated by Lsi1 and Lsi2. The results indicate the potential of using soluble Si to reduce As mobility and biotoxicity at sites with high levels of As in wastewater, tailings, and waste residuals.硅对石门雄黄矿(Shimen Realgar)附近水稻砷形态和分布的影响 保护天然水和农作免受矿区污染是许多地区面临的难题。湖南石门雄黄矿的废水和固废具有高砷毒性风险。研究了硅酸钾(PS)改变水稻-土壤-植物系统砷迁移特性和减少砷积累的机理。在种植试验中,将水稻分别种植于含和不含硅酸钾(PS)的中度和高度污染土壤(30.6和66.9mg/ kg的砷)。分析了根、芽、稻粒的总砷和硅,研究了稻粒中砷的形态。土壤的砷顺序提取试验表明,硅酸钾(PS)显著降低了砷在土壤中的迁移及水稻中的积累。讨论了硅酸钾(PS)的作用机理:(1)硅酸钾(PS)的单硅酸溶解性提高了含硅矿物的砷吸附能力;(2)升高的土壤溶液pH值增强了土壤的砷吸附性;(3)Lsi1和Lsi2形成了硅对砷的诱发竞争性砷(III)迁移抑制作用。结果表明,可溶性Si可降低了废水、尾矿和废渣等含高砷场地的砷迁移和生物毒性。