Comparative effects on arsenic uptake between iron (hydro)oxides on root surface and rhizosphere of rice in an alkaline paddy soil

The iron (Fe) (hydro)oxides deposited around rice roots play an important role in arsenic (As) sequestration in paddy soils, but there is no systematic study on the relative importance of Fe (hydro)oxides on root surface and in rhizosphere soil in limiting As bioavailability. Twenty-seven rice genotypes were selected to investigate effects of Fe (hydro)oxides on As uptake by rice in an alkaline paddy soil. Results indicated that the As content was positively correlated with the Fe content on root surface, and most of As (88–97%) was sequestered by poorly crystalline and crystalline Fe (hydro)oxides in the alkaline paddy soil. The As sequestration by Fe (hydro)oxides on root surface (IAS_root 16.8–25.0 mg As/(g Fe)) was much higher than that in rhizosphere (IAS_rhizo 1.4–2.0 mg As/(g Fe)); therefore, in terms of As immobilization, the Fe (hydro)oxides on root surface were more important than that in rhizosphere. However, the As content in brown rice did not have significant correlation with the As content on root surface but was significantly correlated (R²?=?0.43, P?<?0.05) with the partition ratio (PR_As?=?IAS_root/IAS_rhizo) of As sequestration on root surface and in rhizosphere, which suggested that Fe (hydro)oxides on root surface did not play the controlling role in lowering As uptake, and the partition ratio PR_As would be a better indicator to evaluate effects of Fe (hydro)oxides around roots on As uptake by rice.

     

Spatial variability of arsenic concentration in soils and plants, and its relationship with iron, manganese and phosphorus

Spatial distribution of arsenic (As) concentrations of irrigation water, soil and plant (rice) in a shallow tube-well (STW) command area (8 ha), and their relationship with Fe, Mn and P were studied. Arsenic concentrations of water in the 110 m long irrigation channel clearly decreased with distance from the STW point, the range being 68-136 μg L⁻¹. Such decreasing trend was also noticed with Fe and P concentrations, but the trend for Mn concentrations was not remarkable. Concerning soil As, the concentration showed a decreasing tendency with distance from the pump. The NH₄-oxalate extractable As contributed 36% of total As and this amount of As was associated with poorly crystalline Fe-oxides. Furthermore only 22% of total As was phosphate extractable so that most of the As was tightly retained by soil constituents and was not readily exchangeable by phosphate. Soil As (both total and extractable As) was significantly and positively correlated with rice grain As (0.296 ± 0.063 μg g⁻¹, n = 56). Next to drinking water, rice could be a potential source of As exposure of the people living in the As affected areas of Bangladesh.     

Fate of anilide and aniline herbicides in plant-materials-amended soils

The fate of herbicides trifluralin, pendimethalin, alachlor and metolachlor in paddy field soils amended with plant materials was investigated. The plant materials were purple sesbania, vegetable soybean and rice straw. The investigation was performed at two temperatures (25 and 40°C) and two soil water moistures (60 and 90% water-holding capacity). The results showed linear and Freudlich equations described the adsorption of amide compound to soil. Adsorption coefficient (K _d ) fit to linear equation were in general greater in plant material-amended soils than in non-amended soil, especially in soil amending with rice straw. Increasing temperature and soil water moisture content shortened the half-lives of compounds in various treated soils. The movement of compounds in the soil columns showed the maximum distribution of aniline type compound, trifluralin and pendimethalin, appeared at the upper top of 0 to 5 and 0 to 10 cm of soil column, respectively, and of anilide type, alachlor and metolachlor, were distributed at 0 to 25 cm of the soil column. The mobility of chemicals in the different treated soils was simulated by the behavior assessment model (BAM). There was no significant difference among different plant material incubated soils on dissipation and mobility of compounds in soils.     

The relationship of root porosity and radial oxygen loss on arsenic tolerance and uptake in rice grains and straw

The correlations among arsenic (As) accumulation in grains and straw, rates of radial oxygen loss (ROL), and porosity of roots using 25 rice cultivars were investigated based on two pot experiments: (1) soil with addition of 100 mg As kg^?1 for analysis of As in grains and straw, and (2) deoxygenated solution for analyzing rates of ROL and porosity of roots. The results showed that there were great differences in grain As (0.71–1.72 mg kg^?1) and straw As (15.6–31.7 mg kg^?1), rates of ROL (7.40–13.24 mmol O₂ kg^?1 root d.w. h^?1), and porosity (20.91–33.08%) among the cultivars. There were significant negative correlations between As in grains or straw and ROL and porosity, and significant positive correlations between rates of ROL and porosities, respectively. Rice cultivars with high porosities tended to possess higher rates of ROL, and had higher capacities for limiting the transfer of As to aboveground tissues.     

The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings

A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (C_pw) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8-5.7 and 1.4-2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the C_pw of Cd and Zn, increasing the C_pw of As, and increasing the iron plaque blocking capacity for Cd and Pb.     

Evaluation of bioaugmentation and biostimulation on arsenic remediation in soil through biovolatilization

Arsenic (As) removal through microbially driven biovolatilization can be explored as a potential method for As bioremediation. However, its effectiveness needs to be improved. Biostimulation with organic matter amendment and bioaugmentation with the inoculation of genetic engineered bacteria could be potential strategies for As removal and site remediation. Here, the experiments were conducted to evaluate the impacts of rice straw and biochar amendment, inoculation of genetic engineered Pseudomonas putida KT2440 (GE P. putida) with high As volatilization activity, on microbial mediated As volatilization and removal from three different arseniferous soils. In general, the addition of rice straw (5%) significantly enhanced As methylation and volatilization in comparison with corresponding non-amended soils. Biochar amendments and inoculation of the GE P. putida increased As methylation and volatilization, respectively, but less than that of rice straw addition. The effectiveness of As volatilizations are quite different in the various paddy soils. The combined amendments of rice straw and GE P. putida exhibited the highest As removal efficiency (483.2 μg/kg/year) in Dayu soil, with 1.2% volatilization of the total As annually. The highest water-soluble As concentration (0.73 mg/kg) in this soil could be responsible for highest As volatilization besides the rice straw and bacteria in this soil.     

Occurrence of arsenic in brown rice and its relationship to soil properties from Hainan Island, China

The acquaintance of arsenic concentrations in rice grain is vital in risk assessment. In this study, we determined the concentration of arsenic in 282 brown rice grains sampled from Hainan Island, China, and discussed its possible relationships to the considered soil properties. Arsenic concentrations in the rice grain from Hainan Island varied from 5 to 309 μg/kg, with a mean (92 μg/kg) lower than most published data from other countries/regions and the maximum contaminant level (MCL) for As_i in rice. The result of correlation analysis between grain and soil properties showed that grain As concentrations correlated significantly to soil arsenic speciation, organic matter and soil P contents and could be best predicted by humic acid bound and Fe-Mn oxides bound As fractions. Grain arsenic rises steeply at soil As concentrations lower than 3.6 mg/kg and gently at higher concentrations.     

Partitioning of arsenic in soil-crop systems irrigated using groundwater: a case study of rice paddy soils in southwestern Taiwan

The accumulation of As in rice due to groundwater irrigation in paddy fields represents a serious health hazard in South and Southeast Asia. In Taiwan, the fate of As in long-term irrigated paddy fields is poorly understood. Groundwater, surface soil, and rice samples were collected from a paddy field that was irrigated with As-containing groundwater in southwestern Taiwan. The purpose of this study is to elucidate the source and sink of As in the paddy field by comparing the As fractions in the soils that were obtained by a sequential extraction procedure (SEP) with the As uptake of rice. The risks associated with eating rice from the field can thus be better understood. The concentration of As in groundwater varied with time throughout the growing seasons of rice, but always exceeded the permitted maximum (10 μg L⁻¹) for drinking water by the WHO. The As concentration increased with the concentration of Fe in the groundwater, supporting the claim that a large amount of As was concentrated in the Fe flocs collected from the internal wall of the groundwater pump. The results of the SEP revealed that As bound with amorphous and crystalline hydrous oxides exhibited high availability in the soils. The root of rice accumulated the largest amount of As, followed by the straw, husk, and grain. Although the As concentration in the rice grain was less than 1.0 mg kg⁻¹, the estimated intake level was close to the maximum tolerable daily intake of As, as specified by the WHO.     

Effects of soil attributes and straw accumulation on the sorption of hexazinone and tebuthiuron in tropical soils cultivated with sugarcane

Brazil is the largest sugarcane producer in the world in which hexazinone (3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine-2,4-dione) and tebuthiuron (1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea) are heavily used. Sugarcane harvesting is changing from the manual system with previous straw burning to the mechanized system without straw burning. The lack of burning results in soil organic carbon accumulation mainly in clayey soils, which should affect herbicides availability and fate. Therefore, we evaluated sorption of these herbicides in soil samples with and without straw burning. Both herbicides presented low apparent sorption coefficients (mean K_d,app= 0.6 and 2.4 L kg^?1 for hexazinone and tebuthiuron, respectively), suggesting that they may leach to groundwater. Moreover, their sorption correlated primarily with soil organic carbon (SOC), but iron oxide contents extracted with ammonium oxalate (Fe₂O₃^AOX) also affected it (K_d,app = ?0.228 + 0.0397 SOC + 0.117 Fe₂O₃^AOX for hexazinone and K_d,app = ?1.407 + 0.201 SOC + 0.348 Fe₂O₃^AOX for tebuthiuron). Soil organic carbon accumulation due to straw maintenance in the field positively affected sorption of both herbicides, but its effects were not enough to classify them as “non-leachers.”     

Variation of As concentration between soil types and rice genotypes and the selection of cultivars for reducing As in the diet

Human exposure to toxic heavy metals via the food chain is of increasing concern. In the present study, the effects of soil type and genotype on variation in arsenic (As) concentrations of different organs were investigated by using nine rice cultivars grown in two soils, with two levels of As contamination. There were significant genotypic differences (P < 0.05) in As concentrations of all organs, and As concentrations of polished grain were significantly affected by genotype and soil type. The As concentration in polished grain was higher in red paddy soil under As treatment, with range from 0.24 to 1.03 mg kg⁻¹, and the As concentration of three cultivars exceeded the concentration of Chinese Food Hygiene Standard (0.7 mg kg⁻¹). The As concentrations in stems, leaves and polished grain were all significantly and positively correlated. The As concentrations in polished grain were positively and significantly (P < 0.01) correlated with As root-grain translocation factor. The results indicated that As concentration in grain was partially governed by As uptake and the transfer of As from root to grain. The grain As concentration of the nine cultivars was significantly correlated between the two soil types at different levels of As contamination. Some genotypes, such as japonica rice (e.g. Ning jing 1 and Nan jing 32) had consistently low grain As concentrations. The results suggest the possibility of breeding the As rice cultivars to produce grain for safe consumption from soils with slight and moderate levels of As.     

含铁材料对污染水稻土中砷的稳定化效果

通过化学实验方法,向砷污染水稻土中添加4种含铁材料(FeCl3、FeCl2、Fe0和Fe2O3),分析稳定后土壤中pH、砷形态及砷毒性浸出量的变化,研究4种含铁材料对污染水稻土中砷的稳定化效果。结果表明,FeCl3和FeCl2处理降低了土壤pH,Fe0和Fe2O3处理对土壤pH影响不大。4种含铁材料均明显降低了土壤中易溶态砷(WE-As)和毒性浸出砷含量。在最大添加量为8.00 g/kg时,FeCl3、FeCl2、Fe0和Fe2O3分别使易溶态砷比对照降低了86.4%、63.6%、77.3%和36.4%,使毒性浸出砷比对照降低了96.3%、88.9%、70.4%和30.4%。4种含铁材料均对水稻土壤中砷具有较好的稳定化效果,且能力大小依次为:FeCl3FeCl2、Fe0Fe2O3。Fe0和Fe2O3处理使WE-As、铝型砷(Al-As)、铁型砷(Fe-As)向钙型砷(Ca-As)和残渣态砷(RS-As)转化;FeCl3处理使土壤WE-As、Al-As向Fe-As、Ca-As和RS-As转化;FeCl2处理使土壤WE-As、Ca-As向Al-As、Fe-As转化,对RS-As影响不明显。说明Fe0固砷的机理与Fe2O3相似,与FeCl3有一定差异,与FeCl2的差异可能更大。     

Effects of modified biochar on rhizosphere microecology of rice (Oryza sativa L.) grown in As-contaminated soil

Biochar was carbon-rich and generated by high-temperature pyrolysis of biomass under oxygen-limited conditions. Due to the limitations of surface functional groups and the weakness of surface activity in the field of environmental remediation, the raw biochar frequently was chemically modified to improve its properties with a new performance. In this study, a kind of high-efficiency and low-cost amino biochar modified by nano zero-valent iron (ABC/NZVI) was synthesized and applied to paddy soil contaminated with arsenic (As). Dynamic changes of soil properties, arsenic speciations and rhizosphere microbial communities have been investigated over the whole growth period of rice plants. Pot experiments revealed that the ABC/NZVI could decrease the arsenic concentration in rice straw by 47.9% and increase the content of nitrogen in rice straw by 47.2%. Proportion of Geobacter in soil with ABC/NZVI treatment increased by 175% in tillering period; while Nitrososphaera decreased by 61 and 20% in tillering and maturity, respectively, compared to that of control. ABC/NZVI promotes arsenic immobilization in rhizosphere soil and precipitation on root surface and reduces arsenic accumulation in rice. At the same time, ABC/NZVI would inhibit Nitrososphaera which is related to ammonia oxidation process, and it would have a promising potential as soil amendment to reduce nitrogen loss probably.

     

Effect of industrial waste products on phosphorus mobilisation and biomass production in abattoir wastewater irrigated soil

This study evaluated the effect of alkaline industrial by-products such as flyash (FA) and redmud (RM) on phosphorus (P) mobilisation in abattoir wastewater irrigated soils, using incubation, leaching and plant growth (Napier grass [Pennisetum purpureum]) experiments. The soil outside the wastewater irrigated area was also collected and treated with inorganic (KH₂PO₄ [PP]) and organic (poultry manure [PM]) P treatments, to study the effect of FA and RM on P mobilisation using plant growth experiment. Among the amendments, FA showed the highest increase in Olsen P, oxalic acid content and phosphatase activity. The highest increase in Olsen P for PM treated non-irrigated soils showed the ability of FA and RM in mobilising organic P better than inorganic P (PP). There was over 85 % increase in oxalic acid content in the plant growth soils compared to the incubated soil, showing the effect of Napier grass in the exudation of oxalic acid. Both amendments (FA and RM) showed an increase in phosphatase activity at over 90 % at the end of the 5-week incubation period. The leaching experiment indicated a decrease in water soluble P thereby ensuring the role of FA and RM in minimising P loss to water bodies. FA and RM showed an increase in plant biomass for all treatments, where FA amended soil showed the highest increase as evident from FA’s effect on Olsen P. Therefore, the use of FA and RM mobilised P in abattoir wastewater irrigated soils and increased biomass production of Napier grass plants through root exudation of oxalic acid.     

Can arbuscular mycorrhizal fungi improve grain yield, As uptake and tolerance of rice grown under aerobic conditions?

The effects of arbuscular mycorrhizal fungi (AMF) - Glomus intraradices and G. geosporum on arsenic (As) and phosphorus (P) uptake by lowland (Guangyinzhan) and upland rice (Handao 502) were investigated in soil, spiked with and without 60 mg As kg⁻¹. In As-contaminated soil, Guangyinzhan inoculated with G. intraradices or Handao 502 inoculated with G. geosporum enhanced As tolerance, grain P content, grain yield. However, Guangyinzhan inoculated with G. geosporum or Handao 502 inoculated with G. intraradices decreased grain P content, grain yield and the molar ratio of grain P/As content, and increased the As concentration and the ratio of grain/straw As concentration. These results show that rice/AMF combinations had significant (p < 0.05) effects on grain As concentration, grain yield and grain P uptake. The variation in the transfer and uptake of As and P reflected strong functional diversity in AM (arbuscular mycorrhizal) symbioses.     

Removal of PCBs in contaminated soils by means of chemical reduction and advanced oxidation processes

Although the chemical reduction and advanced oxidation processes have been widely used individually, very few studies have assessed the combined reduction/oxidation approach for soil remediation. In the present study, experiments were performed in spiked sand and historically contaminated soil by using four synthetic nanoparticles (Fe⁰, Fe/Ni, Fe₃O₄, Fe_3???x Ni _x O₄). These nanoparticles were tested firstly for reductive transformation of polychlorinated biphenyls (PCBs) and then employed as catalysts to promote chemical oxidation reactions (H₂O₂ or persulfate). Obtained results indicated that bimetallic nanoparticles Fe/Ni showed the highest efficiency in reduction of PCB28 and PCB118 in spiked sand (97 and 79 %, respectively), whereas magnetite (Fe₃O₄) exhibited a high catalytic stability during the combined reduction/oxidation approach. In chemical oxidation, persulfate showed higher PCB degradation extent than hydrogen peroxide. As expected, the degradation efficiency was found to be limited in historically contaminated soil, where only Fe⁰ and Fe/Ni particles exhibited reductive capability towards PCBs (13 and 18 %). In oxidation step, the highest degradation extents were obtained in presence of Fe⁰ and Fe/Ni (18–19 %). The increase in particle and oxidant doses improved the efficiency of treatment, but overall degradation extents did not exceed 30 %, suggesting that only a small part of PCBs in soil was available for reaction with catalyst and/or oxidant. The use of organic solvent or cyclodextrin to improve the PCB availability in soil did not enhance degradation efficiency, underscoring the strong impact of soil matrix. Moreover, a better PCB degradation was observed in sand spiked with extractable organic matter separated from contaminated soil. In contrast to fractions with higher particle size (250–500 and <500 μm), no PCB degradation was observed in the finest fraction (≤250 μm) having higher organic matter content. These findings may have important practical implications to promote successively reduction and oxidation reactions in soils and understand the impact of soil properties on remediation performance.     

Phytoremediation of arsenic contaminated paddy soils with Pteris vittata markedly reduces arsenic uptake by rice

Arsenic (As) accumulation in food crops such as rice is of major concern. To investigate whether phytoremediation can reduce As uptake by rice, the As hyperaccumulator Pteris vittata was grown in five contaminated paddy soils in a pot experiment. Over a 9-month period P. vittata removed 3.5-11.4% of the total soil As, and decreased phosphate-extractable As and soil pore water As by 11-38% and 18-77%, respectively. Rice grown following P. vittata had significantly lower As concentrations in straw and grain, being 17-82% and 22-58% of those in the control, respectively. Phytoremediation also resulted in significant changes in As speciation in rice grain by greatly decreasing the concentration of dimethylarsinic acid (DMA). In two soils the concentration of inorganic As in rice grain was decreased by 50-58%. The results demonstrate an effective stripping of bioavailable As from contaminated paddy soils thus reducing As uptake by rice.     

Polycyclic aromatic hydrocarbon emission from straw burning and the influence of combustion parameters

A simulated burning experiment was conducted in a tubular furnace system to examine the emission of polycyclic aromatic hydrocarbons (PAHs) from the burning of rice and bean straw, and the influence of combustion parameters was investigated. Total emission amounts of 16 PAHs (∑PAHs) from the burning of rice and bean straw ranged from 9.29 to 23.6 μg g^?1 and from 3.13 to 49.9 μg g^?1, respectively, which increased with the increase of temperatures from 200 to 700 °C. The contribution of combustion to individual PAH yields was about 80.6–100%, which was generally increased with the increase of burning temperature. Moisture content in straw had a negative effect on PAH formation, especially on PAHs with low molecular weight. ∑PAHs emission amounts decreased by 78.2% for bean straw with a moisture content of 30% in comparison with that for dried straw. In addition, PAH emission amounts increased with the increase of O₂ content in supplied air and then decreased, which showed a maximum emission at O₂ content of 40%. The source fingerprint of PAHs in emission from straw burning was established, which showed that naphthalene accounted for 35.0 ± 7.4% of ∑PAHs. Based on the experimental data, emission amounts of ∑PAHs from the burning of rice and bean straw were estimated to be 320–357 and 32.5–76.0 tons to ambient air per year in China, respectively.     

Prediction of Cadmium uptake by brown rice and derivation of soil–plant transfer models to improve soil protection guidelines

Cadmium (Cd) levels in paddy fields across Taiwan have increased due to emission from industry. To ensure the production of rice that meets food quality standards, predictive models or suitable soil tests are needed to evaluate the quality of soils to be used for rice cropping. Levels of Cd in soil and rice grains were measured in 19 paddy fields across the western plains in Taiwan. Cadmium levels in soil range from less than 0.1 mg kg^?1 to 30 mg kg^?1. Measured Cd levels in brown rice were predicted very well (R² > 0.8) based on Cd and Zinc in a 0.01 M CaCl₂ extract or a soil–plant transfer model using the reactive soil Cd content, pH, and cation exchange capacity. In contrast to current soil quality standards used in Taiwan, such models are effective in identifying soils where Cd in rice will exceed food quality standards.     

Mobilization of arsenic in aquifers from the Datong Basin,China: Evidence from geochemical and iron isotopic data

Iron isotope compositions of various Fe pools in aquifer sediments were measured at a known As-contaminated site in the Datong Basin, China. The δ⁵⁶Fe values of HCl-extracted poor-crystalline Fe(III) range widely from ?0.41‰ to 0.36‰. We interpret the low Fe(II)/Fe_Extractable ratios (<50%) and the negative correlation between Fe(II)/Fe_Extractable and δ⁵⁶Fe values in HCl-extracted poor-crystalline Fe to be best explained by redox cycling of Fe induced by microbial Fe(III) reduction. However, the high Fe(II)/Fe_Extractable ratios (?70%) and positive correlation between Fe(II)/Fe_Extractable and δ⁵⁶Fe values for HCl-extracted poor-crystalline Fe indicates production of sulfides (FeSs). The δ⁵⁶Fe values of crystalline Fe(III) extracted by reductant appears to be comparatively small varying from ?0.01‰ to 0.24‰, which is consistent with the δ⁵⁶Fe values for ferric oxides/hydroxides having undergone microbial Fe(III) reduction. The Fe isotope composition of various Fe pools shows the transformation between crystalline Fe(III) and poor-crystalline crystalline Fe(III) and the secondary Fe(II) phases has already occurred or is occurring in aquifer sediments. More importantly, there is a significant difference in the As concentrations in crystalline Fe(III) oxides/hydroxides and HCl-extracted Fe phases. The concentrations of As range from 1.6 to 29.9 mg kg^?1 and from 0.6 to 3.0 mg kg^?1, for crystalline Fe(III) and HCl-extracted Fe phases respectively. Accordingly, the transformation of Fe minerals induced by microbial Fe(III) reduction can contribute to the mobilization of As. This study is the first to examine the Fe isotope compositions in high As aquifer sediments; the results show that the Fe isotope would be an important tool in demonstrating the enrichment of As in groundwater.     

Arsenic toxicity in garden cress (Lepidium sativum Linn.): significance of potassium nutrition

In a hydroponic culture, experiments were performed to study the influence of potassium (K) supplementation (0, 20, 40, 60, 80, and 100 mg L^?1) on the arsenic (As; 0, 8, and 10 mg L^?1)-accrued changes in growth traits (plant biomass, root–shoot length) and the contents of lepidine, As and K, in garden cress (Lepidium sativum Linn.) at 10 days after treatment. The changes in these traits were correlated with shoot proline content, protein profile, and the activities of antioxidant enzymes namely superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), glutathione reductase (GR, EC 1.8.1.7), and ascorbate peroxidase (APX, EC 1.11.1.11). In general, As-alone treatments significantly decreased the growth traits but lead to significant enhancements in shoot proline and enzyme activities. K-supplementation to As-treated L. sativum seedlings decreased shoot-As content, reduced As-induced decreases in growth traits but enhanced the content of shoot proline, and the activities of the studied enzymes maximally with K₁₀₀ + As₈ and As₁₀ mg L^?1. Both 8 and 10 mg L^?1 of As drastically downregulated the shoot proteins ranging from 43–65 kDa. With As₁₀ mg L^?1, there was a total depletion of protein bands below 23 kDa; however, K₈₀ mg L^?1 maximally recovered and upregulated the protein bands. Additionally, protein bands were downregulated (at par with As-alone treatment) above K₈₀ mg L^?1 level. Interestingly, As-stress increased lepidine content in a dose-dependent manner which was further augmented with the K-supplementation. It is suggested that K protects L. sativum against As-toxicity by decreasing its accumulation and strengthening antioxidant defense system and protein stability.