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.

     

Effect of biochar on nitrous oxide emission and its potential mechanisms

Extensive use of biochar to mitigate nitrous oxide (N₂O) emission is limited by the lack of understanding on the exact mechanisms altering N₂O emission from biochar-amended soil. Biochars produced from rice straw and dairy manure at 350 and 500 °C by oxygen-limited pyrolysis were used to investigate their influence on N₂O emission. A quadratic effect of biochar levels was observed on the N₂O emissions. The potential mechanisms were explored by terminal restriction fragment length polymorphism (T-RFLP) and real-time polymerase chain reaction (qPCR). A lower relative abundance of bacteria, which included ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), was observed at 4% biochar application rate. Reduced copy numbers of the ammonia monooxygenase gene amoA and the nitrite reductase gene nirS coincided with decreased N₂O emissions. Therefore, biochar may potentially alter N₂O emission by affecting ammonia-oxidizing and denitrification bacteria, which is determined by the application rate of biochar in soil.

Implications:Biochar research has received increased interest in recent years because of the potential beneficial effects of biochar on soil properties. Recent research shows that biochar can alter the rates of nitrogen cycling in soil systems by influencing nitrification and denitrification, which are key sources of the greenhouse gas nitrous oxide (N₂O). However, there are still some controversial data. The purpose of this research was to (1) examine how applications of different dose of biochar to soil affect emission of N₂O and (2) improve the understanding of the underlying mechanisms.     

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.     

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.     

Adsorption of Pb(II) on variable charge soils amended with rice-straw derived biochar

Two Ultisols and one Oxisol from tropical regions of southern China were incubated with rice straw biochar to investigate the effect of biochar on their surface charge and Pb(II) adsorption using batch methods. The incorporation of biochar induced a remarkable increase in soil cation exchange capacity after 30 d of incubation. The incorporation of biochar significantly increased the adsorption of Pb(II) by these variable charge soils; the enhancement of adsorption of Pb(II) by these soils increased with the addition level of biochar. Adsorption of Pb(II) involved both electrostatic and non-electrostatic mechanisms; however, biochar mainly increased Pb(II) adsorption through the non-electrostatic mechanism via the formation of surface complexes between Pb²⁺ and functional groups on biochar. There was greater enhancement of biochar on the non-electrostatic adsorption of Pb(II) by the variable charge soils at relatively low pH. Therefore, the incorporation of biochar decreased the activity and availability of Pb(II) to plants through increased non-electrostatic adsorption of Pb(II) by acidic variable charge soils.     

不同镉污染农田土壤上秸秆和炭化秸秆分解动态及其对土壤镉的吸附特征

通过温室土壤培养实验,研究不同镉污染农田土壤上不同的作物秸秆和炭化作物秸秆还田后的分解动态和还田秸秆材料对污染土壤中镉的吸附特征,探讨秸秆和炭化秸秆还田做为重金属镉污染农田土壤修复剂的可行性。实验结果表明,还田的油菜秸秆和玉米秸秆在2种镉污染水稻土壤上6个月分解了43％-65％,秸秆炭化后还田则很稳定,2种镉污染土壤上还田6个月时累计分解量小于5％。2种镉污染土壤上还田的秸秆和炭化秸秆随还田时间延长镉含量逐渐增加。模拟镉污染土壤上,相同时期油菜秸秆中镉含量显著高于玉米秸秆,油菜秸秆炭中镉含量显著高于玉米秸秆炭。在镉污染土壤上,还田的玉米秸秆、油菜秸秆、玉米秸秆炭和油菜秸秆炭对土壤镉的净吸附量相近,均小于1．1μg／g。在模拟镉污染土壤上还田的油菜秸秆和油莱秸秆炭对土壤镉净吸附量最高分别达到2．74μg／g和7．03μg／g,分别是玉米秸秆和玉米秸秆炭的2倍,且显著高于其在镉污染土壤上的净吸附量,具有高的吸附能力。     

纳米零价铁的制备及其去除水中对氯硝基苯的研究

通过FeSO4与KBH4反应,利用液相还原法制备纳米零价铁颗粒(NZVI),用XRD、SEM和BET对其性能进行表征。在常温常压下利用纳米铁还原废水中的对氯硝基苯(p-CNB),探讨了反应条件对还原率的影响。结果表明,制备过程中碱性物质(NaOH)的添加可以明显减小颗粒粒径,增大比表面积,提高纳米铁还原反应的效率。NZVI对于对氯硝基苯有很好的去除效果,NZVI用量、p-CNB初始浓度和pH值均对其去除效率产生影响。在纳米铁投加量为1 g/L,pH=2的条件下,添加NaOH的纳米铁能在120 min内将质量浓度为50 mg/L的对氯硝基苯基本完全降解,降解率为98.8%。此外,还对NZVI还原对氯硝基苯的机理进行了初步探讨。     

Effects of pH, Fe, and Cd on the uptake of Fe2+ and Cd2+ by rice

The rhizosphere plays an important role in altering cadmium (Cd) solubility in paddy soils and Cd accumulation in rice. However, more studies are needed to elucidate the mechanism controlling rice Cd solubility and bioavailability under different rhizosphere conditions to explain the discrepancy of previous studies. A rice culture with nutrient solution and vermiculite was conducted to assess the effects of pH, Eh, and iron (Fe) concentration on Cd, Fe fractions on the vermiculite/root surface and their uptake by rice. The solution pH was set from 4.5 to 7.5, with additions of Fe (30 and 50 mg L^?1) and Cd (0.5 and 0.9 mg L^?1). At pH 5.5, the Eh in the rice rhizosphere was higher whereas transpiration, Cd²⁺, and Fe²⁺ adsorption on the vermiculite/root surface and accumulation in rice were lower than the other pH treatments. Cadmium addition had no impact on pH and Eh in rice rhizosphere while Fe addition decreased pH and increased Eh significantly. Compared with control, Fe addition resulted in the decrease of rhizosphere Cd, Fe solubility and bioavailability. Higher redox potential in the rice rhizosphere resulted in the decline of transpiration, Cd, and Fe accumulation in the rice tissues, suggesting that the transfer of two elements from soil to rice was depressed when the rhizosphere was more oxidized.     

Poor efficacy of herbicides in biochar-amended soils as affected by their chemistry and mode of action

We evaluated wheat straw biochar produced at 450 °C for its ability to influence bioavailability and persistence of two commonly used herbicides (atrazine and trifluralin) with different modes of action (photosynthesis versus root tip mitosis inhibitors) in two contrasting soils. The biochar was added to soils at 0%, 0.5% and 1.0% (w/w) and the herbicides were applied to those soil-biochar mixes at nil, half, full, two times, and four times, the recommended dosage (H₄). Annual ryegrass (Lolium rigidum) was grown in biochar amended soils for 1 month. Biochar had a positive impact on ryegrass survival rate and above-ground biomass at most of the application rates, and particularly at H₄. Within any given biochar treatment, increasing herbicide application decreased the survival rate and fresh weight of above-ground biomass. Biomass production across the biochar treatment gradient significantly differed (p < 0.01) and was more pronounced in the case of atrazine than trifluralin. For example, the dose-response analysis showed that in the presence of 1% biochar in soil, the value of GR₅₀ (i.e. the dose required to reduce weed biomass by 50%) for atrazine increased by 3.5 times, whereas it increased only by a factor of 1.6 in the case of trifluralin. The combination of the chemical properties and the mode of action governed the extent of biochar-induced reduction in bioavailability of herbicides. The greater biomass of ryegrass in the soil containing the highest biochar (despite having the highest herbicide residues) demonstrates decreased bioavailability of the chemicals caused by the wheat straw biochar. This work clearly demonstrates decreased efficacy of herbicides in biochar amended soils. The role played by herbicide chemistry and mode of action will have major implications in choosing the appropriate application rates for biochar amended soils.     

Kinetics and the mass transfer mechanism of hydrogen sulfide removal by biochar derived from rice hull

The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperature has great influence on the adsorption of H₂S. At the different pyrolysis temperature, the H₂S removal efficiency of rice hull-derived biochar was different. The adsorption capacities of biochar were 2.09 mg·g^–1, 2.65 mg·g^–1, 16.30 mg·g^–1, 20.80 mg·g^–1, and 382.70 mg·g^–1, which their pyrolysis temperatures were 100 °C, 200 °C, 300 °C, 400 °C and 500 °C respectively. Based on the Yoon-Nelson model, it analyzed the mass transfer mechanism of hydrogen sulfide adsorption by biochar.

Implications: The paper focuses on the biochar derived from rice hull–removed hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperatures have great influence on the adsorption of H₂S. At the different pyrolysis temperatures, the H₂S removal efficiency of rice hull–derived biohar was different. The adsorption capacities of biochar were 2.09, 2.65, 16.30, 20.80, and 382.70 mg·g^?1, and their pyrolysis temperatures were 100, 200, 300, 400, and 500 °C, respectively. Based on the Yoon-Nelson model, the mass transfer mechanism of hydrogen sulfide adsorption by biochar was analyzed.     

稻秆对铜绿微囊藻抑制作用的研究

研究了稻秆浸出液对铜绿微囊藻生长的抑制作用.研究表明,稻秆浸出液中含有的化学物质抑制了铜绿微囊藻的生长繁殖.稻秆浸泡时间的延长,有利于提高浸出液的抑藻效果,但浸泡时间过长则无益于抑藻效果提高,浸泡时间为15 d时,抑制率能高达75.99%.稻秆浸出液投加量达7.5%以上具有显著的抑藻效果.不同部位的水稻秸秆浸出液对铜绿...     

Bioaccessibility of arsenic in various types of rice in an in vitro gastrointestinal fluid system

Rice can be a major contributor to dietary arsenic exposure because of the relatively high total arsenic concentration compared to other grains, especially for people whose main staple is rice. This study employed in vitro gastrointestinal fluid digestion to determine bioaccessible or gastrointestinal fluid extractable arsenic concentration in rice. Thirty-one rice samples, of which 60 % were grown in the United States, were purchased from food stores in New York City. Total arsenic concentrations in these samples ranged from 0.090 ± 0.004 to 0.85 ± 0.03 mg/kg with a mean value of 0.275 ± 0.161 mg/kg (n = 31). Rice samples with relatively high total arsenic (>0.20 mg/kg, n = 18) were treated by in vitro artificial gastrointestinal fluid digestion, and the extractable arsenic ranged from 53 % to 102 %. The bioaccessibility of arsenic in rice decreases in the general order of extra long grain, long grain, long grain parboiled, to brown rices.     

Cry1Ab protein from Bt transgenic rice does not residue in rhizosphere soil

Expression of Cry1Ab protein in Bt transgenic rice (KMD) and its residue in the rhizosphere soil during the whole growth in field, as well as degradation of the protein from KMD straw in five soils under laboratory incubation were studied. The residue of Cry1Ab protein in KMD rhizosphere soil was undetectable (below the limit of 0.5 ng/g air-dried soil). The Cry1Ab protein contents in the shoot and root of KMD were 3.23-8.22 and 0.68-0.89 microg/g (fresh weight), respectively. The half-lives of the Cry1Ab protein in the soils amended with KMD straw (4%, w/w) ranged from 11.5 to 34.3d. The residence time of the protein varied significantly in a Fluvio-marine yellow loamy soil amended with KMD straw at the rate of 3, 4 and 7%, with half-lives of 9.9, 13.8 and 18d, respectively. In addition, an extraction method for Cry1Ab protein in soil was developed, with extraction efficiencies of 46.4-82.3%.     

Phenylurea herbicide sorption to biochars and agricultural soil

Biochar is increasingly been used as a soil amendment to improve water-holding capacity, reduce nutrient leaching, increase soil pH, and also as a means to reduce contamination through sorption of heavy metals or organic pollutants. The sorption behavior of three phenylurea herbicides (monuron, diuron and linuron) on five biochars (Enhanced Biochar, Hog Waste, Turkey Litter, Walnut Shell and Wood Feedstock) and an agricultural soil (Yolo silt loam) was investigated using a batch equilibration method. Sorption isotherms of herbicides to biochars were well described by the Freundlich model (R² = 0.93–0.97). The adsorption K_F values ranged from 6.94 to 1306.95 mg kg^?1 and indicated the sorption of herbicides in the biochars and Yolo soil was in the sequence of linuron > diuron > monuron and walnut shell biochar > wood feedstock biochar > turkey litter biochar > enhanced biochar > hog waste biochar > Yolo soil. These data show that sorption of herbicides to biochar can have both positive (reduced off-site transport) and negative (reduced herbicide efficacy) implications and specific biochar properties, such as H/C ratio and surface area, should be considered together with soil type, agriculture chemical and climate condition in biochar application to agricultural soil to optimize the system for both agricultural and environmental benefits.     

Adsorption of hydrogen sulfide by biochars derived from pyrolysis of different agricultural/forestry wastes

The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different biochars derived from agricultural/forestry wastes through pyrolysis at various temperatures (100 to 500 ºC) were investigated. In this study, the H₂S breakthrough capacity was measured using a laboratory-characterized using pH and Fourier transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface. Certain threshold ranges of the pyrolysis temperature (from 100 to 500 ºC) and pH of the surface are presented. It also concluded that the sorption capacity (for removing H₂S) of rice hull-derived biochar is the largest in three biochars (camphor-derived biochar, rice hull-derived biochar, and bamboo-derived biochar). These observations will be helpful in designing biochar as engineered sorbents for the removal of H₂S.Implications: This paper focuses on the adsorption of hydrogen sulfide (H₂S) by biochars derived from wastes. The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different boichars derived from agricultural/forestry wastes through pyrolysis at various temperatures were investigated. In this study, the H₂S breakthrough capacity was measured using laboratory characterization with pH and Fourier-transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface.     

Assessment of arsenic content in soil,rice grains and groundwater and associated health risks in human population from Ropar wetland,India, and its vicinity

In the present study, potential health risks posed to human population from Ropar wetland and its vicinity, by consumption of inorganic arsenic (i-As) via arsenic contaminated rice grains and groundwater, were assessed. Total arsenic (t-As) in soil and rice grains were found in the range of 0.06–0.11 mg/kg and 0.03–0.33 mg/kg, respectively, on dry weight basis. Total arsenic in groundwater was in the range of 2.31–15.91 μg/L. i-As was calculated from t-As using relevant conversion factors. Rice plants were found to be arsenic accumulators as bioconcentration factor (BCF) was observed to be >1 in 75% of rice grain samples. Further, correlation analysis revealed that arsenic accumulation in rice grains decreased with increase in the electrical conductivity of soil. One-way ANOVA, cluster analysis and principal component analysis indicated that both geogenic and anthropogenic sources affected t-As in soil and groundwater. Hazard index and total cancer risk estimated for individuals from the study area were above the USEPA limits of 1.00 and 1.00 × 10^?6, respectively. Kruskal-Wallis H test indicated that groundwater intake posed significantly higher health risk than rice grain consumption (χ ²(1) = 17.280, p = 0.00003).     

Maize,switchgrass, and ponderosa pine biochar added to soil increased herbicide sorption and decreased herbicide efficacy

Biochar, a by-product of pyrolysis made from a wide array of plant biomass when producing biofuels, is a proposed soil amendment to improve soil health. This study measured herbicide sorption and efficacy when soils were treated with low (1% w/w) or high (10% w/w) amounts of biochar manufactured from different feedstocks [maize (Zea mays) stover, switchgrass (Panicum vigatum), and ponderosa pine (Pinus ponderosa)], and treated with different post-processing techniques. Twenty-four hour batch equilibration measured sorption of ¹⁴C-labelled atrazine or 2,4-D to two soil types with and without biochar amendments. Herbicide efficacy was measured with and without biochar using speed of seed germination tests of sensitive species. Biochar amended soils sorbed more herbicide than untreated soils, with major differences due to biochar application rate but minor differences due to biochar type or post-process handling technique. Biochar presence increased the speed of seed germination compared with herbicide alone addition. These data indicate that biochar addition to soil can increase herbicide sorption and reduce efficacy. Evaluation for site-specific biochar applications may be warranted to obtain maximal benefits without compromising other agronomic practices.     

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like polychlorinated biphenyls in rice straw smoke and their origins in Japan

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) contained in the smoke generated from rice straw burning in post-harvest paddy fields in Japan were analyzed to determine their congener profiles. Both the apportionment of toxic equivalent (TEQ) by using indicative congeners and the comparison of the homolog profiles showed that the PCDDs/PCDFs/DL-PCBs present in the rice-straw smoke were greatly influenced by those present as impurities in pentachlorophenol (PCP) and chlornitrofen (CNP, 4-nitrophenyl-2,4,6-trichlorophenyl ether) formulations that had been widely used as herbicides in paddy fields in Japan. Further, in order to investigate the effects of paddy-field soil on the PCDDs/PCDFs/DL-PCBs present in rice-straw smoke, PCDD/PCDF/DL-PCB homolog profiles of rice straw, rice-straw smoke and paddy-field soil were compared. Rice-straw smoke was generated by burning rice straw on a stainless-steel tray in a laboratory. The results suggested that the herbicides-originated PCDDs/PCDFs/DL-PCBs and the atmospheric PCDDs/PCDFs/DL-PCBs contributed predominantly to the presence of PCDDs/PCDFs/DL-PCBs in the rice-straw smoke while the contribution of PCDDs/PCDFs/DL-PCBs formed during rice straw burning was relatively minimal. The major sources of the PCDDs/PCDFs/DL-PCBs found in the rice-straw smoke were attributed primarily to the paddy-field soil adhered to the rice straw surface and secondarily to the air taken by the rice straw. The principal component analysis supported these conclusions. It is concluded that rice straw burning at paddy fields acts as a driving force in the transfer of PCDDs/PCDFs/DL-PCBs from paddy-field soil to the atmosphere.     

Effects of biochar on the emissions,soil distribution,and nematode control of 1,3-dichloropropene

Emissions of volatile soil fumigant 1,3-dichloropropene (1,3-D) from soil to air are a significant concern in relation to air quality, and cost-effective strategies to reduce such emissions are urgently required by growers to help them comply with increasingly stringent regulations. In this work, application of a rice husk-derived biochar to the surface of a sandy loam soil chamber reduced soil–air emissions of 1,3-D from 42% in a control (no biochar) to 8% due to adsorption onto the biochar. This adsorbed 1,3-D showed a potential for re-volatilization into air and solubilization into the soil–liquid phase. Biochar at the soil surface also reduced soil–gas concentrations in the upper soil; based on the determination of concentration–time values, this may limit 1,3-D-induced nematode control in the upper soil. In batch studies, the mixing of biochar into the soil severely limited nematode control; 1,3-D application rates around four times greater than the maximum permissible limit would be required to give nematode control under such conditions. Therefore, the use of biochar as a surface amendment, while showing an emission reduction benefit, may limit pest control during subsequent fumigations if, as seems probable, it is plowed into the soil.