Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K(d) values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons.     

Variation of the distribution coefficient (Kd) of selenium in soils under various microbial states

This study aimed to (i) evaluate whether the K(d) value of selenium is dependent upon the soil microbial activity and (ii) define the limitation of the use of the K(d) concept to describe selenium behaviour in soils when assessing the long-term radiological waste disposal risk. K(d) coefficients, as well as information on selenite speciation in the soil-solution, were derived from short- and long-term batch experiments with a calcareous silty clay soil in various microbial states. Soil microbial activity induced (i) an increase of the K(d) value from 16 l kg(-1) in sterile conditions to 130 l kg(-1) when the soil was amended with glucose and nitrate, and (ii) changes in selenium speciation both in the solution (presence of seleno-species other than free Se(IV)) and in the solid phase (Se linked to microorganisms). Although the K(d) coefficient adequately reflects the initial fractionation between soil-solid and soil-solution, it does not allow for speciation and microbial processes, which could affect reversibility, mobility and the long-term accumulation and uptake into crops.     

Selenium bioavailability and uptake as affected by four different plants in a loamy clay soil with particular attention to mycorrhizae inoculated ryegrass

The aim of this study was to investigate the influence of plant species, especially of their rhizosphere soil, and of inoculation with an arbuscular mycorrhizal (AM) fungus on the bioavailability of selenium and its transfer in soil-plant systems. A pot experiment was performed with a loamy clay soil and four plant species: maize, lettuce, radish and ryegrass, the last one being inoculated or not with an arbuscular mycorrhizal fungus (Glomus mosseae). Plant biomass and Se concentration in shoots and roots were estimated at harvest. Se bioavailability in rhizosphere and unplanted soil was evaluated using sequential extractions. Plant biomass and selenium uptake varied with plant species. The quantity of rhizosphere soil also differed between plants and was not proportional to plant biomass. The highest plant biomass, Se concentration in plants, and soil to plant transfer factor were obtained with radish. The lowest Se transfer factors were obtained with ryegrass. For the latter, mycorrhizal inoculation did not significantly affect plant growth, but reduced selenium transfer from soil to plant by 30%. In unplanted soil after 65 days aging, more than 90% of added Se was water-extractable. On the contrary, Se concentration in water extracts of rhizosphere soil represented less than 1% and 20% of added Se for ryegrass and maize, respectively. No correlation was found between the water-extractable fraction and Se concentration in plants. The speciation of selenium in the water extracts indicated that selenate was reduced, may be under organic forms, in the rhizosphere soil.     

Aqueous, solid and gaseous partitioning of selenium in an oxic sandy soil under different microbiological states

The aim of this study was to investigate the role of microorganisms on the behaviour of selenium in natural soil maintained under strictly aerobic conditions. Six-day batch experiments were performed with soils constrained to different microbiological states, either by sterilisation or by adding organic substrates. Selenium was added to the soil as selenite. The distribution of selenium in the gaseous, liquid and solid phases of the batch was measured. Selenium partitioning between the various solid phases was investigated by chemical sequential extractions. Active microorganisms played major effects on the distribution of selenium within the soil. On the one hand, microorganisms could promote selenium volatilisation (in relatively small amounts), leading to the spreading of selenium compounds outside the soil. On the other hand, microbial activities increased both amount of selenium retained by the soil and the strength of its retention (less exchangeable selenium), making selenium less susceptible to remobilisation.     

Sorption behavior of selenium on humic acid under increasing selenium concentration or increasing solid/liquid ratio

The sorption of selenium (Se) on humic acid (HA) was investigated in order to better understand the fate of stable and radioactive Se in soils and sediments. An ultrafiltration technique was used to determine size distributions of HA-sorbed-Se when increasing Se concentration and solid/liquid ratio. The results showed that the Se sorption onto HA followed the Freundlich isotherm. No solid/liquid ratio-dependence was observed especially when <3 kDa molecular size fraction was used from solid/liquid separation. The Freundlich isotherm parameters K(F) and n obtained using the <3 kDa molecular size fraction for solid/liquid separation were 3.7 x 10(2) and 0.82, respectively. In addition, since dissolved HA increased with decreased ionic strength in the HA suspension, ionic strength could promote aggregation of HA. The conformational change of HA could affect the sorption behavior of Se on HA.     

Degradation of polycyclic aromatic hydrocarbons by a bacterial consortium enriched from mangrove sediments

The biodegradability of a polycyclic aromatic hydrocarbons (PAHs) mixture consisted of fluorene (Fl), phenanthrene (Phe) and pyrene (Pyr) by a bacterial consortium enriched from mangrove sediments under sediment-free and sediment slurry conditions was investigated. The enriched consortium made up of three bacterial strains, namely Rhodococcus sp., Acinetobacter sp. and Pseudomonas sp., had a good PAH degradation capability with 100% degradation of Fl and Phe in sediment-free liquid medium after 4 weeks of growth. The Fl and Phe degradation percentages in sediment slurry were higher than that in liquid medium. Autochthonous microorganisms in sediments also possessed satisfactory PAH degradation capability and all three PAHs were almost completely degraded after 4 weeks of growth. Bioaugumentation (inoculation of the enriched consortium to sediments) showed a positive effect on PAH biodegradation after 1 week of growth. Complete biodegradation of pyrene took longer time than that for Fl and Phe, indicating the enriched bacterial consortium had preference to utilize low-molecular weight PAHs.     

Selenium geochemistry of paddy soils in Yangtze River Delta

Selenium (Se) content both in total and bioavailable forms were very low (25-35 and 9.5 micrograms/kg, respectively) in waterlogged paddy soils in the central Yangtze River Delta. This was due to changes in geochemistry and the inherent properties of the parent materials of these lowland paddy soils. The very low Se content (23 micrograms/kg) in the parent material resulted in low total Se content in the soil. The main chemical changes under long-term waterlogged conditions are depletion of molecular oxygen, decrease of redox potential, and reduction of Fe (III) to Fe (II) and SeO3(2-) to Se0. This led to low availability of Se in soils, and subsequently low Se content (29 micrograms/kg) in brown rice grain produced in this region. It has been suspected that low Se content in staple food might be one of the major reasons for a high infection rate of the intestine and stomach cancers and the higher death rate caused by these diseases in the region. Foliage spray of Na2SeO3 at early heading stage of rice plant growth improved the Se content of brown rice grain, hull, and straw, and would improve human and animal health.     

(137)Cs and (90)Sr uptake by sunflower cultivated under hydroponic conditions

The (90)Sr and (137)Cs uptake by the plant Helianthus annuus L. was studied during cultivation in a hydroponic medium. The accumulation of radioactivity in plants was measured after 2, 4, 8, 16 and 32 days of cultivation. About 12% of (137)Cs and 20% of (90)Sr accumulated during the experiments. We did not find any differences between the uptake of radioactive and stable caesium and strontium isotopes. Radioactivity distribution within the plant was determined by autoradiography. (137)Cs was present mainly in nodal segments, leaf veins and young leaves. High activity of (90)Sr was localized in leaf veins, stem, central root and stomata. The influence of stable elements or analogues on the transfer behaviour was investigated. The percentage of non-active caesium and strontium concentration in plants decreased with the increasing initial concentration of Cs or Sr in the medium. The percentage of (90)Sr activity in plants decreased with increasing initial activity of the nuclide in the medium, but the activity of (137)Cs in plants increased. The influence of K(+) and NH(4)(+) on the uptake of (137)Cs and the influence of Ca(2+) on the uptake of (90)Sr was tested. The highest accumulation of (137)Cs (24-27% of the initial activity of (137)Cs) was found in the presence of 10 mM potassium and 12 mM ammonium ions. Accumulation of about 22% of initial activity of (90)Sr was determined in plants grown on the medium with 8 mM calcium ions.     

滇池外海规模化控养水葫芦局部死亡原因分析

为了找出外海规模化控养水葫芦(E.crassipes)局部死亡的原因,于2013年8月对控养水域水葫芦空白对照区、健壮区、轻度枯死区以及重度枯死区的水质理化性质、蓝藻生物量及水生植物病理学等方面进行了比较研究。结果表明:轻度和重度枯死区蓝藻生物量高达(4.21±0.49)×109 cells/L和(757.00±19.00)×109 cells/L,均显著高于空白区和健壮区(0.14±0.09)×109 cells/L和(1.46±0.11)×109 cells/L(P0.05);NH+4-N浓度为11.44±0.02mg/L和369.87±15.37mg/L,均显著高于空白区和健壮区0.32±0.01mg/L和0.34±0.01mg/L(P0.05);轻度和重度枯死区溶氧仅1.40±0.13mg/L和0.30±0.04mg/L显著低于空白区和健壮区的7.70±0.83mg/L和6.80±0.97mg/L(P0.05);枯死区水体氧化还原电位(Eh)较低,重度死亡区水体Eh为-279.70±29.70mv显著低于其他3处水域。并且,通过对枯死水葫芦常规病理学检测,并未发现病变迹象。由此推断:水葫芦死亡原因可能主要由下风向种养区蓝藻过量堆积死亡,致使水质恶化,水体严重缺氧,进而引起水体NH+4-N浓度过高,最终导致水葫芦死亡。这为今后种养水葫芦进行水体生态修复理论研究与实践运用提供借鉴和参考,也为利用水葫芦作为蓝藻拦截带,在水葫芦影响下的湖泊营养物质迁移与氮、磷、碳循环动力学提出了新的研究内容。     

Uranium uptake by hydroponically cultivated crop plants

Hydroponicaly cultivated plants were grown on medium containing uranium. The appropriate concentrations of uranium for the experiments were selected on the basis of a standard ecotoxicity test. The most sensitive plant species was determined to be Lactuca sativa with an EC₅₀ value about 0.1 mM. Cucumis sativa represented the most resistant plant to uranium (EC₅₀ = 0.71 mM). Therefore, we used the uranium in a concentration range from 0.1 to 1 mM.Twenty different plant species were tested in hydroponic solution supplemented by 0.1 mM or 0.5 mM uranium concentration. The uranium accumulation of these plants varied from 0.16 mg/g DW to 0.011 mg/g DW. The highest uranium uptake was determined for Zea mays and the lowest for Arabidopsis thaliana. The amount of accumulated uranium was strongly influenced by uranium concentration in the cultivation medium. Autoradiography showed that uranium is mainly localized in the root system of the plants tested. Additional experiments demonstrated the possibility of influencing the uranium uptake from the cultivation medium by amendments. Tartaric acid was able to increase uranium uptake by Brassica oleracea and Sinapis alba up to 2.8 times or 1.9 times, respectively. Phosphate deficiency increased uranium uptake up to 4.5 times or 3.9 times, respectively, by Brassica oleracea and S. alba. In the case of deficiency of iron or presence of cadmium ions we did not find any increase in uranium accumulation.     

Effect of copper-tolerant rhizosphere bacteria on mobility of copper in soil and copper accumulation by Elsholtzia splendens

The role of rhizosphere bacteria in facilitating the solubility of copper (Cu) in contaminated soil and Cu accumulation in plant were studied. The bacteria strains were isolated from the rhizosphere of Elsholtzia splendens, a Cu accumulator growing on Tonglu Mountain copper mines. After the sandy soils containing 237 mg kg(-1) were incubated with the bacteria strains, it was indicated that rhizosphere microbes played an important role in influencing the availability of water-soluble Cu in soils. Soils had greater concentrations of water-extractable Cu compared with axenic soils inoculated with different bacterial strains. Further evidence for bacterial facilitation of increased solubility of Cu in the soil was obtained using the antibiotic ampicillin (0.1 mg g(-1)). There were 36% decreases in Cu concentration in the presence of bacterial strain MS12 and ampicillin together compared with bacterial inoculation alone. Different bacterial strains had different abilities on soil water-soluble Cu. To achieve the highest rates of plant Cu accumulation, it was necessary for bacteria to be present in the rhizosphere of E. splendens. Inoculated plants supplied with 20 micromol L(-1) CuSO4 had significantly greater concentrations of Cu in shoots and roots than uninoculated plants and bacterial strain MS2 was the most effective strain in promoting plant Cu uptake. There were 2.2-fold and 2.5-fold increases in Cu accumulation in the shoots and roots of plants inoculated with strain MS2 compared to axenic controls. Furthermore, when ampicillin and the bacterial strains were added together to the nutrient solution, the Cu concentrations in roots and shoots of ampicillin-treated plants were lower than those in inoculated plants. When ampicillin was added to the nutrient solution, Cu accumulation was inhibited by about 24-44% in shoots and 20-44% in roots. The above results provided a new insight into the phytoremediation of Cu-contaminated soil.     

Flux of heavy metal accumulation in various organs of the intertidal marine blue crab, Portunus pelagicus (L.) from the Kuwait coast after the Gulf War.

The metal levels of arsenic, chromium, copper, lead, magnesium, manganese, selenium, vanadium, and zinc concentrations were determined in various body organs, viz., hepatopancreas, gills, gonad, gastric stomach, and muscle of the blue crab, Portunus pelagicus (Crustacea: Decapoda) to assess the bioaccumulation of metals associated with petroleum input a decade after the 1991 Gulf War oil spillage. Sample solutions prepared were analyzed using an atomic absorption spectrophotometry. High concentrations of Zn and Cu in the muscle and hepatopancreas tissues were a strong indicative of high exposure of P. pelagicus to these metals. However, muscle tissue had been found to accumulate the highest values for all metal speciations analyzed. Copper, zinc, and chromium in samples collected from Station II covering the Kuwait City area were often in excess of those present in Station I and III. Arsenic, lead, magnesium, manganese, selenium, and vanadium were greater in individuals obtained from Station I. A significant correlation was found to exist between Se and V in crab muscle with a surge in Se metal concentration, which was found to be inversely proportional to that of V metal concentration irrespective of the sex of the crab. The difference in patterns of metal occurrence and the significant increase in the Cu and Zn concentrations in various organs of the crab were largely associated with the 1991 Gulf War oil spill. Such results could be used as a baseline for the monitoring of the level of metals in marine organisms of future studies.     

Selenium and 17 other largely essential and toxic metals in muscle and organ meats of Red Deer (Cervus elaphus)--consequences to human health

Concentrations, composition and interrelationships of selenium and metallic elements (Ag, Ba, Cd, Co, Cr, Cs, Cu, Ga, Mn, Mo, Pb, Rb, Sb, Sr, Tl, V and Zn) have been examined in muscle and organ meats of Red Deer hunted in Poland. The analytical data obtained were also discussed in terms of Se supplementation and deficit to Deer as well as the benefits and risk to humans associated with the essential and toxic metals intake resulting from consumption of Deer meat and products. These elements were determined in 20 adult animals of both sexes that were obtained in the 2000/2001 hunting season from Warmia and Mazury in the north-eastern part of Poland. The whole kidneys contained Ba, Cd, Cr, Ga, Pb, Se, Sr and Tl at statistically greater concentrations than liver or muscle tissue from the same animal. Liver showed statistically greater concentrations of Ag, Co, Cu, Mn and Mo than kidneys or muscle tissue, and muscle tissue was richer in Zn, when compared to the kidneys or liver. Cs and Rb were similarly distributed between all three tissue types, while V was less abundant in liver than kidneys or muscle tissue. There were significant associations between some metallic elements retained in Red Deer demonstrated by Principal Component Analysis (PCA) of the data set. In organ and muscle meats (kidneys, liver and muscle tissue considered together) the first principal component (PC1) was strongly influenced by positively correlated variables describing Se, Ba and Cd and negatively correlated variables describing Ag, Co, Cs, Mn, Pb, Tl and V; PC2, respectively, by Cu, Mn and Mo (+) and Zn (-); PC3 by Ga (+) and PC4 by Sb (+). Selenium occurred in muscle tissue, liver and kidneys at median concentrations of 0.13, 0.19 and 4.0mg/g dry weight, respectively. These values can be defined as marginally deficient (< 0.6mg Se/kg liver dw) or satisfactory (≤ 3.0mg Se/kg kidneys dw) for the amount required to maintain the Deer's body condition and health, depending on the criterion for supplementation used. In terms of human nutritional needs, a relatively high selenium content of kidneys can be beneficial. The muscle meat, liver and kidneys of Red Deer can be considered as a very good source of essential Co, Cr, Cu, Mo, Mn, Se and Zn in the human diet. Lead is generally considered as toxic, and the concentrations found in Red Deer (via the food chain intake) were well below the European Union tolerance limit. Pb from the lead bullets can always create food hygienic problem, if not well recognized during sanitary inspection, and this was noted for one muscle meat sample in this study (5% surveyed). There is no tolerance limit of Cd in game animal meats. The median values of Cd noted in fresh muscle tissue, liver and whole kidneys were 0.07, 0.18, and 3.3mg/kg wet weight, respectively. Cd exists as a chemical element present at trace levels in plants and mushrooms in Deer's food chain in background (uncontaminated) areas. When these are consumed by the Deer, the amount of Cd sequestered with metallothioneins and retained in the organ and muscle meat in this study is low enough to be considered safe for human consumption.     

Characterization of the effluent from a nanosilver producing washing machine

The increasing number of nanomaterial based consumer products raises concerns about their possible impact on the environment. This study provides an assessment of the effluent from a commercially available silver nanowashing machine. The washing machine released silver in its effluent at an average concentration of 11μgL(-1), as determined by inductive coupled mass spectrometry (ICP-MS). The presence of silver nanoparticles (AgNPs) was confirmed by single particle ICP-MS as well as ion selective electrode measurements and filtration techniques. Size measurements showed particles to be in the defined nanosize range, with an average size of 10nm measured with transmission electron microscopy (TEM) and 60-100nm determined with nanoparticle tracking analysis (NTA). The effluent was shown to have negative effects on a natural bacterial community as its abundance was clearly reduced when exposed to the nanowash water. If washing machines capable of producing AgNPs become a common feature of households in the future, wastewater will contain significant loadings of AgNPs which might be released into the environment.     

长三角典型地区土壤环境中Se的空间变异特征及其与人类健康的关系

农业土壤环境中硒（Se）的缺乏或过量都会通过食物链最终影响人类健康。在203个土壤采样点的基础上,利用GIS和地统计学相结合的方法,对江苏省如皋市农田土壤环境中Se的空间变异特征及其影响因素进行分析,同时,对土壤中Se的空间分布与长寿人口的空间分布进行空间叠加分析。研究结果表明,如皋市土壤环境中总Se及水溶态Se的平均含量分别为0.13 mg/kg和2.16 μg/kg,研究区处在相对低Se的土壤环境中。总Se的空间变异性不大,其空间分布比较均一;但水溶态Se的空间变异性较大,主要受成土条件及土壤母质、土壤类型及地形地貌等结构性因子的影响。水溶态Se对土壤的理化性质也比较敏感,特别是速效磷、有机质及全钾含量与水溶态硒的相关性较显著,因此在有机质及土壤养分含量较高、土壤颗粒组成较细的东部及北部地区水溶态硒的含量也较高。土壤水溶态Se的空间分异与长寿人口比率的空间分异呈极显著的正相关关系(〖WTBX〗P〖WTBZ〗<001),相关系数达〖WTBX〗r〖WTBZ〗=0325,表明人类的健康长寿现象与环境中水溶态硒的含量有很大关系,但人类长寿的本质和真正机理仍需进一步研究验证。     

Morphophysiological adaptation aspects of different Haloxylon aphyllum (Chenopodiaceae) genotypes along a salinity gradient

The seedlings of Haloxylon aphyllum from seeds with different genetic characteristics, which were collected in three natural subpopulations along a soil salinity gradient, were investigated. The plants grown under various levels of NaCl (0–300 mM) differed in the shoot length, the relative growth rate (calculated for fresh and dry biomass), as well as ions and proline contents. The heterozygous genotypes of xerohalophytic H. aphyllum have shown significant advantages in their productivity and sustainability under moderate and high salinity.     

No evidence of selenosis from a selenium-rich diet in the Brazilian Amazon

Selenium (Se) is an essential element and a well-known anti-oxidant. In the Lower Tapajós River region of the Brazilian Amazon, biomarkers of Se range from normal to very high. The local traditional diet includes important Se sources such as Brazil nuts, chicken, game meat and certain fish species. Some studies have reported alterations in keratin structure, gastrointestinal problems and paresthesia in populations with high Se intake. The objective of the present study was to evaluate cutaneous and garlic odor of the breath signs and sentinel symptoms of Se toxicity (selenosis) in relation to Se status in communities along the Tapajós River.Participants (N = 448), aged 15–87 years, were recruited from 12 communities. Se concentrations were measured in blood (B-Se) and plasma (P-Se) by ICP-MS. A nurse performed an examination of the hair, nails, skin and breath for signs of Se toxicity. Interview-administered questionnaires were used to collect information on socio-demographics, medical history and possible symptoms of Se toxicity.In this population, the median levels of B-Se and P-Se were 228.4 μg/L (range 103.3–1500.2 μg/L) and 134.8 μg/L (range 53.6–913.2 μg/L) respectively. Although B-Se and P-Se surpassed concentrations considered toxic (B-Se: 1000 μg/L (U.S. EPA, 2002)), no dermal or breath signs or symptoms of Se toxicity were associated with the biomarkers of Se status.In the present study population, where Se intake is mostly from traditional diet, there is no evidence of selenosis. These findings support the need to re-assess Se toxicity considering factors such as the chemical form of Se exposure, route of exposure (inhaled versus ingested), co-exposures to toxic elements such as mercury. Considering the current food transition towards a western diet in the Amazon, further studies should address the possible association between high Se status and cardiometabolic health in this study population.     

The bioavailability of selenium and risk assessment for human selenium poisoning in high-Se areas,China

Enshi prefecture of Hubei Province is well known for human selenium (Se) poisoning in the early 1960s in China. Sporadic cases of Se poisoning in livestocks are still being found. In this study, Se levels in water, cropland soils and various crops from high-Se areas of Enshi were measured to investigate the distribution and bioavailability of Se in the environments, as well as probable daily intake (PDI) of Se for local residents. The total Se in surface water ranged from 2.0 to 519.3 μg/L with a geometric mean of 46.0 ± 127.8 μg/L (n = 48), 70.5–99.5% of which was present in the form of Se(VI). The soil Se concentration varied from 2.89 to 87.3 μg/g with a geometric mean of 9.36 ± 18.6 μg/g (n = 45), and most of Se was associated with organic matter (OM-Se). The total Se in rice, corn, and vegetable samples were 2.11 ± 2.87 μg/g (n = 21), 3.76 ± 11.6 μg/g (n = 16), and 2.09 ± 3.38 μg/g (n = 25), respectively. Stream water Se is likely leached from carbonaceous shale and mine wastes, leading to Se accumulation in paddy soils. OM-Se may play an important role in Se uptake by rice plant in high-Se area of Enshi.The PDI of Se is approximately 2144 μg/day, and Se concentration in blood is estimated at about 3248 μg/L, posing a potential chronic Se poisoning risk to local residents. Cereal consumption (48.5%) makes a great contribution to human daily Se intake, followed by vegetables (36.6%), meats (8.5%), and drinking water (6.4%). However, when assessing health risk on human in high-Se areas, the contribution of drinking water to daily Se intake cannot be ignored due to high Se content and dominant Se(VI) species. Local inhabitants should be advised not to grow crops in high-Se lands or irrigate using high-Se water. If possible, they should drink pipe water and consume foods mixed with those from outside the high-Se areas.     

富硒土壤硒生物有效性及影响因素研究

湖北恩施是典型的富硒土壤分布区,在恩施市沙地乡采集了199件表层土壤样品以及60件玉米样品进行分析测试,旨在查明研究区硒元素含量特征,并分析硒生物有效性及其影响因素。结果显示:研究区表层土壤中硒含量的平均值为188 mg/kg,同时土壤中水溶态硒含量只占到总硒含量的004%~291%,处于相对较低水平。研究区内,有机碳含量对硒生物有效性影响很小,影响硒生物有效性的主要因素为土壤总硒含量和土壤pH值,碱性土壤中硒生物有效性更高。由于该区土壤主要呈酸性,且水溶态硒含量较少,导致玉米中硒含量整体处于相对较低水平,可以通过人为手段适当调控土壤酸碱性,提高硒生物有效性     

Acetate biodegradation by anaerobic microorganisms at high pH and high calcium concentration

Acetate biodegradation at a high pH and a high calcium concentration was examined to clarify the effect of bacterial activity on the migration of organic ¹⁴C compounds in cementitious repositories.Tamagawa river sediment or Teganuma pond sediment was anaerobically cultured with 5 mM acetate and 10 mM nitrate at pH 9.5-12 at 30 °C. After 20 and 90 days, the acetate concentration of the culture medium was analyzed and found to have decreased below 5 mM at pH ≤ 11. On the other hand, it did not decrease when either sediment was incubated in the absence of nitrate. These results suggest that nitrate-reducing bacteria can biodegrade acetate under more alkaline conditions than the reported pH range in which nitrate-reducing bacteria can exhibit activity.Acetate biodegradation was also examined at a high calcium concentration. Sediments were anaerobically cultured at pH 9.5 with 5 mM acetate and 10 mM nitrate in solution, equilibrated with ordinary Portland cement hydrate, in which the Ca concentration was 14.6 mM. No decrease in acetate concentration after incubation of the sediments was observed, nor was it lower than in the absence of cementitious composition, suggesting that kinetics of acetate biodegradation by anaerobic microorganisms is lowered by a high Ca concentration.