Modeling spatial variation in microbial degradation of pesticides in soil

Currently, no general guidance is available on suitable approaches for dealing with spatial variation in the first-order pesticide degradation rate constant k even though it is a very sensitive parameter and often highly variable at the field, catchment, and regional scales. Supported by some mechanistic reasoning, we propose a simple general modeling approach to predict k from the sorption constant, which reflects bioavailability, and easily measurable surrogate variables for microbial biomass/activity (organic carbon and clay contents). The soil depth was also explicitly included as an additional predictor variable. This approach was tested in a meta-analysis of available literature data using bootstrapped partial least-squares regression. It explained 73% of the variation in k for the 19 pesticide-study combinations (n = 212) in the database. When 4 of the 19 pesticide-study combinations were excluded (n = 169), the approach explained 80% of the variation in the degradation rate constant. We conclude that the approach shows promise as an effective way to account for the effects of bioavailability and microbial activity on microbial pesticide degradation in large-scale model applications.     

Fermentation of texturized vegetable proteins extruded at different moisture contents: effect on physicochemical,structural, and microbial properties

Food Science and Biotechnology - To investigate the effect of fermentation on texturized vegetable protein (TVP), TVPs extruded at 40 and 50% feed moisture contents (MC) were fermented using...     

The effect of Lactobacillus buchneri 40788 on the fermentation and aerobic stability of high moisture corn in laboratory silos

The production of antifungal compounds during fermentation could be a useful mechanism to improve the aerobic stability of fermented feeds when they are exposed to air. High moisture corn (26% moisture) was ground and inoculated with various amounts of Lactobacillus buchneri 40788, a heterolactic acid bacteria, and ensiled in laboratory silos. Inoculation with L. buchneri 40788 from 1 x 10(5) to 1 x 10(6) cfu/g of corn had minor effects on the end products of fermentation during the early stage of ensiling (< or = 14 d). However, after 49, 92, and 166 d of ensiling, increasing the application rate of L. buchneri 40788 applied to corn increased the concentration of acetic acid when compared to untreated corn. Addition of L. buchneri 40788 had few other effects on the end products of fermentation. Dry matter recovery and aerobic stability were measured after 92 and 166 d of ensiling. At these times, dry matter recovery was not different among treatments, and numbers of yeasts and molds tended to decrease as the application rate of L. buchneri 40788 increased. Aerobic stability (number of h prior to a 2 degrees C rise in temperature after exposure to air) was markedly improved by the addition > or = 5 x 10(5) cfu/g of L. buchneri 40788. Combining L. buchneri 40788 with L. plantarum did not impart better aerobic stability than when L. buchneri 40788 was applied alone to corn. Addition of L. buchneri 40788 did not affect the rate of fermentation in high moisture corn, but after prolonged storage higher application rates increased production of acetic acid and markedly improved aerobic stability.     

Quantifying the contribution of different sorption mechanisms for 2,4-dichlorophenoxyacetic acid sorption by several variable-charge soils

Previous research with phenolic, carboxylic, and urea type organic acids demonstrated that hydrophilic sorption was primarily due to anion exchange, which was linearly correlated to chemical acidity (pKa) and the soil anion exchange capacity. However, for dichlorophenoxyacetic acid (2,4-D), sorption by a kaolinitic soil was much higher than expected relative to all other organic acid-soil data. The enhanced sorption was hypothesized to involve calcium bridging of 2,4-D to hydrophilic domains. In this study, the mechanisms contributing to 2,4-D sorption by variable-charged soils were probed and quantified by measuring sorption from CaCl2, KCl, CaSO4, KH2PO4, and Ca(H2PO4)2 solutions. Linear sorption coefficients estimated for 2,4-D sorption from the different electrolytes decreased as follows: CaCl2 > KCl > CaSO4 > Ca(H2PO4)2 approximately equal to KH2PO4. Differences in 2,4-D sorption from CaCl2 and phosphate solutions were attributed to sorption by hydrophilic domains, which ranged between 46 and 94% across soils. Differences in 2,4-D sorption from CaCl2 and KCl were attributed specifically to Ca-bridging between 2,4-D's carboxyl group and the silanol edge on kaolinite and quartz and ranged from negligible to 40% depending on the soil mineral type. Differences in sorption from CaCl2 and CaSO4 was attributed to anion exchange, which ranged from 16 to 91%, followed the trends with pKa developed previously for other organic acids, and correlated well to the soil anion to cation exchange capacity ratio (AEC/CEC). The sum of anion exchange and Ca-bridging contributions agreed well with the sorption estimated to be from hydrophilic domains. All other sorption was attributed to hydrophobic processes, which correlated well to a linear free-energy relationship between pH-dependent organic carbon-normalized sorption coefficients and pH-dependent octanol-water partition coefficients developed for several other organic acids.     

不同土壤类型饼肥矿化过程中土壤酶活性及理化指标的变化

通过室内模拟试验,研究了3种植烟土壤饼肥矿化过程中土壤酶活性与理化指标的变化。结果表明:饼肥能有效的调节土壤的pH值,增加土壤中有机质、水解氮、速效磷的含量;红壤中速效磷释放效率最高,紫色土脲酶活性最强,水解氮含量最高,蔗糖酶在土壤中活性较稳定;不同土壤饼肥肥效释放速率为紫色土水稻土红壤,紫色土种植烤烟宜施未发酵或者发酵时间较短的饼肥,红壤和水稻土应使用腐熟完全的饼肥。     

土壤水分条件对白肋烟产、质量的影响及白肋烟灌溉的土壤水分指标研究

本项研究采用田间和盆栽试验相结合的方法研究了土壤水分条件对白肋烟产、质量和化学成分的影响.结果表明,白肋烟各生育期土壤相对含水量的适宜指标分别为移栽-团棵为70%、团棵-打顶为81%、打顶-采收为76%;干旱指标分别为移栽-团棵为58%、团棵-打顶为71%、打顶-采收为69%.白肋烟成熟阶段需水量相对较多,成熟期土壤相对含水量对白肋烟的成熟速度和化学成分的协调性及评吸质量的影响最为明显,在适宜的土壤相对含水量以下的范围内,表现出随土壤相对含水量升高,成熟速度加快,烟碱含量明显下降,内在化学成分更为协调和评吸质量提高.适宜的土壤相对含水量能明显提高白肋烟产量、产值和等级比重.     

滴灌条件下不同灌水量对无核白鸡心葡萄果实的生长发育及品质的影响

为了研究在滴灌条件下不同土壤水分下限对无核白鸡心葡萄果实品质的影响,以3组土壤水分下限为处理,大水漫灌为对照,在生育期对无核白鸡心葡萄果实纵横径、采前果穗的生长发育情况及果实糖度进行测定.总结出节水灌溉可以提高葡萄果实的整齐度,且果实糖度比对照增加约3个百分点,明显提高了果实的品质.     

Organochlorine pesticides in the soils and atmosphere of Costa Rica

A survey of the contamination of the physical environment of Costa Rica with banned organochlorine pesticides (OCPs) relied on sampling air and soil at 23 stations acrossthe country in 2004. Average annual air concentrations, determined with XAD-based passive samplers, and surface soil concentrations were generally low when compared to values reported for North and Central America, which is consistent with relatively low historical domestic use and little atmospheric inflow from neighboring countries. Statistical analysis and concentration maps reveal three types of spatial distribution: alpha-hexachlorocyclohexane and p,p'-DDD had a relatively uniform distribution across the country; other DDT-related species were greatly elevated over the national average at Manuel Antonio, a National Park on the Pacific coast; and dieldrin, lindane, and chlordane-related species had higher concentrations in Costa Rica's populated Central Valley. An altitudinal transect of stations in the Central Valley shows declining air-soil concentration ratios with elevation for lindane, likely driven by atmospheric inversions and soil organic carbon content. Enantiomeric composition of chiral OCPs in air and soil was close to racemic, with slight depletion of (-)-alpha-HCH, (-)-cis-chlordane, and (+)-trans-chlordane. Estimated air-soil fugacity fractions are highly uncertain but indicate equilibrium conditions for most OCPs, net volatilization of lindane at some sites, and net deposition for p,p'-DDE. The study demonstrates an approach for quickly evaluating the spatial distribution of OCPs in an understudied area, identifying regionally important contaminants and areas of elevated concentrations.     

The effects of gel-forming polyacrylamides on moisture storage in sandy soils

Gel-forming, cross-linked polyacrylamides are new formulations of soil conditioners for use where short-term or persistent drought inhibits plant growth. Most commercial products absorb water to many times their own weight thus improving the water storage properties of porous soils, and delaying the onset of the permanent wilting percentage where evaporation is intense. However, there is notable variation between products in the binding tension of absorbed moisture, so changes in field capacity are of little diagnostic value for the soil moisture available to plants. Nevertheless, polymers with high absorption capabilities and low binding tensions in the range pF 2 to 4.2 could be important aids to growth of agricultural, horticultural and forestry crops in drought-prone environments.     

Effects of enrichment with salicylate on bacterial selection and PAH mineralization in a microbial community from a bioreactor treating contaminated soil

We investigated enrichment with salicylate as a method to stimulate the degradation of polycyclic aromatic hydrocarbons (PAHs) by a microbial communityfrom a bioreactortreating PAH-contaminated soil. DNA-based stable isotope probing (SIP) was used to compare the effect of alternate methods of salicylate addition (spike vs slow, continuous addition) on the diversity of the enriched microbial community. After identification of salicylate degraders by SIP, real-time quantitative PCR (qPCR) primers were developed to quantify the abundances of three groups containing salicylate-utilizing organisms in the bioreactor community before and after enrichment. The different methods of salicylate addition were found to select for different microbial communities. Two groups containing salicylate-degrading bacteria increased in abundance substantially after enrichment by continuous addition of salicylate but did not increase in abundance in response to the spike addition, whereas a third group increased in abundance in response to both methods of salicylate addition. The initial rate of naphthalene mineralization increased significantly after enrichment by spike addition of salicylate, but neither phenanthrene nor benzo[a] pyrene mineralization rates were enhanced. Continuous addition of salicylate did not enhance the mineralization rate for any of the PAHs. These results suggest that enrichment with salicylate can select for naphthalene-degrading bacteria, but does not select for organisms responsible for degrading PAHs of higher molecular weight. Differences in microbial selection observed in this study that resulted from different rates of carbon source addition also have implications for the design of SIP experiments with water-soluble carbon sources.     

不同温湿度对小麦吸水/散湿速率影响的研究

分别在3个温度(15～30℃)和6个相对湿度条件(60%～95%)下测定了初始水分为11.3%和20.5%的小麦籽粒的吸水/散湿速率,并分析了其变化规律。研究表明:吸水/散湿速率与温度、湿度变化均成正相关,一定时间内呈快速降低而后趋于稳定的状态。当温度一定时,随着湿度的不断增大,小麦的吸水/散湿速率均增大;当湿度一定时,初始吸水/散湿速率均随着温度的不断升高而显著增大(P0.05)。     

不同干制方式对枸杞粉吸湿过程中水分变化的影响

以3种不同干燥方式下的枸杞所制得的粉体为研究对象,通过测定吸湿速率、吸附等温曲线探讨枸杞粉的吸湿规律,并利用低场核磁共振技术分析枸杞粉吸湿过程中的水分迁移特性。结果表明,3种干制方式下的枸杞粉吸湿等温曲线均属于Ⅲ型等温线,当水分活度大于0.5时,在同一水分活度下,其平衡含水率大小为,晒干>烘干>冻干,说明枸杞粉贮藏环境的水分活度低于0.5时较易保存;3种干制方式下的粉体储藏过程中,其核磁共振谱图显示,结合水(T_(21))随时间变化显著升高(P<0.05),不易流动水(T_(22))在前15 d没有显著变化,到第30天时显著升高(P<0.05),自由水(T_(23))无明显变化,说明在枸杞粉吸湿过程中,水分迁移变化主要发生在结合水与不易流动水之间;并发现储藏期在15 d之前,冻干方式所获得的枸杞粉吸湿特性更加稳定。该实验结果对于研究枸杞粉吸湿过程中的水分变化具有重要意义,同时为解释粉体吸湿机理提供理论依据。     

云南曲靖烟区典型植烟土壤氮素矿化规律研究

以云南曲靖烟区的主要植烟土壤为研究对象,采用Warning淹水培养方法,研究了不同类型土壤的氮素矿化过程。结果表明,淹水培养0-14 d宣威水稻土、罗平黄壤、罗平红壤、宣威红壤和宣威紫色土土壤铵态氮含量迅速增加,此期间的氮累积矿化量约占最高氮矿化量的83.7%。14 d后,宣威水稻土、罗平黄壤、宣威红壤和罗平红壤土壤铵态氮含量缓慢增加,表现为氮素的持续矿化;罗平红壤培养28 d土壤铵态氮含量达到最高值,其他3个土壤在42 d达到最高值;而宣威紫色土在14 d后土壤铵态氮含量持续减少,表现为氮素的固定。培养过程中(除42 d外),土壤铵态氮含量均表现为罗平黄壤、宣威水稻土>宣威红壤>罗平红壤>宣威紫色土。土壤氮累积矿化速率随培养时间逐渐降低且符合对数函数,罗平黄壤最高,宣威紫色土最低。罗平黄壤、宣威水稻土、罗平红壤土壤氮矿化率随培养时间逐渐增加,罗平黄壤的土壤氮矿化率最高,宣威紫色土最低。说明罗平黄壤和宣威水稻土的供氮能力较强,生产中应适当降低氮肥用量;宣威紫色土的供氮能力较弱,生产中适当补充氮肥,促进烟苗生长。     

Organic matter chlorination rates in different boreal soils: the role of soil organic matter content

Transformation of chloride (Cl(-)) to organic chlorine (Cl(org)) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl(org) has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by (36)Cl tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl(-) concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl(org) pool and in turn to a high internal supply of Cl(-) upon dechlorination. This provides unexpected indications that pore water Cl(-) levels may be controlled by supply from dechlorination processes and can explain why soil Cl(-) locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl(-) deposition.     

Screening of selected pesticides for oestrogen receptor activation in vitro

Twenty pesticides were tested for their ability to activate the oestrogen receptor in vitro using an MCF7 cell proliferation assay and a Yeast Oestrogen Screen. The fungicides fenarimol, triadimefon, and triadimenol were identified as weak oestrogen receptor agonists, which at 10 mu M induces a 2.0, 2.4, and 1.9-fold increase in proliferation of human MCF7 breast cancer cells (E3 clone). The relative proliferation efficiency (RPE) was 43-69% , indicating partial agonism at the oestrogen receptor. Several pesticides did not have any effect on the proliferation response after 6 days of exposure, including: chlorpyrifos, diuron, iprodion, linuron, pentachlorphenol, prochloraz, propioconazol, propyzamine, quintozen, tetrachorvinphos and tetradifon. Some pesticides resulted in a negligible proliferation response, which was not statistically significant under the present experimental conditions. These were: bromopropylate,chlorfenvinphos, chlorobenzilate, dicofol, heptachlor, and imazalil. Fenarimol and dicofol also gave rise to a positive oestrogenic response in yeast cells transfected with the oestrogen receptor alpha, whereas the remaining compounds resulted in a negative response due either to biological inactivity or cytotoxocity to the yeast cells. The EC₅₀ for fenarimol was estimated to be 13 mu M in the yeast cells, compared with an EC of 3 mu M in the MCF7 cells, indicating 50 higher sensitivity of the latter assay. No in vivo data for fenarimol, triadimefon or triadimenol have previously been published that support oestrogenic activity in the intact animal. Thus, from the present results we suggest that oestrogen receptor activation may not be an important mode of action for these compounds. The need to include at least two bioassays in a screening procedure and for combining in vitro and in vivo data is emphasized.     

Phosphorus sorption by some coconut-growing acid soils of Sri Lanka and its relationship to selected soil properties

Phosphorus (P) sorption in the presence of 10^?2M calcium chloride by ten coconut-growing acid soil samples of Sri Lanka belonging to the Ultisol, Alfisol and Entisol orders was evaluated using the Langmuir sorption isotherm. The data for all samples fitted the single-site Langmuir sorption isotherm when equilibrium P was less than 1 μg ml^?1, but showed some deviations at larger concentrations of P. A two-site Langmuir sorption isotherm was successfully used to describe the sorption data of three samples at these high concentrations. The single-site Langmuir sorption maxima were greater for Ultisols (349–825 μg g^?1) than for the other soils (136–345 μg g^?1). These sorption maxima were significantly correlated with %-clay, %-silt, dithionite-extractable iron, and 1M ammonium acetate (pH 4.8)-extractable aluminium. Regression analysis of P sorption on different forms of iron (Fe) and aluminium (Al) indicated that crystalline ‘free Fe oxides’ (dithionite-extractable Fe minus 0.3M oxalate-extractable Fe) and ‘active Al’ which consists of hydroxy Al monomers and polymers [1M ammonium acetates, (pH 4.8)-extractable Al minus 1M potassium chloride extractable Al] were the important factors contributing towards P sorption.     

Influence of rhamnolipids and triton X-100 on the desorption of pesticides from soils

A rhamnolipid biosurfactant mixture produced by P. aeruginosa UG2 and the surfactant Triton X-100 were tested for their effectiveness of enhancing the desorption of trifluralin, atrazine, and coumaphos from soils. Sorption of both surfactants by the soils was significant and adequately described by the Langmuir-type isotherm. Values of maximum sorption capacity (Qmax) and Langmuir constant (Klang) did not correlate with the amount of soil organic matter. Our results indicate that clay surfaces play an important role in the sorption of surfactants. When surfactant dosages were high enough to reach soil saturation and maintain an aqueous micellar phase, pesticide desorption was only enhanced. At dosages below soil saturation, surfactants sorbed onto soil, increasing its hydrophobicity and enhancing the sorption of the pesticides by a factor of 2. Similar values of water-soil partition coefficients (Ksol*) for aged and fresh added pesticides to soils indicate that the aging process used did not significantly after the capability of either surfactant to desorb the pesticides. A model able to estimate equilibrium distributions of organic compounds in soil-aqueous-micellar systems was tested against experimental results. The determined organic carbon partition coefficients, Koc values, indicate that, on a carbon normalized basis, sorbed Rh-mix is a much better sorbent of pesticides than TX-100 or soil organic matter. These results have significant implications on determining the effectiveness of surfactants to aid soil remediation technologies.