Wenxiang He

Speciation of glyphosate, phosphate and aminomethylphosphonic acid in soil extracts by ion chromatography with inductively coupled plasma mass spectrometry with an octopole reaction system.

Ion-pairing chromatography coupled with inductively coupled plasma mass spectrometry (ICP-MS) used for the speciation of phosphorus is limited as the mobile phase containing organic solvents changes in detection sensitivity and the carbon precipitates on torch and cones. To address this issue, anion-exchange chromatography with ICP-MS has been used for the speciation of glyphosate, phosphate and aminomethylphosphonic acid in soil extracts. The separation of the targets on a new column was achieved within 5 min using an eluent containing 20 mM NH(4)NO(3) at pH 5.1. Furthermore, since the polyatomic ions such as (14)N(16)O(1)H(+) and (15)N(16)O(+) from a nitrogen-based ion-pairing reagent interfered with ICP-MS detection of (31)P, an octopole reaction system was investigated to determine whether the polyatomic interferences could be reduced. The results show that addition of He to the cell can benefit analyses by reducing such interferences, but at the expense of reduced sensitivity. The detection limits in the range of 1.0-1.5 microg L(-1) (expressed as P) was achieved when 50 microL was injected using He as the collusion gas.

Effect of insecticide fenamiphos on soil microbial activities in Australian and Ecuadorean soils.

The effect of fenamiphos, a widely used organophosphorus pesticide, on important soil microbial activities such as dehydrogenase, urease and potential nitrification in four soils from Australia and Ecuador were studied. The results showed fenamiphos in general was not toxic to dehydrogenase and urease up to 100 mg/Kg soil. However potential nitrification was found to be highly sensitive to fenamiphos with a significant inhibition recorded even at 10 mg/Kg soil. In general, the nitrification activity in soils was decreased with an increase in fenamiphos concentration. The calculated EC50 values for nitrification in all the tested soils ranged between 19 and 56 mg fenamiphos/kg dry soil. This study suggests that fenamiphos is likely to be detrimental to nitrification at field application rates.

Bioavailability of lead in contaminated soil depends on the nature of bioreceptor.

Long-term lead (Pb) contaminated soils from two lead-zinc smelters and a shooting range, along with freshly spiked control soil, were studied by means of chemical, biological or a physiological method to examine the effect of ageing on Pb bioavailability. The freshly Pb spiked control soil was subjected to an earthworm toxicity test to observe the avoidance and mortality response of the earthworms. Meanwhile, an extractable fraction of Pb on the spiked soil as a result of ageing was examined and further compared with physiologically based in vitro bioaccessibility extraction tests. Their differences in lethal concentration, LC(50), to the earthworm population from spiked soils varied substantially as a function of soil pH. The strong effect of ageing on toxicity was also reflected in the extractability of Pb which was far greater in acidic soil, labelled AC, compared to the alkaline soil, labelled BC. This demonstrates that the bioavailable fraction causing toxicity to earthworms was achieved at a much lower total Pb content for acidic soils relative to alkaline soils. Moreover, the effect of ageing also exhibits that a marked decline in bioavailable Pb results in lowering toxicity. Significant amounts of weight loss in earthworms during an acute toxicity test in long-term contaminated soils at a relatively low Pb concentration suggested that other metal or combined metal toxicity may also play a significant role. This study demonstrates that the soil characteristics and ageing period greatly influence the bioavailable fraction of Pb which is related to the bioreceptor.

Kinetics of soil dehydrogenase in response to exogenous Cd toxicity

Soil dehydrogenase plays a role in the biological oxidation of soil organic matter and can be considered a good measure of the change of microbial oxidative activity under environmental pollutions. However, the kinetic characteristic of soil dehydrogenase under heavy metal stresses has not been investigated thoroughly. In this study, we characterized the kinetic characteristic of soil dehydrogenase in 14 soil types, and investigated how kinetic parameters changed under spiked with different concentrations of cadmium (Cd). The results showed that the Km and Vmax values of soil dehydrogenase was among 1.4-7.3mM and 15.9-235.2μMh-1 in uncontaminated soils, respectively. In latosolic red soil and brown soil, the inhibitory kinetic mechanism of Cd to soil dehydrogenase was anticompetitive inhibition with inhibition constants (Ki) of 12 and 4.7mM, respectively; in other soils belonged to linear mixed inhibition, the values of Ki were between 0.7-4.2mM. Soil total organic carbon and Ki were the major factors affecting the toxicity of Cd to dehydrogenase activity. In addition, the velocity constant (k) was more sensitive to Cd contamination compared to Vmax and Km, which was established as an early indicator of gross changes in soil microbial oxidative activity caused by Cd contamination.

Influence of soil factors on the soil enzyme inhibition by Cd

A comparative study was conducted on the toxicity of Cd to alkaline phosphatase activity (ALP) and dehydrogenase activity (DHA) in 18 top soils with contrasting soil properties representative of 14 major soil types in China. Soil pH and carbonate content, soil organic matter, and cation exchange capacity (CEC) largely affected the Cd toxicity on two enzyme activities; with the soil pH having only minor effect on the median ecological dose values based on total Cd concentrations (ED50 T). The values of ED50 T/ED50 W (based on water-soluble Cd content) of alkaline phosphatase and dehydrogenase were strongly influenced by pH and CEC contents, which explained up to 71% of the variation for alkaline phosphatase, 82% of the variation for dehydrogenase, and also were significantly correlated with the parameter KF derived from Freundlich adsorption isotherms. This study suggests that the values of ED50 T/ED50 W could be useful to evaluate the buffer capacity of soils which protects soil enzymes from harmful effects of heavy metal.

Effect of arsenate contamination on free, immobilized and soil alkaline phosphatases: activity, kinetics and thermodynamics

Summary Soil alkaline phosphatase plays a vital role in phosphorus cycling in the soil ecosystem. Arsenic, an ecotoxic element, affects the normal function of phosphatase in the soil environment. To understand the effects of arsenic on phosphatase, the activity, kinetic and thermodynamic characteristics were investigated systematically following the addition of arsenate to free soluble, clay-immobilized alkaline phosphatase (ALP) and soil ALP. The results showed that the ALP activity was strongly inhibited by arsenate. The Michaelis constant Km increased linearly with increasing arsenate concentration, indicating a decrease in affinity of the enzyme for the substrate. The inhibition constant Ki increased after the ALP was immobilized on montmorillonite and goethite. Thermodynamic properties such as activation energy, activation enthalpy, Gibbs activation free energy and activation entropy increased when arsenate was added, which suggests that more energy is required to form the activated molecule and the enzyme–substrate complex. The reaction was less spontaneous and the enzyme–substrate complex was less ordered. Immobilization of the ALP on minerals reduced the variation in kinetic and thermodynamic properties in the presence of arsenate, indicating that immobilization provided protection from arsenate stress. Arsenate toxicity to soil ALP was affected markedly by soil texture. The results suggest that the type of arsenate inhibition on free soluble ALP was competitive inhibition, whereas for immobilized and soil ALPs, the inhibition was competitive or mixed inhibition depending on the mineral or soil property. Highlights Alkaline phosphatase (ALP) activity was inhibited by arsenate. The kinetic and thermodynamic properties of ALP were changed in the presence of arsenate. Arsenate inhibition on free, mineral-immobilized ALP and soil ALP was different. ALP immobilization on minerals reduced arsenate toxicity to ALP.

Soil properties influence kinetics of soil acid phosphatase in response to arsenic toxicity

Soil phosphatase, which plays an important role in phosphorus cycling, is strongly inhibited by Arsenic (As). However, the inhibition mechanism in kinetics is not adequately investigated. In this study, we investigated the kinetic characteristics of soil acid phosphatase (ACP) in 14 soils with varied properties, and also explored how kinetic properties of soil ACP changed with different spiked As concentrations. The results showed that the Michaelis constant (Km) and maximum reaction velocity (Vmax) values of soil ACP ranged from 1.18 to 3.77mM and 0.025-0.133mMh-1 in uncontaminated soils. The kinetic parameters of soil ACP in different soils changed differently with As contamination. The Km remained unchanged and Vmax decreased with increase of As concentration in most acid and neutral soils, indicating a noncompetitive inhibition mechanism. However, in alkaline soils, the Km increased linearly and Vmax decreased with increase of As concentration, indicating a mixed inhibition mechanism that include competitive and noncompetitive. The competitive inhibition constant (Kic) and noncompetitive inhibition constant (Kiu) varied among soils and ranged from 0.38 to 3.65mM and 0.84-7.43mM respectively. The inhibitory effect of As on soil ACP was mostly affected by soil organic matter and cation exchange capacity. Those factors influenced the combination of As with enzyme, which resulted in a difference of As toxicity to soil ACP. Catalytic efficiency (Vmax/Km) of soil ACP was a sensitive kinetic parameter to assess the ecological risks of soil As contamination.

Contribution of attendant anions on cadmium toxicity to soil enzymes

Sorption and desorption are critical processes to control the mobility and biotoxicity of cadmium (Cd) in soils. It is known that attendant anion species of heavy metals could affect metal adsorption on soils and might further alter their biotoxicity. However, for Cd, the influence of attendant anions on its sorption in soils and subsequent toxicity on soil enzymes are still unknown. In this work, four Cd compounds with different salt anions (SO42-, NO3-, Cl-, and Ac-) were selected to investigate their impact of on the sorption, soil dehydrogenase activity (DHA) and alkaline phosphatase activity (ALP). Thus, a series of simulated Cd pollution batch experiments including measuring adsorption-desorption behavior of Cd on soils and soil enzyme activities were carried out. Results showed that CdSO4 exhibited highest sorption capacity among the tested soils except in Hunan soil. The Cd sorption with NO3- displayed a similar behavior with Cl- on all tested soils. Compared with soil properties, all four kinds of anions on Cd sorption played a more significant role affecting Cd ecological toxicity to soil DHA and ALP. Cd in acetate or nitrate form appears more sensitive towards DHA than sulphate and chloride, while the later pair is more toxic towards ALP than the former. These results have important implications for evaluation of Cd contamination using soil enzyme as bioindicator.

County-Scale Spatial Distribution of Soil Enzyme Activities and Enzyme Activity Indices in Agricultural Land: Implications for Soil Quality Assessment

Here the spatial distribution of soil enzymatic properties in agricultural land was evaluated on a county-wide (567 km2) scale in Changwu, Shaanxi Province, China. The spatial variations in activities of five hydrolytic enzymes were examined using geostatistical methods. The relationships between soil enzyme activities and other soil properties were evaluated using both an integrated total enzyme activity index (TEI) and the geometric mean of enzyme activities (GME). At the county scale, soil invertase, phosphatase, and catalase activities were moderately spatially correlated, whereas urease and dehydrogenase activities were weakly spatially correlated. Correlation analysis showed that both TEI and GME were better correlated with selected soil physicochemical properties than single enzyme activities. Multivariate regression analysis showed that soil OM content had the strongest positive effect while soil pH had a negative effect on the two enzyme activity indices. In addition, total phosphorous content had a positive effect on TEI and GME in orchard soils, whereas alkali-hydrolyzable nitrogen and available potassium contents, respectively, had negative and positive effects on these two enzyme indices in cropland soils. The results indicate that land use changes strongly affect soil enzyme activities in agricultural land, where TEI provides a sensitive biological indicator for soil quality.

Seasonal dynamics of bacterial communities in a Betula albosinensis forest: Soil temperature modulates bacterial communities

C . D u a, C .Y . X u a, J .S . J i a n b, W .X . H e a, L . H o u c & Z .C . G e n g a aKey Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, College of Natural Resources and Environment, Northwest A & F University, Yangling, Shaanxi 712100, China, bDepartment of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA, and cCollege of Forestry, Northwest A&F University, Yangling, Shaanxi 712100, China