Longhua Wu

Simultaneous extraction of four classes of antibiotics in soil, manure and sewage sludge and analysis by liquid chromatography-tandem mass spectrometry with the isotope-labelled internal standard method

An analytical method for the analysis of four classes of antibiotics (tetracyclines, sulfonamides, fluoroquinolones and macrolides) has been developed and validated in this work. After optimizing the extraction and purification, the solvent consisting of a (EDTA-sodium phosphate buffer with acetonitrile : Mg(NO3)(2)-NH3 center dot H2O ,v/v, 3 : 1) was used as the extraction buffer, these antibiotics were extracted from agricultural soil, manure, and sewage sludge using ultrasonic-assisted extraction aided by mechanical shaking and followed by solid phase extraction (SPE) clean-up with hydrophilic-lipophilic balance (HLB) cartridges. The chromatographic separation was optimized, the analytes were separated and detected by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and quantified by the isotope-labelled internal standard method. Mass spectral acquisition was done in the positive ion mode by applying multiple reaction monitoring (MRM) of two fragmentation transitions per analyte to provide a high degree of sensitivity and specificity. The calibration range used for all the antibiotics was 5.0-300.0 mu g L-1 and each calibration curve was linear with a coefficient of determination (R-2) > 0.997, the instrument detection limits (IDLs) and quantification limits (IQLs) ranged from 0.09 to 3.57 and 0.49 to 11.9 mu g L-1, respectively. Spiked recoveries were obtained in the range 60-140% for these antibiotics from three different matrices, with the exception of NFC and OFC in soil (52-55%). Lower relative standard deviation (RSD < 17%) for seven replicates from each matrix at 50 mu g kg(-1) spiking level and the method detection limits (MDLs) obtained in the ranges 0.5-14.8 mu g kg(-1) from soil, 0.5-14.1 mu g kg(-1) from manure and 1.3-17.3 mu g kg(-1) from sludge for all the antibiotics studied indicate that the method was reliable and sensitive for extraction and determination of the target compounds in soil, manure and sludge matrices. Finally, the method was applied to analyse soil, manure and sewage sludge samples. Fluoroquinolones were the most dominant antibiotics and there were smaller amounts of sulfonamides in the soil, sludge and manure samples collected.

Water management affects arsenic and cadmium accumulation in different rice cultivars

Paddy rice (Oryza sativa L.) is a staple food and one of the major sources of dietary arsenic (As) and cadmium (Cd) in Asia. A field experiment was conducted to investigate the effects of four water management regimes (aerobic, intermittent irrigation, conventional irrigation and flooding) on As and Cd accumulation in seven major rice cultivars grown in Zhejiang province, east China. With increasing irrigation from aerobic to flooded conditions, the soil HCl-extractable As concentrations increased significantly and the HCl-extractable Cd concentrations decreased significantly. These trends were consistent with the As and Cd concentrations in the straw, husk and brown rice. Water management both before and after the full tillering stage affected As and Cd accumulation in the grains. The intermittent and conventional treatments produced higher grain yields than the aerobic and flooded treatments. Cd concentrations in brown rice varied 13.1–40.8 times and As varied 1.75–8.80 times among the four water management regimes. Cd and As accumulation in brown rice varied among the rice cultivars, with Guodao 6 (GD6) was a low Cd but high-As-accumulating cultivar while Indonesia (IR) and Yongyou 9 (YY9) were low As but high-Cd-accumulating cultivars. Brown rice Cd and As concentrations in the 7 cultivars were significantly negatively correlated. The results indicate that As and Cd accumulated in rice grains with opposite trends that were influenced by both water management and rice cultivar. Production of ‘safe’ rice with respect to As and Cd might be possible by balancing water management and rice cultivar according to the severity of soil pollution.

Accumulation and chemical fractionation of Cu in a paddy soil irrigated with Cu-rich wastewater

The accumulation, chemical fractionation and availability of copper (Cu) to rice (Oryza sativa) in a paddy soil previously irrigated with Cu-enriched wastewater were investigated. Chemical fractions of Cu in soil samples were partitioned using single and sequential extractions. The single extractant solutions used were water, ammonium acetate and EDTA for extraction of water-soluble, exchangeable and complexed Cu fractions in the soil. A three-step sequential extraction procedure (HAOc/NH2OH.HCl/H2O2) was also used to fractionate Cu associated with soil solids into three fractions: weak acid-soluble, reducible Fe and Mn oxides bound and oxidisable organic matter bound. The residual fraction was calculated as the difference between total (aqua regia extractable) Cu and the sum of the three sequential fractions. Copper accumulated mainly in the top layer (10 cm) of the soil profile after wastewater irrigation, increased almost seven-fold (158 mg kg−1) compared with non-irrigated soil (23 mg kg−1) from the same area, and was also elevated significantly in low layer (10–20 cm) below the soil surface. Concentrations of Cu in the water-soluble, exchangeable and complexed fractions increased from 0.02, 0.33 and 14.1 mg kg−1, respectively, in unpolluted soil to 0.12, 6.30 and 98.0 mg kg−1 in polluted soil. Irrigation also led to marked increases in the weak acid-soluble, reducible Fe and Mn oxide bound, oxidisable organic matter bound and residual fractions of Cu. In the contaminated paddy soil, the reducible Fe and Mn oxide bound fraction was the largest (36% of total Cu), followed by the oxidisable fraction, then the residual fraction, and the smallest was the acetic acid-soluble fraction. However, in the unpolluted soil, 53% of total Cu was present in the residual fraction followed by the reducible Fe and Mn oxide bound fraction (22% of total Cu). Accumulation of Cu in the bioavailable fractions resulted in a three-fold increase in Cu concentration (up to 38 mg kg−1) in rice plants in the heavily polluted (HP) soil compared with unpolluted soil. Plant yields decreased substantially due to Cu toxicity. Data indicate that the reducible Fe and Mn oxide bound fraction may be more important for controlling the mobility and bioavailability of Cu than the oxidisable organic matter bound fraction in paddy soils.

Improved diffusive gradients in thin films (DGT) measurement of total dissolved inorganic arsenic in waters and soils using a hydrous zirconium oxide binding layer.

A high-capacity diffusive gradients in thin films (DGT) technique has been developed for measurement of total dissolved inorganic arsenic (As) using a long shelf life binding gel layer containing hydrous zirconium oxide (Zr-oxide). Both As(III) and As(V) were rapidly accumulated in the Zr-oxide gel and could be quantitatively recovered by elution using 1.0 M NaOH for freshwater or a mixture of 1.0 M NaOH and 1.0 M H2O2 for seawater. DGT uptake of As(III) and As(V) increased linearly with deployment time and was independent of pH (2.0-9.1), ionic strength (0.01-750 mM), the coexistence of phosphate (0.25-10 mg P L(-1)), and the aging of the Zr-oxide gel up to 24 months after production. The capacities of the Zr-oxide DGT were 159 μg As(III) and 434 μg As(V) per device for freshwater and 94 μg As(III) and 152 μg As(V) per device for seawater. These values were 5-29 times and 3-19 times more than those reported for the commonly used ferrihydrite and Metsorb DGTs, respectively. Deployments of the Zr-oxide DGT in As-spiked synthetic seawater provided accurate measurements of total dissolved inorganic As over the 96 h deployment, whereas ferrihydrite and Metsorb DGTs only measured the concentrations accurately up to 24 and 48 h, respectively. Deployments in soils showed that the Zr-oxide DGT was a reliable and robust tool, even for soil samples heavily polluted with As. In contrast, As in these soils was underestimated by ferrihydrite and Metsorb DGTs due to insufficient effective capacities, which were likely suppressed by the competing effects of phosphate.

Repeated phytoextraction of four metal-contaminated soils using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

A cadmium/zinc hyperaccumulator extracted metals from four contaminated soils over three years in a glasshouse experiment. Changes in plant metal uptake and soil total (aqua regia-extractable) and available metals were investigated. Plant Cd concentrations in a high-Cd acid soil and plant Zn concentrations in two acid soils decreased during repeated phytoextraction and were predicted by soil available metal concentrations. However, on repeated phytoextraction, plant Cd concentrations remained constant in lightly Cd-polluted acid soils, as did plant Cd and Zn in alkaline soils, although soil available metal concentrations decreased markedly. After phytoextraction acid soils showed much higher total metal removal efficiencies, indicating possible suitability of phytoextraction for acid soils. However, DGT-testing, which takes soil metal re-supply into consideration, showed substantial removal of available metal and distinct decreases in metal supply capacity in alkaline soils after phytoextraction, suggesting that a strategy based on lowering the bioavailable contaminant might be feasible.

A Field Lysimeter Study of Heavy Metal Movement Down the Profile of Soils with Multiple Metal Pollution During Chelate-Enhanced Phytoremediation

The agricultural soils near a copper smelter in southeast China were found to be highly contaminated with Cu, Pb, Zn, and Cd. Metal migration from the soil to groundwater presents an environmental risk that depends on the physicochemical properties of the contaminated soils. Soil solution samples were obtained using lysimeters from a loam soil with multiple metal pollutions over a period of about 1 yr. A field lysimeter study was also conducted to examine the potential use of (S, S′)-ethylenediamine-N, N′-disuccinic acid trisodium salt (EDDSNa3) in chelate-enhanced phytoremedation and to evaluate the leaching of heavy metals. The average heavy metal concentrations in the soil solution (without the addition of EDDS) were high (e.g., 0.15 mg Pb L−1 at a 50-cm depth) compared to the upper limit for protection of groundwater in China, but varied during the sampling period. Cu concentrations were not correlated with pH or dissolved organic carbon (DOC), but Zn and Cd concentrations were related to soil solution pH. EDDS enhanced metal solubility in the soil, but plant metal uptake by Elsholtzia splendens Nakai did not increase accordingly. There may be an increasing risk of groundwater pollution by Cu and the EDDS enhanced phytoremediation technique needs to be carefully applied to minimize this side effect.

Effects of water management on arsenic and cadmium speciation and accumulation in an upland rice cultivar

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic (As) and cadmium (Cd) in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3-16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid (from 11.3% to 61.7%) made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal(loid)s in the grain of rice grown in soils polluted with both As and Cd.

Assessment of EDTA heap leaching of an agricultural soil highly contaminated with heavy metals

The efficiency of heavy metal removal from soil by EDTA leaching was assessed in a column leaching experiment at the laboratory scale and field heap leaching at the pilot scale using a sandy loam sierozem agricultural soil contaminated with Cd, Cu, Pb, and Zn. Soil amendment and aging were conducted to recover leaching soils. The percentages of Cd, Cu, Pb, and Zn removed by column leaching were 90%, 88%, 90%, and 67%, respectively, when 3.9 bed volumes of 50mM EDTA were used. At the pilot scale, on-site metal removal efficiencies using the selected leaching procedure were 80%, 69%, 73% and 62% for Cd, Cu, Pb and Zn, respectively. EDTA leaching decreased soil CEC, total P, total K and available K concentrations but increased organic matter and total Kjeldahl N concentrations. The subsequent amendment and soil aging further reduced the DTPA-extractable heavy metals in the leached soils. Growth of the first crop of pak choi in the leached soil was inhibited but the second crop grew well after the soil was aged for one year and the concentrations of Cd and Pb in the edible parts were below the Chinese statutory limits. The results demonstrate the potential feasibility of the field leaching technique using EDTA combined with subsequent amendment and soil aging for the remediation of heavy metal-contaminated agricultural soils.

The heavy metal partition in size-fractions of the fine particles in agricultural soils contaminated by waste water and smelter dust

The partitioning of pollutant in the size-fractions of fine particles is particularly important to its migration and bioavailability in soil environment. However, the impact of pollution sources on the partitioning was seldom addressed in the previous studies. In this study, the method of continuous flow ultra-centrifugation was developed to separate three size fractions (<1 μm, <0.6 μm and <0.2 μm) of the submicron particles from the soil polluted by wastewater and smelter dust respectively. The mineralogy and physicochemical properties of each size-fraction were characterized by X-ray diffraction, transmission electron microscope etc. Total content of the polluted metals and their chemical speciation were measured. A higher enrichment factor of the metals in the fractions of <1 μm or less were observed in the soil contaminated by wastewater than by smelter dust. The organic substance in the wastewater and calcite from lime application were assumed to play an important role in the metal accumulation in the fine particles of the wastewater polluted soil. While the metal accumulation in the fine particles of the smelter dust polluted soil is mainly associated with Mn oxides. Cadmium speciation in both soils is dominated by dilute acid soluble form and lead speciation in the smelter dust polluted soil is dominated by reducible form in all particles. This implied that the polluted soils might be a high risk to human health and ecosystem due to the high bioaccessibility of the metals as well as the mobility of the fine particles in soil.

Changes in antibiotic concentrations and antibiotic resistome during commercial composting of animal manures

The over-use of antibiotics in animal husbandry in China and the concomitant enhanced selection of antibiotic resistance genes (ARGs) in animal manures are of serious concern. Thermophilic composting is an effective way of reducing hazards in organic wastes. However, its effectiveness in antibiotic degradation and ARG reduction in commercial operations remains unclear. In the present study, we determined the concentrations of 15 common veterinary antibiotics and the abundances of 213 ARGs and 10 marker genes for mobile genetic elements (MGEs) in commercial composts made from cattle, poultry and swine manures in Eastern China. High concentrations of fluoroquinolones were found in the poultry and swine composts, suggesting insufficient removal of these antibiotics by commercial thermophilic composting. Total ARGs in the cattle and poultry manures were as high as 1.9 and 5.5 copies per bacterial cell, respectively. After thermophilic composting, the ARG abundance in the mature compost decreased to 9.6% and 31.7% of that in the cattle and poultry manure, respectively. However, some ARGs (e.g. aadA, aadA2, qacEΔ1, tetL) and MGE marker genes (e.g. cintI-1, intI-1 and tnpA-04) were persistent with high abundance in the composts. The antibiotics that were detected at high levels in the composts (e.g. norfloxacin and ofloxacin) might have posed a selection pressure on ARGs. MGE marker genes were found to correlate closely with ARGs at the levels of individual gene, resistance class and total abundance, suggesting that MGEs and ARGs are closely associated in their persistence in the composts under antibiotic selection. Our research shows potential disseminations of antibiotics and ARGs via compost utilization.