Impact of fomesafen on the soil microbial communities in soybean fields in Northeastern China.

Fomesafen, a widely adopted residual herbicide, is used throughout the soybean region of northern China for the spring planting. However, the ecological risks of using fomesafen in soil remain unknown. The aim of this work was to evaluate the impact of fomesafen on the microbial community structure of soil using laboratory and field experiments. Under laboratory conditions, the application of fomesafen at concentrations of 3.75 and 37.5mg/kg decreased the basal respiration (RB) and microbial biomass carbon (MBC). In contrast, treatment with 375mg/kg of fomesafen resulted in a significant decrease in the RB, MBC, abundance of both Gram+ and Gram- bacteria, and fungal biomass. Analysis of variance showed that the treatment accounted for most of the variance (38.3%) observed in the soil microbial communities. Furthermore, the field experiment showed that long-term fomesafen application in continuously cropped soybean fields affected the soil bacterial community composition by increasing the relative average abundance of Proteobacteria and Actinobacteria species and decreasing the abundance of Verrucomicrobia species. In addition, Acidobacteria and Chloroflexi species showed a pattern of activation-inhibition. Taken together, our results suggest that the application of fomesafen can affect the community structure of soil bacteria in the spring planting soybean region of northern China.

Determination of indoxacarb enantiomer residues in vegetables, fruits, and soil by high-performance liquid chromatography.

An effective chiral analytical method was developed for the resolution and determination of indoxacarb enantiomers in cucumber, tomato, apple, pear, and soil samples. Indoxacarb enantiomers were separated on a Chiralpak AS-H column with n-hexane-ethanol (95 + 5, v/v) as the mobile phase. Validation involved complete resolution of each enantiomer, plus determination of linearity, precision, LOD, and LOQ. The estimated LOD was 0.025-0.035 mg/kg, and the LOQ was 0.05 mg/kg for each indoxacarb enantiomer in different matrixes. The average recoveries of the pesticide from all matrixes ranged from 87.0 to 116.9% for fortification levels of 0.05, 0.1, and 5 mg/kg. The precision values associated with the analytical method, expressed as RSD(r) values, were < 10.1% for the pesticide in all matrixes. This method can be used to evaluate environmental residues and the safety of agricultural products.

Determination of 4-chloro-2-methylphenoxyacetic acid residues in wheat and soil by ultra-performance liquid chromatography/tandem mass spectrometry.

A rapid, highly sensitive, and selective method was developed for the identification and quantitation of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in wheat plants, wheat grain, and soil by ultra-performance LC/MS/MS. MCPA was extracted from the sample (5 or 10 g) with acetonitrile, and an aliquot was taken for cleanup with primary secondary amine. Two precursor product ion transitions for MCPA were measured and evaluated to provide maximum confidence in the results. Average recoveries from wheat plants, wheat grain, and soil fortified at levels of 0.01-1.0 mg/kg ranged from 75.1 to 93.9%, with RSD(r) values of 3.0-9.3% and RSDR values of 3.1-8.7%. Coefficients of determination of R2 > or = 0.9994 were obtained for wheat and soil matrix calibration curves at MCPA levels of 0.01-5.0 microg/mL. Under conditions of electrospray ionization in the negative-ion mode, the ion at m/z 141 was monitored for quantitation; the parent ion at m/z 199 was also measured. The LOD values for MCPA in wheat plants, wheat grain, and soil were determined to be 0.005, 0.004, and 0.004 mg/kg, respectively, and corresponding LOQ values were 0.02, 0.01, and 0.01 mg/kg. This method can be used to determinate MCPA residues in wheat products and soils.

[Effects of chlorimuron-ethyl on soil microbial community structure in soybean field].

By using phospholipid fatty acids (PLFA) method, this paper studied the soil microbial community structure in the soybean fields with different chlorimuron-ethyl application history in Weihe district of Heilongjiang Province. In the meantime, the residual amount of chlorimuron-ethyl in soil was determined. There was a very low residual of chlorimuron-ethyl in soil under the conditions of different chlorimuron-ethyl application history. With the increasing year of chlorimuron-ethyl application, the total concentration of soil microbial PLFA and the ratios of fungi/bacteria and Gram negative/Gram positive bacteria decreased, and the microbial stress level increased. Principal component analysis (PCA) showed that long-term application of chlorimuron-ethyl into soybean field changed the soil microbial community structure significantly.

Determination of bromoxynil octanoate in soil and corn by GC with electron capture and mass spectrometry detection under field conditions.

In this paper, a simple, and rapid analysis of bromoxynil octanoate is reported for soil, corn leaves, and corn seeds by utilizing one-step liquid-liquid extraction and partitioning, followed by GC with electron capture (ECD) and mass spectrometry (MS) detection. The method was validated by recovery experiments and assessment of matrix effects. Recoveries for GC-ECD and GC/MS were 82.3-110.7% with a relative standard deviation of <14% using matrix-matched calibration solutions for quantification. The limit of quantitation (LOQ) values were 0.005 and 0.2 mg/kg for the ECD and MS detector, respectively, depending on the sensitivity of the target compound. The concentration levels for bromoxynil octanoate residue found in soil, corn leaves, and corn seeds from field experiments were clearly below the LOQ of the ECD detector. The half-life times of bromoxynil octanoate were 2.2-4.2 days in soil and corn leaves. These results indicated that the developed method was appropriate for analysis of bromoxynil octanoate in soil and corn samples.

Determination of mepiquat chloride residues in cotton and soil by liquid chromatography/mass spectrometry.

A liquid chromatographic/mass spectrometric (LC/MS) method is reported for the determination of the onium-type plant growth regulator mepiquat chloride in cotton and soil. The pesticide was extracted from the sample with ethanol and water containing 2% NH4Cl. The extract was cleaned up on a solid-phase extraction C18 column, and the pesticide was determined by LC/MS. The average recoveries were 85.9-93.8, 81.3-91.7, and 78.1-94.7%, with corresponding relative standard deviations of 3.4-9.6, 3.7-12.3, and 4.0-9.8%, from soil, cotton leaves, and cotton seeds, respectively. A coefficient of determination of R2 = 0.9964 was obtained for the analyte calibration graph, from 0.05 to 100 microg/mL. Decision limits, CCalpha, and detection capability, CCbeta, were calculated. Electrospray ionization LC/MS in the positive-ion mode (ESI+) was used to detect mepiquat chloride in extracts of soil, cotton leaves, and cotton seeds. The ion at m/z 114 in the mass spectrum was monitored.