Residue analysis of glyphosate and its principal metabolite in certain cereals, oilseeds, and pulses by liquid chromatography and postcolumn fluorescence detection.

A postcolumn liquid chromatographic method to determine the extractable residues of glyphosate (GLYPH) and its principal metabolite, (aminomethyl)phosphonic acid (AMPA), in various cereals and beans is described. The finely ground sample is extracted with a mixture of chloroform and water, and the resulting aqueous layer is passed through a cation exchange column. The eluate is adjusted to pH 7-10 and passed through an anion exchange column. The second column is eluted with 0.3M HCl solution and the resulting acidic eluate is analyzed with liquid chromatography coupled with postcolumn fluorescence detection. The mean recoveries for GLYPH in barley, canola, dry pea, flax, soybean, wheat, and white bean ranged from 90.0 to 98.1%, with coefficients of variation (CV) from 2.9 to 10.0% and limits of detection (LOD) from 0.07 to 0.14 ppm. Similarly, mean recoveries for AMPA in the same crops ranged from 87.4 to 98.9%, with CV from 4.6 to 7.7 and LOD from 0.05 to 0.12 ppm. Using this method, an analyst can routinely analyze 6 samples per 1.5 days. The advantages of this procedure are discussed.     

Liquid chromatographic determination of rotenone in fish, crayfish, mussels, and sediments

An analytical procedure is described for determining residues of rotenone in fish muscle, fish offal, crayfish, freshwater mussels, and bottom sediments. Tissue samples were extracted with ethyl ether and extracts were cleaned up by gel permeation chromatography and silica gel chromatography. Sediment samples were extracted with methanol, acidified, partitioned into hexane, and cleaned up on a silica gel column. Rotenone residues were quantitated by liquid chromatography, using ultraviolet (295 nm) detection. Recoveries from sediment samples fortified with rotenone at 0.3 microgram/g were 80.8%, whereas recoveries from tissue samples fortified with 0.1 microgram/g ranged from 87.7 to 96.8%. Samples fortified with 0.3 microgram/g and stored at -10 degrees C for 6 months before analysis had recoveries ranging from 83.2 to 90.5%. Limits of detection were 0.025 microgram/g for sediments and 0.005 microgram/g for tissue samples.     

Rhododendron thickets alter N cycling and soil extracellular enzyme activities in southern Appalachian hardwood forests

Rhododendron maximum L., a spreading understory shrub, inhibits overstory regeneration and alters forest community structure in southern Appalachian hardwood forests. Using paired plots and reciprocal litter transplants in forests with and without R. maximum cover, we examined the influence of R. maximum on litter mass and quality, N cycling and soil extracellular enzymes. Standing stocks of soil organic matter, soil N, leaf litter mass and fine root biomass were greater in forests with R. maximum than those without. Tannin extracts from R. maximum foliage, and leaf litter and fine roots collected under R. maximum had a relatively high capacity to precipitate protein compared to extracts from trees. Across the growing season, soil inorganic N availability was generally lower under R. maximum, mostly due to reduced NO₃⁻ availability. Our data suggest that R. maximum litter alters N cycling through the formation of recalcitrant polyphenol–organic N complexes. Soil extracellular enzymes indicate the potential processing rates of organic substrates. Between forest types, polyphenol oxidase activity was greatest in R. maximum O horizons, regardless of litter type, suggesting that the local microbial community can better degrade and access protein–tannin-complexed N. Protease activity did not differ between forest types, but was greater on R. maximum leaf litter than hardwood leaf litter. The alteration of the N cycle via the formation of polyphenol–organic N complexes may contribute to hardwood seedling suppression, while the enzymatic release of these complexes by ericoid mycorrhizal fungi may increase N acquisition for R. maximum and contribute to its expansion in southern Appalachian forests.     

Determination of Elemental Sulfur in the Presence of Anaerobic Sediments by Extraction Procedure Using High-Performance Liquid Chromatography

Elemental sulfur is the most commonly found form of sulfur in anaerobic sediments. Accurate determination of elemental sulfur is the key step to know physical chemistry and biogeochemical processes in the sediments. A novel method was developed for the analysis of elemental sulfur using high-performance liquid chromatography (HPLC) with a C18 column. The procedure of determination of elemental sulfur concentrations from 0.1 to 100 mg/g (on a basis of the dry weight of sediment) is based on the direct injection of acetone extracts of sediments into a chromatographic column. The linearity range of 20–110 mg/L showed an excellent linearity of response (r = 0.999). The limit of detection and limit of quantitation for elemental sulfur were 9.41 and 4.18 μg/L, and converted sulfur mass per sediment mass was 1.88 × 10^?2 and 8.36 × 10^?3 μg/kg. Besides, a repetitive experiment (ten times) was carried out and the average chromatographic peak area was 141.47 mg L^?1. The sulfur concentration in the solution used for the determination of standard deviation and relative standard deviation was 1.02 and 0.727%, respectively. The average recovery ranges between 98 and 100%. The quantitation of elemental sulfur in sediment samples from anaerobic digestion reactor is obvious, and the average concentration of elemental sulfur on the basis of the dry weight of the sediment is 5.24 mg/g. The method was sensitive and exhibited good signal-to-noise ratio, as well as linear responses over a wide concentration range.     

Selenium Removal from Irrigation Drainage Water Flowing Through Constructed Wetland Cells with Special Attention to Accumulation in Sediments

A flow-through experimental wetland system has been under investigation since 1996 to remove selenium (Se) fromagricultural drainage water in the Tulare Lake Drainage Districtat Corcoran, California, U.S.A. The system consists of ten cellswhich have dimensions of 15 × 76 m continuously flooded andvarious substrates planted. The objectives of this article are topresent the overall performance in Se removal after establishingthe wetland for three years, and to examine factors affecting Seremoval with special attention to accumulation in the sediments.In 1999, The wetland cells reduced Se from inflow water by 32 to65% in concentration and 43 to 89% in mass. Vegetationplays an important role in Se removal as non-vegetated cellshowed the least removal of Se. The inflow drainage water wasdominated by selenate (Se(VI), 91%) with smaller percentages ofselenite (Se(IV), 7%) and organic Se (org-Se(II-), 2%). Theoutflow water from the cells contained an average of 47% Se(VI),32% Se(IV) and 21% org-Se indicating reduction processesoccurring in the wetland cells. The surface sediment appears as alarge sink of Se removal. The highest Se concentration was foundin fallen litter, followed by the fine organic detrital layer onthe sediment surface. The sediment Se concentration dramaticallydecreased with increasing sediment depth. The mass distribution of Se, however, was sediment (0-20 cm) > fine detrital matter >fallen litter. Fractionation of surface sediment (0-5 cm) reveals that elemental Se was the largest fraction (ave. 47%) followedby organic matter-associated Se (34%). Soluble, adsorbed, and carbonate-associated Se accounted for 1.2, 3.1 and 2.5% ofthe total sediment Se, respectively. The major Se sink mechanism in the cells is the reduction of selenate to elemental Se andimmobilization into the organic phase of the sediments.     

Fine litter chemistry, early-stage decay, and nitrogen dynamics under plantations and primary forest in Lowland Amazonia

One year field exposures of leaf litter from replicated plots of Pinus caribaea var. hondurensis Barrett and Golfari, Carapa guianensis Aubl., Euxylophora paraensis Hub., a Leguminosae combination (Dalbergia nigra Fr. All., Dinizia excelsa Ducke, Parkia multijuga Benth.), and adjacent upland (terra firme) forest at the Curuá-Una Forest Reserve, Pará, Brazil were used to examine the factors controlling leaf litter decay and N dynamics in a lowland tropical environment. Initial leaf litter N concentrations ranged from 4.4 (P. caribaea) to 16.3 mg g⁻¹ dry matter (Leguminosae), and initial lignin concentrations from 190.8 (Leguminosae) to 459.3 mg g⁻¹ dry matter (forest). Pinus caribaea leaf litter lost the least mass (28%), and the Leguminosae leaf litter the most (61%), during the year long incubations. Initial and 1-y proximate C fractions, N concentrations and polyphenol concentrations were not related to mass loss. Annual N accumulation or depletion from leaf litter under the plantations and forest was related to C loss (R²=0.93, P=0.007) and holocellulose loss (R²=0.84, P=0.02). When leaf litter was placed outside its stand of origin, there was a significant location effect on decay rates, indicating that differences in the physical and biological microenvironments under the monospecific plots affected litter decomposition.     

珠江三角洲地区土壤与表层沉积物有机质的性质结构研究

通过分析海洋、河流、池塘和稻田四种热带 /亚热带土壤与表层沉积物及用化学方法分离的有机质 ,证明了土壤与沉积物有机质是高度不均匀的 ,除了包括腐殖酸和演化程度较深的干酪根外 ,强调了演化程度更深的碳黑的存在 ,并对不同有机质的来源、性质和结构进行了表征。腐殖酸和干酪根来源于生物体的演化 ,在结构上后者比前者致密 ;碳黑来源于化石燃料和生物体的不完全燃烧 ,具有更致密的结构 ,对有机质的非均质性影响很大。因此可认为 ,系统地研究土壤与表层沉积物有机质的非均质性及组分特征对了解地球表层的生物地球化学过程和疏水性毒害有机污染物在环境中的迁移具有重要的意义。     

第二松花江干流底泥有机无机复合体组成及有机碳分布特征

以第二松花江干流为对象,研究其底泥有机无机复合体的组成及有机碳分布的差异,同时分析底泥有机无机复合体组成及其有机碳分布与岸边土壤之间的关系。结果表明:底泥与岸边土壤在有机无机复合体组成、有机碳分配和腐殖质组成方面表现出较好的一致性,说明岸边土壤对底泥的有机碳组成和分布有显著贡献。底泥的中央粒径呈现上游高、下游低的特点,抚松底泥中央粒径为200μm,吉林底泥中央粒径在70μm左右,榆树、松原底泥中央粒径在50μm左右;底泥的有机碳和腐殖酸含量也表现出上游高于下游的特点。底泥有机无机复合体组成以砂粒复合体为主,黏粒、粉粒复合体含量次之;并且随着复合体粒径的增加,有机碳含量减少。底泥HA/FA均大于1,从上游至下游表现为抚松>吉林>榆树>松原;底泥HA/FA均小于岸边土壤。     

Soil amino acid composition quantified by acid hydrolysis and anion chromatography-pulsed amperometry

Soil organic N accounts for 95-98% of the total soil N content with amino acids (AAs) and amino sugars (ASs) identified as the major soil organic N compounds, but traditional 6 M HCl with reflux or sealed digestions for 24 h and various detection systems have accounted for only 30-40% of soil total N content as AA-N. This study compared traditional HCl extraction methodology with methanesulfonic acid (MSA) hydrolysis and nonderivatized AA and AS quantification by ion chromatography with pulsed amperometric detection for determination of the AA composition of plant litter and soils. MSA (4 M) gave AA-N recovery comparable to or better than 6 M HCl for plant AA digestions (16 h, 121 degrees C, 104 kPa). Use of 4 M MSA (0.5-1.5 h, 136 degrees C, 112 kPa) increased the total recovery of organic N as AAs, ASs, and NH(4)(+) by 46% from soils (n = 22) compared with 6 M HCl (12 h, 110 degrees C, reflux) with a MSA recovery rate of 85.6% of the total N content (n = 22 soils). The shorter MSA soil digestions (0.5-1.5 h) suggested that the majority of soil organic N was not present as protein forms found in plant litter analysis (16 h of digestion). MSA ion chromatographic analysis for soil AA/AS composition is a robust nonderivatization method requiring little sample preparation that can distinguish between small changes in soil AA composition during one growing season due to vegetation and tillage managements.     

Horticultural Use of Copper-Based Fungicides Has Not Increased Copper Concentrations in Sediments in the Mid- and Upper Yarra Valley

The use of Cu-based fungicide can pose a risk to nearby surface water bodies due to the run-off of accumulated Cu from agricultural soils. In 2008, we conducted a reconnaissance survey of the presence and concentration of copper in sediments at 18 sites within the Yarra River Catchment, an important horticultural production system in south-eastern Australia. Observed Cu concentrations in sediment samples from the study sites (mean (95 % confidence interval) 12.0 (10.6–13.6)? mg/kg dry weight) were similar to the concentrations present in the samples from the reference sites (mean (95 % confidence interval) 12.0 (6.7–16.8)? mg/kg dry weight). The data on Cu and other metals in the sediments suggest that that there is unlikely to have been wide spread, diffuse, off-site transport of Cu from the soils of horticultural properties to nearby surface waterways in the Yarra River Catchment and that that observed sediment metal concentrations are unlikely to pose an ecological risk to sediment-dwelling organisms at the study sites.     

Membrane Dialysis Extraction (MDE): A Novel Approach for Extracting Toxicologically Relevant Hydrophobic Organic Compounds from Soils and Sediments for Assessment in Biotests

Goal, Scope and Background   Organic solvents are routinely used to extract toxicants from polluted soils and sediments prior to chemical analysis or bioassay. Conventional extraction methods often require the use of heated organic solvents, in some cases under high pressure. These conditions can result in loss of volatile compounds from the sample and the degradation of thermally labile target analytes. Moreover, extracts of soils and sediments also frequently contain substantial quantities of organic macromolecules which can act as sorbing phases for target analytes and in doing so interfere with both chemical analysis and bioassays. Membrane dialysis extraction (MDE) is described as a simple, passive extraction method for selectively extracting toxicologically relevant hydrophobic organic compounds (HOCs) from polluted soils and sediments and anaylzed for its applicability in ecotoxicological investigations. Methods   Toxicologically relevant hydrophobic organic compounds were extracted from wet and dry sediments by sealing replicate samples in individual lengths of pre-cleaned low-density polyethylene (LD-PE) tubing and then dialysing in n-hexane. The efficacy of the MDE method for use in ecotoxicological investigations was assessed by testing the concentrated extracts in the neutral red assay for acute cytotoxicity, in the EROD assay for the presence of dioxin-like compounds and in the Danio rerio fish egg assay for embryotoxic and teratogenic effects. Conditions of the sediment sample (with or without water content), dialysis membrane length and duration of dialysis were analyzed with respect to their impact on three endpoints. Results of the MDE investigations were compared to data obtained in samples prepared using conventional Soxhlet extraction. Results and Discussion   The membrane dialysis extraction was found to be at least as efficient as Soxhlet methodology to extract toxicologically relevant HOCs from sediment samples. In most cases, MDE-derived extracts showed a higher toxicological potential than the Soxhlet extracts. Lack of any significant effects in any MDE controls indicated these differences were not caused by contamination of the LD-PE membrane used. The elevated toxicological potential of MDE extracts is most likely the result of enhanced bioavailability of toxic compounds in consequence of lower amounts of organic macromolecules (i.e. sorbing phases) in the MDE extracts. This effect is probably the result of a size-selective restriction by the LD-PE membrane. Conclusion   Membrane dialysis extraction was found to be a simple, efficient and cost-effective method for the extraction of sediment samples. MDE can be used to extract toxicologically relevant hydrophobic organic compounds from both wet and dry sediments without the risk of loosing volatile and thermally labile target analytes. The size-selectivity of the LD-PE membrane also appears to have the capacity to increase the bioavailablity of potential target analytes in the resulting extracts by retaining much of the organic macromolecules present in the sample. Thus, results suggest that MDE may be particularly useful for the extraction of toxicologically relevant hydrophobic organic compounds from soils and sediments for bioassays and other ecotoxicological investigations. Recommendation and Perspective   Further validation of MDE has been initiated and the applicability of the methodology to other sample types will be investigated. Of particular interest is the potential application of MDE to recover hydrophobic target analytes from biological samples such as muscle, other soft tissues and blood.     

Decomposition of chestnut oak (Quercus prinus) leaves and nitrogen mineralization in an urban environment

We studied soil processes along an urban to rural gradient. To determine the ecosystem response to the urban soil environment, we measured (1) leaf litter decomposition rates using a reference leaf litter, and (2) net N-mineralization and net nitrification rates using paired in situ soil cores. A significant trend toward slower litter decomposition rates toward the urban end of the gradient was observed. In addition, percent ash-free dry mass remaining of the litter was significantly higher during the course of the study but was not statistically significant at the final sampling date. Litter C:N ratio had a complex response with respect to degree of urban land use, and litter % N did not differ between land-use types. Litter decomposition rates were not significantly correlated with observed soil physicochemical and biological characteristics but were influenced by soil moisture and soil organic matter. Net N-mineralization rates were higher in urban soils. Net nitrification rates did not differ with land-use type. Net N-mineralization rates were positively correlated with soil temperature, indicating a response to the urban heat island effect. Net N-mineralization rates were negatively correlated with the numbers of higher trophic level nematodes.     

Dispersal patterns and behaviour of the nematode Phasmarhabditis hermaphrodita in mineral soils and organic media

The commercially available parasitic nematode Phasmarhabditis hermaphrodita is an effective biocontrol agent for slugs and particularly Deroceras reticulatum, a widespread pest species. Use of the nematode is currently limited by cost and it may be that by developing a fuller understanding of the ecology and behaviour of this nematode, more cost effective application strategies can be developed. We investigated the ability of two strains of P. hermaphrodita (one newly isolated and one that had been maintained in vitro for >15 years) to move through mineral soils and organic media. Active dispersal of both strains was found to be greatest in organic media (bark chips and leaf litter, and to a lesser extent peat) and the nematode was capable of growth and reproduction in leaf litter. Conversely, active dispersal was poor in mineral soils. Nematodes moved further in a clay loam compared with a sandy loam, and moved more at a bulk density of 1.0 vs. 1.2 Mg m⁻³. However, P. hermaphrodita was capable of moving greater distances in mineral soils by using the earthworm Lumbricus terrestris as a phoretic host. Our data suggest that P. hermaphrodita is a facultative parasite that is adapted to living in leaf litter and organic material where slugs frequently rest. The implications of these findings for using the nematode as a biological control agent for slugs are discussed.     

Simultaneous gas chromatographic determination of carbofuran, metalaxyl, and simazine in soils

A method for extraction, cleanup, and simultaneous gas chromatographic detection of carbofuran, metalaxyl, and simazine in soils has been developed. Pesticide residues were extracted from soil with acetone containing 10% 0.2M HCl-KCl buffer (pH 2.0), cleaned up with methylene chloride-carbonate buffer (pH 10.7) solvent partitioning and solid-phase extraction on disposable silica gel columns, and quantitated with gas chromatography using a Supelcowax 10 megabore capillary column and a nitrogen-selective detector. Method limits of detection were 0.02 microgram/g for the 3 pesticides in surface soils (0-30 cm depths) and 0.02, 0.02, and 0.005 microgram/g in soils below 30 cm (subsoils) for carbofuran, metalaxyl, and simazine, respectively. Recoveries for carbofuran, metalaxyl, and simazine were 92.6 +/- 5.5, 93.6 +/- 5.0, and 88.4 +/- 6.7%, respectively, when soil samples were spiked with pesticide concentrations ranging from 0.02 to 2.0 micrograms/g.     

Carbon and nitrogen isotope composition of bulk soils, particle-size fractions and organic material after treatment with hydrofluoric acid

Soils and sediments contain only small amounts of organic matter, and large concentrations of paramagnetic metals can give poor solid‐state nuclear magnetic resonance (NMR) spectra of organic matter. Pretreatment of samples with hydrofluoric acid (HF) dissolves significant proportions of the mineral matrix and extracts paramagnetic elements. We investigated the effects of 10% HF treatment on the stable isotope content of carbon (C) and nitrogen (N) of organic matter from soils, composts and shales. Additionally we inferred molecular and isotopic characteristics of lost materials from calculations of isotope mass balances. Treatment with HF enriched C and N in mineral samples substantially (factors 2.5–42.4), except for Podzol B horizons (1.1–1.7) and organic material (1.0–1.3). After treatment most of the C (59.7–91.7%) and N (53.7–86.6%) was recovered, although changing C/N ratios often indicated a preferential loss of N‐rich material. Isotope ratios of C and N in the remaining material became more negative when net alterations exceeded 0.3‰. The isotope ratios of the lost material contained more ¹³C (1–2‰) and ¹⁵N (1–4‰) than the initial organic matter. Acid hydrolysis typically removes proteins, amino acids and polysaccharides, all of which are enriched in ¹³C, and in the case of proteins and amino acids, enriched in ¹⁵N as well. We conclude that HF treatment released fresh, soluble, probably microbial, biomass in addition to carbohydrates. Net changes of the bulk chemical composition of organic matter were small for most soils, size fractions and plant material, but not for samples containing little organic matter, or those rich in easily soluble organic matter associated with iron oxides, such as Podzol B horizons.     

Copper distribution and acid-base mobilization in vineyard soils and sediments from Galicia (NW Spain)

In northern Spain and elsewhere in the world, many vineyards are located on steep slopes and are susceptible to accelerated soil erosion. Contaminants, notably Cu, originating from repeated application of copper‐based fungicides to the vines to prevent mildew, are transported and stored in the sediments deposited close to valley bottoms. In this study, the contents and distribution of Cu in 17 soil samples and 21 sediment samples collected from vineyard stands were determined. In addition, the effect of pH on Cu release from vineyard soils and sediments was quantified. The total Cu content (Cu_T) in the soils varied between 96 and 583 mg kg^?1, and was between 1.2 and 5.6 times greater in sediment samples. The mean concentration of potentially bioavailable Cu (Cu_EDTA) in the sediments was 199 mg kg^?1 (46% of Cu_T), and was 80 mg kg^?1 (36% of Cu_T) in the soils. Copper bound to soil organic matter (Cu_OM) was the dominant fraction in the soils (on average, 53% of the Cu_T), while in sediment samples Cu_OM values varied between 37 and 712 mg kg^?1 and were significantly greater (P < 0.01) than in the soils. Copper associated with non‐crystalline inorganic components (Cu_IA) was the second most important fraction in the sediments, in which it was 3.4 times greater than in the soils. Release of Cu due to changes in the pH followed a U‐shaped pattern in soils and sediments. The release of Cu increased when the pH decreased below 5.5 due to the increased solubility of the metal at this pH. When the pH increased above 7.5, Cu and organic matter were released simultaneously.     

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of ¹³C labelled rye residues (δ¹³C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO₂, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.     

Electrothermal atomic absorption spectrometric determination of selenium in foods and diets

The validity of 2 electrothermal atomic absorption spectrometric methods for determination of selenium in foods and diets was tested. By using 0.5% Ni(II) as a matrix modifier to prevent selenium losses during the ashing step, it was shown that selenium can be determined in samples containing greater than or equal to 1 microgram Se/g dry wt without organic extraction. The mean recovery tested, using NBS Bovine Liver, was 98%; recovery of added inorganic selenium in Bovine Liver matrix was 100%. In addition, this method gave values closest to the median value of all participating laboratories using hydride generation AAS or the spectrofluorometric method in a collaborative study on high selenium wheat, flour, and toast samples. For samples with concentrations less than 1 microgram Se/g dry wt, separation of selenium from interfering Fe and P ions by organic extraction was necessary. Using inorganic 75Se in meat and human milk matrixes, an ammonium pyrrolidine dithiocarbamate-methyl isobutyl ketone-extraction system with added Cu(II) as a matrix modifier yielded the best extraction recoveries, 97 and 98%, respectively. Accuracy and precision of the method were tested using several official and unofficial biological standard materials. The mean accuracy was within 4% of the certified or best values of the standard materials and the day-to-day variation was 9%. The Se/Fe or Se/P interference limits proved to be low enough not to affect selenium determinations in practically all foods or diets. The practical detection limit of the method was 3 ng Se/g dry wt for 1.0 g dry wt samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determination of triazine and chloroacetanilide herbicides in soils by microwave-assisted extraction (MAE) coupled to gas chromatographic analysis with either GC-NPD or GC-MS

A simple and rapid method based on microwave-assisted extraction (MAE) coupled to gas chromatographic analysis was developed for the analysis of triazine (atrazine, cyanazine, metribuzine, simazine and deethylatrazine, and deisopropylatrazine) and chloroacetanilide (acetochlor, alachlor, and metolachlor) herbicide residues in soils. Soil samples are processed by MAE for 5 min at 80 degrees C in the presence of acetonitrile (20 mL/sample). Mean recovery values of most solutes are >80% in the 10 to 500 microg/kg fortification range with respective RSDs (relative standard deviations) < 20%. The limits of quantification (LOQ) and limits of detection (LOD) are 10 and 1 to 5 microg/kg, respectively. The method was validated with two types of soils containing 1.5 and 3.0% organic matter content, respectively; no statistically significant differences were found between solute recovery values from the two types of soils. The solute mean recovery values from freshly spiked (24 h aging) and spiked samples stored refrigerated for one week before processed were also not statistically different. Residue levels determined in field weathered soils were higher when soils were processed by MAE than with a comparison method based on flask-shaking of soil suspensions overnight. Extracts were analyzed by a gas chromatographic system equipped either with a thermionic (GC-NPD) or a mass spectrometric detector (GC-MS).     

Tillage and amendment effects on soil carbon and nitrogen mineralization and phosphorus release

The influence of tillage and nutrient amendment management on nutrient cycling processes in soil have substantial implications for environmentally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organic matter variables (carbon (C), nitrogen (N) and phosphorus (P)) and C and N mineralization and P release were determined for a Dothan fine-sandy loam soil in southeastern Alabama. Tillage systems investigated were strip (or conservation) and conventional tillage with various soil nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0–10 cm depth increment) organic matter variables were determined for all tillage/amendment combinations. Carbon and N mineralization and P release were determined on surface soils for each field treatment combination in a long-term laboratory incubation. Soil organic P concentration was 60% greater in soils that had been conventionally tilled, as compared with strip-tilled, both prior to and following laboratory incubation. Carbon and N mineralization results reflected the effects of prior tillage amendment regime, where soils maintained under strip-till/broiler litter mineralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readily mineralizable pool of N (6.1%) than with conventional till (4.2%); broiler litter amendments had a larger labile N fraction (6.7%) than was found in soils receiving either mineral fertilizer (4.1%) or no amendment (4.7%). Tillage also affected P release measured during the incubation study, where approximately 20% more inorganic P was released from strip-tilled soils than from those maintained under conventional tillage. Greater P release was observed for amended soils as compared with soils where no amendment was applied. Results from this study indicate that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern US soil.