Air-dried soil

Table 16.17 Guidelines for classification of contaminated soils suggested range of values (ppm) on air dried soils...

In the laboratory, soil samples collected in the held are mixed thoroughly and reduced in size to laboratory samples. The air-dried soils are passed through a 2-mm sieve in order to remove stones and roots, then the water content of the soil is calculated after drying at 105 °C for 5h. If the analytical samples cannot be analyzed immediately after drying and sieving, they should be stored at about —20 °C in glass or Teflon bottles fltted with screw-caps. 

Air-dried soil samples were screened through a 2-mm sieve, then the water content in the soil was calculated after holding the soil samples for 5h at 105 °C. 

Residual dinitroaniline herbicides are generally extracted from 10-25 g of air-dried soil samples using organic solvents such as ethyl acetate, acetonitrile, methylene chloride and acetone by sonication, mechanical shaking or Soxhlet extraction. If necessary, the extract is then cleaned by a Florisil column or SPE. The extract is allowed to evaporate completely to dryness and the residue is dissolved in an appropriate volume of the solvent for GC or HPLC analysis. 

A 20-g sample of air-dried soil is extracted with 100 mL of ethyl acetate in a flask shaker for 45 min. After shaking, the extract is decanted and separated. The soil is re-extracted with 100 mL of ethyl acetate for 45 min. The combined soil extracts are filtered through a Whatman No 1 filter paper and the filter cake is washed with an additional 20 mL of ethyl acetate. The extracts are evaporated nearly to dryness, under vacuum, using a rotary evaporator. The residue is dissolved in an appropriate volume before GC analysis. ... 

The air-dried soils (50 g) are processed similarly to the plant materials. 

Mix 10 g of the air-dried soil with 100 mL of acetone and shake the mixture with a mechanical shaker for 30 min. Filter the mixture through a fluted filter paper into a 300-mL round-bottom flask. Wash the residue on the filter with 50 mL of acetone. Combine the filtrates and concentrate by rotary evaporation. 

Organic solvent extraction. Two analytical methods for acetamiprid have been developed One method is for the parent only and the other determines the total residue of the parent and its metabolites (lM-1-2, lM-1-4 and lC-0). Air-dried soil (20-g equivalent dry soil) is weighed into a centrifuge tube and imidacloprid residue is extracted with 100 mL of methanol-0.1M ammonium chloride (4 1, v/v) using a mechanical shaker for about 30 min. After shaking, the tube is centrifuged at 8000 rpm for 2 min. The supernatant is filtered and the analysis of the soil residue is carried out in the same manner as described above for the parent compound. 

For soil samples, shake 20 g of a prepared air-dried soil sample with methanol-1 N hydrochloric acid [50 mL, 3 1 (v/v)] on a mechanical shaker for 30 min. Centrifuge the sample at 3500 rpm for 5 min and decant the supernatant into a round bottom flask (250-mL). Add a second 50 mL of methanol-1 N hydrochloric acid (3 1, v/v) to the soil sample and shake the mixture on a mechanical shaker for another 30 min. Centrifuge the sample at 3500 rpm for 5 min and then decant the supernatant into the same round-bottom flask (250-mL), combining the extracts. 

Recovery of acetamiprid, IM-1-2 and IM-1-4. Combine 20 g of the air-dried soil with 100 mL of a mixed solvent of methanol and 0.1 M ammonium chloride (4 1, v/v) in a 250-mL stainless-steel centrifuge tube, shake the mixture with a mechanical shaker for 30 min and centrifuge at 8000 r.p.m. for 2 min. Filter the supernatant through a Celite layer (1-cm thick) under reduced pressure into a 500-mL flask. Add a second 100 mL of mixed solvent to the residue and then extract and filter in the same manner. Combine the filtrates and add 150mL of distilled water with 1 g of sodium chloride. Transfer the aqueous methanol solution into a 1-L separatory funnel and shake the solution with 200 mL of dichloromethane for 5 min. Collect the dichloromethane in a flask and adjust the pH of aqueous methanol to 13 with sodium hydroxide. Extract the solution with two portions of 200 mL of dichloromethane for 5 min. Combine the dichloromethane extracts and pass through a filter paper with anhydrous sodium sulfate. Add 0.5 mL of diethylene glycol and then concentrate the dichloromethane extract to about 0.5 mL on a water-bath at ca 40 °C by rotary evaporation. 

Combine 50 g of the air-dried soil with 100 mL of acetone and shake the mixture with a mechanical shaker for 15 min. Filter the mixture through a fluted filter paper into a 500-mL flask. Wash the residue on the filter with 50 mL of acetone. Combine the filtrates and remove acetone by rotary evaporation. Transfer the residue with 150 mL of a potassium chloride solution into a separatory funnel, extract the solution with two portions of 50 mL of dichloromethane and collect the organic extracts in a flask. Filter the combined solvent extracts, together with the washings of the collecting flask, through anhydrous sodium sulfate into a 300-mL flask. Remove dichloromethane by rotary evaporation. Dissolve the residue in 10 mL of carbon tetrachloride. 

When 0.50 mg. of ethylene dibromide was added to 70 grams of air-dried soil and subsequently removed by steam distillation, it was not possible to detect it by their procedure. 

However, in this preliminary work to standardize a procedure, a 70.0-gram portion of air-dried soil was weighed into each flask. With a 50-ml. buret the quantities of aqueous ethylene dibromide solution necessary to give 0.125 to 1.500 mg. of this chemical... 

Soil Column Leaching. Glass tubing (diameter = 1 cm) was cut into 50 cm lengths, and one end was plugged with glass wool and Miracloth . Air dry soil (percent moisture = 2%, 1%, 4%. for Felton, Keeton, Prairie, respectively) was packed into the tubes to a depth of 30 cm. A small layer of white builders sand was then... 

Drying and remoistening air-dry soils greatly lowers their ability to oxidize Cr (Bartlett and James, 1980). Since Cr3+ has a similar ionic radius (0.64 x 10 10 m) to Mg (0.65 x 10 10 m) and trivalent Fe (0.65 x 10 ° m), it is possible that Cr3+ could readily substitute for Mg in silicates and for Fe3+ in iron oxides. This explains the high proportion of Cr found in the residual fraction in the native arid soil. On the other hand, humic acids have a high affinity for Cr (III) (Adriano, 1986). Thus, present results show that when soluble Cr was added to soils, Cr3+ was initially and immediately bound to the organic matter fraction. Due to its slow conversion into the reducible oxide and residual fractions, Cr in the amended soils departed and remained removed from the quasi-equilibrium. However, Cr approached the quasiequilibrium with time. 

Moraghan J.T. Manganese nutrition of flax as affected by FeEDDHA and soil air drying. Soil Sci Soc Am J 1985a 49 668-671. 

Hot water-extractable C accounts for 1-5% of soil organic C (Leinweber et al. 1995 Sparling et al. 1998 Chan and Heenan 1999) and about 50% of this is thought to be present as carbohydrate (Haynes 2005). Because it is usually extracted from air-dried soils much of the pool originates from desiccated microbial cells but it also includes exocellular polysaccharides, root exudates, lysates and humic material (Redl et al. 1990 Leinweber et al. 1995 Sparling et al. 1998). Both hot water extractable C (Sparling et al. 1998 Chan and Heenan 1999) and hot water-extractable carbohydrate (Ball et al. 1996 Haynes and Beare 1997 Debrosz et al. 2002) have been used as indices of soil quality. 

At this point, the samples are ready for analysis. However, before analysis, it is important to determine the moisture content of the air-dried soil. This is reported as the percent water on a dry-weight basis. Air dry soil contains water, usually 1-2%, although as organic matter increases, so does the air dry water content. In extreme cases, limited to organic or high organic matter soils, the percent water may approach 100%. 

Soil is hygroscopic. The water content of air dry soil will increase and decrease as the relative humidity of the air it is exposed to changes. The uptake of water by oven dry soil is shown in Figure 7.10. Thus, determination of water content just before analysis is critical. 

Method 7.1. Determination of Moisture in Air Dry Soil on a Mass Basis... 

A 50- to 100-g sample of air-dried soil is placed in a drying can of known weight and placed in an oven at 105°C for 24 hours. It is removed and weighed and the percentage of moisture on a dry-weight basis determined using the following equation ... 

Direct measurement of soil is most often carried out on air-dried soil and involves spectroscopic instruments and methods. For example, X-ray dispersion (XRD), X-ray fluorescence (XRF), infrared (IR) spectroscopy,... 

A 2-g sample of sieved ( 10 sieve <2 mm), air-dry soil is shaken with 240 mL of distilled water at 20°C for 1 hour. Shaking is accomplished on an end-over-end shaker at 28 rpm (rounds per minute), filtered, and analyzed. 

Air-dry soil is mixed with 0.02 M calcium chloride solution (1 2 ratio, for instance, 10-g soil 20 mL 0.02 M CaCl2 solution) and mixed for 1 hour. The pH of the suspension can be measured directly. In addition, the solution can be filtered for the determination of aluminum or magnesium by atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) spectroscopy (adapted from Reference 5). 

A 2-g air-dry soil sample (weighed to three place accuracy) is placed in a 50-mL Erlenmeyer flask or a similar size centrifuge tube and shaken with 20 mL of a 1 M, pH 7, NHtOAc solution, by shaking for 2 hours. Suspensions can be filtered or centrifuged to obtain a solution suitable for analysis by AAS or ICP (adapted from Reference 8). 

To 1-g sieved air-dry soil add 20 mL add extracting solution. Shake for 5 minutes and filter if filtrate is not clear, repeat filtration. The filtrate can be analyzed by calorimetry or ICP (adapted from Reference 10). 

Add 1.5 g of air-dry soil to a 125-mL Erlenmeyer flask. Add 40 mL of 0.5N NaHC03, pH 8.5, and shake on a mechanical shaker for 30 minutes. Filter through a Whatman No. 2 filter paper. Refilter through the same filter paper if the filtrate is not clear. A 5 mL aliquot of this filtrate is taken for colorimetric determination of phosphate (adapted from Reference 10). 

A 1-g sample of sieved ( 10 sieve, <2.00 mm) air-dry soil is placed in a 20-mL glass centrifuge tube and 10 mL of dichloromethane (CH2C12) added. The mixture is shaken for between 30 minutes and 1 hour. Extracts are centrifuged to separate the extract from soil before analysis (adapted from Reference 5). 

A 1-g sieved, air-dry soil sample is placed in an extraction cell with methanol as a modifier. The sample is extracted at a C02 flow rate of 1.5 mT/min with supercritical carbon dioxide for 15 minutes and analytes trapped in an octadecyl siloxane microextraction disk for subsequent analysis (adapted and condensed from Reference 9). 

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