Distribution and Phytoavailability of Lead in a Soil Contaminated with Lead Shot

Water, Air, &; Soil Pollution - This paper presents a study of Pb contamination of soil at a clay target shooting facility in Canterbury, New Zealand. The spatial distribution of Pb...     

Determination of phosphatase activities of soils and animal wastes

A method is described to determine acid and alkaline phosphatase activities from the rate of decomposition of p-nitrophenylphosphate in the presence of large amounts of organic matter, such as occur in the surface layers of soils or in animal wastes. The p-nitrophenol formed is separated by high pressure liquid chromatography on a cellulose column from p-nitrophenylphosphate and other organic compounds present in the soil or waste extract. After separation, p-nitrophenol is measured on-line in a spectrophotometric flow cell at a wavelength of 405 nm. In this way p-nitrophenol concentrations down to 0.1 μm can be measured, making it possible to work with substrate concentrations of 1 μm.

The necessity of correcting the phosphatase activity measured in this way for adsorption of enzyme, substrate (p-nitrophenylphosphate) and product (p-nitrophenol) is discussed.

Acid and alkaline phosphatases are inhibited strongly at phosphate concentrations greater than 0.1 mm, consequently substrate concentrations in the range of 0.01 to 0.1 mm were used.

The method was applied to a number of sandy soils and to pig slurry. Air drying or freeze drying of soils was found to decrease the phosphatase activity. Freeze drying did not affect the phosphatase activity of pig slurry. Michaelis-Menten kinetics were found to apply reasonably well. The resulting kinetic parameters are compared with values from the literature. Phosphatase activities are correlated with organic P and organic matter contents of soils and pig slurry.     

Microcomputer controlled titration for determination of protein nitrogen in feeds and wheat.

The determination of protein nitrogen in feeds and wheat by microcomputer controlled titration is described. The method involves direct titration of ammonia with standard hypochlorite titrant in the presence of bromide. The titrant is delivered by an automatic buret, and the microcomputer controlled, automatically computed potentiometric end points are precise to 0.1% over a 5-fold concentration range of nitrogen. Digestions performed with both mercury and copper catalysts show comparable results. Samples are weighed before digestion by an electronic balance interfaced to the computer which records sample number and weight. An automatic pipet aliquots, dilutes, and buffers samples directly from the digestion tubes; the samples can be immediately titrated with the automatic titrator. The results for protein in NBS standards and check feed samples from an offical testing program compare closely with average values reported for these standards. Results show that feed and wheat samples contained 10-100% protein. Precision for successive aliquots of the same digests is 0.1-0.4%relative standard deviation; precision for multiple digestions of the same sample is 0.1-0.8%.     

Oxidation-reduction regimes in some Oxisols of tropical China

The oxidation-reduction regimes of some Oxisols of tropical China were investigated on the basis of the Eh values and the amounts of reducing substances, both measured by newly devised methods. The Eh values in the surface layers of soil profiles under natural forest and commercial forest were 400–550 mV, lower by 100–200 mV than the deeper horizons. The concentrations of reducing substances in the surface layers corresponded to 0.5–5.0 · 10^?5M of Mn²⁺. In the cultivated layer of a submerged paddy soil the concentration of reducing substances was as high as 13·10^?5M, with an Eh value of less than 100 mV. There was a negative correlation between the Eh value and the logarithm of the concentration of reducing substances, showing that the intensity aspect and the capacity aspect of the oxidation-reduction status of a soil are closely interrelated.     

Liquid chromatographic determination of barbaloin (aloin) in foods

A simple and rapid liquid chromatographic method is described for the determination of barbaloin (aloin, 10-D-glucopyranosyl-1,8-dihydroxy-3-(hydroxymethyl)-9(10H)-anthraceno ne) in foods. Barbaloin is extracted with water from foods containing aloe and the extract is cleaned up on a disposable cartridge by using methanol-water (55 + 45) as eluant. The eluted barbaloin is separated by liquid chromatography on a YMC A-302 column with methanol-water (50 + 50) mobile phase, and detected at 293 nm. Recoveries of barbaloin added to foods at the levels of 0.05 and 0.50 mg/g were 94.4-100%. Assay results for commercial food samples indicated that the present method is applicable to a variety of foods supplemented with aloe.     

Theoretical effect of wheel loads on subsoil stresses

This study highlights the previously expressed concerns of soil researchers who have indicated that compaction pressures or stresses in the deeper layers of soil are determined by the amount of surface load. Modifications of Boussinesq theory by Froelich and further modification of Froelich's equations by Soehne were used to predict and develop graphical relationships for maximum allowable loads and/or mean surface contact pressures beneath loaded farm machinery tyres. Vertical compressive stresses at different subsoil depths were calculated and design loads for a currently used high flotation tyre were examined for comparative purposes. For highly compactible soils the results indicate that mean surface contact pressures should not exceed maximum allowable stresses in the subsoil for individual wheel loads which exceed approximately 30 kN. Thus, it appears that future designs based upon limited ground contact pressures are essential. This will require limitations on vehicle wheel loads and the use of more tyres and axles on heavy equipment.     

Overload-controlled cultivation shanks under static loads

Cultivators for stony soils have to be protected to prevent breakage. Draft forces of cultivator shanks in hard clod-forming soils are higher than in the temperate soils of wet areas. Load-control devices are used to prevent breakage, but most of them cannot maintain constant depth in hard soils.

Load-controlled light cultivator shanks and chisel plows were tested to define their behaviour under high soil resistances and obstacles. The shanks were loaded with horizontal forces to simulate soil resistances as found in cultivating hard clod-forming soils.

The variations in the depth, the lift angle and the backward deflection were measured. The maximum stresses on the shanks were calculated.

It was found that only the light cultivator shank with a pre-loaded special design moment control device can till hard soils with small reasonable depth variations and still run over an obstacle without being broken.

Only the heavy chisel plow with the rear spring load control device can run over an obstacle without being broken, but it loses cultivation depth under too low a soil resistance, compared with the maximum draft that it can hold.     

An assessment of the core-break method for estimating rooting density of different crops in the field

Most of the methods available for plant rooting studies in field soil are very tedious and time-consuming. Several investigations have shown that the core-break technique, in which roots are counted that appear at the faces of a broken core of soil, provides acceptable estimates of root length density in some situations. We investigated the usefulness of the core-break technique for evaluating rooting density of four plant species in two soil types. We encountered several problems, but recommend the core-break method to researchers who wish to quantify root development rapidly under various soil tillage practices.     

Most probable number method for isolation and enumeration of Staphylococcus aureus in foods: collaborative study

Enumeration of Staphylococcus aureus in foods was collaboratively studied by comparing the present AOAC final action method, 46.062, which uses trypticase soy broth with 10% NaCl to a proposed replacement method which uses the same broth with 1% sodium pyruvate added. Fifteen collaborators analyzed uninoculated samples of milk, tuna salad, and ground turkey, as well as samples inoculated with low (10(2) cells/g), middle (10(4) cells/g), and high (10(6) cells/g) levels of S. aureus. The samples were frozen immediately to maintain the inoculated level of S. aureus in the food. A different strain of S. aureus was used for each food; heat-stressed S. aureus cells were used to inoculate the milk samples. The pyruvate-amended broth significantly (alpha = 0.05) increased enumeration of low, middle, and high levels of S. aureus from milk and ground turkey, and from tuna salad at middle and high levels. The pyruvate-amended media method has been adopted official first action to replace method 46.062.     

Total arsenic in foods after sequential wet digestion, dry ashing, coprecipitation with ammonium pyrrolidine dithiocarbamate, and graphite-furnace atomic absorption spectrometry

A graphite-furnace atomic absorption (GFAAS) method is described for determining total arsenic (organic and inorganic compounds) in foods. Samples ranging from 1 to 40 g (depending on moisture content) were digested with HNO3 and dry-ashed at 500 degrees C overnight after addition of MgO. After dissolution in HCl, the arsenic was reduced with iodide and ascorbic acid and precipitated with ammonium pyrrolidine dithiocarbamate (APDC) in the presence of nickel carrier. Precipitates were collected on 0.3 micron cellulose acetate filters and dissolved in 10% HNO3 containing modifier. Ba(NO3)2 was added to remove a sulfate interference resulting from decomposition of APDC. Arsenic was determined using GFAAS. Accuracy of the method was good for 7 U.S. National Bureau of Standards (NBS) Standard Reference Materials and 3 National Research Council of Canada (NRCC) round-robin samples. Recovery of arsenic(V) from foods averaged 99.2% for peak heights and 97.1% for peak areas, with relative standard deviations (RSD) of 2.2% for peak heights and 3.3% for peak areas for all NBS and NRCC materials. Detection limit of the method was ca 10 ng arsenic.