Extraction rate from soil

Terrestrial plants take up nickel from soil primarily via the roots (NRCC 1981 WHO 1991). The nickel uptake rate from soil is dependent on soil type, pH, humidity, organic content, and concentration of extractable nickel (NAS 1975 WHO 1991). For example, at soil pH less than 6.5 nickel uptake is enhanced due to breakdown of iron and manganese oxides that form stable complexes with nickel (Rencz and Shilts 1980). The exact chemical forms of nickel that are most readily accumulated from soil and water are unknown however, there is growing evidence that complexes of nickel with organic acids are the most favored (Kasprzak 1987). In addition to their uptake from the soils, plants consumed by humans may receive several milligrams of nickel per... 

Onken, A.B., and R.L. Matheson. 1982. Dissolution rate of EDTA-extractable phosphate from soils. Soil Sci. Soc. Am. J. 46 276-279. 

The GC/FID conditions were as follows column, 1.5% OV-17 (2 m x 3-mm i.d.) glass column N2 carrier gas flow rate, 45mLmin temperature of injection port, column and detector, 240,235 and 235 °C, respectively. The recoveries of these amino derivatives with fortification level ranging from 0.5 to lO.Omgkg" were 62-101% for chlornitrofen, 62-101% for nitrofen and 58-101% for chlomethoxyfen, and satisfactory recoveries from soil were obtained at high concentrations, but the recoveries at lower concentration averaged about 66% for the least recovered compound. Interference from other substances in the soil extracts derived from the acetylation reaction was negligible. 

Soil minerals play a stabilizing role in organic matter. The Al and Fe that complex and stabilize organic matter against microbial decomposition are released from soil minerals during soil formation. The supply rates apparently control the content of soil organic matter to a great extent. This is demonstrated by the relationship between pyrophosphate-extractable C and pyrophosphate-extractable Al plus Fe (Wada 1995). 

The relation between microbial diversity and soil functions is poorly understood because we cannot measure easily the microbial diversity, even if we can detect unculturable microorganisms by molecular techniques (Nannipieri et al. 2003). In addition, the present assays for measuring microbial functions determine the overall rate of entire metabolic processes, such as respiration, or specific enzyme activities, without identifying the active microbial species involved. The recent advances in RNA extraction from soil might permit us to determine active species in soil (Griffiths et al. 2000 Hurt et al. 2001). Further advances in understanding require us to determine the composition of microbial communities and microbial functions in microhabitats. 

Brady et al. [52] have discussed pressure-temperature phase diagrams for carbon dioxide polychlorobiphenyls and examined the rate process of desorption from soils. Supercritical carbon dioxide was used to extract polychlorobiphenyls and DDT and Toxaphene from contaminated soils. 

Moisture content of the soil has an effect on initial extraction rates of PCBs, although the final extraction efficiency is not affected. The technology removes all organics from the soil, not just targeted contaminants. The treated soil may be unsuitable for reuse since it is now inert. 

Aside from adding defined compounds, experimental additions of natural DOM mixtures suspected to vary in lability have helped test ideas about the contribution of various DOM sources to aquatic ecosystems. In a nice example using manipulation of natural DOM sources, Battin et al. (1999) used flowthrough microcosms to measure the relative uptake rates of allochthonous and autochthonous DOM by stream sediments. They documented greater than fivefold differences or more in uptake and respiration, depending on whether the DOM was extracted from soil or periphyton. Moreover, they were able to show, via transplant experiments, several cases where prior exposure to a particular source of DOM increased the ability of that community to metabolize the DOM supplied. There appears to be some preadaptation of microbial catabolic capacity when these stream biofilms were re-exposed to a familiar type of DOM. Similarly, the response of heterotrophic bacteria to carbon or nutrient addition was greatest when the source community was particularly active (Foreman et al., 1998). Kaplan et al. (1996) showed that fixed film bioreactors, colonized on one water source, were unable to rapidly metabolize DOC in water from another source. 

The results for the removal of PAHs from the 5 surface substrates are summarized in Table 16. In general, the 23 PAHs listed in the table averaged removal rates around 90% from the smooth surfaces and over 80% for the porous cast magnesium surface. In contrast, supercritical fluid extraction studies using CO2 for the removal of PAHs from soils for environmental applications have shown relatively poor removal efficiencies for many of the compounds listed in the table often requiring the addition of secondary solvents to the C02. However, it appears that from the results on the removal of the PAHs shown in Table 16, surface contamination is... 

The extraction of inorganic species such as Fe [146], and Cu, Pb, As, Se, Hg and Cd [172], from soils was investigated on a pilot plant scale with a view to developing an industrial-scale method for decreasing allowed levels of the metals used to manufacture cement. To this end, kinetic curves for the extraction rate were used that allowed the time... 

In some cases, the flow-rate is the single factor most strongly influencing the extraction efficiency the higher it is, the greater the amount of analyte that is extracted over a given interval [38]. In other cases such as the extraction of fluoranthene from soil, the flow-rate scarcely affects the results above a 0.3 ml/min level [41]. The optimum conditions for a particular extraction cannot be established on the basis of the number of times the extraction cell is vented because the extraction of most analytes is kinetically limited. Occasionally (e.g. in the extraction of cocaine from coca leaves), the process is governed primarily by the solubility of the analyte rather than by its desorption kinetics (see Fig. 7.10) [22]. 

Supercritical fluid extraction (SFE), usually with carbon dioxide and, often, with a modifier, has become of increasing interest in the last few years because of its selectivity, preconcentration effect, efficiency, simplicity, rapidity, cleanness, and safety, mainly concerning the extraction of organic compounds prior to separation and detection by chromatographic techniques. It has several advantages over classical solvent extractions, in comparison with recent extraction techniques. Approaches to obtain quantitative extractions, including fluid choice, extraction flow rate, modifiers, pressure, and temperature, are presented, as well as the potential for SFE to extract polynuclear aromatic hydrocarbons (PAHs) from soils, sediments, and biota. Improvements and new environmental applications are also reported. 

Chromium is rated as an immobile element, most of which is difficult to extract from soils even by aggressive chemical agents. Toxicity of Cr to plants is occasionally seen in unusually Cr-rich soils formed from the parent rock, serpentinite, or under high pH conditions favorable to Cr oxidation. 

---