Relative leachability

Table 7-10. Relative leachability of isotopes from young leaves of squash (Cucurbita pepo) (from Hikey et al., 1958).

Starik et al (1960) and Burkser etai(l962) determined the relative leachability of Th and Pb from pitchblende. Starik et al (1961) found the first decay product of to be easily leached from... 

Stabilization refers to techniques that immobilize the contaminant to reduce the hazard (or mobility) potential of a substance by converting the contaminants into their least migratory (or leachable) form. Processes of stabilization interact with the contaminant to solidify by chemical means, insolubilize, destroy, or sorb it into a relatively stable form. The following factors may limit the applicability and effectiveness of the process ... 

Microscope analyses and leachability tests showed that the microstructural configuration of materials at the site are stable not only relative to the tests and procedural time frame but also because of the recognition of the absence of isolated microstructures made of heavy elements. Heavy elements are most likely trapped in the lattice of the detected relatively insoluble microstructure phases, and leaching of these elements is highly unlikely. In conclusion, the industrial waste present in the brownfield site of Bagnoli is unlikely to contribute metallic pollution to local groundwater, on a reasonable human time scale. Numerous investigations carried out on industrial steelwork waste in the European Community have reached the same conclusions. 

As described above, individual packaging components will invariably contain complex mixtures of chemical entities (e.g., additives and oligomers), many if not most of which are at relatively trace levels (i.e., pg/g and lower). The principles of Trace Organic Analysis, as developed in the environmental, geochemical, and bioanalytical fields, can be applied to the problem of identification and quantification of these individual chemical entities, whether as extractables or as leachables.f The general process is as follows ... 

Note that accurate mass measurements can be obtained for El and Cl as well as ESI and APCI spectra. This relatively simple example gives some idea of the power of modem MS for extractables/leachables testing, and trace organic analysis in general. Using state-of-the-art instruments, such as hybrid TOF and Fourier Transform mass... 

Solidification/stabilization of hazardous wastes is a relatively new treatment process that has the potential to reduce leachability of hazardous eonstituents... 

The relatively low leachable Mn concentrations at depth (Fig. 14) are much lower than expected for soils (Wright et al., 1955), which indicates that some of the Mn escapes the sediment and reenters the estuary. Since Mn is fixed below the zone of dissolution, then both the fraction of the deposited Mn that escapes and the rate of escape may be estimated. If the Mn concentration associated with incoming soil particles is taken to be within the range reported for similar gray-brown podzolic soils (800 200 fjLg/gm), then the concentration below 30 cm in Fig. 14 may be used to estimate the fraction lost ... 

Copper and Cr are prevalently held in the oxidizable (-68%) and residual (-24%) fractions, with other forms making up much less than 10%. Pb is primarily held in the residual mineral fraction (77%) with smaller amounts held in the oxidizable (18%) and reducible (3%) forms. Zn is uniformly distributed between easily extractable (23%), reducible (24%) and residual (49%) fractions, with very small percentage occurring in oxidizable forms (4%). Thus, only Zn appears to occur in the studied soils in consistent amounts as bioavailable and leachable forms. Copper and Cr, which are mainly associated with organic matter, for which both metals have high affinity are characterised by a lower mobility, unless the occurrence of oxidising conditions may induce their release in solution. Lead, and in lower proportion also Cu and Cr, extracted mainly by the fourth step, result relatively immobile. 

For borosilicate glass ceramics, leaching rates of the order of 10" g/(cm day) and greater have been found. Remarkably, the controlled crystallization process used in making these ceramics does not increase the leachability relative to that of the parent glass, in contast to the increased leachability occurring on spontaneous devitrification. 

Although concrete is a monolithic solid, it is quite porous. In contact with water, about a third of the tritium will be released, mainly by isotopic exchange, in the first month. The release may be retarded by coating the cement. Because of the relatively high leachability, cemented HTO would have to be stored in gastight steel cylinders, probably in a nonaccessible geologic repository. 

Discover and develop proton exchange membranes (PEMs) capable of extended fuel cell operation at higher temperatures of 120 to 150°C, at low relative humidity (RH), and without leachable components... 

These complications provide an explanation for the lack of agreement obtained from many studies which have been carried out to assess the effect of pH on heavy metal availability, as well as the relative effectiveness of various reagents for the extraction of these metals from clays, soils, and sediments. The extractability or leachability of these metals should be viewed in terms of the Eh and pH of the system, soil plus extractant, as compared with that of the system soil plus pore water, and the solubilities of Fe(OH)3(a) and Mn02(a ), especially the latter, in the extractant utilized, [(a) indicates an x-ray amorphous solid as opposed to (c), a crystalline phase.]... 

CDAA, molinate, EPTC, vernolate, pebulate, CDEC, and cycloate are all relatively mobile in soil systems (123, 385, 386, 387, 388 389, 390, 391). The herbicides leached more readily in coarse textured soils than in fine textured ones and did not significantly leach in peat or muck soils (386, 387, 388, 391), Leachability of the compounds was related to their water solubilities (compounds of higher solubilities moved more than less soluble ones) and to the organic matter and clay contents of the soils (less movement as the organic matter and clay content increased). 

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