Bioavailability soils

Plant roots stabilize bioavailable soil metal fractions through several mechanisms. Precipitation at the rhizosphere of the solubilized fraction of heavy metals in the soil is the primary mechanism of most metal adsorption to root surfaces (Blaylock et al., 1997). Adsorption also occurs through the binding of free metal cations by pectins on root cell walls and in pectin and other polysaccharide combinations from root-secreted mucilage (Waisel et al., 1996). 

M. I. Kaniu, K. H. Angeyo, A. K. Mwala and M. J. Mangala, Direct rapid analysis of trace bioavailable soil macronutrients by ehemometrics-assisted energy dispersive X-ray fluoreseenee and seattering spectrometry, Anal. Chim. Acta, 2012, 729, 21-25. 

The influence of soil ageing on the recovery of POPs from spiked soil samples was also assessed. Spiked lettuce samples were subjected to in vitro gastrointestinal extraction to assess the bioavailability of Endosulfan compounds. All samples (soil and lettuce) were extracted using pressurised fluid extraction and analysed using gas chromatography with mass selective detection. 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

Another contaminant of concern for the Delta is Se. Selenium occurs in high concentrations in the soils of the western San Joaquin Valley associated with salts that have accumulated in this region [10]. Selenium is recycled through agricultural retom flows to the river and transported to the Delta and San Francisco Bay. The Se is transformed into a more bioavailable form by microbial communities and aquatic plants. The Se is passed through the foodweb with particular concern for bottomfeeding migratory waterfowl and predatory fishes. The hydrodynamics of water from the San Joaquin River is an important consideration in the intensity and distribution of Se contamination within the Delta. 

Bioavailability from Environmental Media. Endosulfan can be absorbed following inhalation of contaminated workplace air and ingestion of insecticide-contaminated food (Ely et al. 1967). Dermal contact with or ingestion of endosulfan that is tightly bound to soil particles is an exposure route of... 

Klienfeld and Tabershaw 1954 Prout et al. 1985 Stephens 1945 Stevens et al. 1992 Templin et al. 1993 Withey et al. 1983), or dermal (Bogen et al. 1992 Jakobson et al. 1982 McCormick and Abdul-Rahman 1991 Sato and Nakajima 1978 Steward and Dodd 1964 Tsuruta 1978) exposure. All these routes of exposure may be of concern to humans because of the potential for trichloroethylene to contaminate the air, drinking water, food, and soil. More information on the absorption of trichloroethylene following ingestion of contaminated soil and plants grown in contaminated soil near hazardous waste sites are needed to determine bioavailability of the compound in these media. 

Kadry AM, Skowronski GA, Turkall RM, et al. 1991a. Kinetics and bioavailability of soil-adsorbed trichloroethylene in male rats exposed orally. Biol Monit 1 75-86. 

Kadiy AM, Turkall RM, Skowronski GA, et al. 1991b. Soil adsorption alters kinetics and bioavailability of trichloroethylene in orally exposed female rats. Toxicol Lett 58 337-346. 

Xenobiotics exist not only in the free state but also in association with organic and mineral components of particles in the water mass, and the soil and sediment phases. This association is a central determinant of the persistence of xenobiotics in the environment, since the extent to which the reactions are reversible is generally unknown. Such residues may therefore be inaccessible to microbial attack and apparently persistent. This is a critical factor in determining the effectiveness of bioremediation (Harkness et al. 1993). Although the most persuasive evidence for the significance of reduced bioavailability comes from data on the persistence of agrochemicals in terrestrial systems (Calderbank 1989), the principles can be translated with modification to aquatic and sediment phases that contain organic matter that resembles structurally that of soils. 

Immobilization of neutral xenobiotics in soils by qnatemary ammoninm cations has been established, and its significance on the bioavailability of naphthalene to bacteria has been examined. Bioavailability was determined by the rates of desorption, and these differed between a strain of Pseudomonas putida and one of Alcaligenes sp. (Crocker et al. 1995). 

Guerin WF, SA Boyd (1992) Differential bioavailability of soil-sorbed naphthalene by two bacterial species. Appl Environ Microbiol 58 1142-1152. 

Guthrie EA, FK Pfaender (1998) Reduced pyrene bioavailability in microbially active soils. Environ Sci Tech-nol 32 501-508. 

A series of soil microcosms were used to study the biodegradation and bioavailability of pyrene during long-term incubation. The nonextractable fraction of -labeled pyrene that had been introduced into pristine soil and incubated with or without the addition of azide was substantially greater in the latter (Guthrie and Pfaender 1998). It was also shown that microbial activity produced a number of unidentified polar metabolites that might plausibly be involved in the association. 

Verstraete W, W Devlieger (1996) Formation of non-bioavailable organic residues in soil perspectives for site remediation. Biodegradation 7 471-485. 

White C, A Quinones-Rivera, M Alexander (1998) Effect of wetting and drying on the bioavailability of organic compounds sequestered in soil. Environ Toxicol Chem 17 2378-2382. 

Chung N, M Alexander (1998) Differences in sequestration and bioavailability of organic compounds aged in different soils. Environ Sci Technol 32 855-860. 

As for PAHs, attempts have been made to increase bioavailability by use of surfactants, and a complex picture has again developed (Fava and Di Gioia 1998). Triton-100 exerted both positive and negative effects in soil slurries even though it was not metabolized by the soil microflora, it adversely affected the degradation of chlorobenzoate intermediates, whereas in fixed-bed reactors, depletion of PCBs was enhanced. 

Adriaens P, Q Fu, D Grbic-Galic (1995) Bioavailability and transformation of highly chlorinated dibenzo-p-dioxins and dibenzofurans in anaerobic soils and sediments. Environ Sci Technol 29 2252-2260. 

Particularly polar contaminants may associate with polymeric humic components of soil, water, and sediment. Their biodegradation then depends on the degree to which these processes are reversible and the contaminants become accessible to microorganisms (bioavailable). This is especially significant after weathering (aging), even for nonpolar compounds. 

S. A. Barber, Soil Nutrient Bioavailability, John Wiley and Son.s, New York. 1995. 

S. Staunton and F. Leprince, Effect of pH and some organic anions on the solubility of soil phosphate implications for P bioavailability. Ear. J. Soil Sci. 47 231 (1996). 

Upon formation of a metal chelate or complex, the next rate-limiting step in delivering iron to the cell is the diffusion of iron complexes through the. soil in response to diffusion gradients. In the vicinity of plant roots, metal chelates and complexes may also move by bulk flow in the transpiration stream as water moves from the soil into the plant. However, depending on their charge characteristics and hydrophobicity, metal chelators and complexes can become adsorbed to clay and organic matter, which may then decrease their mobility and bioavail-... 

Exposures of Children. Children will be exposed to americium in the same manner as adults in the general population (i. e., ingestion of food and water and inhalation of air). Americium is potentially found at hazardous waste sites at elevated levels. Since children may have oral exposure to soil through hand-to-mouth activity, bioavailability studies of americium in soil via the oral route may be useful to assess the risk of this type of exposure. 

Bioavailability from Environmental Media. Oral absorption of DIMP from water was found to be rapid in both the rats and minks (Bucci et al. 1992). Dermal absorption of DIMP in swine was reported to be between 3 and 7% through 7 days (Snodgrass and Metkler 1992). However, no studies were located regarding the bioavailability of diisopropyl methylphosphonate from other environmental media. Studies that investigate the bioavailability of diisopropyl methylphosphonate from soils would be useful in estimating exposure of persons who live near the RMA. 

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