Uptake by organisms

Soil solution is the aqueous phase of soil. It is in the pore space of soils and includes soil water and soluble constituents, such as dissolved inorganic ions and dissolved organic solutes. Soil solution accommodates and nourishes many surface and solution reactions and soil processes, such as soil formation and decomposition of organic matter. Soil solution provides the source and a channel for movement and transport of nutrients and trace elements and regulates their bioavailability in soils to plants. Trace element uptake by organisms and transport in natural systems typically occurs through the solution phase (Traina and Laperche, 1999). 

In ocean water distinct °Si gradients with depth exist (Georg et al. 2006) surface waters are relatively rich in °Si whereas deep waters are more depleted in °Si, which is due to a silicon isotope fractionation during the uptake by organisms... 

Uptake by organism Molecular weight Water solubility Log K Not appropriate... 

In aquatic ecosystems, complexation to organic and inorganic ligands and competition between toxic metals and Ca or Mg ions for biological adsorption sites reduce the actual amount of metal available for uptake by organisms. Chemical equilibrium models applicable to natural systems include RANDOM (Murray and Linder 1983 ... 

Assessment of environmental and human exposure. As a final step, concentrations can be calculated for each of the (groups of) mixture components in different exposure media (inhaled air, ingested water, food items) or environmental compartments (soil, sediment, air, and surface or groundwater). This information may not, however, represent the complete picture often only part of the total concentration in an environmental compartment is biologically available for uptake by organisms. 

Bioavailability Indication of the fraction of the total amount of a chemical present in a specific environmental compartment that, within a given time span, is or can be made available for uptake by organisms (adopted from Peijnenburg and Jager 2003). Also defined as the extent to which the form of a chemical is susceptible to being taken up by an organism. A chemical is said to be bioavailable if it is in a form that is readily taken up (e.g., dissolved) rather than a less available form (e.g., adsorbed to solids or to dissolved organic matter). 

Total concentrations of chemicals in the compartment of exposure are considered of limited relevance because, due to sorption and sequestration processes, often only a small fraction of the total amount is available for uptake by organisms. Properties of the chemical and of the environment determine sorption, chemical speciation, and bioavailability. Information on chemical concentrations therefore is much more... 

The rate of sedimentation is controlled largely by the rate at which an element is converted (uptake by organisms, precipitation, coprecipitation, ion exchange) into an insoluble, setdeable form. Hence the reactivity of the elements influences the time that elements spend, on the average, as constituents of the seawater. For most elements residence times have been determined on the basis of estimates of the input by runoff from the land or from calculations of sedimentation times. Remarkably similar results are obtained by these two... 

In similar studies conducted at ORNL at 10-8 M Pu(IV), formation of Pu(VI) has been observed. If laboratory experiments using Pu and other actinides are to aid in interpreting the behavior of these radionuclides in ecosystems, artifacts associated with experimental methodology must be recognized or eliminated. Mechanisms affecting Pu uptake by organisms likewise cannot be delineated until chemical forms and species in environmental media are defined and understood. 

Iron is a vital component of the proteins involved in readily available for uptake by organisms. Unlike... 

Moreover, the availability of metals for uptake by organisms under field will vary from site to site and is highly dependent on the speciation of the metal and the water chemistry (e.g. pH, Dissolved Organic Carbon [DOC]). Hence it is of utmost importance to take the speciation and/or bioavailability into account. 

Van t Hooft FM, Van Gent T, Van Tol A (1981) Turnover and uptake by organs of radioactive serum high-density hpoprotein cholesteryl esters and phosphohpids in the rat in vivo. Biochem J 196 877-885... 

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