Biological uptake

The biogeochemical processes that generally describe the interaction of elements with particles are quite well known dissolution, flocculation, ion exchange, sorption, (co)precipitation, electron transfer, and biological uptake. In aquatic environments these reactions often occur simultaneously and competitively. In order to utilize marine tracers effectively, we must understand how elements are associated with particles and sediments. 

Photic-zone depletion with Ca, Si, ICOz, NO3, PO4, Cu, Ni Biological uptake and regeneration... 

The sediment reservoir (1) represents all phosphorus in particulate form on the Earth s crust that is (1) not in the upper 60 cm of the soil and (2) not mineable. This includes unconsolidated marine and fresh water sediments and all sedimentary, metamorphic and volcanic rocks. The reason for this choice of compartmentalization has already been discussed. In particulate form, P is not readily available for utilization by plants. The upper 60 cm of the soil system represents the portion of the particulate P that can be transported relatively quickly to other reservoirs or solubilized by biological uptake. The sediment reservoir, on the other hand, represents the particulate P that is transported primarily on geologic time scales. 

The natural circulation of the oceans also exchanges waters between the deep and surface ocean reservoirs. Because biological uptake con-... 

Mahon (1982) measured BCFs of 1,576 and 459 in algae and plankton, respectively. Horikoshi et al. (1981) determined BCFs in several species of bacteria that ranged from 2,794 to 354,000. However, bioconcentration by the bacteria represented adsorption onto the cell surfaces of the bacteria rather than true biological uptake. 

A concept of anion mobility may be considered a useful paradigm for explaining the net retention and loss of cations from soils, and thus exposure pathways. This paradigm relies on the simple fact that total cations must balance total anions in soil solution (or any other solution), and, therefore, total cation leaching can be thought of as a function of total anion leaching. The net production of anions within the soil (e.g., by oxidation or hydrolysis reactions) must result in the net production of cations (normally H+), whereas the net retention of anions (by either absorption or biological uptake) must result in the net retention of cations. 

To describe the dynamics of metals at biological interphases in the presence of various ligands, the kinetics of dissociation of the complexes have to be taken into account in relation to the diffusion and to the uptake kinetics ([14] and Chapters 3 and 10 in this volume). Based on kinetic criteria, labile and inert complexes can be distinguished as limiting cases with regard to biological uptake ([14] and Chapter 3, this volume). 

Wilkinson, K. J. and Buffle, J. (2004). Critical evaluation of physicochemical parameters and processes for modelling the biological uptake of trace metals in environmental (aquatic) systems. In Physio chemical Kinetics and Transport at Biointerfaces, eds. van Leeuwen, H. P. and Koster, W., Vol. 9, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems, Series eds. Buffle, J. and van Leeuwen, H. P., John Wiley Sons, Ltd, Chichester, UK, pp. 445-533. 

Physicochemical Parameters and Processes for Modelling the Biological Uptake of Trace Metals in Environmental (Aquatic) Systems... 

IMPORTANT PHYSICOCHEMICAL PROCESSES LEADING TO BIOLOGICAL UPTAKE... 

When biological uptake does not perturb the external medium, then /int can be given by equation (35). As discussed above, this limiting condition is assumed to occur in both the free-ion activity and biotic ligand models. When Ka[M] < 1, then (cf. equation (7)) ... 

In the case of a diffusion limitation, the free metal ion is largely consumed at the surface of the organism such that the concentration gradient of M in the external medium is strongly perturbed by biological uptake. The flux will depend on the concentration gradient of M that occurs between the bulk... 

The rates of Mn(II) removal in some natural waters are similar to the Mn(II) oxidation rates predicted on the basis of these laboratory studies. However, in other cases the rate of manganese removal in natural waters is much faster than that expected on the basis of this work. In these systems significant manganese removal may occur as the result of adsorption, bacterially mediated oxidation, or biological uptake. 

DHS can significantly affect the environmental behavior of hydrophobic organic compounds and lower the possibility of direct contact of such organic compounds with various solid phases. The rate of chemical degradation, photolysis, volatilization, transfer to sediments/soils, and biological uptake may be different for the fraction of organic pollutant that is bound to DHS. If this is the case, the distribution and total mass of a pollutant in an ecosystem depends, in part, on the extent of humic matter-hydrophobic binding. 

Mo biological uptake and processing. As an essential trace nutrient. Mo uptake and incorporation into enzymes is tightly controlled at the cellular level via selective pumps and... 

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