Radiolabeled particulates

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

In a review of feeding and digestion in the Bivalvia [37], it was proposed that the accumulation of metal-bound particulates in the digestive gland was a two-phase process reflecting extracellular and intracellular digestion, and Viarengo [87] has reached similar conclusions. In a pulse chase study of the uptake of radiolabelled metals (Ag, Cd, Cr, Hg, Se) by the zebra mussel Dreissena... 

Photochemical reagents have been devised for crosslinking both soluble and particulate proteins (Chapter 5). In a recent study, Johnson et al. (1981) were able to crosslink radiolabeled glucagon to its receptor, merely by adding a bifunctional reagent that first reacted with amino groups and could subsequently be induced to form crosslinks by photolysis. 

Radiolabelled particulate or macromolecular species have a variety of applications in diagnostic... 

TCP s low water solubility and high adsorption to particulates causes adsorption onto river or lake sediment and soil. Biodegradation in river water is rapid, almost complete within 5 days. Abiotic degradation is slower with a half-life of 96 days. BCFs of 165-2768 were measured for several fish species in the laboratory using radiolabelled TCP. Radioactivity was lost rapidly on cessation of exposure, depuration half-lives ranged between 25.8 and 90 hours. 

Following centrifugation, continuously take out 1-ml fractions from the top of the gradient, and assay each fraction for particulate content (itis convenientto use radiolabeled(e.g., I-labeled) particulates). 

Particulate solid phases have originally been used for the separation of radiolabeled antibody-antigen complex from free labeled antibody in immunometric assays (Wide and Porath, 1966 Woodhead et al., 1974). 

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