The Effects of Suspended Silts and Clays on Self-purification in Natural Waters: Protein Adsorption

Abstract

The effects of the suspended sediments found in many natural waters on the microbial processes involved in the self-purification of those waters are not known. Clays and silts with their large surface area per unit weight have an immense capacity for adsorbing nutrient molecules from solution, but the extent to which such adsorption takes place is largely unknown. Adsorption of a major portion of a biodegradable substance from solution onto a solid surface would significantly alter its susceptibility to bacterial attack and, hence, also the rate at which it is decomposed. In this paper are reported the results of adsorption experiments with soil materials found in some Alaskan waters which are typically heavily sediment-laden. The affinities of these soils for the protein bovine serum albumin were measured as a function of pH, temperature, and protein concentration. An empirical relationship was discovered, for a given soil material, between the equilibrium protein concentration and the initial protein-to-soil ratio. Temperature variations from 5 to 25°C had no detectable effect on adsorption, whereas variations in pH between 2 and 10 had dramatic effects on the extent of adsorption. The amount of protein adsorbed at the pH of the natural water system was so small as to lead one to predict that adsorption of this protein onto suspended sediments would have a negligible effect on the rate at which the protein would be decomposed by bacteria in the aqueous environment.