Natural aquatic colloidal matter : characteristics and impact on the mobility of trace metals and organics

Sammanfattning: Natural colloidal (<1.0 µm) matter plays an important role for the transport and redistribution of water-borne substances. The aim of this work was to characterise colloidal matter from surface waters and groundwaters, and to improve on the understanding on the role of natural colloidal matter in the redistribution and mobility of trace metals.Laboratory studies of the stability (coagulation rate) of model colloids showed that the stability was dependent on the electrolyte composition, pH and the presence of fulvic acid. The uptake of Zn(II) and Pb(II) on colloidal Al, Fe, and Si (hydr)oxides was studied at high and low concentrations of reactants. The concentration of fulvic acid, pH, and the composition of the solid phase had a strong influence on the interaction between the metal ions and the solid surfaces.Photon correlation spectroscopy was used for measurements of particle size distributions in surface water and groundwater, and was also found to be suitable for on-line measurements in samples sensitive to changes in the partial pressure of atmospheric gases. The intensity of the scattered light was found to be useful for simultaneous estimates of the colloidal particle concentration. A calibration of the light intensity with material from one sample site showed that the spatial variation in sensitivity within a small catchment was relatively large, and there was also a variation in time. The mechanisms behind the concentration and composition of colloids were complex, but were to some extent related to input of organic carbon, pH aluminium and iron.Studies of colloidal matter in an estuary and a saline groundwater demonstrated the coagulating effect of high ionic strength and the presence of divalent ions. The major part of manganese and organic carbon was not bound in colloidal particles in the freshwater and estuarine samples, in contrast to aluminium and iron.