CHARACTERIZATION OF THE SUBMICROMETER PHASE IN SURFACE WATERS - A REVIEW

The need for improved knowledge about the composition and behaviour of solid matter in the colloidal size range (1 nm to 1 mu m) in natural waters has been identified by several authors in the literature. The i ncreased interest in these colloids is due to their large impact on th e transport, redistribution and bioavailability of numerous chemical c ompounds (such as trace metals, nutrients and organic pollutants). Thi s paper presents a review of different analytical techniques available for determination of some of the properties of interest (e.g., colloi d concentration, size distribution, mineral composition and surface pr operties). It is obvious that most methods suffer from limitations and that the only feasible way to overcome these problems is by using a c ombination of different techniques. Sampling in a Swedish lake, as an example, illustrates one promising combination including light scatter ing and gravimetric analysis for determination of colloid concentratio n, photon correlation spectroscopy and scanning electron microscopy fo r size distribution measurements and energy dispersive microscopy; pow der X-ray diffraction and infrared spectroscopy in order to obtain inf ormation about mineral constituents and general surface properties. Si ze fractionations were performed by filtration and centrifugation to g ain information regarding the distribution of metals and organic matte r between dissolved and solid phases. The study indicated, for instanc e, a seasonality of the size distribution of the colloidal matter, wit h smallest colloids (range 120-340 nm) found in spring, while the coll oid samples during summer and autumn have a size distribution in the r ange 280-700 nm. This result also illustrates the limitations when usi ng filters with, e.g., a pore size of 0.45 mu m for the distinction be tween particulate and dissolved substances.