Aquatic colloids: Sampling and characterization - A review

Colloids are abundant in all natural aquatic environments; however, the current knowledge on their environmental behaviour, mobilisation, transport, and deposition is considered to be insufficient because of a lack of analytical instrumentation for colloid measurement. Measurement devices are not standard tools, are expensive and in some cases not even available commercially. Furthermore, at present no technique exists to measure simultaneously size distribution over the full colloidal range or concentration, nor which allow for colloid identification at the extremely low concentrations usually found in subsurface aquatic systems. The combination of a range of different techniques is essential if full understanding of aquatic colloids is the objective. Even more challenging is the determination of colloid surface properties. In addition, sampling of colloids is of major concern and standard sampling protocols are not adequate. Special precautions and protocols for colloid sampling have to be applied if natural undisturbed colloids are to be obtained. This paper gives suggestions and protocols for colloid sampling and discusses some of the major techniques from the numerous methods for colloid measurement.