Colloids: The world of neglected dimensions [Die welt der vernachlässigten dimensionen: Kolloide]

Aquatic colloids are abundant in all natural aquatic systems. Aquatic colloids consist of clay minerals, micro-organisms, humic substances, and anthropogenic colloids like soot and platinum (from catalysts in motor vehicles). Colloids may enhance contaminant transport due to sorption of hydrophobic organic compounds. They can have negative effects on water quality, especially micro-organisms like pathogens or viruses. Colloids also can cause pore blocking and subsequent head loss in groundwater production wells. However, colloids can be useful in groundwater remediation or waster water treatment (e.g. tensides, flocculation, catalysts). The origin of colloids is due to weathering, degradation of organic compounds, dissolution or precipitation as well as hydrochemical or hydraulic gradients. Colloid stability is dominated by surface properties. New analytical tools like field flow fractionation, laser induced breakdown detection and scanning x-ray microscopy will provide new insight into the behaviour of aquatic colloids.