Sorption of micropollutants to natural aquatic particles = Sorptie van microverontreinigingen aan natuurlijke aquatische deeltjes

Sorption to natural aquatic particles plays an important role in the bioavailability and fate of micropollutants. The characteristics of sorption were investigated for hydrophobic organic compounds (HOCs) and heavy metals using a wide variety of natural aquatic particles. Special attention was paid to (bio)sorption to phytoplankton and detritus. The extent of sorption can be quantified by a distribution- ( <em>K _{<font size="-2">d</font>}</em> ) or partitioncoefficient ( <em>K _{<font size="-2">p</font>}</em> ). It was shown in this study that such coefficients in aquatic systems are variable in space and time because:1. At more or less constant environmental conditions <em>K _{<font size="-2">d</font>}</em> values for trace metals depend on the content of iron(hydr)oxides, manganese(hydr)oxides and organic matter in the natural aquatic particles. It was shown for Lake Volkerak/Zoom that this content varies considerably in time and space, and that <em>K _{<font size="-2">d</font>}</em> values for cadmium differ up to factor 30 (field data) or a factor 300 (laboratory). For mineralizing planktonic particles in the laboratory, <em>K _{<font size="-2">d</font>}</em> increases up to a factor 10 - 20 (lead) were observed under conditions similar to those in Lake Volkerak/Zoom.2. When <em>K _{<font size="-2">p</font>}</em> values for HOCs are calculated with respect to an aqueous phase which contains organic matter, the apparent <em>K _{<font size="-2">p</font>}</em> depends on the organic carbon fraction in the aqueous phase and the particle to water ratio. Further, <em>K _{<font size="-2">p</font>}</em> depends on organic matter content and composition. It was shown for 1,2,3,4-tetrachlorobenzene that laboratory <em>K _{<font size="-2">p</font>}</em> values varied a factor 30 for particles from lake Volkerak/Zoom. Organic matter content of suspended solids showed a strong seasonal variation. Normalization to organic carbon removes only a part of the variation. Comparison of carbon normalised HOC concentrations (field data) in settling solids with those in simultaneously sampled suspended solids showed a difference of a factor 2 - 6. Under controlled laboratory conditions, significant <em>K _{<font size="-2">oc</font>}</em> differences between fresh phytoplankton cells, detritus and sediments were found.3. Hydrophobic sorption to suspended solids may not be at equilibrium in many aquatic systems. This is caused by retarded adsorption or desorption, or for phytoplankton by the combined action of retarded bioaccumulation and algal growth.