SPECIATION AND PARTITIONING OF PRIORITY ORGANIC CONTAMINANTS IN ESTUARINE WATERS

The main parameters influencing the speciation and partitioning of pri ority organic contaminants in estuaries are discussed with particular consideration being given to the association of contaminants with coll oidal material. Partitioning and speciation are factors that influence the persistence, transport, bioavailability and toxicity of organic c ontaminants in natural waters. However, most data on aquatic partition ing processes are based on the extrapolation of soil data and there is a need for more information on the partitioning of priority pollutant s in estuaries in order that their transport, fate and toxicity may be adequately assessed. In general, water quality studies concerned with organic contaminants either report total concentrations or at best di fferentiate between ''dissolved'' and particulate forms based on filtr ation. The concept and importance of solution phase speciation is well established for trace metals and it is generally accepted that for ma ny metals it is the free metal ion that is the bioavailable and hence the toxic form. Several reports suggest that the same is true for orga nic contaminants, i.e. association with particulates, colloidal materi al and macromolecular organics reduces bioavailability and toxicity. P hysicochemical data for contaminant-particle interactions in aqueous s ystems are essential for the development of effective environmental ma nagement models. Work on the partitioning behaviour of organic contami nants has been focused on compounds selected from the UK Red List, i.e . atrazine and gamma-hexachlorocyclohexane in estuarine waters. Partic ular emphasis has been placed on evaluating the importance of pesticid e binding to naturally occurring colloids. The influence of physicoche mical parameters such as salinity and suspended solids' concentration on contaminant partitioning behaviour has also been established. Data on the association of specific priority organic contaminants with filt erable organic macromolecules or colloids are discussed.