Speciation and partitioning of priority organic contaminants in estuarine waters

The main parameters influencing the speciation and partitioning of priority organic contaminants in estuaries are discussed with particular consideration being given to the association of contaminants with colloidal material. Partitioning and speciation are factors that influence the persistence, transport, bioavailability and toxicity of organic contaminants in natural waters. However, most data on aquatic partitioning processes are based on the extrapolation of soil data and there is a need for more information on the partitioning of priority pollutants 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 differentiate between "dissolved" and particulate forms based on filtration. The concept and importance of solution phase speciation is well established for trace metals and it is generally accepted that for many 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 organic contaminants, i.e. association with particulates, colloidal material and macromolecular organics reduces bioavailability and toxicity. Physicochemical data for contaminant-particle interactions in aqueous systems are essential for the development of effective environmental management models. Work on the partitioning behaviour of organic contaminants has been focused on compounds selected from the UK Red List, i.e. atrazine and gamma-hexachlorocyclohexane in estuarine waters. Particular emphasis has been placed on evaluating the importance of pesticide binding to naturally occurring colloids. The influence of physicochemical 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 filterable organic macromolecules or colloids are discussed.