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Studies on the bioavailability of contaminants that accumulate in sediments have been complicated by the chemical and structural variability of substrates and by the different biological properties of test organisms that are used by regulators. The purpose of this work was to overcome some of these difficulties by devising a test system that used artificial particles with known chemical surfaces. These were coated with 2,4-dichlorophenol or pentachlorophenol and fed to oligochete worms (Lumbriculus variegatus) and midge larvae (Chironimus riparius). The adsorption coefficient (K d ) of the particle surface was compared with the concentration of contaminant accumulated by the test organisms. There were major differences in bioaccumulation between the two species used despite identical particles and pollutants. This clearly reflects differences in the uptake and detoxification pathways between species. The particle surface and its interaction with the chlorophenols was a major factor in the accumulation of the contaminants in an organism. The techniques that are described provide a way of standardizing results between different natural sediments and different test organisms and provide some insights into the processes involved in bioaccumulation from particle surfaces.

Abstract-Sediments may play an important role in the accumulation of contaminants by benthic organisms. This work uses artificial particles to model natural systems and to provide a way of predicting bioavailability from sediment/contaminant interactions. The artificial particles used were a range of high performance liquid chromatography resins and a dimethylditallow ammoniumexchanged clay. The bioavailability of 2,4-dichlorophenol on these particles to the midge larva Chironomus riparius was compared with that from sand and a natural sediment. The experiments were designed so that water uptake and accumulation due to the ingestion of particles could be distinguished. The results show that very strong or very weak electrostatic interactions of the contaminant with the particles results in little accumulation of the contaminant via ingestion. When the contaminant is weakly bound to the particles by van der Waals forces, the contaminant can be released from the ingested particles. In these experiments, this occurred when the contaminant-particle interaction was hydrophobic, and it is under these conditions that 2,4-dichlorophenol was most bioavailable.