Accumulation, distribution and metabolism of ring labelled, "C-1,1,1, - trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT) in a model marine aquatic ecosystem consisting of sea water, sediment, oysters (Isognomonon alatus) and Humbug fish (Dascillus aruanus) were studied in the laboratory. "C-p,p'-DDT distributes rapidly in the ecosystem immediately after application on the water surface with reduction of its concentration in the water phase from 1.18 ng g"1 to 0.71 ng g'after 2 hours and an increase in its content in the sediment and oysters. The bioconcentration factor reached a maximum of 19x 10* in oysters, and 1657 in Humbug fish after 24 hours. The sediment concentration reached 117 ng g"1 after 168 hours from start of application. A peak bioconcentration factor of 111 x 103 was calculated after 120 hours when 0.24 mg kg"1 of '^>p,p'-DDT was maintained through dosing every 24 hours with 0.002 mg kg' of a mixture of labelled and non-labelled pesticide. The rate of depuration of accumulated "C-p,p'-DDT sediment residues was up to 78.3% after 24 hours while oysters lost only 14.0% during the same period. The loss in Humbug fish was only 22.2% in three days. Volatilisation and sorption losses from seawater alone (without sediment/biota) were found to be very high in the range of 73.8 - 91.5% over 24 h for p,p'-DDT in aerated and non-aerated ecosystem. Gas chromatograph and TLC analysis of water, sediment and oyster samples revealed presence of p,p'-DDT and substantial amounts of p,p'-DDE and p,p'-DDD three days after pesticide dosage.