Distribution Of 14c_DDT on Model Ecosystem Simulating Tropical Marine Environment

Abstract

The distribution of the insecticide l , l, l-trichloro-2,2'-( 4-chlorophenyl)ethane (p,p'-DDT) was monitored in a model aquarium simulating a tropical marine ecosystem comprising oysters, seawater and sediments. The water was spiked with known amounts of 14C_DDT and uniformly stirred to maintain equilibrium. Samples of seawater, sediment and oyster were thereafter withdrawn at various time intervals for a period of one month, and the concentration of free (unbound) 14C_ DOT residues determined using a liquid scintillation counter (LSC) after soxhlet extraction and clean-up. Sediment-bound residues were combusted in a biological material oxidizer (BMO) and the 14C02 liberated trapped in a specific absorbing medium prior to analysis. Concentrations of 14C_DDT residues were found to decline in the water very rapidly within 24 hours and reached less than 10% of the initial level after three days. The oysters accumulated the 14C_DDT at a very fast rate, reaching a maximum level in 24 hours, (with bioconcentration factors as

high as 19,273), before gradually declining. There was a steady build-up of 14C_DDT residues in the sediments during the first 24 hours, with the unbound form accounting for over 95% of the total at

any given time. This fraction was located mainly in the top (one centimetre) layer. The analysis of DOT metabolites using combined thin layer chromatography-Liquid scintillation counting and gas chromatography with electron capture detection gave low concentrations of p,p'-DDE, o,p'-DDT and p,p'-DDD in all samples, indicating a low degradation rate of the spiked pesticide. Determination of the mass balance for the total 14C_DDTadded to the aquarium gave experimental recovery of68.5% at 22°C and 75.8% at 27°C. Results show that the 14C_DDT distributes itself fairly widely in the marine environment with most of it being absorbed by marine organisms and sediments.