The pesticide pollution in a tropical country like Indonesia in the marine and brackish water environment showed mainly a constant background of the pesticide DDT and its metabolites both in fish and sediments, with variations which are probably due to the use of DDT by the malaria control programme. Other pesticides like Dieldrin and Endrin, arriving from old stocks (these pesticides are now forbidden) occurred only in a few marine sediment samples in Sumatra (Medan) and Jakarta, but at low concentrations. In the marine samples from Surabaya, additionally to DDT also the herbicide 2,4 D-isopropyl ester was found. Pesticide residues from those being applied in fish oulture were mainly found in the samples from tambaks, such as BHC and Thiodan.
In general, the observed levels are not higher than those found in other areas of the world, in spite of the continuing application of DDT. As it is discussed in section 7.1, the levels are of no direct concern to the fisheries, but spraying of DDT with the malaria control programme should be avoided close to tambak areas.
The investigations carried out to simplify the methods for pesticide analysis have so far been successful so that these simplified methods can now be applied. Some differences in result could be observed with those obtained with more sophisticated methods such as the Soxhlet extraction. These differences were dependent on the kind of pesticides, but as a whole the rapid simple methods have the advantage of carrying out a quick pre-investigation, upon which it can be decided whether a more time consuming, and organic solvent consuming extraction has to be carried out.
Our bioassay tests with Diazinon and Leptophos showed some very interesting facts on the metabolic processes of pesticide uptake and loss of aquatic organisms. It seems that at sublethal concentrations the organisms are able to actively regulate their pesticide content, where uptake and loss balance each other. At lethal exposure this regulating system seems to be hampered.
Some high DDT concentrations found in fish, killed by Thiodan (Endosulfan), are probably caused by the same phenomenon (Fig.5). This also implies that for DDT the accumulation is equally quick, and that for residue levels found in fish, one might suppose that an equilibrium exists with the environment rather than that the accumulation is caused by a long period of pollution. In relation to this phenomenon cumulative effects might also be envisaged, where pesticide accumulation might be affected by pollution with other compounds. This would for example be true for PCB's, since PCB was found together with DDT in high amounts in the one of the large milkfish which was analysed.
Since PCB's are rarely found, this indicates that the industrial pollution is not so widely spread as in the seas of the northern hemisphere bordering the industrial countries. Whether tropical conditions are also of influence, for example because of a stronger evaporation of PCB's, than in colder climates, is difficult to say.
