All pesticides are poisonous substances to living organisms, including man, and the use and application of pesticides requires measures of strict control in order to protect man and its living resources from deleterious effects. Information exists for aquatic organisms on lethal concentrations in the water (of. review by Duursma and Marchand, 1974). The lethal dosage of pesticides to man is normally related to the lethal dosage by oral intake for rats or mice. Data about these dosages are supplied by the pesticide producing company or health organizations.
These values can be used as a measure for the evaluation of the hazards to man by consumption of fish which contains a certain level of pesticide residue concentration. Two examples are presented which are applicable for the situation in Indonesia.
Example 1: Application of Diazinon in ponds
The oral toxicity for mice is between 73–160 mg of Diazinon/kg bodyweight according to the information given by the pesticide-producing company. This figure might also be representative for man, but in order to be on the safe side, an arbitrary safety factor of ten can be used. This may take into account at the same time sublethal effects on which still little is known. The so-called critical path-way approach can be used as a method of evaluation which takes into consideration the path-way by which the highest amount of Diazinon can pass to man.
Since Diazinon is used for killing chironomid larvae in the ponds, prior to stocking the pond and during the culturing of Chanos, the critical path-way is the consumption of fish or shrimp by the local population. Our highest concentrations in the aquaria, found in shrimp and fish, have been 8 and 14 ppm per wet weight, respectively. Thus, the intake of Diazinon per kg shrimp or fish would be 8 and 14 mg, respectively.
Taking the lowest figure of the oral toxicity as a measure (73 mg/kg), then for mice per kg bodyweight, 9.1 kg shrimp and 5.2 kg fish would cause death. For man, taking the limit as 73 mg/kg bodyweight for the oral intake, a child of 30 kg weight, for example, should not eat more than 273 kg shrimp or 156 kg fish in a short period of a few days.
This is unlikely to be attained even for consumption ten times lower. Nevertheless fish harvested from ponds recently treated with Diazinon should not be used for consumption. A one month interval is recommended, since, as already said, little information exists at present on sublethal effects to man.
Example 2: DDT in marine fish
The main group of pesticides found in fish from tambaks and sea are the pesticides related to DDT, i.e.: DDT and its metabolites TDE, DDE, and DDMU. The levels of concentration were rarely above 1 ppm/wet weight, however some exceptions were found with concentrations up to about 1.5 ppm for total DDT (DDT plus its metabolites).
The hazards for the consumption of sea fish or fish from tambaks with such levels of DDT are negligible, since the oral toxicity of DDT is at the level of 200 mg/kg bodyweight. The limit per kg bodyweight, calculated identically as for the former example, would be a consumption of 100 kg fish containing 2 ppm of total DDT. For a man of 50 kg bodyweight this means that the limit of consumption (in a short period) is 5 000 kg of fish. Even with a safety factor of 10, there is no danger for fish consumption in Indonesia.
The use of pesticides in tambaks for eradiacation of pests has to be carefully planned, since tambaks are enclosed units where in spite of some water exchange with the sea, pesticide residues can build up in the sediments. At present the situation for the Indonesian tambaks does not require any measure of control, but as was demonstrated in our experimental ponds in Jepara, a persistent pesticide such as BHC can build up in the soil to high concentrations. Non-persistent pesticides should be used if required for eradication of pests.
Concerning the still frequent use of DDT in Indonesia for the malaria control programme, attention should be drawn to avoid contamination of fish ponds. Since 1963 about 24 000 tonnes of DDT have been imported from which 75% was used for the malaria control programme (Personal communication from Dr. J. Verdrager, WHO, Jakarta) and for 1975/6 an additional 3 400 tonnes will arrive.
Our results have already shown that incidentally recent DDT contaminations occurred in fish, which could be noticed from a high DDT/total DDT ratio. For tambaks with their limited exchange of water, large-scale DDT spraying should be avoided in their direct neighbourhood. This requires coordination between the local and central fishery officials with the responsable bodies for the malaria control programme.
