Distribution of DDT residues in fish from the Songkhla Lake, Thailand

Abstract

Since the early 1950s DDT has been extensively used in Thailand as a malaria repellent and as an agricultural pesticide, but was finally banned in 1994. In this study concentrations of p,p′-DDT, p,p′-DDE, and p,p′-DDD in 113 fish of four species ( Scatophagus argus, Protosus canius, Channa striata and Zonichthys nigrofasciata) are reported from the large, brackish Songkhla Lake and the Gulf of Thailand. The mean ΣDDT concentrations at different locations in the analysed fish species ranged from 33 to 170 ng/g lipid wt. (0.086–7.7 ng/g fresh wt.). This is well below the recommended maximum residue levels in aquatic animals used for human consumption (5000 ng/g fresh wt.) in Thailand. The comparatively low residue levels could be due to the high temperature and solar radiation in the region, which may result in a high volatilising and degradation rate of DDT. Also, the high productivity of the lake could result in a dilution effect, when DDT is distributed in a large amount of organic matter, followed by a high biological degradation of the substance.