Comparison of the initial metabolic pathway of p,p'-DDT in carp [Cyprinus carpio] and tilapia [Oreochromis niloticus]

Carp Cyprinus carpio and tilapia Oreochromis niloticus injected p, p'-DDT (DDT) intraperi-tonealy were kept in a now-through aquarium systern (FAS) and in a closed aquarium system (CAS). The concentrations of DDT, p, p'-DDE (DDE), p, p'-DDD (DDD) and p, p'-DDT-OH in the whole body and in the CAS were determined by a combination of silica gel column chromato-graphy and GLC-ECD to investigate the initial metabolic pathway of DDT in both fishes. The DDT in both fishes kept in the FAS was rapidly cleared with an experimental time. A rate constant of the clearance was roughly estimated according to first order reaction at 4.2×10-2/day for the carp and 2.4×10-2/day for the tilapia. The metabolite of DDT detected in the carp was only DDE (31% of the original DDT on an average of two fishes, at 7 days after injection and 47% at 35 days, the end of the experiment). In the tilapia, slight increases of DDE and DDD were observed. DDE and DDD injected intraperitonealy into tilapia resulted in no change. In the CAS including the fish and rearing water, about 25% of the DDT injected was meta-bolized to DDE and 73% of the original DDT remained in the carp. On the other hand, about 1% and 7% of the DDT injected was metabolized to DDE and DDD, respectively, and 89% of the DDT remained in the tilapia. These results, together with the previous findings (N. Uchida, T. Musashi, H. Katuura, H. Anzai, and E. Nishide: Nippon Suisan Gakkaishi, 54, 129-133 (1988)), suggest that the carp had only one initial metabolic pathway converting from DDT to DDE and that the tilapia had two pathways which were converting very slowly from DDT to DDE and DDD.