The objectives of the present study were to examine the toxicological effects of 2,4,6-trinitrotoluene on the hepatic ethoxyresorufin-O-deethylase activity and some haematological variables, in rainbow trout (Oncorhynchus mykiss). This study was a first attempt to identify possible biomarkers for forthcoming fish monitoring studies close to ammunition dumping sites at sea and in lakes. The fish were divided into four groups; one received an intraperitoneal injection of peanut oil only (control), while the other three groups were injected with peanut oil and 100, 200 or 400 mg 2,4,6-trinitrotoluene (kg b.w.)−1, respectively. The fish groups were kept in continuously flowing, aerated, and filtered fresh water at a temperature of 12°C for three days. Blood collected from caudal vessels was analysed for haematocrit, haemoglobin, methaemoglobin and different white blood cell number, and the blood plasma was analysed for 2,4,6-Trinitrotoluene and its metabolites by gas chromatograph and mass spectrometer. The microsomal fraction of the liver was analysed for ethoxyresorufin-O-deethylase activity. All fish groups treated with 2,4,6-trinitrotoluene had a significantly increased methaemoglobin concentration compared to the control group. The leukocytes count was increased in rainbow trout treated with the highest dose (400 mg 2,4,6-trinitrotoluene (kg b.w.)−1), and the ethoxyresorufin-O-deethylase activity was significantly inhibited in fish treated with the two highest doses (200 and 400 mg 2,4,6-trinitrotoluene (kg b.w.)−1. Chemical analysis by gas chromatograph and mass spectrometer revealed the presence of 2,4,6-trinitrotoluene in a pooled plasma sample of fish treated with the highest dose. The present study suggests that chemical analysis of 2,4,6-trinitrotoluene in blood plasma may be suitable as a direct confirmation of exposure to this compound, while increased methaemoglobin levels may be a promising aid as a general biomarker in field monitoring of possible exposure in fish caught close to ammunition dumping sites.

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