Acute and chronic toxicity of hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) in deer mice (Peromyscus maniculatus)

Date

2007-08

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Publisher

Texas Tech University

Abstract

Contamination of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been identified at areas of explosive manufacturing, processing, storage, and usage in a variety of environmental media. Conversion of RDX to anaerobic N-nitroso metabolites (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX)) has been demonstrated in the environment and in vivo, in the gastrointestinal tract of mammals. Thus, potential exists for human and wildlife exposure to these N-nitroso compounds. Few papers report acute or chronic toxicity of these N-nitroso metabolites, thus my research is to assess acute and chronic toxicity of these compounds. Acute toxicity was assessed using acute oral median lethal dose (LD50). This was determined in deer mice (Peromyscus maniculatus) of three age classifications (21 d, 50 d, and 200 d) for RDX, MNX, and TNX using the U.S. EPA Up-and-Down Procedure (UDP). Hexahydro-1,3,5-trinitro-1,3,5-triazine and N-nitroso metabolites caused similar overt signs of toxicity. Median lethal dose for 21 d deer mice were 136, 181, and 338 mg/kg for RDX, MNX, and TNX respectively. Median lethal dose for 50 d deer mice were 319, 575, and 999 mg/kg for RDX, MNX, and TNX respectively. Median lethal dose for 200 d deer mice were 158, 542, and 338 mg/kg for RDX, MNX, and TNX respectively. These data suggest that RDX is the most potent compound tested, and age dependent toxicity may exist for all compounds. Chronic toxicity was evaluated with a reproductive study and a multigenerational study. Following exposure, reproductive toxicity of TNX was evaluated in three consecutive cohorts (F1A-C) of deer mice. TNX was administered ad libitum via drinking water at four exposure levels-control (0 µg/L), 1µg/L, 10 µg/L, and 100 µg/L. Endpoints investigated include: reproductive success, offspring survival, offspring weight gain, offspring organ weights, and liver TNX residues. Data from this study indicate that TNX bioaccumulates in the liver and is associated with postpartum mortality, dose dependent decrease in body weight from birth to weaning, and decrease in kidney weight in deer mice offspring. While exposed to TNX via drinking water ad libitum, deer mice were bred in a multigenerational fashion (parents produced offspring, which bred to produce more offspring) to produce three generations F1A-D, F2A-B, and F3A. TNX was administered at four exposure levels-control (0 µg/L), 10 µg/L, 100 µg/L, and 1 mg/L. Endpoints investigated include: reproductive success, offspring survival, offspring weight gain, and offspring organ weights. Data from this study indicate that TNX is associated with decreased litter size and increased postpartum mortality of offspring. Brain weights demonstrated a generational increase in dosed mice euthanized near the time of puberty. No teratogenic effects were linked with exposure to TNX.
With tissue samples from both the reproductive and multigenerational studies, 12 microsatellite DNA loci were amplified and analyzed using both change in original parent allele frequencies and the parent/offspring approach of direct mutation rate calculation to assess genotoxicty of TNX in vivo. Findings demonstrate no dose dependent differences in deviation from parent microsatellite DNA allele frequencies or direct microsatellite mutation rate using the parent/offspring approach.

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