Gunda Reddy

Genotoxicity assessment of an energetic propellant compound, 3-nitro-1,2,4-triazol-5-one (NTO)

3-Nitro-1,2,4-triazol-5-one (NTO) is an energetic explosive proposed for use in weapon systems, to reduce the sensitivity of warheads. In order to develop toxicity data for safety assessment, we investigated the genotoxicity of NTO, using a battery of genotoxicity tests, which included the Ames test, Chinese Hamster Ovary (CHO) cell chromosome aberration test, L5178Y TK(+/-) mouse lymphoma mutagenesis test and rat micronucleus test. NTO was not mutagenic in the Ames test or in Escherichia coli (WP2uvrA). NTO did not induce chromosomal aberrations in CHO cells, with or without metabolic activation. In the L5178Y TK(+/-) mouse lymphoma mutagenesis test, all of the NTO-treated cultures had mutant frequencies that were similar to the average frequencies of solvent control-treated cultures, indicating a negative result. Confirmatory tests for the three in vitro tests also produced negative results. The potential in vivo clastogenicity and aneugenicity of NTO was evaluated using the rat peripheral blood micronucleus test. NTO was administered by oral gavage to male and female Sprague-Dawley rats for 14 days at doses up to 2g/kg/day. Flow cytometric analysis of peripheral blood demonstrated no significant induction of micronucleated reticulocytes relative to the vehicle control (PEG-200). These studies reveal that NTO was not genotoxic in either in vitro or in vivo tests and suggest a low risk of genetic hazards associated with exposure.

Assessing the non-cancer risk for RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) using physiologically based pharmacokinetic (PBPK) modeling.

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is an explosive used in military applications. It has been detected in ground water surrounding US military installations and at manufacturing facilities. RDX has been shown to produce hepatotoxicity, testicular, and neurological effects in animals, the latter also in humans. The current chronic oral reference dose (RfD) of 0.003 mg/kg/day was derived based on prostate effects in rats. Here, we provide a reevaluation of the risk associated with RDX exposure by examining old and new data and using physiologically based pharmacokinetic (PBPK) modeling approaches. Candidate non-cancer endpoints in rodents were evaluated and the most plausible mode(s) of action were determined. A PBPK model was used to derive appropriate internal doses based on the mode of action, and then a benchmark dose (BMD) and the lower confidence limit on the BMD (BMDL) were determined using these internal doses in animals. Uncertainty factors (UF) were applied to the animal BMDL or no-observed effect level and a human PBPK model was used to determine a human equivalent dose resulting in the candidate RfDs (cRfDs). A proposed chronic RfD of 0.07 mg/kg/day, based on multiple effects observed in rats, was selected from among the cRfDs.

Development of a Relative Source Contribution Factor for Drinking Water Criteria: The Case of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)

ABSTRACT The consideration of multiple or cumulative sources of exposure to a chemical is important for adequately protecting human health. This assessment demonstrates one way to consider multiple or cumulative sources through the development of a relative source contribution (RSC) factor for the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), using the Exposure Decision Tree approach (subtraction method) recommended by the U.S. Environmental Protection Agency. The RSC factor is used to ensure that the concentration of a chemical allowed by a regulatory criterion or multiple criteria, when combined with other identified sources of exposure common to the population of concern, will not result in unacceptable exposures. An exposure model was used to identify relevant potential sources for receptors. Potential exposure pathways include ingestion of soil, water, contaminated local crops and fish, and dermal contact with soil and water. These pathways are applicable only to areas that are in close proximity to current or former military bases where RDX may have been released into the environment. Given the physical/chemical properties and the available environmental occurrence data on RDX, there are adequate data to support a chemical-specific RSC factor for RDX of 50% for drinking water ingestion.

Oral Toxicity Evaluation of Thiodiglycol in Sprague-Dawley Rats

Thiodiglycol (TDG) is the main product of sulfur mustard hydrolysis and is an environmental contaminant. Subacute and subchronic oral toxicity studies with TDG were conducted in Sprague-Dawley rats. Neat TDG was administered by gavage at doses of 157, 313, 625, 1250, 2500, 5000, and 9999 mg/kg/d, 5 days per week, for 14 days. In the 14-day study, decreased body weight and food consumption were observed at 5000 mg/kg/d. In the 90-day study, rats received neat TDG at doses of 50, 500, or 5000 mg/kg/d for 5 days per week. A fourth group served as a sham control. Individual body weight and food consumption were measured weekly. At termination of the experiment, urine, blood, and tissue samples were collected. Rats displayed significant decreased body weight with no effect on food consumption following administration of TDG at 5000 mg/kg/d. Both male and female rats showed significant increased kidney weights at 5000 mg/kg/d. The organ to body weight ratios increased significantly for liver, kidneys, testes, and brain in males and adrenals in females for 5000 mg/kg/d. At all doses of TDG, hematological and clinical parameters and tissue histopathology remained unaltered. The no observed adverse effect level (NOAEL) for oral subchronic toxicity was 500 mg/kg/d. Benchmark dose (BMD) was derived from the decreased gain in body weight that was seen in male rats. A BMD based on a 10% decrease in body weight was 1704 mg/kg/d, and the lower confidence limit on the dose BMD, the BMDL, was 372 mg/kg/d.

Subchronic Oral Toxicity of Sodium Tungstate in Sprague-Dawley Rats

The subchronic toxicity of sodium tungstate dihydrate aqueous solution in male and female Sprague-Dawley rats was evaluated by daily oral gavage of 0, 10, 75, 125, or 200 mg/kg/d for 90 days. Measured parameters included food consumption, body weight measurements, hematology, clinical chemistry, and histopathological changes. There was a significant decrease in food consumption and body weight gain in males at 200 mg/kg/d from days 77 to 90; however, there was no effect in food consumption and body weights in females. There were no changes in the hematological and clinical parameters studied. Histopathological changes were seen in kidney of male and female and epididymis of male rats. Histopathological changes were observed in the kidneys of male and female rats dosed at 125 or 200 mg/k/d consisting of mild to severe cortical tubule basophilia in 2 high-dose groups. Histological changes in epididymides included intraluminal hypospermia with cell debris in the 200 mg/kg/d dosed male rats. Histopathological changes were observed in the glandular stomach including inflammation and metaplasia in the high-dose groups (125 or 200 mg/kg/d) of both sexes of rats. Based on histopathology effects seen in the kidneys, the lowest observable adverse effect level was 125 mg/kg/d and the no observable adverse effect level was 75 mg/kg/d in both sexes of rats for oral subchronic toxicity.

Toxicity Assessment of 4-Amino-2-Nitrotoluene

4-Amino-2-nitrotoluene (4A2NT; CAS 119-32-4) is a degradation product of 2,4-dinitrotoluene. The toxicity data on 4A2NT are limited. Therefore, we collected toxicity data from rats to assess environmental and human health effects from exposures. The approximate lethal dose for both sexes was 5000 mg/kg. A 14-day toxicity study in rats was conducted with 4A2NT in the feed at concentrations of 0, 125, 250, 500, 1000, and 2000 ppm. Based on a 14-day oral dose range toxicity study with 4A2NT in the feed, 2000 ppm was selected as highest concentration for a subsequent 90-day study. An oral 90-day subchronic toxicity study in rats was conducted with concentrations of 0, 500, 1000, or 2000 ppm of 4A2NT in the feed. The calculated consumed doses of 4A2NT in the feed were 0, 27, 52, or 115 mg/kg/d for males and 0, 32, 65, or 138 mg/kg/d for females. A no-observed adverse effect level could not be determined. The lowest observed adverse effect level was 27 mg/kg/d for males and 32 mg/kg/d for female rats based upon decreased body weight gain. The decreased body weight gain in male rats was the most sensitive adverse event observed in this study and was used to derive a benchmark dose (BMD). A BMD of 23.1 mg/kg/d and BMD with 10% effect level of 15.5 mg/kg/d were calculated for male rats, which were used to derive an oral reference dose (RfD). The human RfD of 1.26 μg/kg/d was derived using current United States Environmental Protection Agency guidelines.

Genotoxicity assessment of ethylenediamine dinitrate (EDDN) and diethylenetriamine trinitrate (DETN).

Ethylenediamine dinitrate (EDDN) and diethylenetriamine trinitrate (DETN) are relatively insensitive explosive compounds that are being explored as safe alternatives to other more sensitive compounds. When used in combination with other high explosives they are an improvement and may provide additional safety during storage and use. The genetic toxicity of these compounds was evaluated to predict the potential adverse human health effects from exposure by using a standard genetic toxicity test battery which included: a gene mutation test in bacteria (Ames), an in vitro Chinese Hamster Ovary (CHO) cell chromosome aberration test and an in vivo mouse micronucleus test. The results of the Ames test showed that EDDN increased the mean number of revertants per plate with strain TA100, without activation, at 5000μg/plate compared to the solvent control, which indicated a positive result. No positive results were observed with the other tester strains with or without activation in Salmonella typhimurium strains TA98, TA1535, TA1537, and Escherichia coli strain WP2 uvrA. DETN was negative for all Salmonella tester strains and E. coli up to 5000μg/plate both with and without metabolic activation. The CHO cell chromosome aberration assay was performed using EDDN and DETN at concentrations up to 5000μg/mL. The results indicate that these compounds did not induce structural chromosomal aberrations at all tested concentrations in CHO cells, with or without metabolic activation. EDDN and DETN, when tested in vivo in the CD-1 mouse at doses up to 2000mg/kg, did not induce any significant increase in the number of micronuclei in bone marrow erythrocytes. These studies demonstrate that EDDN is mutagenic in one strain of Salmonella (TA100) but was negative in other strains, for in vitro induction of chromosomal aberrations in CHO cells, and for micronuclei in the in vivo mouse micronucleus assay. DETN was not genotoxic in all in vitro and in vivo tests. These results show the in vitro and in vivo genotoxicity potential of these chemicals.