Bioreactor strategies for the treatment of growth-inhibitory waste: an analysis of thiodiglycol degradation, the main hydrolysis product of sulfur mustard

Toxicity Assessment of Thiodiglycol

Sulfur mustard (HD) undergoes hydrolysis to form various products such as thiodiglycol (TG) in biological and environmental systems. TG is a precursor in the production of HD and it is also considered as a “Schedule 2” compound (dual-use chemicals with low to moderate commercial use and high-risk precursors). Several toxicological studies on TG were conducted to assess environmental and health effects. The oral LD50 values were >5000 mg/kg in rats. It was a mild skin and moderate ocular irritant and was not a skin sensitizer in animals. It was not mutagenic in Ames Salmonella, Escherichia coli, mouse lymphoma, and in vivo mouse micronucleus assays, but it induced chromosomal aberrations in Chinese hamster ovarian (CHO) cells. A 90-day oral subchronic toxicity study with neat TG at doses of 0, 50, 500, and 5000 mg/kg/day (5 days/week) in Sprague-Dawley rats results show that there are no treatment-related changes in food consumption, hematology, and clinical chemistry in rats of either sex. The body weights of both sexes were significantly lower than controls at 5000 mg/kg/day. Significant changes were also noted in both sexes in absolute weights of kidneys, kidney to body weight ratios, and kidney to brain weight ratios, in the high-dose group. The no-observed-adverse-effect level (NOAEL) for oral toxicity was 500 mg/kg/day. The developmental toxicity conducted at 0, 430, 1290, and 3870 mg/kg by oral gavage showed maternal toxicity in dams receiving 3870 mg/kg. TG was not a developmental toxicant. The NOAEL for the developmental toxicity in rats was 1290 mg/kg. The provisional oral reference dose (RfD) of 0.4 mg/kg/day was calculated for health risk assessments. The fate of TG in the environment and soil showed biological formation of thiodiglycalic acid with formation of an intermediate ((2-hydroxyethyl)thio)acetic acid. It was slowly biodegraded under anaerobic conditions. It was not toxic to bluegill sunfish at 1000 mg/L and its metabolism and environmental and biochemical effects are summarized.

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.

Microbial responses to mustard gas dumped in the Baltic Sea

Microbiological studies were carried out on chemical weapon dump sites in the Baltic Sea. The effect of mustard gas hydrolysis products (MGHPs) on marine microbiota and the ability of microorganisms to degrade MGHPs were studied. Many stations at the dump sites demonstrated reduced microbial diversity, and increased growth of species able to use mustard gas hydrolysis products as sole source of carbon. Significant amounts of MGHP-degrading bacteria were revealed in the near-bottom water. The MGHP-degrading microorganisms identified as Achromobacter sp., Pseudomonas sp., and Arthrobacter sp. were isolated. These microorganisms were capable of utilizing the major product of hydrolysis, thiodiglycol, as the sole source of carbon and energy. The bacteria were capable of metabolizing MGHPs at a low temperature. The metabolic pathway for thiodiglycol degradation was proposed. The results suggest the potential for MGHPs biodegradation by naturally occurring populations of near-bottom-water and sediment microorganisms.

Soil bacteriumPseudomonas sp.: destroyer of mustard gas hydrolysis products

A bacterial culture capable of utilizing products of mustard gas hydrolysis as a source of carbon was isolated from soil. This culture was tolerant to organochlorine substances in the hydrolysate. The bacterium was identified as Pseudomonas sp. The bacterium utilizes the major product of mustard gas hydrolysis, thiodiglycol, through two pathways. One involves the oxidation of the primary alcoholic groups in thiodiglycol, yielding thiodiglycolic and thioglycolic acids. The cleavage of the C-S bonds in these acids gives rise to acetate, which is then used further in the cell metabolism. The other pathway involves the cleavage of the C-S bond in the thiodiglycol molecule, yielding beta-mercaptoethanol, which is transformed by Pseudomonas sp. into thioglycolic acid. The results show the promise of this bacterium for the bioremediation of mustard gas-contaminated soils.

Drip-feed bioreactor for the treatment of concentrated wastes with minimal dilution

Avoiding substrate inhibition is a significant challenge in designing biological treatment systems for concentrated or toxic wastes. Substrate inhibition is commonly avoided by diluting the waste before treatment, however, dilution of a waste before treatment is not always feasible. In the case of radioactive mixed wastes and chemical warfare materiel (CWM), dilution presents regulatory and safety concerns. In this study, we investigated a "drip-feed" reactor configuration as an alternative approach for the biological treatment of concentrated waste streams with minimal dilution and complete containment. In the drip-feed reactor undiluted waste is slowly fed to biomass in a reactor at a rate sufficient to maintain activity, but at a low enough rate so that bacterial degradation maintains the reactor concentration below the toxic threshold. The reactor has no effluent, but rather fills as the undiluted waste is fed to the reactor, which has the advantage of preventing the release of hazardous material into the environment during treatment. Volatile releases are prevented with the use of condensers. The drip-feed bioreactor configuration was tested under aerobic conditions, at 25 degrees C, using a 10% acetonitrile feed solution. The treatment of acetonitrile to less than 0.1 mg l(-1) was achieved with a dilution factor of only 3.4. The acetonitrile degradation reaction was pH sensitive, where the optimal pH range for the biodegradation process was approximately between 6.5 and 7.1 and the biodegradation rate declined precipitously above pH 7.2. The applicability of the drip-feed reactor configuration to the treatment of mixed wastes and CWM is discussed.

Modeling of the biotransformation of crotonobetaine into L-(-)-carnitine by Escherichia coli strains

A simple unstructured model, which includes carbon source as the limiting and essential substrate and oxygen as an enhancing substrate for cell growth, has been implemented to depict cell population evolution of two Escherichia coli strains and the expression of their trimethylammonium metabolism in batch and continuous reactors. Although the model is applied to represent the trans-crotonobetaine to L-(-)-carnitine biotransformation, it is also useful for understanding the complete metabolic flow of trimethylammonium compounds in E. coli. Cell growth and biotransformation were studied in both anaerobic and aerobic conditions. For this reason we derived equations to modify the specific growth rate, mu, and the cell yield on the carbon source (glycerol), Y(xg), as oxygen increased the rate of growth. Inhibition functions representing an excess of the glycerol and oxygen were included to depict cell evolution during extreme conditions. As a result, the model fitted experimental data for various growth conditions, including different carbon source concentrations, initial oxygen levels, and the existence of a certain degree of cell death. Moreover, the production of enzymes involved within the E. coli trimethylammonium metabolism and related to trans-crotonobetaine biotransformation was also modeled as a function of both the cell and oxygen concentrations within the system. The model describes all the activities of the different enzymes within the transformed and wild strains, able to produce L-(-)-carnitine from trans-crotonobetaine under both anaerobic and aerobic conditions. Crotonobetaine reductase inhibition by either oxygen or the addition of fumarate as well as its non-reversible catalytic action was taken into consideration. The proposed model was useful for describing the whole set of variables under both growing and resting conditions. Both E. coli strains within membrane high-density reactors were well represented by the model as results matched the experimental data.

Observations of metabolite formation and variable yield in thiodiglycol biodegradation process : impact on reactor design

The complete microbial degradation of thiodiglycol (TDG), the primary hydrolysis product of sulfur mustard, by Alcaligenes xylosoxydans ssp. xylosoxydans (SH91) was accomplished in laboratory-scale stirredtank reactors. An Andrews substrate inhibition model was used to describe the cell growth. The yield factor was not constant, but a relationship with initial substrate concentration has been developed. Using a substrate-inhibition and variable-yield kinetic model, we can describe the cell growth and substrate consumption in batch and repeated batch fermentations. Several reactor-operating modes successfully degrade TDG concentration to below 0.5 g/L. According to the experimental results, the two-stage repeated batch operation has the best degradation efficiency, and it also can degrade 500 mM TDG (= 60 g/L) to 5 mM (= 0.7 g/L) in <5 d. A hypothesis for explaining variable-yield and byproduct formation based on the capacity and utilization of metabolic loads is presented.