1,1-Dimethylhydrazine (also known as unsymmetrical dimethyl hydrazine, UDMH) is a commonly used rocket fuel. In some locations, such as the surroundings of the Baikonur Cosmodrome in Kazakhstan, extensive pollution by 1,1-dimethylhydrazine has occurred, mainly from the early stages of rockets falling back to earth. The Baikonur Cosmodrome was constructed in the Soviet era, and has been used for numerous rocket launches since, including the first manned spaceflight by Yuri Gargarin in 1961.
For each launch, about 0.6 to 4 tons of unburnt early stage fuel is released; it is estimated that 10-30 kg of this reaches the ground. The falling fuel is spread over a wide area, thus making remedial measures difficult. Crashed rockets can give rise to even greater pollution. An unmanned rocket that crashed immediately after launch in 2013 is estimated to have carried 600 tons of fuel. Some Kazakhs have called for the suspension of launches from the Baikonur site.
1,1-Dimethylhydrazine is a corrosive and irritating volatile liquid. It is a toxic compound, so the amounts present in the environment should be carefully monitored. Long term exposure can cause liver damage in humans. Tests have shown that 1,1-dimethylhydrazine is an animal carcinogen, and it is considered possibly carcinogenic to humans on that basis.
Although 1,1-dimethylhydrazine can undergo microbial degradation, it can persist for many years when deposit in dry soils through atmospheric deposition.
A study on the degradation of 1,1-dimethylhydrazine
A 2008 study by Carlsen et al investigated the degradation of 1,1-dimethylhydrazine in the vicinity of the Baikonur Cosmodrome. A large number of transformation products were detected by headspace GC from environmental samples. These included simple degradation products such as ammonia, dimethylamine and N-nitrosodimethylamine (a known carcinogen), along with more unexpected cyclic products, such as methyl triazoles.
It is conceivable that some of the products detected, such as trimethylhydrazine and tetramethylhydrazine, may have been impurities in the 1,1-dimethylhydrazine. However, the authors of the paper do not mention this possibility.
Quantitative structure-activity relationships (QSAR) and quantitative structure-toxicity relationships (QSTR) were used to model the properties of the 1,1-dimethylhydrazine and its various transformation products. Calculations were carried out using the EPI suite software from the EPA. Various properties, such as the octanol water partition coefficient, log Kow and vapour pressure, were calculated for these compounds. These values were compared with experimental values where the latter were available.
It was calculated that the transformation compounds were significantly soluble in water, possessing a large migration potential, but were readily biodegraded once in solution. However, the situation on land is less clear cut. As most of the compounds are basic, they may bind strongly to some minerals. Also, the sterilizing effect of the 1,1-dimethylhydrazine may inhibit terrestrial degradation by microbes.
None of the compounds were bioaccumulating, since they were all relatively polar (log Kow <1). In general, bioaccumulation tends to occur with much less polar compounds, examples being DDT, polychlorinated biphenyls (PCBs), methylmercury, etc.
The half-lives of the various compounds in the aquatic environment were calculated using the software. The expected toxicity of the compounds to aquatic organisms (daphnia, green algae, and fish) were also calculated.
The authors commented that certain transformation compounds of concern, due to their high toxicity to aquatic organisms and relatively slow degradation, should be further investigated.
These compounds were trimethylhydrazine, tetramethylhydrazine, 1-formyl-2,2-dimethylhydrazine, and the hydrazones of 1,1-dimethylhydrazine with formaldehyde and acetaldehyde. The other transformation compounds were considered to pose a lesser threat to the environment.
The study of 1,1-dimethylhydrazine shows that it is not only the toxicity of the initial pollutant that needs to be considered when dealing with chemical pollutants. Various transformation products may also be toxic, so their concentrations and fate also need to be considered. QSAR and QSTR calculations can aid the investigation of these transformation products. Such modelling enables researchers to focus on the compounds of greatest concern.
EPA, Air Toxics Website: 1,1-Dimethylhydrazine. http://www3.epa.gov/airtoxics/hlthef/dimethyl.html
Carlsen, L. et al., ‘A QSAR/QSTR Study on the Environmental Health Impact by the Rocket Fuel 1,1-Dimethyl Hydrazine and its Transformation Products’, Environmental Health Insights, 2008, vol.1, 11-20. See http://www.researchgate.net/publication/275019848_A_QSARQSTR_Study_on_the_Environmental_Health_Impact_by_the_Rocket_Fuel_11-Dimethyl_Hydrazine_and_its_Transformation_Products
Bodner, M, ‘Toxic Russian Fuel Target of Kazakh Anger’, The Moscow Times, Jan 24th 2014. http://www.themoscowtimes.com/news/article/toxic-russian-rocket-fuel-target-of-kazakh-anger/493275.html