Degradation trichloroethane

An index is included at the end of the book which lists potential sources or origins for the contaminant of concern of interest. The index also includes compounds for which degradation products are known, e.g., the presence of 1,1-dichloroethane at a site may be indicative of a release containing 1,1,1-trichloroethane (where 1,1-dichloroethane is present as an impnrity) or it may be a degradation product of 1,1,1-trichloroethane. Therefore, under the 1,1-dichloroethane entry, the reader is directed to the chemical profile 1,1,1-trichloroethane. Moreover, the index inclndes compounds which occur as additives to various products, e.g., acrolein nsually contains hydroqninone to prevent polymerization. Many commercial prodncts released into the enviromnent may contain other compounds present as impurities, e.g., 1,4-dioxane may contain the impurities acetic acid, 2-methyl-1,3-dioxolane, and bis(2-chloroethyl) ether. 

In a model aquatic ecosystem, methoxychlor degraded to ethanol, dihydroxy ethane, dihy-droxyethylene, and unidentified polar metabolites (Metcalf et al, 1971). Kapoor et al. (1970) also studied the biodegradation of methoxychlor in a model ecosystem containing snails, plankton, mosquito larvae, Daphnia magna, and mosquito fish Gambusia affinis). The following metabolites were identified 2-(/5-methoxyphenyl)-2-(p-hydroxyphenyl)-l,l,l-trichloroethane, 2,2-bis (p-hydroxyphenyl) -1,1,1 -trichloroethane, 2,2-bis (p-hydroxyphenyl) -1,1,1 -trichloroethylene,... 

Biological. Monodechlorination by microbes under laboratory conditions produced 1,1,2-trichloroethane (Smith and Dragun, 1984). In a static-culture-flask screening test, 1,1,2,2-tetrachloroethane (5 and 10 mg/L) was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum. No significant degradation was observed after 28 d of incubation (Tabak et al., 1981). 

A methanogenic consortium derived from municipal anaerobic digester sludge was placed into a reactor containing 1,1,1-trichloroethane. The reactor was operated at 20 °C on an average 50-d hydraulic retention time. Degradation followed first-order kinetics and reported rate coefficients for filtered and unfiltered supernatant from the settled consortium were 0.11 and 0.12/day, respectively. 1,1-Dichloroethane was the only product detected which accounted for 46% of the initial 1,1,1-trichloroethane concentration (Gander et al, 2002). 

Chen et al. (1999) studied the anaerobic transformation of 1,1,1-trichloroethane, 1,1-dichloroethane, and choroethane in a lab-scale, municipal wastewater sludge digester. 1,1,1-Trichloroethane degraded via reductive dechlorination to give 1,1-dichloroethane, chloroethane, and then ethane. When cell-free extracts were used, 1,1,1-trichloroethane degraded to acetic acid (90% yield) and 1,1-dichloroethylene, the latter degrading to ethylene. 

Groundwater. Under aerobic conditions, 1,1,1-trichloroethane slowly degraded to 1,1-dichloroethane (Parsons and Lage, 1985 Parson et al, 1985). Based on a study conducted by Bouwer and McCarty (1984), the estimated half-life of 1,1,1-trichloroethane in groundwater three months after injection was 200-300 d. 

Trichloroethane Degradation temperatnre Glass transition temperatnre(s) Thermogravimetric analysis Tetrahydrofnran Trintrobenzene Trinitrotolnene... 

Hydrolysis is important in the transformation of 1,1,1-trichloroethane (1,1,1 -TCA) to acetic acid [27]. Hydrolysis is also one of the steps in the reaction pathway for degradation of the pesticide dichloro-diphenyl-trichloroethane (DDT) [21]. 

Much effort has been concentrated on the fate of chlorinated aliphatic hydrocarbons in aquifers (e.g., trichloroethylene, dichloroethylene). These chemicals undergo reductive dehalogenation under anaerobic conditions. By contrast, these compounds are degraded under aerobic conditions by methane-utilizing bacteria. For example, methan-otrophic bacteria can transform more than 50% of trichloroethane into CO2 and bacterial biomass. 

Data from landfill sites with a documented contamination history were examined by Cline and Viste (1984). They observed that 1,1-dichloroethane was detected in groundwater at sites where the compound had not been handled or disposed of and concluded that 1,1-dichloroethane had been produced by anaerobic degradation of other compounds present, particularly 1,1,1 -trichloroethane. 

Trichloroethane tends to be stable in the atmosphere and is transported considerable distances. The rate of degradation is increased by the presence of chlorine radicals and nitrogen oxides. In water, its primary loss is by evaporation into the atmosphere. At a vapor pressure of 23mmHg at 25°C, 1,1,2-trichloroethane is expected to exist almost entirely in the vapor phase in the ambient atmosphere. It will gradually degrade by reaction with photohemically produced hydroxyl radicals. 

Trichloroethane may very slowly undergo abiotic degradation in soil or water by elimination of hydrochloric acid (HCl) to form 1,1-dichloroethene, which also can be considered a pollutant, or it can undergo hydrolysis to form the naturally occurring acetic acid. Direct photochemical degradation is not expected to be an important fate process. 

The dominant atmospheric fate process for 1,1,1-trichloroethane is predicted to be degradation by interaction with photochemically-produced hydroxyl radicals. Earlier experimental rate constants for this gas-phase reaction ranged from 2.8x1 O to 1.06x10 cm /mol-sec (20-30 °C) (Butler et al. 

Direct photochemical degradation of 1,1,1-trichloroethane in the troposphere is not expected to be an important fate process, because there is no chromophore for absorption of ultraviolet light (>290 nm) found in sunlight at tropospheric altitudes (Hubrich and Stuhl 1980 VanLaethem-Meuree et al. 1979). A laboratory experiment performed in sealed Pyrex ampules showed loss of 1,1,1-trichloroethane in 2 weeks under the influence of sunlight however, catalysis by the Pyrex surface was probably responsible for the enhanced reactivity (Buchardt and Manscher 1978). 

---