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Environmental fate & pathways

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CTC is not persistent and gets transformed both biotically and abiotically at least in soils, sediments, anaerobic reactors and in the stratosphere, where it is significantly involved in ozone layer depletion.

A number of microorganisms facultatively dechlorinate CTC (eg. Egli et al 1988). A detailed review of biodegradability of chlorinated aliphatic compounds has been done by J. A. Field and R. Sierra-Alvarez and has been published by EuroChlor in 2004. With respect to CTC, this review reports several observations made under real environmental conditions such as landfills and in bioreactors. It is concluded that CTC is almost completely biodegraded under anaerobic conditions by co-metabolism.

 

Environmental distribution

CTC is likely to volatilize rapidly from soil. Adsorption of CTC to soil and sediment may occur to a small extent but CTC is likely to be mobile in such media. Willis et al 1994: “Carbon tetrachloride is introduced into water bodies either by direct input from man-made sources or by transfer from the atmosphere. The major removal process from water bodies is volatilisation to the atmosphere. Laboratory tests have suggested a volatilisation lifetime from water between 29 minutes and a few hours, depending on the degree of agitation (Dilling et al, 1975; Versar Inc., 1979). Zoeteman et al (1980) have calculated half-life values for carbon tetrachloride in rivers and lakes, and groundwaters of 0.3-3 days and 30-300 days respectively.”Willis et al 1994: “Anderson et al (1991) studied the loss of carbon tetrachloride from two different soil types, a silt loam (1.49% organic carbon) and a sandy loam (0.66% organic carbon). Carbon tetrachloride was applied to the soil (in a mixture with 14 other compounds) at a concentration of 100 mg/kg (dry weight) and the soil was incubated in the dark at 70°C for 7 days. The half-life for disappearance of carbon tetrachloride in both sterile and non-sterile systems was around 5 days, indicating that volatilisation was the likely removal process.” Willis et al 1994: “Jury et al (1984) predicted that carbon tetrachloride would have a volatilisation half-life of 0.2 days at a depth of 1 cm and 0.8 days at a depth of 10 cm in soil, assuming a uniform distribution of the chemical with depth”.

 

Terrestrial Fate

CTC is slightly removed during infiltration of river water into adjacent wells (Zoeteman 1980). However, CTC is expected to evaporate rapidly from soil due to its high vapour pressure and migrate into ground water due to its low soil adsorption coefficient. Based on the estimated aqueous aerobic biodegradation half-life of carbon tetrachloride, the half-life of CTC in soil is estimated to be 6–12 months (Howard. 1991).

 

Aquatic Fate

Evaporation of CTC from water is a significant removal process (half-life - minutes to hours). Based upon EPIWIN model, the estimated half-life in rivers is 1.2 hour; in lakes, 4.9 days. Biodegradation may be important under aerobic or anaerobic conditions, but the data are limited. Adsorption to sediment should not be an important process.

 

CTC dissolved in water does not photodegrade or oxidize in any measurable amounts (Howard. 1991). The rate of hydrolysis in water is extremely slow, with a calculated half-life of 7,000 years at a concentration of 1 ppm (Mabey and Mill 1978). The reported aqueous hydrolysis rate calculated from gas phase measurements was <2x10-6M-1s-1 (Haag and Yao 1992), 1–2 orders of magnitude less than other chlorinated alkanes. Others have suggested that hydrolysis may be the cause of decreasing CTC concentrations with depth in the ocean (Lovelock. 1973). However, this observation might also be explained by the biodegradation of carbon tetrachloride, which occurs much more rapidly than hydrolysis, particularly under anaerobic conditions. Biodegradation may occur within 16 days under anaerobic conditions (Tabak. 1981). Based upon acclimated aerobic screening test data, the aqueous aerobic half-life of CTC was estimated to be 6–12 months (Howard. 1991). Based upon unacclimated anaerobic screening test data and acclimated aerobic sediment/aquifer grab sample data, the aqueous anaerobic halflife of CTC was estimated to be 7–28 days (Howard. 1991). The carbon atom in CTC is in its most oxidized state, therefore it is much more likely to undergo reductive degradation, as opposed to oxidative degradation. A detailed discussion of degradation pathways can be found in Field & Sierra-Alvarez review, EuroChlor, 2004.

 

Atmospheric Fate

CTC is assessed to be very stable in the troposphere with long residence times. Its main loss mechanism is diffusion to the stratosphere where it undergoes some direct photolysis, while indirect photolysis is an even less relevant process. This is primarily because CTC does not react with hydroxyl radicals that initiate breakdown and transformation reactions of other volatile hydrocarbons. In addition, CTC does not photodissociate in the troposphere because, in the vapour state, it has no chromophores that absorb light in those visible or near ultraviolet regions of the electromagnetic spectrum, which prevail in the troposphere. Photo oxidation by hydroxyl radicals is thought to be so slow that its estimated tropospheric half-life exceeds 330 years according to Cox (1976).In view of the indirect photolysis by hydroxylation CTC is assessed inert. It is estimated that <1% of the CTC released to the air is partitioned into the oceans. Ultimately, CTC that is not removed from the troposphere by rainfall (Pearson and McConnell 1975) diffuses upward into the stratosphere where it may be photodegraded by shorter wavelength ultraviolet light (185–225 nm) more prevalent in this region of the atmosphere to form the trichloromethyl radical and chlorine atoms (Molina and Rowland 1974). The rate of photodissociation begins to become important at altitudes >20 km, and increases as altitude increases (Molina and Rowland 1974). Estimates of the atmospheric lifetime (the overall persistence of CTC in the troposphere and the stratosphere combined) are variable, with the most recently refined value being 34 +/- 5 years (Allen et al., 2009). Chlorine atoms and other chlorine species formed by photodecomposition of CTC in the stratosphere can catalyze reactions that destroy ozone. As the manufacture of chlorofluorocarbons from CTC is phased out according to an international agreement, the impact of CTC on atmospheric ozone is likely to decrease.

References of this section (other references can be located in IUCLID file):

Allen NDC, Bernath PF, Boone CD, Chipperfield MP, Fu D, Manney GL, Toon GC, Weisenstein KD (2009) Global carbon tetrachloride distributions obtained from the Atmospheric Chemistry Experiment (ACE), Atmos. Chem. Phys. Discuss., 9, 13299-13325, doi:10.5194/acpd-9-13299-2009, 2009

Anderson T A, Beauchamp JJ, Wilson BT (1991) Organic chemicals in the environment. Fate of volatile and semivolatile organic chemicals in soils: Abiotic versus biotic losses - J Environ Qual 20:420-4

Cox RA, Derwent-RG, Eggleton AEJ and Lovelock JE (1976) Photochemical oxidation of halocarbons in the troposphere, Atmos-Environ 10 305-308

Dilling WL,, Kallos GJ (1975) Evaporation rates and reactivities of methylene chloride, chloroform, l,l,l-trichloroethane, trichloroethylene, tetrachloroethylene and other chlorinated compounds in dilute aqueous solutions.Environ Sci Technol 9:833-8.

Egli C, Tschan T, Scholtz R, Cook AM and Leisinger T (1988) Transformation of tetrachloromethane to dichloromethane and carbon dioxide byAcetobacterium woodii– Appl Environ Microbiol 54:2819-24

Egli C, Stromeyer S, Cook AM and Leisinger T (1990) Transformation of tetra- and trichloromethane to CO2by anaerobic bacteria is a non-enzymic process - EMS Microbiol Lett 68:207-12

Faroon O, Taylor J, Roney M, Fransen ME, Bogaczyk S, Diamond G (2005) Toxicological profile for CTC - U. S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry (ASTDR) http://www.atsdr.cdc.gov/ToxProfiles/tp30.pdf.

Ferguson JF, Pietari JM (2000) Anaerobic transformations and bioremediation of chlorinated solvents - Environ Pollut 107(2):209-15

Field J. A. & Sierra-Alvarez R., Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds, Euro Chlor 2004, http://www.eurochlor.org/download-centre/science-dossiers/sd-biodegradation-alphatic.aspx

Gribble G. W. (2004) Natural Organohalogens, Euro Chlor 2004, http://www.eurochlor.org/media/41291/sd6-organohalogens-final.pdf

Howard PH, Boethling RS, Jarvis WF, Meylan WM & Michalenko EM (1991) Handbook of environmental degradation rates. Lewis, Chelsea,

Lovelock, J.E., R.J. Maggs and R.J. Wade, Halogenated hydrocarbons in and over the

Atlantic,Nature,241, 194-196, 1973.

Jury WA, Spencer WF, Farmer WJ (1984) Behavior assessment model for trace organics in soil: III Application of screening model - J Environ Qual 13:573-9

Molina MJ, Rowland FS (1974) Predicted present stratospheric abundances of chlorine species from photodissociation of carbon tetrachloride, Geophys-Res-Lett 1 309-312

Versar Inc. (1979) Water Related Environmental Fate of 129 Priority Pollutants – 2, Chap. 41,Environmental Protection Agency Report No. EPA-440/4-79-029B

Willis B, Rea JD, Crookes MJ, Howe PD,(1994) Environmental Hazard Assessment: Carbon Tetrachloride: Toxic Substances Division – ISBN

Zoeteman BCJ, Harmsen K, Linders JBHJ, Morra CFH, Slooff W (1980) Persistent organic pollutants in river water and groundwater of the Netherlands - Chemosphere 9:231-249

 

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