Shape 5 Levels off CFC-eleven, CFC-12 and you can CFC-113 when you look at the closed ampoules out-of Withlacoochee River-water out-of southern area-eastern Georgia appearing destruction of CFC-11 and CFC-113 and you can visible balances away from CFC-12 (out of Plummer ainsi que al., 1998b).
CFCs were not degraded inside the ampoules of river water held lower than white during the room temperature. Development of alga is observed in such ampoules hence most likely suffered aerobic criteria (Plummer et al., 1998b).
Create et al. (1995) presented almost done degradation off CFC-11 and balances out-of CFC-12 for the an excellent sulphate-reducing mud aquifer close Sturgeon Drops, Ontario, Canada. Indeed there new groundwater decades based on CFC-twelve consented really into the noticed depth of your middle-sixties step three H bomb peak. Less than marine, sulphate-cutting requirements when you look at the a beneficial Norwegian fjord, Shapiro mais aussi al. (1997) receive fast destruction of CFC-11, and you can, in uncertainties of one’s measurements, CFC-12 destruction could not were more than step one/600 that CFC-eleven. Brand new 1 / 2 of-lives to have CFC-11 degradation from inside the sulphate-cutting, natural steeped seawater is actually 0.step one ± 0.02 decades and you can much more smaller compared to you to definitely found because of the Prepare ainsi que al. (1995) regarding 0.nine to just one.seven years.
Oster (1996) claimed degradation regarding CFC-eleven and you may CFC-twelve in numerous (most likely methanogenic, however, basically unspecified) anoxic environment, which have speed of CFC-11 degradation up to ten-flex regarding CFC-twelve
The presence of sulphate (and nitrate) in anaerobic environments slows the rates of dehalogenation reactions (Mohn and Tiedje, 1992; Sylvestre et al., 1997) by competing with highly halogenated aliphatic compounds as terminal electron acceptors. Inhibition of dehalogenation by sulphate may explain the persistence of CFC-12 in sulphate-reducing environments (as in Cook et al., 1995, Shapiro et al., 1997, and Plummer et al., 1998a,b) where dissolved sulphate is still present, and more rapid degradation of CFC-12 in methanogenic environments (Deipser and Stegmann, 1997; Oster et al., 1996) where sulphate concentrations are usually very low. Parks et al. (1995) reported complete removal of CFC-11 and CFC-12 under methanogenic conditions in the Memphis (sand) aquifer, south-west Tennessee (1.3 mg L -1 CH4, 7.3 mg L -1 SO4 2- , 5.3 mg L -1 Fe 2+ ). The measured tritium activity of 13.8 TU indicated post-bomb water that would otherwise contain easily measurable concentrations of CFCs. Shapiro et al. (1998) also found significant degradation of CFC-11 and CFC-12 under methanogenic conditions in a buried-valley aquifer near Dayton, Ohio. Fluvial and glacial drift deposits often female escort in Anchorage AK contain particulate organic carbon and are low in sulphate. Such environments are usually methanogenic, and degradation of CFCs appears to be rapid.
Inside the pure surroundings brand new electron donor is normally some form of reduced carbon dioxide for example dissolved all-natural carbon dioxide, lignite, or other form of particulate normal carbon dioxide integrated about deposit otherwise h2o column. It is currently extremely hard evaluate pure pricing of degradation from a single environment or laboratory reactor to a different because of variability in several affairs and abundance and you will diversity of mini-organisms, availability of substrate, organic composition, and you will visibility off you’ll be able to inhibitors.
Sorption
Like microbial degradation, sorption is another process that can remove CFCs from groundwater, leaving the impression of apparently older age and lower groundwater velocities. Cook et al. (1995) observed uptake of CFC-113 relative to CFC-12 and 3 H at the Sturgeon Falls site, Ontario, Canada. The vertical profiles of CFC-12 and tritium could be modelled with a recharge rate of approximately 130 mm yr -1 and were apparently not affected by sorption or degradation. The agreement in transport of CFC-12 and 3 H was so strong that, if sorption of CFC-12 were occurring, the solid-liquid partition coefficient, Kd, must be less than 0.03 (retardation factor 3 H at Sturgeon Falls. Most of the uptake of CFC-113 occurred in the aerobic upper 4 m of the water column, suggesting sorption of CFC-113, rather than microbial degradation (Cook et al., 1995). The CFC-113 profile indicates a Kd value of 0.09-0.14 (retardation factor 1.4-1.7) for CFC-113 in the sand aquifer, which contained, on average, 0.03% organic carbon.
