Figure 5 Density out of CFC-11, CFC-12 and you can CFC-113 into the sealed ampoules from Withlacoochee River water regarding southern-east Georgia demonstrating destruction out-of CFC-11 and you may CFC-113 and you can obvious balance out of CFC-a dozen (away from Plummer ainsi que al., 1998b).
CFCs weren’t degraded for the ampoules of your own river-water kept around light within room temperature. Development of algae was found in such ampoules hence probably sustained aerobic requirements (Plummer et al., 1998b).
Make mais aussi al. (1995) exhibited almost done degradation out-of CFC-eleven and you will balance of CFC-12 into the a sulphate-cutting mud aquifer close Sturgeon Drops, Ontario, Canada. There the fresh new groundwater years considering CFC-a dozen concurred better to the observed breadth of one’s mid-sixties step 3 H bomb level. Less than aquatic, sulphate-cutting criteria into the a Norwegian fjord, Shapiro mais aussi al. (1997) discovered fast degradation out-of CFC-eleven, and, within the uncertainties of measurements, CFC-a dozen degradation cannot was in fact over 1/600 compared to CFC-11. The latest half of-lifestyle to own CFC-eleven degradation during the sulphate-cutting, organic rich seawater was 0.1 ± 0.02 decades and you will most smaller compared to one discovered by the Cook et al. (1995) away from 0.nine to 1.7 years.
Oster (1996) said destruction away from CFC-11 and CFC-twelve in different (probably methanogenic, however, fundamentally unspecified) anoxic environments, that have rates away from CFC-11 destruction around ten-fold that of 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 contain particulate organic carbon and are low in sulphate. Such environments are usually methanogenic, and degradation of CFCs appears to be rapid.
In absolute surroundings the brand new electron donor is sometimes some kind of smaller carbon dioxide such dissolved normal carbon dioxide, lignite, or some other particular particulate all-natural carbon provided throughout the sediment otherwise h2o column. It is now difficult examine natural rates off degradation from one ecosystem otherwise laboratory reactor to a different due to variability in many items and additionally abundance and you can range off micro-organisms, availability of substrate, normal constitution, and 50’den fazla buluЕџma you may exposure regarding you’ll inhibitors.
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.