Contour 5 Density out-of CFC-11, CFC-twelve and you may CFC-113 during the shut ampoules regarding Withlacoochee River-water clover dating site of south-east Georgia exhibiting destruction off CFC-11 and you may CFC-113 and you may visible stability out-of CFC-12 (off Plummer et al., 1998b).
CFCs weren’t degraded into the ampoules of the river-water stored not as much as light during the room-temperature. Growth of alga are seen in these types of ampoules hence probably sustained cardiovascular requirements (Plummer mais aussi al., 1998b).
Make ainsi que al. (1995) displayed nearly done degradation from CFC-11 and you may balances out-of CFC-a dozen inside the an excellent sulphate-cutting mud aquifer near Sturgeon Drops, Ontario, Canada. Indeed there the fresh groundwater ages centered on CFC-several conformed well on seen breadth of your own middle-1960s 3 H bomb height. Less than aquatic, sulphate-cutting standards within the a Norwegian fjord, Shapiro et al. (1997) receive quick destruction regarding CFC-eleven, and, for the concerns of your specifications, CFC-12 degradation cannot had been more 1/600 regarding CFC-eleven. The fresh new half-existence for CFC-eleven destruction into the sulphate-cutting, natural steeped seawater try 0.step 1 ± 0.02 many years and most smaller compared to that receive by Cook mais aussi al. (1995) from 0.9 to just one.eight age.
Oster (1996) advertised destruction regarding CFC-eleven and you can CFC-a dozen in numerous (probably methanogenic, but basically unspecified) anoxic environments, that have rate away from CFC-eleven degradation everything 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.
During the natural environments the brand new electron donor can often be some sort of quicker carbon dioxide such dissolved organic carbon, lignite, or another brand of particulate organic carbon included in the sediment otherwise water column. These days it is not possible examine absolute cost from destruction from a single ecosystem otherwise research reactor to another on account of variability in a lot of circumstances and additionally wealth and you can assortment away from small-organisms, supply of substrate, all-natural structure, and you will visibility regarding you’ll 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.