CFC-11 and you will CFC-113 were totally degraded contained in this eight hundred weeks and you may CFC-a dozen demonstrated hardly any degradation more than almost a thousand months

CFC-11 and you will CFC-113 were totally degraded contained in this eight hundred weeks and you may CFC-a dozen demonstrated hardly any degradation more than almost a thousand months

Figure 5 Density off CFC-11, CFC-several and you can CFC-113 for the close ampoules out-of Withlacoochee River water of southern area-east Georgia proving destruction off CFC-eleven and you may CFC-113 and apparent stability from CFC-several (regarding Plummer mais aussi al., 1998b).

CFCs weren’t degraded within the ampoules of your river-water kept below light at room temperature. Development of algae was seen in these types of ampoules and therefore most likely suffered cardio conditions (Plummer et al., 1998b).

Make mais aussi al. (1995) displayed almost over degradation out-of CFC-11 and you can balances from CFC-twelve when you look at the a great sulphate-reducing sand aquifer close Sturgeon Falls, Ontario, Canada. Truth be told there this new groundwater age based on CFC-a dozen arranged really toward noticed breadth of your mid-sixties 3 H bomb height. Around marine, sulphate-reducing criteria inside an effective Norwegian fjord, Shapiro et al. (1997) receive fast destruction from CFC-eleven, and you will, when you look at the concerns of proportions, CFC-12 destruction cannot had been over step one/600 compared to CFC-11. The new half of-life getting CFC-11 degradation inside the sulphate-cutting, organic steeped seawater is 0.1 ± 0.02 years and you can more smaller than you to discover from the Plan ainsi que al. (1995) away from 0.nine to one.seven decades.

Oster (1996) advertised degradation out of CFC-11 and you may CFC-twelve in numerous (probably methanogenic, however, essentially unspecified) anoxic surroundings, with price of CFC-11 degradation approximately 10-flex 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.

Inside absolute surroundings brand new electron donor is https://datingmentor.org/escort/abilene/ commonly some form of reduced carbon dioxide instance dissolved all-natural carbon dioxide, lignite, or any other variety of particulate natural carbon provided regarding the sediment or liquids line. It is currently impossible examine absolute prices out-of destruction from just one ecosystem or research reactor to some other on account of variability in several affairs as well as variety and you may variety from small-bacteria, supply of substrate, organic composition, and you can exposure off you can 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.

Trả lời

Email của bạn sẽ không được hiển thị công khai. Các trường bắt buộc được đánh dấu *