Report No DWI0111

Jul 1986

We have developed the necessary skills required to use perfluorodecalin (PFD) and sulphur hexafluoride (SF6) as marine tracers. An automated analyser for PFD has been constructed.

Below we summarise the relevant information on the use of SF6 and PFD as marine tracers. For comparison, equivalent information on the well-established fluorescent dye technique is also included

1. Toxicity:

SF6, PFD	- No toxic effects reported to date.
Fluorescent dyes	- Some carcinogenic activity suspected.

 

2. Environmental impact:

SF6, PFD	- Colourless, odourless and used at low concentrations. No deleterious evnironmental effects reported
Fluorescent dye	- At concentrations >10 p.p.b. these visibly colour water.

3. Detection limit:

SF6	- 10-16 moles litre-1
PFD	- 2 x 10-15 moles litre-1
Fluorescent dye	- 2 x 10-12 moles litre-1

 

4. Volatility:
 

SF6, PFD	- volatile compounds which tend to escape from surface waters into atmosphere.
Fluorescent dye	- Non-volatile

 

5. Conservative behaviour:

SF6	- excellent conservative properties in subsurface water.
PFD	- Some loss, possibly due to absorption on particles.
Fluorescent dye	- Some loss due to absorption on particles and photo-degredation.

 

6. Injection method:

SF6	- pre-dissolution in water (slow) or bubbling gas directly into sea.
PFD	- preparation of micro emulsion
Fluorescent dye	. - Direct dissolution in water.

 

7. Detection method:

SF6,PFD	- Automated purge and trap apparatus followed by electron capture gas chromatography. (Ship-borne).
Fluorescent dye	- Fluorometer (ship borne or in situ)

 

8. Time constant for detection:

SF6, PFD	- 3 minutes
Fluorescent dye	- 1 second

 

9. Appropriate Scale for tracer experiments:

SF6	- up to whole ocean.
PFD	- up to 1000 km
Fluorescent dye	- up to 50 km