FEW things are quite as bubble-bursting as cancer. Fizz is fun, not least for the effervescence it injects into the copywriters' cliches, but the discovery of the carcinogenic chemical benzene in carbon dioxide from the UK's major manufacturer of the gas, flattened a significant chunk of the country's fizzy drinks business, whose 10 billion litres a year is worth #6bn.

The soft drinks manufacturers and the Ministry of Agriculture, Fisheries and Food (Maff) became aware of the problem on Friday and have been involved in equal measures of detective work and public reassurance since. Those not affected, including AG Barr, however, say they knew they were in the clear last Thursday, when the source of contamination had been traced through the chain of three major suppliers to the carbon dioxide manufactured by Terra Nitrogen UK at Severnside near Bristol.

Manufacturers whose business is supra-national, including SmithKline Beecham and Coca-Cola Schweppes, moved swiftly to play down the health risk, citing both the Department of Health and Maff in their claim that ''this is not a health and safety issue''.

There is no UK limit for benzene

levels in food and drink, but the World Health Organisation puts the safe level at 10 parts per billion. It is believed that tests on the CO2 supplied by Terra Nitrogen UK's Severnside plant contained levels twice that at 20 parts per billion. In 1990 benzene contamination in Perrier water was 22 parts per billion and caused a global recall followed by an aggressive product relaunch. With the phrase ''customer confidence'' ringing round the corporate affairs offices as manufacturers stressed the responsible nature of their response, most were still waiting for test results yesterday, but Coca-Cola Schweppes cleared thousands of bottles of mineral water from the shelves after traces of benzene (which is widely used in inks, dyes,

lacquer, and as a solvent) were found

in sparkling Malvern water and Brecon Carreg, sold as Boots' own brand. A spokeswoman for Coca-Cola Schwep-pes said: ''The suspect CO2 was used in the Malvern factory and, as a matter of quality control and as a responsible manufacturer, CCS is withdrawing all Malvern spring water from the trade. Malvern still and 150ml cans of spring water are unaffected. Limited supplies of suspect CO2 have been delivered to one of the secondary canning plants of other CCS carbonated products and all suspect stock has been frozen until independent analysis has been carried out. It has affected a small share of Coca-Cola Schweppes beverages.''

Other companies, including Matthew Clarke, the parent company of several cider brands, were anxiously awaiting the results of tests ''in the next day

or two'', but refused for obvious

marketing reasons to say which products were being analysed. A spokesman for Maff said it was keeping tabs on

the situation.

Terra Nitrogen (UK) Limited had

little option but to put up its hands, once identified as the source of the benzene, but replied to all questions with a statement of classic non-information, saying the company ''believes that the trace levels of benzene identified in some drink products is linked to the process on our CO2 plant at Severnside. We have advised our clients not to transfer any CO2 from Severnside to the food and drink industry. We are working alongside our customers and Maff, who are being kept fully informed. There is a negligible risk to the public. We believe that this is a quality, not a health issue. We have launched a comprehensive inquiry to establish the cause of the problem.''

SmithKline Beecham confirmed that samples of both Lucozade and carbonated Ribena were being tested. ''The company also quarantined the affected CO2 supply, ceased distribution of potentially affected products, and is using guaranteed benzene-free CO2 from the suppliers. Any decision on what further action may be taken will be made once the results become available,'' added its spokesman.

If you must have bubbles, it seems safe to go for an auld alliance of the Scottish or the French variety. No problem with Strathmore mineral water, whether fizzy or still, said the man from Forfar cheerfully, while the message from Britain's largest producer of natural mineral water, Highland Spring, at Blackford was

equally bubbly: no CO2 from Terra Nit-rogen. AG Barr has a ''categorical assurance'' from its supplier that no carbon dioxide from the affected plant at Severnside has been supplied to any of its factories, so traditionalists can continue to attack hangovers with Irn Bru or dispense Tizer, Orangina, and Red Cola to their children without fear they are drinking carcinogenic benzene, whatever other dietary or dental dangers they are swallowing.

Daphne Barrett, Perrier's spokeswoman in the UK, said: ''Perrier is a French water which is bottled at source and contains no factory-produced gas. Vittel is a still water and Buckstone from Derbyshire uses gas supplied from the north of England.'' Ms Barrett's delight was almost palpable, presumably because eight years ago the company had to withdraw 160 million bottles of Perrier, then the world's biggest-selling mineral water, when it admitted that gas filters at the source in the town of Vergeze in Southern France had not been cleaned as regularly as they should. It was the chink in a hitherto dominant marketing campaign, which allowed other spring waters, particularly Scottish ones, to grab a share of the market. There's always champagne, of course.