DAVID Stubley (Letters, March 27) in reference to the World Health Organisation (WHO) report on glyphosate seems unaware that half of all known chemicals test as carcinogenic and that includes the thousands of natural pesticides that Mr Stubley eats happily in fruit and vegetables.

The WHO places at highest risk alcoholic beverages and sunlight. Hazard is a combination of dose and exposure. Half-a-glass of wine a day, a low dose, is very low risk. A bottle of scotch a day places the consumer at very high risk of gastric or oesophageal cancer because alcohol is a potent carcinogen. Short exposures to of sunshine are beneficial, long exposures as Australians in particular have found to their cost, induce melanomas.

The WHO report refers to occupational exposure, those that synthesise and package the chemical but even with these high dose/exposure conditions the claimed effect is marginal and given the very few men available as a sample may disappear when larger numbers are reported because other more extensive investigations have failed to substantiate it.

For the ordinary consumer, Roundup or glyphosate will probably join the list of chemicals for whom safe limits will be deployed and anyway refers to only one kind of weed control technology, using one kind of herbicide.

Professor Tony Trewavas,

Scientific Alliance Scotland,

7-9 North St David Street,