Researchers looked at the health and occupational records in the west of Ireland and found a general rise in the incidence of non-Hodgkin's lymphoma and chronic lymphocytic leukaemia - a pattern repeated elsewhere in the world.

However, the rise in the rate of cancers was particularly marked in farmers and other workers on their land.

This included not only non-Hodgkin's lymphoma, but also three types of leukemia.

There is even some evidence of a rise in testicular cancer in agricultural workers.

The researchers, writing in The British Medical Journal, say there appears to be a link between those who developed cancer and those who did not use the safest methods for applying farm chemicals.

Chemical spraying

This link was established by asking 90 people with cancer and 54 people in a control study to complete a questionnaire on work practices.

This showed that the farmers and land workers who got cancer were also the ones less likely to wear a mask and to use tractor-mounted techniques for chemical spraying.

"This would lead to them being very exposed to particular chemicals or pesticides," said Dr Cecily Kelleher from the Clinical Sciences Institute in Galway, "but we did not find any specific pesticide or chemical was significant."

"We would be reasonably conservative about the link, but we did find such an association."

Dr Kelleher says the whole matter is of concern in Ireland because 14% of the population is employed in the agricultural sector.

She wants better education about the health dangers that exist on farms.

Health and safety

"This doesn't just apply to what would be a rare incidence of cancer, it applies generally to hazards in the farm environment.

"We know from other work that farmers have relatively low knowledge of chemical safety and there are other possible risks to their general health and well being.

"So my bottom line would be to use protective masks and clothing and follow manufacturers' instructions to the letter."