Fruit and vegetables are healthy eating: Could pesticides alter that?
Friends of the Earth (FoE) say nearly half the fruit and vegetables sold in UK supermarkets since 1998 contained pesticide residues.
The pressure group says the news will surprise many customers in view of supermarkets' claims that they minimise pesticide use.
Most residues were within legal limits, but FoE fears individual chemicals could be dangerous in combination.
And it says the unborn, infants and children may be at particular risk.
They say Marks & Spencer and Somerfield came out worst, with 63% and 59% respectively of their fruit and vegetables containing residues. The best was Waitrose, with 29%.
In a statement, Marks & Spencer said: "We are absolutely determined to reduce pesticide use on our crops."
It said it would "significantly" expand its list of prohibited pesticides, to cover 79 chemicals, which are to be phased out by January 2002.
'Bigger microscope'
A Somerfield spokesman told BBC News Online: "FoE are misrepresenting the government's report.
"The residues are well within tolerance levels, but the science is getting better all the time, so you find more - it's like having a bigger microscope.
"The whole industry has come on by leaps and bounds over the last 20 years. We've developed our expertise in harnessing nature by using natural predators in many cases."
FoE acknowledges that most of the chemicals found were within legal limits, but says: "The high incidence of residues means that we are regularly exposed to a cocktail of pesticides in our food.
"The regulatory system assesses the safety of pesticides on an individual basis, and does not take into account the possible effects of being exposed to a mixture."
The group is especially concerned about some chemicals which it says "turn up regularly" and "are known or suspected hormone disrupters which can work on the hormone system at very low levels".
It says: "There is increasing concern that these chemicals may be linked to serious health effects, including testicular and breast cancers."
Sandra Bell of FoE told BBC News Online: "The European Commission identifies one of these chemicals, vinclozolin, as a high-priority hormone disrupter.
"With the other two we're particularly worried about, carbendazim and iprodione, there's a lot of evidence against them, mainly from wildlife and laboratory studies, and they may have long-term effects.
Importance recognised
"We're very concerned about the effects of low-level, long-term exposure to hormone disrupters. There's evidence that they can affect the developing foetus, and infants and children as well."
FoE says it recognises that fruit and vegetables are crucial to a healthy diet, and it does not want to scare people out of eating them.
But it says that makes it even more important that the government acts to ensure consumers are not exposed to pesticides.
It wants ministers to develop a strategy for reducing pesticide use, and to tax them. It also wants research into alternatives, and a start to testing chemicals' effects in combination, not just singly.
'Vanishingly small'
Richard Trow-Smith, of the Crop Protection Association, told BBC News Online: "The retailers know from hard experience that pesticides are essential if they are to keep their shelves reliably filled with affordable food.
"FoE ignores the fact that the samples are selected purposely from produce where residues are likeliest to occur.
"Residues, where they are present, are at vanishingly small levels. Our chemists are confident that the tiny residue of one product is extremely unlikely to react with that of another."