Nearly every orange, 94% of pineapples and 90% of pears sampled were laced with traces of chemicals used to kill bugs. High proportions of apples, grapes and tomatoes were also tainted, as were parsnips, melons and cucumbers.

Alarmingly, as much as a quarter of the food on sale in 2008 – the date of the latest figures – was found to contain multiple pesticides. In some cases, up to ten different chemicals were detected in a single sample.

Experts warn that the “cocktail effect” of so many different chemicals endangers health. They also point out that some of the pesticides are not only cancer-causing but also so-called “gender-benders” – chemicals that disrupt human sexuality.

The revelations about the widespread contamination of conventionally-produced food have also prompted renewed attacks on the government’s Food Standards Agency.

The FSA published a report last week casting doubt on the health benefits of eating organic food, which is mostly produced without pesticides.

Over 4000 samples of more than 50 kinds of food on sale to the public in 2008 have been tested by scientists for some 240 pesticides.

Detailed reports for the government’s Pesticide Residues Committee show that 46% of all the food samples were found to contain detectable levels of pesticides. Just over 25% contained more than one pesticide.

In 57 cases the levels of contamination were so serious that they breached the government’s safety limits. They included 13 samples of beans in pods, and 10 yams, as well as potatoes, spinach and chilli peppers.

There were hardly any types of fruit and veg found to be completely free of contamination, although the vast majority of organic food tested was clean. As well as fruit and vegetables, smoothies, whole-grain breakfast cereals, oily fish and wine all contained pesticides (see accompanying table).

Hundreds of pages of tables released by the Pesticide Residues Committee show that many of the contaminated products were bought at well-known supermarkets in Scotland. They include an iceberg lettuce, a courgette and a packet of Cheerios from a Tesco store in Glasgow.

Asda was found to be selling parsnips in Glasgow, Chinese leaves in Edinburgh and apricots in Aberdeen, all with pesticides. Baby food and oranges from Sainsbury’s in Glasgow were contaminated, as were white bread and bagels at Morrisons in Aberdeen.

Government scientists say that the residues would be “unlikely” to damage the health of those that eat them. But this is disputed by a growing body of experts concerned about the impact of mixtures of different chemicals.

“Researchers are concerned about the possible adverse health effects of very low-level exposures to mixtures of chemicals,” said professor Andrew Watterson, head of the Occupational and Environmental Health Research Group at the University of Stirling.

Watterson pointed out that several of the pesticides found on food were thought to be carcinogenic. Others were suspected of being endocrine disruptors, meaning that they could cause sex changes.

He also criticised the Food Standards Agency (FSA) for failing to include the impact of pesticides in last week’s report on organic food. “Why did the FSA apparently frame the recent research project to exclude the human and environmental health impacts of so-called food contaminants?” he asked.

The FSA report reviewed previous studies and concluded that there were “no important differences” in the nutrition content of organic food compared to conventionally-farmed food.

But the FSA has since come under fire. The Soil Association’s Scottish director, Hugh Raven, said: “Many consumers buy organic food because they’re worried about pesticide residues.

“The FSA itself recommends buying organic food if you want to avoid residues. Yet they were specifically excluded from this study.”

The FSA accepted that the report only examined the nutritional content of food, and did not deal with pesticides. “It’s a fact that conventional production methods permit the use of a wider range of pesticides than organic,” said an FSA spokeswoman.

“The FSA is neither for nor against organic food. Our interest is in providing accurate information to support consumer choice.”