Many vegetables and fruit have been treated
The finding, uncovered by the BBC, has prompted calls for a review of the safe residue limits set by government.
Many of the different items in our weekly diet have been exposed to some form of pesticide at some point in their production, and although the majority of these chemicals have disappeared by the time the food reaches the consumer, residues can remain.
Some scientists blame increasing pesticide use in modern agriculture for a variety of "modern" health problems, such as an increase in particular cancers and a decrease in male fertility over recent years.
Tenfold increase
Scientists at Liverpool University found that, when working in tandem, combinations of different pesticides proved far more toxic to human cells than similar quantities applied individually.
The research is based on experiments on cultured brain tissue in the laboratory, and is due to be published next year.
Dr Vyvyan Howard, leading the research, told the BBC's Countryfile: "Pesticides are tested one at a time but virtually nothing is known about taking pesticide A and pesticide B, putting them together and seeing what happens then.
"If you consider that each one of us is walking around with hundreds of chemicals in our bodies, that couldn't have been there 50 or 60 years ago because they didn't exist on the planet, you can see the level of complexity of the problem."
His research on mixtures of pesticides suggested that, in some circumstances, toxicity could be amplified by a factor of ten over the expected.
Unborn worry
He said that unborn babies might be particularly vulnerable to brain damage from pesticides in their mothers' diet.
He said: "There is concern, I think, though not as big a problem as many people would make out.
"The margins between the doses that people receive from eating foods, and the levels of exposure that would cause health effects are so large that in general we would not expect, even where people are exposed to combinations of pesticides or other chemicals in their foods, that it would cause problems."