Researchers have found high levels of antimony - which can be lethal in large doses - in many popular brands.
Scientists from the University of Copenhagen found that bottles of fruit juice and squash contained up to 2.5 times more of the substance as is deemed 'safe' in tap water, under EU guidelines.
In some cases the levels of antimony were ten times higher.
The scientists believe that the chemical is leaching its way into the fruit juice from the plastic bottles which hold it.
Previous research found traces of the chemical in bottled mineral water which experts believed was leaching in from the plastic container.
The team has expressed 'concern' over their findings, published by the Royal Society of Chemistry, which they say raises fears for the health of millions of children.
They have called for an investigation 'straight away'. The substance can cause cancer, heart and lung problems, according to previous studies.
Although the scientists have not specifically named any brands, the chemicals are believed to have been found in 16 of the most popular blackcurrant and strawberry squash and fruit drinks consumed by children.
Claus Hansen, a PhD student at the department of pharmacology, who took part in the research, speculated that the citric acid in the fruit juices could speed up the leaching process.
He said: 'The antimony concentrations in the products tested exceed the limit of drinking water but no legalisation exists for foodstuffs so no legislation has been broken.
Previous research in Germany in 2006 found antimony was leaching into bottled mineral waters from their plastic containers.
In 2005 Volvic mineral water was at the centre of a health scare after a potentially harmful chemical was found in some of its bottles.
Danone Waters, which produces Volvic, launched an investigation after a mother of two reported a strong 'burning' chemical taste to the Food Standards Agency.
It found the water, which is advertised as being filtered through volcanic rocks, contained naphthalene – a chemical which can cause liver damage in high doses.
Responding to the research, the British Soft Drinks Association today defended the industry.
'Fruit juices and juice drinks are safe,' said a spokesman. 'There is no read across between the levels of antimony permitted in drinking water and those that might be acceptable in a fruit juice or a juice drink.
'It is not uncommon that different product types should have different regulatory requirements.'
He added: 'The packaging is safe. The data in the study does not confirm any conclusions about the packaging: the authors themselves conclude that "further studies are warranted".'
'All ingredients and packaging are carefully regulated to make sure that soft drinks are safe to drink.'