Baby foods used to wean infants off milk have been found to contain "alarming" levels of toxic contaminants including arsenic, lead and cadmium.
Last night there were calls for urgent new safety rules to control the presence of the poisons in foods intended for young children.
The findings come as officials at the Food Standards Agency and the European Commission are conducting an urgent review to establish new limits for the long term exposure of these contaminants in food.
The products tested by the researchers were made by major baby food manufacturers including Organix, Hipp, Nestle and Holle - some of which are available in British supermarkets.
Researchers found feeding infants twice a day on the shop-bought baby foods such as rice porridge can increase their exposure to arsenic by up to fifty times when compared to breast feeding alone.
Exposure to other toxic metals such as cadmium, which is known to cause neurological and kidney damage, increased by up to 150 times in some of the foods tested by Swedish scientists, while lead increased by up to eight times.
Although none of the levels of the toxic elements found in the foods exceeded official safety limits, scientists believe they are still of concern if fed to very young children and have demanded new guidelines to restrict their presence in food.
Young infants are thought to be particularly vulnerable to these substances because they are going through rapid development.
Writing in the journal of Food Chemistry, the scientists from the Unit of Metals and Health at Karolinska Institutet in Stockholm, Sweden, where the research was carried out, said: "Alarmingly, these complementary foods may also introduce high amounts of toxic elements such as arsenic, cadmium, lead and uranium, mainly from their raw materials.
"These elements have to be kept at an absolute minimum in food products intended for infant consumption.
"In infant foods, the high concentrations of arsenic in the rice-based foods are of particular concern."
Experts now believe there are no safe limits for arsenic and manufacturers should be making more efforts to remove it from their food.
Professor Andrew Meharg, a biogeochemist at Aberdeen University who has studied the presence of arsenic in rice, said the latest research highlighted the urgent need for new restrictions on arsenic and other toxic elements in food.
He said: "For an adult with an average consumption of rice every day, it makes little difference, but for young babies who are the most vulnerable receptors we should be doing everything we can to reduce that risk. You don't want DNA damage during infant development.
"There are ways to decrease the toxic load in food. It is only recently that we have started using rice in baby foods and formulas. You can reduce the arsenic in infant foods very rapidly by sourcing the rice from different parts of the world. You can reduce it by four or five fold by carefully selecting the right rice."
The researchers tested nine different brands of baby food, which were intended to be fed to children from the age of four months old, and nine baby milk formulas.
They found that when compared to breast milk, the baby foods had elevated levels of toxic contaminants measured in micrograms - a millionth of a gram, or 35 billionths of an ounce.
The daily safe intake limit for arsenic was set by the World Health Organisation as two micrograms for every kilogram of body weight, but this was suspended earlier this year amid growing evidence that arsenic can cause cancer even at low levels.
The limits for lead have also been suspended while those for cadmium are one microgram for every kilogram of body weight.
Arsenic and the other heavy metals found in the study are often found in food as they are absorbed from the soil by plants such as rice, wheat and oats.
Among the baby foods found to contain elevated levels of arsenic, cadmium and lead in the tests by the researchers was Organix First Organic Whole Grain Baby Rice, which they found contained two micrograms of arsenic per portion, along with 0.03 micrograms of cadmium and 0.09 micrograms of lead. This product is sold by Boots in the UK.
HiPP Organic Peach and Banana Breakfast porridge, which is sold by supermarkets in the UK including Tesco, contained 1.7 micrograms of arsenic, 0.13 micrograms of cadmium and 0.33 micrograms of lead.
Holle Organic Rice Porridge, which is sold by specialist retailers, was found to contain 7.3 micrograms of arsenic per portion - the highest found in the study - along with 0.38 micrograms of cadmium and 0.26 micrograms of lead.
The Swedish National Food Administration is now conducting its own review of toxic elements and metals in baby food and food for older children as a result of the research. The results will be reported to the European Food Safety Authority and the European Commission, which is responsible for setting food safety limits.
The Sunday Telegraph contacted each of the major manufacturers of leading brands of baby food sold in the UK but most refused to reveal the levels of toxic contaminants found in their products. Heinz, Cow & Gate, Nestle, and HiPP all insisted their foods contained levels that were within safety limits.
Dr Karin Ljung, who led the Swedish research, said: "The producers will say they are not above any guideline values and it is true – they are following all the rules.
"The trouble is that the guidelines are not based on infant exposure. As we are getting more information coming out, it is may be time to reconsider what these safety limits are."
She added that breast feeding until babies were six months old appeared to be the best way to keep infants' exposure to these toxic contaminants as low as possible as they seemed to be filtered out by the mothers' body.
There are currently no EU-wide regulations for arsenic levels in food after the European Food Safety Authority ruled that previous safety limits were inadequate.
Jackie Schneider, from the Children's Food Campaign, said: "We expect full transparency from baby food manufacturers and are disappointed that they are choosing to not share the relevant data.
"Parents aren't stupid and they deserve to be given the facts so they can make an informed choice"
A spokesman for the Food Standards Agency said previous reviews of the levels of toxic elements in baby food found them to be present at low levels.
He added: "The Agency is actively engaging with the European Commission to review and establish long term limits for these environmental contaminants in food."
"That selection of suitable ingredients ensures the lowest possible occurrence of certain naturally-occurring substances. Ingredients that do not meet stringent specifications are not used in baby foods."
A spokesman for HiPP insisted the levels of arsenic and cadmium in their Organic Peach and Banana Breakfast porridge were under the official daily intake limits and so were safe as part of a daily diet.
She said: “The levels of cadmium and arsenic in HiPP products are safe and all raw materials are routinely tested following the strictest quality criteria.”
A spokesman for Organix said: “Organix operates rigorous finished food testing to ensure food safety is monitored regularly. This includes testing for elements, microbiological, allergen and pesticide residues.
“Our further testing of finished foods and raw materials show ALL results conform to the current UK food standard. We continue to monitor both our own internal results together with those of our suppliers.
“Please rest assured that we fully assess both the Food Standards Agency’s guidelines and any new research and will continue to do so.”
A spokesman for Plum added: “Sampling of our recipe shows levels for arsenic are well below those in this latest study, and again these are well within the generally regarded safe and acceptable limits.”
Nestle said it did not recommend the use of it infant cereals before six months of age, but they carefully selected their raw materials to ensure substances absorbed from the soil were as low as possible.