Lead poisoning in children may be a bigger UK public health issue than is currently appreciated, say experts.
Young children are particularly vulnerable
The Health Protection Agency says more research needs to be done to establish the exact threat.
The agency is concerned that even widely accepted safe levels of exposure may pose a risk of neurological damage.
The World Health Organization recommends children should not be exposed to blood levels of more than 100microgram/litre.
But toxicologists at the HPA Chemical Hazards and Poisons Division say this level may not be appropriate for use in the UK - and that neurological development may be affected in children with blood lead levels below this concentration.
It is known that lead is stored in the grey matter of the brain, and thus is particularly dangerous for children, whose brains are constantly evolving throughout the early years of life.
US studies have suggested that subtle neurological impairment may occur at lower blood levels.
Currently no data exists to suggest whether there may be similar effects in the UK and no routine programme exists to monitor any effects.
The HPA is only usually only notified of severe cases of lead exposure - where blood levels exceed 400microgram/litre or the patient is particularly unwell.
Yet many children in the UK are inadvertently exposed to low levels of lead.
For example, in buildings where lead-based paint remains, children can inhale or eat lead as the paint peels, chips or is removed.
Children may eat flaking lead paint
Toxicologist Professor Virginia Murray said: "We are concerned that lead may pose a bigger problem in this country than is realised.
"Currently we are only alerted of cases by doctors where lead has made children very ill.
"Yet we fear that lower levels of exposure in this country could also be damaging our children.
"Research is required if we are to establish the effects of low blood lead levels in children and the necessary actions."
Professor Pat Troop, HPA chief executive, said: "One of the new roles of the Health Protection Agency is to look at some of the effects of long-term chemical exposures as well as the effects from acute incidents.
"Children are particularly vulnerable and are therefore one of our top priorities. We are working with partners to establish the levels of threat that chemicals such as lead may pose to their health."
The sale of lead paint was prohibited only in the late 1980s. As lead paint deteriorates house dust and soil may become contaminated.
So far this year, the Health Protection Agency has been notified of five cases of lead poisoning in children.
However, researchers say the true number of residential incidents may be higher.