Parents are being urged to check their freezers for a popular children's snack amid fears they could be laced with a dangerous toxin.

Investigators at the Food Safety and Inspection Service (FSIS) issued a health alert Wednesday last week saying that tests found Walmart's Great Value brand ready-to-eat dinosaur-shaped chicken nuggets may contain elevated levels of lead.

There is no safe level of lead exposure, experts warn. The toxic heavy metal is linked to developmental delays, a higher risk of cancer and autism — and is especially dangerous for young children, infants and pregnant women.

The nuggets were sold at Walmart stores nationwide under its 'Great Value' brand and were available in 29oz plastic bags that contained 36 nuggets. 

They were on shelves as recently as February 10, and have a best if used by date of February 10, 2027.

No recall was issued because the nuggets had already been removed from shelves, but parents were urged to check their freezers in case they still have the affected nuggets at home.

Anyone who had purchased the product is advised not to consume it and to throw it out immediately or return it to stores for a full refund.

Officials withdrew the warning on Tuesday the following week after follow-up testing found the nuggets did not contain lead levels that posed a health risk. They said the initial alert was based on routine testing carried out by the New York State Department of Public Health. 

Doctors say that those who believe they have been exposed to lead should contact their physician for advice. They may be offered a blood test to check for elevated lead levels.

The FSIS said other Walmart-brand products were now being tested, and warned that more could be added to the health alert.

The FDA says there is no safe level of lead exposure. However, to track lead exposure, the agency sets a daily dietary intake limit for children at no more than 2.2 micrograms of lead per day. 

Initial tests on the dinosaur nuggets suggested that they may contain lead levels five times above the safe level.

The products had a lot code of 0416DPO1215 and an establishment number of P44164. These are printed on the back of the packaging.

Children and adults can be exposed to lead from multiple sources, including paints, water pipes, toys and zippers. About 500,000 children in the US are estimated to have lead levels in their blood that are above the safe limit, according to the CDC.

Warning signs of elevated lead levels include behavioral problems, speech and hearing problems and learning difficulties. Adults are also at risk from the toxin.

In the body, lead can affect neurons in the brain, potentially raising the risk of autism, and damage cells, which can increase the risk of cancer. 

Officials say the best way to treat lead exposure is to remove the main source of lead from the home environment.

If parents are concerned, children may also be offered tests to check the lead levels in their blood.