Lead is a metal which is toxic at very low levels of exposure. It accumulates in the body, so that regular exposure to even very low quantities may result in harmful levels which can badly damage intellectual and behavioural development of infants and young children.

A level of 10 micrograms of lead per decilitre of blood (10 μg/dL) is generally recognized as a threshold level of concern with respect to lead poisoning. Children who wear metal jewellery containing accessible lead which can leach out can ingest the lead by handling jewellery and putting their fingers in their mouths, or by putting jewellery directly in their mouths, or by ingesting either parts or whole pieces of the jewellery. This is behaviour that may occur regularly over time (eg, every day that a child has access to an item) and so results in chronic exposure.

Ingestion that occurs all at once (e.g., swallowing an entire object) may result in acute exposure if the item concerned contains a high enough amount of accessible lead. The  blood lead level would be chronically elevated, equally as harmful as continual exposure to small amounts of lead.

Extensive test data developed by American researchers has led them to believe that the amount of lead that is  absorbed by swallowing an item of jewellery would be much greater than the amount of lead that would be absorbed by sucking or handling the same piece. Accordingly, they believe that keeping lead content low enough will give protection against the possibility of excess exposure through swallowing or sucking an item.

The Canadian Authorities have also considered the possibility of ingestion of lead by children handling jewellery and putting their fingers in their mouths afterwards, or physically chewing or sucking jewellery – a situation which may commonly occur with a necklace or pendant.

Unlike the Americans the Canadian Authorities have given equal importance to both situations and have imposed a limit for total lead and a limit for leach able lead.