Documents released Thursday from a Congressional investigation showed that four leading baby food companies knowingly sold baby food containing high levels of toxic heavy metals. Gerber, Beech-Nut, Walmart Inc.’s store brand and several organic lines of baby foods contained “dangerously high levels” of arsenic, lead, cadmium and mercury according to the report.

“Dangerous levels of toxic metals like arsenic, lead, cadmium and mercury exist in baby foods at levels that exceed what experts and governing bodies say are permissible,” said Democratic Rep. Raja Krishnamoorthi of Illinois, chair of the House Subcommittee on Economic and Consumer Policy.

Arsenic, lead, cadmium and mercury are in the World Health Organization’s top 10 chemicals of concern for infants and children. It was noted that Walmart Inc, Campbell Soup Co and Sprout Organic Foods refused to cooperate with the investigation.

These natural elements are found in soil where crops are grown, and can enter the food supply through soil, water or air. But some regions have more toxic levels than others, mostly due to the use of pesticides and to industrial pollution.

Baby food makers admit that their products contain these metals but say that the levels are safe. Some of the companies are looking to reduce heavy metals by looking for new suppliers.

The FDA was called on to mandate maximum levels of metals in baby food. Toxic heavy metals can affect brain development in babies, though to what extent is unknown.

“It’s time that we develop much better standards for the sake of future generations,” said Krishnamoorthi.