SALINA, Kan. (AP) — Kansas health officials said they are investigating after 30 Saline County children were found to have high levels of lead in their blood.

Saline County Health Department Director Jason Tiller said routine blood testing discovered the high lead levels between January 2015 and March 2016. He said investigators have not found an obvious cause or connection between the cases.

The state health department is planning a public hearing June 21 to discuss the investigation.

Health officials say no obvious symptoms indicate lead poisoning and there is no way to correct lead’s health effects.