Ohio residential landlord tenant law, dispute over return of security deposit

Renters rights, health concerns: We rented a house 4 months ago my grandson was fine at his 9 month checkup. He recently had his 1 year checkup and they found an elevated level of lead. We also have black mold growing in our bathroom. We have notified the landlord about both problems and he hasn't done anything so we want to move. He refuses to return our $550 security deposit. What can we do?