We propose a graphene-based terahertz metamaterial approach to the detection of heavy metal ions (HMIs). Theoretical calculations and numerical simulations show that the amplitude and phase of electromagnetically induced transparency/reflection resonance of the devices depending on the concentration and type of the HMI in the solution. By changing the bias voltage, the devices can be easily adjusted to their linear working regime for enhanced response speed and performance. By adding specific functional groups to the graphene, the devices may even recognize one specific HMI out of many due to selective adsorption. The proposed concept and discussed method can be helpful to design highly sensitive, fast, and reusable HMI detectors.