Risk Quotient

The risk quotient (RQ), also called the risk characterization ratio, is the ratio of expected exposure to the no-effect threshold: PEC divided by PNEC for a chemical. A predicted environmental concentration above the predicted no-effect concentration gives RQ greater than 1, signaling unacceptable risk that triggers risk management or a refined higher-tier assessment; RQ below 1 indicates acceptable risk at that exposure. It is the quantitative output of deterministic ecological risk assessment under EU REACH and the US EPA, computed separately per environmental compartment (water, sediment, soil) and per protection goal.