The Office of Pesticide Programs (OPP) models daily aquatic pesticide exposure values for 30 years in its risk assessments. However, only a fraction of that information is typically used in these assessments. The population model employed herein is a deterministic, density-dependent periodic matrix model for integrating time-varying pesticide exposure effects on the marine invertebrate Americamysis bahia. The external exposure concentrations are converted to time-varying scaled internal concentrations by coupling a one-compartment toxicokineticstoxicodynamics model with the matrix model. Several exposure scenarios (each with the same risk as determined by OPPÃ¢â‚¬â„¢s traditional approach) were created within which population modeling documented different risk conclusions than assessments based on the traditional approach. Population modeling incorporates all available toxicological and exposure data, making a more complete assessment of the potential risk of time-varying aquatic concentrations.