Most tokamak experimental results (Bessenrodt-Weberpals M. et al1993 Nucl. Fusion33 1205) indicate dependence of the ion thermal conductivity on the isotopic mass close to , i.e. inverse gyro-Bohm in mass scaling. This is in stark contradiction to most present theoretical models predicting Bohm or gyro-Bohm scaling. A basic physics experiment (Sokolov V. and Sen A.K. 2002 Phys. Rev. Lett.89 095001) on the anomalous ion thermal conduction due to ion temperature gradient instabilities in two different gases (hydrogen and deuterium) closely confirms the tokamak results.We now report another series of experiments designed to explore the physical basis of this scaling, which appears to lead to a new model for this scaling based on three-wave coupling of two ion temperature gradient radial harmonics and an ion acoustic (IA) wave. The resulting isotopic scaling of transport is , dictated primarily by the IA damping. This basic physics is deemed to be extrapolatable to tokamaks resolving the paradox and is tantamount to a new paradigm for plasma turbulent transport.