Electron paramagnetic resonance (EPR) uses the resonant microwave radiation absorption of paramagnetic substances to detect highly reactive and, therefore, short-lived oxygen and nitrogen centered radicals. Previously, steady state concentrations of nitric oxide, ascorbyl radical (A•) and the labile iron pool (LIP) were determined in digestive gland of freshly collected animals from the North Sea bivalve Mya arenaria. From these data by By the application of a simple kinetic analysis based on elemental reactions to these data allowed us to estimate the steady state concentrations of superoxide anion, the rate of A• disappearance and the content of unsaturated lipids. This analysis applied to a marine invertebrate opens the possibility of a mechanistic understanding of the complexity of free radical and LIP interactions in a metabolically slow, cold water organism under unstressed conditions. This data can be further used as a basis to assess the cellular response to stress in a simple system as the bivalve M. arenaria that can then be compared to cells of higher organisms.