Abstract <p>The long-term (1990–2023) dynamics of accumulation of essential (Cu, Zn) and toxic (Cd, Pb) heavy metals (HMs) were analyzed in the stomach contents (<i>n</i> = 428) and liver (<i>n</i> = 561) of individuals of the Herb Field Mouse (<i>Sylvaemus uralensis</i>), living at different distances from a large non-ferrous metallurgy plant (Russia, Revda) during periods of high, reduced, and almost cessation of emissions. Testable hypotheses about directed spatiotemporal changes in HM concentrations in the diet and the body of <i>S. uralensis</i> were partially confirmed. In the pollution gradient, the concentrations of all elements in the stomach contents, as well as toxic elements in the liver, increased consistently as they approached the plant, reaching maximum values in the immediate vicinity, while the accumulation of essential elements in the liver of animals did not depend on the level of pollution in the area. Multiple (50-fold) reductions in plant emissions during the observation period did not result in an equivalent decrease in element concentrations in the analyzed substrates. In the vicinity of the plant, clear time trends were noted for Pb, the levels of which over 34 years of observations monotonically decreased by 2–3 times both in feed and in the liver of <i>S. uralensis</i>. In unpolluted areas, directional changes were noted only for Cd in the liver, the concentration of which decreased by half over the same period.</p>