Anthropogenic activities related to 100 years of industrialization in the metropolitan Detroit area have significantly enriched the bed sediment of the lower reaches of the Rouge River in Cr, Cu, Fe, Ni, Pb, and Zn. These enriched elements, which may represent a threat to biota, are predominantly present in sequentially extracted reducible and oxidizable chemical phases with small contributions from residual phases. In size-fractionated samples (>300, 300−75, 75−38, 38−17, and 17 μm) trace metal concentrations generally increase with decreasing particle size, with the greatest contribution to this increase from the oxidizable phase. Experimental results obtained on replicate samples of river sediment demonstrate that the accuracy of the sequential extraction procedure, evaluated by comparing the sums of the three individual fractions, is generally better than 10%. Oxidizable and reducible phases therefore constitute important sources of potentially available heavy metals that need to be explicitly conside...