The purpose of this work was to examine the chemistry of N-, O-, and S- heterocycles (NOSHs) from fossil duels and pyrogenic sources in estuarine sediment-water with emphasis on relative rates and pathways of transformation. The effects of redox potential and sediment particle size of NOSH degradation were examine using a)stirred, controlled Eh sediment-water microcosms and, b) sealed, unstirred batch bill microcosms approximating natural sediments.