A suspension of fluorescent pigment particles (total mass, 120 kg) was injected over a period of several hours into a sewage outfall discharging into Salem Sound, MA. Flow cytometric analysis was successfully used to identify, quantify, and size the fluorescent pigment particles in bottom sediment and sediment trap samples collected 1-8 days after their release. Typical areal concentrations after 8 days were 1000 micrograms/cu m (or roughly 100 ppb in the top 0.5 cm of sediment cores) corresponding to approximately 7% of the total released. The size distributions of recovered pigment particles are identical with the size distribution in the initial suspension, indicating that, despite their exceptionally low coagulation efficiency, net deposition of the pigment particles is effected by coagulation with other solids either in the water column or at the sediment-water interface. (Copyright (c) by the American Chemical Society, 1990.)