Two laboratory studies were conducted to determine the effects of coal particles in aquatic sediments on survival and organ tissues of rainbow mussels Villosa iris (Lea, 1929). First, mussel survival was assessed using treatments comprised of sand substrates with different percentages of pulverized coal, including 0%, 10%, 25%, and 50%. At the end of this 7-wk pilot experiment, there were no significant differences in survival of V. iris among substrate treatments. Second, effects of coal particles in substrate on organ tissues of V. iris, including gills, digestive glands, kidneys, and gonads, were assessed during a 20-wk experiment. Two sand substrates, containing 0% coal (control) and 50% coal (treatment), were tested. Organ tissues of five mussels from each of the treatment and control tanks were collected at 8, 16, and 20 wk. Sublethal alterations in organ tissues of coal-exposed mussels were observed. Fractions of gill filaments without cilia and digestive cells of digestive glands with condensed cytoplasm were significantly greater in coal-exposed mussels compared with those from the control. Females from the coal treatment showed significantly higher fractions of acini containing atretic, resorbing oocytes than the control females. Significantly higher fractions of lipofuscin, an insoluble lipid peroxidation byproduct that can be related to contaminant exposure, in kidney diverticula of the coal-exposed mussels suggested that unidentified contaminants were present in the water. Further study of the effects of these contaminants on freshwater mussels are warranted given the co-occurrence of declining mussel populations and coal mining and processing operations in Appalachian watersheds.