Oil drilling operations generate very large volumes of produced waters which contain a complex mixture of sub-surface water and solid and liquid geological materials, including crude oil, drilling fluids, and treatment chemicals. In coastal regions, these produced waters are discharged into fresh or brackish marshes or wetlands which also serve as the spawning sites for a wide variety of economically important species of fish and shellfish. Recently, concern has focused on potential impacts of produced waters upon these productive and sensitive ecosystems. In the present study, we report the results of investigations which characterize the chemical contaminants present in produced waters and surficial sediments collected at two sites in coastal Louisiana. Trace organic analyses of the produced waters revealed a complex and variable mixture of normal-, alkyl-, and heterocyclic polynuclear aromatic hydrocarbons. Examination of surficial and sub-surface sediments demonstrate that extensive areal distribution of the produced water hydrocarbons has occurred through time. Embryonic stage genotoxicity bioassays of the produced waters indicate that the polycyclic aromatic hydrocarbons being discharged in these coastal waters cause increased mutational frequencies in Cyprinodon variegatus. Since the observation of chromosomal aberrations is usually rare in the cells of the organism and since cell replication and differentiation are maximal in the early developmental stages of these and other species of aquatic organisms, the results suggest that the potential exists for adverse effects of these discharges on estuarine productivity. Further study of the impacts of produced waters in this and other species is indicated.