The ball of Izmit is the focus of much of Turkey's industrial development and three of the most important of the wastes discharged into its surface waters have been studied as a necessary step in minimising their environmental impact. Gas chromatography/mass spectrometry of the extracted wastes revealed the presence of organic xenobiotics listed as priority pollutants. Nevertheless, measurements of cell populations, chlorophyll fluorescence and the consumption of nutrients demonstrated that most of the wastes stimulated the grow th of both batch and chemostat cultures of Phaeodactylum tricornutum (Bohlin). Experiments showed the growth of the cultures to be phosphate limited and it appears that the major effect of the wastes was due to their excessive loading of phosphate. (C) 1998 Elsevier Science Ltd. All rights reserved.