Synergistic interactions could prove to be relevant when evaluating the toxicity of environmental pollutants in a complex mixture, especially when organic and inorganic substances co-occur at concentrations currently considered to be low-toxic or sublethal. Escherichia coli cells (SR-9 strain) were used as a model system for studying the cellular toxicity of environmental pollutants. Exposure of bacterial cells to a combination of pentachlorophenol (PCP) and a positively charged complex of iron or copper caused a dramatic inhibition of growth and an increase in cell death. Incubation of bacterial cells with PCP and either ferric-1,10-phenanthroline complex [Fe3+(OP)3]3+ (500 and 5 microM, respectively) or cupric-1,10-phenanthroline complex [Cu2+(OP)2]2+ (400 and 0.05 microM, respectively) showed two and four log units of cell death, respectively, in 30 min. In contrast, only minor amounts of cell death were observed with each component alone. Similar effects have been shown for other positively charged complexes of transition metals and for other biocides. The observed synergism was associated with the formation of novel noncharged and lipophilic ternary complexes, which contain PCP anions (or other polychlorinated anions) and the iron (or copper) complex. The ternary complexes demonstrated effective transport of their components into the cells.