4 Biological Activity of Waters Containing Nonionogenic Surfactants Nonionogenic surfactants are second to anionic surfactants by the amount of their production and discharge into aquatic ecosystems (Surfactants 1984; Steinberg et al. 1995; Bailey 1996; Thiele et al. 1997). The main classes of nonionogenic surfactants are alcohol ethoxylates and oxides of fatty amines. In 1988, the worldwide annual consumption of nonionogenic surfactants belonging to the alkyl phenol ethoxylates was approximately equal to 360,000 tons (Ahel et al. 1993). Along with the worldwide use of nonionogenic surfactants in industry and other branches of the economy, chemicals of this class have other applications: nonionogenic surfactant. | 4 Biological Activity of Waters Containing Nonionogenic Surfactants Nonionogenic surfactants are second to anionic surfactants by the amount of their production and discharge into aquatic ecosystems Surfactants 1984 Steinberg et al. 1995 Bailey 1996 Thiele et al. 1997 . The main classes of nonionogenic surfactants are alcohol ethoxylates and oxides of fatty amines. In 1988 the worldwide annual consumption of nonionogenic surfactants belonging to the alkyl phenol ethoxylates was approximately equal to 360 000 tons Ahel et al. 1993 . Along with the worldwide use of nonionogenic surfactants in industry and other branches of the economy chemicals of this class have other applications nonionogenic surfactant nonoxy-nol-9 NP-9 is frequently used as intravaginal spermicide Meyer et al. 1988 . This chemical is a usual component used for lubricating individual AIDS protection devices. By its structure NP-9 is nonylphenoxyl poly ethylenoxyl 9 ethanol Meyer et al. 1988 . Nonionogenic surfactants belonging to the group of alkyl phenol derivatives are also used as hair dyes Meyer et al. 1988 . The problems of environmental pollution with nonionogenic surfactants were discussed in Stavskaya et al. 1988 Lewis 1991 and Holt et al. 1992 . The amount of nonionogenic surfactants in sewage waters reaches significant concentrations up to 30 g l Stavskaya et al. 1988 . Nonionogenic surfactants were found in natural aquatic systems at concentrations of up to 1 or even mg l Holt et al. 1992 . We emphasize however that owing to the property of nonionogenic surfactants to form complexes with many compounds a great proportion of nonionogenic surfactants can exist in masked states and cannot be revealed using analytical methods. Hence the probability of obtaining underestimated results is high. The real amount of noniono-genic surfactants in aquatic ecosystems can be even higher than that given by the water analysis. The efficiency of water purification as far as nonionogenic surfactants
