The Science of the Total Environment, Supplement 1993 Elsevier Science Publishers B.V., Amsterdam 773 Application of Lemna species in ecotoxicological studies of heavy metals and organic biocides Gyula Lakatos a, Ilona M6szfiros b, Sfindor Bohfitka c, Sfindor Szab6 a, Mariann Makfidi a, Margit Csatl6s c and Gfibor Langer ~ aDepartment of Ecology, L. Kossuth University, H-4010 Debrecen, Hungary b Department of Botany, L. Kossuth University, H-4010 Debrecen, Hungary Clnstitute of Nuclear Research of the Hungarian Academy of Sciences, H-4026 Debrecen, Hungary ABSTRACT Owing to their small size and easy manipulation under aseptic conditions, duckweeds (Lemnaceae) provide good material for studying the effectsof toxicants and organic biocides. Applying static acute ecotoxicological tests the responses of threeduckweed species to different chemicals were compared. In each species the IC50 values of copper an Bonion biocide reached 10 mg/1 and 15 mg/l, respectively. Comparing the two Lemna species L. minor proved to be more sensitive than L. gibba. Simultaneously with the measurement of the productivity the changes in the CO 2 and 02 exchange were also determined during the static acute tests of biocide (methylene bisthiocyanate) by means of gas analyser (Quadrupole MS) in special growth chambers. There were no correlations between the respiration of duckweeds and the concentration of biocide. Differences wer found in the intensity of the photosynthesis as a function of the biocide treatment. Key words: Ecotoxicology; Duckweeds; Heavy metals; Biocides, Lemna; QMS INTRODUCTION Duckweeds (Lemna minor, Lemna gibba, Spirodela polyrrhiza), the nonrooted, floating, vascular aquatic plants have recently been proposed to apply in studies on ecotoxicological effects of toxic chemicals (Filbin and Hough, 1979; Huber et al., 1982; Wang, 1986a; Srivastova and Jaiswal, 1989).These species are widespread and fast-growing and reproduce themselves faster than other vascular plants (Hillman, 1961). The main advantages of using duckweeds instead of algae are that test solutions can 1993 Elsevier Science Publishers B.V.