EFFECTS OF THE PHENYLUREA HERBICIDE ISOPROTURON ON PERIPHYTIC DIATOM COMMUNITIES IN FRESH-WATER INDOOR MICROCOSMS

The toxic effects of the phenylurea herbicide Isoproturon - IPU: (3-(4 -isopropylphenyl)-1, 1-dimethylurea) - were studied on the colonizatio n of periphytic diatom communities, within indoor microcosms consistin g of a mixed biotope (water column and natural sediment) and two biolo gical species-rooted macrophyte cuttings (Elodea densa) and benthic bi valve molluscs (Corbicula fluminea). The periphyton, essentially compo sed of diatoms, was collected on artificial substrata (glass slides) i n the upper layers of the water column, after two periods of exposure (34 and 71 days). IPU was initially added in the water or in the sedim ent compartment, at two nominal concentrations (LI and L2 levels) for each contamination source - 5 and 20 mu g litre(-1) and 100 and 400 mu g kg(-1) in sediment (w/w) respectively. The effects of IPU on the de nsity and community structure of periphytic diatoms are described. A m arked reduction in the diatom density was observed after 34 days expos ure to the lower concentration of IPU in the water (5 mu g litre(-1)). For the L2 levels, the very small number of live cells present did no t permit quantification of the diatom density. After 71 days, recovery in community parameters occurred for the two contamination levels of the sediment and water column sources. Samples collected in the experi mental units contaminated with the L2 levels were dominated by heterot rophic and smaller diatom species, such as Sellaphora seminulum. Data treatment based on factorial discriminant analysis enabled us to disti nguish the different contamination conditions, with only II species fr om the 130 taxa identified. (C) 1997 Elsevier Science Ltd.