EFFECTS OF THE ORGANOTIN PESTICIDE AZOCYCLOTIN IN AQUATIC MICROCOSMS

Effects of the organotin acaricide azocyclotin were studied in freshwa ter microcosms. Run-off conditions were simulated by applying the subs tance as soil slurry to nominal concentrations of 5, 15, 35, 135 and 4 05 mu g/L, respectively. Plankton and benthon as well as physico-chemi cal water parameters were analysed regularly for effects over a period of 7 months. Zooplankton was affected at nominal concentrations great er than or equal to 45 mu g/L. Phyllopoda and nauplia of copepods reac ted sensitively whereas direct effects on rotifers and ostracodes were not observed. Within the phytoplankton, picoplankton < 2 mu m and alg ae of 2-10 mu m were inhibited at nominal concentrations greater than or equal to 135 mu g/L and blooms of less sensitive species were obser ved. Anaerobic microbial degradation activity in the sediment was stim ulated in microcosms with high plankton mortality, but microbial bioma ss, measured as dehydrogenase activity, was not affected. Changes in m eiozoobenthon structure were evident in microcosms treated with greate r than or equal to 135 mu g/L azocyclotin. The results indicate that u nder the experimental conditions nominal concentrations of 135 mu g/L azocyclotin applied as soil slurry had severe effects on the biocenose s. (C) 1997 Elsevier Science Ltd.