Effects of the organotin pesticide azocyclotin in aquatic microcosms

Effects of the organotin acaricide azocyclotin were studied in freshwater microcosms. Run-off conditions were simulated by applying the substance as soil slurry to nominal concentrations of 5, 15, 35, 135 and 405 mu g/L, respectively. Plankton and benthon as well as physico-chemical water parameters were analysed regularly for effects over a period of 7 months. Zooplankton was affected at nominal concentrations greater than or equal to 45 mu g/L. Phyllopoda and nauplia of copepods reacted sensitively whereas direct effects on rotifers and ostracodes were not observed. Within the phytoplankton, picoplankton < 2 mu m and algae 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 observed. Anaerobic microbial degradation activity in the sediment was stimulated in microcosms with high plankton mortality, but microbial biomass, measured as dehydrogenase activity, was not affected. Changes in meiozoobenthon structure were evident in microcosms treated with greater than or equal to 135 mu g/L azocyclotin. The results indicate that under the experimental conditions nominal concentrations of 135 mu g/L azocyclotin applied as soil slurry had severe effects on the biocenoses. (C) 1997 Elsevier Science Ltd.