TOXICITY OF ORGANOTINS TOWARDS CYANOBACTERIAL PHOTOSYNTHESIS AND NITROGEN-FIXATION

Inhibition of photosynthesis by a range of organotin compounds in Plectonema boryanum was concentration-dependent and decreased in the order tributyltin (Bu3SnCl) > tripropyltin (Pr3SnCl) greater-than-or-equal-to dibutyltin (Bu2SnCl2) greater-than-or-equal-to triphenyltin (Ph3SnCl) > triethyltin (Et3SnCl) > trimethyltin (Me3SnCl) > monobutyltin (BuSnCl3). IC50 values were determined for the most toxic organotin species and varied from approximately 1.2-mu-M for Bu3SnCl to approximately 13-mu-M for Ph3SnCl. A similar order of inhibition of photosynthesis was observed in Anabaena cylindrica, although here IC50 values were slightly lower (e.g. approximately 1-mu-M for Bu3SnCl and 5-mu-M for Ph3SnCl). Nitrogenase activity was generally more sensitive to inhibition by organotin compounds than photosynthesis in A. cylindrica and this was particularly evident for Bu2SnCl2; approximate lC50 values for Bu2SnCl2 were 3 and 9-mu-M, as estimated by nitrogenase activity and photosynthesis, respectively. These results indicate that organotin compounds have the potential to inhibit cyanobacterial metabolism in aquatic systems.