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) ≥ dibutyltin (Bu2SnCl2) ≥ triphenyltin (Ph3SnCl) > triethyltin (Et3SnCl) > trimethyltin (Me3SnCl) > monobutyltin (BuSnCl3). IC50 values were determined for the most toxic organotin species and varied from approximately 1.2 μM for Bu3SnCl to approximately 13 μM 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 μM for Bu3SnCl and 5 μM for Ph3SnCl).Nitrogenase activity was generally more sensitive to inhibition by organotin compounds than photosynthesis in A. cylindrica and this was particularlyy evident for Bu2SnCl2; approximate IC50 values for Bu2SnCl2 were 3 and 9 μM, as estimated by nitrogenase activity and photosynthesis, respectively. These results indicate that organotin compounds have the potential to inhibit cyanobacterial metabolism in aquatic systems.