TOXICITY OF CYANIDE AND CYANIDE COMPLEXES TO THE MARINE DIATOM NITZSCHIA-CLOSTERIUM

The effect of sodium cyanide (NaCN), iron-cyanide complexes and a blas t furnace effluent on the growth of the unicellular marine diatom Nitz schia closterium was investigated. Due to the volatile nature of HCN, the free and total cyanide concentrations in ail test solutions were m onitored dairy to ensure that average daily losses of free cyanide did not exceed 5%. The iron-cyanide complexes were less toxic than the Na CN, with 72-h EC50 values of 57, 127 and 275 mu g total-CN litre(-1) f or NaCN, K3Fe(CN)(6) and K4Fe(CN)(6), respectively. The estimated lowe st observed effect concentration (LOEC) for NaCN was 10 mu g litre(-1) . The toxicity of the cyanide complexes was largely due to free cyanid e (HCN + CN-) with possible additional toxicity caused by dissociation of the complexes at the algal cell membrane. The toxicity of an efflu ent from a blast furnace drawdown episode also correlated well with th e toxicity of free cyanide. (C) 1997 Elsevier Science Ltd.