Copper speciation and toxicity in Macquarie Harbour, Tasmania: an investigation using a copper ion selective electrode

Abstract

Growth inhibition bioassays using Nitzschia closterium were used to determine the relationship between the reduction in the growth rate and the concentration of free copper ion (Cufree) as measured with a copper Ion-Selective Electrode (ISE). At a salinity of 20, no toxicity was found for Cufree=10−11.79 M while, for Cufree=10−8.20 M, the growth rate was reduced to <8% of the control. Copper was found to be less toxic at S=30 and the growth rate was reduced to 40% of the control at Cufree=10−8.50 M. These results are comparable to other estimates of the toxicity of copper to marine organisms. Macquarie Harbour is a large semi-enclosed bay that is heavily polluted with copper and measurements of Cufree, using an ISE, ranged from 10−11.27 to 10−12.04 M even though total copper concentrations were as high as 390 nM. In line with these low concentrations of Cufree, Macquarie Harbour waters (S=20) were not found to be toxic to N. closterium. A reduction in growth rate was observed in some Macquarie Harbour waters at S=30 but this was attributed to some factor other than copper toxicity. These results are in direct contrast with ASV measurements, which predicted high toxicity for all water samples. More than 99.9% of the total copper was bound to ligands that were probably based on the high concentrations of humics entering the harbour and we propose that at least some of the copper was associated with colloids containing humic matter and iron and manganese (hydr)oxides.