Measurement of shipwreck-derived waterborne trace metals using DGT samplers

A contemporary approach to the assessment of metal pollutants in aquatic environments has been to measure contaminant concentrations in biological indicator species (mussels, oysters). However, for environments in which such indicator species do not occur naturally and cannot be deployed, alternative approaches for monitoring trace-metal pollution are required. Three years after the 2011 grounding of the MV Rena, diffusive gradients in thin films (DGT) samplers were deployed at Otaiti (the offshore reef where the Rena grounded) to assess levels of waterborne trace-metal contamination. Although the probability of detecting waterborne contaminants within a dynamic open ocean reef environment would seem low, due to mixing and dilution, our analyses confirmed the presence of copper (≤0.43 vs ≤0.27 nmol kg−1), iron (≤6.3 vs ≤4.2 nmol kg−1), aluminium (≤8.9 vs ≤1.3 nmol kg−1), zinc (≤2.8 vs ≤2.0 nmol kg−1) and manganese (≤0.11 vs ≤0.09 nmol kg−1) at elevated concentrations in the Rena debris field relative to reference sites. The results demonstrate the utility of DGTs as a tool for measuring waterborne contaminants and suggest further research is required to characterise the contaminant plume and determine what effect it might have on the recovery of Otaiti's impacted biological communities.