The Gellyfish: An in situ equilibrium-based sampler for determining multiple free metal ion concentrations in marine ecosystems.

Free metal ions are usually the most bioavailable and toxic metal species to aquatic organisms, but they are difficult to measure because of their extremely low concentrations in the marine environment. Many of the current methods for determining free metal ions are complicated and time-consuming, and they can only measure 1 metal at a time. The authors developed a new version of the "Gellyfish," an in situ equilibrium-based sampler, with significantly reduced equilibration time and the capability of measuring multiple free metal ions simultaneously. By calibrating the Gellyfish to account for its uptake of cationic metal complexes and validating them in multi-metal competition experiments, the authors were able to determine free metal ion concentrations previously collected over 10 mo at 5 locations in Boston Harbor for Cu, Zn, Pb, Ni, and Cd. This generated 1 of the largest free metal ion datasets and demonstrated the applicability of the Gellyfish as an easy-to-use and inexpensive tool for monitoring free ion concentrations of metal mixtures in marine ecosystems.