67-Copper (half-life 62 h; incubation) & 64-Cu (half-life 12.7 h; lab) uptake
| Copper uptake (67/64Cu) |
|---|
| Approach: radiotracer (67Cu for in situ; 64Cu for lab) incubation |
| Context: incubation, lab |
| Spatial scale: point sample |
| Temporal scale: 4–24 h |
| Units: (x)mol Cu biomass-1 d-1; (x)mol Cu L-1 d-1 |
| Community captured: all (usually > 0.2 or 0.7 µm) |
| Co-measurements: biomass (Chl, cells, POC, cell volume) |
Method Overview
Copper uptake rates are measured using radioactive copper isotope tracers. Two isotopes are available depending on context: 67Cu (half-life 61.8 h, gamma emitter; suitable for shipboard incubations of up to ~3 days) and 64Cu (half-life 12.7 h, positron/gamma emitter; suitable for short lab incubations). The tracer (CuCl2) is added to seawater samples under trace-metal-clean conditions, equilibrated with the ambient copper-ligand pool, and samples are incubated for 4–24 h. Cells are collected by filtration, rinsed with a chelating wash to remove surface-adsorbed copper, and counted by gamma spectrometry. Uptake rates are calculated from the fraction of radiolabelled Cu incorporated relative to total dissolved radiolabelled Cu[1].
Copper is both an essential micronutrient (for plastocyanin, cytochrome oxidase) and potentially toxic at elevated concentrations, making uptake rate measurements particularly relevant for understanding Cu nutrition and toxicity thresholds.
Scale of measurement
Sampling after 4–24 h incubation under trace-metal-clean conditions.
Data generated
Copper uptake rates (mol Cu L-1 d-1 or mol Cu biomass-1 d-1). Combined with Cu quotas, cellular Cu:C ratios can be derived.
Units & currency
Units are (x)mol Cu biomass-1 d-1 or (x)mol Cu L-1 d-1. The currency is Cu.
Sample size
Typical samples are < 1 L in volume.
Repositories & databases
Limitations
Isotopic fractionation between 64/67Cu and ambient 63/65Cu is minimal. The short half-life of 64Cu limits its use to rapid lab experiments and requires proximity to a cyclotron or nuclear reactor for tracer production. Natural organic ligand complexation strongly controls Cu bioavailability; the equilibration step must achieve realistic speciation. Bottle effects and steady-state assumptions apply.
Example Applications & Protocols
Classic examples
- Semeniuk et al. (2016) Using 67Cu to study the biogeochemical cycling of copper in the northeast subarctic Pacific Ocean [1]
Recent applications
- González-Dávila et al. (2024) Cu transport and complexation by the marine diatom Phaeodactylum tricornutum [2]
Common calculations/conversions
- Cu uptake rate = (cpmcells / cpmdissolved) × [Cudissolved] / incubation time.
References
- ↑ 1.0 1.1 Semeniuk, D. M., Bundy, R. M., Bhatt, S., Landry, M. R., Twining, B. S., & Bruland, K. W. (2016). Using 67Cu to study the biogeochemical cycling of copper in the northeast subarctic Pacific Ocean. Frontiers in Marine Science, 3, 78. https://doi.org/10.3389/fmars.2016.00078
- ↑ González-Dávila, M., Santana-Casiano, J. M., Laglera, L. M., & Millero, F. J. (2024). Cu transport and complexation by the marine diatom Phaeodactylum tricornutum: implications for trace metal complexation kinetics in the surface ocean. Science of The Total Environment, 919, 170752. https://doi.org/10.1016/j.scitotenv.2024.170752