Testing a new approach to quantify intracellular trace metal contents in microphytoplankton using sequential...

Area of Science:

• Marine biogeochemistry
• Trace metal analysis
• Phytoplankton physiology

Background:

• Existing methods for quantifying intracellular trace metals (TM) in microphytoplankton are flawed, assuming no inorganic particle contamination.
• Accurate TM quantification is crucial for understanding their role in phytoplankton biology and marine biogeochemical cycles.

Purpose of the Study:

• To develop and validate a sequential selective extraction protocol for analyzing TM in suspended particulate matter.
• To preserve phytoplankton cellular integrity during extraction for accurate intracellular TM quantification.

Main Methods:

• A four-step sequential extraction protocol using ascorbate, NaOH, EDTA, and HCl was developed.
• Scanning electron microscopy (SEM) assessed extractant impact on phytoplankton integrity; hydrogen peroxide proved destructive.
• Polycarbonate membranes containing filtered seawater were subjected to sequential extraction followed by Aqua Regia digestion for intracellular TM analysis.

Main Results:

• The protocol effectively preserved phytoplankton integrity, enabling accurate TM quantification in diatoms and silicoflagellates.
• Al, V, Mn, Fe, Cu, As, Pb, and Th showed limited internalization (<20% in Aqua Regia fraction).
• Cr (93±3%), Co (74±23%), and Ni (79±17%) were predominantly intracellular, indicating significant roles in TM biogeochemical cycles.

Conclusions:

• The proposed sequential extraction protocol is robust and effective for quantifying intracellular TM in microphytoplankton.
• Cr, Co, and Ni are significantly internalized by phytoplankton, suggesting key roles in their biogeochemical cycling.
• This method improves the accuracy of TM quantification in marine samples, crucial for ecological and biogeochemical studies.