An algal probe for copper speciation in marine waters: laboratory method development

Area of Science:

• Marine biology
• Environmental chemistry
• Algal physiology

Background:

• Copper bioavailability is critical for marine phytoplankton growth.
• Accurate measurement of copper's effects requires controlled laboratory conditions.
• Synthetic ligands like ethylenediaminetetraacetic acid (EDTA) can interfere with natural metal speciation.

Purpose of the Study:

• To develop and validate laboratory-based algal assays for assessing copper bioavailability.
• To investigate the effects of copper on the marine alga Thalassiosira weissflogii.
• To establish a method for studying ambient metal speciation without synthetic ligands.

Main Methods:

• Laboratory algal assays using Thalassiosira weissflogii.
• Development of a calibration strategy avoiding ethylenediaminetetraacetic acid (EDTA) in Aquil growth medium.
• Use of 65Cu stable isotope additions to examine growth, chlorophyll a, copper uptake, phytochelatin production, and dissolved organic carbon excretion.
• Determination of optimal assay duration (30 hours) through concentration-response experiments.

Main Results:

• Algal growth rates significantly decreased with increasing copper concentrations (pCu from 8.8 to 7.8).
• Intercellular copper concentrations in T. weissflogii increased with higher external copper levels.
• Established critical copper thresholds: pCu = 7.7 for 50% growth reduction and 625 µg/g copper per algal mass.

Conclusions:

• The developed EDTA-free algal assay enables accurate study of copper's effects on T. weissflogii.
• This method allows for the investigation of copper speciation in marine waters under ambient conditions.
• Findings provide essential data for understanding copper's ecological impact on marine phytoplankton.