Comparative trace metal assessment in phytoplankton using size and density fractionation

Abstract

Trace metal assessment in marine phytoplankton is challenging due to complex assemblages and variable amounts of abiogenic suspended particulates. Using aliquots, this study were able to compare trace metal concentrations in plankton samples subjected to size and density fractionation. Elements including Cr, Mn, Fe, Ni, Cu, Zn, As, Sr, Hg, and Pb were analyzed by inductively coupled plasma mass spectrometer (ICP-MS). Trace metals were found to be significantly higher in size fractionated than density fractionated plankton for both small (1.2–50 μm) and large (50–120 μm) fractions. Metals from abiogenic sources (61–88%) also significantly contributed to trace metals detected in 1.2–120 μm suspended particulates collected from Kaohsiung Harbor. Results suggest that size fractionation can potentially overestimate trace metals in phytoplankton. It is therefore recommended combining the two methods by first isolating different size fractions followed by density fractionation to separate phytoplankton from zooplankton, and abiogenic particulates from phytoplankton assemblages, respectively.