Accumulation of metal(loid)s in plankton in coastal waters

The Gulf of Trieste (northern Adriatic Sea) is principally affected by the metal polluted Isonzo/Soča River as a result of historical Hg, and Pb and Zn mining activities in the hinterland. Analysis of metal(loid)s of the gulf waters, made using ICP-MS and CVAFS (Hg), showed the generalized order Fe>Zn>Cu>V>Mn>As>Ni,Se>U,Cr>Cd>Hg. Hg (nearly 100%), Cu (20%), Cr (10%) and Se (10%) had the highest affinity to colloidal organic matter (COM, >5 kDa). Similarly to COM, the levels of colloidal Hg and Cu peaks in summer due to their sequestration in accumulated COM (transfer to particulate phase). The partition coefficients of metal(loid)s between its colloidal phase and free ion and inorganic complexes in the water (K_dcoll) confirmed a strong binding of Hg and in lesser extent of Cu and Se in seawater colloids. Concentrations in suspended particulate matter (SPM, 0.45-20 µm) and fractionated plankton (20-50 µm, 50-200 µm, >200 µm) showed the following order Fe>Zn>Mn>Ni>Cu,Cr>Pb,As>V>Co>Se>Cd>U>Hg. Seasonal variations of metal(loid)s levels in plankton were related to plankton biomass (AFDW) and its organic matter content. The data for SPM and plankton showed increasing concentrations of Cr, As, Se, U and Pb with size while the highest levels of Fe, Mn, Cu, Zn (essential metals), Ni, V and Hg occured in the 50-200 µm fraction, and Co and Cd in the 20-50 µm fraction. Variations were related to the taxonomic composition and feeding behaviour of organisms: microzooplankton (50-200 µm) feed on nanoflagellates (20-50 µm) and copepods (>200 µm) prey on diatoms (20-50 µm) and microzooplankton, and cladocerans (>200 µm) on other autotrophs and heterotrophs. Log BCFs, mostly ranging between 4-5, were similarly distributed, considering that Hg and Cu, Cr and Se were colloidally bonded and can be less bioavailable to plankton. These data established metal(loid)s levels at the base of coastal food web providing information for marine organism consumed by humans.