Particulate Trace Metal Composition in Coastal Waters Surrounding Taiwan

Coastal zones are dynamic environments where materials are transported from the land and where biomass is the most abundant, feeding on the terrestrial nutrients supplied. Therefore, compositions of particulate matter in coastal waters are complex. We collected size-fractionated particulate matter from Taiwan’s coastal waters and determine trace metal concentrations, along with some key parameters that allow for the assessment of contribution of particulate matter from different sources. Al content in the particles is used to derive a mineralogical contribution (largely terrestrial) in the particle samples, based on the fact that Al concentrations in common clay minerals and in biota are 2-3 orders of magnitude different. Thereafter, trace metal concentrations in biotic particles can be derived after subtracting contribution from mineral particles (using a reference trace metal concentration in mineral phase), and the results can be compared directly. In the four size classes of particulate matter we collected (0.4-10 µm, 10-60 µm, 60-153 µm, and >153 µm), Al concentration, i.e. mineralogical contribution, decreased with increasing size. The derived biotic trace metal concentrations in near-shore coastal waters showed large variations in different size fractions. Biotic Cd concentrations increased with increasing particle size, implying bioaccumulation along the food chain. For Pb, higher concentrations were mostly associated with smaller size fractions. This may suggest the particle-reactive characteristics applied here for biotic particles. For other elements of biological and environmental significance, such as Cu, Ni, and Zn, their bulk particulate concentrations were relatively constant regardless sample locations and size fraction, but large variations in the biotic contents were found among different size fractions, as well as among samples collected from different locations with various extent of anthropogenic influence.