It has long been known that most metal sorption in natural waters involves organic surfaces and the organic coatings ubiquitously present on all inorganic surfaces. Unfortunately, organic surfaces display none of the properties that are so advantageous in studies of inorganic surfaces. For instance, they boast a bewildering variety of functional groups whose dominance shifts intricately with ambient pH, yielding a large dynamic range of metal affinities. Moreover, metal sorption on living organisms may be driven by active physiological in addition to passive chemical processes.
In this project, researchers at the Chesapeake Biological Laboratory of the University of Maryland Center for Environmental Sciences will conduct a novel combination of solution (ICP-MS) and surface (XAFS) experiments to study the sorption of transition metals on the green macroalga Ulva lactuca, an organism possessing many attributes of a ?prototype? organic substrate. Preliminary work has demonstrated that the initial choice of U. lactuca and the chemically coherent yttrium and rare earth element (YREE) series allows unresolved problems to be addressed in a more straightforward manner than published studies that paired single metals with simple organisms (e.g., phytoplankton) or fairly elaborate ones (e.g., vascular plants). In particular, surface site identifications can be made from patterns of relative YREE distribution coefficients and verified independently with EXAFS techniques. The experimental strategy is specifically designed to answer such fundamental questions as: (A) Which are the dominant functional groups interacting with metals in solution? (B) How do distribution coefficients vary as a function of pH and other key parameters? (C) Do ternary complexes form on organic surfaces? (D) Is metal sorption affected by exopolymer sheaths and organic ligand exudates? (E) What interplay occurs between active physiological and passive chemical pathways of metal sorption?
The project is expected to have significant broader impacts in a variety of research areas related to transition metal interactions with organic surfaces in aquatic and marine systems. These include the surfaces of living organisms as well as other solid surfaces with complex organic coatings. The project will serve as the M.Sc. thesis research of one or, if possible, two graduate students.
