USE OF XAS TO DETERMINE THE CHEMICAL SPECIATION OF BIOACCUMULATED MANGANESE IN POTAMOGETON PECTINATUS

Manganese (Mn) accumulation was measured in Potamogeton pectinatus L. (sago pondweed) over a growing season. Leaf tissue Mn content increase d from 120 mg kg(-1) in June to 4990 mg kg(-1) by October. Our objecti ve was to chemically speciate bioaccumulated Mn in P. pectinatus with x-ray absorption spectroscopy (XAS). Differences were found in Mn vale nce in leaf tissue between June, October, and January when compared to model inorganic Mn compounds. Manganese in June leaf tissue was most like [Mn2+(H2O)(6)]. By October, average valence of Mn in leaf and roo t tissues was similar to Mn3O4. However, there was little agreement in the chemical structure of Mn in these tissues and Mn3O4. Senescent le af tissue in January differed from October because the valence had shi fted back toward Mn2+. The Mn3+ fraction had leached from leaf tissue between October and January. This coincided with a decrease in total M n concentration during this same period. Manganese bioaccumnlation in this aquatic species occurs in two phases: (i) Mn2+ is bound in finite sites and coordinated by water, (ii) once filled, Mn2+ is oxidized an d stored as a Mn3+ oxide within the plant that can be leached upon sen escence.