Geochemical phases of metals in Hudson River estuary sediments

Bottom sediment samples were collected from six locations along a section of the Hudson River Estuary, 5.3 to 82.7 km from the ocean. These samples were analyzed for particle size and, due to the bimodal distribution of the sediment, were separated into two size fractions, fine (<7.8 um) and coarse (7.8-62 um). These fractions were subject to a sequential chemical phase extraction procedure to differentiate the ion exchangeable, carbonate, metallic oxide coating, and organic phases. The extracted phases were analyzed with an inductively coupled plasma atomic emission spectrophotometer for Cd, Co, Cc, Cu, Fe, Ni, Pb, and Zn. Metals were found to be associated largely with the fine particle-size fraction. The concentration of fine particles (especially the <2 um size mode within the fine fraction) is crucial in influencing overall metal content. This is evidenced by strong correlations between the <2 mu m or clay mode and concentrations in the metallic-oxide coating phase. Various metal/metal relationships exist among the phases and fractions studied and are highlighted by strong correlations, such as Ni and Zn, and Cu and Cd. The trends associated among the metal and mud concentrations are significant in terms of assessing the bioavailability of heavy metals within the river and estuary system, and, as a result, provide valuable insight into the ultimate fate of pollutants which are introduced to this unique environment.