SPECIATION OF HEAVY METALS IN DISTURBED AND UNDISTURBED SEDIMENTS FROM ATCHAFALAYA BAY, HOUMA NAVIGATION CANAL, AND SOUTHWEST PASS; LOUISIANA

In coastal Louisiana it is common to use dredge spoil to build marshland that has been lost due to a variety of factors. Under various conditions such as deposition in a drained oxygenated environment, metals in the spoil can become more bioavailable posing a threat to the ecosystem. This study compares metal availability in natural and dredged sediments to determine what changes occur in nature.

Forty four samples from three locations, Atchafalaya Delta, Houma Navigation Canal, and Southwest Pass, were analyzed for 13 common elements with known or potentially harmful health effects; Al, As, Ba, Be, Cd, Cr, Co, Cu, Fe, Mn, Pb, Sb and Zn. The Tessier sequential extraction procedure was used to obtain four fractions: soluble and exchangeable; carbonate bound; associated with Fe and Mn oxides; and bound to organic matter. All samples were processed in triplicate. Quantitative estimates of elemental abundance were obtained with inductively coupled plasma optical emission spectroscopy (ICP-OES). A mixed analysis of variance (ANOVA) was employed to determine differences due to location, fraction, sediment type, and element.

Visual inspection of the individual and mean results suggests variation with respect to geochemical fraction, sediment type, and location dependent on the geochemical affinities of each metal. Spoil often contained higher concentrations of metals than natural sediment. Location seemed to have little effect. ANOVA results confirm significant variation among the fractions for most metals. Between sediment type variation is limited to Al, Co, Mn, Pb, Sb and Zn and between the three locations to Ba and Fe. Internal variability at each location is more prevalent than variations between sediment type and the different locations.