Heavy metal content in relation to particle size and organic content of surficial sediments in Miami River and transport potential

Transport of contaminants in Miami River (Florida, USA) sediments with river currents is a concern due to their potential impact in areas that are away from the potential sources. Accumulation profiles of five metals (As, Cd, Hg, Zn, Pb) in the surficial sediments of the Miami River were evaluated in relation to grain size (from less than 0.075 mm to 6.3 mm) and organic content. Surficial sediment samples were collected along the river basin as well as in bay waters. Fine sediments (<0.106 mm) contained more than 10 times the levels of Cd and Hg and more than 6 times the levels of arsenic in comparison to the sediments that are larger than 0.850 mm. Zn and Pb levels were more than 10 times in the fine sediments (<0.106 mm) in comparison to those that were larger than 4.750 mm. Cd, Hg, and Zn levels had significant correlation with the total organic carbon content of the sediments. This indicates that Cd, Hg, and Zn in fine sediments have the potential to be metabolized in addition to potential to be mobilized with river currents. Analysis of the Gibbs settling velocities of particles showed that particles smaller than 0.5 mm can be transported with the river currents. The levels of heavy metal in fine sediments (<0.425 mm) along the river bed showed that fine particles had tendency to be mobilized and accumulate at locations where the rivers currents are low and carried out to the bay.