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Florida Scientist


A 1992 survey of metal concentrations in sediments and clams from the Indian River Lagoon, Florida, was repeated during 2006–7. Concentrations of Cr, Ni, Se and V in sediments were at background values during both surveys with no indication of anthropogenic inputs. Average values for Ag, Cd and Zn in sediments, normalized to Al, were unchanged, but contamination was identified at several locations during both surveys. The proportion of sites with elevated values for sediment Cu, Hg and Pb increased between 1992 and 2006–7 from 22 to 65%, 9 to 35%, and 13 to 39%, respectively, with highest values near harbors and marinas. Concentrations of Hg and Zn exceeded sediment quality guidelines for an effects range low in the same two harbors during both surveys. Data from age-dated sediment cores collected in 2006–7 showed that Ag and Pb concentrations peaked during the 1970s whereas Cu values increased since the 1960s. For the clam Mercenaria mercenaria, mean values for Ag, Cd, and Zn were unchanged whereas mean concentrations of Cu and Pb were 30–40%lower in 2006–7 due to an absence of clams near urban areas. Mean values for Hg, Se and V in clams were ,2 times higher in 2006–7.

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