Vertical fluxes and accumulation of trace metals in superficial sediments of the Río de la Plata estuary, Argentina.

Superficial sediments and settling material collected in Buenos Aires coastal area were analyzed to evaluate the accumulation and sources of trace metals. Residual elements showed homogeneous sedimentary concentrations (Fe: 23,846 +/- 4,367; Ni: 10 +/- 2.7; Mn: 706 +/- 314 μg g(-1)) whereas anthropogenic metals presented exponentially decreasing offshore gradients (Zn: 98 +/- 69; Cr: 28 +/- 21; Cu: 19 +/- 15; Pb: 18 +/- 13 μg g(-1)). Anthropogenic impact was evaluated through metal-Fe relationships, Fe-normalized enrichment factors and sediment quality guidelines. The slopes of metal-Fe regressions from background sites were comparable to upper crust metal ratios, excepted Cr which is impoverished, and Mn which is diagenetically enriched. Metal-Fe relationships also hold for most 2.5 km offshore sites but with higher slopes denoting human influence, and are completely lost in 1-2.5 km sediments and trap material which plot over the regressions and exceed sediment quality guidelines.