Inventory of Anthropogenic Metals in Surface Sediments and Diffusive Fluxes Across Sediment-Water Interface of a Heavily Polluted Urban River: The Matanza-Riachuelo River, Argentina

The Matanza-Riachuelo River, a tributary of the Río the la Plata estuary that drains the Metropolitan Area of Buenos Aires, has been historically polluted by untreated urban and industrial discharges. To quantify the inventories of anthropogenic metals stored in surface sediments and their diffusive fluxes into the water column of this highly polluted urban river, surface water, sediment and interstitial waters were collected from 10 sampling stations along the middle and lower basin, as well as from a reference site far from urban and industrial centers. Metal concentrations in surface sediments (Zn: 569 ± 355 > Cr: 560 ± 659 > Cu: 164 ± 96 > Pb: 144 ± 97 > Ni: 30 ± 21 > Cd 1.1 ± 0.4 μg g−1) greatly exceed background concentrations (by factors of 2 to 24, and up to 37–77 times for Cr at the lower basin stations) highlighting the strong impact of anthropogenic sources. These elevated concentrations indicate that the sediments of the Matanza-Riachuelo River act as a massive long-term reservoir of metals. Inventory estimates suggest an accumulation of ~0.3–194 tons of anthropogenic metals within the top 10 cm of sediment across the middle and lower basin. Steep concentration gradients between surface and interstitial water result in substantial diffusive fluxes across the sediment-water interface amounting to 31 and 1323 kg year−1 of metals for the entire middle and lower basin. These findings suggest that the contaminated sediments of the Matanza-Riachuelo River are a persistent source of metal pollution to the overlying water column. These data provide a scientific basis for the development of effective management and remediation strategies in the basin.