Concentrations of ²¹⁰Pb and ¹³⁷Cs in sediment samples collected from two cores at a drainage channel to the La Plata river estuary in Buenos Aires, Argentina, were measured using ultralow-background detection systems. The ²¹⁰Pb data were used to determine the rate of sediment accumulation of the sites. These results were correlated with some heavy metal (chromium and lead) concentrations of the samples in an attempt to characterize the historical input of contaminants due to the industrial development, which has taken place in this area over the last century. The ¹³⁷Cs measurements demonstrate that cesium dating is not adequate in regions of the southern hemisphere.