Pb levels in the de la Plata River vary widely among seasons (2 to 58 μg L− 1). This is likely due to seasonal fluctuations in industrial activity because this area is one of the most densely populated in the country (Guerrero and Kesten, 1994). Regardless, high levels of Pb (120–200 mg kg− 1) have been observed in sediments of tributaries to de la Plata River (Ronco et al., 2008).