Environmental toxicity assessment in the Parana river delta (Argentina): simultaneous evaluation of selected pollutants and mortality rates of Corbicula fluminea (Bivalvia) early juveniles

Water and sediment samples were collected in the lower Parana delta at four sites with different levels of exposure to pollution to evaluate the anthropogenic impact through chemical analyses and mortality bioassays. Individual polychlorinated biphenyls, chlorinated pesticides, aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, and heavy metals were measured in waters, porewaters and sediments. The same three phases were also subjected to toxicity assays with straight-hinged juveniles of Corbicula fluminea. Concentrations of several pollutants were above levels recommended for the protection of aquatic life: in waters, Zn, Cu and Cr were 1.6-4.9 times higher, whereas in the sediments Cr was 1.8-3.6, and benzo(a)pyrene was 2.8-5.6 times higher. Pollutant concentrations followed a clear geographic pattern with highest values in the densely populated area of the Reconquista and Lujan rivers, lower levels in the San Antonio, and lowest loadings in the remote Parana de las Palmas. This gradient was adequately matched by the pattern of mortality rates of C. fluminea early juveniles, which were highest in the Reconquista-Lujan (40-93 %) and lowest land not significantly different from the control) in the Parana (3.3-23%). Mortality rates also increased from surface waters (3.3-53%), to porewaters (12-73%), to sediments (23-93%). Although toxicity was probably mainly due to dissolved contaminants, agreement between chemical and biological evidence of pollution was best for the sediment compartment, whereas porewater and surface water showed a higher degree of variability. (C) 2001 Elsevier Science Ltd. All rights reserved.