Ecotoxicology and Environmental Safety ] (]]]]) ]]]–]]] Piranhas (Serrasalmus spp.) as markers of mercury bioaccumulation in Amazonian ecosystems Jose´ G. Do´ rea, a, Antonio C. Barbosa, b Jurandir Souzade, c Pedro Fadini, d and Wilson F. Jardim e a Faculdade de Cieˆncias da Sau´de, Universidade de Brası´ lia, C.P. 04322, Brası´ lia DF, 70919-970 Brazil b IBAMA (Brazilian Environmental Agency), Brası´ lia, Brazil c Instituto de Quı´ mica, Universidade de Brası´ lia, Brası´ lia, Brazil d Faculdade de Quı´ mica, PUC, Campinas, Brazil e Instituto de Quı´ mica, UNICAMP, Campinas, Brazil Received 12 March 2003; received in revised form 2 July 2003; accepted 19 July 2003 Abstract Mercury (Hg) concentration in fish depends on feeding strategies and age/size within the species as well as on water parameters related to acidity and Hg speciation. We chose two species of piranhas (Serrasalmus aff. eigenmanni and Serrasalmus rhombeus) to test their suitability as markers of Hg bioaccumulation. The results of Hg concentrations in piranhas of the Rio Negro, with no history of gold-mining activity, are similar to other Amazonian rivers with intensive gold mining. An increase in water Hg associated with low pH favored higher mean Hg concentrations in the two species. S. rhombeus in this habitat showed a consistently higher Hg concentration than S. eigenmanni. This result was attributed to fish size because of differences in correlation coefficient between S. rhombeus (r ¼ 0:4443; Po0:0001) and S. eigenmanni (r ¼ 0:1520; P ¼ 0:0135). Matching for fish weight resulted in comparable ranges of Hg concentrations between the two species. r 2003 Elsevier Inc. All rights reserved. Keywords: Bioaccumulation; Serrasalmus spp; Mercury; Piranha; Rio Negro; Amazon 1. Introduction Mercury occurs naturally in the environment in three oxidation states (Hg 0 , Hg 1+ , and Hg 2+ ), and is wide- spread because of the chemical and physical properties of elemental Hg and its compounds formed both in nature and by humans. The methylation process of microorganisms in aquatic systems forms monomethyl- mercury (MMHg), the most important step in mercury’s entrance into the aquatic food chain (Clarkson, 1998). MMHg constitutes an important contaminant that can cause neuromotor disturbances and neuropathies (Clarkson, 1998). Fish are important concentrators and serve as indicators of Hg contamination of the aquatic systems of marine and freshwater environments (Clarkson, 1998). Numerous biochemical variables related to Hg methylation in the aquatic environment modulate its acquisition by organisms in the aquatic food web. However, it is accepted that there is a predictive association between fish feeding strategy, age and size within a particular species, and fish Hg concentration. Nichols et al. (1999) described a simplified Hg bioaccu- mulation model with phytoplankton at the base of the aquatic food chain (with zooplankton as the primary consumer), followed by small forage fishes (secondary consumers) and piscivorous fishes (tertiary consumers), in which higher MMHg concentrations are expected to occur. Mercury contamination of the biota in aquatic ecosystems involves an initial complex process of methylation, with subsequent acquisition and retention of MMHg by fish. Trophic position in the food web is an important determinant of Hg bioaccumulation in fish species. Fish physiology tolerates relatively high levels of MMHg without apparent signs of toxicity (Sweet and ARTICLE IN PRESS  Corresponding author. Fax: +55-61-368-5853. E-mail address: dorea@rudah.com.br (J.G. Do´rea). 0147-6513/$ - see front matter r 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2003.07.012