Environmental Research 97 (2005) 287–292 Mutagenic effects of mercury pollution as revealed by micronucleus test on three Amazonian fish species $ Jorge I.R. Porto, a,Ã Cleusa S.O. Araujo, b and Eliana Feldberg a a Instituto Nacional de Pesquisas da Amazoˆnia, Coordenac ¸a˜o de Pesquisas em Biologia Aqua´tica, Cx. Postal 478, Manaus AM 69011-970, Brazil b Centro Universita´rio Nilton Lins, Av. Professor Nilton Lins-3259, Manaus AM 69058-940, Brazil Received 14 November 2003; received in revised form 7 April 2004; accepted 12 April 2004 Available online 19 June 2004 Abstract Genotoxic effect of mercury pollution over Amazonian fish species was evaluated by using the micronucleus test (MNT). Distinct mean frequencies of micronuclei (MN) were observed in three trophically distinct characin fish species collected in two riverine environments in the Amazon Basin: the Madeira (polluted area) and the Solimo˜ es (unpolluted area) rivers. Mean frequencies of MN observed in Prochilodus nigricans (detritivore), Mylossoma duriventris (omnivore), and Hoplias malabaricus (piscivore) from the Madeira River were significantly higher compared to the frequencies from the same species from the Solimo˜es River. In addition, mean frequencies of MN from piscivore species were almost fivefold higher than the detritivore and/or omnivore species. We conclude that MNT in fish erythrocytes may be useful for indicating genotoxity of mercury in Amazon rivers. r 2004 Elsevier Inc. All rights reserved. Keywords: Amazon basin; Bioaccumulation; Characins; Mercury; Micronucleus 1. Introduction Mercury is considered one of the most dangerous of the heavy metals because of its high toxicity, bioaccu- mulative properties, and other deleterious effects on biota including genetic alteration or mutagenesis (WHO, 1990). Mercury contamination in Amazon rivers is generally associated with gold mining, since almost all gold produced in the Amazon is obtained by a process where mercury is used to amalgamate and concentrate gold (Lacerda et al., 1987). If we consider only anthropogenic sources, compared to gold-mining activ- ity, neither industrial nor municipal wastewater has been considered relevant for heavy metal pollution in the major Amazonian rivers. However, soil erosion and forest fires also have been advocated as other sources of mercury pollution in the region (Roulet et al., 1999). Key variables such as dissolved organic carbon and pH are thought to influence mercury levels in freshwater biota (Silva-Forsberg et al., 1999). A huge concern about mercury pollution in Amazon rivers has been demonstrated in several papers and the incorporation and bioaccumulation of mercury in the aquatic food chain or in the riverside population has been investigated in different places in the Amazon Basin such as Amapa´ (Fostier et al., 2000), Gurupi (Palheta and Taylor, 1995), Madeira (Barbosa et al., 1995; Boischio and Henshel, 1996), Negro (Forsberg et al., 1995; Silva-Forsberg et al., 1999), Tapajo´ s (Akagi et al., 1994), Tocantins (Aula et al., 1994), Uatuma˜ (Kehrig et al., 1998), and Xingu (Barbosa et al., 1995) river drainages. Of these, Tapajo´s and Madeira are probably the best-studied sites given the historic gold- mining activities. Fish are important indicators of water pollution and the piscine micronucleus test (MNT) is one method used ARTICLE IN PRESS www.elsevier.com/locate/envres 0013-9351/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2004.04.006 $ The care and treatment of the animals utilized in our study as well as all fish handing in the wild were in accordance with international guidelines and received institutional approval from INPA (Instituto Nacional de Pesquisas da Amazoˆnia). Ã Corresponding author. Fax: +5592-643-3240. E-mail address: jirporto@inpa.gov.br (J.I.R. Porto).