Temporal Trends of Persistent Organochlorine Contamination in Russia: A Case Study of Baikal and Caspian Seal Shinsuke Tanabe, 1 Satoko Niimi, 1 Tu Binh Minh, 1 Nobuyuki Miyazaki, 2 Evgeny A. Petrov 3 1 Center for Marine Environmental Studies, Ehime University, Tarumi 3-5-7, Matsuyama, 790-8566, Japan 2 Otsuchi Marine Research Center, The Ocean Research Institute, The University of Tokyo, Akahama, Otsuchicho, Iwate 028-1102, Japan 3 Limnological Institute of the Siberian Division of the Academy of Science of Russia, 664033 Irkutsk, Uran-Batorskaya 3, Russia Received: 17 April 2002 /Accepted: 19 August 2002 Abstract. To examine temporal trends of organochlorine (OC) contamination in Lake Baikal and the Caspian Sea, concentra- tions of persistent OCs, such as DDT and its metabolites (DDTs), polychlorinated biphenyls (PCBs), hexachlorocyclo- hexane (HCHs), chlordane compounds (CHLs), tris(4-chloro- phenyl)methane (TCPMe), and tris(4-chlorophenyl)methanol (TCPMOH), in the blubber of female seals were determined. Collections were made in 1992, 1993, 1995 and 1998. DDT concentrations in Baikal and Caspian seals showed a rapid decline during 1992 to 1998, while the concentrations of PCBs declined slowly. Elevated concentrations of HCHs were found in Caspian seals and there was no decline in their concentra- tions during 1993 to 1998, which could be due to extensive usage of HCHs around Caspian Sea in recent years. Trends of TCPMe and TCPMOH residues in Caspian seals were similar to that of DDTs. The pattern of PCB isomers in both Baikal seals and Caspian seals exhibited little temporal variations. Concentrations of non-ortho coplanar PCBs have declined at a faster rate than those of mono-ortho congeners. Compilation of available data on OC contamination in the North Pacific, Ant- arctic, Caspian Sea, Lake Baikal, and India suggested that the time trend of residues of contaminants during the 1990s were different among these regions. Residue levels of OC insecti- cides have declined slowly while PCBs remained at a steady state in the open oceans and the Antarctic. The magnitude of temporal variation in Lake Baikal seemed to be higher than that in the Caspian Sea. Residue concentrations of OCs have in- creased in Ganges River dolphins from 1989 –92 to 1994 –96, suggesting that tropical, developing countries are potential emission source of OCs. Widespread contamination by persistent organochlorines (OCs) and their toxic impacts on humans and wildlife have been a major concern over the past four decades. Despite the increasing numbers of monitoring studies in developed nations and tropical developing countries, the status of OC contami- nation in the former USSR and Middle East countries has been scarcely investigated (Iwata et al. 1995; Kannan et al. 1995; Prudente et al. 1997). Among these locations, the Caspian Sea, the biggest landlocked body of salt water, and the Lake Baikal, the oldest and deepest lake in the world, are among target areas deserving particular attention due to their numerous unique geographical and ecological characteristics. In recent years, our research group has been actively involved in the research program dealing with environmental contaminants in Lake Baikal and Caspian Sea, which was supported by the Baikal International Center for Ecological Research (BICER) and the Japan Association of Baikal International Research Program (JABIRP). In the context of this program, we carried out extensive investigations to understand the transport, fate, and bioaccumulation features of persistent OCs in the aquatic eco- systems from Lake Baikal and the Caspian Sea (Iwata et al. 1995; Nakata et al. 1995, 1997; Watanabe et al. 1999a). Our studies showed that contamination by OCs has been a major concern for higher trophic animals, particularly Baikal seals (Phoca sibirica) and Caspian seals, inhabiting these areas (Phoca caspica) (Nakata et al. 1995; Watanabe et al. 1999a). This indicated a need for an investigation into the future trend of OC contamination in Lake Baikal and Caspian Sea in order to preserve their unique ecosystems. However, no investigation to examine the temporal trends of OC concentration in Lake Baikal and Caspian Sea has been conducted. Time trend studies are useful tools to trace the history of contamination, to predict future trends of OC levels in the environment and to explore new clues for understanding possible toxic effects of these contaminants in aquatic organisms. In this study, we used the seals as bioindicators for under- standing temporal trend of contamination in Lake Baikal and Caspian Sea. During sampling surveys in 1995 and 1998, we collected seals from Lake Baikal and Caspian Sea and deter- mined the concentrations of persistent OCs, such as DDT and its metabolites (DDTs), polychlorinated biphenyls (PCBs), hexachlorocyclohexane (HCHs), and chlordane compounds (CHLs), and two newly-identified contaminants, tris(4-chloro- phenyl)methane (TCPMe) and tris(4-chlorophenyl)methanol. Concentrations of OCs were compared to those reported in our Correspondence to: S. Tanabe; email: shinsuke@agr.ehime-u.ac.jp Arch. Environ. Contam. Toxicol. 44, 533–545 (2003) DOI: 10.1007/s00244-002-2092-4 ARCHIVES OF Environmental Contamination and T oxicology © 2003 Springer-Verlag New York Inc.