Correlation of natural and technogenic mercury sources in the Baikal polygon, Russia

The Baikal polygon occupies the entire Lake Baikal watershed and the adjace nt areas drained by the Angara and Lena rivers, including the well-known Ir kutsk and Bratsk man-made water reservoirs. It is characterized by large di fferences of landscape, geology, mineralization and technogenic pollution. The main anthropogenic Hg-sources occur in the Irkutsk-Cheremkhovo industri al zone where chemical industries are prominent (Usolie-Sibirskoe, Sayansk, Zima). In addition, some Hg bedrock occurrences and anomalies related to f aults are known in the region. In the past decade, several geochemical stud ies have been carried out: multi-media (stream sediment, soils, bedrock, wa ter, snow, plants) mapping of the Baikal area (110,000 km(2), 1 site/simila r to 100 km(2)) and the Irkutsk and Osa districts (6000 km(2), 1 site/13-16 km(2)); regional soil and snow geochemical monitoring profiles; geochemica l studies of water reservoirs and surroundings of industrial enterprises. H g-analyses were made using AAA (detection limit 2 ppb) and AAA with prelimi nary chemical concentration on sorbents (detection limit 0.02 ppb). The pre liminary data indicated mean values (in ppb) as follows: bedrock 11; stream sediment 21; alluvial soil 29; Baikal bottom sediment 66; snow water 0.12; bottom sediment of the Irkutsk water reservoir 30; bottom sediment in the Bratsk water reservoir 30-6000; Bratsk plankton 130-6500; Bratsk algae 6-65 00; Bratsk fish 50-6000. Three typical Hg-distribution patterns were recogn ized in sediment profile of the Bratsk reservoir: (1) increasing concentrat ion from bottom to surface; (2) decreasing concentration from bottom to sur face; and (3) irregular distribution of values with 1-2 maxima. The latter is typical of sites with high technogenic pollution. The strong positive co rrelation of Hg-contents and rates of sedimentation is also indicative of p olluted sediments in the Bratsk reservoir. The Hg chemical time bomb proble m can be a reality for the Baikal region. The following anomaly types were noted: (1) bedrock-related natural anomalies; (2) fault-related natural ano malies and possibly Baikal rift zone anomalies; (3) technogenic haloes near industries and settlements; (4) technogenic anomalies related to Au placer mining; (5) technogenic anomalies in dispersion flows (sedimentary bars). (C) 1999 Elsevier Science B.V. All rights reserved.