Biotesting of surface water and bottom sediments from the Ile River and the southwestern part of the Balkash Lake

Abstract

During the expedition trips to the Southern Balkhash in June 2018, samples of surface waters and
bottom sediments from various sites of the Ile River and Lake Balkash (the southwestern part) were collected and investigated. As a result of the hydrochemical analysis of surface waters, it was determined
that the waters of the Ile (Bakanas) and Topar rivers and Balkash lake (Kuygan) were the most polluted
with heavy metals: Pb, Cd, Zn and Fe, their level exceeded the maximum permissible concentration
(MPC) by 1.6-fold to 5.5-fold. At the same sites of the studied water basin, the MPC for Pb, Cr, Co, Ni,
Cd, Zn and Fe in bottom sediments was found to be exceedeng. At the same time, the level of heavy
metals found in sediments largely exceeded their content in surface waters, especially in terms of Fe
content (MPC is higher by 2.9-fold to 6.9-fold). Biotesting of surface waters and sediments on zebrafish
(Danio rerio) and African clawed frog (Xenopus laevis) embryos revealed their significant embryotoxic
effect, expressed in their 20-40% mortality. In this regard, possible reduction in the number of fish and
amphibians in the studied areas was suggested. The results of the study are important for the development of environmental protection measures in the Southern Balkhash region. It is suggested that the
decline in the number of fish and amphibians in the studied water bodies is associated with their death
in early stages of development.
Key words: Ile river, Balkash lake, surface waters, sediments, heavy metals, biotesting, Danio rerio,
Xenopus laevis, embryotoxicity.