Risk Management Scenario for Multiple Heavy Metal Contamination at River Sediments in the Middle Iskar Cascade

TODOROVA, Y., St. LINCHEVA and Y. TOPALOVA, 2014. Risk management scenario for multiple heavy metal contamination at river sediments in the Middle Iskar cascade. Bulg. J. Agric. Sci., Supplement 1: 100–104 In the middle part of Iskar River, the effects of complex pollution with organics and diffi cult-biodegradable compounds have been observed from decades. Nowadays this part of the river is a subject of intensive hydrotechnical activity for construction of a cascade of 9 mini-hydroelectric power stations and this strongly poses the question of ecological improvement and achievement of high energy effi ciency. The main objective of this work was to design, develop and apply a management scenario to indicate the potential risk level of heavy metal concentrations in river sediments, related to response of sediment microbial communities – one of the most sensitive indicators for pollution and ecosystem self-purifi cation potential. The study was realized on 5-step schedule including: a long-term monitoring of water and sediment quality; identifi cation of risk with primary signifi cance and real risk situations for this period; analyses of the risk factors; evaluation of response of the microbial communities; assessment of relation between level of risk factor and response by correlative dependences. The heavy metals concentrations were determined by atomic absorption spectrophotometry; the total microbial count and number of bacteria cultivated on Endo-media were analyzed by standard BDS-EN-ISO cultivation methods. The assessment of relevant microbial response shows an obvious effect of risk metals concentrations – a strong reduction of total microbial count with high correlation coeffi cients at the beginning of the cascade where organics accumulation processes are not signifi cant. At the other sampling sites the relation is more clearly presented with the Endo-bacteria. The correlative description of this relationship and implementation of specifi c risk management scenario allows to collect updated information for ecosystem response at shock pollution with hazardous materials and to initiate the development of bioremediation strategy for improving of the environmental status of the river sediments.