A risk situation of organic pollutants accumulation in the sediments of the dams from Cascade\nââ?¬Å?Middle Iskarââ?¬Â (NW Bulgaria) is simulated in the present study. The aim is risk modelling of organic\npollution in lake sediments and on base of the investigated key chemical and enzymological\nparameters to risk assessment. A model process in lab scale with addition of whey as a source of\norganic pollutants was simulated. Two situations near to real conditions were studied: 1) at a decreased\nconcentration of organic pollutants (chemical oxygen demand was 0.265 gO2âË?â?¢kgâË?â??1) in the\ncase of discharge of sediments downstream of the river (control situation); 2) at an accumulation\nof organic pollutants (chemical oxygen demand was 1.463 gO2âË?â?¢kgâË?â??1) in the sediments (risk event).\nThe dynamics of chemical oxygen demand (COD), concentration of proteins and lactose as well as\nof the key enzymological indicators (phosphatase activity indexââ?¬â?PAI, anaerobic dehydrogenase\nactivity, protease and Ã?Ÿ-galactosidase activities) were investigated. The data from Risk Assessment\nshowed that there is a hazard from higher protein concentration at the end of the process in\ncomparison with the control situation. The risk about COD and lactose concentration during the\nrisk modelling was acceptable. The obtained results showed that the PAI can be used as an indicator\nfor early warning of the organic pollution with protein nature.
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