A Large-Scale Identification of Sediment-Associated Risks of Contamination with Heavy Metals and Organics: Indicators and Algorithms

As mediators in key biotransformation processes, the complex enzyme activities (measured as a total of extracellular and intracellular activity on sub-organism, organism and supra-organism level) have a high potential to be used as reliable indicators for risk identification in co-contaminated sediments with organics and heavy metals. Two enzyme activities—dehydrogenase activity (TTC-DHA) and phosphatase activity index (PAI) were measured by use of methods with tetrazolium chloride and p-nitrophenyl phosphate in polluted sediments of Middle Iskar River part, Bulgaria. The environmental state of river sector has been strongly influenced by the organics, nutrients, xenobiotics pollutants and by the intensive hydrotechnical activity for construction of 9 micro-hydro power plants. The change of hydrological regime was a factor for intensive sediment accumulation and concentration of pollutants in the area of the cascade. Data for total activities of dehydrogenases and phosphatases in sediments were compared with total count of culturable sediment bacteria and pollutants concentrations. The results showed that the enzyme activities correlated positively with bacterial abundance in sediments and organics content in sediments and negatively with concentrations of xenobiotic pollutants (heavy metals). This approves a high potential of enzyme indicators for regulation of ecosystem self-purification capacity and for early assessment of sediment-associated risks of co-contamination. The correlative relations allow dividing the mathematical algorithms for control and management of processes in technologically influenced hydroecosystem.

Risk Modelling of Organic Pollution in Lake Sediments

A risk situation of organic pollutants accumulation in the sediments of the dams from Cascade “Middle Iskar” (NW Bulgaria) is simulated in the present study. The aim is risk modelling of organic pollution in lake sediments and on base of the investigated key chemical and enzymological parameters to risk assessment. A model process in lab scale with addition of whey as a source of organic pollutants was simulated. Two situations near to real conditions were studied: 1) at a decreased concentration of organic pollutants (chemical oxygen demand was 0.265 gO2.kg-1) in the case of discharge of sediments downstream of the river (control situation);2) at an accumulation of organic pollutants (chemical oxygen demand was 1.463 gO2.kg-1) in the sediments (risk event). The dynamics of chemical oxygen demand (COD), concentration of proteins and lactose as well as of the key enzymological indicators (phosphatase activity index—PAI, anaerobic dehydrogenase activity, protease and ?-galactosidase activities) were investigated. The data from Risk Assessment showed that there is a hazard from higher protein concentration at the end of the process in comparison with the control situation. The risk about COD and lactose concentration during the risk modelling was acceptable. The obtained results showed that the PAI can be used as an indicator for early warning of the organic pollution with protein nature.