Sandimirov S. Screening studies of POP levels in fish from selected lakes in the Paz watercourse / In State of the environment in the Norwegian, Finnish and Russian border area. The Finnish Environment. Finland, Jyvaskyla: Kopijyva Oy. 2007, №6.

Screening studies o f POPs in fish from the Paz watercourse 6 Effect of contaminants: Biomarker studies Two locations within the study area (Kuetsjarvi and Rajakoski) were selected for a screening of potential effects of contaminants on fish. Some selected biomarkers were chosen as indicators for effects. These were: cytochrome P450 hydroxylase activity level in liver microsomes and bile acids content in pike and whitefish. A biomarker can be defined as a xenobiotically induced variation in cellular or biochemical components or processes, structures, or functions that are measurable in a biologic system or in samples (NRC, 1989). Cytochrome P-450 (P450) is a superfamily of microsomal enzymes involved in the synthesis and degradation of steroids, fatty acids, and prostaglandins. Cytochrome P450s chemically transform xenobiotic compounds (PCBs, PAHs, etc.) and many contaminants also induce cyrochrome P450 activity. Cytochrome P450 can transform nonpolar hydrocarbons into more water soluble epoxide or hydroxyl metabolites through the addition of molecular oxygen. As a biomarker of exposure to PAHs, planar PCBs, and other environmental contaminants, cytochrome P450 has been used in numerous environmental assessment studies (Arctic Monitoring and Assessment Programme, Joint Monitoring and Assessment Programme etc.). Another biochemical index to show early hepatic pathological changes is bile acids content in bile and in blood. Bile acids are useful indicators of a liver function. Normally, the liver is very efficient at capturing and removing bile acids from the hepatic-portal circulation. This is why circulating bile acid levels are quite low in healthy animals. The liver has tremendous reserve capacity and can easily meet the body's demand for bile acids despite severe disease. As a result of this reserve, the bile acid levels do not typically drop due to liver disease. Therefore, as liver function is compromised, more bile acids appear in the blood. The test for serum bile acids will detect liver changes before the formation of more advanced clinical signs of illness. 6.1. Cytochrome P-450 hydroxylase activity The highest cytochrome P-450 activity was measured in females pike hepatic microsomes from Lake Kuetsjarvi. It is interesting to notice that pike males and females from relatively clean region (Rajakoski) have significantly different values of cytochrome P-450 activity, whereas no clear difference between the sexes were apparent in the samples from Lake Kuetsjarvi (Figures 11-13). Levels of male and female whitefish hydroxylase activities from Lake Kuetsjarvi were comparable (see (Figure 12). It is known from other studies that cytochrome P-450 activity is sex dependent and is highly related to the reproduction cycle of the fish. Akvaplan-niva report APN 514-3365.02 22