Ecotoxicological assessment of water quality and ecosystem health: a case study of the Volga river / Moiseenko T. I., Gashkina N. A., Sharova Yu. N., Kudryavtseva L. P. // Ecotoxicology and Environmental Safety. - 2008. - Т. 71, № 3. - С. 837-850.

T.I. Moiseenko et al. / Ecotoxicology and Environmental Safety 71 (2008) 837-850 847 6.2. An integrated impact dose In rivers and reservoirs, aquatic organisms are exposed to a mixture of all toxicants. It is important to find a numerical parameter describing the total toxic impact on fish. The integrated impact dose of contaminants is determined by their number, concentration, toxic properties of each and aquatic medium—pH, Ca, TOC (Forstner and Wittman, 1983). The values of Maximum Permeation Concentrations (MPC) largely differ by country, in spite of the fact that experimental research techniques to establish the MPCs are universal. In Russia, the MPC values for Cu, V, and some other elements are possibly underestimated, whereas the MPCs for Cd, As and some other elements are possibly overestimated. For example, in Canada for Cu and Cd guideline values are 2-4 and 0.01—0.06 j.ig/1 , respectively, in dependence of CaC03, for As it is equal 5 j.ig/1; in the Netherlands the MPC value for Cu, V, and Cd are 3.8, 5.1, and 2 j.ig/1 , respectively (Canadian Water Quality Guidelines, 1994; Environmental Quality Objectives for Hazardous Substances in Aquatic Enviroment, 2001; Bioassey Methods for Aquatic Organisms, 1985; Methodo­ logical Recommendations, 1998). Because the Volga River is in Russia we used data on the toxicological properties of each toxicant based on the MPC adopted in Russia (see Tables 1 and 2). For the investigated areas of the Volga basin, Fig. 6 presents the total exceedance of the actual concentrations of toxic elements over their respective MPC values. For inorganic compounds, the maximum concentration values, standardized to the respective MPCs, are typical of Mn, V, and Cu. Water contamination with metals (from 13 to 20 units) is typical o f the Upper Volga (I, II, III). For the whole set of toxic elements, the most heavily contami­ nated areas were found in the Gorkii Reservoir (sites IV, V, VI) and the Lower Volga (IX, X, XI, XII, XIII). In the middle and lower courses of the Volga, the toxic properties of water were due to its contamination with organic compounds (mainly with phthalic acid ethers), the sum of the exceedance factors of which reaches 70. 6.2. Criteria o f ecosystem health The different types of pathology and dysfunction diagnosed in the bream result from comprehensive chronic impact of numer­ ous toxic substances, found in the Volga River water, on the fish organisms. Histological analysis of fish organs and tissues revealed serious disturbances in the morphology and function of the liver and kidneys, as well as in the hematopoietic system; many of these disturbances are irreversible. These pathologies are 90 - 80 - 70 - 60 - Й 50- “ 40- 30 - 20 - 10 - 0 - Fig. 6. Sum of the concentrations of toxic substances divided by the respective MPC values for the investigated sections of the Volga River (1—microelements; 2—organic compounds). □ 2 □ 1 IV V VI VII VIII IX X XI XII XIII sections based on the physiological reactions through disturbing the homeostasis and proper functioning of vital biological processes. Determination of the critical levels of water contamination requires numerical biological criteria, which also adequately reflect the effect of toxic substances in the water. Thus, the following biological parameters were used as criteria for fish and ecosystem health (the average weighted for individual river sections): (i) the percentage of fish in which the second or third stages of diseases were diagnosed; (ii) the Z-index defined above; (iii) the percentage of fish with hemoglobin concentration below 90 g/1; and (iv) the low levels of neutrophils in the blood, etc. 6.3. Dose- effect dependencies and critical levels Basing on dose-effect dependencies (between numerical indices of fish health and the chemical parameters of water quality, in particular the total concentration of toxic substances in the water standardized to MPC), the critical levels of water contamination can be determined. The dose-effect dependencies were plotted for the above biological parameters (Fig. 7). The following factors are assumed to have affected the results: (i) the biased nature of the values of MPC, to which the pollutant concentrations were standardized in the process of the integral dose determination (especially for toxic organic compounds); 2 . 5 - | 2 - 1 . 5 - N 1- 0 . 5 - 0 - 0 100 8 0 - 6 0 - 4 0 - 20- o H--------------1--------------1------------- 1--------------1--------------1 0 20 40 60 80 100 1 1 " \ Fig. 7. Dependencies ofZ (a) and the percentage of fish demonstrating the second and third stages of disease (b) on the total concentration of toxic substances standardized to MPC values. у = 0.53x03 r = 0.77 jtxO.Ol —I— 20 —I— 80 40 60 100 p < 0.005