Scientific validation and development of an ecological risk assessment methodology in the context of surface water bodies pollution by chemical substances

Abstract for the application:

The project aims to develop a science-based validation of the risk theory application for the existing system of surface water bodies environmental assessment based on the hydrological, hydrochemical and hydrobiological parameters, as well as to analyze the existing scientific-methodological approaches to evaluating ecological risks when chemical products flow into water bodies (WB). Impact on the ecological risk level of the following processes and characteristics of the polluting substances (PS) will be assessed: physical-chemical and biological properties; concentration and volumes of the PS inflow into water bodies; transformation processes in the aquatic environment and bottom sediments of WB; the principles of prioritizing PS in terms of their biological hazards; conditions of emergency situations, which contribute to the extremely high levels of WB pollution; possible accumulation of PS in separate components of WB with their following explosive release. In order to implement the given tasks, we are planning to apply methods of mathematical modelling of pollutant migration and transformation in WB, to take into account the stochastic variability of parameters depending on the hydrological seasons (mean water, flooding), consider the type of the PS input (regular discharge, diffuse pollution, explosive release), as well as use information technologies and data bases to estimate the biological activity and ecological hazard of PS. The data base developed to systematize information about the physical-chemical and toxic properties of the prioritized organic PS groups will be used to provide information support for ecological risk assessment. In the course of the work, we will justify the necessity of Russia’s nature protection system to introduce the risk-oriented approach to regulating surface water bodies pollution, and also elaborate projects of methodologies and guidelines on ecological risk assessment.

Abstract of the final report:

Today, in developed countries, the risk-oriented approach has a central position in the water quality management system. Risk assessment is not only corporate practice, but also a regulatory procedure provided in the legislation of developed countries. There are 2 main approaches to water risk assessment: from the point of view of damage to public health and from the point of view of damage to the environment and ecosystems.

In the water management system, the risk-oriented approach includes identification, analysis and evaluation of risks. Its core elements are:

-       risk identification – defining the situations that involve risks, influencing the development and condition of the managed system;

-       determining inner and outer parameters, which will help to realize risk management;

-       risk analysis – determining the nature and level of risk;

-       risk evaluation – comparison with the established risk criteria in order to define whether the risks are acceptable or permissible;

-       risk modification (change);

-       risk monitoring, i.e. control of risks in order to achieve the goals.

Regarding water quality and the condition of aquatic ecosystems, the risk management system uses data on the scale of PS input into water bodies and the degree of their toxicity, as well as the data on the current state of a water body, including hydrological, hydrochemical and hydrobiological characteristics. When assessing the dynamics of these characteristics, one should use mathematical models.

The risks of irregularities of the water quality parameters in the Ucha reservoir being polluted through tributaries and diffuse runoff were considered as an example. A hydrological and hydrochemical model of the reservoir was analyzed, after which it was possible to identify the areas with a high risk of pollution by heavy metals:

-       areas of maximum depth, where toxicants accumulate, heavy metals being the most dangerous of them;

-       areas with a maximum gradient of oxygen content with water mass stratification;

-       areas with maximum speeds of pollution transit, where pollution is transferred from outer sources and bottom sediments.

The figure illustrates these areas, which influence the risks of pollutant inflow into water preparation stations. Quantitatively, the risk is defined as a level of exceeded pollutant concentration.

Figure. Areas with a high risk of pollution by heavy metals in the Ucha reservoir: a – areas of maximum depth, b – areas with a maximum gradient of oxygen content, c – areas with maximum speeds of pollution transit and a zero gradient of electric conductivity.

The notion of risk is stochastic by nature. That is why it is essential to take into account the probabilistic character of the parameters that impact the risk level, including hydrological and hydrochemical ones. In particular, these are the characteristics of background concentrations relating to gauging stations beyond the influence of anthropogenic contamination. It is necessary to analyze the statistical stability of the estimated indicators. It has been shown that the pollutant concentration is normally described by the Cauchy distribution. Instability of the first and second statistical moments is its particular feature. It means that, with an increased number of measurements, such characteristics as the mean and variance do not converge to a certain value. That is why the use of arithmetic means is not effective when assessing the characteristic pollutant concentrations in water bodies. It is recommended to use non-parametric estimates, in particular, median ones, which are much more effective for the analysis of hydrochemical information.

A method of evaluating regional MAC taking into account their stochastic nature has been offered.

The most representative part of pollutants is formed by organic compounds, and among them, xenobiotics, i.e. chemical substances that are alien to living organisms and obviously not entering the biotic cycle. The presence of analytically defined concentrations of xenobiotics in the environment are directly or indirectly related to human economic activity.

Among plenty of xenobiotics, one can identify those which are produced on a large scale and which represent a particular hazard to the aquatic ecosystems. For the vast majority of xenobiotics, there are no approved values of MAC, therefore, it is necessary to use calculation methods of evaluation of their toxicity and dangerous concentrations, which are formed based on the knowledge about the substance structure and/or physical-chemical properties, and also information technologies that have to do with searching for the evidence of the hazards of substances in international data bases and registers. A database which includes international lists of prioritized pollutants has been created. It has been offered to estimate the value of one of the main toxicology indicators – the xenobiotic dose, under which one can observe a statistically validated death of 50% of living organisms in the tested sample (LD50) with the help of a computer programme.