STOCHASTIC RISK ASSESSMENT OF NATURAL ENVIRONMENTS IN KAZAKHSTAN

Abstract

Heavy metals are ubiquitous toxic contaminants with two types of sources: natural (trace amounts) and anthropogenic. Industrial activities and vehicular emissions lead to excessive concentrations of metals in the environment. Kazakhstan is a developing country with many industrial enterprises, and therefore, soil contamination with heavy metals can be present in the soil, water, and air. The existing literature primarily focuses on measurements of concentrations only, without considering these contaminants' effect on people. However, the contamination can have a detrimental impact on people's well-being due to the accidental intake of heavy metals by people residing near the contamination source. The thesis aims to summarize contamination status in Kazakhstan and find out the impact of pollution on people. Data were obtained from the governmental institution for five heavy metals (Pb, Cd, Cr(VI), total Cr, Cu, and Zn) in Kazakhstan's urban soils and surface waters. Firstly, soil and water contamination states were examined with different indices. Secondly, risk assessment was conducted following the United States Environmental Protection Agency's guidelines for screening contaminated sites for remediation. Stochastic risk assessment was done in Matlab R2018b using Monte-Carlo simulation (10,000 runs). Overall, soil pollution is significant in industrial cities (Shymkent, Ust-Kamenogorsk, Ridder, Balkhash, Taldykorgan, and Zhezkazgan). Four of the most contaminated cities were selected for further risk assessment (Shymkent, Ust-Kamenogorsk, Ridder, and Balkhash). High risk levels are found in these cities for both carcinogenic (cancer risks are up to 2.5×10-6) and non-carcinogenic assessments (hazard indices are up to 2). The accidental intake of Pb through oral exposure and the inhalation of Cd-containing dust are the most serious exposure scenarios. For the water case, the Caspian Sea was selected for the analysis due to its importance locally and globally. Water quality analysis demonstrated that the water has marginal to fair quality for aquatic life, and concentrations deviate from the natural condition. Risk assessment results for the swimming exposure scenario demonstrated overall acceptable low risks, which increase significantly with the increase in exposure duration. Additional risks could be present in addition to swimming and contribute to overall risks. The study is beneficial for (1) the overall overview of the contamination state of heavy metals in Kazakhstan, (2) the decision-making process on the implementation of soil remediation practices in the country, (3) the development of human health-oriented soil quality guidelines. Moreover, the study is one of the few examining risk assessment and the first in water risk assessment and applying stochastic methods for risk assessment in Kazakhstan.