Natural hazards have always been with mankind. However, the twentieth century has witnessed the appearance of a whole new series of man-made or technological hazards, resulting from enormously increased urbanization, industrial growth and chemical utilization. Presently it is a well known fact that in addition to the acute (short-term) risks posed by industrial hazards, toxic substances present in the ambient environment may cause chronic (long-term) health risks to the receptors at large. The sources of toxic substances released into different environmental media may be natural as well as man-made. However, anthropogenic sources of toxic chemicals are increasing day by day. Thus, to protect environment and health of the people from ill effects of pollutants, and to ensure safety to on-site workers and off-site community in case of a chemical emergency, it is required to take appropriate measures at every stage of siting, planning and management of hazardous chemical industries. The role of mathematical models and analytical techniques cannot be overemphasized to achieve this aim. With this view, an attempt has been made in the thesis to develop various technical models and propose an integrated approach to carry out air quality impact assessment and corresponding risk analysis due to episodic as well as continuous releases of extremely hazardous and toxic pollutants into the atmospheric environment.

As a matter of fact, the area of environmental risk analysis is new. It is in a developing stage even in the developed countries. Nevertheless, the advanced countries are equipped with better know-how than the developing nations like India. This kind of situation has created a need to generate a comprehensive body of methodologies and techniques for risk assessment and risk management in Indian context. It is expected that such a body of knowledge and expertise would not only help in bridging the existing gap, but also add to the thrust towards research and development (R & D) works in the area of environmental risk analysis. Keeping this conviction as an objective, the thesis work was undertaken to propose an integrated approach for carrying out quantitative risk assessment and environmental risk analysis pertaining to acute and chronic effects caused by toxic releases from industrial accidents and exposure to contaminated atmospheric environment.

Keeping in mind the fact that art and science of environmental risk analysis (ERA) is still in its infant stage, the emphasis has not been given to the high degree of precision of risk estimates. Rather, the approximate and conservative risk results have been preferred to avoid or minimize the negative implications of uncertainties involved in input data as well as in mathematical models. This has an additional benefit of requiring simple expertise and less time for carrying out impact assessment and risk analysis exercises. It may help the statutory bodies in a sense that the policy and regulatory decisions could be made quickly and actions regarding emergency preparedness or hazard minimization may be planned and executed without any delay. Further, the traditional approach of risk assessment and risk management deals with just one chemical, one environmental medium, and one risk at a time. In contrast to this, an innovative and comprehensive approach has been proposed to carry out environmental risk analysis in an integrated manner considering risks from more than one source and medium.