The book chapters are prepared by a team comprising university faculty and subject experts affiliated with environmental science. The chapters are the collection of published materials relevant to the subject, and summarized with suggested references for details or further learning. The revised MSc Environmental Science curriculum contains 20 theory papers (10 compulsory and 10 specialized/electives). Altogether there are 102 units in these theory papers. We confess that the present volume of book only serves a small portion of this total requirement as rendered by the curriculum in its contents and references. The users, both the faculty and graduate students may take it as an indicative resource rather than a complete subject chapter. Their suggestions and feed backs will surely be valuable in bringing publications of similar kind but in better shape in the future.