Following books on Environmental Studies are available over internet with certain licensing rules. Few books have limited preview permission.
Part - A
Asthana, D. K. & Asthana, M. A textbook of Environmental Studies.
Asthana, D. K. & Asthana, M. Environment: problems and solutions.
Bharucha, E. A textbook of Environmental Studies undergraduate courses.
Castree, N. Companion to Environmental Studies.
Chawla, S. A textbook of Environmental Studies.
Dash, M. C. & Dash, S. Fundamentals of Ecology and Environment.
De, A. K. Environmental Chemistry.
Part -B: Full-text availability in Internet Archive.
Full-text of following books are also available in the Internet Archive. You may borrow and read them for a limited time. To request for your free account fill up this Request form.
Odum, E. P., Odum, E. & Barrett, G.W. Fundamentals of Ecology.
Masters, G. M. Introduction to Environmental Science and Technology. (1974)