User:Shresths/Sandbox

References: for definition of pollution: http://www.merriam-webster.com/dictionary/pollution Retrieved 3/3/2012

Biological incidicators Tingey, David T. (1989). "Bioindicators in Air Pollution Research -- Applications and Constraints". Biologic Markers of Air-Pollution Stress and Damage in Forests. (Washington, DC: National Academies Press): 73–80. ISBN 978-0-309-07833-7.