https://en.wikipedia.org/wiki/Litter
http://www.litteritcostsyou.org/9-interesting-facts-and-statistics-about-littering/
http://www.conserve-energy-future.com/various-littering-facts.php
https://www.ncdps.gov/DPS-Services/Crime-Prevention/Litter-Free-NC/Litter-Facts
http://articles.latimes.com/keyword/littering
http://www.litteritcostsyou.org/9-interesting-facts-and-statistics-about-littering/
http://www.conserve-energy-future.com/various-littering-facts.php
https://www.ncdps.gov/DPS-Services/Crime-Prevention/Litter-Free-NC/Litter-Facts
http://articles.latimes.com/keyword/littering