1. Fedorova A, Fedotov V, Shunelko E. Landscape bioindication of an urban system: a research report//Newsletter RFBR, 5 (1997) Earth science [Electronic resource]//elibrary.ru: Scientific Electronic Library. URL: http://elibrary.ru/item.asp?id=232718 document format: PDF (date accessed 01.04.2014). Access is free. [in Russian].
2. El-Hasan T, et al. Cypress tree (Cupressus semervirens L.) bark as an indicator for heavy metal pollution in the atmosphere of Amman City, Jordan/El-Hasan T, Hamzeh Al-Omari, Anvar Jiries, Farh Al-Nasir//Environment International 28 (2002) 513-519. [Electronic resource]//URL: http://dzumenvis.nic.in/Microbes%20and%20Metals%20Interaction/pdf/Heavy%20metal%20pollution%20in%20the%20atmosphere.pdf Document format: PDF. (date of access 24.02.2014). Access is free.
3. Khakhathi L, Mandiwana et al. The application of tree bark as bio-indicator for the assessment of Cr (VI) in air pollution/Khakhathi L. Mandiwana, Tabby Resane, Nikolay Panichev, Prince Ngobeni//Journal of Hazardous Materials. B137 (2006) 1241-1245 . [Electronic resource]//Academia.edu: Site. URL: http://www.academia.edu/5016090/The_application_of_tree_bark_as_bio-indicator_for_the_assessment_of_Cr_VI_in_air_pollution# Document format: PDF. (date of access 18.02.2014). Access is free.
4. Majolagbe AO, et al. Concentration of heavy metals in tree barks as indicator of atmospheric pollution in Oyo Town, Southwest, Nigeria/AOMajolagbe, A.A. Paramole, H.O. Majolagbe, O. Oyewole and Sowemimo M.O.//Archives of Applied Science Research, 2010, 2 (1): 170-178. [Electronic resource]//URL: http://scholarsresearchlibrary.com/aasr-vol2-iss2/AASR-2010-2-2-170-178.pdf Document format: PDF. (date of access 24.02.2014). Access is free.
5. Kord B and Kord B Heavy metal levels in pine (Pinus eldarica Medw.) Tree barks as indicators of atmospheric pollution//Bioresources 6 (2) (2011) 927-935 [Electronic resource]//BioResources: ‘smagazine “BioResources” URL: http://www.ncsu.edu/bioresources/BioRes_06/BioRes_06_2_0927_Kord_K_Heavy_Metal_Pine_Barks_Indicat_Air_Pollution_1363.pdf Document format: PDF. (date of access 24.02.2014). Access is free.