E. E. Koslow, W. H. Smith and B. J. Staskawicz, “Lead-Containing Particles on Urban Leaf Surfaces,” Environmental Science & Technology, Vol. 11, No. 10, 1977, pp. 1019-1020. http://dx.doi.org/10.1021/es60133a003
 E. G. McPherson, D. J. Nowak and R. E. Rowntree, “Chicago’s Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project,” US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station Radnor, PA, General Technical Report 18, 1994.
 M. M. Viana, “Levels, Composition and Origin of Particulate Atmospheric Materials in the Northern and the Eastern Part of the Iberian Peninsula and Canary Island,” Ph.D. Thesis, University of Barcelona, Barcelona, 2003.
 T. Sawidis, A. Marnasidis, G. Zachariadis and J. Stratis, “A Study of Air Pollution with Heavy Metals in Thessaloniki City (Greece) Using Trees as Biological Indicators,” Archives of Environmental Contamination and Toxicology, Vol. 28, No. 1, 1995, pp. 118-124.
 P. H. Freer-Smith, S. Holloway and A. Goodman, “The Uptake of Particulates by an Urban Woodland: Site Description and Particulate Composition,” Environmental Pollution, Vol. 95, No. 1, 1997, pp. 27-35.
 D. Dongarrá, D. Varrica and G. Sabatino, “Occurrence of Platinum. Palladium and Gold in Pine Needles of Pinus pinea L. from the City of Palermo (Italy),” Applied Geochemistry, Vol. 18, No. 1, 2003, pp. 109-116.
 E. L. Hoffman and A. Pidruczny, “The Application of Low-Cost Multi-Element Data by Neutron Activation Analysis Suitable for Exploration Geochemical Techniques (abst),” Journal of Geochemical Exploration, Vol. 29, No. 1, 1987, pp. 417-418.
 M. Viladevall and X. Font, “Landscape Geochemistry in Catalonian Coastal Ranges (NE Spain) Using Streams Sediments Water Streams and Vegetation,” Catalonian Geological Survey Report, Barcelona, 1993.
 W. Veshi and L. Wuang-Quing, “JM-3 Digital Gold-Film Hg Meter,” Journal of Geochemical Exploration, Vol. 38, No. 1, 1990, pp. 157-171.
 M. Viladevall, X. Font and A. Navarro, “Geochemical Mercury Survey in the Azogue Valley (Betic area, SE Spain),” Journal of Geochemical Exploration, Vol. 66, No. 1-2, 1999, pp. 27-36.
 P. P. Parekh, H. A. Khwaja, A. R. Khan, R. R. Naqvi, A. M. Khalid Khan and G. Hussain, “Lead Content of Petrol and Diesel and Its Assessment in an Urban Environment,” Environmental Monitoring and Assessment, Vol. 74, No. 3, 2002, pp. 255-262.