Leaves of common urban tree species (Aesculus hippocastanum, Acer platanoides, Betula pendula and Tilia cordata) as a measure of particle and particle-bound pollution: a 4-year study

Magnetic biomonitoring using tree leaves has been proven as a proxy for airborne particle matter (PM) pollution. Since the leaf entrapment of PM is species-specific, in this study, four tree species common in urban areas of Europe and wider (Aesculus hippocastanum, Acer platanoides, Betula pendula and Tilia cordata) were investigated to evaluate which biomonitor enables consistent 'signal' to particle and particle-bound toxic elements. The tree leaves were sampled in the central urban and suburban parks in Belgrade (Serbia) in May and September from 2011 until 2014. Magnetic PM fractions in the samples were quantified by saturation isothermal remanent magnetization (SIRM) while the concentrations of Al, Cr, Cu, Fe, Ni, Pb and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Magnetic and elemental measurements were considered in relation to regulatory PM10 data. Median leaf SIRM values of T. cordata, A. hippocastanum and A. platanoides (174, 140 and 123 x 10(-5) x A m(2) kg(-1), respectively) implied the considerable magnetic enhancement contrary to B. pendula (68 x 10(-5) x A m(2) kg(-1)). However, B. pendula leaves showed the significant correlation between SIRM and PM10 values (r = 0.75) and SIRM and element concentrations and significant spatio-temporal differences in SIRM/element content between the studied parks/years. These results recommend B. pendula as a valuable biomonitor of PM and the associated elements. Nevertheless, both the results (high SIRM values, the significant correlation between SIRM and PM10-r = 0.71) and literature findings (abundance, adaptability, PM removal efficiency) favour A. platanoides over B. pendula in magnetic particle biomonitoring