Air pollution assessment using tree barks as biomonitors

Abstract

In the last decades tree barks have become a very common bioindicator of air pollution because of its several advantages over other bioindicators. In the present study, tree barks were collected from different sites of Metropolitan Region of São Paulo (MRSP) and from two control sites far away from MRSP. The barks were analyzed by neutron activation analysis (NAA) for determinations of As, Br, Ca, Cl, Co, Cr, Cs, Fe, K, La, Mg, Mn, Ni, Rb, Sb, Sc, V and Zn and for Cd, Cu and Pb by graphite furnace absorption spectrometry (GF AAS). Results obtained for samples collected in different sampling sites in the MRSP presented wide variability due to the different pollutants levels that each tree was exposed to. High concentrations of Cd, Pb, Sb and Zn were obtained in tree barks sampled close to high vehicular traffic. The principal components analysis (PCA) applied a identify four possible emission sources, soil resuspension plus vehicular emission, industrial, marine aerosols as well as the tree bark structure itself. The enrichment factor (EF) results indicated that all the elements originated from anthropic sources, with the exception of Cs. The cluster analyses indicated no significant differences between MRSP and control sites were observed with regards to characteristics of element emissions, probably due to the control sites are located also in urban areas. The results of certified reference material analyses indicated that NAA and GF AAS provided reliable data for element concentrations with standardized differences, |Z score| < 2.