Concentration and Distribution of Metal Elements at the Surface of Balsam Fir Foliage by Micro-Proton Induced X-ray Emission

Metal contaminations at the surface of balsam fir ( Abies balsamea (L.) Mill.) needles collected at two locations in southern Quebec were determined by micro-PIXE (micro-proton induced X-ray emission) with scanning depth of 3−4 or 45−50 μm and scanning spacing from 15 to 250 μm. At adaxial surfaces, concentrations of Al, Si, Ca, Ti, Fe, and Zn were significantly ( P < 0.05) higher at the near-urban site than at the mountainous location. Accumulation of Mg, Al, Si, K, Mn, Fe, and Zn was significantly ( P < 0.01) higher at surfaces of unwashed needles as compared to chloroform-washed needles, which shows significant metal accumulation in/on epicuticular wax layers. Metal deposits, except Mn, in epicuticular wax layers were significantly affected by washing with acidic solution. Distributions of Mg, K, Mn, and Zn deposits at the surface were lower around central regions than near foliar edges, while Si was higher around the central area. Scanning to the 45−50 μm depth showed significant accumulation of Ni on either side of the foliar center groove.