Elan 9000 drc e

SFB samples (25 ml) were heated at 80°C until their volume was reduced to 2–3 ml. Then, the concentrated samples were digested at 120°C with 5 ml nitric acid and 1 ml hydrogen peroxide. After cooling to room temperature, these digested solutions were diluted to 25 ml with Milli‐Q water. The concentrations of major metals, such as Na, K, Ca, Mg, Al, and Fe, were determined by ICP‐OES (Optima 8000; PerkinElmer), and the concentrations of trace metals, such as Ag, As, Ba, Be, Cd, Cr, Cu, Li, Mn, Ni, Pb, Sr, Ti, Zn, La, Pr, Nd, Sm, Eu, and Gd, were determined by ICP‐MS (ELAN 9000/DRC‐e; PerkinElmer).

Leaf dust. From the total number of collected birch leaves in each individual urban zone (surface area of ca. 500 cm² for each tree), 60 leaves were selected, placed in a sterile flask with 50 mL of deionized water, and thoroughly mixed on the shaker at 200 rpm for 15 min. The area of leaves was determined. Coarse impurities were removed from the obtained solutions by filtration through a 100-μm mesh. The filtrate was then placed in an oven at 65 °C for complete evaporation of the water. Evaporated deionized water was used as a control. The concentration of different metals (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cs, Cr, Cu, Dy, Eu, Er, Fe, In, Ir, Hf, Ho, Ga, Ge, Gd, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Pb, Pd, Pt, Pr, Rb, Re, Ru, Rh, Ta, Tb, Te, Ti, Tm, Th, Tl, Sb, Sc, Se, Si, Sm, Sn, Sr, U, V, Y, Yb, W, Zn, Zr) in the sample was measured using the ELAN 9000 DRC-e (Perkin Elmer, Waltham, MA, USA) mass spectrometer with inductively coupled plasma (ICP MS).
Road dust. An amount of 1 g of the sieved dust was taken from each of three replicate dust samples. The metals were separated by a mass spectrometer with inductively coupled plasma that is described in the previous paragraph.

Soil soluble salt content was determined after drying residue; soil moisture was detected after oven drying at 105 °C for 24 hours; available phosphorus was measured by using spectrophotometer (UVmini-1240, Shimadzu, Japan); available potassium was determined by using atomic absorption spectrum analyzer (240-AA, Agilent, USA)⁴⁵ . Soil electrical conductivity (EC) was detected by using electrolytic conductivity meter (soil:water = 1:5). Soil pH was measured by using pH meter after shaking the soil/water (1:5, w/v) suspension for 30 min. Soil total carbon (TC) and total nitrogen (TN) were measured by CN Analyzer (Vario Max CN, Elementar, Germany). Mineral N was determined by using Skalar SAN plus Segmented Flow Analyzer (Skalar Analytic B.V., De Breda, the Netherlands). Ion concentrations were detected by using inductively coupled plasma mass spectrometry (ICP-MS) (ELAN 9000/DRC-e, PerkinElmer, USA).