Table 4.

The pH and the geo-accumulation index values⁸⁵ computed in this study for the HMs in soils at four locations: a control area of the silver birch growth in Kórnik, Poland⁴⁷, urban soil in a small Polish city Grajewo⁴⁸, Budapest, Hungary³ and in Bukowna, a highly polluted by HM silver birch growth area in industrial part of Silesia, Poland⁴⁷.

	Kórnik	Grajewo	Budapest	Bukowna
pHH2O	3.9 ± 0.0	7.8 ± 0.9	7.6 ± 0.3	6.6 ± 0.0
	Geo-accumulation index: Igeo = log2(Cn/1.5Bn) for heavy metals
Pb	− 0.38 ± 0.079	− 0.51 ± 0.63	3.3 ± 0.50	6.3 ± 0.48
Cd	2.3 ± 0.65	3.5 ± 0.56	No data	9.7 ± 0.54
Cu	− 1.9 ± 0.18	− 1.9 ± 0.63	0.58 ± 0.59	0.96 ± 0.079
Zn	− 0.78 ± 0.22	No data	− 1.2 ± 0.50	6.6 ± 0.18

The geo-accumulation index values were computed in comparison to the geochemical background⁴⁶.