Changes in the Heavy Metal Levels in Highway Landscaping and Protective Effect of Vegetative Materials

Table 1

Classification of soil samples.

Sample class-land use type	Sample number	Description	Vegetation (tree and shrub cover)
Residential area (RA)	4^a, 7^a, 10^a, 19^a, 22^a, 23^a, 12^b, 13^b, 14^b	^aPopulation <50.000; ^bPopulation >50.000	4, 7, 12, 13, 14, 19, 22
Agriculture area (AA)	2, 21	Plowed wheat field	—
Natural landscape (NL)	9, 11, 15, 17	Natural vegetation (Quercus sp.)	9, 11, 15, 17
Road slope (RS)	3, 5, 16, 18, 20	At least 30% slope	—
Unqualified areas (UA)	1, 6, 8	Useless land	—