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

Table 6

Mann–Whitney U test results of Zn and Pb contents.

Element	Group	N	Mean rank	Sum of ranks	U
Zn	Yes	22	29.86	657	124	0.00
	No	24	17.67	424
Pb	Yes	22	28.09	618	163	0.03
	No	24	19.29	463

 < .05.