Impact of road transport on soil physicochemical characteristics and heavy metal concentrations in the bark of purple willow (Salix purpurea L.)

Piotr Sugier,Danuta Sugier

doi:10.5586/aa.1753

Abstract

The aim of this study was to determine the impact of road transport on soil physicochemical characteristics and concentration of heavy metals in the bark of purple willow. The study was carried out at two groups of sites situated along a national road at a distance of 5–10 m and ca. 100 m from the road. At each of the sites, annual willow shoots were cut and surface soil samples were taken. The concentrations of Zn, Pb, and Cd in bark samples were measured and of K, Ca, Mg, Zn, Cr, Cu, Ni, Mn, Pb, and Cd in the soil. The concentrations of Mn and Pb were predictably higher in soils located near the road, which may indicate an impact of road transport on the soil content of these metals. The concentrations of Zn, Pb, and Cd in S. purpurea bark from the sites located at distances of 5–10 m and ca. 100 m from the road were similar. However, the Cd concentration in the bark exceeded the maximum permissible concentration in the dried material, despite the low Cd concentrations in the soils at of all the sampling sites. It is important to pay due attention to the concentrations of this heavy metal in this plant material when it is intended for pharmaceutical use, even in that obtained from plants growing on soils qualifying as “uncontaminated”. Salix purpurea used for Salicis cortex should therefore be cultivated under controlled conditions.

Highlights

Willows (Salix species) have an ability to synthesize diverse phenolic compounds such as salicylates, cinnamic acid derivatives, flavonoids, and condensed tannins, which are important secondary metabolites [1,2,3,4]
The analyses reveal that the mean concentrations of heavy metals can be arranged in the following decreasing series: Fe > Mn > Zn > Pb > Cu > Cd > Ni for SPR, and Fe > Zn > Mn > Pb > Cu > Cd > Ni for SPN
Given the widespread occurrence of the purple willow, its bark can be obtained as a raw material from both natural and anthropogenically-transformed stands, such as those located near roads

Summary

Introduction

Willows (Salix species) have an ability to synthesize diverse phenolic compounds such as salicylates, cinnamic acid derivatives, flavonoids, and condensed tannins, which are important secondary metabolites [1,2,3,4]. Willows with high salicylate concentrations, e.g., S. purpurea L., S. daphnoides Vill., S. fragilis L., and S. myrsinifolia Salisb., are recommended for herbal production and are a promising source of herbal drugs [5,6,7,8,9,10,11]. Several studies have shown that Salix species exhibit a capacity to accumulate high concentrations of heavy metals, especially in the leaves and in and on the bark [16,17,18,19,20]. Noteworthy are Cd and Zn, which are more transported to the shoots [23] and accumulated in the wood and bark, i.e., the pharmaceutical raw material from willow

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