Influence of some soil characteristics on heavy metal content in Hypericum perforatum L. and Achillea millefolium L.

Abstract

Hypericum perforatum L. and Achillea millefolium L. are plants which can be characterized as heavy metal accumulators. Including relating soils samples differing in pH reaction, 14 samples of St. John's wort and 9 samples of yarrow were collected from different localities in Yugoslavia and Republic Srpska. The total heavy metal content (Mn, Zn, Cu, Pb, Ni and Cd) was determined in the collected herb material (for St. John's wort - 25 cm from the top of plant and for yarrow - 30 cm) by standard analytical methods. Heavy metal content in the herb mostly dependent on soil composition, for both species. Concentration of Mn and Zn in the herb decreased linearly with the increase of soil pH (Mn: r = - 0.62* for yarrow and r = - 0.66* for St. John's wort; Zn: r = - 0.71* for yarrow and r = - 0.62 * for St. John's wort), while Cd concentration decreased exponentially (r = - 0.77* for yarrow and r = - 0.58 * for St. John's wort). Cd content in St. John's wort was mostly above limit of 0.5 ppm when soil pH (in nKCl) was lower than 5.9, and 4.5 for yarrow. Higher Cd content in the yarrow herb, and especially St. John's wort herb from acidic soils, points to significance of: 1. Required control of Cd content in the raw materials collected in the wild and 2. Necessary avoidance of such soils for cultivated production of those species. A relationship of Ni content in the herb with soil pH was found only for St. John's wort (r = - 0.80***). Correlation between heavy metal content in the herb and humus content in the soil was analyzed but statistically significant regression coefficients were not obtained. Positive linear dependence was found between Pb and Ni content in the herb and their total content in the soil, for Achillea millefolium L. (r = 0.88 ** and r = 0.65*, respectively), which can be explained by the origin of the samples. Also, there is increase of Cu, Pb and Ni content in the yarrow herb with the increase of their available content in the soil (r = 0.67*, r = 0.88**, r = 0.65 *, respectively), while such dependence was obtained only for Pb content in St. John's wort herb (0.56*).