INFLUENCE OF SOME SOIL CHARACTERISTICS ON HEAVY METAL CONTENT IN HYPERICUM PERFORATUM L. AND ACHILLEA MILLEFOLIUM L.

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*). INTRODUCTION Harmful accumulation of heavy metals in plants has lately become more frequent in agricultural ecosystems, especially the accumulation of cadmium (Cd), lead (Pb), chromium (Cr), mercury (Hg) and nickel (Ni). These are mostly elements that have been shown to be non-essential to plants. Their uptake is governed by the genetic characteristic of particular species and by the soil properties. Higher amounts of heavy metals entering the food chain could, eventually, be harmful to humans and animals. The better knowledge of factors affecting the uptake and accumulation of heavy metals in some species is especially important for the cultivation of medicinal plants. Hypericum perforatum L. and Achillea millefolium L. are plants which have been characterized as heavy metal accumulators (Schneider and Marquard, 1996). Elevated contents of Cd, Ni and Pb in numerous samples of St. John’s wort and yarrow, from bothretail trade and wild habitats, have been revealed in earlier research in our country (Radanovic et al., 2000). Proc. Int. Conf. on MAP Eds. J. Bernath et al. Acta Hort. 576, ISHS 2002 296 Therefore, the applied agro technique during the growth of these species must provide the minimum uptake of potentially harmful elements. Heavy metal uptake by plants is a complex process, governed by the numerous factors influencing each other: plant species, genotype, availability and mobility of the metals in a soil, and soil properties, such as: pH, organic matter, clay content, rH, etc. (Marchner, 1986, KabataPendias and Pendias, 1992, Alloway, 1995). Knowledge of the influence of soil properties on the heavy metal uptake could be very useful when a choice of growing site or possible agrotechniques are issued for cultivation of these plants. MATERIALS AND METHODS Material. Plant material for this research was collected in the wild during the growing season 1999 in Yugoslavia and Republic Srpska. Samples of Hypericum perforatum L. were collected at 11 different sites, while samples of Achillea millefolium L. originated from 9 localities. An additional three Hypericum samples came from cultivated production. Along with herb samples, corresponding soil samples were also taken. Plant Analyses. Herb samples were dried at 70 C and ground. Wet digestion was done in the mixture of acids: HNO3 + HClO4, with the addition of H2O2. Heavy metal content (Mn, Zn, Cu, Pb, Ni, Cd) was measured by flame AAS. Soil Analyses. In the air-dried soil samples, crushed in the porcelain mortar to pass a 2 mm sieve, the following properties were determined: pH (in H2O and n KCl); humus content; total heavy metal content (by AAS, after digestion in HNO3 + H2O2) and available heavy metal content (by AAS, after extraction with 0.005 M DTPA). Relationships between heavy metal content in the herb and soil properties were determined by statistical analysis (correlation and regression coefficients). RESULTS AND DISCUSSION Main soil chemical characteristics as well as heavy metal content in soil and plant material are shown in Tables 1 and 2. Heavy metal content in the herb mostly depended on soil reaction, for both analyzed species. Concentration of Mn, Zn and Ni in the herb decreased linearly with the increase of soil pH, while Cd concentration decreased exponentially (Table 3.). Exponential dependence found for Cd refers to the greater influence of soil pH on the Cd uptake, as compared with other investigated elements. Cd content in St. John’s wort was mostly above limit of 0.5 ppm (Schiller, 1994) when soil pH (in n KCl) was lower than 5.9 (Fig. 1). For yarrow, Cd content in the herb was above limit (0.3 ppm) when soil pH (in n KCl) was lower than 5.1 (Fig. 2). According to the results of this research, St. John’s wort has higher potential for Cd uptake, compared with yarrow, at the same pH and Cd content in the soil. When growing sites for these species are considered, soil pH is most important limiting factor, especially for St. John’s wort growth, since higher Cd concentration in its herb could be found on the soils with relative high pH reaction. Higher Cd content in the yarrow herb and especially St. John’s wort herb from acid soils points to the necessity of: 1. permanent control of Cd content in the raw materials collected in the wild, 2. avoidance of such soils for cultivated production of those species. Dependence of Ni content in the herb on soil pH was found for St. John’s wort (r = -0.80 ***), since Ni content in the herb was higher than its natural level for plant material (0.1 – 5 ppm, Hutchinson, 1981) when soil pH was less than 5.5 (Fig. 3.). That is in agreement with the well-known fact that available amounts of Ni are higher in the acid soils (Adriano, 1986, Alloway, 1995). For yarrow, dependence of Ni content in the herb on soil pH wasn’t obtained, although Ni content in almost all analyzed plant samples was higher then 5 ppm. The higher content of this element in plants was found even at soil pH > 7.0, which points to the greater influence of genetic tendency of that species for Ni uptake, comparing with soil composition. Content of Mn and Zn in both analyzed species had negative correlation