The main impact area of the Šoštanj Thermal Power Plant (TPP) is the Šalek valley (Slovenia). The research was conducted to study the accumulation of heavy metals in different plant tissues of wild growing medicinal plants (MAP). The specimens of MAP were collected on eight locations (4-15 km from Šoštanj, 500-1000 m altitude). The herb of Hypericum perforatum, Achillea millefolium, Urtica dioica, Thymus serphyllum and Sambus nigra as well as Tilia plathypyllos flowers were collected, dried and the content of Cd, Pb, As and Hg measured and analyzed by atomic absorption spectrometer. The results were compared to legislative values valid in Slovenia (Off. Gaz. SFRJ 59/83) and recommended values issued by the German Federal Ministry of Health (GFMH).

The results indicated that there are no significant differences in heavy metal content between different locations. However, they were significantly connected to the plant species. The levels of Cd exceeded recommended doses in Hypericum perforatum. Other species accumulated Cd in the following sequence: Achillea millefolium > Thymus serphyllum > Tilia plathypyllos > Urtica dioica > Sambus nigra. The levels of Pb, As and Hg were low and comparable in all the specimens. None of these plants accumulated any heavy metal above the allowed limits.

The Šalek Valley is situated in the Sub-alpine part of Slovenia near the Austrian border. The Šalek Valley is overloaded with different human activities such as electricity production and coal-mining. Besides gaseous pollutants also trace elements are emitted into the environment by the Šoštanj Thermal Power Plant. Before the 1995, when desulfurisation device on one part of TPP was built, as much as 134 t Pb, 122 t Zn, 6 t Cd, 0.6 t Hg had been emitted into the environment (Stropnik, 1994).

Innitially, a research project was carried out in the NW part of the Šalek Valley around Zavodnje village, on most affected area. The results showed increased concentrations of Cd in some medicinal plants (Kugonič and Rode, 1997). Afterwards, expanded research on the surrounding of the Šalek Valley impact area was done on this starting point. Heavy metal uptake in some most applicable wild growing medicinal plants was determined in different distance from TPP Šoštanj. The main objective was to estimate the quality of wild growing medicinal plants in the area.

Figure 1. Map of Slovenia with the Šalek Valley, where the study was carried out


MATERIALS AND METHODS

Eight sites were selected in distance 4 to 15 km from TPP Šoštanj and on altitudes about 500 to 1000 m a.s.l. No local pollution sources were present on this area. As reference location was chosen the Savinja Valley.

Figure 2. Map of the Šalek Valley with locations of sampling points

The herb of Hypericum perforatum, Achillea millefolium, Urtica dioica, Thymus serphyllum and Sambus nigra as well as Tilia plathypyllos flowers were collected in the optimal picking period and dried on 36°C. Plants samples were homogenized with Büchi B-400 equipped with ceramic knife and passed trough 1 mm plastic sieve. A CEM MSP 1000 microwave digestion system was used for acid digestion. The heavy metal content was determined using a Perkin Elmer SIMAA 6000 atomic absorption spectrometer. The electro-thermal technique was used for the determination of Pb and Cd, the cold vapour AAS technique was used for determination of Hg, while hydride generation AAS technique was used for determination of As. Standard reference material was used for analytical quality assurance. Results were compared to legislative values valid in Slovenia (Off. Gaz. SFRJ 59/83) and Recommendation on Heavy Metals in Herbal Drugs issued by the German Federal Ministry of Health (Kabelitz, 1998).

The content of Cd in Hypericum perforatum, Tymus serphyllum and Achillea millefolium exceeded officially determined levels (0.3 mg/kg) on almost all locations. However, other herbs were not polluted with Cd. The amounts of Pb, As and Hg were below the permitted levels destined as 3 mg/kg, 1 mg/kg, and 0.1 mg/kg, respectively (Off. Gaz. SFRJ 59/83)

Our research revealed that on all sampling sites Cd content in plant tissues of Hypericum perforatum, Tymus serphyllum and Achillea millefolium, except on reference location, exceed permitted levels. The soils in the Šalek Valley are not polluted (Stegnar, 1993, Kugonič, 1996, Svetina, 1999), we concluded that the main pathway of Cd to plant tissues is probably input trough airborne emissions. Accumulation of heavy metals trough foliar absorption depends on the plant species, its nutritional status, and the thickness of its cuticle and the age of the leaves (Alloway, 1990). Results of our research confirmed that different plant species can derive significant amounts of Cd by leaf systems. The average content of Cd for Hypericum perforatum was 0.97 mg/kg DW and exceeded even the recommended limit levels 0.5 mg/kg (Kabelitz, 1998). Species vary considerably in their ability to Cd uptake as shown by the following order of decreasing cadmium contents: Hypericum perforatum > Thymus serpyllum > Achillea millefolium > Tilia cordata > Urtica dioica > Sambucus nigra.
 

Graph 1. Average content of Cd in herbs

Graph 2. Average content of Pb in herbs

The last three species contain lower amounts of Cd in comparisson with officialy determined level. Moreover, contents of Pb (Graph 2), As and Hg were lower in comparisson with perscribed amounts (Off. Gaz. SFRJ 59/83) and recommended levels by GFMH (Kabelitz, 1998).

The results indicated that there are no significant differences in heavy metal content between different locations. They were significantly connected to the plant species. The differences could be ascribed to specific heavy metal uptake mechanisms in different plants. Hypericum perforatum accumulated the highest amount of Cd in comparison with tested species.

The research was financially supported by the Šoštanj Thermal Power Plant and Cultural Centre "Ivan Napotnik" Velenje, the owner of Kavčnik homestead.

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