Abstract
The main objective of this research was to study heavy metal absorption by the leaves of main forest species which were planted for that purpose at post-lignite mining landscapes in Northern Greece (Ptolemais, Prefecture of Kozani), as well as in a neighboring region (Kato Grammatiko), 30 km far from the mining area. Four species were studied; two conifers (Pinus nigra Arn., Cupressus arizonica Greene) and two broad-leaved (Robinia pseudoacacia L., Populus nigra L.). The four species varied in their leaf morphology (needles, scale-like leaves, blade, compound or simple, with rough or smooth surfaces). Eighty (80) leaf samples were collected, (10 from each tree species at either site). The heavy metal concentrations measured were iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), cadmium (Cd), manganese (Mn), zinc (Zn) and cobalt (Co). Statistically significant differences (p = 0.01) were found between the lignite deposit and control areas and among the studied species. Higher concentrations were measured for the studied species at the lignite deposit. Moreover, no species demonstrated maximum absorption for all metals. The metal absorption pattern by coniferous trees’ leaves at the mining landscape was similar, with highest concentrations observed for iron and lowest for cobalt [iron (Fe) > zinc (Zn) > manganese (Mn) > copper (Cu) > chromium (Cr) > nickel (Ni) > cobalt (Co)]. Both broadleaved species absorbed highest concentrations of iron, but differed in the amount of the remaining metals [black locust: iron (Fe) > manganese (Mn) > zinc (Zn) > copper (Cu) > nickel (Ni) > chromium (Cr); black poplar: iron (Fe) > zinc (Zn) > manganese (Mn) > copper (Cu) > nickel (Ni) > chromium (Cr) > cobalt (Co)]. Cadmium was detected only in black poplar at both sites. In general, black pine was found to absorb the highest concentration of iron (Fe), and black poplar zinc (Zn). We discuss the importance of carefully selecting the appropriate mixture of tree species in order to achieve maximum habitat restoration effect at heavy metal polluted sites.
Highlights
Lignite is enriched with heavy metals during its mineral formation stage, which, during combustion, are emitted in the form of suspended particles or accumulated in the produced ash [1]
We examined the heavy metal concentration in leaves of the main forest species planted in the region for this purpose, and the effect of the morphological features of leaves on heavy metal concentration
Only for Populus nigra was cadmium concentration (Cd) possible to measure at both sites, as for other species, the concentration was below ICP detection limits
Summary
Lignite is enriched with heavy metals during its mineral formation stage, which, during combustion, are emitted in the form of suspended particles or accumulated in the produced ash [1]. Lignite power stations produce the highest percent of electricity in Greece. Four such stations, with a combined >4000 MW capacity, are located in the prefectures of Kozani and Florina, in western Macedonia. The heavy metals in the fly ashes are very important because they are mixed with overburden and interbedded sediments and used as landfill. There are no globally accepted limits on what heavy metals concentrations are hazardous to living organisms. There is no national regulation that defines the maximum metal concentrations in nonhazardous sewage for land applications, except in the case of waste sludge (86/278/EEC) [2]
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