The dust samples collected, including rain water, were evaporated to dryness in a porcelain evaporator. Subsequently, the samples were mineralised in a muffle furnace in the temperature of 420^oC for 24 hours. The mineralised samples were weighed, and then the samples weighing 1g were dissolved hot in 2 cm³ of condensed nitrogen acid (analytically pure) with 0,5 cm³ of 30% hydrogen peroxide (analytically pure). The solution was percolated into the measuring flasks of 50 cm³ capacity. The sediment on the filter was washed hot with approx. 10 cm³ 1 mole HNO₃ dm^-3. The content of the measuring flasks was supplemented with distilled water up to the marking line.

The soil samples collected were dried with air, the samples were homogenized and subsequently, 5-gramm samples were weighed and mineralised in the muffle furnace in the temperature of 420^oC for 24 hours. After the mineralisation, the samples were dissolved similarly as the dusts sediments.

The leaves and roots of the dandelion were washed thoroughly with distilled water and dried in the air. The samples were averaged and the dry mass was collected from 2-gramm samples of the leaves and roots. Subsequently, mineralization in the muffle furnace took place in the temperature of 420^oC for 24 hours. The next procedures were the same as for the dusts and soil samples.

In the solutions achieved as a result of mineralization and dissolving of the remaining parts in nitrogen acid, the quantities of the following selected elements: Cd, Pb, Cu, Zn, Mn, Fe and Ni were marked by means of the AAS method. Marking the heavy metals with the AAS method was conducted by means of a Carl Zeiss Jena AAS 30 device, using the acetylene – oxygen flame in the analysis. The content of Cd and Pb in the plant samples was analysed with the use of a graphite tray.

Apart from the metal content, the reaction of the examined soils was determined. In order to specify the pH of soil, 10-gramm dry soil samples were weighed in the air, 25 cm³ 1-mole KCl dm^-3 was added. Subsequently, the reaction of the suspension was measured with a pH meter after 24 hours.

Given the weight of the dust collected, the amount of days of sampling, the tray’s surface (0,1 m²) and the results of the heavy metal content in the samples analysed, the following values were calculated: daily dust deposition, daily deposition of each metal per unit of surface and metal concentration in the falling dust. Furthermore, mean concentration of chemical elements in the soil was calculated, and the reaction of the soil was determined. Moreover, the concentration of metals in the leaves and root of the dandelion was specified.

On the basis of the results of metal concentration in the dusts, soil and dandelion, the enrichment coefficients were calculated in the following arrangement: dandelion leaves/air, dandelion root/soil and air/soil. When calculating the enrichment coefficients, the following dependence was used [4,17]:

C₁Me – the examined element content in the examined environment
C₂Me – the examined element content in the reference environment
C_1n - the reference element content in the examined environment
C_2n - the reference element content in the reference environment,
when Mn was applied as the reference element.

The results of the mean contents of the elements in the analysed, for particular collection points, samples underwent statistical analysis with the calculation of the (Pearson’s) simple correlation coefficients between the metal concentration in the dandelion leaves and root, the metal concentration in the dandelion root and in the soil, the metal concentration in the falling dusts and the dandelion leaves, and the metal concentration in the falling dusts and soil. When calculating the correlation coefficients, the "Statistica" computer programme was applied [35].

RESEARCH RESULTS

The dusts. The mean daily metal deposition in the area under study was as follows: for cadmium and nickel it was at the level of single µg · m^-2, for copper, manganese and lead, it reached the values of several dozen µg · m^-2, the deposition of zinc was slightly above 800 µg · m^-2 on average, and iron above 1000 µg · m^-2. After conversion into the annual deposition, particular metals subsided on average in the following amounts: Cd – 0.8, Pb – 23.7, Cu – 5.8, Zn – 296.5, Mn – 19.8, Fe – 469.5 and Ni –2.15 mg m^-2. As for metal concentration in the falling dusts (µg · g^-1), it amounted to: Cd – 42.0, Pb – 561.7, Cu – 82.9, Zn – 3442.6, Mn – 333.4, Fe – 9015.4, Ni – 29.9 (Table 1) in the area of Southern Podlasie Lowland.

The soil. Among the marked metals, Fe and Mn were in the highest concentration in the soil. The mean concentration of Fe in the examined area was 2529.3 µg · g^-1, and of Mn - 135.4 µg · g^-1. The concentration of Zn and Pb was at the values of tens of µg · g^-1; the values were 57.5 and 23.1 respectively. Cu and Ni were in the single values of µg · g^-1; 4.9 and 3.6 respectively. The reaction of the examined soils was in a broad range of pH values, from 4.61 (acid soils) to 7.80 (basic soils) (Table 2).

Dandelion (Taraxacum officinale Webb.). Among the marked elements, Fe and Zn were in the highest concentrations in the dandelion leaves. Their mean concentrations were 236.7 and 64.6 µg · g^-1 respectively. Similarly as zinc, Mn (28.8) and Cu (10.6) were in the values of tens of µg · g^-1 in the leaves. Pb (4.55) and Ni (1.56) were at the level of single µg · g^-1. Cd was in the lowest concentration. Its mean value was 0.37 µg · g^-1. In the dandelion root, the elements were in the decreasing concentration values, similarly as in the leaves, in the sequence Fe>Zn>Mn>Cu>Pb>Ni>Cd. Mean concentrations of particular metals in the dandelion root (µg · g^-1) amounted to: Fe – 189.9, Zn – 34.8, Mn – 21.2, Cu –8.35, Pb – 2.63: Ni – 1.04 and Cd – 0.3.

In order to check the existence of dependencies between the metal concentration:

• in dandelion leaves and root,

• in dandelion root and in soil,

• in falling dusts and in dandelion leaves,

• in falling dusts and in soil,

the correlation coefficients were calculated. Statistically significant dependencies were noticed among:

• the content of the following elements in the dandelion leaves and root: Cd (r = 0.62^***), Pb (r = 0.71^***), Cu (r = 0.57^***), Zn (r = 0.69^***), Mn (r = 0.71^***) and Fe (r = 0.45^**),

• the concentration of Cu in falling dusts and in dandelion leaves (r = 0.30),

• the content of Pb (r = 0.42^*), Zn (r = 0,35^*) in dandelion root and in the soil,

• the concentration of Zn in falling dusts, and its content in the soil (r = 0.35^*) (Table 4).

The values of enrichment coefficients calculated in the following arrangements: falling dusts/soil, dandelion leaves/dusts, dandelion root /soil are compiled in Table 5. Among the elements under study, in relation to the metal content in the soil, the falling dusts were most enriched with: Cd (EC = 56.9), Zn (EC = 24.3), Cu (EC =17) and Pb (EC = 9.9) and least enriched with Ni (EC = 3.4) and Fe (EC = 1.4). In the arrangement: metal concentration in dandelion leaves / metal concentration in falling dusts, the enrichment coefficients were below 1; only the enrichment coefficient value for Cu equalled 1.5. The enrichment coefficient values for the arrangement of: dandelion root /soil indicate that the dandelion root, in relation to the content in the soil, is enriched mainly with metals: Cu (EC = 10.9), Cd (EC = 6.3) and Zn (EC = 3.9).

DISCUSSION

In the area of Southern Podlasie Lowland, the deposition of metals per unit of surface and their concentration in the falling dusts were, as expected, lower than the values recorded in the 1990s in the area of Upper Silesia [6,37], higher, however, than those recorded also in the 1990s in Western Europe [24,25], and also in Lithuania [5] or Saudi Arabia [28].

The main sources of environmental pollution in the area under study are the power engineering processes. In the Eastern areas of Mazowieckie region (the areas of Southern Podlasie Lowland), a higher deposition and concentration of Zn and Pb dusts are recorded in the heating season than in the summer [22]. This is also confirmed by the results available in this elaboration. The highest enrichment coefficients values in the arrangement of: falling dusts/soil are achieved by the metals that are the most volatile ones among the examined elements, i.e. Cd, Pb and Zn and that reach high emission indicators from the processes of power-engineering use of fuels [12]. Therefore, the main sources of heavy metals in the area under study are the power engineering processes connected with fuel combustion. Both the local sources and the incoming contamination contribute to the atmosphere pollution in the researched area. Hryniewicz and Przybylska [14] proved that the Eastern regions of Poland are under th e influence of pollution coming from the regions of Western and South-Western Poland.

The usefulness of the enrichment coefficients in the evaluation of the anthropogenic environmental pollution with heavy metals is indicated in the literature [36]. It is assumed that at the enrichment coefficient values (EC) below 2, there is no anthropogenic pollution, the values of EC between 2 and 5 indicate temperate pollution, from 5 to 20 – significant pollution, over 20 – high heavy metal enrichment from anthropogenic sources. In the area under study, the enrichment coefficients reached the highest values for Cd, Zn, Cu and Pb in the arrangement of: metal concentration in falling dusts/ metal concentration in the soil. This confirms the fact that metals get into the environment mainly from the anthropogenic sources.

In the researched area, the exceeding of values standardized by the Polish legislature was not recorded for the mean values in the falling dusts, i.e. the deposition of Pb and Cd (Appendix 1998). However, some local exceeding of the norms of lead deposition was recorded in some points and research periods.

The mean metal content in the soil for the majority of analyses corresponded to the natural metal content in the soils. Yet in some sample collection points, a higher level of metal content in the soil was recorded in relation to the natural content ("I" degree of soil pollution with heavy metals) [16].

In the examined soils, higher content of Cd, Pb and Zn was recorded in comparison with the mean contents of these elements in parent rocks adopted as the geo-chemical background [7]. Therefore, the elements that get into the atmosphere in the largest quantities from the coal combustion processes gather in the soils in higher amounts in relation to their content in parent rocks. This is confirmed by a statistically significant dependence (r=0.35^*) that occurred between the concentration of zinc in the falling dusts and its concentration in the soil. This indicates that the dust deposition in Southern Podlasie Lowland has a significant impact on the environment pollution with this element.

The level of metal concentration in dandelion leaves and root appeared to be interesting. In accordance with the ranges of dandelion concentrations suggested in the literature and adopted as the background [18,32], the mean metal contents in dandelion leaves and root did not exceed the following values respectively for: Cd – 0.1 and 0.1, Pb - 6.5 and 5.0, Cu –20.0 and 43, Zn –110 and 60, Mn – 170 and 50, Fe –550 and 300, Ni – 6.2 and 6.6 µg · g^-1. However, when analysing the range of the marked metal concentrations in dandelion leaves and root, it is possible to notice that in the area researched, the background concentration values in the leaves were exceeded practically for all the researched metals and in dandelion roots for Cd, Pb, Zn, Mn and Fe. When comparing, for example, the mean values of metal concentration in dandelion leaves with the values recorded in Warsaw [8], several-fold lower values were recorded in Southern Podlasie Lowland than the metal concent rations in the samples of this plant collected near busy streets or parks of Warsaw. According to Czarnowska and Milewska [8], traffic causes the increase of the content of Zn, Fe, Cd and Pb in dandelion leaves. In Southern Podlasie Lowland, the enrichment coefficients in the arrangement of: metal concentration in falling dusts/ metal concentration in dandelion leaves reached relatively low values, usually below 1. Only for copper, the enrichment coefficient in the arrangement in question amounted to 1.5. Also for copper, sufficiently statistically significant correlation (r=0.30, p<0.1, n=33) was noted between the concentration of this element in falling dusts and its concentration in dandelion leaves.

Among the examined heavy metals, copper is found in the largest quantities (approx. 30%) in the falling dusts in the form of soluble compounds, whereas the quantity of iron is only several per cent [23,27]. The forms of copper occurrence in falling dusts may contribute easier to the accumulation of this element in dandelion leaves.

Among the marked elements, statistically relevant correlation between the metal concentration in dandelion root and in the soil was recorded only for Pb (r=0.42^*) and Zn (r=0.35^*). The enrichment coefficient values calculated in the arrangement of: dandelion root /soil reached values above 1 for Cd, Cu, Zn and Ni. Burczyk et al [4] indicated higher enrichment coefficient values in the plant/soil arrangement in comparison with the plant/air arrangement. High correlation coefficient values in the arrangement of: dandelion leaves/root and enrichment coefficients with metals in the arrangement of: dandelion root /soil indicate that the main way of metal absorption by the dandelion is the root system. This way of metal absorption by plants was pointed by, among others, Hegemayer et al [11] and Gambuś [9]. The research results indicate that dandelion root is a rich source of micro-elements: Cu and Zn. In the conditions of distinctly higher content of Cu, Zn and Cd in the soi l, the dandelion root may contribute to the de-toxication of the soil from these elements. This latter statement requires, however, confirmation on a research material collected from the areas of higher heavy metal contamination than Southern Podlasie Lowland.

The research results indicate that in the agricultural lands not contaminated excessively with heavy metals, the dandelion root may be a good indicator of the metal level, predominantly Pb and Zn in the soil. The usefulness of dandelion leaves is less significant in the evaluation of the metal deposition value and the metal concentrations in dusts. These elements get into the environment in the largest quantities with the power engineering processes, and reach higher emission levels during the heating season than in the period of plant vegetation.

CONCLUSIONS

1. In selected areas of Southern Podlasie Lowland, the mean deposition of Cd and Pb from 1995 to 1999 did not exceed the values standardised in the Polish legislature, and the mean metal concentration in the soils corresponded to their natural content. The mean metal concentration in dandelion leaves and root was in the range of values suggested as the background in the literature.

2. The main sources of Cd, Pb, and Zn in the researched areas are the coal combustion processes, which is indicated by high values of enrichment coefficients in dusts in the arrangement of: metal concentration in dusts/metal concentration in soil. The mean concentration of these elements in the soils exceeds the values of the geo-chemical background.

3. In agricultural lands not loaded excessively with heavy metals, the metal level in the root is of higher significance than in the leaves of the plant when using dandelion for the bio-indicatory purposes. This is indicated by high enrichment coefficient values in the arrangement of: dandelion root /soil for the following elements: Cd, Cu, Zn and Ni and statistically significant correlation between the content of Pb and Zn in the soil and dandelion root.

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