Zs. P. Komáromy szerk.: Studia Botanica Hungarica 16. 1982 (Budapest, 1982)
Hably, Lilla: The relation between Pb-pollution along mainroads and the trace element-composition in soil and vegetation (Examination of section rectangular to M3 mainroad)
why section No. 32 contains less Pb than the upper layer of section No. 34. (Soluble concentration was measured.) Both of them are on the enrichment levels which, however, are not equal. The upper sample of 32 is part of the pH = 6 enrichment level whereas that of 34 is part of pH = 5.5 enrichment level. The relatively lower value of the lead content of section No. 37 can be explained by the vegetation "catching" the polluting lead. This sampling place is right in the middle of the roadside patch of bushes and trees. Anomalies exist not only in relation to distance from the road, but also to depth. The decrease in lead in relation to depth can be explained in different ways. In the figure only the values greater that 5 ppm are shown. From this it can be seen that downwards the Pb concentration decreases. Then between 80 and 100 cm it reaches a value below 5. Between 100 and 120 cm, however, it is high again and appears in a concentration higher even then 20-40 cm. This can not be the result of pollution. As pointed out this is an element enrichment level notably in this depth there is a pH = 8 level. From this it can be seen that with different elements the enrichment levels are not equal. Lead more thoroughly examined yielded more extreme pH values, the two extreme enrichment levels were pH = 5.5 and pH = 8. This is probably due to the amphoteric nature of lead which is the reason why with lead pH = 6 and 7.5 seems to be on a weaker level. The lead content of plants will be dealt with separately since its toxic effect is directly harmful to humans. In Hungary lead content of leaves and of the upper 10 cm layer of soil has been tested (KOVÁCS, M. & PODANI, J. & OPAUSZKY, I. & KLINCSEK, P. & DINKE, M. in the Botanical Research Institute of the Hungarian Academy of Sciences, in Vácrátót). Our examinations extended to the different organs of plants (Table 9). It was held by scientific circles but without the basis of adequate tests - that in trees more lead accumulates in the lignificated stalk than in the leaf which falls at the end of the vegetational period. This seems to be logical, but measurements indicate that it is otherwise. The row of poplars we examined and where the samples were taken from different trees at different distances, show that the leaves contain more lead than the stalks. Only one sample, No. 35 3 taken at 30 meters from the road shows the same lead concentration in the leaf and the stalk, but the Pb-content of the stalk does not exceed that of the leaf even here (Fig. 13). It can not be decided then, which organ of a plant accumulates lead in highest concentration. This accumulation probably varies according to species. In may samples both in case of yearling and of woody plants it was the leaf which seemed to be the most suitable for accumulation. The stalk was in second place, then the root, and at last the fruit. My samples, however, are not numerous enough to allow general conclusions to be drawn. It has been pointed out that in some cases there are very great differences between the washed and unwashed control samples, while in other cases there is no substantical difference. This probably depends on the adsorption of different plant organs. The statement concerning the Pb-intake of plants is of much greater importance. According to a widespread theory plants take up lead from the air. Our data contradict this statement. If lead was built into plant organism only from the air, the lead concentration in plants would decrease proportionally with the increase of the distance. Our samples do not agree with this model unequivocally. In the samples taken from the poplar-row 13-94 meters away from the road, lead is almost on the level both in the stalk and the leaf. Plant samples from our main section line were examined with the following results: For the examination, such a species is selected which serves for sampling several times, at different distances. This with the purpose of excluding species-dependence. The plant easiest to examine is maize ( Zea mays) , which is present 25 m away from the road, (at section No. 32) at 45 m, 56 m (soil-section No. 33) and at a distance of 106 m (soil-section No. 34). In addition, it was possible to examine all the organs of this plant (except its flower). Figure 13 shows the lead concentration of maize separately for the different organs and in relation to distance. The accumulation was highest in the leaf. Tracing the changes in the lead concentrations of maizeleaves in relation to distance, we experience no unequivocal decrease. The quantity of lead is 20 ppm at 55, 9 ppm at 45 and 32 ppm at 56 meters away from the road. So far it really shows decrease. But at a distance of 106 meters, the ppm rises to almost 11, so the leaf contains more Pb than that only 45 m away from the road. This can not be attributed to the lead pollution of the air, so air can not be regarded the only source of lead intake by plants. Looking back to the accumulation levels of lead in the soil, the above phenomenon can be given a geochemical explanation Fig. 13).
