Heavy metal dispersion detected in soils and plants alongside roads in Hungary

Soil and plant samples from roadside areas contaminated with toxic by-products of vehicular traffic (for example, lead compounds from leaded fuel, metal contaminants derived from spare parts) were analysed in the case of five Hungarian sampling sites. The analyses were carried out with a new analytical method which is based on the use of a high performance sample introduction unit in the conventional ICP spectrometry. By using this system, significantly lower detection limits were obtained related to the conventional ICP-AES method. The analysis results showed a close correlation between the daily mean volume of traffic and metals accumulated in the soil samples. On the other hand, using this method similar heavy metal profiles were gained, ie. the total and plant-available heavy metal concentrations were the highest in the 0-1 m region from the road, and the further sampling points (0-90 m) showed significantly lower and lower heavy metal contents until at about 90 m distance from the road, where heavy metal contamination reached such a low value that can be considered to be the environmental background level. A similar trend was also recognised in plants; the plants very near to the road surface accumulated very high amounts of lead, cadmium and other heavy metals derived from vehicular traffic. The results revealed different behaviours of contaminants in different conditions inside the roadside areas (soil pH and heavy metal content, species and abundance of flora at the different sampling points, etc.). For example, total and available concentrations were apparently low only in one sampling site where each sampling point of the cross-section showed acid soil medium. Generally, acid pH means higher mobility of heavy metals, which was verified in our study too, as low concentrations in soil are associated with high accumulation factors in plants. Both single-and two-factor ANOVA results showed that total and available lead contents were not significantly different between sampling sites, therefore they were considered as traffic as the main contaminating source produced near the same lead content in different conditions. Single-factor ANOVAs showed significant differences, meanwhile two-factor ANOVAs did not show significant differences among mean lead contents detected in plants sampled in the five sites. These different results for lead showed that with the increase of variables (from one to two factors) the mathematical differences between lead contents became less and less significant. It calls for paying attention to the evaluation of bioindication and requires use of all the available variables in order to gain precise results from sampled areas. Some plants such as Echinocloa crus-galli, Clematis recta, Artemisia vulgaris, Crepis biennis, Portulaca oleracea and Lathyrus pratensis were found to be good indicators, as they accumulated three or four different heavy metals in high concentrations. in addition to their sensitive indicating ability, the majority of these plants are weeds of cereals in arable lands, and so are easily available in roadside areas.