Abstract
In order to study the effect of road structure and road side planting on soil heavy metal content, the variation of these contents in soils were examined. Soil samples were collected at Joban Highway for bank, viaduct, cut, canal, semi underground structures and near tunnel and at National road route No.16 for level structure. National road route No.296 was selected as control site. Acid soluble metal contents in the soil were analyzed by an atomic spectrophotometer.
Results of studies are as follows:
1) Metal content in the roadside decreased with distance from the roadside or noise barrier. Metals content within the area 7 to 16 m from the roadedge or noise barriar indicated zinc, lead, copper and acid soluble iron in the roadside of level road structure were higher than those of near tunnel, semi underground, canal, viaduct, bank and cut road structure. The highest concentration of manganese and acid soluble calcium were measured at the cut and bank road structure, respectively.
2) Roadside trees planting influenced metals content of soil. We found that lead content in the soil with roadside trees planting was higher than that in the open field. However, zinc and acid soluble calcium content were higher in the open field. Zinc and acid soluble calcium content in the soil with trees planting decreased drastically with distance than that in the open field. In the planting area, calcium content decreased charply at the point of 3 m from roadside, and after that no reduction was observed.
3) Zinc, lead and acid soluble calcium contents in the soil may be influenced by the particulate that originated from the road. On the other hand, marked variation in the copper, manganese and acid soluble iron content were not observed. Therefore their variation may be due to difference in the soil characters of investigated road.
4) The extent of dispersion and deposition of particulate near road were influenced by the factors such as road structures, the presence of roadside planting and with direction. To clarify their effect more studies are necessary.
