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Heavy metal pollution of soils and seepage water concentrations along the AVUS Berlin (BAB 115) - immobilization with lime -

  • Kluge, Björn
Publication Date
Oct 22, 2010
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Transport emissions on busy roads and highways could cause increased pollution and accumulation of heavy metals in roadside soils. Low pH values and small sorption capacity of these soils can lead to significant heavy metal concentrations in water seepage, which could cause groundwater pollution. For this purpose a monitoring program was carried out along the edge of Europe’s oldest highway, the “AVUS-Highway” (A115) near the centre of Berlin, Germany. Soil samples of roadside soils at different distances and depths were collected and analyzed to study soil contamination of the heavy metals Pb, Cu, Cd, Zn, Ni, Cr. Soil solutions at different depths were collected by soil lysimeters and suction cups over a period of about 12 months. Rainwater run-off was also collected and analyzed. In terms of prevention of high heavy metal concentration in water seepage, a liming of a polluted roadside soil was realized in laboratory and field conditions in order to determine the influence of soil solution concentrations. Long-term predictions for the leachate concentrations of metals Cd, Pb and Zn for the AVUS site with and without liming treatments were carried out using a numerical model. The almost ninety-year history of AVUS-Highway has significantly changed the roadside soils. This is reflected both 1) in changes in soil profiles by entries of foreign materials, as well as 2) higher pH values and heavy metal contents compared with soils without influence of traffic emissions. Because of alkaline dust depositions from the road surface and traffic depositions, the soil pH (CaCl2) was observed at a range of 7-8 within the first 5 meters. The concentration of the heavy metals at the soil surface (0-30 cm) greatly increased up to a distance of 20 m. Cu was the highest in the soil and ranged from 5 to 4480 mg/kg. Zn concentrations ranged from 8 to 1070 mg/kg, Pb from 4 to 475 mg/kg, Cr from 12.5 to 43 mg/kg, Ni from 6 to 27 mg/kg and Cd from 0.7 to 6 mg/kg. In most cases this leads to an excess of up to 10 times more than the precautionary value of the German Federal Soil Protection and Contamination Ordinance (BBodSchV) for heavy metal concentration in soil for all investigated metals, except Ni and Cr. In contrast to these exceedings, only the concentrations of Zn and Cu exceeded the trigger values for leachate concentrations of the BBodSchV. A comparison of the leachate concentrations from the AVUS site with those of the reference site (distance 800m from the roadside) shows that concentrations of Cu, Zn and Cd are in a very similarly range, despite very high heavy metal contents. Substantially higher concentrations were measured in soil-lysimeters at a 1-2.5 m distance from the roadside, demonstrating an excess of trigger values of the BBodSchV up to six fold for Zn, Cu and Cr at 1m. In addition, the metals Cu and Pb exceeded the trigger values at a 2.5 m distance from the highway. Heavy metal concentrations in rainwater run-off at the AVUS are high but in the same range as those found in other studies. Very high concentrations of metals Cr and Zn were also measured. The Lime-batch experiments confirm that the influence of pH increases the reduction of leachate concentrations. The concentrations of all soils treated with lime showed a substantial reduction of the heavy metals Ni, Pb, Cr, Zn and Cd leachate concentrations. By contrast, an increase of Cu concentrations by liming was observed in both soil saturation extracts and sorption isotherms as well as in water elution of column samples. The liming of the soil columns resulted in an increase of soil pH up to a depth of 10 cm. Effects of liming on heavy metal concentrations in leachate were not detected. On the other hand, water elution of column samples after liming showed a significant reduction of heavy metals at the water soluble fraction. The field monitoring showed that liming leads to an increase of soil pH to a depth of up to 10 cm. In comparison with the control plot no differences in heavy metal concentration in leachate were found within the period of measurement. Due to high heavy metal concentrations at the soil surface, high solution concentrations of heavy metals are predicted for a time-period of 100 years within the upper centimetres of soil profile by using a numerical model. At the end of the assumed depth (1m) the leachate concentrations were low and above the trigger values of the BBodSchV. With regard to the present site conditions, despite low pH and low humus content, the leachate concentrations at the AVUS-Highway does not lead to a groundwater pollution by water seepage. A risk could result in the construction of a new highway or extension of an old highway. This is showed by the high leachate concentrations of a scenario for a sandy site with low pH and low organic C content for the first years of use.

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