Sequential extraction analysis was used to characterize the geochemical partitioning of Pb in roadside soils of the Detroit, MI area. Four soil profiles (10, 30, 60, and 100 m from road) were sampled at 15-cm intervals to a depth of 75 cm at each of five locations along an urban-rural transect. The observed concentrations increase with increasing traffic volume and proximity to the highway, indicating that vehicle emissions are the principal source of Pb. Concentrations in roadside soils of urban sites (>100,000 vehicles per 24 h) are 10 to 15 times greater than the background level of 12 to 22 mg/kg found at rural sites. Sequential extraction data show that the Pb is mainly in carbonate and oxide forms in the most heavily contaminated soils; organically bound forms tend to predominate elsewhere. Both surface and subsurface horizons of soils are polluted at urban sites where translocation in the vadose zone is suggested by elevated levels of Pb to depths of 75 cm. Mobilization is attributed primarily to partial dissolution of organic matter by excess NaCl derived from highway deicing salts and complexation of Pb with organic chelates. Mobilization appears to be occurring in soils up to 60 m from the highway at urban sites.

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The aim of the paper is to present results of the ten years long monitoring of the treatment processes, efficiency and operation of a wastewater treatment plant combined mechanical pre-treatment, horizontal sub-surface flow reed beds and stabilisation pond as a final purification equipment. The treatment system was built in the Dražovice village (the Czech Republic, South Moravia Region) for 800 population equivalent (P.E.) in 1999. The constructed wetlands with horizontal sub-surface continual flow reed beds, as a main biological step of wastewater treatment, has been built and operated in the Czech Republic since 1990. In case of sources over 500 P.E., there is the legislative requirement for ammonia nitrogen sufficient removal in the Czech Republic. The monitored system represents a category of sources between 500 and 2000 P.E. with the higher treatment efficiency requirements. The plant has been monitored in detail since the start of operation in 1999. A detailed monitoring programme includes: wastewater flow measurement, water temperature and oxygen regime measurement, organic and nutrient pollution removal rate assessment, hydraulic characteristics of the reed bedś filtration medium. Results of the survey include treatment efficiency calculation, hydraulic and mass load assessment. The differences in the achieved efficiency are compared between vegetation and non-vegetation periods.