The Measurement Of Heavy Metals And Magnetic Susceptibility Of Soil Adjacent A Steel Factory Near Lanzhou And Its Environmental Implications

Soil is an important part of environment, it plays an important role in migration and transformation of matter and energy. However, waste which comes from steel factories pollutes the air, water and soil seriously. Therefore studying the soil pollution adjacent the steel factory is practically significant. With the advantage of simple, fast, inexpensive, non-destructive measurement, environmental-magnetic methods have been widely used in environmental pollution studies. Based on the measurement of the contents of Pb, Zn, Cu, Fe, Mn and magnetic susceptibility of the soils adjacent a steel factory near Lanzhou city, together with the rock-magnetism parameters of representative samples (including isothermal remanent magnetization (IRM), magnetic remanent coercivity (Bcr), saturation magnetization (Ms) and saturation remanent magnetization (Mrs), magnetization unblocked temperature), this paper evaluates the pollution of the soils in this region, and proposes a new indicator-the magnetic susceptibility concentration.The contents of the measured heavy metals are significantly increased in the topsoil. And the similar fluctuant trend depth-dependent for each measured heavy metal with a correlation coefficient of 0.66～0.86 is found in the measured profile. All these show that the anthropogenic dust input into the topsoil. This suggests that the steel factory is probably the predominant cause for strong metal signals. Pollution is mainly found in the downwind direction area, of which the strongest part is in a range of 2 km and a depth of 2 cm. All the individual pollution indexes and Nemerow indexes of heavy metals of topsoil are higher than 1, pollution indexes of sampling A9 of topsoil are higher than 3, which show that the topsoil is contained seriously.The magnetic susceptibility in uppermost soil horizons (0～2cm) increases significantly relative to the deep soil, and gradually decrease at 2～5 cm. The magnetic susceptibility of soils below 5 cm has not been disturbed, thus it can refer to the background values of soil here. Negative correlation between magnetic susceptibility and frequency indicates that high susceptibility values of the topsoil are caused by the steel factory emissions. The variation of the susceptibility is consistent with the measured heavy metals, indicating that the pollution area estimated by the magnetic susceptibility corresponds to that by the heavy metals. Rock-magnetism measurement show that magnetite and hematite exist in the deep soils (below 5cm levels) and the magnetite predominates in the polluted topsoil samples. The plot of Day indicates the grain sizes of magnetite are mainly pseudo-domain and a few of multi-domain.A strong correlation between the magnetic susceptibility and metals indicates they have the same source. Here we propose magnetic susceptibility concentration factor (S) as a new indicator to evaluate the magnitude of the soil pollution, whose criteria calculated from the correspondent index system of Nemerow, i.e. Si≤l referring to non-pollution,120 to heavy pollution. It is expected that the S would be used as an effective indicator to monitor and evaluate the magnitude of soil pollution instead of the chemical parameters.