open access

https://hdl.handle.net/2115/38429

Integration of magnetism and heavy metal chemistry of soils to quantify the environmental pollution in Kathmandu, Nepal

英語

isothermal remanence

2005-12

Blackwell

Island arc

14(4)

424-435

Soil profiles of Kathmandu urban area exhibit significant variations in magnetic susceptibility (χ) and saturation isothermal remanence (SIRM), which can be used to discriminate environmental pollution. χ can be used to delineate soil intervals by depth into normal ( < 10^[-7] m^3 kg^[-1]), moderately enhanced (10^[-7] to <10^[-6] m^3 kg^[-1]) and highly enhanced (≥10^[-6] m^3 kg^[-1]). Soils far from road and industrial sites fall commonly into 'normal' category. Close to a road corridor, soils at several cm depth possess highest χ, which remains high within the upper 20 cm interval, and decreases with depth through 'moderately magnetic' to 'normal' at ~30-40 cm. Soils in the upper parts profiles in urban recreational parks possess moderate χ. Soil SIRM has three components of distinct median acquisition fields (B_[1/2]): soft (30-50 mT: magnetite-like phase), intermediate (120-180 mT: probably maghemite or soft coercivity hematite) and hard (550-600 mT: hematite). Close to the daylight surface, SIRM is dominated by soft component implying that urban pollution results in enrichment by magnetite-like phase. Atomic absorption spectrometry of soils from several profiles for heavy metals (HM) reveals remarkable variability (ratio of maximum to minimum contents) of Cu (16.3), Zn (14.8) and Pb (9.3). At Rani Pokhari, several metals are well correlated with χ as shown by linear relationship between the logarithmic values. At Ratna Park, however, both χ and SIRM show significant positive correlation with Zn, Pb and Cu but poor and even negative correlation with Fe (Mn), Cr, Ni and Co. Such differences result from a variety of geogenic, pedogenic, biogenic and man-made factors, which vary in time and space. Nevertheless, for soil profiles affected by pollution (basically traffic-related), χ exhibits significant linear relationship with a pollution index based on the contents of some urban elements (Cu, Pb, Zn), and therefore it serves as an effective parameter for quantifying the urban pollution.

学術雑誌論文

Accepted Manuscript

The definitive version is available at www.blackwell-synergy.com

1038-4871

AA10848628