Mineralogical study of some arsenic contaminated soils of West Bengal, India

Five arsenic affected soil profiles, one each from Ghentugachhi and Gotera village of Chakdah block, Gayeshpur, Kalyani block, Nadia district; Ramnagar village of Baruipur block and Sonarpur mouza of Sonarpur block of South 24 Parganas district of West Bengal, India covering the soils of Typic Haplustepts, Typic Endoaquepts, Vertic Baplustepts and Aquic Haplustepts respectively have been studied for their detail mineralogical, chemical composition and also to know the level of arsenic contamination and their probable source. These soils are very deep, developed on Alluvium and are under rice, vegetable and guava cultivation. Sand mineralogy data of these soils are dominated by opaque and limonite, whereas silt is mainly constituted of micas followed by kaolinite and chlorite. The clay mineralogy of the soils indicates that smectite is in higher proportion in Ghentugachhi and Gotera soils followed by mica, kaolinite, chlorite and vermiculite and in the other soils, mica is the dominant clay mineral. In some of these soils, the interstratified mixed layer minerals are also present. The mineralogy class for the soils of Ghentugachhi, Gayeshpur, Baruipur is 'mixed' and for Gotera and Sonarpur it is 'illitic'. Differential thermal analysis (DTA) of clay fraction of surface soil of the profiles displayed the presence of the minerals like magnetite, marcasite, arsenopyrite, illite, montmorillonite and quartz. The source of arsenic in these soils are probably due to the presence of arsenic bearing minerals, marcasite and arsenopyrite, and also it may occur as adsorbtion on iron hydroxide coated sand grains and clay minerals. Arsenic concentration is very high in the surface horizon of pedon 2 (20.2 mg kg(-1)) and it shows a decreasing trend down the subsurface horizon. The higher concentration of arsenic in the surface horizon may be due to higher abundance of opaque minerals, limonite, and marcasite. (c) 2006 Elsevier B.V. All rights reserved.