The land-sea interface is considered as a threatening environment due to anthropogenic development activities. Unplanned developments can cause effects on important ecosystems, water and human health as well. In this study, the influence of rapid regional development on the accumulation of trace elements to the sediments of an important ecosystem, Batticaloa lagoon, Sri Lanka was examined. Surface sediment pollution status and ecological risk was compared with that of the recent sedimentary history of about 1 m depth. Sediment core samples were collected and analyzed for grain size, organic matter and carbonate contents and trace elements (As, Pb, Zn, Cu, Ni and Cr) by the X-Ray Fluorescence (XRF) technique. The chemical results of core samples and recently published data of surface sediments of the same project were evaluated by pollution load index (PLI), potential ecological risk index (PERI) and sediment quality guidelines (SQG). Except for Cr, all other elements in cores show lower concentrations than the SQGs confirming the high Cr contents as recorded in the most of other Sri Lankan sediments. The sediment cores indicate an unpolluted, low ecological risk sedimentary history for all core sampling locations, whereas most of the surface sediments of the lagoon are less polluted with low potential ecological risk. Present anthropogenic practices and illiteracy of this rapid developing region can damage the green environment and hence environmental management planning is suggested for a sustainable future.
This study presents the first structural report of iranite, ideally CuPb10(CrO4)6(SiO4)2(OH)2 [copper decalead hexachromate bis(orthosilicate) dihydroxide], based on single-crystal X-ray diffraction data. Iranite is isomorphous with hemihedrite, with substitution of Cu for Zn and OH for F. The Cu atom is situated at the special position with site symmetry 1. The CrO4 and SiO4 tetrahedra and CuO4(OH)2 octahedra form layers that are parallel to (120) and are linked together by five symmetrically independent Pb2+ cations displaying a rather wide range of bond distances. The CuO4(OH)2 octahedra are corner-linked to two CrO4 and two SiO4 groups, while two additional CrO4 groups are isolated. The mean Cr-O distances for the three nonequivalent CrO4 tetrahedra are all slightly shorter than the corresponding distances in hemihedrite, whereas the CuO4(OH)2 octahedron is more distorted than the ZnO4F2 octahedron in hemihedrite in terms of octahedral quadratic elongation.
We have determined the crystal structure of tvalchrelidzeite, Hg 3 SbAsS 3 , for the Þ rst time with single-crystal X-ray diffraction. It is monoclinic, with space group P2 1 /n and unit-cell parameters a 11.5526(4), b 4.3852(1), c 15.6373(5) Å,  91.845(2)°, V 791.79(5) Å 3 . There are eight symmetrically distinct sites in the structure, three occupied by Hg, one by Sb, one by As, and three by S. There is no disorder between Sb and As. Each Sb is surrounded by six S 2anions, with three at distances shorter than 2.51 Å and three at distances longer than 3.20 Å. In contrast, each As is coordinated by six Hg 2+ cations, with three at distances shorter than 2.51 Å and three at distances longer than 3.31 Å. All three independent Hg ions are situated in considerably distorted octahedral sites, with two opposite bonds (one Hg-S and one Hg-As) shorter than 2.51 Å and four equatorial bonds longer than 2.98 Å. The structure of tvalchrelidzeite can be viewed as a sequence of sheets parallel to (101). These sheets are composed of [Hg 6 Sb 2 As 2 S 6 ] ribbon-like units (extending along the b axis) linked together by the short Hg1-As bonds (2.494 Å). The linkage between sheets is achieved through the weak Hg-S (>3.0 Å) and Sb-S (>3.2 Å) bonds, accounting for the observed perfect cleavage in one direction. Tvalchrelidzeite represents one of very few sulfosalt minerals that contain both Sb and As, with the latter behaving as an anion.
Structure D 2000Iranite, CuPb10(CrO4)6(SiO4)2(OH)2, Isomorphous with Hemihedrite. -The structure of natural iranite is determined by single crystal XRD (triclinic, space group P1, Z = 1). The structure contains SiO4 and CrO4 tetrahedra and CuO4(OH)2 octahedra which form layers that are separated by Pb 2+ cations. -(YANG*, H.; SANO, J. L.; EICHLER, C.; DOWNS, R. T.; COSTIN, G.; Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 63 (2007) 12, i122-i124; Dep. Geosci., Univ. Ariz., Tucson, AZ 85721, USA; Eng.) -Schramke 09-010
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