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Mn oxides are one of the most significant groups of substances which control the distribution of heavy metals in river sediments. This occurs because of their favourable structures, sizes and surface areas. In the Tyne, Tees and Yorkshire Ouse river basins in northeast England, heavy metal-bearing, X-ray amorphous Mn oxides are common (forming upto 15 modal % of heavy metal-bearing grains) though not always abundant phases in river channel and floodplain sediment. Manganese oxides, however, contain significantly more Pb (upto 23 wt.%) than do Fe oxides, and also contain Zn, Cd and Cu (up to 19 wt.%, 0.5 wt.% and 0.8 wt.%, respectively). Within floodplain alluvium, Mn oxides play a major role in controlling the post-depositional redistribution of heavy metals. This is shown by authigenic, Pb-, Zn-, Cd- and Cu-bearing Mn oxides in alluvial profiles at Blagill and Prudhoe in the Tyne basin, and overbank alluvial sediments at Myton-on-Swale and York in the Yorkshire Ouse basin containing multiple horizons of X-ray amorphous Mn-Ba oxides, some of which contain up to 1.0 wt.% Zn. The overbank alluvial sediments at Myton-on-Swale contain the Ba (-Mn) silicate verplanckite [Ba2(Mn,Fe,Ti)Si2O6(OH)2.3H2O], although this contains negligible (<0.1 wt.%) amounts of Zn, Pb, Cr, Ni and Co. Manganese oxides play an environmentally significant role in sequestering heavy metals, as shown by contents of upto 39—74% of total sediment-borne Pb, and 10—35% of total Zn, held by Mn oxides in north-east England fluvial sediments. Lower proportions of readily removable Pb and Zn (0.8 — 18% of total Pb, and 3—26% of total Zn) under ambient conditions suggest that the Mn oxides may be long-term sinks for heavy metals in the fluvial environment.

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