Factor analysis and sequential extraction unveil geochemical processes relevant for trace metal distributions in fluvial sediments of a pyrite mining area, China.

Four fluvial sediment cores were geochemically analysed for their major elements and for their trace metal contents and represent a sensitive environmental record for heavy metal contamination in a pyrite mining area, Pearl River Basin, South China. While an identification of depositional and post-depositional processes is not possible by means of the vertical profiles of the trace metal contents alone, factor analysis uncovers four main factors that control trace metal distributions in the sediment cores. After analysing the geochemical fractions of heavy metals by a sequential extraction procedure, these four factors could be explained as (i) complexation with organic matter in the sediment (As, Cu, Ni and Zn), (ii) weathering processes by iron reduction and oxidation (Pb, Mo and Cr), (iii) weathering by Mn reduction and oxidation (Tl and Co) and (iv) binding effects of sulphur in the sediment or physical transport of pyrite tailings (Zn). The environmental evaluation by geoaccumulation indices and enrichment factors reveals that the studied sediment cores are significantly contaminated and enriched with As, Tl, Pb and Zn. The risk assessment code additionally suggests low to medium risk of these studied heavy metals on the whole