Distribution, source and enrichment of some chemical elements in sediments of the Pearl River Estuary, China

Abstract

Chemical elements (Al2O3, Fe2O3, CaO, TiO2, Cu, Pb, Cr, Zn, Co, Ni, V, Ba, Sr and Y) and grain size of sediment cores (25–45cm long), taken at 12 stations in the Pearl River estuary by an undisturbed multicorer in the summer of 1999, were analyzed. Sediments in the Pearl River estuary were characterized as having a relatively coarse grain size. Frequent resuspension, transportation and redistribution of settled sediment on the estuary floor could be deduced from the spatial and depth distribution of chemical elements, combined with the survey data of suspended particle matter in the water column. The grain size and heavy minerals are factors controlling the distribution of chemical elements in the estuary. Except for CaO and Sr, the chemical elements were always enriched on the western side, in the middle and at the northern side of the estuary. Three main patterns (complex, top enrichment and uniform distribution) of heavy metals in depth profiles reflected the sedimentary and preservation conditions in Pearl River estuary. Fe2O3, Al2O3, TiO2, V, Cr, Ni, Zn, Cu and Y in the Pearl River estuary sediments mainly originated from terrestrial (rock and soil) weathering, however, Cr, Ni, Zn, Cu, TiO2, V and Y may have had some anthropogenic sources. CaO and Sr in sediments originate from marine sources. TiO2 and V might be related to ilmenite. Although both Co and Pb are mainly derived from anthropogenic sources, Pb in the Pearl River estuary sediments may be supplied by precipitation of aerosols and Co may originate from industrial drainage in the region. Concentrations of heavy metals in the Pearl River estuary sediments are higher than those from the Yellow River estuary and Changjiang River estuary sediments. The input of heavy metals into the Pearl River estuary has been increasing during recent decades and is becoming a serious pollution problem. As a reference element, Fe2O3 has proved to be a good predictor of naturally occurring concentrations for TiO2, V, Ni, Cr, Zn and Cu in the Pearl River estuary. The maximum gap between observed concentration and predicted concentration for these elements reached 0.105% (i.e. 36.07, 18.76, 82.67, 67.3 and 16.28mgkg-1, respectively). Two zones were identified to be seriously contaminated by heavy metals in the estuary. One was nearby the Humen mouth and the other was near the western and mid-western part of the Pearl River estuary.