Necessity of normalization to aluminum to assess the contamination by heavy metals and arsenic in sediments near Haiphong Harbor, Vietnam

Abstract

While assessing many different aspects of contamination by heavy metals and arsenic in sediments, the natural variability in element contents which depends on the grain-size and mineralogical composition of sediments, needs to be taken into account. In previous studies, the normalization of element contents to a reference element such as Al was commonly applied to compensate for granulometric and mineralogical effects. In the present study, through the investigation on the contamination of heavy metals and arsenic in sediments near Haiphong Harbor, the necessity of the normalization towards Al is assessed. The results indicate that before Al-normalization, the occurrences on the source and historical trend of contamination by heavy metals and arsenic can be masked by the distribution of clay (Φ<2μm) or fine (Φ<63μm) fractions as well as Al, Fe and organic matter. In contrast, after Al-normalization, spatial distribution of elements illustrates that Cr, Ni, Pb and Mn are enriched by the anthropogenic activities in the Haiphong industrial and harbor zone while As, Cd and Cu come from upstream sources, and Co and Zn indicate only locally-elevated contaminations. The vertical profile of elements in core sediments illustrates that the anthropogenic input of heavy metals and arsenic increased in recent years. Moreover, the assessment of the degree of contamination based on the Enrichment Factor (EF) and obtained local background values indicates a minor enrichment of all heavy metals and arsenic. This is not in line with the assessment based on the sediment quality guidelines or reference values from upper-continental or average-continental crust which states the “serious” contamination of Cd, Pb, Cu, Zn and especially As. Therefore, the normalization to Al is necessary in interpreting the source, historical trend and degree of contamination by heavy metals and arsenic in sediments of the study area.