Abstract
Estuaries, being the transitional zones between freshwater and marine environments, are important for protecting and rehabilitating the aquatic environments. Sediments from freshwater and marine environments were studied in Jiulong River Estuary (JRE) in different years for rare earth elements (REEs) and some environmentally important metal and metalloid elements (MMEs). The concentration of REEs ranged from 0.11 (Tm) to 296.20 mg kg−1 (Ce), while that of MMEs ranged from 0.40 (Cd) to 86,000 mg kg−1 (Al). The temporal analysis indicated an increase of both REEs and MMEs contaminants from 2012 to 2018. Fractionation of REEs and Ce and Eu anomalies indicated natural weathering, erosion processes and changes in redox chemistry at the sampling sites. Spatial structure analysis showed relatively higher levels of both REEs and MMEs in the freshwater sediments. These variations among the sampling sites indicated different land use and anthropogenic activities. The values of enrichment factor (EF) and geoaccumulation index (Igeo) indicated anthropogenic sources of accumulation, while, ecological risk assessment (Eix) and potential ecological risk index (PERI) indicated potential hazards for biota due to the accumulation of Pb, Zn and As elements.
Highlights
Estuaries are the transitional zones between freshwater and marine environments and act as sinks for the organic and inorganic contaminants resulting from anthropogenic as well as geogenic influences [1]
The study area encompassing Jiulong River (JLR) and estuary is situated in a subtropical monsoon zone in the developed area of Fujian province
The estuarine area of JLR and the proceeding marine environment provide a good source of contrasting aquatic environments especially for salinity
Summary
Estuaries are the transitional zones between freshwater and marine environments and act as sinks for the organic and inorganic contaminants resulting from anthropogenic as well as geogenic influences [1]. The sediments are the important component of the estuarine environment that act as a major sink for different pollutants especially the metals due to their specific physicochemical properties [1,2]. The complex hydrodynamics play an important role in the transportation and resuspension of suspended solids to influence the distribution and transformation of metals in an estuary [13,14]. Physicochemical changes such as temperature, pH, and salinity in the estuarine environment influence the absorption and release of metals back into the water bodies to cause secondary pollution [15,16]. The concentration alone, especially, that of metals is not a good indicator to predict the bioavailability and associated toxicities, an insight about the distribution and speciation of the metals is necessary to understand the underlying impacts and potential risks [18]
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