Distribution and speciation of four heavy metals (Cd, Cr, Mn and Ni) in the surficial sediments from estuary in daliao river and yingkou bay

Heavy metal pollution in the surficial sediments derived from estuary in Daliao River and Yingkou Bay is investigated in the present work in order to assess environmental quality and pollution levels. Physicochemical parameters of surficial sediments (sediment type and TOC) and the overlying water (temperature, EC, pH and dissolved oxygen) are also studied. The total concentrations of Cd, Cr, Mn and Ni in the samples are determined using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). The result indicates the comparatively low concentrations of the four metals (the max. of 0.67 mg/kg of Cd, 85.80 mg/kg of Cr, 1073.00 mg/kg of Mn and 38.62 mg/kg of Ni), the distribution rule of four metals in different regions of the studying area and the sources of the pollution. The methods of index of geoaccumulation, potential ecological risk index and pollution load index are used to assess the degree of contamination, distribution character and the sequence of pollution level in different regions which reflect the overall low values and low pollution level. The six-step sequential extraction method is used to determine the chemical forms of the four metals in order to evaluate their possible mobility, bioavailability and toxicity in surficial sediments. Cd and Mn are mostly concentrated in the CARB fraction, while Ni and Cr are mostly concentrated in the RES fraction. The mobility of the metals has the following order (average value): Cd > Mn > Ni > Cr.