Increase in the bioavailability of trace metals after sediment resuspension

Abstract

This study evaluated the potential mobility of metallic contaminants (Cd, Cr, Cu, Ni, Pb and Zn) present in sediments at the mouth of São Francisco Channel (Sepetiba Bay, RJ), using resuspension tests. Fourteen surface sediment and superficial water samples were collected along a salinity gradient from the river mouth into the bay. The resuspension tests consisted in the mechanical agitation of humid sediment aliquots in local unfiltered water, in a ratio of 7.5 g:100 mL, during 1 h and 24 h. The determination of the metals in the bioavailable fraction was performed in ICP-OES, after extraction in 1 mol L −1 HCl. Significant differences were observed between the central and external sectors for Cd (p = 0.009), Cr (p = 0.017), Ni (p = 0.047) and Zn (p = 0.007) concentrations (Kruskal-Wallis). The water's temperature (p < 0.001), pH (p < 0.05) and dissolved oxygen (p < 0.001) decreased in both time intervals in comparison to the initial measures before resuspension. The concentrations of Zn in the sediment increased from 222 to 316.2 mg kg −1 after 24 h agitation (Kruskal-Wallis; p < 0.05) at the external sector, possibly because this region has stronger oxidizing conditions. In general, a significant increase in the metals' concentrations was observed after resuspension, especially for the samples from the central sector that showed more than 90% of increase in metals concentrations after 24 h of agitation. These increases could lead to higher ecological risks to the local biota, especially during dredging activities.

Impacts of Human Activities and Environmental Changes on Spatial-Seasonal Variations of Metals in Surface Sediments of Zhanjiang Bay, China

“…Besides, almost all the studied metals showed significant positive correlations with TOC content, clay fraction and silt fraction, and showed significant negative correlations with sand fraction. This indicates that sediment grain size and TOC content both had significant influences on the distribution of metals in the surface sediments of ZJB, which has also been found in other areas such as the coastal Bohai Bay (Gao and Chen, 2012) and the mouth of São Francisco Channel (Freitas et al, 2019). Finegrained sediments (clay + silt) have a larger specific surface area than coarser fraction of sediments (sand), providing them with more binding sites for the adsorption of organic matter and metals (Salomons and Förstner, 1984;Keil et al, 1994;Mayer, 1994).…”

“…Finegrained sediments (clay + silt) have a larger specific surface area than coarser fraction of sediments (sand), providing them with more binding sites for the adsorption of organic matter and metals (Salomons and Förstner, 1984;Keil et al, 1994;Mayer, 1994). Organic matter is also an important mechanism of metals complexation in sediment (Freitas et al, 2019). The high concentrations of studied metals in the channel and coastal sediments of Zhanjiang bay were also related to the grain size compositions and TOC contents of sediments in these areas.…”

“…With the rapid industrialization and economic development in coastal regions, metals are continuing to be introduced to coastal environment through river runoff and land-based point source discharge (Yu et al, 2008;Anandkumar et al, 2018;Hossain et al, 2020). Anthropogenic sources such as industrial sewage and domestic sewage have led to an increase of metal concentrations in the coastal environments (Gao et al, 2014;Freitas et al, 2019). A major fraction of metals entering into the aquatic systems are rapidly transported into sediments (Wang and Chen, 2000;Gu et al, 2016).…”

“…The study of metal speciation in sediments is essential for estimating the mobility and bioavailability of metals (Chakraborty et al, 2015;Chakraborty et al, 2017). The chemical forms that are weakly bounded to the sediment (such as acid soluble, reducible and oxidizable forms) are considered as the bioavailable forms (Peña-lcart et al, 2014;Freitas et al, 2019). Under certain conditions, the bioavailable forms of metals in sediments can be released from sediment.…”

A method to reproduce pH and Eh environmental changes due to sediment resuspension

“…The dredge intensification related to world economic development increased the concern with possible ecosystem damages due to sediment resuspension, this encouraged research to pursue knowledge over the sediment metals release process and kinetic. In order to predict those metals release impacts, several resuspension experiments were developed during the last Decades [ 1 , 2 , [5] , [6] , [7] , 9 , 11 , 13 ].…”