Cadmium Mixing Behavior in Estuaries: Redox Controls on Removal and Mobilization

Abstract

This study investigates various hydrological and redox conditions controlling phase transformation, removal and remobilization of Cd in three different estuaries in Taiwan. It was found that Cd mixing patterns in estuarine waters are controlled mainly by redox conditions and salinity. In a highly urbanized estuary segment low oxygen conditions caused sulfide production and the formation of stable Cd sulfide minerals. In oxygen-replete waters [dissolved oxygen (DO) > 200 μM], high concentrations of Mn(II), likely from exchange with bottom sediments were oxidized into Mn oxides, on which Cd is adsorbed. However, in the lower estuary regions elevated chloride concentrations are likely able to compete for Cd, with large proportions of Cd becoming complexed with chloride. The stable Cd sulfide minerals, resistant to oxidation in estuaries having short flushing time, are likely settling out and depositing into bottom sediments. Reversible Cd adsorption onto Mn oxides can enhance Cd mobility in lower estuary and coastal regions where Cd chloro-complexes form, resulting in greater Cd transport fluxes into the ocean.

Spatial and temporal variations of geochemical processes and toxicity of water, sediments, and suspended solids in Sibuti River Estuary, NW Borneo

“…7 a). The negative loading of Al and Se along with pH and DO indicate the absorption of Se by Al-oxyhydroxides under high pH and high DO conditions due to their reactive surfaces (Hsu 1989 ; Jiann and Ho 2014 ; Hao et al 2020 ). The low negative factor scores at stations 20 and 40 km confirm such absorption in the upper part of the estuary (Fig.…”

“…The association of Al, Se, Ba, and Co indicates absorption by Al oxyhydroxides under ideal pH (4–7) levels in the upper region of the estuary. In this pH range, Al-oxyhydroxides stay in insoluble particulate form (Ferguson and Eyre 1999 ) and absorb metals like Co, Se and Ba due to high surface reactivity (Hsu 1989 ; Jiann and Ho 2014 ; Qin et al 2018 ; Mori et al 2019 ; Hao et al 2020 ). But the influential region for this process in factor-1 (NEM) is higher compared to SWM.…”

“…The chalcophile elements (Cu, Cd, and Zn) are derived from pyrite and shale concretion, and distribution is mainly controlled by clay minerals and phyllosilicates such as illite and kaolinite (Nagarajan et al 2017a ). The higher loading of Cd might be due to the absorption of Cd onto the clay minerals in the lower part of the estuary (Hao et al 2020 , Jiann and Ho 2014 ; Namiesnik and Rabajczyk 2010 ) (Fig. 6 b).…”

High‐Resolution Coral Records of Cadmium in Surface Seawater: Biogeochemical Cycling and a Novel Proxy for Winter Monsoon

“…At the bottom of the ocean, Cd can be divided into dissolved phase, particulate phase and sedimentary phase (Zhang et al., 2018). Affected by reductant‐oxidant conditions (Jiann & Ho, 2014), Cd content is usually higher in sediments and particulates, and can be reversibly adsorbed on iron and manganese oxides. The interaction between ions is enhanced, leading to the reversal of the adsorption process, and part of the combined Cd can be transformed into free Cd when surrounding salinity increases (Guinoiseau et al., 2018; Jiann & Ho, 2014; Lao et al., 2019).…”

“…Affected by reductant‐oxidant conditions (Jiann & Ho, 2014), Cd content is usually higher in sediments and particulates, and can be reversibly adsorbed on iron and manganese oxides. The interaction between ions is enhanced, leading to the reversal of the adsorption process, and part of the combined Cd can be transformed into free Cd when surrounding salinity increases (Guinoiseau et al., 2018; Jiann & Ho, 2014; Lao et al., 2019). As shown in Figure 4, the SSS was lower in the wet season but higher in the dry season.…”