Clay minerals as a source of cadmium to estuaries

Abstract

Given the high surface reactivity of clay minerals, it is assumed that flocculation will lead to metal accumulation in marginal marine settings. However, the degree of metal sorption to clays is impacted by solution pH and ionic strength, and it remains unknown whether riverine clays indeed serve as a metal sink once they encounter seawater where pH and ionic strength markedly increase. Here, we conducted cadmium (Cd) adsorption experiments to three types of common clay minerals – kaolinite, illite and montmorillonite. We found that 20–30% of Cd from illite and montmorillonite surfaces were desorbed when transitioning from freshwater to seawater pH and ionic strength conditions, while kaolinite showed no discernible differences. Synchrotron X-ray adsorption spectroscopy confirmed that Cd release corresponded to a change in bonding from outer- to inner-sphere complexes when clays encountered seawater pH and ionic strength conditions. If other trace nutrients (such as Cu, Zn, Co) adsorbed onto riverine clay minerals behave in a similar manner to Cd, we speculate that their desorption in marginal marine settings should exert a significant impact on the productivity of the biosphere.

The kaolinite shuttle links the Great Oxidation and Lomagundi events

“…The phosphate concentration in these samples was analyzed by ICP-MS. Detailed experimental information could also be found in Hai et al 64 .…”

Trace Elemental Partitioning on Clays Derived From Hydrothermal Muds of the El Tatio Geyser Field, Chile

“…Besides surface protonation/deprotonation reactions, hydrolysis reactions may also control the behavior of trace elements. Hydrolysis is, likewise, pH-dependent (e.g., Coup & Swedlund, 2015 inner-sphere complexes on clay surfaces and thus increase the adsorption of Cd on clays (Hao et al, 2020). Further, hydrolysis of Cd can lead to the formation of hydroxide secondary precipitates, such as Cd(OH) 2 , which is susceptible to dissolution under acidic conditions.…”

“…For example, Hao et al. (2020) measured decreased Cd adsorption to illite and montmorillonite in solutions with increasing both pH (6–8) and ionic strength (0.01–0.56 M), mimicking changes from freshwater to seawater aqueous conditions. Those authors subsequently hypothesized that metal desorption in marginal marine settings could liberate trace metals to seawater, impacting primary productivity.…”

“…Those authors subsequently hypothesized that metal desorption in marginal marine settings could liberate trace metals to seawater, impacting primary productivity. The next step in assessing the Hao et al (2020) hypothesis is to study the association of trace elements with clay minerals in naturally acidic environments. In this regard, terrestrial hydrothermal settings are suitable because vent effluents are commonly acidic and rich in an assortment of trace metals, while the acidic steam actively promotes the in-situ formation of clay minerals.…”

The influence of invertebrate faecal material on compositional heterogeneity, diagenesis and trace metal distribution in the Ogeechee River estuary, Georgia, USA

“…Cadmium was chosen based on its wide use in biosorption studies and it is representative of a wide range of trace metals (e.g. Liu et al, 2015;Hao et al, 2019Hao et al, , 2020. Initially 100 ml of 0.56 M NaCl was added to a 150 ml glass beaker.…”