Testing the component additivity approach to surface complexation modeling using a novel cadmium-specific fluorescent probe technique

Clay minerals as a source of cadmium to estuaries

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.

Using FluoZin-3 and fura-2 to monitor acute accumulation of free intracellular Cd2+ in a pancreatic beta cell line

The understanding of cellular Cd²⁺ accumulation and toxicity is hampered by a lack of fluorescent indicators selective for intracellular free Cd²⁺ ([Cd²⁺]_i). In this study, we used depolarized MIN6 mouse pancreatic beta cells as a model for evaluating [Cd²⁺]_i detection with commercially available fluorescent probes, most of which have been traditionally used to visualize [Ca²⁺]_i and [Zn²⁺]_i. We trialed a panel of 12 probes including fura-2, FluoZin-3, Leadmium Green, Rhod-5N, indo-1, Fluo-5N, and others. We found that the [Zn²⁺]_i probe FluoZin-3 and the traditional [Ca²⁺]_i probe fura-2 responded most consistently and robustly to [Cd²⁺]_i accumulation mediated by voltage-gated calcium channels. While selective detection of [Cd²⁺]_i by fura-2 required the omission of Ca²⁺ from extracellular buffers, FluoZin-3 responded to [Cd²⁺]_i similarly in the presence or absence of extracellular Ca²⁺. Furthermore, we showed that FluoZin-3 and fura-2 can be used together for simultaneous monitoring of [Ca²⁺]_i and [Cd²⁺]_i in the same cells. None of the other fluorophores tested were effective [Cd²⁺]_i detectors in this model.

Heavy metal behaviour at mineral-organo interfaces: Mechanisms, modelling and influence factors

The mineral-organo composites control the speciation, mobility and bioavailability of heavy metals in soils and sediments by surface adsorption and precipitation. The dynamic changes of soil mineral, organic matter and their associations under redox, aging and microbial activities further complicate the fate of heavy metals. Over the past decades, the wide application of advanced instrumental techniques and modelling has largely extended our understanding on heavy metal behavior within mineral-organo assemblages. In this review, we provide a comprehensive summary of recent progress on heavy metal immobilization by mineral-humic and mineral-microbial composites, with a special focus on the interfacial reaction mechanisms of heavy metal adsorption. The impacts of redox and aging conditions on heavy metal speciations and associations with mineral-organo complexes are discussed. The modelling of heavy metals adsorption and desorption onto synthetic mineral-organo composites and natural soils and sediments are also critically reviewed. Future challenges and prospects in the mineral-organo interface are outlined. More in-depth investigations are warranted, especially on the function and contribution of microorganisms in the immobilization of heavy metals at the complex mineral-organo interface. It has become imperative to use the state-of-the-art methodologies to characterize the interface and develop in situ analytical techniques in future studies.