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Traditional working electrodes are not sufficient to realize the low detection limit and wide detection range necessary for the detection of heavy metals. In this study, a microelectrode array electrode was proposed using a design scheme based on microelectromechanical systems that was optimized with finite element software. The working electrode adopted an innovative composite structure to realize the integrated design of the working and counter electrodes, which improved the system integration. Performance tests showed that the electrode realized the quantitative analysis of Cd(II), Pb(II), and Cu(II) with a low detection limit (0.1 μg/L) and a wide detection range (0.1–3000 μg/L). The electrode successfully measured the lead and copper ion concentrations in the Sanya River, including both seawater and freshwater environments. The experimental results demonstrate that the electrode exhibits excellent adaptability to environmental conditions and can be potentially applied for technical support in environmental monitoring and sewage treatment. [ABSTRACT FROM AUTHOR]

The simultaneously extracted metals/acid volatile sulfide (SEM/AVS) method is widely used to estimate the toxicity of metals in sediment. In this study, SEM and AVS concentrations were obtained by the cold-acid purge-and-trap technique during spring (April) and winter (December) at six sites in the Pearl River estuary. Total organic carbon, grain size distribution, and total metals were also measured in winter samples. AVS concentrations in spring sediments were slightly higher than those in winter sediments, except at site 2. AVS concentrations showed more distinct locational and temporal variation compared with SEM concentrations. Generally, AVS contents increased downcore, whereas SEM concentrations decreased slightly with depth. Higher SEM concentrations were observed in the west shoal (sites 2, 6, and 7) and site 4 (1.24 ∼ 4.28 μmol•g−1) compared with those at sites 1 and 3 (0.73 ∼ 2.14 μmol•g−1) in the middle shoal. Most SEM metals have a significant linear positive correlation with the total metals, especially for Cd, Zn, and Pb, which were easily extracted by 1 M HCl compared with Cr and Ni. According to the toxicity threshold value of 1.7 μmol•g−1for the difference of SEM-AVS, a toxic effect is expected at sites 1, 2, and 4 in spring and at sites 4, 6, and 7 in winter, which also indicates a relatively obvious seasonal variation in heavy metal bioavailability. However, comparisons between the total heavy metal concentrations in winter sediments with the sediment quality guidelines of ERLs/ERMs and TELs/PELs showed that adverse biological effects may occasionally occur at sites 2, 4, 6, and 7. Therefore, SEM/AVS prediction in conjunction with sediment quality guidelines can give a more reliable evaluation of the bioavailability of heavy metal in sediments. [ABSTRACT FROM PUBLISHER]

Abstract: Total metal concentrations (Cr, Ni, Cu, Zn, and Pb), acid volatile sulfide and simultaneously extracted metals (AVS–SEM), and heavy metal fractionation were used to assess the heavy metals contamination status and ecological risk in the sediments of the Pearl River Estuary (PRE) and adjacent shelf. Elevated concentrations at estuarine sites and lower concentrations at adjacent shelf sites are observed, especially for Cu and Zn. Within the PRE, the concentration of heavy metals in the western shore was mostly higher than that in the middle shore. The metals from anthropogenic sources mainly occur in the labile fraction and may be taken up by organisms as the environmental parameters change. A combination of total metal concentrations, metal contamination index and sequential extraction analysis is necessary to get the comprehensive information on the baseline, anthropogenic discharge and bioavailability of heavy metals. [Copyright &y& Elsevier]

Due to the high capacity of impurities in its structure, calcite is regarded as one of the most attractive minerals to trap heavy metals (HMs) and radionuclides via substitution during coprecipitation/crystal growth. As a high-reactivity mineral, calcite may release HMs via dissolution. However, the influence of the incorporated HMs and radionuclides in calcite on its dissolution is unclear. Herein, we reported the dissolution behavior of the synthesized calcite incorporated with cadmium (Cd), cobalt (Co), nickel (Ni), zinc (Zn), and uranium (U). Our findings indicated that the HMs and U in calcite could significantly change the dissolution process of calcite. The results demonstrated that the incorporated HMs and U had both inhibiting and enhancing effects on the solubility of calcite, depending on the type of metals and their content. Furthermore, secondary minerals such as smithsonite (ZnCO3), Co-poor aragonite, and U-rich calcite precipitated during dissolution. Thus, the incorporation of metals into calcite can control the behavior of HMs/uranium, calcite, and even carbon dioxide. [ABSTRACT FROM AUTHOR]

Calcium oxalate (CaOx) crystals in plants act as a sink for excess Ca and play an essential role in detoxifying heavy metals (HMs). However, the mechanism and related influencing factors remain unclear. Amaranth (Amaranthus tricolor L.) is a common edible vegetable rich in CaOx and a potential Cd hyperaccumulation species. In this study, the hydroponic experiment was carried out to investigate the effect of exogenous Ca concentrations on Cd uptake by amaranth. The results showed that either insufficient or excess Ca supply inhibited amaranth growth, while the Cd bioconcentration factor (BCF) increased with Ca concentration. Meanwhile, the sequence extraction results demonstrated that Cd mainly accumulated as pectate and protein-bound species (NaCl extracted) in the root and stem, compared to pectate, protein, and phosphate-bound (acetic acid extractable) species in the leaf. Correlation analysis showed that the concentration of exogenous Ca was positively correlated with amaranth-produced CaOx crystals but negatively correlated with insoluble oxalate-bound Cd in the leaf. However, since the accumulated insoluble oxalate-bound Cd was relatively low, Cd detoxification via the CaOx pathway in amaranth is limited. [Display omitted] • Insufficient and excess Ca inhibited amaranth growth. • The NaCl-extracted Cd dominated all organs of amaranth. • The CaOx-bound Cd in leaves was significantly higher than in roots and stems. • Excessive Ca promoted Cd bioconcentration while reducing CaOx-bound Cd accumulation. • CaOx is not the dominant Cd detoxification pathway in amaranth. [ABSTRACT FROM AUTHOR]