Understanding the risks of mercury sulfide nanoparticles in the environment: Formation, presence, and environmental behaviors

Mercury(Hg) could be microbially methylated to the bioaccumulative neurotoxin methylmercury(Me Hg), raising health concerns. Understanding the methylation of various Hg species is thus critical in predicting the Me Hg risk. Among the known Hg species, mercury sulfide(HgS) is the largest Hg reservoir in the lithosphere and has long been considered to be highly inert. However, with advances in the analytical methods of nanoparticles, HgS nanoparticles(HgS NPs) have recently been detected in various environmental matrices or organisms. Furthermore, pioneering laboratory studies have reported the high bioavailability of HgS NPs. The formation, presence, and transformation(e.g., methylation) of HgS NPs are intricately related to several environmental factors, especially dissolved organic matter(DOM). The complexity of the behavior of HgS NPs and the heterogeneity of DOM prevent us from comprehensively understanding and predicting the risk of HgS NPs. To reveal the role of HgS NPs in Hg biogeochemical cycling, research needs should focus on the following aspects: the formation pathways, the presence, and the environmental behaviors of HgS NPs impacted by the dominant influential factor of DOM. We thus summarized the latest progress in these aspects and proposed future research priorities, e.g., developing the detection techniques of HgS NPs and probing HgS NPs in various matrices, further exploring the interactions between DOM and HgS NPs. Besides, as most of the previous studies were conducted in laboratories, our current knowledge should be further refreshed through field observations, which would help to gain better insights into predicting the Hg risks in natural environment.

Deep-sea coral evidence for dissolved mercury evolution in the deep North Pacifi c Ocean over the last 700 years

The ocean is an important inventory of anthropogenic mercury(Hg),yet the history of anthropogenic Hg accumulation in the ocean remains largely unexplored.Deep-sea corals are an emerging archive of past ocean chemistry,which take in sinking or suspended particulate organic matter as their food sources.Such organic matter would exchange Hg with the local seawater before being consumed by the deepsea corals.As such,the organics preserved in the coral skeleton may record the Hg evolution of the ambient seawater during the time of coral growth.Here,we report the first data on Hg concentrations variability of a deep-sea proteinaceous coral in the oligotrophic North Pacific at the water depth of 1249 m,in attempt to understand the transfer of anthropogenic Hg into the deep Pacific ocean over the last seven centuries.We find that the Hg concentrations of different coral growth layers have remained relatively constant albeit with considerable short-term variability through time.The overall stable Hg concentration of the last seven centuries recorded in our sample suggests that anthropogenic pollution is not yet a clearly resolvable component in the deep oligotrophic North Pacific waters,in agreement with rece nt estimation from modelling works and observational studies of modern seawater profiles.As there is hardly an unambiguous way to separate anthropogenic Hg from the natural background based on recent seawater profiles,our historical data provide valuable information helping to understand the oceanic cycle of Hg through time.

Embracing digital mindsets to ensure a sustainable future

The 19th Asian Games astounded global audiences with an opening spectacle that showcased stunning digital fireworks(International Olympic Committee,2021;Zhe,2023).The groundbreaking display was brought to life through virtual reality(VR)and augmented reality(AR)technologies.It sets a pioneering example to replace conventional fireworks in major international events as well as in other large-scale entertainment activities,marking a historic milestone in the pursuit of a sustainable and healthy future.

Remediation of mercury-contaminated soils and sediments using biochar:a critical review

The transformation of mercury(Hg)into the more toxic and bioaccumulative form methylmercury(MeHg)in soils and sediments can lead to the biomagnification of MeHg through the food chain,which poses ecological and health risks.In the last decade,biochar application,an in situ remediation technique,has been shown to be effective in mitigating the risks from Hg in soils and sediments.However,uncertainties associated with biochar use and its underlying mechanisms remain.Here,we summarize recent studies on the effects and advantages of biochar amendment related to Hg biogeochemistry and its bioavailability in soils and sediments and systematically analyze the progress made in understanding the underlying mechanisms responsible for reductions in Hg bioaccumulation.The existing literature indicates(1)that biochar application decreases the mobility of inorganic Hg in soils and sediments and(2)that biochar can reduce the bioavailability of MeHg and its accumulation in crops but has a complex effect on net MeHg production.In this review,two main mechanisms,a direct mechanism(e.g.,Hg-biochar binding)and an indirect mechanism(e.g.,biochar-impacted sulfur cycling and thus Hg-soil binding),that explain the reduction in Hg bioavailability by biochar amendment based on the interactions among biochar,soil and Hg under redox conditions are highlighted.Furthermore,the existing problems with the use of biochar to treat Hg-contaminated soils and sediments,such as the appropriate dose and the long-term effectiveness of biochar,are discussed.Further research involving laboratory tests and field applications is necessary to obtain a mechanistic understanding of the role of biochar in reducing Hg bioavailability in diverse soil types under varying redox conditions and to develop completely green and sustainable biochar-based functional materials for mitigating Hg-related health risks.

Characterization of colloidal arsenic at two abandoned gold mine sites in Nova Scotia, Canada, using asymmetric flow-field flow fractionation-inductively coupled plasma mass spectrometry

Asymmetric flow-field flow fractionation-inductively-coupled plasma-mass spectrometry was used to determine whether colloidal arsenic（As） exists in soil pore water and soil extract samples at two arsenic-contaminated abandoned gold mines（Montague and Goldenville, Nova Scotia）. Colloidal arsenic was found in 12 out of the 80 collected samples（= 15%）, and was primarily associated with iron（Fe） in the encountered colloids. The molar Fe/As ratios indicate that the colloids in some samples appeared to be discrete iron–arsenic minerals, whereas in other samples, they were more consistent with As-rich iron（oxy）hydroxides. Up to three discrete size fractions of colloidal As were encountered in the samples, with mean colloid diameters between 6 and 14 nm. The pore water samples only contained one size fraction of As-bearing colloids（around 6 nm diameter）, while larger As-bearing colloids were only encountered in soil extracts.

Rates and processes affecting As speciation and mobility in lake sediments during aging

Sediments from an arsenic（As） contaminated groundwater vent site were used to investigate As（ Ⅲ） binding, transformation and redistribution in native and iron oxide amended lake sediments using aging spiked batch reactions and a sequential extraction procedure that maintains As（V） and As（ Ⅲ） speciation. In the native sediments, fractionation analysis revealed that 10% of the spiked As（ Ⅲ） remained intact after a 32-day aging experiment and was predominantly adsorbed to the strongly sorbed（NH4H2PO4 extractable） and amorphous Fe oxide bound（H3PO4 extractable） fractions. Kinetic modelling of the experimental results allowed identifying the dominant reaction path for depletion of dissolved As（ Ⅲ） to As（ Ⅲ）absorbed on to the solid phase, followed by oxidation in the solid phase. Arsenite was initially adsorbed primarily to the easily exchangeable fraction（（NH4）2SO4 extractable）, then rapidly transformed into As（V） and redistributed to the strongly sorbed and amorphous Fe oxide bound fractions. Oxidation of As（ Ⅲ） in recalcitrant fractions was less efficient. The iron oxide amendments illustrated the controls that iron oxides can have on As（ Ⅲ） binding and transformation rates. In goethite amended samples As（ Ⅲ） oxidation was faster and primarily occurred in the strongly sorbed and amorphous Fe oxide bound fractions. In these samples,19.3 μg Mn was redistributed（compared to the native sediment） from the easily exchangeable and crystalline Fe oxide bound fractions to the strongly sorbed and amorphous Fe oxide bound fractions, indicating that goethite may act as a catalyst for Mn（Ⅱ） oxidation, thereby producing sorbed Mn（ Ⅲ/Ⅳ ）, which then appears to be involved in rapidly oxidizing As（ Ⅲ）.

Mercury transformation processes in nature: Critical knowledge gaps and perspectives for moving forward

The transformation of mercury(Hg) in the environment plays a vital role in the cycling of Hg and its risk to the ecosystem and human health. Of particular importance are Hg oxidation/reduction and methylation/demethylation processes driven or mediated by the dynamics of light, microorganisms, and organic carbon, among others. Advances in understanding those Hg transformation processes determine our capacity of projecting and mitigating Hg risk. Here, we provide a critical analysis of major knowledge gaps in our understanding of Hg transformation in nature, with perspectives on approaches moving forward. Our analysis focuses on Hg transformation processes in the environment, as well as emerging methodology in exploring these processes. Future avenues for improving the understanding of Hg transformation processes to protect ecosystem and human health are also explored.

Man-made reactive oxygen species as green disinfectants

The ongoing pandemics boost the demand for chemical disinfectants,including surface disinfectants and hand sanitizers[1].This is largely driven by increasing public health awareness and hygiene standards in public and private settings[2].The global surface disinfectant market size in 2019 was valued at US$3.4 billion and estimated to experience a 6.0%compound annual growth rate,reaching US$5.42 billion in 2027[3].

The role of phosphorus in the metabolism of arsenate by a freshwater green alga, Chlorella vulgaris

A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations（〈 10–500 μg/L P） and environmentally realistic concentrations of arsenate（As（Ⅴ））（5–50 μg/L As）. Arsenic speciation in the culture medium and total cellular arsenic were measured using AEC-ICP-MS and ICP-DRC-MS, respectively, to determine arsenic biotransformation and uptake in the various phosphorus scenarios. At high phosphate concentration in the culture medium, 〉 100 μg/L P, the uptake and biotransformation of As（Ⅴ） was minimal and dimethylarsonate（DMAs（Ⅴ）） was the dominant metabolite excreted by C. vulgaris, albeit at relatively low concentrations. At common environmental P concentrations, 0–50 μg/L P, the uptake and biotransformation of As（Ⅴ） increased. At these higher As-uptake levels, arsenite（As（Ⅲ）） was the predominant metabolite excreted from the cell. The concentrations of As（Ⅲ） in these low P conditions were much higher than the concentrations of methylated arsenicals observed at the various P concentrations studied. The switchover threshold between the（small） methylation and（large） reduction of As（Ⅴ） occurred around a cellular As concentration of 1 fg/cell. The observed nearly quantitative conversion of As（Ⅴ） to As（Ⅲ） under low phosphate conditions indicates the importance of As（Ⅴ） bio-reduction at common freshwater P concentrations. These findings on the influence of phosphorus on arsenic uptake, accumulation and excretion are discussed in relation to previously published research. The impact that the two scenarios of As（Ⅴ） metabolism, As（Ⅲ） excretion at high As（Ⅴ）-uptake and methylarsenical excretion at low As（Ⅴ）-uptake, have on freshwater arsenic speciation is discussed.