Metal Inputs Research Articles

Potential ecological risks of heavy metals and Cd accumulation characteristics of Suaeda salsa under different Cd input and water logging conditions in the Yellow River estuary, China.

To improve the remediation of heavy metal pollution by typical wetland vegetation and maintain the health of wetland ecosystems under the water-sediment regulation scheme (WSRS) application, we evaluated the potential ecological risk of heavy metals in surface sediment in the Yellow River estuary affected by the WSRS. The ranges of Cr, Cu, Zn, Cd, and Pb content in surface sediment were 52.44-100.80 mg·kg-1 dry weight (DW), 16.38-21.19 mg·kg-1 DW, 64.77-255.50 mg·kg-1 DW, 0.12-0.24 mg·kg-1 DW, and 5.40-8.63 mg·kg-1 DW, respectively, and potential ecological risk coefficients showed that Cd was associated with moderate potential risk. We further examined effects of Cd in a greenhouse experiment to explore the influence of short-term Cd input and water logging condition changes induced by WSRS on the Cd absorption characteristics of Suaeda salsa (L.) Pall in the Yellow River estuary. The results showed that total biomass decreased but Cd content in tissue of S. salsa increased with increasing Cd input and the accumulation factor reached maximum values at 100 μg·L-1 of Cd, indicating that S. salsa efficiently accumulated Cd. Water logging depth significantly affected S. salsa growth and Cd absorption with deeper water logging being detrimental to growth. The interaction effect of Cd input and water logging depth on Cd content and accumulation factor was significant. These results suggest that WSRS caused short-term heavy metal input and changes in water conditions affect wetland vegetation growth and heavy metal absorption in the downstream estuary.

Straw removal or non-removal affects cadmium (Cd) accumulation in soil–rice (Oryza sativa L.) system at different ambient air Cd levels

Despite the potential importance of the removal of contaminated straw for heavy metal output from agricultural soils, previous studies have primarily focused on the variation in the metal concentration without considering the impact input of heavy metals from atmospheric deposition. Here, rice was grown under field conditions, and, as a reference, in a deposition-free environment, and exposed to different ambient air Cd levels. Two consecutive years of pot experiments were conducted in two study areas (ZZ and LY) to examine the changes in soil physicochemical properties as well as Cd accumulation in the soil–rice (Oryza sativa L.) system in response to straw return or removal. The results showed that rice straw return enhanced the soil pH and organic matter (OM) content, but reduced the soil redox potential (Eh); and the variation in amplitude increased with number of cultivation years. After two years of cultivation, the concentrations of soil total Cd and extractable Cd in the straw-removal treatments reduced by 9.89–29.49% and 4.88–37.74%, respectively, whereas those in the straw-return treatments exhibited a slight decrease, or even an increase. This indicated that straw removal could effectively reduce the concentration and bioavailability of Cd in contaminated farmland, which was further confirmed by the results for accumulation of Cd in rice tissues. In addition, the contribution from atmospheric deposition was confirmed by the greater variation in Cd concentration in soils and rice tissues under deposition-free conditions. A major implication of our findings is that the adoption of reasonable straw-treatment measures and proper control over ambient air heavy metals can promote the remediation efficiency of Cd-contaminated fields.

A modified critical load assessment method of heavy metals in paddy soil at large scale

The environmental capacity of agro-ecosystem is the basis of sustainable development of agriculture, but this is hard to evaluate quantitatively due to complex input and output processes of heavy metals. Therefore, in this study, leaching of heavy metals based on PROFILE weathering model were integrated into the steady-state critical load (SSCL) of heavy metals. The results showed that the leaching rates of Hg, As, Cd, Cr, Pb, Cu and Zn in paddy soil were 0.08, 4.69, 0.22, 44.31, 18.13, 21.96 and 64.42 g/ha‧a, respectively, while the leaching rates were significantly correlated with pH, CaO, TFe2O3 and Corg.. Atmospheric deposition was the main input source of heavy metals in agricultural soil, while rice plant uptake and leaching were the main output pathways. The spatial distribution of SSCL were mainly affected by the content of heavy metals in soil, Aw (specific area of soil mineral), and ρ (bulk density). Values of SSCL hardly changed after about 40 years (Hg ≈ 0.02 kg/ha, As≈0.60 kg/ha, Cd ≈ 0.07 kg/ha, Cr ≈ 5.59 kg/ha, Pb ≈ 3.55 kg/ha, Cu ≈ 1.49 kg/ha and Zn ≈ 4.45 kg/ha). However, the sensitivity analysis indicated that soil leaching had 24.30%–27.90% positive effects on SSCL model. Based on the relationship among leaching, pH, standard limit and SSCL of heavy metals, the standard limit could be appropriately raised to cope with the increased human activities on the premise of the ecological capacity. Thus, the SSCL model provides a new insight for the establishment of environment management in agricultural soils.

Heavy metal characterization of land-based waste dumped at three ocean dumping sites in the Republic of Korea

From 1991 to 2021, 16 categories of land-based waste, totaling 131,400,000 m3, were dumped at three sites in Korea. The concentration of heavy metals varied by waste type, with organic sludge showing higher levels than liquid waste. While wastewater treatment sludge was the most commonly discarded waste, the quantity and types of waste disposed of varied by site. Before the 2015 ban on ocean dumping, 62,330 tons of heavy metals were introduced, including zinc, copper, chromium, lead, arsenic, cadmium, and mercury in descending order of frequency. In each heavy metal category, the portion of land-based waste varied by dumping site. Compared to heavy metals from atmospheric deposition, anthropogenic heavy metal input from dumping was up to 141 times higher for copper. This study serves as a reference for estimating the impact of pollutants from dumped waste.

Input Flux and the Risk of Heavy Metal(Loid) of Agricultural Soil in China: Based on Spatiotemporal Heterogeneity from 2000 to 2021

Identifying the current status of the heavy metal(loid) input of agricultural soils is vital for the soil ecological environment of agricultural-producing areas. Most previous studies have typically carried been out in small regions with limited sampling sites, which is insufficient to reveal the overall status of China. This study reviewed publications from over the past 20 years and calculated the input fluxes of heavy metal(loid)s in agricultural soil via atmospheric deposition, fertilizer, manure, and irrigation in different regions of China based on spatiotemporal heterogeneity using a meta-analysis, providing more accurate and reliable results. It was found that the heavy metal(loid) input flux of atmospheric deposition in China is large, while that of fertilizer and manure is relatively low compared to Europe. The major sources of As, Cd, Cr, Ni, and Pb entering the soil was atmospheric deposition, which accounted for 12% to 92% of the total input. Manure was responsible for 19% to 75% of the Cu and Zn input. Cd is the element presenting the most significant risk to the environment of agricultural soils in China and its safety limit will be reached within 100 years for most regions. The region we need to be concerned about is Huang-Huai-Hai due to its comprehensive pollution.

Submarine groundwater discharge and associated metal elements into an urbanized bay

In this study, geochemical tracers (radium isotopes) and heavy metals (Pb, Zn, Cd, Cr and As) were analyzed to derive the submarine groundwater discharge (SGD) and associated metal fluxes during four seasons in an urbanized bay (Daya Bay, China). Results showed that Pb and Zn were the main pollutants in bay water. SGD was found to exhibit an obvious seasonal trend (autumn > summer > spring > winter). Such seasonal patterns may be related to the hydraulic gradient between groundwater level and sea level, storm surges and tidal range. SGD was a dominant source of marine metal elements, contributing 19 %–51 % of the total inputs of metals into Daya Bay. The bay water was classified as slight pollution to heavy pollution, which could be linked to SGD-derived metal fluxes. This study provides a better understanding of the important role that SGD plays in metal budgets and ecological environments of coastal waters.

Trace metals and nutrients in tropical volcanic island rivers: Insights on chemical weathering and anthropogenic influences of Pohnpei, Micronesia

River systems in tropical islands play a vital role in maintaining the ecosystem function of surrounding oceans by delivering land-derived materials. Researches on tropical river systems frequently focused on continents and peninsulas, while little research has been conducted in tropical islands. In the present study, we conducted field surveys in a Pacific volcanic island, Pohnpei, Micronesia, and determined the substance composition of river waters (major ions, trace metals, nutrients, etc.) to quantify terrestrial material loading and biogeochemical influence on the surrounding oceans. In Pohnpei, total dissolved solutes were observed to be 71.4 mg/L; the NH4+, NO3−, PO4−, and SiO32- concentrations were 0.46, 3.9, 0.52, 221.7 μmol/L, respectively; and NO2− was lower than the detection limit (0.14 μmol/L). The trace metals concentrations of rivers in Pohnpei Island were much lower than records in tropical rivers of the world. The variation in concentration levels of major ions and nutrients among rivers was relatively limited. A similar pattern was observed in the distribution of Al and V. Trace elements, including As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr, U and Zn in rivers were most enriched in Urban Area (human activity dominated region), compared with the Mixing Area (Multiple effect region) to Natural Area (natural weathering region). Exchangeable trace metals concentrations from suspended particulate matter (SPM) were lower than in dissolved state in river waters, while water-soluble, while acid-soluble metals concentrations in the sediment were much higher than in dissolved state in rivers. In our results, trace metals in Pohnpei rivers may mainly be influenced by domestic sewage and agricultural activity—these data can be used in biogeochemical models to estimate the contribution of domestic sewage. Furthermore, we have quantified the land-derived input of trace metals from tropical volcanic islands in Pacific (TVIP) into the surrounding oceans. Though the land area of TVIP only accounts for 0.1 % of global land area, the terrigenous inputs of some trace metals from TVIP account for approximately 1 %—and even more than 2 % of those in global riverine flux. Therefore, the nutrients and trace metals inputs from TVIP would be significant for the cycle of biogenic elements in the receiving ocean.

Spatial distribution of heavy metal contaminants: The effects of water-sediment regulation in the Henan section of the Yellow River

Water-sediment regulation (WSR) affects sediment transport in the middle and lower reaches of the Yellow River through periodic interception of sediment by dams and alteration of downstream flow rates, which leads to redistribution and recycling of elements. In this study, based on the evaluation of seven heavy metals (V, Cr, Ni, Co, Cu, Zn, and Cd) in water, sediment and suspended particulate matter (SPM) in the Henan section of the Yellow River, the effects of WSR on the redistribution and risk of release of metals to the downstream aquatic environment were investigated, and the range of impact and pollution sources were determined. Dissolved metals were well below guideline values for water quality, but Cd, Cr, and Cu were enriched in the sediments, especially in the reservoir, and the pollution load index (PLI) results indicated that the contamination in the study area remained very low. The level of contamination was decreased, and metals migrated downstream after WSR. The chemical speciation of metals indicates that anthropogenic input of metals occurs in upstream tributaries, and the risk of release of metals in the sediments increases after WSR, but the spatial distribution of the risk is more homogeneous. The distribution coefficient explains the distribution pattern of pollution, where SPM carries pollutants to the downstream while formed surface sediments through natural deposition during the sand-discharge stage. Based on geological and field investigations, upstream gold mining and downstream riverbank cultivation activities in the study area are potential sources of Cu and Cd pollution. These findings are crucial to the better understanding of patterns of metal release from artificial impoundments in river systems and provide a theoretical basis for ecological development in the Yellow River Basin.

Responses of biogenic dimethylated sulfur compounds to environmental changes in the northwestern Pacific continental sea

AbstractContinental seas are facing rapid environmental shifts, but how biogenic dimethylated sulfur compounds, including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO), will respond to these environmental changes remains poorly understood. Here we investigated the effects of nutrient input, ocean acidification, and dust deposition on the phytoplankton community and organic sulfur cycle in the East China Sea. Nutrient input promoted phytoplankton growth and increased the concentrations of DMS, DMSP, and DMSO. With sufficient nutrients, especially nitrate, the dissolved DMSP degradation was inhibited, and the bacterial DMSP‐cleavage pathway (inferred by dddP gene abundance) was enhanced, causing increased DMS production. The sensitivity of phytoplankton biomass and DMS to ocean acidification varied with different initial nutrient levels, demonstrating insensitivity under eutrophic conditions and negative responses under nutrient‐limited conditions. The ocean acidification promoted the dissolved DMSP degradation and bacterial DMSP‐demethylation pathway (inferred by dmdA gene abundance) and weakened the DMS production, causing the decreases of DMS and DMSP. The nutrient from dust deposition (2 mg L−1) was identified as the key factor in enhancing phytoplankton biomass and the organic sulfur compounds concentrations, but trace metals input from dust deposition had no significant effect. This study has identified environmental drivers and suppressors of phytoplankton and biogenic dimethylated sulfur compounds in a changing marine environment, which will enable the effective modeling of future climate change.

Three gorges dam shifts estuarine heavy metal risk through suspended sediment gradation

Damming alters downstream sediment supply relationships and erosion in the estuarine delta. Given that sediment grainsize serves as a key parameter for the ability to adsorb heavy metals from water, the assessment of estuarine heavy metal risk needs to get connected initially. Hence, fine suspended sediment (<63 μm) in the Yangtze River estuary (YRE) was divided into four grainsize fractions to simulate the surface suspended sediment concentration (SSC) and grainsize composition before and after the completion of the Three Gorges Dam (TGD). Representative months were selected for flood peak reduction (October) and runoff compensation in the dry season (March) to maximize the scheduling impact of the TGD on runoff and riverine sediment input to the YRE. An improved Water Quality Index (WQI) approach was proposed to assess the combined risk alteration of five heavy metals in six estuarine sensitive targets due to TGD-induced sediment characteristics. The results demonstrated that TGD significantly but tardily reduced the SSC and the proportion of fine sediment in the YRE, decreasing the risk of heavy metals resuspension. Seasonally, the total SSC became higher in the flood season than in the dry season during post-TGD period. However, the fine SSC in the flood season was averaged only 59.7% of that in the dry season due to the pronounced grainsize coarsening effect. As the significant reduction in fine SSC overcomes the increase in heavy metal content per unit of SS, the integrated resuspension risk declined significantly, particularly for Pb and Cr. Spatially, the risk reduction for sensitive targets near the turbidity maximum zone (TMZ) is 8.4 times greater than for inner river channel. However, undiminished anthropogenic metal inputs to the YRE signified greater pressures on the depositional environment.

A methodology to liberate critical metals in waste solar panel

The availability of critical metals is one of the driving factor to secure the transition of energy production to a renewable, low carbon one because of the material requirement in photovoltaic technology (PV), wind power generation and batteries. For example, precious metals are vital to manufacture crystalline silicon solar panel and tellurium, germanium, indium and gallium are essential in thin film photovoltaic panels. However, the pressure on the supply of critical metals increases with the growth of photovoltaics. Considering the resource availability, the recycling of critical metals from waste solar panels can enhance the sustainability of end-of-life management, although the recycled metal input is limited in present state. Among the recycling techniques, the separation and liberation of metals from non-metals are crucial. This study investigate a methodology to liberate thin film materials from copper indium gallium selenide (CIGS) thin-film solar panel to recycle photovoltaic material including indium and gallium via a mechanical process.An experimental technique using mineral processing techniques, crushing and grinding, are proposed to recycle critical metals from CIGS solar panel. In this study, the crushing experiments were conducted and the size based elemental distribution was analysed. The results showed crushing is capable to delaminate glass substrate and Fuerstenau upgrading curves and the ore separation degree were used to show that selective liberation occurs and the critical metals concentrate in coarse size fraction but may not be fully liberated. The morphology test using SEM-EDS to observe the surface of broken panel and the classification of broken particle based on size, metal concentration and surface morphology were conducted. The results suggested that approximately 90 w% of functional materials are still laminated on EVA in the size fraction larger greater than 2360 μm. It shows crushing alone will not fully liberate the material. Grinding can be used as a second stage recycling method, de-coating the target materials. The grinding test resulted in a more than 80 w% recovery rate of indium and the fine particle less than 38 μm contains more than 1500 ppm indium, more than 480 ppm gallium and 1500 ppm molybdenum. It could show that the combination of crushing and grinding is suitable to delaminate the panel and de-coat the critical metals to liberate and concentrate the metals.

Understanding heavy metal distribution in timberline vegetations: A case from the Gongga Mountain, eastern Tibetan Plateau

To quantify impacts of vegetation and topographic factors on heavy metal accumulation in montane forests, we assessed the spatial distribution and determined the sources of mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu) and zinc (Zn) in timberline forests of Gongga Mountain. Our results show that vegetation type has little impact on the soil Hg, Cd and Pb concentrations. The soil concentrations of Cr, Cu and Zn are controlled by litter return, moss and lichen biomass, and canopy interception, with the highest concentrations in shrub forest. In contrast to other forests, the soil Hg pool in coniferous forest is significantly high due to the elevated Hg concentration and greater biomass production in litter. However, the soil pool sizes of Cd, Cr, Cu and Zn show a distinct increase along the elevation, which are attributed to the elevated heavy metal inputs from litter and moss, as well as the greater cloud water-induced atmospheric heavy metal depositions. The highest Hg concentrations of the aboveground parts of plant are in the foliage and bark, while the concentrations of Cd, Pb, Cr, Cu and Zn in the branch and bark are the highest. The decreased biomass density leads to a downward trend in the total vegetation pool sizes of Hg, Cd, Pb, Cr, Cu and Zn by 0.4–4.4 times with increasing elevation. The statistical analysis finally suggests that Hg, Cd and Pb mainly originate from anthropogenic atmospheric deposition, whereas Cr, Cu and Zn are mainly from natural sources. Our results highlight the importance of vegetation types and terrain conditions on distribution patterns of heavy metal in alpine forests.

Chemical vectoring in continental geothermal systems: Composition of altered rocks and illite as guides to magmatic degassing

The Taupō Volcanic Zone, New Zealand, is one of the most voluminous volcanic regions on Earth. Over the last 1.8 Myr, bimodal volcanism in this rifted-arc setting has been dominated by voluminous rhyolite ignimbrite eruptions (>6000 km3 cumulative) and minor arc-type andesite and dacite, underpinned by basaltic intrusions. The combination of the magmatism and extensionally thinned arc crust with high heat flow has resulted in more than 23 active geothermal fields in the region. The fluids sampled in the geothermal systems are dominated by dilute meteoric fluids that are low in components such as acids, alkalis, and some trace metals commonly ascribed to magmatic sources but can contain large amounts of deep sourced magmatic volatiles such as CO2.This study was designed to assess the long-term (>20,000yr) fluid and metal input into two Taupō geothermal systems, and the amount and proportion of magmatic-derived components in these fluids. We collected major and trace element compositions of hydrothermal altered whole rocks and clay minerals from two active geothermal systems and compared them with hydrothermally altered rocks of the fossil (0.6 Ma) Ngatamariki magmatic-hydrothermal system, which has a demonstrated large magmatic contribution. The Ohaaki and Rotokawa geothermal systems have both been drilled to a depth of 3000 m, with sampled reservoir fluids containing low concentrations of chloride (∼1000 mg/kg) but high levels of gas (CO2, N2) that have previously been interpreted to reflect subduction components derived from arc-type magmas. Whole-rock samples lack enrichment in chloride-transported metals such as Cu, Pb or Zn but have minor anomalies of bisulfide-complexed Au, Sb, and As in the uppermost 1500 m of the geothermal reservoirs. Hydrothermal water-rock interactions in the deep reservoirs of both geothermal systems at temperatures between 220 and 300 °C produced assemblages of illite + albite + adularia + calcite + pyrite that are in equilibrium with the observed neutral to slightly acidic pH (6 ± 1) of the present-day fluids. In the lower temperature end of this range, Mg and Fe increasingly enter the illite crystal lattice via Tschermak-type (phengite) substitution, whereas a few high-temperature (>300 °C) samples contain scarce muscovite compositions. The illites commonly have low contents of most trace metals, although minor amounts of Cs, Li, Cu, Sb and Sn occur in near-surface samples. Based on these data, over the >20,000-year lifetime of the Ohaaki and Rotokawa geothermal systems, fluids were dominated by chloride-poor meteoric water and contained little magmatic contributions other than conducted heat, some gases (CO2 - N2 ± H2S), and a small fraction of the total H2O of geothermal waters. Therefore, the inferred magma bodies of intermediate to silicic composition that lie at shallow depth beneath these geothermal systems currently are not, and likely have not been for >20,000 years, degassing significant water and chloride despite the high water and chloride contents of the magmas. By inference, the intermediate to silicic magmas at depth have not transferred large amounts of volatiles to the geothermal systems over this period, and rather are storing them in the magmatic bodies to be released in volcanic eruptions that are commonly explosive and pyroclastic in nature and highly hazardous.

Atmospheric dry deposition fluxes of trace metals over the Eastern China Marginal Seas: Impact of emission controls

Atmospheric deposition is an important exogenous input of trace metals to Eastern China Marginal Seas (ECMS), which is strongly affected by human activities. With emission control practices implemented in China, it still remains unknown what changes have taken place in the atmospheric dry depositions of the trace metals over ECMS. This study aimed to estimate the atmospheric dry depositions of Zn, Pb, Cu, and Cd over ECMS via Weather Research and Forecasting Model-Community Multiscale Air Quality Modeling System (WRF-CMAQ) in the two winter periods of January 2012 and January 2019 as well as to explore the impacts of emission control on the depositions. The anthropogenic metal emissions from China, the Korean Peninsula, Japan, and marine ships were investigated in this study. In 2012, the dry deposition fluxes of Zn, Pb, Cu, and Cd over ECMS were in the ranges of 0.50–3.4 μg m−2 d−1, 0.22–1.9 μg m−2 d−1, 0.14–0.90 μg m−2 d−1, and 12–88 ng m−2 d−1, respectively. The deposition fluxes of the four metals over Bohai Sea (BS) and Yellow Sea (YS) were 2–3 times those over East China Sea (ECS). Outflow of polluted air masses from East Asia increased the metal depositions by 3– 5-fold relative to clear days. Compared with 2012, a 5–85 % reduction in the metal depositions over ECMS were estimated in 2019, largest reductions were found over YS and BS. Meteorological variation was able to decrease or increase the metal depositions. However, the emission control only caused a reduction in the entire study region. The metal inputs to the sea were significantly lower from the ship emissions than from the continental anthropogenic emissions, although the proportion of the ship emissions in the total metal depositions rose slightly from 2012 to 2019.

To what extent can recycling batteries help alleviate metal supply shortages and environmental pressures in China?

Recycling metals contained spent lithium-ion batteries (LIBs) may be a viable way to relieve metal supply pressures. The European Union has set a minimum content of secondary metal input in LIBs in 2035. Based on a stock-driven model and a comprehensive bottom-up estimation of LIBs and metals in 13 end-using sectors, achievable recycled metals goal for the China was given: spent LIBs was expected to provide 27.4–42.0 %, 50.4–77.5 %, 50.4–77.6 %, 50.4–77.6 %, 45.3–69.3 %, 44.6–68.3 %, 26.8–39.8 % of Li, Co, Ni, Mn, Cu, Al and Fe to produce new LIBs, respectively. Additionally, in the short- to middle- term, uninterrupted power supply (UPS) will be the important end user to LIBs. Spent UPS batteries management should be paid more attention. What is more, the total environmental benefits of LIB recycling were quantified at the national level. By 2050, the amount of energy, metal, greenhouse gas and human toxicity reduced by LIB recycling will be 146.76, 164.86, 171.02 and 392.30 times higher than in 2020, respectively.

Pollution status and ecological risk assessment of metal(loid)s in the sediments of the world's largest mangrove forest: A data synthesis in the Sundarbans

The Sundarbans is the largest single-mass mangrove forest in the world, experiencing environmental and anthropogenic stress from metal(loid) inputs. We undertook a comprehensive assessment of sediment contamination and ecological risks posed by metal(loid)s in the Sundarbans using previously published data. There was a distinct difference in metal(loid) content, pollution level and ecological risk in Bangladeshi and Indian parts of the Sundarbans, with the Indian counterpart experiencing relatively higher metal(loid) pollution. The higher pollution level in India might be attributed to its vicinity to municipal and industrial areas that act the primary source of metal(loid)s in the Sundarbans. The cumulative ecological risks of metal(loid)s pointed out that the south-eastern part of Bangladeshi Sundarbans and north-eastern Indian part are at moderate ecological risk. This research will provide valuable data to inform the responsible authorities and will underpin future policies and management to reduce future metal(loid) inputs in the Sundarbans.

Integrated Assessment of Chemical and Biological Recovery After Diversion and Treatment of Acid Mine Drainage in a Rocky Mountain Stream.

Responses of stream ecosystems to gradual reductions in metal loading following remediation or restoration activities have been well documented in the literature. However, much less is known about how these systems respond to the immediate or more rapid elimination of metal inputs. Construction of a water treatment plant on the North Fork of Clear Creek (NFCC; CO, USA), a US Environmental Protection Agency Superfund site, captured, diverted, and treated the two major point-source inputs of acid mine drainage (AMD) and provided an opportunity to investigate immediate improvements in water quality. We conducted a 9-year study that included intensive within- and among-year monitoring of receiving-stream chemistry and benthic communities before and after construction of the treatment plant. Results showed a 64%-86% decrease in metal concentrations within months at the most contaminated sites. Benthic communities responded with increased abundance and diversity, but downstream stations remained impaired relative to reference conditions, with significantly lower taxonomic richness represented by a few dominant taxa (i.e., Baetis sp., Hydropsyche sp., Simulium sp., Orthocladiinae). Elevated metal concentrations from apparent residual sources, and relatively high conductivity from contributing major ions not removed during the treatment process, are likely limiting downstream recovery. Our study demonstrates that direct AMD treatment can rapidly improve water quality and benefit aquatic life, but effectiveness is limited, in part, to the extent that inputs of metals are captured and treated. Consideration should also be given to the effects of elevated major ion concentrations from the treated effluent not removed during the lime treatment process. Continued chemical and biological monitoring will be needed to quantify the NFCC recovery trajectory and to inform future remediation strategies. Environ Toxicol Chem 2023;42:512-524. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Transport and transformation of atmospheric metals in ecosystems: A review

Human activities emit large amounts of metals into the atmosphere, and which migrate or settle with atmospheric activities, thus entering the ecosystem. Atmospheric metals can be harmful to humans, soil and plants when they enter the ecosystem. This review provides an overview of the processes by which atmospheric metals enter plants, soils, water bodies, humans, and mountainous areas, and the hazards arising from atmospheric metals. Atmospheric metals are transported by adsorption on the surface of particles as they migrate and enter the ecosystem through sedimentation. Atmospheric metals enter plants in two ways: they are absorbed by the leaves of the plants and by the roots of the plants after deposition on the ground. The absorption of metal particles by the blade depends mainly on the size of the particles and the surface structure of the blade. The uptake of metals by roots is mainly related to the form and type of metals, deposited atmospheric metals have a higher biological activity and are more easily absorbed by plants compared to soil metals. The human body absorbs metals from the atmosphere through skin absorption, respiratory absorption and food intake, of which food intake is the main route, and most of metals are more harmful to children. Atmospheric metals enter water bodies mainly through deposition as well as surface runoff after rain. When atmospheric metals enter water bodies, they are mainly deposited in the sediments. Atmospheric metals are deposited into local ecosystems through atmospheric transport to remote areas, and atmospheric metals input is generally the main source of pollution in remote areas because they are less disturbed by humans. Atmospheric metals are widely migratory, persistent and toxic, so understanding their transport and transformation in the ecosystem plays an important role in the control of metals in the atmosphere.

Deep photoautotrophic prokaryotes contribute substantially to carbon dynamics in oxygen‐deficient waters in a permanently redox‐stratified freshwater lake

AbstractIn lakes, seasonal phytoplankton blooms and allochthonous plant debris intensify particulate organic carbon fluxes to the lakebed. Microbes associated with these particles likely vary with organic substrate lability and redox conditions. To explore microbial compositional responses to these variables, we analyzed particle‐associated and free‐living assemblages in the permanently redox‐stratified Fayetteville Green Lake using 16 S rRNA amplicon sequencing during the peak and end of cyanobacterial and photoautotrophic sulfur bacterial blooms. Assemblage compositions were strongly influenced by redox conditions and particle association. Assemblage compositions varied seasonally above the lower oxycline boundary (summer—generalist heterotrophs; autumn—iron reducers and specialist heterotrophs), but not in the anoxic region below. Particle‐associated assemblages were less diverse than free‐living assemblages and were dominated by heterotrophs that putatively metabolize complex organic substrates, purple sulfur bacteria, sulfur‐cycling Desulfocapsa, and eukaryotic algae. The least diverse particle‐associated assemblages occurred near the lower oxycline boundary, where microbial activities and abundances were highest, and anoxygenic photoautotrophs were enriched. The low‐diversity particle‐associated heterotrophs likely remineralize complex organic substrates, releasing simpler organic substrates to free‐living assemblages during transit, thereby influencing surrounding microbial diversity and function. Our results challenge the paradigm that phytoplankton from the shallow photic zone are the primary contributor to the vertical flux. We suggest that photoautotrophic prokaryotes from the deep photic zone contribute significantly to deep‐water carbon in this environment, and possibly in other oxygen‐deficient waters with sulfidic photic zones. Furthermore, results suggest that seasonally variable terrestrial carbon and metal inputs also influence microbial diversity and function in similar systems.

Integration of Transcriptome and Metabolome Analyses Reveals the Mechanistic Basis for Cadmium Accumulation in Maize.

Cadmium (Cd) pollution in soil has become a major environmental issue worldwide. However, the underlying molecular mechanism of low grain-Cd accumulation (GCA) in maize is still largely unknown. Herein, we report the mechanistic basis for low GCA in maize by a multiomics approach. The low GCA genotype L63 showed normal vacuolar formation and a lower capacity of xylem loading of Cd than the high-accumulator L42 under Cd stress. Transcriptomic sequencing identified 84 low-GCA-associated genes which are mainly involved in the S-adenosylmethionine (SAM) cycle, metal transport, and vacuolar sequestration. A metabolome analysis revealed that L63 plants had a more active SAM cycle and a greater capacity for terpenoid synthesis and phenylalanine metabolism than L42. Combining the analysis of transcriptome and metabolome characterized several genes as key genes involved in the determination of Cd accumulation. Our study identifies a mechanistic basis for low Cd accumulation in maize grains and provides candidate genes for genetic improvement of crops.