Metals In Aquatic Environment Research Articles

Effects of copper and cadmium on stream leaf decomposition: evidence from a microcosm study.

We seek to understand how copper and cadmium act on leaf litter decomposition by their effects on microbial conditioning and litter fragmentation by invertebrates. In this study, we evaluated, in an integrated manner, different biological elements responsible for functioning of streams. Thus, we performed a microcosm assay with different concentrations for the two metals and their combination, evaluating their effects on fungi sporulation rate, consumption rate by shredders, and, consequently, the leaf litter decomposition rates. Sporulation rates were affected by all copper concentrations tested 10 × = 16µg L-1 and 25 × = 40µg L-1) but significantly reduced only at the highest concentration of cadmium (25 × = 22.5µg L-1). Increased copper and cadmium concentrations reduced the consumption of leaf litter by Phylloicus at 60%. The concentrations (10 × and 25 ×) of both metals resulted in a reduction in decomposition rates. When combined, copper and cadmium negatively affected microbial conditioning, consumption by shredders, and leaf litter decomposition. Increases in concentrations of copper and cadmium directly affected organic matter decomposition in aquatic environments. Thus, the presence of a high concentration of heavy metals in aquatic environments alters the functioning of ecosystems. As trace-elements occur in a combined manner in environments, our results show that the combined effects of different metals potentiate the negative effects on ecosystem processes.

Influence of extracellular polymeric substances on arsenic bioaccumulation and biotransformation in biofilms

It is well recognized that biofilms can biosorb and biotransform heavy metals in aquatic environments. However, the effects of extracellular polymeric substance (EPS) on inorganic arsenic (As) bioaccumulation and biotransformation in biofilms are still unrevealed and need to be investigated. In order to explore the above scientific issues, the As accumulation and speciation in EPS-containing or EPS-free biofilms and growth medium under As(V)/As(III) exposure conditions were measured. After the removal of EPS, the amount of As uptake (Asup) and As adsorption (Asad) in biofilms were significantly reduced, no matter whether exposed to As(V) or As(III). FTIR analysis further suggested that the interaction between these functional groups with As was limited after the removal of EPS. In the EPS-containing biofilms, the Asad was mainly As(V) with low toxicity. However, after the removal of EPS, the Asad was mainly As(III) with high fluidity, and no methylated As was found. Moreover, the removal of EPS inhibited As(III) oxidation and methylation by biofilms, resulting in the decrease of As(V) and methylated As in the growth medium. The findings of this study emphasized the essential impact of EPS on the biosorption and biotransformation of As in biofilms. This study provides a unique understanding of the role of biofilms in As biogeochemical cycle, and water quality purification function in water environments.

Spatial and temporal distribution of geochemical elements and their processes in different size fractions–Miri River (NW Borneo)

The toxicity, persistence, and propensity for accumulation of metals in aquatic environments have raised significant concerns globally. Expansion of urbanization with the growth of industrial and agricultural sectors in Miri City results in a high concentration of pollutants that flow directly into the Miri River. Hence, this study provides a comprehensive analysis of the Miri River water quality, focusing on spatial and temporal variations. River water samples were collected in two different time periods and analysed for physico-chemical parameters includes major ions, nutrients, metals and isotopes. Particularly, the metals were analysed in different size fractions (particulate and colloid) of the suspended solids. Geochemical plots, pollution index, geochemical modelling and factor analysis were used for the data analysis. Interpretation of data reveals that the mean concentration of metals in river water were increased from downstream to the upstream of the river irrespective of the seasons. Major ions were mostly derived from the chemical weathering of source rocks, which was supported by the Gibbs plot. Piper plot indicates the seasonal shifting of water types from Ca–Mg to Na–Cl. Isotopic signatures reveal direct atmospheric precipitation and evaporation were the major origins of river water. Fe was the dominant metal concentration in river water irrespective of the seasons (mean concentration 1.05 mg/L). Fe and Zn were the dominant metal concentration observed in all the 3 size fractions of suspended solids. Industrial activities and seawater influx dominate in the downstream, whereas weathering and agricultural inputs are significant in the upstream of the river. Particulate and colloidal fractions are the major contributors for the metal transport in the midstream and downstream of the river. The outcome of this study offer a thorough understanding of the seasonal elemental distribution at different size fractions, geochemical behaviour and the pollution status of the Miri River. With this knowledge, sustainable management strategies can be developed for this crucial water resource to the benefit of Miri community.

Investigation of dissolved organic matter's influence on the toxicity of cadmium to the cyanobacterium Microcystis aeruginosa by biochemical and molecular assays.

Rapid economic development has increased the accumulation of dissolved organic matter (DOM) and heavy metals in aquatic environments. In addition,Microcystis aeruginosa can cause the outbreak of cyanobacteria bloom and can produce microcystin, which poses a threat to human water safety. Therefore, this study analyzed the biochemical and molecular assays of DOM (0, 1, 3, 5, 8, 10 mg C L-1) extracted from four different sources on the toxicity of cadmium (Cd) to M. aeruginosa. The results showed that the addition of different concentrations of DOM from sediment, biochar, and humic acid alleviated the toxicity of Cd to M. aeruginosa. But the addition of rice hulls DOM at high concentrations (8 and 10 mg L-1) significantly reduced the normal growth and metabolic activities of M. aeruginosa. DOM from four different sources promoted the expression level of microcystin-related gene mcyA and the production of microcystin-leucine-arginine (MC-LR), and mcyA was positively correlated with MC-LR. DOM from biochar, sediment, and humic acid were able to bind Cd through complexation. The results will help to understand the toxic effects of heavy metals on toxic-producing cyanobacteria in the presence of DOM, and provide certain reference for the evaluation of water environmental health.

Development of cellulose/hydroxyapatite/TiO2 scaffolds for efficient removal of lead (II) ions pollution: Characterization, kinetic analysis, and artificial neural network modeling

The utilization of nano-biodegradable composites for removing pollutants and heavy metals in aquatic environments has been widespread. This study focuses on synthesizing cellulose/hydroxyapatite nanocomposites with titanium dioxide (TiO2) via the freeze-drying method for the adsorption of lead ions in aquatic environments. The physical and chemical properties of the nanocomposites, including structure, morphology, and mechanical properties, were analyzed through FTIR, XRD, SEM, and EDS. In addition, parameters affecting the adsorption capacity, such as time, temperature, pH, and initial concentration, were determined. The nanocomposite exhibited a maximum adsorption capacity of 1012 mg⸱g−1, and the second-order kinetic model was found to govern the adsorption process. Additionally, an artificial neural network (ANN) was created using weight percentages (wt%) of nanoparticles included in the scaffold to predict the mechanical behavior, porosity, and desorption of the scaffolds at various weight percentages of hydroxyapatite (nHAP) and TiO2. The results of the ANN indicated that the incorporation of both single and hybrid nanoparticles into the scaffolds improved their mechanical behavior and desorption, as well as increased their porosity.

Unravelling the metal uptake process in mosses: Comparison of aquatic and terrestrial species as air pollution biomonitors

Transplanted mosses have been widely shown to be excellent tools for biomonitoring air pollution; however, it is not clear how the functional groups present on their surfaces affect the uptake of metal cations. In the present study, we examined differences in trace metal accumulation in two terrestrial and one aquatic moss species, and investigated whether the differences depended on their physico-chemical characteristics. In the laboratory, we determined C, N and H contents in their tissues and obtained the ATR-FTIR spectra (to identify the presence of functional groups). We also conducted surface acid-base titrations and metal adsorption assays with Cd, Cu and Pb. In the field, we exposed transplants of each species near different air-polluting industries, and determined the mosses enrichment of Al, Cd, Co, Cr, Cu, Fe, Ni, Pb and V. Laboratory results demonstrated higher metal uptake capacity in the terrestrial mosses Sphagnum palustre and Pseudoscleropodium purum, compared to that in the aquatic moss Fontinalis antipyretica, which can be attributed to a greater abundance of acidic functional groups (i.e. negatively charged binding sites) on the surface of the terrestrial mosses. The affinity of moss for certain elements depends on the abundance and nature of surface functional groups. Accordingly, the metal concentrations generally reached higher levels in S. palustre transplants compared to the other species, except for the uptake of Hg, which was higher in F. antipyretica. However, the findings also suggest an interaction between the type of environment (terrestrial or aquatic) and the moss characteristics that may influence the abovementioned trend. Thus, irrespective of the physico-chemical characteristics, metal uptake varied depending on the environment of origin of the mosses “i.e. atmospheric or aquatic”. In other words, the findings suggest that species that accumulate more metals in terrestrial environments will accumulate lower amounts of metals in aquatic environments and vice versa.

Applying synchronous fluorescence spectroscopy combined with Gaussian band fitting and two-dimensional correlation to characterize interactions of copper (II) with dissolved organic matter from urban river sediments

Dissolved organic matter (DOM) and heavy metals can form strong complexes, which might determine distribution, toxicity, bioavailability, and environmental trend of heavy metals in aquatic environment. Synchronous fluorescence spectroscopy combined with Gaussian band fitting and two-dimensional correlation (2DCOS) was applied to characterize Cu2+ interactions with DOM fractions from sediments in Xihe River. DOM from four layers was mainly associated with tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humic-like (MHLF), fulvic-like (FLF), and humic-like fluorescence (HLF) substances based on Gaussian band fitting. At the first layer, the f value of FLF was the highest among five components, while TRLF at the second and third layers represented the highest f values. Besides, at the fourth layer, the f value of TYLF was the highest. According to 2DCOS and moving window 2DCOS, the decreasing binding sensitivities were HLF→MHLF→TYLF→TRLF→FLF in the first layer, which almost represented high efficiencies at 40 μM Cu2+. The binding order was MHLF→HLF→FLF→TRLF→TYLF in the second layer, where TYLF and TRLF shared the identical efficiencies at 120 μM Cu2+. For the third layer, the varying order was TYLF→FLF→TRLF→MHLF→HLF, whose high efficiencies occurred at 10 μM Cu2+. In the fourth layer, the order was TYLF→FLF→MHLF→TRLF→HLF, whose efficiencies almost covered whole titrate concentrations. At a given layer, structural equation model showed Cu2+ concentration negatively affected the fluorescence intensity of DOM components except FLF at the substrate layer. This study might provide an effective method to illustrate the interaction mechanism of the heavy metals and DOM fractions.

Investigation of Efficient Adsorption of Toxic Heavy Metals (Chromium, Lead, Cadmium) from Aquatic Environment Using Orange Peel Cellulose as Adsorbent

Heavy metals in the environment cause adverse effects on living organisms. Agro-wastes have the potential to remove heavy metals from aqueous solutions. In this study, the orange peel cellulose (OPC) beads were utilized as adsorbents to remove metals from wastewater. The surface of the adsorbent was studied by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS). The concentrations of the metals before and after adsorption were measured using inductively coupled plasma mass spectrometry. The removal of the metal ions (i.e., Cr6+, Cd2+, and Pb2+) using the OPC was investigated by varying the pH, contact time, and adsorbent dosages parameters. The maximum removal efficiency obtained for the metal ions occurred at pHs 4–8. The use of the Langmuir isotherm and Freundlich isotherm models demonstrated the statistical significance of the heavy metal adsorption processes (R2 > 0.96). At a neutral pH, the OPC adsorption order was Pb2+ > Cd2+ > Cr6+ with % removal values of 98.33, 93.91, and 33.50, respectively. The adsorption equilibrium for Cr6+ was reached after 36 h. For Cd2+ and Pb2+, equilibrium was reached after 8 and 12 h, respectively. The FT-IR and SEM-EDS confirmed the presence of many functional groups and elements on the adsorbent. The adsorption of heavy metals using the OPC is a low-cost, eco-friendly, and innovative method for the removal of metals in aquatic environments. The findings of this study will be highly significant for the public in the affected areas worldwide that have credible health concerns due to water contamination with heavy metals.

Impacts of the Residual Trace Metals of Aquaculture in Net Cages on the Quality of Sediment

Anthropogenic pollution by trace metals in aquatic environments in semiarid zones is a critical area of investigation. The objective of this study was to investigate the concentration and spatial distribution of trace metals in surface sediments in the Rosário reservoir, which is affected by the intensive aquaculture of Tilápia-do-Nilo (Oreochromis niloticus). Sediment samples were collected in three different areas, postculture (PCTV), cultivation (CTV) and control (CTRL) in the dry season in 2019. The granulometric composition, organic matter and concentrations of Fe, Mn, Zn, Cu, Cr, Cd, Pb and Ni metals were determined. Multivariate statistics were used. Geochemical and ecotoxicological indices and a comparison with sediment quality guidelines (SQG) were used. The sediment was characterized by silty clay loam with an average organic matter of 18.76 ± 4.27. The analytical merit figures demonstrated accuracy (metal recoveries in certified standards) between 89 to 99% and high precision (RSD < 5%). The concentration ranges for the metals were Fe: 0.11-0.85 (%), Mn: 14.46-86.91, Zn: 2.6-220.56, Cu: 26.89-98.75, Cr: 60.18-76.06, Cd: 0.38-0.59, Pb: 18.13-43.13, and Ni: 34.4-46.75, all in (mg/kg-1). The highest concentration values were found in the CTV areas (Fe: 40 ± 0.22, Mn: 66.48 ± 19.11, Zn: 114.83 ± 59.75 and Cr: 70.85 ± 2.62) and PCTV (Cd: 0.53 ± 0.04, Cu: 71.83 ± 21.20, Pb: 33.71 ± 4.34 and Ni: 44.60 ± 1.79). Pearson's correlation, hierarchical cluster analysis and principal component analysis confirmed the influence of fish farming on metals. Only Ni presented concentration values higher than the reference value established in the SQG. Thus, considering the probable geochemical and ecotoxicological effects, they comprise the two lowest levels of impact.

Aging dependent plastic bag derived-microplastics as a vector of metals in lake water

The adsorption of microplastics (MPs) for metals in aquatic environment remains poorly understood due to the use of either commercial MPs, which have different property from the MPs in environments, or artificial solutions, which have not only the significantly higher concentration of metals than natural aqueous environment but also the different natures. In this study, we elaborated the adsorption throughout the aging process of plastic bag derived-MPs (initially 1–2 mm) by potassium persulfate (K2S2O8) solution to metals in lake water. Comparatively, plastic bag derived-MPs had the highest adsorption capacity for Zn2+ followed by Fe3+, Pb2+, Mn2+, Cr6+, Ni2+, Cu2+ and Cd2+, which is not completely consistent with the literature. Both the adsorption capacity and distribution coefficients of Cu2+, Ni2+, Zn2+, Mn2+ and Pb2+ had significant linear correlation with carbonyl index (p < 0.05). Although the aging overall enhanced the adsorption, the adsorption capacities of MPs might fluctuate depending on metal.

Pollution status and risk assessment of heavy metals in the sediment of a historically contaminated lake treated by oxidation pond in China.

Sediment plays animportant role in controlling biogeochemical cycling of heavy metals in aquatic environment. The Ya-Er Lake is a typical lake which was historically contaminated by heavy metals in Hubei province, China. After industries surrounding the Ya-Er Lake being shut down, oxidation pond treatment and dredging program were conducted for pollution management since 1970s. To date, the Ya-Er Lake has been used for aquaculture for several decades. However, the status of heavy metal levels and ecological risks in this lake remains unclear. Herein, concentrations, chemical fractions, and risk assessment of heavy metals were investigated in the Ya-Er Lake sediment. Results showed that concentrations of heavy metals in the Ya-Er Lake sediment were higher than other reported lake systems, suggesting that heavy metal pollution in the Ya-Er Lake is still serious. Relatively higher proportions of carbonates bound form of Cd and Ni indicated high-risk potential of these two heavy metals, and Cd and Ni should be listed as the primary heavy metal pollutants in the Ya-Er Lake according to the results of potential ecological risk index (PERI) and sediment quality guidelines (SQGs). The risk assessment code (RAC) analysis showed that Ni and Cd poses higher bioavailability and mitigation potential, and may affect the Ya-Er Lake ecosystem and downstream aquatic environment. These findings reflected that oxidation pond treatment and dredging sediment to near place are not effective to control heavy metal pollution, and a long-term ecological risk is still posed to surrounding aquatic environment. Our study provides scientific basis on pollution control and management in aquatic system contaminated by heavy metals.

Adsorption of Cadmium(II) Ions from Aqueous Solutions Using Calcium Molybdate

The presence of toxic metals in aquatic environments poses serious problems for ecosystems and especially for human health. Numerous types of metal oxides have been used to remove these metals and other toxic organic compounds, using adsorption systems. In this work, CaMoO4 was synthesized via coprecipitation and processed for different periods of time using a microwave-assisted hydrothermal system. It was possible to synthesize CaMoO4 on room temperature without any heat treatment. In addition, small processing times in HTMW were able to produce CM with different morphologies. The effect of the reaction time on the morphology of the product and particle size was examined in SEM images. A plausible CaMO4 formation mechanism was proposed based on time and temperature parameters. The potential application of CaMO4 as an adsorbent in water treatment was also investigated and this material exhibited a favorable adsorption performance in the fast removal of cadmium(ii) ions from aqueous solution of 1 mg L-1 concentration. So, CM showing a promising potential for use in environmental remediation.

Genomic and Transcriptomic Analysis Reveal Multiple Strategies for the Cadmium Tolerance in Vibrio parahaemolyticus N10-18 Isolated from Aquatic Animal Ostrea gigas Thunberg.

The waterborne Vibrio parahaemolyticus can cause acute gastroenteritis, wound infection, and septicemia in humans. Pollution of heavy metals in aquatic environments is proposed to link high incidence of the multidrug-resistant (MDR) pathogen. Nevertheless, the genome evolution and heavy metal tolerance mechanism of V. parahaemolyticus in aquatic animals remain to be largely unveiled. Here, we overcome the limitation by characterizing an MDR V. parahaemolyticus N10-18 isolate with high cadmium (Cd) tolerance using genomic and transcriptomic techniques. The draft genome sequence (4,910,080 bp) of V. parahaemolyticus N10-18 recovered from Ostrea gigas Thunberg was determined, and 722 of 4653 predicted genes had unknown function. Comparative genomic analysis revealed mobile genetic elements (n = 11) and heavy metal and antibiotic-resistance genes (n = 38 and 7). The bacterium significantly changed cell membrane structure to resist the Cd2+ (50 μg/mL) stress (p < 0.05). Comparative transcriptomic analysis revealed seven significantly altered metabolic pathways elicited by the stress. The zinc/Cd/mercury/lead transportation and efflux and the zinc ATP-binding cassette (ABC) transportation were greatly enhanced; metal and iron ABC transportation and thiamine metabolism were also up-regulated; conversely, propanoate metabolism and ribose and maltose ABC transportation were inhibited (p < 0.05). The results of this study demonstrate multiple strategies for the Cd tolerance in V. parahaemolyticus.

Effect of dissolved organic matter on the bioavailability and toxicity of cadmium in zebrafish larvae: Determination based on toxicokinetic–toxicodynamic processes

The presence of dissolved organic matter (DOM) strongly influences the bioavailability of metals in aquatic environments; however, the association between the binding activities and the concentrations of DOM compositions is not well documented, leading to uncertainties in metal toxicity assessment. We creatively quantify the mitigation and acceleration effects of DOM compositions on cadmium (Cd) bioaccumulation and toxicity in zebrafish larvae using abiotic ligand (ABLs) and biotic ligand (BLs) in a toxicokinetic–toxicodynamic (TK–TD) model. The BL–TK–TD model could accurately predict the protective effect of fulvic acid while overestimating the complexing capacity of citric acid. The model also could successfully simulate the protective effects of native DOM in most cases from 32 natural water bodies in China. The observed LC50 values of Cd showed a peak effect for the native DOM fraction comprising hydrophilic acidic contents (3.55 ± 0.44 mg L − 1) in natural water from 32 sites. The BL–TK–TD model provides practically useful information to identify the effect of different DOM compositions on metal bioavailability and toxicity in aquatic environments and guides future water management policies aimed at controlling aquatic heavy metal pollution.

Determination of Mn, Cu and Pb background level in higher aquatic plants within Belarusian reservoirs based on National Monitoring System Data

AbstractThe intensity of heavy metal accumulation by aquatic plants can be used as an indicator of the water body ecological status. Macrophyte‐based assessment of the contamination level by heavy metals in aquatic environments assumes their background content data. The background level of Mn, Cu, and Pb contents in aquatic plants of lakes has been determined according to the monitoring data. During the National Environment Monitoring 827 macrophyte samples have been collected from 47 Belarusian reservoirs and lakes. Background and anomalous values have been established empirically with help of such statistical methods as (median ± 2MAD), Tukey Box Plot and cumulative probability (or Q‐Q) plot. The highest threshold values of analyzed elements are obtained for submersed aquatic plants and amount 5817.0 mg/kg for Mn, 78.0 mg/kg for Cu, and 54.7 mg/kg for Pb. The lakes with abnormal metal contents in macrophyte tissues have been revealed. Spatial distribution of Mn, Cu, and Pb anomalous have been analyzed. Some differences in spatial patterns between ecological groups are mainly caused by varying predominant sources of elements intake into plants.

Effects of waterborne Pb/Cu mixture on Chinese toad, Bufo gargarizans tadpoles: morphological, histological, and intestinal microbiota assessment.

Coexistence of heavy metals in aquatic environments exert complex effects on amphibians. Here, the adverse effects of Pb (0.14 μM) combined with Cu at concentrations of 0, 0.25, and 1.0 μM were investigated in Bufo gargarizans tadpoles. Tadpoles were chronically exposed from Gosner stage (Gs) 26 to Gs 38, and morphology of tadpoles as well as intestinal histology and bacterial community were assessed. Our results indicated that Pb+Cu1.0 exposure induced significant retardation of somatic mass, total length, intestine mass, and intestine length as well as intestinal histological alterations. Pb+Cu0.25 and Pb+Cu1.0 exposure were associated with the loss of gut bacterial diversity. Proteobacteria and Bacteroidetes were two dominant phyla in tadpoles independently of heavy metal exposure, but the abundance of Proteobacteria increased significantly in Pb+Cu1.0 group and Bacteroidetes decreased significantly in all treatment groups. Furthermore, functional prediction indicated that metabolic disorders were associated with Pb+Cu0.25 and Pb+Cu1.0 exposure. Overall, relative limited shifts in intestinal bacterial diversity, composition, and functionality caused by Pb+Cu0 exposure, while coexistence of Pb and Cu induced gut dysbiosis and might further cause disturbance of metabolic homeostasis. The findings of this study provide insights into the effects of Pb and Cu coexistence on the health of amphibians.

The role of microplastics biofilm in accumulation of trace metals in aquatic environments.

Microplastics are one of the major contaminants of aquatic nature where they can interact with organic and inorganic pollutants, including trace metals, and adsorb them. At the same time, after the microplastics have entered the aquatic environments, they are quickly covered with a biofilm - microorganisms which are able to produce extracellular polymeric substances (EPS) that can facilitate sorption of trace metals from surrounding water. The microbial community of biofilm contains bacteria which synthesizes EPS with antimicrobial activity making them more competitive than other microbial inhabitants. The trace metal trapping by bacterial EPS can inhibit the development of certain microorganisms, therefore, a single microparticle participates in complex interactions of the diverse elements surrounding it. The presented review aims to consider the variety of interactions associated with the adsorption of trace metal ions on the surface of microplastics covered with biofilm, the fate of such microplastics and the ever-increasing risk to the environment caused by the combination of these large-scale pollutants - microplastics and trace metals. Since aquatic pollution problems affect the entire planet, strict regulation of the production, use, and disposal of plastic materials is needed to mitigate the effects of this emerging pollutant and its complexes could have on the environment and human health.

Quantifying the bioaccumulation of Pb to Chlorella vulgaris in the presence of dissolved organic matters with different molecular weights.

Dissolved organic matter (DOM) is ubiquitous in natural waters which exhibits obvious effects on the toxicity of heavy metals. However, information on the toxicity of heavy metals in the presence of DOMs with different molecular weights (MWs) was still unclear. In this study, Suwannee river humic acid (SRHA) and algae-derived organic matter (ADOM) were selected as typical terrestrial and microbial DOMs, with the bulk DOMs fractionating into high MW (HMW-, 1kDa ~ 0.45μm) and low MW (LMW-, < 1kDa) fractions to explore the MW-dependent heterogeneities in the bioaccumulation of Pb to Chlorella vulgaris. Results showed that, regardless of DOM types, the LMW fraction exhibited more acidic groups and humic-like substances than the HMW counterparts. Presence of bulk DOM can decrease the bioaccumulation of Pb, while the specific effects were MW- and type-dependent. The LMW-SRHA enhanced the bioaccumulation of Pb while the HMW counterpart alleviated the effects. However, both the HMW- and LMW-ADOM can reduce the bioaccumulation of Pb to C. vulgaris. Moreover, the correlation analysis showed a significant positive correlation between the content of phenolic-OH and the adsorbed/internalized amounts of Pb, demonstrating that the phenolic-OH played a critical role in altering the bioaccumulation of Pb. The results obtained in this study suggest that distribution of MWs, number of acidic functional groups, and metal complexation capacity within DOM pool should be considered for the eco-environmental risk assessment of heavy metals in aquatic environments.

Single-Step Hydrothermal Synthesis of Biochar from H3PO4-Activated Lettuce Waste for Efficient Adsorption of Cd(II) in Aqueous Solution.

Developing an ideal and cheap adsorbent for adsorbing heavy metals from aqueous solution has been urgently need. In this study, a novel, effective and low-cost method was developed to prepare the biochar from lettuce waste with H3PO4 as an acidic activation agent at a low-temperature (circa 200 °C) hydrothermal carbonization process. A batch adsorption experiment demonstrated that the biochar reaches the adsorption equilibrium within 30 min, and the optimal adsorption capacity of Cd(II) is 195.8 mg∙g−1 at solution pH 6.0, which is significantly improved from circa 20.5 mg∙g−1 of the original biochar without activator. The fitting results of the prepared biochar adsorption data conform to the pseudo-second-order kinetic model (PSO) and the Sips isotherm model, and the Cd(II) adsorption is a spontaneous and exothermic process. The hypothetical adsorption mechanism is mainly composed of ion exchange, electrostatic attraction, and surface complexation. This work offers a novel and low-temperature strategy to produce cheap and promising carbon-based adsorbents from organic vegetation wastes for removing heavy metals in aquatic environment efficiently.

Aging of microplastics and their role as vector for copper in aqueous solution

Microplastics (MPs), considered to be potential vectors for the transfer of heavy metals, undergo aging in the environment. However, the aging mechanisms of MPs and their interactions with heavy metals in aquatic environments still require additional studies. This study investigated the aging of micro-sized polyethylene terephthalate (mPET) and polyamide (mPA) in simulated seawater and changes in their physical and chemical properties, as well as the adsorption of copper by virgin and aged MPs. The effect of pH on adsorption behavior of MPs on copper was also elucidated. The results showed that the aging process of MPs was characterized by some wrinkles along with rough and fractured surface textures, as well as the changes in functional groups such as hydroxyl groups (–OH), aromatic carbon–carbon double bond (CC), and carbon hydrogen bond (C-H). These changes further influence the aromaticity of the aged MPs and their affinity to pollutants. The aged MPs have higher sorption abilities as compared with that of virgin MPs (e.g., aged mPA > aged mPET > virgin mPA > virgin mPET) and the maximum adsorption capacity of mPA and mPET was achieved at pH 10. This study would contribute to understand the interactions among aged MPs, copper, and environmental factors, which can serve as a baseline for further studies on the toxicity of MPs in combination with heavy metals in the environment.