Modification of pristine biochars has received increasing attentions due to the significant potential in enhancing adsorption performance. In this work, the co-modification of KOH and KMnO4 on ...biochar (K-Mn-BC) was performed, with the effect of KOH/KMnO4 modification on biochar properties and their adsorption toward tetracycline (TC) being extensively explored. Results showed that KOH/KMnO4 modification can significantly regulate biochars to form hierarchical structure. The obtained K-Mn-BC was characterized with a high specific surface area (1524.6 m2 g−1) and total pore volume (0.85 cm3 g−1). In addition, the K-Mn-BC exhibited a high adsorption capacity of 584.19 mg g−1 toward TC at 318 K, and pseudo-second-order (R2:0.993～0.998) and Langmuir (R2: 0.834～0.874) models can fit well with the adsorption behavior. Moreover, the obtained K-Mn-BC can efficiently adsorb TC within a wide pH range (3.0–10.0), and were not affected by the co-existing ions. The possible mechanisms for the high adsorption capacity were ascribed to the pore filling and π-π interaction, following by hydrogen bonding and metal complexation. The obtained K-Mn-BC is a suitable adsorbent for TC removal from water due to the hierarchical structure, high adsorption capacity, and stable adsorption effect.
Display omitted
•Co-modification of KOH and KMnO4 on biochar for enhanced TC adsorption was studied.•K-Mn-BC exhibited a hierarchical structure.•Pseudo-second-order and Langmuir models can well fit the adsorption behavior.•The maximum adsorption capacity of K-Mn-BC toward was 584.19 mg g−1.•The prevailing mechanisms of TC on K-Mn-BC were revealed.
Evaluating the bioavailability of Cd to rice (Oryza sativa L.) was essential in the karst region, Southwestern China, where the soils have previously been shown to be anomalously enriched in Cd ...through geogenic processes. In this research, we examined the bioavailability of Cd to rice samples collected from 278 sites in Guangxi province, where rice is the most widely cultivated cereal crop that is responsible for the largest human dietary exposure to Cd. Both soil chemical extraction and soil-plant transfer modelling approaches were used to predict the bioavailability to rice. Some of the soil types were highly enriched in Cd, but their bioavailability was low, since the soil carbonates raised soil pH and remarkably reduced Cd bioavailability. In contrast, acidic soils (Ca was largely leached) with relatively low total Cd, the grown rice plants accumulated higher Cd in their grains. Results from CaCl2 extraction experiments provided good predictions for Cd in rice grain grown in soils of different types. Stepwise multiple regressions revealed soil pH and soil Ca content were the dominant factors that control the transfer of Cd from soil to rice. An extended Freundlich-type model and a polynomial surface model provided good prediction for Cd in rice grains. The diffusive gradients in thin films (DGT) technique gave the best estimation of soil Cd bioavailability, whereas water-extracted soil solution Cd provided relatively poor fits. Regional soil threshold that derived using the models, can avoid exceedance of Cd in rice and thereby enable local agricultural practitioners or authorities to develop appropriate management for croplands with high Cd background.
Display omitted
•The bioavailability of Cd in soils with high geochemical background was characterized as highly soil-type dependent.•Soil Ca, pH, and total Cd are the controlling factors of Cd bioavailability.•The DGT technique was a better approach to assess Cd bioavailability to rice.•Derived regional soil threshold can prevent exceedance of Cd in rice.
Using various approaches to characterize soil behaviors and the bioavailability of Cd to rice grown in high Cd background soils derived under unique karst geologies.
Effects of photochemical and microbial degradation on variations in composition and molecular-size of dissolved organic matter (DOM) from different sources (algal and soil) and the subsequent ...influence on Cu(II) binding were investigated using UV–Vis, fluorescence excitation-emission matrices coupled with parallel factor analysis, flow field-flow fractionation (FlFFF), and metal titration. The degradation processes resulted in an initial rapid decline in the bulk dissolved organic carbon and chromophoric and fluorescent DOM components, followed by a small or little decrease. Specifically, photochemical reaction decreased the aromaticity, humification and apparent molecular weights of all DOM samples, whereas a reverse trend was observed during microbial degradation. The FlFFF fractograms revealed that coagulation of both protein- and humic-like DOM induced an increase in molecular weights for algal-DOM, while the molecular weight enhancement for allochthonous soil samples was mainly attributed to the self-assembly of humic-like components. The Cu(II) binding capacity of algal-derived humic-like and fulvic-like DOM consistently increased during photo- and bio-degradation, while the soil-derived DOM exhibited a slight decline in Cu(II) binding capacity during photo-degradation but a substantial increase during microbial degradation, indicating source- and degradation-dependent metal binding heterogeneities. Pearson correlation analysis demonstrated that the Cu(II) binding potential was mostly related with aromaticity and molecular size for allochthonous soil-derived DOM, but was regulated by both DOM properties and specific degradation processes for autochthonous algal-derived DOM. This study highlighted the coupling role of inherent DOM properties and external environmental processes in regulating metal binding, and provided new insights into metal-DOM interactions and the behavior and fate of DOM-bound metals in aquatic environments.
Display omitted
•Effect of photo-/microbial degradation on metal binding with DOM from different origins was studied.•Different variations in abundance, composition, and size were observed for different DOMs under photo-/bio-degradation.•logKM increased during algal-DOM degradation but varied for soil-DOM depending on degradation.•Metal binding with allochthonous DOM was controlled by aromaticity and molecular size.•Metal binding with autochthonous DOM was regulated by both DOM properties and degradation processes.
Metal-DOM binding was mostly controlled by aromaticity and molecular size for the allochthonous DOM, but was regulated by both DOM property and degradation process for the autochthonous DOM.
In peri-urban critical zones, soil ecosystems are highly affected by increasing urbanization, causing probably an intense interaction between dissolved organic matter (DOM) and heavy metals in soil. ...Such interaction is critical for understanding the biogeochemical cycles of both organic matter and heavy metals in these zones. However, limited research has reported the correlative distribution of DOM and heavy metals at high seasonal and spatial resolutions in peri-urban critical zones. In this study, 160 soil samples were collected from the farmland and forestland of Zhangxi watershed, in Ningbo, eastern China during spring, summer, fall and winter four seasons. UV–visible absorption and fluorescent spectroscopy were used to explore the optical characteristics of DOM. The results indicated a mixture of exogenous and autogenous sources of DOM in the Zhangxi watershed, while DOM in farmland exhibited a higher degree of aromaticity and humification than that in forestland. Fluorescent results showed that humic acid-like, fulvic acid-like and microbial-derived humic-like fractions were mostly affected by seasons. The distribution of heavy metals was affected mainly by land-use changes and seasons. Correlation analysis between heavy metals and DOM characteristics and components suggested that aromatic and humic substances were more favorable in binding with EDTA extractable Ni, Cu, Zn and Cd. The bioavailable Cd and Pb decreased due to binding with humic fractions, indicating its great effects on the bioavailability of Cd and Pb. Overall, these findings provide an insight into the correlative distributions of DOM and heavy metals in peri-urban areas, thereby highlighting their biogeochemical cycling in the soil environment.
Display omitted
•DOM in farmland showed a higher degree of aromaticity than that in forestland.•The distribution of heavy metals extracted with different methods was explored.•Humic fractions can reduce the bioavailability of Cd and Pb.
Phytohormones, including auxin, abscisic acid, gibberellic acid, ethylene, cytokinin, brassinosteroids, salicylic acid, and jasmonic acid, provide beneficial effects for plants against metal(loid) ...toxicity. However, their mechanisms in alleviating metal(loid) toxicity in plants have not been fully understood. Here, we summarize phytohormone-mediated detoxification mechanisms of metal(loid)s in plants, including As, Cd, Cr, Hg, and Pb. First, we discussed the functions of phytohormones on plant growth and nutrient uptake, and the effects of metal(loid)s on plant growth and hormone contents. We then discussed the underlying mechanisms of selected phytohormones in alleviating metal(loid) toxicity in plants. Those phytohormones protect plants against metal(loid) toxicity mainly by enhancing plant growth, increasing antioxidant capacity, promoting cell wall synthesis and nutrient uptake, and decreasing metal(loid) accumulation. This review highlights the beneficial roles of phytohormones in reducing plant metal(loid) uptake and in enhancing crop yields, which helps to improve crop production and food safety.
This study investigated the fluoride (F−) concentrations and physicochemical parameters of the groundwater in a fluorite mining area of the flood plain region of the River Swat, with particular ...emphasis on the fate and distribution of F− and the hydrogeochemistry. To better understand the groundwater hydrochemical profile and F− enrichment, groundwater samples (n=53) were collected from shallow (24–40m), mid-depth (48–65m) and deep (85–120m) aquifers, and then analysed using an ion-selective electrode. The lowest F− concentration (0.7mg/L) was recorded in the deep-aquifer groundwater, while the highest (6.4mg/L) was recorded in shallow groundwater. Most groundwater samples (62.2%) exceeded the guideline (1.5mg/L) set by the World Health Organization (WHO); while for individual sources, 73% of shallow-groundwater samples (F− concentration up to 6.4mg/L), 42% of mid-depth-groundwater samples, and 17% of deep-groundwater samples had F− concentrations that exceeded this permissible limit. Assessment of the overall quality of the groundwater revealed influences of the weathering of granite and gneisses rocks, along with silicate minerals and ion exchange processes. Hydrogeochemical analysis of the groundwater showed that Na+ is the dominant cation and HCO3− the major anion. The anionic and cationic concentrations across the entire study area increased in the following order: HCO3>SO4>Cl>NO3>F>PO4 and Na>Ca>Mg>K, respectively. Relatively higher F− toxicity levels were associated with the NaHCO3 water type, and the chemical facies were found to change from the CaHCO3 to (NaHCO3) type in calcium-poor aquifers. Thermodynamic considerations of saturation indices indicated that fluorite minerals play a vital role in the prevalence of fluorosis, while under-saturation revealed that – besides fluorite minerals – other F− minerals that are also present in the region further increase the F− concentrations in the groundwater. Finally, a health risk assessment via Dean's classification method identified that the groundwater with relatively higher F− concentrations is unfit for drinking purposes.
Display omitted
•Groundwater of flood plain area of river Swat, Pakistan was analysed for F−.•Groundwater samples (62.2%) exceeded the WHO safe limit of F− (1.5mg/L).•Fluoride enrichment was due to weathering of rocks and ion exchange processes.•Minerals phases suggested both saturated (55%) and unsaturated (38%) groundwater.•Health risk via (CFI) identified that groundwater is unfit for drinking purposes.
The relationship between iron manganese plaque (IP) and cadmium (Cd) accumulation by rice in the microenvironment of rice rhizosphere at varying field scales needs to be further explored. In this ...study, we selected different rice varieties and implemented tailored amendments to ensure the safe production of rice grains in heavily Cd-contaminated farmland situated around an E-waste dismantling site. Through regional surveys, we elucidated the role of IP in facilitating safe rice production. The selection of low-Cd accumulating rice varieties and application of appropriate amendments with sufficient dosages allowed for the effective reduction of Cd transport from soil to rice, resulting in a safe concentration of Cd in rice grains. Analysis using a random forest algorithm indicated that iron (Fe) played a more pivotal role than manganese in soil-rice systems in mitigating Cd accumulation in brown rice. The presence of Fe in IP (IP-Fe) at a low loading mass was unfavorable to the Cd-safe production of rice, while at an IP-Fe loading mass of 52 g/kg, the Cd content in brown rice decreased to a safe level. Furthermore, precipitation, coprecipitation, and complexation of surface functional groups contributed to Cd fixation on IP, as indicated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, electron probe microanalysis, and Fourier-transform infrared spectroscopy with attenuated total reflection. Our results highlighted the key role of IP in the production of Cd-safe rice at different field scales.
Soil plays an important role in controlling the biogeochemical cycling of nutrients and contaminants in the environment. Reliable analytical techniques are critical to better understand their ...transformation in soils. Diffusive Gradients in Thin-films technique (DGT) is one of such techniques, which has become increasingly popular in soil research since 1998. Undeniably, DGT attracts increasing attentions from multidisciplinary researchers worldwide. This is mainly due to its inherent merits, including ease of use, in situ measurement, and biomimetic applications. Further, four important aspects of DGT applications in soil research were summarized. They include: 1) chemical speciation, 2) bioavailability measurement, 3) desorption kinetic modeling, and 4) interfacial process mapping of nutrients and contaminants, with main focus on the progresses achieved during the past five years. In short, DGT is effective in studying the biochemical behaviors of nutrients (e.g., phosphate and nitrate), trace elements (e.g., Cd, Ni, Zn, Cu, Pb, and As), and polar organic compounds (e.g., antibiotics, pesticides, and bisphenols) in soils. Toward the end, we proposed several aspects of applying DGT as a versatile tool in soil research.
Selenium (Se) is a necessary micronutrient for humans, and its supplementation from crop grains is important to address the ubiquitous Se deficiency in people worldwide. Se uptake by crops largely ...depend on soil bioavailable Se rather than soil total Se content, which provides possibilities to explore the Se-rich crops in Se-poor area. Here, the possibility of cultivating Se-rich maize grains in Se-poor farmland was tested based on intensive field sampling and mathematical modelling. Sampling was conducted at county scale, and a total of 7779 topsoil samples and 109 maize samples with paired rhizosphere soils samples were collected. Results showed that although the soil Se content in the study county from southwestern China was at a low level (0.01–2.75 mg kg−1), 54.1% of the maize grain samples satisfied the standard for Se-rich products (0.02–0.30 mg kg−1). Soil organic matter, iron oxide, and phosphorus levels were correlated negatively with Se bioconcentration factor (BCF) of maize grain. Compared with the multivariate linear regression model, the artificial neural network (ANN) model was more accurate and reliable in predicting maize Se BCF. Prediction using the ANN model showed that 22.7% of the county's farmland was suitable for cultivating naturally Se-rich maize, which increased 21.3% growing areas than that from cultivation based on simply soil total Se. This study provided a new methodological framework for natural Se-rich maize production and verified the probability of cultivating naturally Se-rich maize in Se-poor farmland.
Display omitted
•High percentage of Se-rich maize existed in Se-poor area.•ANN model had excellent performance in maize Se prediction.•A new methodological framework for natural Se-rich maize production.
Nonferrous metal tailings have long posed a significant threat to the surrounding environment and population. Previous studies have primarily focused on heavy metal pollution in the vicinity of ...sulfide tailings, while little attention was given to metal mobility and bioavailability within skarn-type tailings profile during weathering. Therefore, this study aimed to investigate the fractionation, bioaccessibility, and ecological risk associated with metallic elements (MEs, including Pb, Cd, Cr, Zn, and Cu) in two representative weathering copper-tailings profiles of Tongling mine (China). This was achieved through the use of mineralogical analyses, BCR extractions (F1: exchangeable, F2: reducible, F3: oxidizable, F4: residual fraction), in-vitro gastrointestinal simulation test (PBET) and risk assessment models. The mineral compositions of two weathering profiles were similar, with quartz and calcite being the dominant minerals, along with minor amounts of siderite, hematite and spangolite. The mean concentration in the tailings profile was approximately 0.31 (Cr), 1.8 (Pb), 12 (Zn), 33 (Cd) or 34 (Cu) times of the local background values (LBVs). The mean content of the bottom weakly-weathering layer in profile was about 0.36 (Cr), 0.91 (Pb), 1.91 (Cd), 2.73 (Zn) or 2.68 (Cu) times of the surface oxide layer, indicating a strong weathering-leaching effect. The average proportion of BCR-F1 fraction for Cd (30.94 %) was the highest among the five MEs, possibly due to its association with calcite. The PBET-extracted fractions for Cd, Zn and Cu were significantly positively correlated with the F1, F2 and F3 fractions of BCR, suggesting that these elements have higher bioavailability/bioaccessibility. The assessment results indicated that Cd posed a higher health risk, while the risk of Cu, Zn, and Pb is relatively low and Cr is safe. In conclusion, this study provides valuable insights into the environmental geochemical behavior and potential risks of MEs in skarn-type non-ferrous metal tailings ponds.
Display omitted
•Cd, Zn, and Cu in skarn-type copper tailings were present at high levels.•The high exchangeable fraction of Cd may be associated with calcite minerals.•The bioaccessibility of Cu and Cd in tailings was higher than Cr, Zn and Pb.•Cadmium has a high ecological risk in the process of tailings weathering.
