Ecological risks of heavy metals as influenced by water-level fluctuations in a polluted plateau wetland, southwest China

Silicon's Influence on Polyphenol and Flavonoid Profiles in Pea (Pisum sativum L.) under Cadmium Exposure in Hydroponics: A Study of Metabolomics, Extraction Efficacy, and Antimicrobial Properties of Extracts

The current study aimed to investigate the impact of silicon (Si) supplementation in the form of Na2SiO3 on the metabolome of peas under normal conditions and following exposure to cadmium (Cd) stress. Si is known for its ability to enhance stress tolerance in various plant species, including the mitigation of heavy metal toxicity. Cd, a significant contaminant, poses risks to both human health and the environment. The study focused on analyzing the levels of bioactive compounds in different plant parts, including the shoot, root, and pod, to understand the influence of Si supplementation on their biosynthesis. Metabolomic analysis of pea samples was conducted using a targeted HPLC/MS approach, enabling the identification of 15 metabolites comprising 9 flavonoids and 6 phenolic acids. Among the detected compounds, flavonoids, such as flavon and quercetin, along with phenolic acids, including chlorogenic acid and salicylic acid, were found in significant quantities. The study compared Si supplementation at concentrations of 1 and 2 mM, as well as Cd stress conditions, to evaluate their effects on the metabolomic profile. Additionally, the study explored the extraction efficiency of three different methods: accelerated solvent extraction (ASE), supercritical fluid extraction (SFE), and maceration (MAC). The results revealed that SFE was the most efficient method for extracting polyphenolic compounds from the pea samples. Moreover, the study investigated the stability of polyphenolic compounds under different pH conditions, ranging from 4.0 to 6.0, providing insights into the influence of the pH on the extraction and stability of bioactive compounds.

Water level-driven agricultural nonpoint source pollution dominated the ammonia variation in China's second largest reservoir

Rainfall-runoff and water flooding are the driving mechanisms of agricultural nonpoint source pollution (ANPSP), but existing research has hardly focused on water level-driven ANPSP. Danjiangkou Reservoir was the second largest reservoir in China, and its water quality was dominated by ANPSP. This study explored the effect of water level on water quality of Danjiangkou Reservoir and aimed to provide basis for water quality management of large reservoirs. The effect of water level-driven ANPSP on the concentration of reservoir ammonia was studied employing the methods of factor decomposition and multiple regression on a extensive time series data of reservoir ammonia, water level, rainfall, fertilizer usage, and inflow river ammonia. The long-term trend revealed the reservoir ammonia peaked in 2011 and the inflow river ammonia peaked in 2012 (Han River) and 2013 (Dan River), which indicated the success of point source control in the past 15 years and the dominant role of ANPSP in the reservoir ammonia in recent years. With the long-term trend series, the multiple regression results showed that 56% of the variation of the reservoir ammonia concentration was due to the water level (standardized regression coefficient 0.422), fertilizer usage (standardized regression coefficient 0.522), and inflow river ammonia (standardized regression coefficient 0.219). However, the rainfall was insignificant. The predominance of water level and fertilizer usage in explanation of the reservoir ammonia variation indicated that water level-driven ANPSP was the primary factor influencing the reservoir ammonia. The effect of water level was primarily reflected in the long-term variation of ammonia concentration rather than the seasonal variation within the year. This study showed that when compared with rainfall-driven ANPSP, water level-driven ANPSP had a greater impact on the reservoir ammonia. Water quality protection should center on the management of the water level-fluctuation zone.

Influence of heavy metals on Saunders's Gull (Saundersilarus saundersi) reproduction in the Yellow River Estuary: risk assessment and bioaccumulation

The heavy metal migration in the food chain exerted significant influence on the survival and reproduction of wetland birds and then disturbed and threatened the balance and health of the estuary ecosystem. In this study, the concentration of heavy metals (Cu, Cr, Fe, Mn, Cd, Ni, and Pb) in surface sediment of the Yellow River Estuary (YRE), the food sources of Saunders's Gull (Saundersilarus saundersi) nestlings, and the egg structure of birds were analyzed to determine the bioaccumulation and reproductive influence on wetland bird. The results indicated higher mean concentrations of sediment heavy metals than their corresponding background values in 2019, with the exception of Fe. Notably, the metal Cd exceeded geochemical background value by 1561.5% in 2018 and 1353.9% in 2019, resulting in severe contamination associated with Cd in the YRE (with geo-accumulation indexes of 3.44 and 3.23). Biomagnification factor (BMF) of heavy metals demonstrated that the concentrations of Cr, Ni, and Cu decreased with the trophic level rising while Cd, Mn, Pb, and Fe denoted bio-amplification in the food chain. The residual indexes showed that the food resources of Saunders's Gull were polluted by Cr, Pb, and Cu. Additionally, a higher enrichment of heavy metals was observed in the eggshell membrane. Metal concentrations had significant influences on the reproduction of Saunders's Gull, except for Cd, among which Ni, Pb, Cu, and Fe may have contributed to the reproductive success of birds, whereas the hatching failure of birds may be caused by Cr and Mn. It is of great importance to monitor the contamination of the wetland ecosystem and provide effective management and protection of the wildlife in the YRE.

Assessment of some trace elements accumulation in Karst lake sediment and Procambarus clarkii, in Guizhou province, China

Lake wetland quality has decreased with the elevated concentrations of some trace elements. The consumption of crayfish in the trace elements concentrated lake wetland can be a hazard for the waterbirds and human health. Thus, the bioaccumulations of Cd, Ni, Pb and Zn in sediments and abdominal muscles of Procambarus clarkii in Caohai lake wetland, China were quantified. Sediment-bound Cd, Ni, Pb and Zn were remarkably elevated compared to the parent rock, while 64.71-94.12% of adverse effect index in sediment-bound Cd, Ni, Pb and Zn were > 1. Abdominal muscle-bound Cd, Pb and Zn in several samples were all above the maximum permissible limits. Pb, Zn and Ni in abdominal muscles were significantly linked with those in sediments (R² =0.60-0.89, p < 0.01) and lake sediment might be the important feed sources of P. clarkii. Target hazard quotients of Cd, Ni, Pb and Zn at the 95th percentile was all below the benchmark, normal consumption of the abdominal muscle of P. clarkii posed low or no probabilistic health risk to the Grus nigricollis and local inhabitants.

Transformation and fate of thallium and accompanying metal(loid)s in paddy soils and rice: A case study from a large-scale industrial area in China

Thallium (Tl) is an extremely toxic metal, while its occurrence and fate in paddy soil environment remain understudied. Herein, the enrichment and migration mechanisms and potential health risks of Tl and metal(loid)s were evaluated in paddy soils surrounding an industrial park utilizing Tl-bearing minerals. The results showed that Tl contamination was evident (0.63-3.16 mg/kg) in the paddy soils and Tl was generally enriched in root of rice (Oryza sativa L.) with a mean content of 1.27 mg/kg. A remarkably high level of Tl(III) (30-50%) was observed in the paddy soils. Further analyses by STEM-EDS and XPS indicated that Tl(I) in the paddy soils was jointly controlled by adsorption, oxidation, and precipitation of Fe/Mn(hydr)oxide (e.g. hematite and birnessite), which might act as important stabilization mechanisms for inhibiting potential Tl uptake by rice grains. The health quotient (HQ) values indicated a potentially high Tl risk for inhabitants via consumption of the rice grains. Therefore, it is critical to establish effective measures for controlling the discharge of Tl-containing waste and wastewater from different industrial activities to ensure food safety in the rice paddy soils.

Assessment of toxicity and potential health risk from persistent pesticides and heavy metals along the Delhi stretch of river Yamuna

The present study aims at the assessment of environmental quality of the most polluted stretch of river Yamuna along the megacity of Delhi. The study was conducted in order to examine toxicity and health hazards associated with persistent pollutants present in the fluvial ecosystem. Eighty four sediment and 56 vegetable samples from same locations were collected from the Delhi segment of river Yamuna flood plain in order to examine 20 organochlorine pesticides (OCPs) and 9 heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Both the organic and inorganic groups of persistent toxic substances were monitored and analysed for the extent of eco-toxicological as well as dietary health risks posed to the local population. Eco-toxicological assessment was done based on sediment quality guidelines, enrichment factor, geo-accumulation index, degree of contamination and Pollution Load Index. The dietary-risk was assessed with the help of translocation factors (TF) of these pollutants in vegetables. Carcinogenic and non-carcinogenic health risks from consumption of vegetables were also investigated. The level of concern for heavy metals was greater than that of OCPs as per the sediment quality guidelines. DDT, Cd, Pb and Zn had maximum concentrations corresponding to level 3 of concern, while Cr and Ni reached up to the highest i.e., 4th level of concern. Sediment samples were found to be enriched and contaminated significantly with Cd and moderately with Pb, as represented respectively by enrichment factors and contamination factors (CF). CF for metals lied in order Zn > Cd > CrNi > PbCu. Pollution load index was highest at the location lying on the exit point of Yamuna in Delhi. TF values greater than 1 were observed in majority of samples analysed for Ni, Cr, Cu and Zn. Spinach topped among vegetables in terms of metal contamination. Cd, Ni and Pb accumulated more in the roots, as against Mn, Zn, Cu and Cr which had higher accumulation in the shoots. Translocation factors were substantially high in vegetables for most of the OCPs, clearly indicating bioaccumulation and potential health risk to the consumers. Health risk to humans was assessed for non-carcinogenic and carcinogenic potentials from ingestion of vegetables. Hazard Quotient (HQ) > 1 due to radish (roots and leaves) and cauliflower consumption in children indicated non-carcinogenic risk. Hazard Index (HI) beyond 1 for all the vegetables (except onion leaves) confirmed substantial cumulative risk. Lifetime cancer risk (LCR) revealed moderate (spinach, radish, beet root and cauliflower) to low (all the others) levels of carcinogenic risk to humans. Cancer risks from γ-HCH, β- HCH, Hept, Hept Ep, Ald, p,p'-DDT, and Cr exposure through the food chain could be well established.

Fulvic acid: A key factor governing mercury bioavailability in a polluted plateau wetland

Fulvic acids (FAs) are known to regulate the fate of mercury (Hg) in sediments, but the key effects of their properties are still unclear. In this study, field investigations and simulation experiments were conducted in a heavy metal-polluted wetland to identify FA characteristics and their association with the production and bioaccumulation of methylmercury (MeHg). Compared to permanently inundated areas (PIA), seasonally inundated areas (SIAs) had lower total Hg levels in sediments, whereas higher MeHg levels in sediments (0.20 ± 0.09 ng g^-1 vs. 0.55 ± 0.31 ng g^-1) and benthos (0.25 ± 0.22 ng g^-1 vs. 1.62 ± 1.78 ng g^-1). Meanwhile, the THg and MeHg concentrations in the same macrophyte species between PIA and SIA also followed a similar rule with benthos. FA-bound Hg in the sediment was significantly correlated with MeHg in the sediment (p < 0.01), as well as THg and MeHg in benthos (p < 0.05), indicating that FAs have the capacity to promote MeHg production and bioaccumulation. Moreover, the FAs in the sediments of the SIA had lower fractions and alkyl C/O-alkyl C ratios, but higher molecular weights and THg/MeHg concentrations than those in the PIA, indicating that FAs in SIA have increased bioavailability and enhanced competition for Hg, favoring significantly elevated FA-bound Hg levels. Biological exposure testing further demonstrated that FAs extracted from SIA had a greater ability to increase the production and bioaccumulation of MeHg than those extracted from PIA. Overall, these results highlight that the molecular composition and sources of FAs, excluding their concentrations, are one of important factors responsible for the obvious spatial heterogeneity of MeHg in sediments and aquatic organisms in the wetland.

Genome-Wide Identification, Structure Characterization, Expression Pattern Profiling, and Substrate Specificity of the Metal Tolerance Protein Family in Canavalia rosea (Sw.) DC

Plant metal tolerance proteins (MTPs) play key roles in heavy metal absorption and homeostasis in plants. By using genome-wide and phylogenetic approaches, the origin and diversification of MTPs from Canavalia rosea (Sw.) DC. was explored. Canavalia rosea (bay bean) is an extremophile halophyte with strong adaptability to seawater and drought and thereby shows specific metal tolerance with a potential phytoremediation ability. However, MTP genes in leguminous plants remain poorly understood. In our study, a total of 12 MTP genes were identified in C. rosea. Multiple sequence alignments showed that all CrMTP proteins possessed the conserved transmembrane domains (TM1 to TM6) and could be classified into three subfamilies: Zn-CDFs (five members), Fe/Zn-CDFs (five members), and Mn-CDFs (two members). Promoter cis-acting element analyses revealed that a distinct number and composition of heavy metal regulated elements and other stress-responsive elements existed in different promoter regions of CrMTPs. Analysis of transcriptome data revealed organ-specific expression of CrMTP genes and the involvement of this family in heavy metal stress responses and adaptation of C. rosea to extreme coral reef environments. Furthermore, the metal-specific activity of several functionally unknown CrMTPs was investigated in yeast. These results will contribute to uncovering the potential functions and molecular mechanisms of heavy metal absorption, translocation, and accumulation in C. rosea plants.

Cadmium isotopic fractionation in lead-zinc smelting process and signatures in fluvial sediments

Cadmium (Cd) is a toxic heavy metal pollutant. Various industrial activities, especially metal smelting, are the main sources of Cd pollution. Cd isotopes have exhibited the ability to be excellent source tracers and can be used to assess the pollution contributions from different sources. Herein, in a typical lead-zinc smelter, Shaoguan, China, significant Cd isotopic fractionation was found during the high temperature smelting process and followed a Rayleigh distillation model. The heavier Cd isotopes were concentrated in the slag, while the lighter Cd isotopes were concentrated in the dust. In the downstream sediment profile of the smelter, sediments have extremely high Cd concentrations that far exceed the Chinese background sediment, indicating severe pollution levels. The ε^114/110Cd of the sediment core, ranged from - 0.62 ± 0.5-1.73 ± 0.5, are found between slag (ε^114/110Cd=10.42) and dust (ε^114/110Cd=-5.68). The binary mixture model suggests that 88-93% of the Cd in sediment profile was derived from the slag, and 7-12% from the deposition of dust. The findings demonstrate the great potential to apply Cd isotopes as a new geochemical tool to distinguish anthropogenic sources and quantify the contribution from various sources in the environment.

Soil redox dynamics under dynamic hydrologic regimes - A review

Electron transfer (redox) reactions, mediated by soil microbiota, modulate elemental cycling and, in part, establish the redox poise of soil systems. Understanding soil redox processes significantly improves our ability to characterize coupled biogeochemical cycling in soils and aids in soil health management. Redox-sensitive species exhibit different reactivity, mobility, and toxicity subjected to their redox state. Thus, it is crucial to quantify the redox potential (E_h) in soils and to characterize the dominant redox couples therein. Several, often coupled, external drivers, can influence E_h. Among these factors, soil hydrology dominates. It controls soil physical properties that in turn further regulates E_h. Soil spatial heterogeneity and temporally dynamic hydrologic regimes yield complex distributions of E_h. Soil redox processes have been studied under various environmental conditions, including relatively static and dynamic hydrologic regimes. Our focus here is on dynamic, variably water-saturated environments. Herein, we review previous studies on soil redox dynamics, with a specific focus on dynamic hydrologic regimes, provide recommendations on knowledge gaps, and targeted future research needs and directions. We review (1) the role of soil redox conditions on the soil chemical-species cycling of organic carbon, nitrogen, phosphorus, redox-active metals, and organic contaminants; (2) interactions between microbial activity and redox state in the near-surface and deep subsurface soil, and biomolecular methods to reveal the role of microbes in the redox processes; (3) the effects of dynamic hydrologic regimes on chemical-species cycling and microbial dynamics; (4) the experimental setups for mimicking different hydrologic regimes at both laboratory and field scales. Finally, we identify the current knowledge gaps related to the study of soil redox dynamics under different hydrologic regimes: (1) fluctuating conditions in the deep subsurface; (2) the use of biomolecular tools to understand soil biogeochemical processes beyond nitrogen; (3) limited current field measurements and potential alternative experimental setups.

Ecological adaptability and population growth tolerance characteristics of Carex cinerascens in response to water level changes in Poyang Lake, China

Water level conditions are the key factors that affect the growth and distribution of wetland plants. Using Carex cinerascens (C. cinerascens) as the study species, we employ indoor simulations and field surveys. Our results show that C. cinerascens can adapt to rhythmic changes in the water level through different adaptation strategies. Compared to that of the control group, plant growth was better with a 0-0.4 cm/d water level rate, and plant growth was in the 42-56 cm range to that a 1.0-1.4 cm/d water level rate. Furthermore, it was observed that 0-0.4 cm/d was the most suitable growth rate, with 0.6-1.0 cm/d and 0-32 cm being the ideal plant tolerance ranges, and increasing to 1.0-1.4 cm/d and 32-56 cm exceeds the plant tolerance threshold. In the middle and late period of the experiment (25-45 d), the ecological characteristics of the plants changed significantly. For example, the root-to-shoot ratio of the plant in the stable water level reached 26.1. In our field observations, plant biomass can be influenced by a variety of environmental factors. The frequency of the species was the largest at an elevation of 15 m, and the growth status of the dominant and companion species of C. cinerascens was weakened with an increase in soil moisture content. The suitable water content for C. cinerascens growth was 27.6-57.3%, the distribution elevation was 12.54-16.59 m, and the optimum elevation was 13.56-15.54 m. The study is expected to provide a reference for wetland ecology research and wetland protection and restoration, a theoretical reference for the coordination of water resource development and utilization of Poyang Lake and ecological protection of important lakes and wetlands, and an important scientific basis for wetland hydrologic regulation, ecological restoration and biodiversity conservation.

Mercury Bioaccumulation in Freshwater Snails as Influenced by Soil Composition

Soil properties largely control the fate of mercury (Hg), including the synthesis of neurovirulent methylmercury (MeHg). Here, the freshwater snail (Cipangopaludina cahayensis), a snail species commonly bred in flooded farmland, was used in a test of biotoxicity exposure to explore the effects of soil components on Hg bioavailability. The results show that snails incubated on the surface of slightly Hg-polluted flooded soil (2.0 mg/kg) have MeHg concentrations of 7.9 ± 1.5 mg/kg, which greatly exceed the limit of contaminants in food in China (0.5 mg/kg). The addition of ferrous disulfide can significantly increase the MeHg concentrations in soils while reducing the concentrations of total Hg (THg) and MeHg levels in snails by 59.1% and 64.3%, respectively. Peat-derived fulvic acid has the capacity to reduce the MeHg concentrations in soils and snails by 23.8% and 33.2%, respectively, whereas it increases the dissolved Hg levels in overlying water by 104.3%. Moreover, Fe-Mn oxides and humic acid can consistently reduce THg and MeHg concentrations in snails. Overall, freshwater snails bred in Hg-polluted areas may suffer from a high risk of Hg exposure, and importantly, some soil components such as ferrous disulfide and humic acid have strong inhibitory effects on Hg bioaccumulation in snails.

Emerging risks of toxic metal(loid)s in soil-vegetables influenced by steel-making activities and isotopic source apportionment

Industrial activities tend to deteriorate adjacent agricultural lands due to accumulation of potentially toxic elements in soils and crops. However, better understanding of their distinctive source partitions and transfer process remains insufficient in steel-making area. The paper focuses on the pollution levels, health risks, and provenance identification of Tl, As, Pb, Cu, Ni, Co, Sb, Cd, Zn, Be, Cr, Fe, Mn, Mo, Sn, and V in common vegetables from different farmlands near a steel-making plant. The results showed that the Tl, As, Pb, Cd, Cr, Cu and Mn were of high-level contamination in soils and generally above the maximum permissible level (MPL). Calculation using hazard quotients (HQ) exhibited that consumption of the studied vegetables may entail significant health risks to residents, especially for children, resulting from the elevated contents of Tl, As and associated toxic elements. Calculation by binary mixing model using Pb isotopic compositions suggested that steel-making activities contributed to 35-80% of the contamination of Pb and As in vegetables. It is necessary to adopt appropriate remediation measures to mitigate the farmland contamination and ensure the food safety of the agricultural products.