Enrichment Of Heavy Metals Research Articles

Effect of Land Use/Land Cover Change on the Concentration of Se and Heavy Metals in Soils from a "Return Cropland to Forest" Area, Southwest China

Human activities (land use) and environmental change (land cover change) affect the concentration of Se and heavy metals in soils. The implementation of the "Return Cropland to Forest (RCF)" ecological project has changed the land use and cover, which has provided an ideal experimental area for studying the effects of land use and cover change on selenium (Se) and heavy metals in the soil. In this study, 91 top soil samples from different land use and land cover types, including dry land, paddy land, natural forest land, and secondary forest land, were collected, and the contents of Se, heavy metals, and soil organic matter (SOM) and pH were analyzed. The results showed that:① the average values of ω(Se) (0.42×10-6), ω(As) (13.0×10-6), and ω(Sb) (1.03×10-6) were higher than the soil background values of western Chongqing. ② The concentrations of Se, Cd, Cr, Ni, Pb, and Zn in soils from secondary forest land were significantly higher than those from dry land soils, suggesting that the Se and heavy metals might have significantly increased in the surface soil after the implementation of the RCF ecological project. ③ The SOM was the key controlling factor for the enrichment and distribution of Se and heavy metals in the top soils. Our results indicated that the land use and land cover change would deeply impact the concentrations of Se and heavy metals in the top soils via influencing the soil properties, especially the SOM.

Heavy Metal Contamination and Ecological Risk Assessments in Urban Mangrove Sediments in Zhanjiang Bay, South China.

With the acceleration of industrialization and urbanization, increasing attention has been paid to the problem of heavy metal pollution in mangroves and its ecological restoration. Urban mangroves can be used to measure the impact of human activities on the urban ecological environment because mangroves are sensitive to human activities. However, studies on the evaluation of heavy metal elements in urban mangroves are still limited. Consequently, this study selected the urban mangroves in a central commercial area of Zhanjiang Bay as a case study to investigate the content and distribution of the heavy metals (Co, V, Cu, Pb, Ni, As, Cd, and Hg) in mangrove surface sediments. Risk levels and possible sources of heavy metals were evaluated based on multivariate statistical analysis methods and pollution indices. The results showed that the average concentrations of heavy metals for Co, V, Cu, Pb, Ni, As, Cd, and Hg were 2.91, 29.96, 18.24, 20.07, 7.86, 5.0, 0.20, and 0.09 mg/kg, respectively. Cd, Cu, and Hg were most prominent within the Zhanjiang Bay mangrove sediments, whereas other metals showed a low contamination factor of therm. Cd displayed a high potential ecological risk followed by Hg and Cu. The sampling site, the sewage outlet sampling site, exhibited the highest pollution degree followed by the surrounding area of the sewage outlet sampling site. Those polluted heavy metals could arise from anthropogenic sources, including domestic sewage and automobile exhaust emission. Correlation analysis between the heavy metals and physicochemical properties indicated that fine particles and organic matter play a key role in controlling heavy metal enrichment.

The addition of exogenous low-molecular-weight organic acids improved phytoremediation by Bidens pilosa L. in Cd-contaminated soil

Enhancing the uptake and enrichment of heavy metals in plants is one of the important means to strengthen phytoremediation. In the present study, citric acid (CA), tartaric acid (TA), and malic acid (MA) were applied to enhance phytoremediation by Bidens pilosa L. in Cd-contaminated soil. The results showed that by the addition of appropriate concentrations of CA, TA, and MA, the values of the bioconcentration factor increased by 77.98%, 78.33%, and 64.49%, respectively, the translocation factor values increased by 16.45%, 12.61%, and 5.73%, respectively, and the values of the phytoextraction rates increased by 169.21%, 71.28%, and 63.11%, respectively. The minimum fluorescence values of leaves decreased by 31.62%, 0.28%, and 17.95%, while the potential efficiency of the PSII values of leaves increased 117.87%, 2.25%, and 13.18%, respectively, when CA, TA, and MA with suitable concentration were added. Redundancy analysis showed that CA and MA in plants were significantly positively correlated with plant growth, photosynthesis, and other indicators, whereas TA showed a negative correlation with most indicators. Moreover, CA addition could significantly increase the abundances of Azotobacter, Pseudomonas, and other growth-promoting bacteria, and the abundance values of Actinophytocola and Ensifer were improved in TA treatments. Therefore, our results demonstrated that low-molecular-weight organic acids could enhance phytoremediation, and exogenous CA could significantly improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L.

Arsenic and selected heavy metal enrichment and its health risk assessment in groundwater of the Haridwar district, Uttarakhand, India

Arsenic and selected heavy metal enrichment and its health risk assessment in groundwater of the Haridwar district, Uttarakhand, India

Source Identification and Apportionment of Potential Toxic Elements in Soils in an Eastern Industrial City, China.

The extensive pattern of economic growth has an inestimable negative impact on the ecological environment, which causes the soil pollution problem to become increasingly prominent. In order to improve the effectiveness and rationality of prevention and control of heavy metal pollution in regional soil, it is necessary to understand the current situation of pollution, identify pollution sources and clarify future pollution risks. In this paper, an industrially developed city in eastern China was taken as the study region. The positive matrix factorization model (PMF) model and Unmix model was applied to identify and apportion the pollution sources of soil potential toxic elements after evaluating the ecological risk of soil potential toxic elements. The PMF model identified six factors, including single source and composite source. The Unmix model also identified six sources, including sources of nature, industrial discharge and traffic emissions. The comparison between the two models showed that Hg and Ni pollution, as well as Cr enrichment in the study region, were related to the industrial discharge from enterprises and factories. Cd pollution was related to traffic emission sources. Cu and Zn pollution were related to the multiple sources mixed with soil parent material, traffic emissions and industrial discharge from electronic enterprises. Pb pollution was related to natural sources (e.g., soil pH) but also to industrial sources (e.g., industrial wastes discharge). Enrichment was related to soil parent material and agricultural inputs. Our study also implies that soil heavy metal pollution or enrichment in the study region was mainly from anthropogenic sources and supplemented by natural sources.

Rare earth elements and other critical elements in the magnetic fraction of fly ash from several Polish power plants

Fly ash is a promising alternative source of many critical raw materials, including rare earth elements. According to the EU report, the demand for these metals is set to grow due to the economic growth of the developing countries, along with the development of new innovative technologies. A geochemical analysis showed that the overall content of critical and excessive elements in fly ash from several Polish power plants was higher than in the magnetic fraction. However, the outlook coefficient values for magnetic concentrates were higher than for ashes. Ashes and the magnetic fraction from brown coals seem to be the most promising source of REY recovery. The separation of fine-size grades from the analyzed ashes does not have a significant impact on REY concentration in the obtained products. A microanalysis showed that iron spinels were enriched in Co, Cu, Ni, Mn, Mo, and Zn. The concentration of these metals in magnetic concentrates insignificantly exceeded the world average value of fly ash. The sample with the highest heavy metal enrichment factor also had the highest Fe enrichment factor. The phase composition of the magnetic fraction was dominated by: magnetite, hematite, magnesioferrite, and other iron spinels with Mn and Al substitutions. The chemical composition of ferrospheres was determined using energy dispersive spectroscopy (EDS) together with the SEM technique, and was then linked to their morphology. It was concluded that the impact on the enrichment efficiency and thus the composition of the magnetic fraction had: the diversity of morphological structures of iron spinels, the presence of AlSi glass interlayers, the presence of substitutions in the magnetite crystal structure as well as the ash particle size distribution.

Enrichment of heavy metals from spent printed circuit boards by microwave pyrolysis

This study reports the enrichment behaviors of heavy metals, including copper, tin, lead and zinc, in the process of microwave pyrolysis of spent printed circuit boards (SPCBs). The SPCB had good microwave absorptivity. Under the optimal conditions of microwave power of 700 W, pyrolysis temperature of 400 °C, dwell time of 5 min, N2 gas flow rate of 1.2 L/min, and load mass of 5 g, the yield of pyrolyzed SPCB was 79.16%. The contents of copper, tin, lead, and zinc in the pyrolyzed SPCB were increased to 28.52 wt%, 7.15 wt%, 1.31 wt%, and 1.13 wt%, respectively, with the corresponding retention percentages of 99.98%, 85.89%, 92.59% and 82.06%. The loss of metals was attributed to volatilization of the elements, which was affected by metal discharge due to excitation of electrons in the metals under microwave irradiation. Little copper loss was found because of the difficult reaction between copper and hydrogen bromide and the very high temperature required by the volatilization of copper. Tin, lead and zinc were mainly volatilized in the form of their metal bromides, including SnBr4, ZnBr2, and PbBr2. By controlling the pyrolysis conditions and metal discharge induced in the microwave field, the metals could be effectively enriched for subsequent treatment with high efficiency.

Quantification of heavy metals and health risk assessment in Sichuan pickle.

Sichuan pickle is one of popular traditional fermented foods in China. However, the contamination of heavy metals in Sichuan pickle, particularly home-made Sichuan pickle and aged pickle brine, is little known. Therefore, the content of trace (Cr, Cu, and Zn) and toxic elements (As, Pb, and Cd) in Sichuan industrial pickle (SIP), Sichuan home-made pickle (SHP), and aged pickle brine collected from local markets and families in Sichuan province, respectively, was detected by inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) and the health risk was assessed by target hazard quotients including target hazard quotient (THQ) and total target hazard quotient (TTHQ). Consequently, the mean concentrations of Cr, Cu, Zn, As, Pb, and Cd were 0.122, 0.540, 2.516, 0.023, 0.015, and 0.106mg/kg in SIP and 0.071, 0.364, 2.698, 0.014, 0.015, and 0.289mg/kg in SHP, respectively, lower than the maximum allowable concentrations set by Chinese regulations, except for Cr and Cd in few samples. Principal component analysis of the heavy metal content could obviously distinguish between SIP and SHP. The content of As, Pb, and Cd in leaf pickles was significantly higher than that in pickles fermented with other types of vegetables. A significant enrichment of heavy metals in aged pickle brine over 10 years was observed, but pickle jars had no significant effect on heavy metal content in aged pickle brine. The intake of heavy metals through daily consumption of SIP and SHP was at a safe level, whereas the TTHQ of leaf pickle was 1.006, indicating a potential health risk. In conclusion, this study provided fundamental data for food safety assurance of Sichuan pickle. PRACTICAL APPLICATION: Sichuan pickle is one of popular traditional fermented foods in China. In the present study, we investigated the contamination of heavy metals in Sichuan pickles by detecting the content of Cr, Cu, Zn, As, Cd, and Pb in Sichuan industrial pickle, Sichuan home-made pickle, and aged pickle brine, and estimated the health risk to local residents. This study can provide a reference for the safety risk of Sichuan industrial and home-made pickle in terms of heavy metal contamination, and enhance the food safety in the processing, production, and consumption of Sichuan pickle in local families and pickle industry.

Evaluation of Environmental Geochemistry of Trace Metal Pollutant in Sediments of Outlet Jeneberang River, Indonesia

The Jeneberang River flows between settlements, rice fields, traditional ports which are located in the southernmost part of Makassar. Regional development and increasing population are anthropogenic as a source of heavy metal input to rivers, and require a sustainable geochemical study of the environment. Study objectives, concentration and spatial distribution, use of sediment samples for grain size and Coupled Plasma-Osiloscope Emission Spectroscopy (ICP–OES) method for trace elements. The average yield of the seven river sediment samples was (Cr)149 mg kg-¹ (Mn)1388.14 mg kg-¹, (Cd)0.74 mg kg-¹, (Cu)54.71 mg kg-¹, (Zn)130.28 mg kg- , (Pb)3675 mg kg-1.
 The conclusion on the grain size of the sand, it is known that the order is dominated by concentration: Mn>Zn>Cr>Pb=Cu then changes to the grain size of silt clay: Mn>Cr>Zn>Cu>Pb, showing indications of migration, exchange phase and heavy metal enrichment. The order of heavy metal contamination uses the Igeo average value: Cd>Cr=Pb>Mn>Cu>Zn is class 1, namely 0 < Igeo < 1 = not polluted to moderately polluted, and the order of heavy metal enrichment uses EF: Cu (0.64), Mn (0.58), Pb (0.56), Zn (0.73), Cd (0.41), Cr (0.55), generally EF < 2 is deficiency to minimal enrichment. It seems that the heavy metals in the minimum contamination and enrichment criteria which are strengthened by statistical analysis of correlation factors and multiple scatter are Pb and Zn.

Heavy metal content and potential ecological risk assessment of sediments from Khnifiss Lagoon National Park (Morocco)

Coastal lagoons are important but sensitive environments, being transitional zones between land and sea. The Khnifiss lagoon is the most important desert wetland in Morocco, but little data have been produced concerning heavy metal geochemistry and enrichments in the sediments. Therefore, 26 surface sediments (15 intertidal and 11 subtidal) and 2 sediment cores were collected in 2016 and analyzed for a selection of heavy metals. The data were processed to assess the degree of contamination and the corresponding potential ecological risk, using several accumulation/enrichment indices, and the singular and multi-metal risk indices. Mean concentrations in the bottom layers of the two cores, dating from a pre-industrial age according to geochronological analysis, were used as the local geochemical background. The resulting values were on the whole lower than those reported for other areas of the northeastern coast of Morocco. Multivariate statistics were also applied to better understand relationships among variables (metals and other geochemical parameters) and to reveal similarities among sample groups. The results showed that, although the lagoon is not yet affected by significant anthropogenic influences, small enrichments can be recognized, especially for Ni and Cd. The cause may be related to the proximity to the main national highway, the vehicles and machinery used in the saltworks located in the area, and the small harbors used principally for fishing. In addition, industrial emissions from the Atlantic coast of Morocco and adjacent countries can be reasonably attributed as additional contributors to the enrichments. In terms of potential ecological risk, Cd shows the greatest impact compared to the other metals investigated.

Convolutional neural network-based applied research on the enrichment of heavy metals in the soil-rice system in China.

The enrichment of heavy metals in the soil-rice system is affected by various factors, which hampers the prediction of heavy metal concentrations. In this research, a prediction model (CNN-HM) of heavy metal concentrations in rice was constructed based on convolutional neural network (CNN) technology and 17 environmental factors. For comparison, other machine learning models, such as multiple linear regression, Bayesian ridge regression, support vector machine, and backpropagation neural networks, were applied. Furthermore, the LH-OAT method was used to evaluate the sensitivity of CNN-HM to each environmental factor. The results showed that the R2 values of CNN-HM for Cd, Pb, Cr, As, and Hg were 0.818, 0.709, 0.688, 0.462, and 0.816, respectively, and both the MAE and RMAE values were acceptable. The sensitivity analysis showed that the concentrations of Cd and Pb, mechanical composition, soil pH, and altitude were the main sensitive features for CNN-HM. Compared with CNN-HM based on all input features, the performance of the quick prediction model that was based on the sensitive features did not degrade significantly, thereby indicating that CNN-HM has stronger stability and robustness. The quick prediction model has extensive application value for timely prediction of the enrichment of heavy metals in emergencies. This study demonstrated the effectiveness and practicability of CNNs in predicting heavy metal enrichment in the soil-rice system and provided a new perspective and solution for heavy metal prediction.

Study on the risk of soil heavy metal pollution in typical developed cities in eastern China

Enrichment of heavy metals in urban soils has become a major regional environmental risk. At present, research on the soil heavy metals in cities lacks risk spatial correlation analyses between different heavy metals, and there is a relative lack of assessments of the ecological and health risks. We selected Wuxi, a typical developed city of eastern China, collected and tested the contents of heavy metals in the urban soils of Wuxi in May 2020. Combined with Pb isotope analysis, ecological and health risk assessment, we found that the high heavy metal concentrations in Wuxi are mainly located in the central and western regions, and that the changes in spatial fluctuation are relatively small. The Pb isotopes in the urban soils of Wuxi are distributed in areas, such as those are related to coal combustion, automobile exhaust and urban garbage, indicating that the heavy metals in the urban soils of Wuxi are affected by human activities such as coal combustion and automobile exhaust. The average value of the potential ecological risk index of soil heavy metal Cd is 80.3 (the threshold: 40), which represents a high-risk state. Whether adults or children, the risk of soil heavy metals via ingestion is much higher than that through skin exposure. High health risk values are present in the central area of Wuxi and decrease in a ring-shaped pattern, which is similar to the population distribution of Wuxi and greatly increases the potential risk from soil heavy metals, which should be given close attention. We should develop and use clean energy to replace petroleum fossil fuels, especially in densely populated areas. This study provides technical support for the prevention and control of urban heavy metal pollution.

Urbanization influences the distribution, enrichment, and ecological health risk of heavy metals in croplands

The contamination of urban soils with heavy elements due to the rapid development of urbanization and urban services has become a major environmental and human health challenge. This study provides insight into the urbanization controls on combined pollution severity and health risk potential of heavy metals in corn-cultivated urban versus non-urban soils. A multifaceted assessment was conducted using enrichment factor (EF), ecological risk (ER), bioconcentration factor (BCF), transmission factor (TF), hazard index (HI), and carcinogenic risk (CR). The results indicate a significant increase in the concentration of all metals in urban farmlands. When compared to the non-urban soils, EF implies a significant increase of all metals in the urban soil, downgrading this index from minimal enrichment (EF < 2) in the control soils to moderate enrichment (2 ≤ EF < 5) in the urban soils. Likewise, the average ER value showed an increase in the urban soils than in the control soils in the order of Fluvisols (66.6%) > Regosols (66.1%) > Cambisols (59.8%) > Calcisols (47%). The BCF and TF values for different elements decreased in the order of Cd (0.41–0.92) > Cu (0.1–0.23) > Zn (0.1–0.18) > Ni (0.01–0.03) > Pb (0.005–0.011) and Zn (0.75–0.94) > Cu (0.72–0.85) > Pb (0.09–0.63) > Cd (0.17–0.22) > Ni (0.01–0.21), respectively, which indicates that certain metals were not mobilized to the extent that they had been accumulated in the plant roots. The total carcinogenic risk was ranged from 5.88E−05 to 1.17E−04 for children and from 1.17E−04 to 2.30E−04 for adults, which implies a greater associated health risk for children.

Geochemical Characteristics and Source Apportionment of Soil Elements in an Urban-rural Integration Area: A Case Study in the Qinglong Area of Tianfu New District

The Qinglong Area of Tianfu New District in China is the connection area of Chengdu city, Sichuan Province, which dominantly supports the primary agricultural products for the metropolis. The soil quality, therefore, has been deteriorating in recent decades due to the intensive planting and industrial pollution. Thus, the evaluation of soil quality and the identification of the pollution sources are significant for sustainable soil planting and regulation. To this end, 395 soil samples were collected, and the parameters of pH, soil organic matter (SOM), total potassium (TK), available potassium (AK), total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), total phosphorus (TP), available phosphorus (AP), Se, B, V, Zn, Mn, Mo, Ni, Co, As, Cd, Cr, Cu, Hg, and Pb were analyzed. The results revealed that TN, Se, Hg, and TP were obviously higher than the background value of the Chengdu Economic Zone, and the Cr, Mn, pH, and TK were depleted. The combination of correlation statistics, geostatistics, and positive matrix factorization (PMF) source analysis revealed that heavy metal enrichments were mainly affected by four sources, namely natural sources (32%)>industrial sources (30%)>agricultural sources (25%)>traffic sources (14%). Likewise, the source apportionments were verified regarding topography, industrial boundary, farmer density, and traffic flow. It was estimated that Mo, Co, Ni, and V were affected by slope; the enrichment of Hg and As was the result of agricultural activities; Cd, Mn, Cr, and Zn were affected by industrial waste diffusion; and Pb, Zn, Cu, Cd, and Hg were related to transportation. To a certain extent, agricultural fertilization and pesticide application have partially controlled soil fertility and pollution (Hg and As).

Identification of the sources and influencing factors of the spatial variation of heavy metals in surface sediments along the northern Jiangsu coast

Determining the sources and factors influencing the spatial variation of heavy metals in the surface sediments of tidal flats is important for controlling and reducing heavy metal pollution. We used principal component analysis and partial least square regression to analyse the distribution characteristics, sources, and factors influencing the spatial variation of nine heavy metals (As, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) in the surface sediments of tidal flats along four sites located on the northern Jiangsu coast. Our results indicate that the northern three sampling areas had a high heavy metal content, whereas the southern sampling area had a low heavy metal content. The heavy metals Mn and Pb are related to both natural and anthropogenic sources, whereas V and Cr are primarily derivatives of human activities, and As, Co, Cu, Ni, and Zn are primarily a result of natural processes. The spatial variation of Mn and Pb was primarily affected by the total inorganic carbon and clay content (positive affect) as well as the sand and silt content (negative affect). The spatial variation of V and Cr was primarily related to silt, clay, and total phosphorus content (positive influence) as well as sand (negative influence). In addition, the spatial variation of As, Co, Cu, Ni, and Zn was primarily influenced by the total organic carbon and clay content (positive effect) as well as sand and pH (negative effect). The grain size of sediments plays an important role in the spatial variation of heavy metals in the surface sediments of tidal flats, with fine-grained clay materials being related to the enrichment of heavy metals. The results of our study are important for the control and reduction of heavy metal pollution in coastal sediments, protecting both the ecological environment and human health.

Magnetic susceptibilities of surface sediments from estuary rivers in volcanic regions.

Estuaries have very complex mechanisms because they are influenced by seawater intrusion, which causes enrichment of contaminants in the maximum turbidity area. Magnetic susceptibility measurements have been used for monitoring a wide variety of environments. However, there have been few studies of the magnetic properties of surface sediments from estuaries in volcanic environments in the tropics. This study investigates the magnetic properties and their correlations with the geochemistry of surface sediments in estuaries in volcanic areas and was conducted in the Krueng Aceh River, Indonesia. Measurements consist of magnetic susceptibility measurements, chemical analysis, and mineralogical analysis. Measurements of magnetic susceptibilities were performed using a Bartington MS2 instrument with an MS2B sensor using frequencies of 460 and 46kHz. X-ray fluorescence (XRF) and energy-dispersive spectroscopy (EDS) were used to identify elements in the sediments. Scanning electron microscopy (SEM) analysis was used to analyze sediment grains. X-ray diffraction (XRD) analysis was used to determine mineral contents. For the first time, χLF/χFD ratios were found to be an obvious parameter for identifying areas of sediment traps and metal enrichment in the estuary turbidity maxima (ETM) zone. The magnetic properties carried by volcanic rock minerals consist of pigeonite and enstatite. These two minerals have not been previously considered as carriers of sediments with magnetic properties when monitoring heavy metal enrichment in urban rivers. These results provide an extension of the use of magnetic susceptibility measurements in environmental studies, particularly in estuary river environments in volcanic areas such as the Krueng Aceh River, Indonesia.

Assessment of Heavy Metals Enrichment and Sources in Different Functional Areas of Sixian City

Assessment of Heavy Metals Enrichment and Sources in Different Functional Areas of Sixian City

Nanocelluloses affixed nanoscale Zero-Valent Iron (nZVI) for nickel removal: Synthesis, characterization and mechanisms

Application of nanoscale Zero-Valent Iron (nZVI) for heavy-metal enrichment and recovery have been hampered by aggregation induced by its high surface energy and intrinsic magnetic interactions. Herein, we present nanocelluloses (NC) affixed nZVI composite (NC-nZVI) with enhanced efficiency for Nickel(Ni) removal. The anchoring of nZVI at the functional sites of biomass derived NC was initiated by one-step liquid-phase reduction method, generating varied morphology and dispersion status of nZVI. Among developed composites, cellulose nanocrystals (CNC) modified nZVI (CNC-nZVI) showed most evenly distributed nZVI with uniform particle size. Characterizations with FTIR, XPS and XRD demonstrated that bindings between NC and nZVI were through hydrogen bonds, electrostatic attractions, coordination-covalent bonds and/or steric hindrance. For Ni2+ removal, 0.2 g/L CNC-nZVI achieved 98.5% removal rate at 100 mg/L initial Ni2+ concentration and pH = 5.0, significantly higher than bare nZVI (P < 0.05). The removal efficiency remained over 80% under wide pH range (3–5) and varied interference ions (NO3-, Cl- and Ca2+), indicating potential practical applicability. The observed "hollow-out" structure from scanning transmission electron microscopy after reactions with Ni2+ and Tafel extrapolation curves inferred that CNC activated diffusion path and accelerated electronic transfer from nZVI. The superior removal performance of NC-nZVI and abundance of raw materials offer promising prospects for environmental remediation and wastewater treatment.

Spatio-temporal distribution of heavy metals in sediments of Biyyam Backwater, Kerala, Southwest India; its environmental implications

Biyyam backwater is a developing eco-tourism hub and prone to increased pollution due to urbanization and agricultural waste disposal. This study investigates the distribution, temporal variation, enrichment and accumulation of heavy metals in the surface sediments from Biyyam backwaters. Samples were collected from four locations during post-monsoon (December 2017), pre-monsoon (March 2018) and monsoon (July 2018) seasons. Sediment texture, organic matter and heavy metals such as Mn, Co, Zn, Ni, Cr, Pb, Sc, Cd, and As were analyzed. The metal concentration in surface sediments decreased in the following order, i.e., Mn > Cr > Zn > Ni > Pb > As > Co > Sc > Cd. Spatio-temporal variability in distribution pattern of heavy metals show higher concentrations in upstream region. Heavy metal concentrations in surface sediments show relatively higher Igeo factors indicating contribution of heavy metals from agricultural and urban waste disposal. These relatively high values indicate that the Biyyam backwater is threatened by metal contamination, specifically by As, Cd, Cr and Ni. Biyyam backwater is an eco-tourism hub and a beautiful aquatic ecosystem, thus our results would help the local environmental managers to develop strategies to conserve the natural state of the kayal via managing the sources of pollution and sediment remediation in the area.

Characteristics of Plant Diversity and Heavy Metal Enrichment and Migration Under Different Ecological Restoration Modes in Abandoned Mining Areas

In order to select plant materials suitable for the ecological restoration of abandoned mining land, ecological restoration experiments were set up in landfills. The effects of different ecological restoration measures on plant diversity and heavy metal enrichment and migration characteristics were studied. The results showed that under different ecological restoration measures, a total of eight families and 10 species of surviving plants appeared, most of which were herbs. The restoration effect of the arbor shrub and grass plots was the best; the plant coverage reached 100%, and the survival rate was over 69%. The diversity index of the plant community was as follows:arbor shrub grass > shrub grass > joe grass > grass. The dominant plants under different ecological restoration measures were Pinus elliottii, Ligustrum lucidum, Boehmeria nivea, Lagerstroemia indica, and Plantago asiatica. The contents of most heavy metals in plants were higher than the normal values. Among them, the enrichment and transfer coefficients of the leaf stems of P. elliottii and L. indica were close to or greater than 1, showing a strong ability of enrichment and transfer to Cd; these two plants belong to Cd-enrichment type plants. The roots of L. lucidum Ait and P. asiatica, which are root-hoarding plants, had a high retention rate of heavy metals. Boehmeria nivea was a heavy metal-avoidance plant with a low content of heavy metals in each part and had the ability to fix and repair potential soil heavy metal pollution. Considering the diversity of plants and the ability of plant enrichment and migration, the combination of trees, shrubs, and grasses was the best restoration mode. Pinus elliottii, L. indica, and P. asiatica can be the target plants for ecological restoration in the abandoned land of mining areas.