Pollution evaluation of total and acid-leachable trace elements in surface sediments of Hooghly River Estuary and Sundarban Mangrove Wetland (India)

Trace metals and pesticides in water-sediment and associated pollution load indicators of Netravathi-Gurupur estuary, India: Implications on coastal pollution

Various environmental indicators were used to evaluate the water and sediment quality of the Netravathi-Gurupur estuary, India, for trace metals and pesticide pollution. The descended order of studied metal concentrations (μg/L) in the water was Fe (592.71) > Mn (98.35) > Zn (54.69) > Cu (6.64) > Cd (3.24) > Pb (2.38) > Cr (0.82) and in sediment (mg/kg) was Fe (11,396.53) > Mn (100.61) > Cr (75.41) > Zn (20.04) > Cu (12.77) > Pb (3.46) > Cd (0.02). However, pesticide residues were not detected in this estuarine environment. The various metal indexes categorised the water as uncontaminated, whereas contamination factor, enrichment factor, geo-accumulation index, degree of contamination and pollution load index indicated low to moderate sediment contamination. Multivariate statistics showed that the dominance of natural sources of trace metals with little anthropogenic impact. Improvement in water/sediment quality during the study period might be due to COVID-19 imposed lockdown.

Transfer of chromium from environment to fish in East Kolkata wetlands - evaluation by structural equation modeling

Chromium (Cr) is a significant pollutant in the effluents from leather industries and domestic city sewage. Cr was determined in water, sediment, and different tissues (gill, muscle, intestine, liver, and kidney) of Nile tilapia, Oreochromis niloticus harvested from wastewater-fed aquaculture (WFA) situated at Bamonghata, Bantala, Chowbaga and Chingrighata of East Kolkata Wetlands (EKW), a Ramsar site in West Bengal, India. The results showed that Cr concentration in surface water ranged between 0.05 to 0.15 mg/L, while Cr was detected at high concentration (100-300 mg/kg) in the sediment soil of the first three WFAs and in moderate concentration (50-110 mg/kg) in Chingrighata WFA. Average Cr concentrations in the tissues were ranked in the following sequence: kidney>liver>intestine>gill>muscle. However, the extent of accumulation of Cr in different tissues varied between the WFAs. We used Structural Equation Modeling (SEM) to determine the route of Cr transfer. The fitness of the model was evaluated by the performance measures. Cr accumulation pathways varied between the sites depending upon the level of Cr in water or sediment. Except for Bamonghata WFA, sediment was found as the principal source of accumulation of Cr in different tissues of O. niloticus. Cr refluxed from sediment into overlying water and accumulated in fish either through the food chain or through direct accumulation from water. In Bamonghata WFA, the role of sediment in the transfer of Cr could not be established due to the high water depth or biological non-availability of Cr in the sediment. It is concluded from this study that fish reared in the WFAs of EKW are still not hazardous in respect to Cr but require proper management to avoid the influx of Cr-containing effluents into the WFAs.

Distribution, speciation, and bioaccumulation of potentially toxic elements in the grey mangroves at Indian Sundarbans, in relation to vessel movements

Sundarban is the world's largest mangrove wetland and home of 4.6 million people (Indian part), whose principal mode of communication is motorized boats (ferries). This study shed light on the role played by ferry movement in the speciation (following the BCR three-step sequential extraction method), ecological impact and bioaccumulation of potentially toxic elements (PTEs) in plant tissues (root and lamina) of grey mangrove (Avicennia marina) found near the five ferry ghats (ports). One-way ANOVA showed variation in major soil parameters (silt, clay, organic carbon, pH, Electrical conductivity) and PTEs (As, Cd, Cr, Cu, Hg, and Pb) between sites. Sequential extraction revealed that Cd was present in the 'exchangeable' form across the sites, Pb was in the 'reducible' form, and the rest of the PTEs were majorly found in 'residual' phase. Pollution indices revealed moderate to heavy contamination and considerable potential ecological risk due to Cd. Pearson correlation statistics and concentration variations indicate a relation between Pb and ferry movement frequency in the sites. Higher bioconcentration of Pb in the roots of A. marina, indicates phytostabilization action. Translocation factor for Cd in the leaves, indicates phytoextraction by A. marina. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a close association between vehicle movement and Hg, Pb, Silt fraction, electrical conductivity, Cr, and As. This study recommends regular pollution monitoring across Sundarbans, as the PTEs in sediment-plant matrix can impact the higher trophic levels, human health through possible biomagnification in the detritus food chain, and can adversely impact the existing conservation initiatives.

Seasonal heavy metal speciation in sediment and source tracking via Cu isotopic composition in Huangpu River, Shanghai, China

The present study systematically analyzed and evaluated the variations in chemical speciation, pollution assessment, and source identification of heavy metals in sediments of Huangpu River. The methods employed included heavy metal concentration, chemical speciation and Cu isotopic compositions analysis. Results showed that the chemical speciation of sediment-bound heavy metals, characterized by significant seasonal variation, shifted from non-residual fractions dominating in spring and summer to residual fractions dominating in autumn and winter. Precipitation was identified as an important factor influencing the chemical speciation of sediment-bound heavy metals. Furthermore, ratio of the secondary phase to the primary phase, RSP (=C_non-residual/C_residual) values in Huangpu River sediments were higher than 1 in spring and summer, indicating that sediment-bound heavy metals in Huangpu River were mainly composed of non-residual fractions and could potentially be released into the river water. Principal component analysis (PCA) revealed that navigation, traffic, agricultural, and industrial activities could be the potential sources of heavy metal pollution. Notably, the δ⁶⁵Cu values in Huangpu River sediments were observed to be isotopically lighter (from -0.37 to +0.18 ‰), suggesting that navigation might be the primary pollution source. These results will not only provide guidance in reducing heavy metal concentrations, but also serve as a crucial basis for policy making regarding heavy metal control.

Ecological health risk assessment of microplastics and heavy metals in sediments, water, hydrophytes (Alternanthera philoxeroides, Typha latifolia, and Ipomoea carnea), and fish (Labeo rohita) in Marala wetlands in Sialkot, Pakistan

For the ecological risk assessment of heavy metals and microplastics in Marala wetlands in Sialkot, Pakistan, samples of sediments, water, aquatic plants (Alternanthera philoxeroides, Typha latifolia, and Ipomoea carnea), and fish (Labeo rohita) were studied from five different locations. Pb, Cd, and Cr concentrations were above permissible limits devised by WHO in sediments and water at most of sites. High concentrations of Cd were recorded in water samples compared to sediments with maximum values recorded at Site-2 (52.08 ± 9.55 mg kg-1) and Site-5 (62.29 ± 10.12 mg kg-1). The maximum concentrations of Cr (7.23 ± 0.40 mg kg-1) and Pb (22.87 ± 0.83 mg kg-1) were found at Site-4 in water samples. The maximum abundance of microplastics (3047 pieces kg-1 of sediments) was at Site-1 with filaments in the highest proportion among the other types. Zn, Ni, and Cu remained generally low in concentrations in both sediments and waters. Plants showed accumulation of heavy metals, notably the amount of Cd (33.36 ± 0.26 mgkg-1) and Ni (163.3 ± 1.30 mgkg-1) absorbed by T. latifolia and A. philoxeroides, respectively were high. Also, photosynthetic pigments in plants seemed to be affected. However, estimated daily intake (EDI) and provisional tolerable weekly intake (PTWI) calculations for the human population consuming fish from this wetland remained below the FAO/WHO limits. PCA analysis revealed the anthropogenic origin of metals that might be causing adverse effects on the biota which depend on this wetland for their food.

Spatial distribution of potentially harmful trace elements and ecological risk assessment in Zhanjiang mangrove wetland, South China

Global mangrove wetlands face increasing anthropogenic impacts along the coast. The Zhanjiang mangrove wetland is the largest and adjacent to the most developed bay area in China. Surface sediments were collected in different plant transit and used for potentially harmful trace elements (PHTEs) measurement. Mean contents of Hg, Cr, Ni, Cu, Zn, As, Cd and Pb were 0.01 mg/kg, 56.16 mg/kg, 10.06 mg/kg, 9.61 mg/kg, 43.58 mg/kg, 8.76 mg/kg, 0.25 mg/kg, 28.12 mg/kg. Most of the PHTEs were slightly enriched but the Cd pollution is significant, and the potential ecological risk is moderate. The risk of the mangrove wetland is larger than the grassland and the farmland. The PCA and PMF indicate Hg, Ni, Cu, Zn, As, and Pb mainly originated from local anthropogenic activities, Cr originated from the natural geological process, and Cd mainly originated from atmospheric deposition of regional industrial pollution. In view of the impact of surrounding industry and agriculture and the signs of PHTEs pollution, it is necessary to implement the wetland protection law more strictly to truly realize the construction of ecological civilization. This provides a valid reference for the wetland conservation and management in coastal cities.

Geochemical Speciation, Risk Assessment, and Sources Identification of Heavy Metals in Mangrove Surface Sediments from the Nanliu River Estuary of the Beibu Gulf, China

To better understand heavy metal pollution and the potential ecological risk of mangrove sediments in the Nanliu River estuary, the speciation and distribution characteristics of heavy metals Fe, Mn, Zn, Co, Ni, Cd, Cr, Cu, and Pb in 13 surface sediments in the study area were determined and analyzed using a modified four-step BCR extraction method, and the ecological risk of heavy metals was assessed using the Geo-accumulation Index (Igeo), Potential Ecological Risk Index (RI), Risk Assessment Code (RAC), Pollution Load Index (PLI), Individual contamination factors (ICF) and Global contamination factor (GCF) methods, and source analyses were performed using correlation analysis and cluster analysis. The results showed that the heavy metal was in the order of Fe > Mn > Cu > Zn > Cr > Pb > Co > Ni > Cd. Except for Fe, Zn, Ni, Cr, Pb, and Co, the average heavy metal content of Mn, Cd, and Cu all exceeded the environmental background value; the Fe, Zn, Co, Ni, Cr, Cu, and Pd are mainly in the residual speciation, while Mn and Cd are mainly weak acid extraction and oxidation, respectively, both of which are predominantly in unstable speciation and are easily released into the environment. Mn and Cd pose a substantial ecological risk, while Cu and Pb present a moderate risk and require precaution. The source analysis results indicate that Fe, Mn, Zn, Ni, Cr, and Pb are most likely to originate from natural sources and the transportation industry, Co and Cu are likely to be mainly from ship manufacturing industrial activities, and Cd is likely to be mainly from agriculture and aquaculture. The GCF and PLI results show that places with high heavy metal enrichment and ecological risk are primarily located in areas with high industrial, agricultural, or human activity impacts.

Geospatial modeling and ecological and human health risk assessments of heavy metals in contaminated mangrove soils

Heavy metal-contaminated wastes can threaten mangrove forests, one of the most biodiverse ecosystems in the world. The study evaluated the geospatial distribution of heavy metals concentrations in soils, the ecological and human health risks, and metal contents in soil fractions and mangrove organisms in the Botafogo estuary, Brazil, one of the most environmentally impacted estuaries in the country. The metal concentrations exceeded by up to 2.6-fold the geochemical background; 91%, 59%, 64%, 31%, and 82% of the soils were contaminated with Cr, Zn, Pb, Cu, and Ni, respectively. Adverse effects to the biota may occur due to Cr, Cu, Ni and Pb exposures. Contents of clay and organic matter were the main factors governing the distribution of metals in soil, contributing to up to 63% of the total variability. However, the geospatial modeling showed that the predictive ability of these variables varied spatially with the metal and location. The ecological and human health risks assessments indicated that the metal concentrations in soils are safe for the environment and human beings. There was a low transfer of metals from the soil to the biota, with values of sediment-biota accumulation factor (SBAF) and biological accumulation coefficients (BAC) lower than 1.0, except for Zn (SBAF = 13.1). The high Zn bioaccumulation by Crassostrea rhizophorae may be associated with the concentrations of Zn in the bioavailable fractions.

Have any effect of COVID-19 lockdown on environmental sustainability? A study from most polluted metropolitan area of India

The long-term lockdown due to COVID-19 has beneficial impact on the natural environment. India has enforced a lockdown on 24th March 2020 and was subsequently extended in various phases. The lockdown due to the sudden spurt of the COVID-19 pandemic has shown a significant decline in concentration of air pollutants across India. The present article dealt with scenarios of air quality concentration of air pollutants, and effect on climatic variability during the COVID-19 lockdown period in Kolkata Metropolitan Area, India. The result showed that the air pollutants are significantly reduced and the air quality index (AQI) was improved during the lockdown months. Aerosol concentrations decreased by - 54.94% from the period of pre-lockdown. The major air pollutants like particulate matters (PM_2.5, PM₁₀), sulphur dioxide (SO₂), carbon monoxide (CO) and Ozone (O₃) were observed the maximum reduction ( - 40 to  - 60%) in the COVID-19 lockdown period. The AQI has been improved by 54.94% in the lockdown period. On the other hand, Sen's slope rank and the Mann-Kendal trend test showed the daily decreased of air pollutants rate is  - 0.051 to  - 1.586 μg /m3. The increasing trend of daily minimum, average, and maximum temperature from the month of March to May in this year (2020s) are 0.091, 0.118, and 0.106 °C which is lowest than the 2016s to 2019s trend. Therefore, this research has an enormous opportunity to explain the effects of the lockdown on air quality and climate variability, and it can also be helpful for policymakers and decision-makers to enact appropriate measures to control air pollution.

Spatial distribution of trace elements in surface sediments of Hooghly (Ganges) river estuary in West Bengal, India

The spatial distribution of trace elements in surface sediments of the Hooghly estuary was studied over the monsoons in 2014-2017. As, Cd, Ni, Pb and U were two- to sixteen-fold the crust means with increasing levels toward the estuary, with Ni peak during the post-monsoon. Pearson's correlation matrix, cluster analysis, enrichment factors and pollution index revealed the anthropic source and association of trace elements with Fe, Mn and Al and of Pb with U. Geoaccumulation index revealed for Ni an extremely contaminated situation at the estuary water during monsoon and for Cd a heavily contaminated situation at freshwater location. The potential contamination index was >6; thus, sediments were very severely contaminated by As, Cd and Ni with worst situation for As and Cd at fresh and brackish water and during post-monsoon. The overall ecological risk was severe, 300≤RI<600 at all sites and seasons, especially after the monsoon, at fluvial and brackish locations.

Baseline, enrichment, and ecological risk of arsenic and antimony in the Jiaozhou Bay, a semi-enclosed bay of the Yellow Sea, China

Arsenic (As) and antimony (Sb) are toxic metalloids widely distributed in coastal sediments, but are seldom studied for their geochemical baselines. In this study, sediment samples were collected from Jiaozhou Bay (JZB) to evaluate their baselines, contamination, and ecological risk. Results showed that the As and Sb concentrations were between 3.15 and 11.94 mg/kg and 0.20-0.61 mg/kg, respectively. Sc and Fe showed good performance in developing geochemical baseline functions for the metalloids. Organic matter content and clay had significant positive correlations with metalloid abundance in sediments (p < 0.01). In the JZB, As and Sb were not enriched in the sediments, with the enrichment factors below 1. Furthermore, the contamination degrees of As and Sb were low in the JZB. In addition, the ecological risks of As and Sb were relatively low in the JZB, with the risk index between 4.02 and 12.70 and 1.68-5.09, respectively.

Assessment of the genotoxicity of sediment elutriates from an aquatic ecosystem on Allium cepa: Limache stream in central Chile

The aim of this study was to assess the genotoxic effects of sediment elutriates of an aquatic ecosystem. Sediment samples were taken from Limache stream, located in central Chile. The tests were carried out on sediment elutriates. Genotoxicity was determined by bioassay with Allium cepa. The percentage of germination, root growth, mitotic index, and frequency of chromosome aberrations were determined. The results show a significant increase in chromosome aberrations and decrease of the mitotic index in Allium cepa in all the sediment elutriates compared to the control. No significant differences were observed in the percentages of germination or root growth among the sediment elutriates. A negative correlation was found between the mitotic index and chromosomal aberrations. In conclusion, genotoxic variables are more sensitive than growth variables. The sediments contain chemical agents in bioavailable concentrations that produce genotoxic effects. Allium cepa test proved to be a sensitive indicator of genotoxic contaminants in sediment elutriates of the Limache stream in central Chile.

Health Risk and Geochemical Assessment of Trace Elements in Surface Sediment along the Hooghly (Ganges) River Estuary (India)

This study investigated sediment spatial and seasonal distribution of trace elements (TEs) (n = 16) and human health effects along the Hooghly River Estuary (India). The index of geo-accumulation (Igeo), enrichment factor (EF), hazard quotient (HQ), modified hazard quotient (mHQ) and toxic risk unit (TRI) were calculated to estimate sediment pollution level, while hazard index (HI) and lifetime cancer risk (LCR) were used to assess TEs enrichment vs. human health. The concentrations (µg/g dry weight) of TEs were: Cd (0.01–1.58), Cr (41.98–105.49), Cu (16.41–51.09), Ni (28.37–63.90), Fe (22075–47919), Mn (423–630), Co (11.43–23.11), Zn (48.82–105.81), V (63.92–138.92), Pb (25.01–43.27) and Ti (0.18–3.50); As (2.92–16.26), B (59.34–98.78), Si (11.52–98.78); Be (1.71–4.81), Ba (95.23–293.72). From Igeo and EF, Cd was the major contaminant, while Ni presented moderate/high contamination (HQ and TRI). Children were more exposed to carcinogenic and non-carcinogenic risks compared to adults. For non-carcinogenic substances, no significant risk was found to both children and adults (HIs < 1). The LCR for Cr (3.924 × 10−4 for children) and As (1.379 × 10−4 for children) was higher than the threshold limit value (TLV, 10−4 and 10−6) indicating significant carcinogenic risks to be managed.

Metal concentration and its ecological risk assessment in the beach sediments of Coromandel Coast, Southern India

The present study investigates the concentration of acid leachable trace metals (ALTMs) and their ecological risk in the beach sediments of Coromandel Coast, Southern India. In total, thirty-six beach sediments (eighteen samples from low tide and eighteen samples from high tide) were collected from the study area. The results of the study of the ALTMs suggest that the sediments are enriched by natural processes with significant anthropogenic influences. The distribution of ALTMs in beach sediments is in the following descending order: Fe > Cr > Mn > Pb > Ni > Cu > Co > Zn. The statistical results indicate that the metal concentrations were chiefly originated from natural processes such as leaching, weathering, and fluvial action. In addition, the textural characteristics, organic matter, and calcium carbonate percentage play an important role in the distribution of metals in the beach sediments.

The distribution and risk of mercury in Shenzhen mangroves, representative urban mangroves affected by human activities in China

Sediments were collected from urban mangroves in Shenzhen, China, including Shajing (SJ) and Xixiang (XX) featured with industrial district; Futian (FT) and Baguang (BG) featured with central business district and ecological preserve, respectively. Distributions, pollution levels and human health risks of Hg were explored. In both surface and vertical sediments, mean Hg concentration was highest in SJ mangrove, which may be due to its proximity to point-source discharge of Maozhou River in Pearl River Estuary, China. Sediment properties (pH, salinity, TOC and particle size) had limited impact on Hg accumulation due to their non-significant correlations. Geo-accumulation index, pollution load index, potential ecological risk index, and the ecological risk assessment code showed the highest ecological risk in SJ mangrove, followed by XX, FT, and BG mangroves. The assessment of human health risks showed that public experience little adverse health risk due to exposure to Hg polluted sediment in urban mangroves.

Distribution, ecological risk assessment and source identification of heavy metals in surface sediments of Huixian karst wetland, China

In this study, heavy metals including Cd, Pb, Zn, Mn, Cu, Ni, Cr, As, and Hg, in the surface sediment (0-10 cm) of the Huixian wetland in a karst region were investigated in terms of their spatial distribution, ecological risks, and possible sources. Samples were collected from 13 typical sites throughout the Huixian wetland and were analyzed via inductively coupled plasma-mass spectrometry. The results revealed that the mean concentrations of Cd, Pb, Mn, Cr, As, and Hg were higher than the background and Chinese safe standard values. Based on spatial distribution and ecological risk, the study area was differentiated into three groups of sites with the following order of risk: group 3 > group 2 > group 1. The observed concentrations fluctuated slightly with depth. However, an irregular decreasing trend in the concentration with soil depth was observed among the groups. Multivariate statistical analyses showed that the high accumulation of Cd, Pb, Zn and Cu in the sediments of group 3 sites is due to the natural ancient deposition of minerals rich in heavy metals, while the accumulation of Mn, Cr, As, and Hg is attributed to an anthropogenic origin. Agricultural activities, the use of fertilizers and, pesticides, and local automobile repair stations most probably enriched these heavy metals in the Huixian wetland sediments. Hg and Cd have the highest potential ecological risk, which follows the order Hg > Cd > Pb > As > Ni > Cu > Cr > Mn > Zn. The mean geoaccumulation index (I_geo) values of Pb (0.48) and Hg (1.12) suggested moderate contamination in the study area.

Metal Contamination of Water and Sediments of the Vieira River, Montes Claros, Brazil

Vieira River is the main recipient of domestic and industrial wastewater in the city of Montes Claros, MG, Brazil. Until 2010, domestic sewage was dumped in it without any kind of treatment. Concentrations of arsenic (As), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were determined in water and sediment samples in eight locations along the Vieira River during the dry season of 2015. Concentrations of Cu, Ni, and Zn detected in the water at some sites along the Vieira River were superior to the reference limits for toxicity. The concentration of Cu and Ni restricts the use of water for irrigation in some sites of the river. The level of sediment contamination was assessed by five approaches, including contamination factor (CF), pollution load index (PLI), geo-accumulation index (I_geo), cluster analysis (CA), and principal component analysis/factor analysis (PCA/FA). The results showed that Cr and the downstream sampling site nearest to the Wastewater Treatment Plant of the city of Montes Claros had the highest values of PLI, I_geo, and CF, which reinforces the influence of domestic and industrial wastewater discharge in pollution of the Vieira River. In addition, CA and PCA/FA reinforced the assumption that Cr comes from anthropogenic pollution sources.

Trace metals contamination in different compartments of the Sundarbans mangrove: A review

This review study aimed to decipher distribution of trace metals (Al, As, Cd, Cr, Cu, Hg, Pb, Ni, Mn, V, and Zn) in different compartments and human health risk in the Sundarbans mangrove ecosystems. The literature suggested relatively higher contamination of soils and sediments than fish, crustaceans, and water. Cd, Fe, Ni, and Pb are most likely to accumulate in roots of mangrove trees, while Al, As, Co, Cr, Cu, Mn, and Zn tend to accumulate in the leaves. According to human health risk studies, fish consumption is the main route of trace metals exposure to human. Majority of the studies conducted in the Indian Sundarbans; whereas, in Bangladesh part, there is an evident lack of such kind of studies. Finally, this review highlights the foremost data and research gaps, which will help to refine the risk of trace metals and scarcity of researches in the Sundarbans mangrove ecosystem.

Phytomanagement of trace metals in mangrove sediments of Hormozgan, Iran, using gray mangrove (Avicennia marina)

Trace elements (Zn, Cu, Pb, and Cd) in root and leaf tissues of the gray mangrove (Avicennia marina) and in corresponding sediment samples were studied. Samples were taken from the inflow/outflow points in two distinct habitats, i.e., the Hara Protected Area and the Azini Bay, of Hormozgan Province in south Iran. Heavy metal concentrations (μg g^-1 of dry weight) in the sediments of the Hara Protected Area ranged from 16.0 to 68.0 for Pb, 15.0 to 52.0 for Zn, 9.0 to 27.0 for Cu, and 1.0 to 3.3 for Cd. In the Azini Bay, these concentrations ranged from 7.1 to 27.5 for Pb, 17.1 to 55.9 for Zn, 12.1 to 37.9 for Cu, and 0.2 to 2.3 for Cd. The accumulation trend of heavy metal concentrations in the roots of A. marina was in the order Pb (16.1) > Zn (15.8) > Cu (9.3) > Cd (1.3) μg g^-1 of dry weight in the Hara Protected Area and in the order Zn (13.7) > Cu (9.4) > Pb (5.5) > Cd (0.6) μg g^-1 of dry weight in the Azini Bay. The value of translocation factor (TLF) was smaller than 1 in both regions. It was estimated from 0.44 to 0.62 in the Hara Protected Area and from 0.51 to 1.01 in the Azini Bay. The enrichment coefficient for root (ECR) varied from 0.32 to 0.93 in the Hara Protected Area and from 0.32 to 0.51 in the Azini Bay. The ratio of heavy metals in leaves/sediments (ECL) also varied from 0.01 to 0.67 in the Hara Protected Area and from 0.01 to 0.47 in the Azini Bay. The enrichment coefficient for leaf (ECL) was always lower than ECR in both regions. Based on the above findings, A. marina can be regarded as an excluder for the heavy metals examined in this study, given its low efficiency in translocating and accumulating the heavy metals in the shoots. Apart from serving as a baseline for the study area, findings could be useful for mitigating heavy metal contamination in these sensitive ecosystems through possible phytomanagement using gray mangrove.

Historical accumulation and ecological risk assessment of heavy metals in sediments of a drinking water lake

Heavy metal contamination in sediments is progressively being recognized as a challenging problem in large parts of the developing world, particularly in Asian countries. A drinking water lake in Yunnan-Guizhou plateau, China named Hongfeng Lake was selected as the research target. Forty surface sediment samples and 4 sediment cores were collected to reveal the accumulation of heavy metals in the sediments of the lake. The mean concentrations of Cr, Cu, Pb, Cd, As, and Hg in surface sediments were 81.67, 45.61, 29.78, 0.53, 22.71, and 0.25 mg/kg, respectively, which exceeded the background levels of sediment 1.1~3.3 times. The calculation of geoaccumulation (I_geo) and potential ecological risk (PER) index analysis were preformed, and the results showed a considerable risk for Cd and Hg on the whole. Spatially, the northern part showed a higher risk than the southern part and tributaries of the lake, and a moderate risk in the overall sediment of the lake. The historical level of heavy metals in Hongfeng Lake was traced by vertical sediments study and it was dated back approximately 35 years. The EF trends of a feature sampling site HF8 showed strong temporal variations, and peaked in the year 1995. After that, the EFs exhibited a declining trend, which reflects productive environmental protection and management by the local government. For the Hongfeng Lake, a typical lake with heavy metal-contaminated sediments, the in-situ remediation technique could be a suitable method for its remediation.