Assessment of trace metal contamination level and toxicity in sediments from coastal regions of West Bengal, eastern part of India

Origin, spatial distribution, sediment contamination, ecological and health risk evaluation of trace metals in sediments of ship breaking area of Bangladesh

Eleven trace metals (Cd, Cr, Fe, Mn, Cu, Ni, Co, Zn, As, Pb, and Ag) in sediments of Bangladesh's ship breaking area were measured by an atomic absorption spectrometer to determine origin, contamination extent, spatial distributions, and associated ecological and human health hazards. This study found considerable quantities of Pb, Cd, Mn, Zn, and Cu when compared with standards and high levels of Pb, Cd, Zn, Cu, As, and Ag contamination according to pollution evaluation indices. Different indices indicate most of the sampling sites were highly polluted. However, spatial distribution maps indicate that trace metals were predominantly deposited in the northern and southern region. The ecological risk index revealed that Cd has the highest while Pb and As had moderate risk. Based on the health index values, Zn for both adults and children were higher than the safe limit while Mn, Pb, Cr, As, Fe, Cu, Ni, and Co for children were close to the threshold. The mean total carcinogenic risk values of Cr, As, and Ni for children and Ni for adults exceeded the permissible threshold. The cancer risk possibilities were further assessed using Monte Carlo simulation. Most trace metals have anthropogenic origins, which were attributed to ship breaking activities.

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.

Vertical distribution and trace element contamination in sediment cores affected by gold mining in Colombia

The vertical distribution, level of contamination, potential ecological risks, and historical fluxes of trace elements (Pb, As, and Hg) were evaluated from 210Pb-dated sediment cores in three different areas with gold mining impacts in northern Colombia: the Atrato River (AR), the Delicias Marsh (DM) and the Encaramada Marsh (EM). All cores spanned ∼100 years; the mass accumulation rates followed the order AR > DM > EM. The average trace elements concentrations in the sediment cores were: Pb 2.41 ± 0.72, As 0.65 ± 0.32, Hg 0.07 ± 0.02 μg g-1 in the Atrato River; Pb 23.49 ± 2.59, As 2.46 ± 0.88, Hg 0.10 ± 0.02 μg g-1 in the Delicias Marsh; and Pb 9.76 ± 4.18, As 2.44 ± 1.26, Hg 0.17 ± 0.06 μg g-1 in the Encaramada Marsh. Sediments are classified according to the contamination factor (CF) and geoaccumulation index (Igeo) as low to very highly contaminated. The Pollution load index (PLI) indicates environmental deterioration (PLI> 1), and the Sediment quality guidelines (SQGs) indicate that only Hg may produce adverse biological effects in the EM core. This study is an example of the reconstruction of temporal changes in pollution levels and impacts of potentially toxic elements caused by gold mining in remote ecosystems, which can be reproduced in other areas where environmental monitoring is scarce or non-existent.

Risk assessment and binding mechanisms of potentially toxic metals in sediments from different water levels in a coastal wetland

The excessive accumulation of potentially toxic metals (Pb and Cd) in coastal wetlands is among the main factors threatening wetland ecosystems. However, the effects of water table depth (WTD) on the risk and binding mechanisms of potentially toxic metals in sediments remain unclear. Here, sediments from different WTD obtained from a typical coastal wetland were evaluated using a newly developed strategy based on chemical extraction methods coupled with high-resolution spectroscopy. Our findings indicated that the WTD of the coastal wetland fluctuates frequently and the average enrichment factor for Pb was categorized as minor, whereas Cd enrichment was categorized as moderate. High-resolution spectroscopy techniques also demonstrated that organic functional groups and partly inorganic compounds (e.g., Fe-O/Si-O) played a vital role in the binding of Pb and Cd to surface sediments. Additionally, mineral components rather than organic groups were mainly bound to these metals in the bottom sediments. Collectively, our findings provide key insights into the potential health effects and binding characteristics of potentially toxic metals in sediments, as well as their dynamic behavior under varying sediment depths at a microscale.

Anthropogenic and natural contribution of potentially toxic elements in southwestern Ganges-Brahmaputra-Meghna delta, Bangladesh

Elemental composition, multivariate statistical analyses with the absolute principal component score-multiple linear regression (APCS-MLR) model, and different pollution indices in Upper and Lower Southwestern Ganges-Brahmaputra-Meghna (GBM) delta sediments were studied to characterize pollution, ecological risk and quantify potential toxic element sources of the area. Toxic metals concentrations were higher in Lower Delta and individual pollution indices showed Upper Delta was moderately polluted by arsenic, chromium, cobalt, copper and lead, and Lower Delta was moderately-strongly polluted by the same metals. Synergistic indices include Potential Ecological, Toxic, Nemerow, and Pollution Risk indices in Upper and Lower Delta sediment ranged from 47.17-128.07, 2.03-12.19, 29.92-65.42, 0.28-1.62, and 69.17-246.90, 8.00-13.47, 20.53-152.92, 1.18-1.58, indicated low and moderate risk pollution, respectively. Statistical models represent the metals dominantly originated from nature for Upper Delta, and both natural and anthropogenic activities contributed to Lower Delta sediment. The study found that the modern deposit in Lower Delta became more contaminated and thus enhanced ecological risk.

Ecological risk assessment and phytomanagement of trace metals in the sediments of mangroves associated with the Ramsar sites of Kerala, southern India

The study investigated trace metal accumulation in the sediments of three major mangrove ecosystems associated with the Ramsar sites of Kerala state, the ecological risks they pose, and the absorption, accumulation, and translocation of metals in five dominant mangrove species, as these systems are heavily impacted by anthropogenic interventions. The trace metal concentrations (mg kg^-1) in the sediment of different mangrove habitats of Kerala ranged from 20 to 295 for Cu, 65 to 350 for Zn, 72 to 151 for Pb, 11 to 210 for Ni, 42 to 228 for Mn, 0 to 6 for Cd,124 to 565 for Cr, and 0 to 2.9 for Ag. An overall enrichment of metals was recorded in sediment, exceeding the prescribed effects range median (ERM) of consensus-based sediment quality guidelines (SQGs) for Cu and Cr concentrations at Munroe Island and Ni at Vypin, indicating a detrimental risk to biota in the sediments. Principal component analysis and a higher geoaccumulation index indicated the contribution of trace metals from industries, agricultural runoff, and urban waste disposal. The ecological risk index suggested that cadmium poses a very high risk to the mangrove ecosystem at Vypin. Furthermore, the bioconcentration factor for various trace metals in Avicennia marina and Lumnitzera racemosa in Ayiramthengu was > 2, suggesting that these species can accumulate trace metals, particularly Cr, Cd, and Pb. Further, our findings suggest that A. marina may be considered as an efficient metal trap for Cd in aerial parts, as indicated by the significant translocation factor (> 1) combined with the bioconcentration factor. Therefore, the study revealed that Munroe island and Vypin had a considerable level of contamination for toxic metals and Avicennia marina could be a promising candidate species for the phytoremediation of these trace metals in the coastal settings of Kerala state.

Spatial distribution of benthic toxicity and sediment-bound metals and arsenic in Guangzhou urban waterways: Influence of land use

The effects of land use on pollutant loads in sediments have been well documented; however, its influence on spatial variations in sediment toxicity remains largely unknown. In the present study, the toxicological effects of 17 sediments collected from Guangzhou waterways were evaluated using two benthic invertebrates (Chironomus dilutus and Hyalella azteca), along with quantification of heavy metals and arsenic in the sediments. The impacts of land-use configuration on sediment toxicity and occurrence of heavy metals and arsenic were analyzed. The sediments presented moderate lethality (<40 %) in the two test species and significantly altered their enzymatic activity, including the activities of oxidative stress biomarkers and acetylcholine esterase. Metals (Ag, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) and arsenic were detected in all the sediments, with total concentrations ranging from 238 to 1019 mg/kg of dry weight. Both the toxicity and chemical results displayed spatially dependent patterns but were related to different land use types. Toxicity was most influenced by agricultural and aquacultural activities, while metal and arsenic pollution was most influenced by urban land areas. The present findings are expected to provide essential knowledge for developing strategies that reduce the chemical pollution and ecotoxicological risk in sediments.

Nexus between potentially toxic elements' accumulation and seasonal/anthropogenic influences on mangrove sediments and ecological risk in Sundarbans, Bangladesh: An approach from GIS, self-organizing map, conditional inference tree and random forest models

Mangroves play a vital role in protecting the coastal community from the climate change effect and in the restoration of the coastal ecosystem. This research has been designed to determine the spatial and seasonal changes of potentially toxic elements' (PTEs) concentration in sediments and their potential source contribution among the different human-driven processes in Sundarbans, Bangladesh. Different pollution evaluation indices, random forest (RF) model, conditional inference tree (CIT), self-organizing map (SOM), geographical information system (GIS), and principal component analysis (PCA) were used for the interpretation of sources and risk assessment of PTEs. The mean concentration of PTEs both in winter and monsoon seasons has fallen below the threshold effect level but exceeded the rare effect level of marine sediments quality standards. Results showed that the PTEs were significantly enriched (EF > 1.00 < 70.00) in sediments, whereas the Cd enrichment (7.00% samples) was very alarming (EF = 60-70). Except for Zn and Cd, other PTEs were enriched in 30-60% samples. The highest geoaccumulation and contamination factors for Cd were observed in 46-72% of samples. The ecological risk (ER) factors showed similar results where Cd showed strong to very strong factors (ER = 110-2218) in 80% of samples. The CIT explained the natural/geogenic and anthropogenic sources of pollution, where the higher CIT values for Cd indicated industrial, aquaculture, and coal-based thermal powerplant. The RF model provided that shrimp firms, power plants, industry, and seaport were recognized as the influential sources for Zn, Pb, Cr, Cd, and As in sediments. Though Pb and As were found as the most significant pollutants, Cd was identified as a severe threat to ecology and public health. Based on CIT, RF, SOM and PCA the order of PTEs in mangroves sediment were:industrial/urban > aquaculture/shrimpfirm > powerplant > seaportoperation > tourism > geogenic/natural. The present study will help the policymakers for effective and sustainable management of the mangrove ecosystem.

Spatial and seasonal trends of trace metals in the surficial sediments from off Kochi - Geochemistry and environmental implications

Fifty four sediment samples representing pre and post-monsoon seasons were collected along a transect from off Kochi, lying between the latitudes 9°57'59.5″-9°54'30.4″ and longitudes 76°11'7.04″-75°38'50.3″ of the South eastern Arabian Sea. The present study investigates the levels of trace metals (Zn, Cd, Pb, Cu, Fe, Ni, Mn, Co and Cr), total organic carbon (TOC), total inorganic carbon (TIC), elemental composition and grain size to assess the extent of environmental pollution and to discuss the distribution of these trace metals in the surficial sediments. Sediment pollution assessment was done using the Contamination factor (C.F), Geoaccumulation Index (Igeo), Enrichment Factor (EF), and Pollution Load Index (PLI). The majority of trace metals analysed in this study exhibited the highest concentrations at stations 1, 2 and 3 where the land-based anthropogenic input was found to be maximum.

Risk assessment of heavy metals in a typical mangrove ecosystem - A case study of Shankou Mangrove National Natural Reserve, southern China

Mangroves bear enormous ecosystem value, while the ecosystems are facing increasing environmental pressures. In this study, 73 samples of soil sediments in mangroves, paddy fields, grasslands, forests, and shrimp ponds were collected from Shankou Mangrove National Nature Reserve (SKMNNR), Guangxi Zhuang Autonomous Region, China. The pollution status and ecological risks of heavy metal elements of Cr, Ni, Cu, Zn, As, Cd, Pb, V, and Co were determined using the enrichment factor (EF), geoaccumulaton index (I_geo), and potential ecological risk index (PERI). The average concentration is shown to be substantially lower than the background value. In general, the I_geo values indicated that the pollution conditions of different land use types in SKMNNR are relatively minor. Most of the PERI values were at the moderate level. This study demonstrates that the current status of sediment quality in SKMNNR is relatively good, and the pollution level is relatively low. Large-scale coastal aquaculture development and industrial expansion should not no longer be permitted there.

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.

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.

Heavy metal pollution and toxicity assessment in Mallorquin swamp: A natural protected heritage in the Caribbean Sea, Colombia

This work reports the level and ecotoxicity impact of metals in the sediments of the Mallorquín swamp, a protected coastal lagoon in the Caribbean coast of Colombia. The distribution of metals was in the following decreasing order: Zn > Cu > Pb > Cd > Hg, showing statistically significant differences among sites. The average Pb and Cd concentrations in sediments were about 17 and 5 times higher, respectively, compared to those in background values. Several contamination indices suggested moderate contamination of Hg, Cu, and Zn, and strong pollution due to Cd and Pb. Multivariate analysis revealed spatial variations for metals and its anthropogenic origin, such as municipal and industrial wastewater discharges (Pb, Zn, and Hg) and agricultural activities (Cd and Cu). These findings showed the negative impact of human activities and the need to apply protective management strategies.

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.

Spatial and seasonal distribution of multi-elements in suspended particulate matter (SPM) in tidally dominated Hooghly river estuary and their ecotoxicological relevance

The present work represented first study of the spatio-seasonal distribution of the multi-elements in the suspended particulate matter (SPM) of the tropical Hooghly river estuary (HRE), eastern part of India. The high load of SPM (20-3460 mg/l) might have induced negative impact on the phytoplankton density. The relative abundance of the studied elements exhibited the following decreasing trend (concentration in μg/g and %): Si(26.44 ± 3.75%) > Al(7.94 ± 1.52%) > Fe(6.17 ± 1.9%) > K(3.05 ± 1.5%) > Ca(1.97 ± 1.11%) > Mg(1.57 ± 1.71%) > Na(1.45 ± 8.40%) > Mn(1273 ± 2003) > Zn(178.43 ± 130.95) > V(151.54 ± 27.13) > Cr(147.08 ± 32.21) > Cu(62.06 ± 14.03) > Ni(49.64 ± 12.09) > Pb(21.5 ± 10.45). The accumulation of Ni, Cr, Pb, and Cu is mainly controlled by the formation of Fe hydroxides along with particulate organic carbon (POC) and salinity. The average geo-accumulation index (I_geo) and enrichment factor (EF) endorsed the substantial input of Cr (I_geo = 0.037; EF = 1.61) and Zn (I_geo = 0.123; EF = 2.07) from diffused pollution sources. From ecotoxicological point of view, the quality guidelines (QGs) suggested that Cr and Ni might possess frequent adverse biological effects. However, the mean probable effect level (PEL) quotient values revealed 49% probability of toxicity to the aquatic biota for five toxic elements (Cr, Ni, Cu, Zn, and Pb). The geochemical approaches, pollution indices, and statistical evaluation together revealed low to moderate contamination in the estuary. This baseline data would be beneficial in adopting proper management strategies for sustainable utilization and restoration of the water resources. The authors strongly recommend continuous systematic monitoring and installation of treatment plants for management of this stressed estuary.

A preliminary study on upstream migration of mangroves in response to changing environment along River Hooghly, India

Environmental changes and anthropogenic activities can be linked to altered distribution and abundance of species. However, the ecological impacts of change in the microenvironment have not been well documented. Herein, we have identified the distribution of mangroves and associated species and characterized surface sediment and water samples along the banks of River Hooghly. The application of Combined Mangrove Recognition Index (CMRI) and its validation with the available ground data on satellite image of 2015 indicates that some mangrove species have reclaimed the upper course of the river, which was earlier absent before 1995. This study is the first report on the upstream migration of mangrove species such as Sonneratia caseolaris, Sonneratia apetala, Derris trifoliata, Hibiscus tiliaceus, and Thespesia populnea in River Hooghly. The changes in pollution load, varied sedimentation pattern, high chemical oxygen demand, mean sea-level rise, and anthropogenic activity might have played a significant role in the upstream migration of mangroves.

Spatial Variation of Metallic Contamination and Its Ecological Risk in Sediment and Freshwater Mollusk: Melanoides tuberculata (Müller, 1774) (Gastropoda: Thiaridae)

Heavy metal pollution has been on the rise with serious implications for the wellbeing of aquatic ecosystems. Benthic sediments and freshwater mollusk (snail): Mellanoides tuberculata were sampled from five stations for determination of heavy metals concentrations and measurement of antioxidant enzyme activities. The spatial variation was studied using an enrichment factor, potential ecological risk index, and mean probable effect limit quotient (mPELq). From the results, Cu, Zn, Cd, Cr, Pb, Ni, and Co contamination levels were high at stations S3, S4, and S5 with an mPEL quotient of 94.40%. The variation of metal concentration and Enrichment factor were in the order S5 > S3 > S4 > S2 > S1, which was attributed to anthropogenic influences at the catchment due to industrial activities and atmospheric deposition of metals. Station five in this study is downstream and requires the most monitoring and management to prevent several ecological risks of metal pollutants in River Kaduna.

Spatial and Temporal Variations of Arsenic Distribution in a Tropical Estuary Along the West Coast of India

Arsenic (As) contamination was studied and reported for the first time in the sediments of the Cochin estuary. Surface sediment samples were collected from twenty-seven stations encompassing the entire estuary constituting south, central and north estuary. The total As concentration varied from 0.01 mg/kg to 9.28 mg/kg and undetected to 23.37 mg/kg during the pre and post-monsoon. The degree of contamination assessed in terms of geochemical indices such as contamination factor (CF), geoaccumulation index (I_geo) and enrichment factor (EF) unraveled the As contamination to be meager. The application of risk index factor and sediment quality guidelines showed that the As concentration in the estuary is below the background concentration. Pearson correlation analysis of As with iron and TOC exhibited significant weak and poor correlations with these variables.

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.

Sediment quality, elemental bioaccumulation and antimicrobial properties of mangroves of Indian Sundarban

Mangroves have wide applications in traditional medicines due to their several therapeutic properties. Potentially toxic elements (PTEs), in mangrove habitats, need serious concern because of their toxicity, bioaccumulation capacity and ecotoxicological risks. In the current study, we aimed to examine sediment quality and bioaccumulation of PTEs in a mangrove-dominated habitat of Sundarban, India, and their relation with antimicrobial property of ten mangrove species of the region. Antimicrobial activity of different solvent fractions of mangrove leaves was assessed against seven microorganisms. The highest antimicrobial activity was detected in ethyl acetate and acetone-extracted fractions of Avicennia alba. Various sediment quality indices revealed progressively deteriorating nature of surface sediment having moderate contamination, however, low ecotoxicological risk. The accumulation factors (AF) for different PTEs indicate a gradual metal bioaccumulation in leaf tissue. Antimicrobial activities indicated both positive and negative correlations with manganese (Mn), copper (Cu), iron (Fe) and zinc (Zn) concentrations of mangrove species. Concentration of Mn showed a significant correlation with almost all the fractions, whereas Cu had correlation with ethyl acetate, acetone and methanol fractions (P < 0.05). The AF of Mn and Cu exhibited correlation with antimicrobial activities of acetone and methanol fractions, whereas Fe and Zn had correlation with hexane and ethyl acetate fractions. Overall, Mn, Fe, Cu and Zn concentrations of Acanthus ilicifolius and Avicennia alba leaves and in the surface sediments demonstrated the strongest association (P < 0.05) with their antimicrobial activity as also depicted in correlation and cluster analysis studies. Thus, this study will help to establish a link between the PTEs in mangrove ecosystem with their bioactivity.

Elemental geochemistry in acid sulphate soils - A case study from reclaimed islands of Indian Sundarban

Sundarban along with its networks of rivers, creeks and magnificent mangroves form a unique ecosystem. Acid sulphate soils have developed in this ecosystem under anoxic reducing conditions. In the present study, we have investigated the distribution of acid sulphate soils along with its elemental characterization and possible sources in four reclaimed islands of Indian Sundarban like Maushuni (I1), Canning (I2), Bally (I3) and Kumirmari (I4). Elements show moderate to strong correlation with each other (P < 0.01; P < 0.05). Except Si, Ca and Pb, a higher enrichment factor was observed for K, Cr, Mn, Fe, Ni, Cu and Zn. Geo-accumulation index values of all sampling locations reveal that Cr, Fe, Cu and Zn are in I_geo class 1. The pollution load index value of the reclaimed islands of Indian Sundarban varies between 1.31 and 1.48. The observation of this study could help to strategize policies to mitigate and manage acid sulphate soils in Indian Sundarban.

Assessment of potentially toxic metal (PTM) pollution in mangrove habitats using biochemical markers: A case study on Avicennia officinalis L. in and around Sundarban, India

Spatial distribution of potentially toxic metals (PTMs) and their accumulation in mangrove Avicennia officinalis L. were studied along 8 locations in and around Sundarban mangrove wetland, India. Among 8 locations, S3 (Chemaguri) and S5 (Ghushighata) showed higher concentration of PTMs (Cd, Cr, Cu, Ni, Pb, Zn) characterized by higher enrichment factors (3.45-10.03), geo-accumulation indices (0.04-1.22), contamination factors (1.14-3.51) and pollution load indices (1.3-1.45) indicating progressive deterioration of estuarine quality and considerable ecotoxicological risk. Metal concentration in A. officinalis leaves showed significant correlation with sediment metals implying elevated level of bioaccumulation. Significant statistical correlation between photosynthetic pigments (Chlorophyll a, Chlorophyll b), antioxidant response (free radical scavenging and reducing ability) and stress enzymatic activity (Peroxidase, Catalase, Super-oxide dismutase) of A. officinalis with increasing metal concentration in the contaminated locations reflects active detoxification mechanism of the plant. The study indicates the potentiality of biomonitoring metal pollution using studied biochemical markers in mangrove habitats.

Historical records, distributions and sources of mercury and zinc in sediments of East China sea: Implication from stable isotopic compositions

The distribution and source of mercury (Hg) and zinc (Zn) in surface sediments from East China Sea (ECS) were studied using stable isotopes. Hg concentrations in surface sediments varied from 12.6 to 133.2 ng g^-1. Zn concentrations ranged between 45.9 and 133.6 ng g^-1. Hydrodynamic circulation and sedimentary process within the ECS were the dominant factors controlling the distribution and fate of heavy metals, referring from relationships of Hg and Zn concentrations and total organic carbon (TOC) and clay contents. Spatial variations in Hg isotopic compositions (δ²⁰²Hg) were observed in the ECS, with δ²⁰²Hg ranging from -1.86 to -0.83‰ and Δ¹⁹⁹Hg ranging from -0.07 to +0.26‰. The high δ²⁰²Hg values and relatively negative Δ¹⁹⁹Hg values in estuarine and inner shelf sites indicated that the riverine inputs from Yangtze River played an important role in delivering Hg to ECS. In contrast, Hg isotopic signatures in outer shelf sediments had relatively low δ²⁰²Hg and positive Δ¹⁹⁹Hg, implying that atmospheric Hg deposition could be relatively dominant source for Hg. Moreover, application of zinc isotopes to trace anthropogenic sources has been tested, with δ⁶⁶Zn ranging from 0.20 to 0.67‰. The results showed significant variations of δ⁶⁶Zn in the ECS, implying that Zn isotope compositions can be tracers of anthropogenic sources. Using these Hg isotope compositions, the source attributions of sediments in ECS were estimated based on a mixing model, suggesting that river-dominated inputs, discharging pollutants from industrial sources, and atmospheric deposition could dominate in the occurrence and fate of Hg in sediments of ECS.

Seasonal assessment of trace element contamination in intertidal sediments of the meso-macrotidal Hooghly (Ganges) River Estuary with a note on mercury speciation

The spatial and seasonal distribution of trace elements (TEs) (n=16) in surficial sediment were examined along the Hooghly River Estuary (~175km), India. A synchronous elevation of majority of TEs concentration (mgkg^-1) was encountered during monsoon with the following descending order: Al (67070); Fe (31300); Cd (5.73); Cr (71.17); Cu (29.09); Mn (658.74); Ni (35.89). An overall low and homogeneous concentration of total Hg (T_Hg=17.85±4.98ngg^-1) was recorded in which methyl mercury (MeHg) shared minor fraction (8-31%) of the T_Hg. Sediment pollution indices, viz. geo-accumulation index (I_geo) and enrichment factor (EF) for Cd (I_geo=1.92-3.67; EF=13.83-31.17) and Ba (I_geo=0.79-5.03; EF=5.79-108.94) suggested high contamination from anthropogenic sources. From factor analysis it was inferred that TEs primarily originated from lithogenic sources. This study would provide the latest benchmark of TE pollution along with the first record of MeHg in this fluvial system which recommends reliable monitoring to safeguard geochemical health of this stressed environment.

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

The present work investigated the spatial distribution and ecological risk assessment of total and mild acid-leachable trace elements in surface sediments (top 0-10 cm; grain size ≤ 63 μm) along the Hooghly (Ganges) River Estuary and Sundarban Mangrove Wetland, India. The trace elements, analyzed by ICPMS, showed wide range of variations with the following descending order (mean values expressed in milligrams per kilogram): Fe (25,050 ± 4918) > Al (16,992 ± 4172) > Mn (517 ± 102) > Zn (53 ± 18) > Cu (33 ± 11) > Cr (29 ± 7) > Ni (27 ± 6) > Pb (14 ± 3) > As (5 ± 1) > Se (0.37 ± 0.10) > Cd (0.17 ± 0.13) > Ag (0.16 ± 0.19) > Hg (0.05 ± 0.10). In the acid-leachable fraction, Cd (92%) is dominated followed by Pb (81%), Mn (77%), Cu (70%), and Se (58%) indicating their high mobility, imposing negative impact on the adjacent benthos. The sediment pollution indices (both enrichment factor and contamination factor) suggested severe pollution by Ag at the sampling site Sajnekhali, a wildlife sanctuary in Sundarban. The mean probable effect level quotient indicated that surface sediments in the vicinity of the studied region have 21% probability of toxicity to biota. The result of multivariate analyses affirms lithogenic sources (e.g., weathering parent rocks, dry deposition) for As, Pb, Cr, Cu, and Ni, whereas Cd and Hg originated from anthropogenic activities (such as urban and industrial activities). Both human-induced stresses and natural processes controlled trace element accumulation and distribution in the estuarine system, and remedial measures are required to mitigate the potential impacts of these hazardous trace elements.

Trace metal distribution, assessment and enrichment in the surface sediments of Sundarban mangrove ecosystem in India and Bangladesh

Comparative study of trace metals distribution in the surface sediment of Sundarban mangrove ecosystem in India and Bangladesh is one of the primary baseline study done so far. Trace metal distribution assessment covering lower salinity zone to higher salinity zone was done along Matla River (tidal river) in Indian side and freshwater zone to higher salinity zone along Passur River in Bangladesh side of Sundarban; representing anthropogenic influenced area, agricultural area, tourist site and pristine area. Trace metals distribution in the surface sediments of Sundarban mangrove ecosystem shows relatively higher value of trace metals, Co, Cr, Cu, Fe, Ni, Pb and Zn in Indian part when compared to Bangladesh. Enrichment factor shows the highest enrichment of Pb in both parts of Sundarban mangroves. Co, Cr, Cu, Pb and Zn show EF>1 indicates sediment contamination from anthropogenic activities. Cr, Ni and Pb were found to have moderate accumulation in geoaccumulation index with Fe showing high accumulation. Normalized data of trace metals shows 87.5% from Indian site and 80% of Bangladesh site as outlier, indicating anthropogenic influence. Out of total sampling site 50% of Indian and 40% of Bangladesh site show trace metal values enriched more than predicted value of trace metals indicating Indian part have more polluted sites than Bangladesh side of Sundarban, which is also confirmed by enrichment factor, I-geo and normalization values in both the sides.

Assessment of the distribution, bioavailability and ecological risks of heavy metals in the lake water and surface sediments of the Caohai plateau wetland, China

In this study, selected heavy metals (Hg, As, Cd, Pb, Cr, Cu and Zn) in the lake water and sediments from the Caohai wetland, which is a valuable state reserve for migrant birds in China, were investigated to assess the spatial distribution, sources, bioavailability and ecological risks. The results suggested that most of the higher concentrations were found in the eastern region of the lakeshore. The concentration factor (CF) revealed that Hg, Cd and Zn were present from moderate risk levels to considerable risk levels in this study; thus, based on the high pollution load index (PLI) values, the Caohai wetland can be considered polluted. According to the associated effects-range classification, Cd may present substantial environmental hazards. An investigation of the chemical speciation suggested that Cd and Zn were unstable across most of the sites, which implied a higher risk of quick desorption and release. Principal component analysis (PCA) indicated that the heavy metal contamination originated from both natural and anthropogenic sources.

Temporal evolution of the environmental quality of the Vallona Lagoon (Northern Mediterranean, Adriatic Sea)

Guidance Document 25/2010, suggests sediment and biota are the most suitable matrices for the trend monitoring purpose, because they integrate the pollution over time and space. So, from 2005 to 2014, the sediment and biota concentrations of heavy metals (As, Cd, Cr, Hg, Ni, Pb) were analysed in the Vallona Lagoon (northern Adriatic Sea, Italy), widely used for intensive and extensive bivalve farming. The contamination levels in sediment and biota were compared with Environmental Quality Standard (EQS) and threshold levels (TL) for human health. The results identified critical issues related to Cd in sediment samples as well as to Hg and Pb in biota which were not only ascribable to the physiological and seasonal variability of organisms. The Cr and Ni levels in sediment were higher than the EQS. However, the concentration increases at biota stations close to sites where EQS excesses were observed in sediment were not verified.

Trace elements in surface sediments of the Hooghly (Ganges) estuary: distribution and contamination risk assessment

Our objective was to evaluate distribution and accumulation of trace elements (TEs) in surface sediments along the Hooghly (Ganges) River Estuary, India, and to assess the potential risk with view to human health. The TE concentrations (mg kg^-1 dry weight) exhibited a wide range in the following order: Al (31.801 ± 15.943) > Fe (23.337 ± 7584) > Mn (461 ± 147) > S (381 ± 235) > Zn (54 ± 18) > V (43 ± 14) > Cr (39 ± 15) > As (34 ± 15) > Cu (27 ± 11) > Ni (24 ± 9) > Se (17 ± 8) > Co (11 ± 3) > Mo (10 ± 2) > Hg (0.02 ± 0.01). Clay, silt, iron, manganese and sulphur were important for the accumulation of TE in the sediments as confirmed by factor analysis and Pearson correlation. The accumulation and dispersal of TEs were most likely to be governed by both tide-induced processes and anthropogenic inputs from point and non-point sources. Enrichment factor analysis and geoaccumulation index revealed serious contamination of the sediments with Se and As, while comparing the consensus-based sediment quality guidelines (SQGs), adverse biological effects to benthic fauna might be caused by As, Cu, Ni and Cr. This investigation may serve as a model study and recommends continuous monitoring of As, Se, Cu, Ni and Cr to ascertain that SQGs with respect to acceptable levels of TEs to safeguard geochemical health and ecology in the vicinity of this estuary.

Contamination and ecological risk assessment of trace elements in sediments of the rivers of Sundarban mangrove forest, Bangladesh

In this study, total concentrations of 16 trace elements (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sb, Hg, Pb, Th and U) in sediments of the rivers of the Sundarban mangrove forest, after the catastrophic oil spill accident in the Sela river of Sundarban, were determined. The overall mean concentrations of V, Cr, Fe and Cd in surface sediments of the Sundarban are remarkably higher than available literature data of those elements. Trace element contamination assessment, using different environmental contamination indices, reveals that As, Sb, Th and U are low to moderately contaminated while Cd is moderately to severely contaminated in the sediments of this area. The multivariate statistical analyses were applied to reveal the origin and behavior of the elements during their transport in the mangrove ecosystem. High Cr, Ni, Cu and As concentrations suggest the risk of potentially adverse biological effects in the ecosystem.

Preliminary evaluation of heavy metal contamination in the Zarrin-Gol River sediments, Iran

The major objectives of the study were to test the hypothesis of the Zarrin-Gol River as a reference site for ecotoxicological studies and to assess the contamination degree of heavy metals and metalloids in the river using four contamination indices. For these purposes, eleven heavy metal and metalloid concentrations were analyzed. The average concentrations (mgkg^-1) in the sediments were: 37.67 (chromium) 286.28 (manganese), 13,751.04 (iron), 8.79 (cobalt), 12.39 (nickel), 32.68 (zinc), 21.91 (arsenic), 40.59 (selenium), 2923.86 (aluminum), ND (silver) and 785.96 (magnesium). Contamination factor, enrichment factor, pollution load index, and geoaccumulation index were calculated to evaluate the contamination degree and influence of human activities on heavy metal levels. The contamination indices of the sediment samples showed that arsenic and selenium were the highest pollutants. The results indicated that the Zarrin-Gol River could not be used as a reference site at least for arsenic and selenium.

Influence of introduced Sonneratia apetala on nutrients and heavy metals in intertidal sediments, South China

To investigate the influence of Sonneratia apetala on nutrients and heavy metals in intertidal sediments, sediment cores of S. apetala marsh and mudflat in Shenzhen Bay, China were analyzed. The results showed that S. apetala improved sediment nutrient properties due to increased total carbon (TC), total nitrogen (TN), and total sulfur (TS). The levels of heavy metals were higher in S. apetala site than in mudflat, including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). In S. apetala site, TC, TN, and TS were not positively correlated with Cr, Ni, As, Cd, and Pb, indicating their less important roles in trapping heavy metals. There were positive correlations among Ni, Cu, Zn, and Cd in both sites, suggesting similar anthropogenic source. Levels of As were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation index and potential ecological risk index revealed higher metal contaminations in S. apetala site, especially for Cd, Hg, and As. Multivariate analysis implied that S. apetala alter the biogeochemical cycle of Cd and Cr to a certain extent. These findings indicate that S. apetala may improve soil nutrient properties and facilitate heavy metal accumulation in intertidal sediments.