Geochemical partitioning of Cu and Ni in mangrove sediments: relationships with their bioavailability

The Effect of Microplastics-Plants on the Bioavailability of Copper and Zinc in the Soil of a Sewage Irrigation Area

It is essential to understand the occurrence from and plant bioavailability of soil microplastics to heavy metals in soils to assess their environmental fate and risk. The purpose of this study was to evaluate the effect of different microplastic concentrations on the bioavailability of copper and zinc in soil. The relationship between the availability of heavy metals in soil assessed by chemical methods (soil fractionation) and the bioavailability of copper and zinc assessed by biological methods (accumulation in maize and cucumber leaves) in relation to the concentration of microplastics. The results showed that copper and zinc in soil shifted from stable to effective fraction with increasing polystyrene concentrations, which would increase the toxicity and bioavailability of heavy metals. When the concentration of polystyrene microplastics increased, copper and zinc accumulation in plants increased, chlorophyll a and chlorophyll b decreased, and malondialdehyde increased. It is shown that the addition of polystyrene microplastics promoted the toxicity of copper and zinc and inhibited plant growth.

Biogeochemical behaviour of cadmium in sediments and potential biological impact on mangroves under anthropogenic influence: A baseline survey from a protected nature reserve

Cadmium is a toxic element and its effects are well understood for human health, but its biogeochemical behaviour is still poorly studied and understood in natural ecosystems. This work addresses knowledge gaps concerning its presence, biogeochemical behaviour and impacts in mangrove ecosystems. Through geochemical data and multivariate analysis (i.e., factor and cluster analysis) of data from mangroves of Isla del Carmen, one of the largest extents in Mexico we explored the biogeochemical behaviour of Cd, a potentially toxic element, to identify its anthropogenic sources and interactions with sediments. Pollution indices, including enrichment factor (EF), geo-accumulation index (Igeo), sediment quality guidelines (SQG) and toxicological studies were used to assess the biological impacts of Cd and infer the natural levels tolerated by mangrove trees that form the basis of this natural ecosystem. Our results highlighted that Cd accumulation is driven by interactions between organic matter (OM), sulphur and fine particles; whereas enrichment factor showed values of 6.9 (EF) and 3.5 (EF) associated with point sources and ranged between 2 and 2.9 (EF) in relation to non-point sources. Finally, our geochemical approach revealed that Cd enrichment originates from urban activities and from the poor management of urban residuals.

Assessment of role of rhizosphere process in bioaccumulation of heavy metals in fine nutritive roots of riparian mangrove species in river Hooghly: Implications to global anthropogenic environmental changes

Biota of coastal estuarine habitats of tropics and subtropics are extremely vulnerable. In the study, we have investigated the role of rhizosphere process in bio-accumulation of heavy metals in fine nutritive roots of riparian mangroves at eleven sampling locations of river Hooghly. The rhizospheric sediment of river Hooghly was accumulating HMs due to the presence of organic content and anthropogenic inputs. The mean EF (2.03-8.3), Igeo (-2.27-0.71), and CF (0.62-2.53) values signifies the enrichment of HMs in sediment fine fraction (<62.5 μm) whereas, the mean PLI (0.83 to 1.18) indicates gradual environmental degradation of river Hooghly. Low BCF observed in the river Hooghly might be due to barrier to hypodermal structures and/or any prevailing mechanism of saturation of HMs. However, BCF > 1 for Al, Cu, Cr, Mn, and Zn, signifies the phyto-remediation potential of riparian mangroves to mitigate amplified global anthropogenic environmental changes.

Seasonal variation and mobility of trace metals in the beach sediments of NW Borneo

Miri city has a dynamic coastal environment, mainly influenced by intensive sedimentation from the Baram River and excessive trace metal loading by the Miri River, which are significant environmental concerns. As the mobility, bioavailability, and toxicity of the trace metals in the sediments are largely controlled by their particulate speciation, the modified BCR sequential extraction protocol was applied to determine the particulate speciation of trace metals in the coastal sediments of Miri, to unravel the seasonal geochemical processes responsible for known observations, and to identify possible sources of these trace metals. The granulometric analysis results showed that littoral currents aided by the monsoonal winds have influenced the grain size distribution of the sediments, enabling us to divide the study area into north-east and south-west segments where the geochemical composition are distinct. The Cu (>84%) and Zn (82%) concentrations are predominantly associated with the exchangeable fraction, which is readily bioavailable. Pb and Cd are dominant in non-residual fractions and other metals viz., Fe, Mn, Co, Ni, and Cr are dominant in the residual fraction. Using Pearson's correlation and factor analysis, the major mechanisms controlling the chemistry of the sediments are identified as association of Cu and Zn with fine fraction sediments, sulphide oxidation in the SW segment of the study area, atmospheric fallout of Pb and Cd in the river basins, precipitation of dissolved Fe and Mn supplied from the rivers and remobilization of Mn from the coastal sediments. Based on various pollution indices, it is inferred that the coastal sediments of NW Borneo are contaminated with Cu and Zn, and are largely bioavailable, which can be a threat to the local aquatic organisms, coral reefs, and coastal mangroves.

Impact of municipal solid waste dumpsites on trace metal contamination levels in the surrounding area: a case study in West Africa, Abidjan, Cote d'Ivoire

The impact of uncontrolled municipal dumping sites on metal contamination in the surrounding waters, sediments, and soils are of great concern in many developing countries. Total concentrations of trace metals Cd, Zn, Cu, Pb, Ni, and Co were measured in 33 sediments collected in the vicinity of the Akouedo dumpsite (Abidjan, Cote d'Ivoire) and in a baseline station. The Cu, Zn, Cd, and Pb concentrations in surface sediments around the dumpsite were at least three times higher than those at the reference station, suggesting that the Akouedo dumping site is a significant contamination source of these metals to the surrounding sediments. The extent of contamination affects sediment as deep as 100 cm. Sediment pH and total organic carbon content control the distribution of Cu, Zn, and Cd in subsurface sediments. Significant Cd, Zn, and Cu enrichments were measured at the dumpsite and its surrounding environment. Zn concentrations in the sediments might cause high ecological risks at 46% of the samples based on the sediment quality guidelines (SQGs). Single and sequential extraction results showed a low mobility rate of Cd, Cu, Pb, and Ni from sediments around the dumpsite. However, the results suggest that the high total metal concentrations in the dumpsite sediments have resulted in a significant metal load in the surrounding environment.

Geochemical fractionation study in combination with equilibrium based chemical speciation modelling of Cd in finer sediments provide a better description of Cd bioavailability in tropical estuarine systems

Geochemical fractionation study of cadmium (Cd) in combination with equilibrium based chemical speciation modelling (visual MINTEQ) in finer sediment samples (silt and clay portion), provided a better description of Cd bioavailability for sessile organisms (like oysters) in the Zuari estuary, west coast of India. A substantial fraction of total Cd in the finer sediment samples was present as water soluble, exchangeable and carbonate/bicarbonate forms and showed a strong positive relationship with Cd-bioaccumulation in oysters (Magallana sp.) from the study area. Cadmium bioaccumulation (ranged from 2.4-7.9 mg·kg^-1) in soft tissues of the edible oyster was high (higher than the maximum permissible limit for human consumption) throughout the study period of one year. Equilibrium based speciation modelling suggest that sedimentary CdCl₂, CdCl⁺ and Cd²⁺ were responsible for Cd bioaccumulation in the oysters. This study describes that combination of geochemical fractionation study of metals in finer sediments and equilibrium based speciation modelling can be very useful in comprehending link between sedimentary metal speciation and its bioaccumulation in sessile organisms.

Copper dynamics in a tropical estuarine system during dry season

This is the first study to comprehend copper (Cu)-dynamics in a monsoon fed Indian estuarine system (the Mandovi estuary from the central west coast of India). Distribution and speciation of Cu in estuarine sediment, pore water, suspended particulate matter (SPM) and water column was used to understand geochemical cycling of Cu in the estuary. Geochemical fractionation study reveals that sedimentary organic carbon (C_org) was the major hosting phase for non-residual Cu in the sediments. Experimental analysis and chemical speciation modelling suggests that leaching of sedimentary Cu²⁺, CuCO₃ and a fraction of Cu-C_org complexes increased Cu-concentrations in the pore water towards the downstream of the estuary. Dissolved Cu concentration in overlying water column was observed to increase with increasing Cu concentrations in the pore water. This study suggests that chemical speciation of sedimentary Cu play key role in controlling its distribution and dynamics in the tropical estuarine system during dry period.

Evidence for increasing anthropogenic Pb concentrations in Indian shelf sediments during the last century

India is industrializing rapidly and with this there comes higher releases of contaminants into the environment. Change in Pb deposition over the last century on the eastern (off Andhra Pradesh) and western (off Karnataka) shelves of India was investigated based on the data extracted from two sediment cores covering the past ~114 and ~145 yrs. The variations of the total Pb content, its enrichment factor, and concentrations of non-residual Pb in both the sediment cores document that there was a gradual increase in anthropogenic Pb input into the coastal sediments of India over the last century. Sediment leachates were used to monitor the increase in anthropogenic Pb input and its Pb isotope composition. The anthropogenic end member composition of the western shelf sediment location (²⁰⁶Pb/²⁰⁷Pb: 1.105; ²⁰⁶Pb/²⁰⁸Pb: 2.149) was significantly less radiogenic than the eastern shelf isotopic composition (²⁰⁶Pb/²⁰⁷Pb: 1.145; ²⁰⁶Pb/²⁰⁸Pb:2.120). A binary mixing model suggests that Pb emitted from the heavy industries (e.g., ore mining, Pb processing and smelting plants) of India has been the major source of anthropogenic Pb to the sediments of western continental shelf. In contrast, the isotopic signatures suggest that coal combustion is responsible for elevated anthropogenic Pb levels in the sediments from the eastern shelf of India.

Spring-neap tides influence on bioavailability of metals and bioaccumulation in edible biota of the Zuari (tropical) Estuary

Role of spring and neap tides on metal bioavailability and bioaccumulation in edible biota was studied in the Zuari Estuary. Moderate to very high range of contamination factor for Fe, Mn, Cr, Zn, Cu, Cd, and Pb at one or more stations and tides suggesting their anthropogenic origin. The anthropogenic input of metals was supported by pollution load index. Relatively high bioavailable concentration of Fe, Mn, Cr, Zn, Cu, Cd, and Pb indicated their toxicity to biota. Total metal concentration, viz., Fe, Mn, Cr, Zn, Cu and Cd, and bioavailable content Mn, Cd, and Pb were higher during spring tide than neap tide at one or more stations which revealed their low mobility under flooded conditions. The above observation was well supported by higher concentration of Fe, Mn, Cr, Zn, Cu, and Pb in Polymesoda erosa at the middle estuary during neap tide than subsequent spring tide. Further, an increase in concentration of metals bound to certain bioavailable fractions toward the surface of the cores revealed their possible bioavailability to the biota with changes in the physicochemical properties of the Zuari estuary. Biota sediment accumulation factor revealed macro level accumulation of Cd and suggested its toxicity to marine biota.

Distribution, contamination status and bioavailability of trace metals in surface sediments along the southwest coast of India

This study investigates the influence of upwelling induced seasonal hypoxia in the sediment-water interface on the distribution, bioavailability and geochemical partitioning of selected trace metals in surficial sediments along the southwest coast of India based on two successive cruises. The first cruise was during the southwest monsoon (SWM) season when coastal waters exhibited intermittent bottom hypoxia due to upwelling. The second cruise during the northeast monsoon (NEM) season was characterised by a uniformly warm and well-oxygenated water column in the study region. The results showed that grain size, organic carbon and Fe are the major factors influencing the distribution of trace metals in the surface sediments. Based on the geochemical indices (contamination factor, enrichment factor and geo-accumulation factor), the study region appears to be moderately contaminated by Ni, Cr, and Pb. Based on the ecological risk assessment criteria, the enrichment of Pb, Cr and Ni may cause adverse effects on the benthic organisms. The fractionation studies demonstrated that the major pathway of metal deposition in the sediment is lithogenic. The data also showed that labile and organic fractions are the second dominant forms, while other fractions (exchangeable and carbonate) are insignificant. The consistency in the reactive Fe concentrations during SWM and NEM could be due to the absence of Fe dissolution in sediments under mild reducing condition (intermittent hypoxia). In addition to the above, an enrichment of organic matter also leads to increased deposition of trace metals in sediments. Conversely, the secondary phase enrichment factor and risk assessment code calculated based on the metal fractionation data indicated low risk and contamination along the southwest coast of India except for Zn that showed moderate contamination in some transects. The study provides the need for regular geochemical assessment to control metal pollution in the coastal environment, which is a major resource of the fishery.

Can severe drought periods increase metal concentrations in mangrove sediments? A case study in eastern Brazil

Mangrove ecosystems are essential to society, providing ecological and economic services, and play a crucial role in the geochemical land-ocean interface as a sink for potentially toxic metals. This study assessed metals (Al, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn) and arsenic in sediments from three mangrove zones (Tidal Flat, Rhizophora mangle L. and Avicennia schaueriana Stapf & Leechman ex Moldenke forests) during two seasons: spring of 2015 and autumn of 2016, with the latter being a severe drought year. Overall results suggest that Fe/Mn oxyhydroxides and clay minerals control the distribution of metal and arsenic in the Tidal Flat zone. In the mangrove forest however, sulfur and organic matter dominate complexation, with Fe mainly present as insoluble sulfide, and As, Cd, Cu and Zn as metal sulfides or organometallic complexes. In the autumn of 2016, all elements except Cd and Pb had lower concentrations compared to the spring of 2015. Cd and Pb were probably transferred from sources other than mangrove sediments, due to increased saline water intrusion, a consequence of reduced riverine flow, and precipitated in the Rhizophora mangle and Avicennia schaueriana mangrove forests. This increase of Cd and Pb in the mangrove forest suggests potential storage of metal contaminants in the organic rich areas, a change in availability and potential toxicity to fauna and flora and a need for regulatory responses to sediment quality. These results indicate a change in sediment metal contaminant dynamics with the increasing occurrence of extreme weather events - an increased risk to the ecosystem.

Variable protein expression in marine-derived filamentous fungus Penicillium chrysogenum in response to varying copper concentrations and salinity

Copper is one of the essential trace dietary minerals for all living organisms, but is potentially toxic at higher concentrations, mainly due to the redox reactions in its transition state. Tolerance of microbes towards copper is primarily attributed to chelation and biosorption. In this study, marine-derived filamentous fungi were evaluated for their ability to remove Cu(ii) from a culture medium. Further, the cellular response of a select isolate to salinity stress (0, 35 and 100 PSU) and Cu(ii) stress (0, 100, and 500 ppm) was studied using the peptide mass fingerprinting technique, which revealed expression of 919 proteins, of which 55 proteins were commonly expressed across all conditions. Housekeeping proteins such as citrate synthase, pyruvate carboxylase, ribosomal proteins, ATP synthases, and more were expressed across all conditions. Reactive oxygen species scavenging proteins such as glutaredoxin, mitochondrial peroxiredoxins and thioredoxins were expressed under Cu(ii) and salinity stresses individually as well as in combination. Up-regulation of glutaredoxin under Cu(ii) stress with fold change values of 18.3 and 13.9 under 100 ppm and 500 ppm of Cu(ii) indicated active scavenging of free radicals to combat oxidative damage. The common mechanisms reported were enzymatic scavenging of free radicals, activation of DNA damage and repair proteins and probable intracellular metal chelation. This indicated multiple stress mechanisms employed by the isolate to combat the singular and synergistic effects of Cu(ii) and salinity stress.

Fractionation of trace metals in coastal sediments from Trinidad and Tobago, West Indies

Sequential extraction was used to determine the geochemical distribution of trace metals in coastal sediments from Trinidad and Tobago. The results showed that there was considerable variation in the bioavailability, mobility and ecological risk of the metals determined. Cadmium had very high ecological risk: 57-88% of cadmium was associated with the exchangeable and carbonate bound metal fraction (F1). Ecological risk decreased in the order manganese> nickel> lead> zinc. Copper had the lowest ecological risk: lowest percentages of copper were associated with F1 (1-15%) and F2 (3-15%), while considerable percentages (48-55%) were associated with the residual fraction. Management of the risks posed by these metals in the marine environment requires a holistic approach including reduction in trace metal inputs from point and non-point sources of pollution, particularly off the west coast of Trinidad, and public education on the impacts of trace metals in the environment and on human health.

Assessment of a coastal lagoon metal distribution through natural and anthropogenic processes (SE, Brazil)

The present study intends to assess the metal pollution of a eutrophic coastal lagoon, analyzing the long-term and actual metal content in surface sediments, suspended particles, aquatic macrophyte and fish species, and the loads emitted from natural processes and anthropogenic sources, including the relative emission of domestic untreated sewage. Distribution indicated contamination of suspended particles with Cd and the predominance of Pb in the bioavailable form in surface sediments which may explain Cd and Pb contamination in fish. Domestic untreated sewage was an important source of Cu and due to the lagoon's management, this source may be increasing the metal content in the lagoon's surface sediments. Soil loss, atmospheric deposition and solid waste disposal also contributed to metal inputs to the lagoon. Extensive contamination has been prevented by the lagoon's management such as sandbar opening. Metal retention within the watershed soils reduce the effective metal transference and lagoon pollution.

Combination of DGT and fluorescence spectroscopy for improved understanding of metal behaviour in mangrove wetland

Understanding bioavailable metal behaviour in situ is critical for pollution evaluation and contaminant management in mangrove wetland. Here, the diffusive gradients in thin films technique (DGT) was used for characterizing the (bio)available portions of Cr, Zn, Pb, Cu, Fe and Mn in two mangrove wetlands affected by industrial waste discharges (Jiulong Estuary) and domestic discharges (Zhangjiang Estuary), in Fujian Province, China. In addition, fluorescence excitation emission matrices-parallel factor analysis (EEM-PARAFAC) was applied for characterizing the occurrence and behaviour of dissolved organic matter (DOM) in soil solution, as well as their feasibility for assessing behaviours of metals. The results demonstrated that the combination of DGT and EEM, which are well suitable for studying DOM impacted metal behaviors in mangrove sediments. Discharge of difference wastewater into the mangrove wetlands of Jiulong and Zhangjiang Estuaries, gave rise to the DGT-labile metal concentration of Zn > Cu > Cr > Pb and Zn > Cr > Pb > Cu, respectively. A variety of humic-like fluorescent components was characterized here, providing valuable insights into the chemical composition of DOM in rhizosphere and bulk sediment. Terrestrial humic-like compounds indicated a different binding affinity for heavy metals in mangrove sediments. These findings are useful for the future understanding of the metal speciation and molecular binding mechanisms in such mangrove wetlands.

Assessment of metal enrichment and bioavailability in mangrove and mudflat sediments of the tropical (Zuari) estuary, west coast of India

Mangrove and mudflat sediment cores at the confluence point of the Cumbarjua Canal and the Zuari River were collected and analyzed to assess metal enrichment and bioavailability, with the background of significant bioaccumulation reported in earlier studies within the Zuari Estuary, a recipient of open-cast mining waste containing Fe and Mn. Metals were enriched in mangrove and mudflat sediments due to additions from natural and anthropogenic sources. Contamination factor showed moderate degree of contamination of Fe, Mn, Cu, and Co in mangroves while of Fe, Mn, and Co in mudflats. Pollution load index suggested metal pollution in the sediments of the Zuari Estuary. Metal speciation study indicated largely lithogenic source of Fe (in mudflats), Cu, Zn, and Co, whereas abundant bioavailable Fe (in mangroves) and Mn (in both mangroves and mudflats) suggest their possible mobilization, preferential accumulation, and bioavailability. Further, sediment quality values indicated toxicity of bioavailable Mn and Co, and risk assessment code revealed medium risk of Mn to sediment associated organisms.

Bioaccumulation of trace metals in the coastal Borneo (Malaysia) and health risk assessment

The concentration of nine trace elements were analyzed in the different tissue organs of commonly available crabs (Portunus sanguinolentus, Portunus pelagicus and Scylla serrate) and bivalve (Polymesoda erosa) species collected from the Miri coast, Borneo in order to evaluate the potential health risk by consumption of these aquatic organisms. Among the analyzed organs, metal accumulation was higher in the gill tissues. The essential (Cu and Zn) and non-essential (Pb and Cd) elements showed the highest (i.e. Zn) and lowest concentrations (i.e. Cd) in their tissue organs, respectively. The estimated daily intake and hazard indices of all metals in the muscle indicate that the measured values were below the provisional tolerable daily intake suggested by the joint FAO/WHO Expert Committee on Food Additives. Compared to Malaysian and international seafood guideline values the results obtained from the present study are lower than the permissible limits and safe for consumption.

Distributions and Sources of PAHs and OCPs in Surficial Sediments of Edremit Bay (Aegean Sea)

In this study, levels, distributions, and sources of polycyclic aromatic hydrocarbons (18 compounds) and organochlorine pesticides (19 compounds) in surface sediments of 14 stations from Edremit Bay (Aegean Sea) were investigated in April and November 2015. ΣPAH concentrations (0.65-175 ng/g) in Edremit Bay sediments indicated low pollution. ΣPAH levels were decreased in the order of inner (81.1 ± 47.0 ng/g), northern (48.4 ± 15.9 ng/g), and southern (19.0 ± 15.8 ng/g) bays. p,p'-DDE was the only organochlorine pesticide detected in Edremit Bay sediments and found between nd to 1.16 ng/g dw. According to sediment quality guidelines, PAHs and p,p'-DDE levels in Edremit Bay were below the threshold effect level, effect range low, and threshold effect concentration limits and the sediments have no potential ecological risks. Two- to 3-ring PAHs were found at higher levels than 4- to 5-ring PAHs. Molecular PAHs ratios and Principal Component Analysis-Multiple Linear Regression analyses indicated combustion of wood-coal and vehicle emissions might have contributed to PAH levels in the bay.

State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques

Polycyclic aromatic hydrocarbons (PAHs) are amongst the most abundant contaminants found in the aquatic environment. Due to their toxicity and carcinogenicity, their sources, fate, behaviour, and cleanup techniques have been widely investigated in the last several decades. When entering the sediment-water system, PAH fate is determined by particular PAH and sediment physico-chemical properties. Most of the PAHs will be associated with fine-grained, organic-rich, sediment material. This makes sediment an ultimate sink for these pollutants. This association results in sediment contamination, and in this manner, sediments represent a permanent source of water pollution from which benthic organisms may accumulate toxic compounds, predominantly in lipid-rich tissues. A tendency for biomagnification can result in critical body burdens in higher trophic species. In recent years, researchers have developed numerous methods for measuring bioavailable fractions (chemical methods, non-exhaustive extraction, and biomimetic methods), as valuable tools in a risk-based approach for remediation or management of contaminated sites. Contaminated sediments pose challenging cleanup and management problems, as conventional environmental dredging techniques are invasive, expensive, and sometimes ineffective or hard to apply to large and diverse sediment sites. Recent studies have shown that a combination of strategies including in situ approaches is likely to provide the most effective long-term solution for dealing with contaminated sediments. Such in situ approaches include, but are not limited to: bioaugmentation, biostimulation, phytoremediation, electrokinetic remediation, surfactant addition and application of different sorbent amendments (carbon-rich such as activated carbon and biochar) that can reduce exposure and limit the redistribution of contaminants in the environment.

Metals geochemistry and ecological risk assessment in a tropical mangrove (Can Gio, Vietnam)

Mangrove sediments act as natural biogeochemical reactors, modifying metals partitioning after their deposition. The objectives of the present study were: to determine distribution and partitioning of metals (Fe, Mn, Ni, Cr, Cu, Co and As) in sediments and pore-waters of Can Gio Mangrove; and to assess their ecological risks based on Risk Assessment Code. Three cores were collected within a mudflat, beneath Avicennia alba and Rhizophora apiculata stands. We suggest that most metals had a natural origin, being deposited in the mangrove mainly as oxyhydroxides derived from the upstream lateritic soils. This hypothesis could be supported by the high proportion of metals in the residual fraction (mean values (%): 71.9, 30.7, 80.7, 80.9, 67.9, 53.4 and 66.5 for Fe, Mn, Ni, Cr, Cu, Co, and As respectively, in the mudflat). The enrichment of mangrove-derived organic matter from the mudflat to the Rhizophora stand (i.e. up to 4.6% of TOC) played a key role in controlling metals partitioning. We suggest that dissolution of Fe and Mn oxyhydroxides in reducing condition during decomposition of organic matter may be a major source of dissolved metals in pore-waters. Only Mn exhibited a potential high risk to the ecosystem. Most metals stocks in the sediments were higher in the Avicennia stand than the Rhizophora stand, possibly because of enhanced dissolution of metal bearing phases beneath later one. In a context of enhanced mangrove forests destruction, this study provides insights on the effects of perturbation and oxidation of sediments on metal release to the environment.

Seasonal variations and relationships between environmental parameters and heavy metal concentrations in tissues of Crassostrea species and in its ambience from the tropical estuaries

This study aimed to evaluate the relationship between physicochemical parameters and heavy metal (Cu, Ni, Pb, and Cd) concentrations from sediment, seawater, and its accumulation in tissues of oyster species (Crassostrea madrasensis and C. gryphoides) from the three sites (Chicalim Bay (CB), Nerul Creek (NC), Chapora Bay (ChB)) along the Goa coast (India). Results showed enrichment of Cu and Ni in sediment exceeding the effect range low (ERL) level. The higher concentrations of Cu and Ni in sediments and in suspended particulate matter (SPM) from all the study sites are indicative of severe contamination of estuarine and associated habitats. Moreover, particulate Ni (at all the sites), Cu (at NC and ChB), Pb (at NC), and Cd (at CB and NC) concentrations were recorded more than its total loadings in surface sediment. Concentration of Cu and Cd in oyster tissue was several folds higher than its concentration in ambience. Further, this study showed that the levels of metal in oysters and their ambient environment were higher during the monsoon season. Hence, the consumption of oysters needs to be considered carefully with respect to the health hazards posed by the elevated levels of metal contaminants in certain seasons. The present study concludes that metals associated with the particulate matter in water column are the main source of metal accumulation in oyster. It is also suggested that concentration of metal pollutants in coastal and estuarine water bodies should be monitored regularly to ensure the acceptable limits of metal concentrations.

Iron plaque formation and heavy metal uptake in Spartina alterniflora at different tidal levels and waterlogging conditions

Tidal flat elevation in the estuarine wetland determines the tidal flooding time and flooding frequency, which will inevitably affect the formation of iron plaque and accumulations of heavy metals (HMs) in wetland plants. The present study investigated the formation of iron plaque and HM's (copper, zinc, lead, and chromium) accumulation in S. alterniflora, a typical estuarine wetland species, at different tidal flat elevations (low, middle and high) in filed and at different time (3, 6, 9, 12 h per day) of waterlogging treatment in greenhouse conditions. Results showed that the accumulation of copper, zinc, lead, and chromium in S. alterniflora was proportional to the exchangeable fraction of these metals in the sediments, which generally increased with the increase of waterlogging time, whereas the formations of iron plaque in roots decreased with the increase of waterlogging time. Under field conditions, the uptake of copper and zinc in the different parts of the plants generally increased with the tidal levels despite the decrease in the metals' exchangeable fraction with increasing tidal levels. The formation of iron plaque was found to be highest in the middle tidal positions and significantly lower in low and high tidal positions. Longer waterlogging time increased the metals' accumulation but decreased the formation of iron plaque in S. alterniflora. The binding of metal ions on iron plaque helped impede the uptake and accumulation of copper and chromium in S. alterniflora.

Effects of different humic substances concentrations on root anatomy and Cd accumulation in seedlings of Avicennia germinans (black mangrove)

Mangrove areas are among most threatened tropical ecosystems worldwide. Among polluting agents Cadmium is often found in high concentrations in mangrove sediments. Humic substances, complex biomolecules formed in soil and sediments during animal and plant residuals decomposition, have a known biostimulant activity and can be adopted to counteract various plant stresses. This study explores, in controlled conditions, the effect of humic substances on Avicennia germinans seedlings, with or without cadmium contamination. Humic compounds significantly changed plant root architecture, and, when coupled with cadmium, root anatomy and Cortex to Vascular Cylinder diameter ratio. These modifications led to lower Cd uptake by humic substances-treated plants. Humic substances amendment could be effective, depending on their concentrations, on improving plant health in mangrove areas, for forest recuperation and/or dredged sediments phytoremediation purposes.

Potential of Marine-Derived Fungi to Remove Hexavalent Chromium Pollutant from Culture Broth

Chromium (Cr) released from industrial units such as tanneries, textile and electroplating industries is detrimental to the surrounding ecosystems and human health. The focus of the present study was to check the Cr(VI) removal efficiency by marine-derived fungi from liquid broth. Amongst the three Cr(VI) tolerant isolates, #NIOSN-SK56-S19 (Aspergillus sydowii) showed Cr-removal efficiency of 0.01 mg Cr mg^-1 biomass resulting in 26% abatement of total Cr with just 2.8 mg of biomass produced during the growth in 300 ppm Cr(VI). Scanning Electron Microscopy revealed aggregation of mycelial biomass with exopolysaccharide, while Electron Dispersive Spectroscopy showed the presence of Cr₂O₃ inside the biomass indicating presence of active Cr(VI) removal mechanisms. This was further supported when the Cr(VI) removal was monitored using DPC (1,5-diphenylcarbazide) method. The results of this study point to the potential of marine-derived fungal isolates for Cr(VI) removal.

Major and trace metals in suspended and bottom sediments of the Mandovi and Zuari estuaries, western India: distribution, source, and pollution

Major elements and trace metals in suspended sediments along transect stations of the Mandovi and Zuari estuaries showed three types of distribution: (a) high concentrations of most metals (Al, Fe, Mn, Cr, Pb, Cu, Ni, Zn, Co, Sc, Mo, and U) in the upper estuary and their decreasing concentrations seaward in every season, (b) lower concentrations of some metals (Mg, Cr, Zr, V, Al, Th) in the upper estuary and bay and their increased concentrations in the lower estuary, and (c) higher concentrations of some metals (Cu, Ni, Zn, Pb, and Cr) in the upper estuary and bay and their decreased concentrations in the lower estuary. Mn was the most significant pollutant in both the estuaries. The Zn, Cr, Fe, and Mo in Mandovi during the monsoon and post-monsoon and, Pb, Ni, and Cr in Zuari during the post- and pre-monsoons were in the range "moderately to heavily polluted." The pollution load index of metals was high at upstream stations, with higher values in Mandovi during monsoon and Zuari during the post- and pre-monsoons. Most trace metals were correlated with Fe and Mn indicating their association primarily with Fe-Mn ore material. The principal component analysis indicated natural and anthropogenic inputs and the latter was predominantly related to ore material in both the estuaries. The distribution factor was high for Al, Mg, Zr, Th, and U in < 2-μm fraction and Cr, Cu, Ni, Zn, Co, V, Sc, and Zr in 2-4-μm size fraction sediments suggesting two sources of sediments. More than 60% concentrations of all trace metals were associated with < 2-μm fraction sediments. The distribution of trace metals along transect was affected by the physico-chemical conditions of the estuary, grain size of sediments, and anthropogenic contribution of metals.

Comprehensive and comparative ecotoxicological and human risk assessment of polycyclic aromatic hydrocarbons (PAHs) in reef surface sediments and coastal seawaters of Iranian Coral Islands, Persian Gulf

The concentration and spatial distribution along with ecotoxicological risk of 30 polycyclic aromatic hydrocarbons were investigated in the reef surface sediments (RSSs) and coastal seawater (CSW) of ten coral Islands from the Persian Gulf, Iran, in January 2015. For all sampling sites, assessment of ecological risk was undertaken using several approaches. Mean concentration of ∑30PAHs varied between 70 and 884ngL^-l with an overall mean value of 464ngL^-l in the CSW, while the RSS ranged from 274 to 1098ngg^-1dw with a total average of 619ngg^-1dw. The results showed a gradient in PAH concentration and toxicity estimates from the northern Hormoz site increasing to the eastern Kharg site. Most of the toxicity estimates were in the moderate range or less than risk values for damage to the marine environment. The calculated Dermal Hazard Quotient (HQs), the sum of HQs (HI) and other cancer risk values of most compounds were less than safety values at most sites. It means that the possibility of negative effects of PAHs via dermal absorption from sediments for children and adults is low. Some sampling sites studied have already been impacted with hazardous pollutants for an extended period of time and evidence from this investigation demonstrates that mixtures of PAHs may be carcinogenic to humans, especially in the western part of the Gulf.

Kinetic and equilibrium based fractionation study of Pb in continental shelf sediment of India

Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0±0.6 to 30.4±0.1mg·kg^-1 and 15.9±0.3 to 36.7±0.4mg·kg^-1 in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~24% of total Pb) than the western shelf sediments (~14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in the coastal sediment of India.

Geochemical fractionation and pollution assessment of Zn, Cu, and Fe in surface sediments from Shadegan Wildlife Refuge, southwest of Iran

This research focuses on the fractionation and distribution patterns of heavy metals (Zn, Cu, and Fe) in surficial sediments collected from Shadegan Wildlife Refuge, the biggest wetland in southern part of Iran, to provide an overall classification for the sources of metals in the study area using a sequential extraction method. For this purpose, a four-step sequential extraction technique was applied to define the partitioning of the metals into different geochemical phases of the sediment. The results illustrated that the average total level of Zn, Cu, and Fe in surface sediments were 55.20 ± 16.04, 22.86 ± 5.68, and 25,979.01 ± 6917.91 μg/g dw, respectively. On the average, the chemical partitioning of all metals in most stations was in the order of residual >oxidizable-organic > acid-reducible > exchangeable. In the same way, the results of calculated geochemical indices revealed that Cu, Zn, and Fe concentrations are mainly influenced by lithogenic origins. Compared with consensus-based SQGs, Cu was likely to result in occasionally harmful biological effects on the biota.

Geochemical source, deposition, and environmental risk assessment of cadmium in surface and core sediments from the Bohai Sea, China

Geochemical sources, spatio-temporal distribution, and associated environmental risk of Cd in the Bohai Sea were investigated using data from 405 surface sediment samples and two sediment cores. Local point Cd sources, TOC content, and currents are the main controlling factors of Cd distribution. The contribution of Cd from river discharge surpasses that from atmospheric deposition. Sediment-quality guidelines, enrichment factors, and chemical fraction analysis were used to assess metal toxicity in the collected sediments. Results show that Bohai Sea sediments have a moderate Cd enrichment level. This enrichment poses a high risk due to the relatively high mobility and bioavailability of Cd despite measured levels below sediment-quality guidelines at most stations. Vertical profiles of Cd concentrations, Al-normalized enrichment factors, and excess burial fluxes combined with ²¹⁰Pb dating reveal the history of Cd pollution in the Bohai Sea over the last century. Data show Cd unvaried before the 1800s, a slight increase from the 1800s to the late 1950s, a decrease from the late 1960s to the 1970s, and an increase from the 1980s to 2001, including a relatively high value in 1998. Historic variation in Cd is closely associated with both natural and anthropogenic activities.

Microplastics and potentially toxic elements in coastal sediments of Iran's main oil terminal (Khark Island)

Marine pollutants are becoming a growing concern due to their ecological consequences. This study investigates the potential risk posed by microplastics and toxic elements in coastal sediments of Khark Island, the main oil export hub of Iran. Principal component biplots exhibited a significant positive correlation between microplastic quantities (ranging in shape and color) and concentration of heavy metals with industrial activity. Source identification of the heavy metals indicated both natural and anthropogenic origin. Quality and risk assessment of the sediments revealed low to moderate pollution of Zn, Mo, Pb, Cu, Cd and As in some stations. Results of metal fractionation in sediments demonstrated that Cd, Mn, Zn, As and Pb are capable of posing a serious ecological risk due to potential bioavailability. Microplastics, mostly fragments and fibers, were detected in all sediment samples (ranging from 59 to 217 items/200 g dry sediment). A relatively good significant linear relationship exists between microplastic quantities and potentially toxic element/polycyclic aromatic hydrocarbon concentrations in coastal sediments. The results of this study confirmed the key role of microplastics as a "potential contaminant vector" for other types of pollutants.

Effects of bottom water dissolved oxygen variability on copper and lead fractionation in the sediments across the oxygen minimum zone, western continental margin of India

This study describes the effect of varying bottom-water oxygen concentration on geochemical fractionation (operational speciation) of Cu and Pb in the underneath sediments across the oxygen minimum zone (Arabian Sea) in the west coast of India. Both, Cu and Pb were redistributed among the different binding phases of the sediments with changing dissolved oxygen level (from oxic to hypoxic and close to suboxic) in the bottom water. The average lability of Cu-sediment complexes gradually decreased (i.e., stability increased) with the decreasing dissolved oxygen concentrations of the bottom water. Decreasing bottom-water oxygen concentration increased Cu association with sedimentary organic matter. However, Pb association with Fe/Mn-oxyhydroxide phases in the sediments gradually decreased with the decreasing dissolved oxygen concentration of the overlying bottom water (due to dissolution of Fe/Mn oxyhydroxide phase). The lability of Pb-sediment complexes increased with the decreasing bottom-water oxygen concentration. This study suggests that bottom-water oxygen concentration is one of the key factors governing stability and lability of Cu and Pb complexes in the underneath sediment. Sedimentary organic matter and Fe/Mn oxyhydroxide binding phases were the major hosting phases for Cu and Pb respectively in the study area. Increasing lability of Pb-complexes in bottom sediments may lead to positive benthic fluxes of Pb at low oxygen environment.

Trace metal geochemistry in mangrove sediments and their transfer to mangrove plants (New Caledonia)

Because of their physico-chemical inherent properties, mangrove sediments may act as a sink for pollutants coming from catchments. The main objective of this study was to assess the distribution of some trace metals in the tissues of various mangrove plants developing downstream highly weathered ferralsols, taking into account metals partitioning in the sediment. In New Caledonia, mangroves act as a buffer between open-cast mines and the world's largest lagoon. As a result of the erosion of lateritic soils, Ni and Fe concentrations in the sediment were substantially higher than the world average. Whatever the mangrove stand and despite low bioaccumulation and translocations factors, Fe and Ni were also the most abundant metals in the different plant tissues. This low bioaccumulation may be explained by: i) the low availability of metals, which were mainly present in the form of oxides or sulfur minerals, and ii) the root systems acting as barriers towards the transfer of metals to the plant. Conversely, Cu and Zn metals had a greater mobility in the plant, and were characterized by high bioconcentration and translocation factors compared to the other metals. Cu and Zn were also more mobile in the sediment as a result of their association with organic matter. Whatever the metal, a strong decrease of trace metal stock was observed from the landside to the seaside of the mangrove, probably as a result of the increased reactivity of the sediment due to OM enrichment. This reactivity lead to higher dissolution of bearing phases, and thus to the export of dissolved trace metals trough the tidal action. Cu and Zn were the less concerned by the phenomenon probably as a result of higher plant uptake and their restitution to the sediment with litter fall in stands where tidal flushing is limited.

Aliphatic and polycyclic aromatic hydrocarbons risk assessment in coastal water and sediments of Khark Island, SW Iran

The potential sources and ecotoxicological risks of 26 aliphatic hydrocarbons (AHs), 16 polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs) were investigated in coastal water and sediments of Khark Island, SW Iran. The major sources of the contamination were petroleum and petroleum combustion based on the PCA analysis and diagnostic indices of AHs and PAHs, and also ring classification of PAHs. The ecological risk of both individual and multiple PAHs was quite low in sediments compared with screening benchmarks. Likewise, the low concentration of TEQ, MEQ and TEQ(carc) of sediments suggest low toxicity of PAHs in the study area. However, environmental control is recommended to reduce the pollution burden of PAHs in seawater. The human health risk assessment for PAHs through dermal adsorption indicated that the possibility of negative adverse effects of PAHs in sediments is rare but swimming in the vicinity of industrial facilities should be done cautiously.

Linkage between speciation of Cd in mangrove sediment and its bioaccumulation in total soft tissue of oyster from the west coast of India

This study established a mechanistic linkage between Cd speciation and bioavailability in mangrove system from the west coast of India. High bioaccumulation of Cd was found in the oyster (Crassostrea sp.) even at low Cd loading in the bottom sediment. Bioaccumulation of Cd in the oyster gradually increased with the increasing concentrations of water soluble, exchangeable and carbonate/bicarbonate forms of Cd in the sediments. Fe/Mn oxyhydroxide phase was found to control Cd bioavailability in the sediment system. Cd-associated with sedimentary organic matter was bioavailable and organic ligands in the sediments were poor chelating agents for Cd. This study suggests that bioaccumulation of Cd in oyster (Crassostrea sp.) depends not on the total Cd concentration but on the speciation of Cd in the system.

Partitioning of metals in different binding phases of tropical estuarine sediments: importance of metal chemistry

Distribution of metals in different binding phases of estuarine sediments provides chemically significant description of metal-sediment interactions. This study describes the influences of ligand field stabilization energy (LFSE), Jahn-Teller effect, and water exchange rate (k-w) on metal distribution in different binding phases of estuarine sediments. It was found that Cu had highest affinity for organic binding phases in the studied sediments followed by Ni and Pb. However, Pb showed strong association with Fe/Mn oxide phases followed by Ni and Cu. Faster k-w of Cu (II) (1 × 10(9) s(-1)) increased the rate of complex formation of Cu(2+) ion with ligand in the organic phases. The Cu-ligand (from organic phase) complexes gained extra stability by the Jahn-Teller effect. The combined effects of these two phenomena and high ionic potential increased the association of Cu with the organic phases of the sediments than Ni and Pb. The smaller ionic radii of Ni(2+) (0.72 Å) than Pb(2+) (1.20 Å) increase the stability of Ni-ligand complexes in the organic phase of the sediments. High LFSE of Ni(II) (compared with Pb(2+) ions) also make Ni-organic complexes increasingly stable than Pb. High k-w (7 × 10(9) s(-1)) of Pb did not help it to associate with organic phases in the sediments. The high concentration of Pb in the Fe/Mn oxyhydroxide binding phase was probably due to co-precipitation of Pb(2+) and Fe(3+). High surface area or site availability for Pb(2+) ion on Fe oxyhydroxide phase was probably responsible for the high concentration of Pb in Fe/Mn oxyhydroxide phase. Increasing concentrations of Cu in organic phases with the increasing Cu loading suggest that enough binding sites were available for Cu in the organic binding phases of the sediments. This study also describes the influence of nature of sedimentary organic carbon (terrestrial and marine derived OC) in controlling these metal distribution and speciation in marine sediment.

Distribution and nature of sedimentary organic matter in a tropical estuary: An indicator of human intervention on environment

Sediment texture controls the spatial distribution of sedimentary organic matter (SOM) in the Vembanad Lake. Influences of marine derived organic matter (OM) on SOM decreased inner-wards in the northern part of the lake. However, SOM from the southern part of the lake was dominated by terrestrial OM. Marine-derived OM showed the highest affinity for the clay-sized fraction (<2 μm) of the sediment in the northern part of the lake. However, aged and humified soil-derived OM was predominant in the clay-sized fractions from the southern part. Alteration of sediment texture led to a change in the distribution pattern of SOM in the lake after bund construction. Human intervention and changes in land-use pattern were also found to influence the SOM content in the southern part of the lake.

Lead distribution in coastal and estuarine sediments around India

This study describes the geochemical distribution of lead (Pb) and identifies the critical factors that significantly control Pb distribution and speciation in coastal and estuarine sediments around India by using published data from the literature. Crustal sources influence the abundance of Pb in coastal sediment from the south-east and central-west coast of India. Parts of north-east, north-west, and south-west coast of India were polluted by Pb. Distribution of Pb in sediments, from the north-east and north-west coasts of India, were controlled by Fe-Mn oxyhydroxide mineral phases of the sediments. However, organic carbon (OC) seemed to be a dominant factor in controlling the distribution of Pb in sediments from the central-east and south-west coasts of India. The outcome of this study may help in decision-making to predict the levels of Pb from natural and anthropogenic sources and to control Pb pollution in coastal and estuarine sediments around India.