Metal Contamination In Aquatic Environment Research Articles

Exploring the Sublethal Impacts of Cu and Zn on Daphnia magna: a transcriptomic perspective

Metal contamination of aquatic environments remains a major concern due to their persistence. The water flea Daphnia magna is an important model species for metal toxicity studies and water quality assessment. However, most research has focused on physiological endpoints such as mortality, growth, and reproduction in laboratory settings, as well as neglected toxicogenomic responses. Copper (Cu) and zinc (Zn) are essential trace elements that play crucial roles in many biological processes, including iron metabolism, connective tissue formation, neurotransmitter synthesis, DNA synthesis, and immune function. Excess amounts of these metals result in deviations from homeostasis and may induce toxic responses. In this study, we analyzed Daphnia magna transcriptomic responses to IC5 levels of Cu (120 µg/L) and Zn (300 µg/L) in environmental water obtained from a pristine lake with adjusted water hardness (150 mg/L CaCO3). The study was carried out to gain insights into the Cu and Zn regulated stress response mechanisms in Daphnia magna at transcriptome level. A total of 2,688 and 3,080 genes were found to be differentially expressed (DEG) between the control and Cu and the control and Zn, respectively. There were 1,793 differentially expressed genes in common for both Cu and Zn, whereas the number of unique DEGs for Cu and Zn were 895 and 1,287, respectively. Gene ontology and KEGG pathways enrichment were carried out to identify the molecular functions and biological processes affected by metal exposures. In addition to well-known biomarkers, novel targets for metal toxicity screening at the genomic level were identified.

Assessment of health risks associated with heavy metal contamination in selected fish and crustacean species from Temsah Lake, Suez Canal

Marine pollution caused by heavy metals has emerged as a significant environmental concern, garnering increased attention in recent years. The accumulation of heavy metals in the tissues of marine organisms poses substantial threats to both marine ecosystems and human populations that rely on seafood as a primary food source. Fish and crustaceans are effective biomonitors for assessing heavy metal contamination in aquatic environments. In this study, we determined the concentrations of several heavy metals, including cadmium (Cd), lead (Pb), nickel (Ni), mercury (Hg), and tin (Sn), in four fish species (Mugil cephalus, Mugil capito, L. aurata, and Morone labrax) and five crustacean species (S. rivulatus, Cerastoderma glaucum, Paratapes undulatus, R. decussatus, Callinectes sapidus, and Metapenaeus Stebbingi) from Temsah Lake during both winter and summer seasons. To evaluate the potential ecological and health risks associated with consuming these fish and crustacean species, we calculated the metal pollution index (MPI), weekly intake (EWI), target hazard quotient (THQ), and carcinogenic risk (CR) values. The results revealed a noticeable increase in metal levels during the summer compared to winter in the studied samples. Moreover, the concentration of heavy metals in the muscles of the species generally exceeded those in the liver and gills. The MPI values indicated that Morone labrax exhibited the highest values during winter, while L. aurata showed the highest values during summer. Mugil cephalus demonstrated the lowest MPI values in both seasons. The EWI values for the studied metals were found to be lower than the corresponding tolerable weekly intake (TWI) values. Additionally, under average exposure conditions, the THQ and HI data were generally below one for most study species in the area. The calculated CR values for investigated metals in the studied species indicated acceptable carcinogenic risk levels. Therefore, this suggests that consuming studied species within Temsah lake does not present any potential health hazards for consumers.

Assessing organism differences in mixed metal sensitivity

Metal contamination of aquatic environments remains a major concern and has received significant attention in recent years. The present study aimed to evaluate the effects of metal mixtures of varying concentrations over time in a lake receiving runoff water from a decommissioned mine. By subjecting several organisms to this water, we aimed to identify the most susceptible species, thus enabling a comprehensive evaluation of the risk posed by different toxins to the biotic environment.We have evaluated the effects of mixed metal exposure on survival and stress gene expression in selected invertebrate and vertebrate model species. Our observations revealed differences in sensitivity among the invertebrate models Caenorhabditis elegans, Daphnia magna, Ceriodaphnia dubia, and Heterocypris incongruens, as well as in the vertebrate model Zebrafish (Danio rerio) and two cell lines; a zebrafish liver cell line (ZFL) and a human hepatocellular carcinoma cell line (HepG2). While the sensitivity shows great variation among the tested species, the expression of metallothionein was consistent with the levels of metals found in the mixed exposure media. Despite differences in acute toxicity, the universal induction of mt1/A and mt2/B genes make them important biomarkers for assessing the environmental risk of metals.

Do the individual and population-level traits of Donax trunculus reflect the effects of metal contamination in aquatic environments?

Heavy metals are considered a major threat to aquatic ecosystems, due to their ability to penetrate and accumulate through the food chain, putting marine organisms and the ecosystem at risk. This research presents a case study of the Taghazout coast, located in the central Atlantic of Morocco, which has become the focal point of various development projects, including the Taghazout Bay tourist resort. The study aimed to gain a deeper understanding of the harmful effects of these metals on the reproductive cycle and population dynamics of the bivalve Donax trunculus. The assessment of cadmium (Cd), lead (Pb), and copper (Cu) levels in D. trunculus bivalves and sediment at the research location provides evidence of exposure to these metal sources by these bivalves. The analysis of the reproductive cycle revealed a balanced sex ratio of males to females. The Sexual Maturity Index (SMI) and Condition Index (CI) of the bivalves were found to be significantly influenced by trace elements Pb and Cu, as well as environmental factors like temperature, dissolved oxygen, and salinity. The maturity stages of the gonads were classified into five stages: undifferentiated, developing, mature, spawning, and spent. Two spawning periods were observed aligning with the population dynamics study that identified a bimodal recruitment (early autumn and spring) in D. trunculus. The population was found to have 11 size cohorts, with a maximum length of 37.96 cm, a yearly growth rate of 1.93 cm, and a short lifespan of 1.5 years. The high mortality rate of 3.30 per year was attributed to the presence of trace elements in Taghazout coast. These findings shed light on heavy metal's impact on the population of D. trunculus, revealing that a sole emphasis on its physiological or cellular effects may overlook its larger impact.

Heavy metals accumulation in some important fish species cultured in commercial fish farm of Natore, Bangladesh and possible health risk evaluation

Heavy metal contamination in aquatic environment is a serious concern throughout the world. Metal contamination are responsible for the accumulation of metals within the fish body. And, consumption of these contaminated fish possess serious threat to the associated consumers. In this current study, five commonly cultured freshwater fishes (rui, Labeo rohita; mrigal, Cirrhinus mrigala; silver carp, Hypophthalmicthys molitrix; bata, Labeo bata, and sarpunti, Puntius sarana) were collected from a commercial fish farm of Natore district, Bangladesh to analyze metals levels in edible portion (flesh), and to assess the associated human health risk. Several heavy metals such as zinc (Zn); cadmium (Cd); chromium (Cr); arsenic (As); lead (Pb); and nickel (Ni) were analyzed by a flame atomic absorption spectrophotometer. Besides, the target hazard quotient (THQ), hazard index (HI) and lifetime cancer risk (TR) were also estimated for assessing the associated human health risk. In this study, concentrations of Zn, Cd, Cr, As, Pb and Ni in different fish species were found 6.36 ± 1.48 to 13.31 ± 1.33; 0.017 ± 0.01 to 0.049 ± 0.02; 0.654 ± 0.04; 0.015 ± 0.01 to 0.033 ± 0.01; 0.534 ± 0.11 and 0.08 ± 0.05, respectively. All the analyzed values were within the recommended level except Cr in C. mrigala. The THQ, HI and TR values of all the analyzed metals in the fishes indicated that no associated cancer risk resulting from the consumption of those fishes. Therefore, the current study revealed that fishes of the target area might be free from associated metals contamination and hence, might be safe for human consumption.

The Importance Of Seaweed As Bioremediation Natural Agent

Seaweed has emerged as a promising bioremediation agent for addressing heavy metal contamination in aquatic environments. This study presents a comprehensive review of ten selected references to explore the potential of seaweed-based bioremediation and its implications for environmental sustainability. The findings highlight the significant capacity of seaweed species to accumulate heavy metals, emphasizing the importance of species selection based on their metal uptake capabilities. Seaweed biomass and biochar demonstrate remarkable adsorption properties, providing efficient means of removing heavy metals from contaminated water through physical adsorption and ion exchange processes. Seaweed-based bioremediation techniques offer several advantages over traditional methods. The studies underscore the importance of considering environmental conditions and the presence of coexisting pollutants in designing seaweed-based bioremediation strategies. Optimal light availability, temperature, nutrient levels, and water quality parameters are critical for maximizing seaweed's metal removal efficiency. Overall, seaweed-based bioremediation offers a promising and sustainable approach for addressing heavy metal pollution in aquatic environments. Future research should focus on overcoming challenges related to biomass management, ecological impacts, and scaling up cultivation and processing methods to ensure the widespread implementation of this eco-friendly solution.

Evaluation of Water Quality Pollution Indices for Heavy Metal Contamination Monitoring in Surface Water of Sutlej River (India)

Globally, heavy metal contamination in aquatic environment is a growing dilemma and currently reached at an alarming rate. Surface water receives metal contamination both naturally and anthropogenically. A study was conducted during October 2018 – Dec 2019 to examine the present status of heavy metal pollution in the river Sutlej (Downstream junction of Buddha Nullah), Punjab. The prime thrust is to determine the heavy metal concentrations (Arsenic, Nickel, Cadmium, Cobalt, Chromium, Boron, Manganese, Copper, Iron, Lead and Zinc) of surface water from two points at the location site and to determine the water quality indices (Heavy metal pollution index, heavy metal evaluation index and degree of contamination). Heavy metal analysis has been done using inductively coupled plasma atomic emission spectrophotometer. The results of this study showed that the average concentration of heavy metals such as As, B, Cd, Co, Cr, Cu, Fe, Mn, Ni, Zn and Pb were 0.123?g/l, 0.144 ?g/l, 0.047 ?g/l, 0.059 ?g/l, 0.189 ?g/l, 0.281?g/l, 1.424?g/l, 0.097?g/l, 0.291?g/l, 0.904 ?g/l and 0.631 ?g/l respectively. The overall mean concentration of heavy metals was observed in the following order Fe >Zn>Pb>Cu>Ni>Cr>B>As>Mn>Co>Cd. The HPI and HEI (water quality indices) for As, Fe, Mn, Ni, Zn, Pb, Cd, Cr and Cu were 503.05, 55.55 respectively. It is concluded that the study area is critically polluted with heavy metals that are lethal to aquatic life and humans.

CNT-sorbents for heavy metals: Electrochemical regeneration and closed-loop recycling

Heavy metal contamination of aquatic environments is a major concern. Carbon nanotubes (CNTs) are among the most effective adsorbents for heavy metal removal due. However, their high cost and their uncertain environmental impact necessitates a closed-loop process through sorbent regeneration and recycling for practical application. Our work demonstrates heavy metal adsorption by carboxylic acid-functionalized single-walled/double-walled carbon nanotubes (f-SW/DWCNTs) and their regeneration using electric fields. We follow a multi-step process: 1) copper in an aqueous solution is adsorbed onto the surface of f-SW/DWCNTs, 2) the copper-saturated f-SW/DWCNTs are filtered onto a microfiltration (MF) membrane, 3) the f-SW/DWCNT coated membrane is used as an anode in an electrochemical cell, 4) an applied electric field desorbs the metals from the CNTs into a concentrated waste, and 5) the CNTs are separated from the membrane, re-dispersed and reused in copper-contaminated water for successive adsorption. With an applied positive electric potential, we achieved ∼90 % desorption of Cu from f-SW/DWCNTs. We hypothesize that the electric field generated at the anode causes electrostatic repulsion between the anode and the electrostatically adsorbed heavy metal ions. The effect of applied voltages, electrode spacing and electrolyte conductivity on the desorption of Cu from CNTs was also investigated.

Deleterious effects of chronic mercury exposure on in vitro LTP, memory process, and oxidative stress.

Heavy metal contamination in aquatic environments plays an important role in the exposure of humans to these toxicants. Among these pollutants, mercury (Hg) is one main concern due to its high neurotoxicity and environmental persistence. Even in low concentrations, Hg bioaccumulation is a major threat to human health, with higher impact on populations whose diet has fish as chief consumption. Mercury compounds have high affinity for neuronal receptors and proteins, which gives Hg its cumulative feature and have the ability to cross cell membranes and blood-brain barrier to show their neurotoxicity. Intoxication with Hg increases levels of reactive oxygen species (ROS), thus depleting faster the resource of antioxidant proteins. To evaluate Hg-induced hippocampal ROS production, synaptic plasticity, anxiety, and memory, a total of 11 male Wistar rats were exposed to HgCl2 (Hg30 group) to produce a residual concentration of 8 ng/mL at the end of 30 days. Behavioral tests (plus-maze discriminative avoidance task), in vitro electrophysiology, and ROS assays were performed. Western blot assay showed decreased levels of antioxidant proteins GPx and SOD in Hg30 group. Increased ROS production was observed in the CA1 and CA3 regions in the Hg-exposed group. Plus-maze task detected long-term memory impairment in Hg30 group, linked to poorer in vitro long-term potentiation as compared to control group. Hg intoxication also promoted higher anxiety-like behavior in the exposed animals. In conclusion, our data suggests that low doses of HgCl2 resulted in impaired long-term memory and unbalance between decreased antioxidant protein expression and increased ROS production in the hippocampus.

Bioconcentration of Aluminium and Copper in Giant Freshwater Prawns (Macrobrachium Rosenbergii) From Several Rivers in Kuantan, Pahang Malaysia

Mining activities at the upstream of the Kuantan River basin can be resulted to adverse impacts for both human and aquatic lives. The heavy metal contamination of aquatic environment has gained the public attention. In fact, in recent decades, urban activities and industrial waste have led to an increase in contamination of heavy metals in the water bodies which may have direct effect on aquatic ecosystem. Therefore, this study aims to determine the level of Aluminium (Al) and Copper (Cu) in the muscle and gills of giant freshwater prawns (Macrobrachium rosenbergii) collected from five selected rivers in Kuantan, Pahang. Field sampling was conducted between September and December 2017. The giant freshwater prawns were digested and then analysed with inductively coupled plasma-mass spectrometry. The obtained results revealed that, Al levels in muscle of M.rosenbergii among all rivers occurred in the rank order: Pandan river>Riau river> Pinang river> Kuantan>Balok river, while in gills: Pandan river>Kuantan river>Balok river>Pinang river>Riau river. The concentration of Cu in muscle were in order of: Pandan river>Pinang river> Riau river> Balok river > Kuantan river, whereas Cu in gills were: Pandan river>Balok river>Kuantan river>Pinang river > Riau river. The highest content level of Al and Cu in both prawn’s muscle (14.03 ± 3.55 and 12.28 ± 3.87) mg/kg and gills (7.06 ± 2.53 and 12.28 ± 3.87) mg/kg were caught from Pandan River. In risk and safety assessment, the metal concentrations in the edible muscle of prawn were found to be below the established limits by WHO (1982), MFA (1983, US FDA (2001), and JECFA (2000). Thisstudy suggests that the prawns caught from Kuantan river are safe for human consumption.

A review on feasibility of phytoremediation technology for heavy metals removal

Quick jump of urbanization and industrialization is responsible for birth of heavy metal pollution. In the aquatic systems, heavy metals are one of the most dangerous pollutants that may be found. It can have both natural and anthropogenic origins. In aquatic ecosystem heavy metal pollution have a serious hazard to biodiversity of aquatic ecosystems, and drinking polluted water contaminated with heavy metals can have severe health risks in humans as well as in all living-beings. The commercial characteristics and side effects of conservative treatment equipment in aquatic environment flagged the way to eco-sustainable technology like phytoremediation. In phytoremediation, Plants are used to clean up the environment from numerous dangerous contaminants. Phytoremediation is cost-effective and ecofriendly expertise for environmentally friendly cleanup. The present review reflects the characteristics of heavy metals and possible environmental threats together with this, review also inspects the role played by the macrophytes in phytoremediation studies in the recent past. In the reduction of heavy metal contamination in aquatic environments which receive the industrial discharges and municipal wastewater, aquatic macrophytes are powerful tools to remediate them.

Novel insights into Pb source apportionment in sediments from two cascade reservoirs, North China

Sediments act as crucial sink and source for metal contamination in aquatic environment of reservoir systems. However, the high complexity and heterogeneity of sediments make it difficult to trace the sources of metals in reservoir sediments. As a toxic metal, how to trace anthropogenic Pb sources in sediments is important for the water quality safety, especially in reservoir. Herein, 98 sediment samples collected from the connected Panjiakou Reservoir (PJKR) and Daheiting Reservoir (DHTR) were analyzed. A novel approach for tracing anthropogenic Pb sources was established by combining the regional geochemical baseline (RGB) and Pb isotopic ratios. The results showed that the mean concentration of Pb in these two reservoirs was 44.59 mg/kg, and the RGB value of Pb was 43.77 mg/kg. Pollution assessments using RGB and enrichment factor indicated that the influence of anthropogenic Pb is greater in DHTR sediments than in PJKR sediments. Based on the RGB model, samples influenced by anthropogenic activities (SS-AA) were screened and found in the DHTR. The anthropogenic Pb contribution in DHTR SS-AA was totally 35.29%. Moreover, the mean value of 206Pb/207Pb in DHTR SS-AA (1.107 ± 0.029) was slightly lower than those of natural inputs, indicating there was a small amount of anthropogenic Pb input in DHTR. The anthropogenic Pb sources were further identified using Pb isotopic ratios (206Pb/207Pb and 208Pb/207Pb) for DHTR SS-AA. Their apportionments were calculated with the help of the RGB model. The results showed that iron mining (20.42%) and coal combustion (14.87%) were the two main anthropogenic Pb sources. Aerosol deposition was likely the main pathway for coal combustion input. The results confirm that the proposed method of combining RGB and Pb isotopic ratios was a good attempt to trace the anthropogenic Pb sources in reservoir sediments.

Arginine and lysine-functionalized layered double hydroxides as efficient sorbents for radioactive Co2+ removal by chelate-facilitated immobilization

An increase in heavy metal contamination in aquatic environments require an efficient sorbent for the removal and reuse of toxic elements. We attempted to synthesize arginine/lysine-functionalized MgAl LDHs in one-pot without using any hazardous alkaline reagents. The LDHs produced at lower temperatures showed larger numbers of amino acids on their surfaces, while these are exchanged with CO32− at higher temperatures. The arginine/lysine present on the surface of LDH enhanced the adsorption of Co2+ and showed the highest adsorption capacity of 1.159 and 1.170 mmol/g for the LDHs functionalized with lysine and arginine, respectively. Kinetics studies indicated that the adsorption of Co2+ occurred by multiple mechanisms. The Co2+ adsorption on these amino acid functionalized LDHs occurs by the formation chelation complex with amino acid, which provide better vicinity of Co2+ to basic LDH that facilitating the enhanced immobilization. The sorption of other divalent metal ions on these arginine/lysine functionalized LDHs followed the order of Co2+ > Ni2+ > Mn2+ > Fe3+. The Co2+ forms diamine-like coordination that is stable on the surface of LDH and causes higher sorption densities, while other metals form partial glycine-like coordination that detaches the amino acid from the surface of LDH, thereby leading to lesser sorption capacity. The conversion of anionic LDH in to a cationic sorbent was successfully fabricated by these arginine/lysine-assisted methods and explored for the remediation of Co2+ from aqueous solution.

An Ultrasensitive Gold Nanoband Aptasensor for Mercury(II) Detection in Aquatic Environment

Heavy metal contamination in aquatic environment has made great adverse impacts on human health and environment. In this work, a label-free electrochemical gold nanoband aptasensor (GNA) was developed using thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry for Hg2+ detection in drinking water. The gold nanoband sensor contains gold nanoband working electrode with a band thickness of 100 nm. The nanoscale working electrode increases the mass transfer rate and sensitivity for Hg2+ detection. Moreover, the gold nanoband sensors are cost-effective and can be easily regenerated by cutting the edge after the performance decreases dramatically compared with microelectrodes and disk electrodes. T-rich oligonucleotides modified with thiol group was self-assembled onto the working electrode through Au-S covalent bonding. In the presence of Hg2+, oligonucleotides will capture Hg2+, thus inducing the conformational change from single-strand to duplex-like structure that would promote electron transfer. Electrochemical impedance spectroscopy (EIS) was used to detect the Hg2+-mediated conformational changes. By optimizing experimental conditions, the linear range of proposed biosensor is from 0.1 nM to 1 μM, and the limit of detection is 40 pM (8 ppt). Furthermore, this nanobiosensors exhibited high selectivity and a great potential to detect trace Hg2+ in real samples from aquatic environment.

A comprehensive risk assessment of metals in riverine surface sediments across the rural-urban interface of a rapidly developing watershed

Metal contamination in aquatic environments is a severe global concern to human health and aquatic ecosystems. This study used several risk assessment indices, to evaluate metal (Cu, Zn, Pb, Cd and Cr) environmental risk of riverine surface sediments across the rural-urban interface of the rapidly developing Wen-Rui Tang River watershed in eastern China. Risk assessments were determined for 38 sites based on the potential ecological risk index (RI), consensus-based sediment quality guidelines (SQGs) and risk assessment code (RAC). Land-use cluster analysis showed that sediments were severely contaminated, especially for Cd, whose concentrations were ∼100 times higher than background levels and had a high proportion in the bioaccessible fraction. According to RI, ErCd was identified with extremely high risk potential, resulting in the highest ecological risk of Cluster 4 (industrial). Similarly, risk within Cluster 4 (industrial) was also ranked highest by SQGs assessment due to the high proportion of industrial land use. Zinc was determined with high risk due to its high concentration compared to its effect range medium (ERM) value. Discrepancies in predicting environmental risks from metals among the three indices were mainly attributed to the contrasting definitions of these metrics. Environmental risk uncertainty derived from spatial variation was further estimated by Monte Carlo simulation and ranked as: Zn > Cd > Cr > Pb > Cu. This comprehensive environmental risk assessment provides important information to guide remediation strategies for management of metal contamination at the watershed scale.

Hyperspectral Imaging of Macroinvertebrates—a Pilot Study for Detecting Metal Contamination in Aquatic Ecosystems

The applicability of spectral analysis in detection of freshwater metal contamination was assessed by developing and testing a novel hyperspectral imaging (HSI) application for aquatic insect larvae (Trichoptera: Hydropsychidae). Larvae were first exposed to four different cadmium (Cd) concentrations: 0, 1, 10, and 100 μg L−1 for 96 h. Individual larvae were then preserved in ethanol, inspected with microscopy for the number of anomalies in larval gills, and imaged by hyperspectral camera operating with wavebands between 500 and 850 nm. Three additional larvae from each exposure were analyzed for tissue Cd concentration. Although the larval tissue Cd concentrations correlated positively with actual water concentrations, the toxicity response of larvae, i.e., frequency of gill abnormalities, did not differ among the Cd concentrations. In contrast, hyperspectral imaging data indicated some concentration-response relationship of larval spectral properties to the Cd exposure, but it was too weak for reliable automatic distinction between exposed and unexposed larvae. In this pilot study a workflow for data processing for a novel application of hyperspectral imaging was developed. Based on the results of this preliminary study, the workflow in the imaging process will be optimized and its potential for detecting metal contamination of aquatic environments reassessed.

Odonata larvae as a bioindicator of metal contamination in aquatic environments: application to ecologically important wetlands in Iran

The objectives of this study were twofold: (i) assess the bioaccumulation characteristics of a suite of metals associated with several different species of Odonata and (ii) examine Odonata species richness as a reflection of ecosystem health in two ecologically important wetlands of southwestern Iran, the Shadegan and Hawr Al Azim wetlands. Levels of arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), lead (Pb), and zinc (Zn) were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) in nine different Odonata larva species. Based on these data, biota-sediment accumulation factors (BSAFs) were calculated and generally, it was found that Cr, Cu, Mn, and Zn were being taken up by the Odonata (BSAFs >1). Because of its prevalence in the wetland and its observed ability to take up metals, it is suggested that Ischnura ramburii is an appropriate indicator of ecosystem health for these wetlands with respect to metal contamination. Odonata species richness across all sites was 49, while for the individual sites, the greatest species richness was 26 and the lowest species richness was 13. The species richness value across all sites is quite healthy, given the arid climate of the region.

Heavy metal accumulation during the last 30 years in the Karnaphuli River estuary, Chittagong, Bangladesh

Heavy metal contamination of aquatic environment has attracted global attention owing to its abundance, persistence, and environmental toxicity, especially in developing countries like Bangladesh. Five heavy metals, namely chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were investigated in surface and core sediments of the Karnaphuli River (KR) estuary in Chittagong, Bangladesh, in order to reveal the heavy metal contamination history in estuarine sediments and its response to catastrophic events and human activities. The surface sediment was predominantly composed of silt and sand, and the surface sediment was contaminated with Cr and Pb. Based on the 210Pb chronology, the sedimentation rate in the inter-tidal zone of KR estuary was 1.02 cm/a before 2007, and 1.14 cm/a after 2008. The core sediment collected from 8 to 20 cm below the surface mainly originated from terrestrial materials induced by catastrophic events such as cyclone, heavy rainfall and landslides in 2007 and 2008. The values of contamination factor (CF) showed that the sediment became moderately contaminated with Cr and Pb in the last 30 years. The variation and accumulation of heavy metals in core sediment before 2000 was mainly related to natural variations in sediment sources; however, in subsequent years, the anthropogenic inputs of heavy metals have increased due to rapid physical growth of urban and industrial areas in the Chittagong city. In general, the accumulation pattern of heavy metals after normalization to Aluminum in sediments of KR estuary indicated an accelerated rate of urbanization and industrialization in the last 30 years, and also suggested the influence of natural catastrophic event on estuarine environment.

A study on the Phytoremediation Potential of Azolla pinnata under laboratory conditions

Heavy metal contamination in aquatic environments has become one of the major environmental problems all over the world. Phytoremediation is a plant based technology that utilizes special plants known as hyperaccumulators to purify heavy metal contaminated sites. Hyperaccumulators are capable of absorbing heavy metals in greater concentrations. Azolla pinnata is an aquatic macrophyte that has been earmarked for its hyperaccumulation ability. This green technology is often more favoured over conventional methods due to its low cost, low environmental impacts and wider public acceptance. This study was conducted under laboratory conditions to assess the ability of A. pinnata for the removal of Cr, Ni, Cd and Pb through rhizofiltration, which is one of the phytoremediation strategies under laboratory conditions. Under three main experiments, the fern’s phytoremediation ability was investigated. In the first experiment, A. pinnata was exposed to prepared solutions of Cr, Ni and Pb of 2ppm, 4ppm, 6ppm, 8ppm and 10ppm and of Cd solutions of 0.5ppm, 1.0ppm, 1.5ppm, 2.0ppm, 2.5ppm and 3.0ppm respectively. Experiments were carried out separately for Cr, Ni, Cd and Pb concentrations for 7 days. The concentrations of heavy metals used in the experiments largely agreed with the environmentally measured values, although in certain experiments, the initial concentrations exceeded the environmental pollution levels. The presence of Cr, Ni, Cd and Pb caused a maximum inhibition of A.pinnata growth by 47%, 54%, 52% and 45% respectively while the highest removal percentages of Cr- 98%, Ni- 57%, Cd- 88% and Pb- 86% were recorded in 2ppm, 2ppm, 0.5ppm and 8ppm treatments respectively. The highest Bio Concentration Factor (BCF) for Cr was 1376.67 when treated with 6ppm, 684.95 at 4ppm for Ni, 1120.06 at 0.5ppm for Cd and 1332.53 at 8ppm for Pb respectively. At the end of the experiments toxic symptoms were observed in plats exposed to Cd and Ni. The findings of this experiment revealed that A. pinnata is an excellent candidate for the removal of Pb and Cr even at higher concentrations and for Cd at lower concentrations while it is only partially efficient for Ni removal. The ability of A. pinnata to remove Cr, Ni, Cd and Pb from open dump site leachate was investigated in the experiment two. A. pinnata was exposed to a leachate dilution series of 5%, 15%, 25%, 50%, 75% and 100%. For all four metals, the highest removal percentages as well as the highest BCFs were given by the plants exposed to 5% leachate concentration. The maximum removal percentages were 70%, 52%, 50% and 72% and highest BCFs were 1248.51, 1199.19,867.33 and 1355.43 for Cr, Ni, Cd and Pb respectively. Growth of the fern was limited by around 90% when exposed to leachate treatments. The influence of interactive effects of Cr, Cd, Ni and Pb on their removal capacities of Azolla pinnata and the metal selectivities were determined bythe experiment three. Two treatments were prepared based on the findings of experiment one and two. Treatment I consisted of Cr, Ni, Cd and Pb concentrations that gave the highest BCFs in experiment one where treatment II was based on concentrations of 5% leachate treatment that gave the highest BCFs in experiment two. BCFs obtained from the treatment I were 1023.77, 679.97, 1048.39 and 939.77 for Cr, Ni, Cd and Pb respectively, hence all the BCFs were lower than of experiment one results proving the influence of interactive effects among the heavy metals on the uptake efficiency. In treatment I and II, the removal efficiency of Cr was 81% and 100%, for Ni it was 56% and 93%, 83% and 100% for Cd and for Pb it was 85% and 99%. Thus the metal selectivity of A. pinnata was Pb> Cd> Cr> Ni. Azolla pinnata can be designated as a good phytoremediation tool for the mitigation of heavy metal pollution due to its high BCFs (over 1000) in relation to Pb (2-10ppm), Cr (2-10ppm) and Cd (0.5-1ppm). However, field studies are warranted to further our claims. Key words: Phytoremediation, Azolla pinnata , Heavy metals, Bio Concentration Factor, Metal accumulation

Razor Clams (Class Bivalvia) of Kuala Selangor, Malaysia: Morphology, Genetic Diversity and Heavy Metal Concentration

Razor Clam (Bivalvia) could be easily identified as having two long, narrow shell valves connected by hinges, two siphons and one strong foot. It plays important role in ecological services besides providing food and extra income for the coastal communities. As filter feeder, razor clam is a good indicator for heavy metal contamination in aquatic environments. In Selangor, razor clam is locally known as ‘siput buluh’, yet, there is no proper scientific documentation on this species. This short study was carried out to assess the morphology of razor clams in Selangor for species identification and to sequence the Cytochrome Oxidase I (COI) gene for determination of its genetic diversity. Heavy sea traffics occurred in the sea near to the mudflat where razor clams were abundantly found has raised question whether razor clams were safe to be consumed. Therefore, this study is also designed to determine the level of selected heavy metals concentration in different body parts of razor clams. Based on selected morphometric and meristic data, razor clams of Kuala Selangor obtained during this study were Solen sarawakensis although many individuals displayed darker outer shell colouration and slightly thicker, longer and heavier shells. Based on analyses of putative COI gene sequences of approximately 677bp, there was a strong genetic divergence (11.7%) between S. sarawakensis inhabiting Kuala Selangor and Kuching Bay, Sarawak suggesting that although both razor clams were very similar morphologically, they could actually be two different species. Tissues of razor clams sampled from mudflat area in Kuala Selangor showed high concentration of Fe (146.50 mg/kg) and Mn (94.00 mg/kg). Other heavy metal elements namely Cr (42.50 mg/kg) and Cd (33.00 mg/kg) were also recorded during this study, occurring mainly in the shells. Traces of Hg were also detected, and its concentration did not differ much among the different parts analyzed.