Characterization of native microalgal strains for their chromium bioaccumulation potential: phytoplankton response in polluted habitats

Biological and green remediation of heavy metal contaminated water and soils: A state-of-the-art review

Contamination of the natural ecosystem by heavy metals, organic pollutants, and hazardous waste severely impacts on health and survival of humans, animals, plants, and microorganisms. Diverse chemical and physical treatments are employed in many countries, however, the acceptance of these treatments are usually poor because of taking longer time, high cost, and ineffectiveness in contaminated areas with a very high level of metal contents. Bioremediation is an eco-friendly and efficient method of reclaiming contaminated soils and waters with heavy metals through biological mechanisms using potential microorganisms and plant species. Considering the high efficacy, low cost, and abundant availability of biological materials, particularly bacteria, algae, yeasts, and fungi, either in natural or genetically engineered (GE) form, bioremediation is receiving high attention for heavy metal removal. This report comprehensively reviews and critically discusses the biological and green remediation tactics, contemporary technological advances, and their principal applications either in-situ or ex-situ for the remediation of heavy metal contamination in soil and water. A modified PRISMA review protocol is adapted to critically assess the existing research gaps in heavy metals remediation using green and biological drivers. This study pioneers a schematic illustration of the underlying mechanisms of heavy metal bioremediation. Precisely, it pinpoints the research bottleneck during its real-world application as a low-cost and sustainable technology.

Review on rewiring of microalgal strategies for the heavy metal remediation - A metal specific logistics and tactics

Phycoremediation of heavy metals are gaining much attention and becoming an emerging practice for the metal removal in diverse environmental matrices. Still, the physicochemical state of metal polluted sites is often found to be complex and haphazard in nature due to the irregular discharge of wastes, that leads to the lack of conjecture on the application of microalgae for the metal bioremediation. Besides, the foresaid issues might be eventually ended up with futile effect to the polluted site. Therefore, this review is mainly focusing on interpretative assessment on pre-existing microalgal strategies and their merits and demerits for selected metal removal by microalgae through various process such as natural attenuation, nutritional amendment, chemical pretreatment, metal specific modification, immobilization and amalgamation, customization of genetic elements and integrative remediation approaches. Thus, this review provides the ideal knowledge for choosing an efficient metal remediation tactics based on the state of polluted environment. Also, this in-depth description would provide the speculative knowledge of counteractive action required for pass-over the barriers and obstacles during implementation. In addition, the most common metal removal mechanism of microalgae by adsorption was comparatively investigated with different metals through the principal component analysis by grouping various factor such as pH, temperature, initial metal concentration, adsorption capacity, removal efficiency, contact time in different microalgae. Conclusively, the suitable strategies for different heavy metals removal and addressing the complications along with their solution is comprehensively deliberated for metal removal mechanism in microalgae.

Variation in phytoplankton diversity during phycoremediation in a polluted Colombian Caribbean swamp

Phytoplankton composition and abundance are considered among the bioindicators of variations in water quality, due to its sensitivity and rapid responses to changes in environmental parameters. The selection and scaling of the Microalgal Predominant Microbial Consortium (MPMC) were based on live samples collected from the Santiago Apóstol Swamp (SAS) and the Arroyo Grande de Corozal (AGC). The inoculum was scaled in a phycoculture plant, and the inoculation process was performed in the AGC that flows into the SAS. The phytoplankton community monitoring was performed from May 2019 to September 2021. In the process, a total of 1,652,258 gallons were inoculated. Precisely, 103 and 124 species were found in the AGC and SAS, respectively. By evaluating the physical, chemical, and microbiological variables in SAS in a multitemporal way based on the inoculation of the MPMC, it is possible to identify the variables that presented the greatest reduction. The density of SAS presented associations with dissolved oxygen, thermotolerant coliforms, Enterococci, pH, phosphorus, nitrates, speed, and Secchi. The AGC and SAS presented high trophic levels (eutrophication). This contamination by organic matter is probably due to the discharges of the domestic tributaries. The diversity of microalgae and cyanobacteria found in this study allows us to know the anthropogenic impact. The density of microalgae showed the positive impact of the treatment with MCPM, where there was a decrease in the species that denote organic contamination. The phytoremediation treatment was effective in terms of the changes observed in the physicochemical variables, and these changes were directly due to the efficiency of the treatment and not the natural behavior of the water sources in the region.

The emerging potential of natural and synthetic algae-based microbiomes for heavy metal removal and recovery from wastewaters

Heavy Metal (HM) bioremoval by microbes is a successful, environment-friendly technique, particularly at low concentrations of HMs. Studies using algae, bacteria, and fungi reveal promising capabilities in isolation and when used in consortia. Yet, few reviews have emphasized individual and collective HM removal rates and the associated mechanisms in natural or synthetic microbiomes. Besides discussing the limitations of conventional and synthetic biology approaches, this review underscores the utility of indigenous microbial taxon, i.e., algae, fungi, and bacteria, in HM removal with adsorption capacities and their synergistic role in microbiome-led studies. The detoxification mechanisms studied for certain HMs indicate distinctive removal pathways in each taxon which points to an enhanced effect when used as a microbiome. The role and higher efficacies of the designer microbiomes with complementing and mutualistic taxa are also considered, followed by recovery options for a circular bioeconomy. The citation network analysis further validates the multi-metal removal ability of microbiomes and the restricted capabilities of the individual counterparts. In precis, the study reemphasizes increased metal removal efficiencies of inter-taxon microbiomes and the mechanisms for synergistic and improved removal, eventually drawing attention to the benefits of ecological engineering approaches compared to other alternatives.

Studies on Zero-cost algae based phytoremediation of dye and heavy metal from simulated wastewater

In the present study, filamentous algae, an emerging candidate for biofuel and other useful chemical production, has been investigated as a biological adsorbent for the removal of contaminants from synthetic wastewater. Operational parameters were optimized in batch phytoremediation experiments. The adsorption equilibrium isotherm models such as Langmuir, Freundlich, and Dubinin-Radushkevitch and kinetics models such as pseudo-1st and pseudo-2nd order in methylene blue decolorization and Cr(VI) removal were also investigated. The D-R isotherm theory provided the best fit. The pseudo-2nd order model accurately described the adsorption kinetic data. Maximum adsorption capacities were observed to 5.03 mg.g^-1 and 0.77 mg.g^-1 along with removal efficiencies were achieved to 91.3% and 91.4% for methylene blue and Cr(VI) remediation, respectively. Moreover, intra-particle diffusion kinetic theory was used to describe the mechanism. These outcomes are significant in the development of algae-based zero-cost pollutants removal technology in wastewater treatment.

Why the Stall? Using metabolomics to define the lack of upstream movement of invasive bigheaded carp in the Illinois River

Bigheaded Carp have spread throughout the Mississippi River basin since the 1970s. Little has stopped the spread as carp have the ability to pass through locks and dams, and they are currently approaching the Great Lakes. However, the location of the leading edge in the Illinois River has stalled for over a decade, even though there is no barrier preventing further advancement towards the Great Lakes. Defining why carp are not moving towards the Great Lakes is important for predicting why they might advance in the future. The aim of this study was to test the hypothesis that anthropogenic contaminants in the Illinois River may be playing a role in preventing further upstream movement of Bigheaded Carp. Ninety three livers were collected from carp at several locations between May and October of 2018. Liver samples were analyzed using gas chromatography-mass spectrometry in a targeted metabolite profiling approach. Livers from carp at the leading edge had differences in energy use and metabolism, and suppression of protective mechanisms relative to downstream fish; differences were consistent across time. This body of work provides evidence that water quality is linked to carp movement in the Illinois River. As water quality in this region continues to improve, consideration of this impact on carp spread is essential to protect the Great Lakes.

Phycoremediation potential of Chlorella sp. on the polluted Thirumanimutharu river water

Rivers are the most significant natural resources that afford outstanding habitation and nourishment for numerous living organisms. Urbanization and industrialization pollute rivers rendering their water unhealthy for consumption. Hence, this work was designed to find a potential native pollutant removing algae from polluted water. The physicochemical properties of the tested river water such as Electric Conductivity (EC), turbidity, total hardness, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Ca, SO²-, and NH₃, NO₃, NO₂, PO₄, Mg, F^- and Cl^- contents were not within the permissible limits. Lab-scale and field-based phycoremediation treatments with the indigenous native microalgal species, Chlorella sp. from the Thirumanimutharu river water sample were set up for 15 days with three different (Group I, II, and III) biomass densities (4 × 10⁴, 8 × 10⁴, and 12 × 10⁴ cells mL^-1). Group III of both the lab-scale and field based treatments showed the maximum reduction in the physicochemical parameters compared to the other groups. Further, the group III of the field based study showed an extensive reduction in BOD (34.51%), COD (32.53%), NO₃, NO₂, free NH₃ (100%) and increased dissolved oxygen (DO) (88.47%) compared to the lab scale study. In addition, the trace elements were also reduced significantly. The pollutant absorbing active functional moieties (O-H, CO, and CN) found on Chlorella sp. had been confirmed by Fourier-Transform Infrared Spectroscopy (FTIR) analysis. In the Scanning Electron Microscope (SEM) study, significant morphological changes on the surface of the treated Chlorella sp. were noticed compared with the untreated Chlorella sp. biomass, which also confirmed the absorption of the pollutants during treatment.

Microplastics and suspended particles in a strongly impacted coastal environment: Composition, abundance, surface texture, and interaction with metal ions

The composition and the interaction of the suspended particulate matter (SPM) with metal ions, along with the presence and characteristics of microplastics, were analyzed for the first time in the water column of the inner zone of Bahía Blanca Estuary during winter (June, July, and August) 2019. Surface analysis techniques (Scanning Electron Microscopy combined with Energy Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray Diffraction) were employed to obtain an in-depth characterization of the particulate matter, suggesting the presence of Fe in our samples, with a mixture of Fe³⁺/Fe²⁺ oxidation states. Microplastics ranged in concentrations between 3 and 11.5 items L^-1, with an average of 6.50 items L^-1 (S.E: ±4.01), being fibers the most abundant type. Infrared Spectroscopy suggests that these fibers correspond to semi-synthetic cellulose-based and poly(amide) remains. We concluded that the SPM is a significant vehicle for metals which might have adverse effects on marine organisms.

Extraction of heavy metal complexes from a biofilm colony for biomonitoring the pollution

An extraction method was tested for biomonitoring the biofilm samples containing heavy metals. The fractionation of metal complexes was performed via C-18-HPLC-ICP-MS and MALDI-MS, respectively. The extraction power of some reagents was determined for the heavy metal extraction from biofilm samples collected in Erdemli coast in the Mediterranean Sea. The ammonium acetate solution giving the highest extraction results was found as a suitable extraction reagent. The concentration and pH of the ammonium acetate solution were optimized and found as 1 M and 5, respectively. The chromatograms of metal complexes with the C-18-HPLC-ICP-MS system were taken to determine the effect of the pH of the metal complexes. After performing the extraction, metal bounded biomolecules were characterized by MALDI-MS for the fractions in the C18-HPLC system. It was seen that ammonium acetate extraction (1M, pH 5) might be used in biomonitoring studies due to relatively simple procedure, short analysis period, and low cost. The evaluation of the applicability of the method in biomonitoring studies might be supported by further studies with biofilms having similar characteristics.

Unique biocenosis as a foundation to develop a phytobial consortium for effective bioremediation of Cr(VI)-polluted waters and sediments

This paper analyzes a unique, aquatic phytobial biocenosis that has been forming naturally for over 20 years and operating as a filter for Cr(VI)-polluted groundwater. Our study presents a thorough taxonomic analysis of the biocenosis, including filamentous algae, vascular plants, and microbiome, together with the analysis of Cr accumulation levels, bioconcentration factors and other environmentally-significant parameters: siderophore production by bacteria, biomass growth of the plants or winter hardiness. Among 67 species identified in the investigated reservoir, 13 species were indicated as particularly useful in the bioremediation of Cr(VI)-polluted water and sediment. Moreover, three species of filamentous algae, Tribonema sp., and three easily culturable bacterial species were for the first time shown as resistant to Cr concentration up to 123 mg/dm3, i.e. 6150 times over the permissible level. The work presents a modern holistic phytobial consortium indispensable for the remediation of Cr(VI)-contaminated aquatic environment in temperate zones worldwide.

Diversity, structure and regulation of microbial metallothionein: metal resistance and possible applications in sequestration of toxic metals

Metallothioneins (MTs) are a group of cysteine-rich, universal, low molecular weight proteins distributed widely in almost all major taxonomic groups ranging from tiny microbes to highly organized vertebrates. The primary function of this protein is storage, transportation and binding of metals, which enable microorganisms to detoxify heavy metals. In the microbial world, these peptides were first identified in a cyanobacterium Synechococcus as the SmtA protein which exhibits high affinity towards rising level of zinc and cadmium to preserve metal homeostasis in a cell. In yeast, MTs aid in reserving copper and confer protection against copper toxicity by chelating excess copper ions in a cell. Two MTs, CUP1 and Crs5, originating from Saccharomyces cerevisiae predominantly bind to copper though are capable of binding with zinc and cadmium ions. MT superfamily 7 is found in ciliated protozoa which show high affinity towards copper and cadmium. Several tools and techniques, such as western blot, capillary electrophoresis, inductively coupled plasma, atomic emission spectroscopy and high performance liquid chromatography, have been extensively utilized for the detection and quantification of microbial MTs which are utilized for the efficient remediation and sequestration of heavy metals from a contaminated environment.

Trace metal effects on gross primary productivity and its associative environmental risk assessment in a subtropical lake, China

The transport of trace metals in river-lake systems can potentially increase or decrease primary productivity in some basins and subsequently affect the carbon cycle of watersheds. In this study, we investigated a variety of trace metal concentrations and transport flux in the Poyang Lake basin during four seasons. Results show that the Gan River transports 78% of selenium (Se) and 42% of lead (Pb) into Poyang Lake each year, resulting in heavy metal pollution dominated by Pb and Se in 30%-75% of its water. Although toxic heavy metals, such as Pb, chromium (Cr), and copper (Cu), inhibit phytoplankton growth and decrease its gross primary productivity (GPP), excessive Se could effectually promote productivity. However, the negative effect of Pb on GPP is more significant than the positive effect of Se on GPP; hence, their interaction effectuates a decrease in total primary productivity. Additionally, under high nutrients level, the synergistic effect of heavy metals and nutrients will reduce GPP. Agricultural fertilizer is likely the source of both Pb, Cu, Se and N. Gan River contributes 35%-80% of the heavy metal inputs to Poyang Lake. It is therefore necessary to improve the ecological environment of phytoplankton and promote productivity in the Poyang Lake basin by reducing the application of agricultural chemical fertilizers to control pollution. Our results indicate that the role of certain, less studied trace elements (e.g., Pb, Cr, Cu, and Se) in regulating primary productivity of watershed ecosystems is more important than previously thought. This study also discusses potential impacting mechanisms associated with these metals on phytoplankton, whose biological functions need to be verified in future experiments.

Self-cleansing properties of Ganga during mass ritualistic bathing on Maha-Kumbh

The deterioration of water quality of river Ganga is a huge concern for Govt. of India. Apart from various pollution sources, the religious and ritualistic activities also have a good share in deteriorating Ganga water quality. Thus, the aim of the present study was to evaluate the changes in physico-chemical properties, microbial diversity and role of bacteriophages in controlling bacterial population of Ganga water during mass ritualistic bathing on the occasion of Maha-Kumbh in 2013. The BOD, COD, hardness, TDS and level of various ions significantly increased, while DO decreased in Ganga water during Maha-Kumbh. Ganga water was more affluent in trace elements than Yamuna and their levels further increased during Maha-Kumbh, which was correlated with decreased level of trace elements in the sediment. The bacterial diversity and evenness were increased and correlated with the number of devotees taking a dip at various events. Despite enormous increase in bacterial diversity during mass ritualistic bathing, the core bacterial species found in pre-Kumbh Ganga water were present in all the samples taken during Kumbh and post-Kumbh. In addition, the alteration in bacterial population during mass bathing was well under 2 log units which can be considered negligible. The study of bacteriophages at different bathing events revealed that Ganga was richer with the presence of bacteriophages in comparison with Yamuna against seven common bacteria found during the Maha-Kumbh. These bacteriophages have played a role in controlling bacterial growth and thus preventing putrefaction of Ganga water. Further, the abundance of trace elements in Ganga water might also be a reason for suppression of bacterial growth. Thus, the current study showed that Ganga has characteristic water quality in terms of physico-chemical property and microbial diversity that might have a role in the reported self-cleansing property of Ganga; however, the increased pollution load has surpassed its self-cleansing properties. Since water has been celebrated in all cultures, the outcome of the current study will not only be useful for the policy maker of cleaning and conservation of Ganga but also for restoration of other polluted rivers all over the world.

Heavy metal resistance in algae and its application for metal nanoparticle synthesis

The ungenerous release of metals from different industrial, agricultural, and anthropogenic sources has resulted in heavy metal pollution. Metals with a density larger than 5 g cm^-3 have been termed as heavy metals and have been stated to be potentially toxic to human and animals. Algae are known to be pioneer organisms with the potential to grow under extreme conditions including heavy metal-polluted sites. They have evolved efficient defense strategies to combat the toxic effects exerted by heavy metal ions. Most of the algal strains are reported to accumulate elevated metal ion concentration in cellular organelles. With respect to that, this review focuses on understanding the various strategies used by algal system for heavy metal resistance. Additionally, the application of this metal resistance in biosynthesis of metal nanoparticles and metal oxide nanoparticles has been investigated in details. We thereby conclude that algae serve as an excellent system for understanding metal uptake and accumulation. This thereby assists in the design and development of low-cost approaches for large-scale synthesis of nanoparticles and bioremediation approach, providing ample opportunities for future work.

Ganga water pollution: A potential health threat to inhabitants of Ganga basin

BACKGROUND

The water quality of Ganga, the largest river in Indian sub-continent and life line to hundreds of million people, has severely deteriorated. Studies have indicated the presence of high level of carcinogenic elements in Ganga water.

OBJECTIVES

We performed extensive review of sources and level of organic, inorganic pollution and microbial contamination in Ganga water to evaluate changes in the level of various pollutants in the recent decade in comparison to the past and potential health risk for the population through consumption of toxicant tainted fishes in Ganga basin.

METHODS

A systematic search through databases, specific websites and reports of pollution regulatory agencies was conducted. The state wise level of contamination was tabulated along the Ganga river. We have discussed the major sources of various pollutants with particular focus on metal/metalloid and pesticide residues. Bioaccumulation of toxicants in fishes of Ganga water and potential health hazards to humans through consumption of tainted fishes was evaluated.

RESULTS

The level of pesticides in Ganga water registered a drastic reduction in the last decade (i.e. after the establishment of National Ganga River Basin Authority (NGRBA) in 2009), still the levels of some organochlorines are beyond the permissible limits for drinking water. Conversely the inorganic pollutants, particularly carcinogenic elements have increased several folds. Microbial contamination has also significantly increased. Hazard quotient and hazard index indicated significant health risk due to metal/metalloid exposure through consumption of tainted fishes from Ganga. Target cancer risk assessment showed high carcinogenic risk from As, Cr, Ni and Pb as well as residues of DDT and HCHs.

CONCLUSION

Current data analysis showed that Ganga water quality is deteriorating day by day and at several places even in upper stretch of Ganga the water is not suitable for domestic uses. Although there is positive impact of ban on persistent pesticides with decreasing trend of pesticide residues in Ganga water, the increasing trend of trace and toxic elements is alarming and the prolong exposure to polluted Ganga water and/or consumption of Ganga water fishes may cause serious illness including cancer.

Cytotoxic Assessment of Chromium and Arsenic Using Chromosomal Behavior of Root Meristem in Allium cepa L

A study was performed for phyto-genotoxic assay of chromium (Cr) and arsenic (As) through Allium cepa. Various concentrations (0, 1, 3, 6 and 12 mg L^-1) of Cr and As for 48 and 168 h time points exposed to A. cepa. The phytotoxic effects of metal(loid) were evident through inhibited root length and root protein. Metal(loid) toxicity also lead to genotoxic effects, which included depression of mitotic index and increased frequency of chromosomes aberrations like break, fragments, c-metaphase, multipolar arrangements etc. Genotoxic endpoint as progressive frequency of micronuclei in interphase of root meristem cells in treated plants was also observed. This genotoxic endpoint revealed carcinogenic nature of both aforementioned metal(loid). Along with inhibition in root length and protein content, depression in mitotic index as well as stimulation of various abnormality in mitotic cell division indicated that both metal(loid) are hazardous in nature and causing harmful effect on the environment.

Ecotoxicological effects of enrofloxacin and its removal by monoculture of microalgal species and their consortium

Enrofloxacin (ENR), a fluoroquinolone antibiotic, has gained big scientific concern due to its ecotoxicity on aquatic microbiota. The ecotoxicity and removal of ENR by five individual microalgae species and their consortium were studied to correlate the behavior and interaction of ENR in natural systems. The individual microalgal species (Scenedesmus obliquus, Chlamydomonas mexicana, Chlorella vulgaris, Ourococcus multisporus, Micractinium resseri) and their consortium could withstand high doses of ENR (≤1 mg L^-1). Growth inhibition (68-81%) of the individual microalgae species and their consortium was observed in ENR (100 mg L^-1) compared to control after 11 days of cultivation. The calculated 96 h EC₅₀ of ENR for individual microalgae species and microalgae consortium was 9.6-15.0 mg ENR L^-1. All the microalgae could recover from the toxicity of high concentrations of ENR during cultivation. The biochemical characteristics (total chlorophyll, carotenoid, and malondialdehyde) were significantly influenced by ENR (1-100 mg L^-1) stress. The individual microalgae species and microalgae consortium removed 18-26% ENR at day 11. Although the microalgae consortium showed a higher sensitivity (with lower EC₅₀) toward ENR than the individual microalgae species, the removal efficiency of ENR by the constructed microalgae consortium was comparable to that of the most effective microalgal species.

Microalgal consortia differentially modulate progressive adsorption of hexavalent chromium

A set of experiments was conducted to provide significant insights of micro-algal consortia regarding chromium adsorption. Four monocultures; Scenedesmus dimorphus, Chlorella sp., Oscillatoria sp., and Lyngbya sp., and their synthetic consortia were evaluated initially for chromium bio-adsorption at four different regimes of hexavalent chromium i.e. 0.5, 1.0, 3.0 and 5.0 ppm. Based on findings, only 1.0 and 5.0 ppm were considered for future experiments. Consequently, three different types of monoculture and consortia cells namely; live cells, heat-killed cells, and pre-treated cells were prepared to enhance their adsorption potential. Maximal adsorption of 112% was obtained at the dose of 1.0 ppm with 0.1% SDS pre-treated consortia cells over live consortia cells. In support, atomic absorption spectroscopy, laser induced breakdown spectroscopy, pulse amplitude modulated chlorophyll fluorescence, and scanning electron microscopy were performed to assess the structural and functional changes within consortia and their utilization in mitigation of elevated chromium levels.

Phytoplankton communities of polar regions--Diversity depending on environmental conditions and chemical anthropopressure

The polar regions (Arctic and Antarctic) constitute up to 14% of the biosphere and offer some of the coldest and most arid Earth's environments. Nevertheless several oxygenic phototrophs including some higher plants, mosses, lichens, various algal groups and cyanobacteria, survive that harsh climate and create the base of the trophic relationships in fragile ecosystems of polar environments. Ecosystems in polar regions are characterized by low primary productivity and slow growth rates, therefore they are more vulnerable to disturbance, than those in temperate regions. From this reason, chemical contaminants influencing the growth of photoautotrophic producers might induce serious disorders in the integrity of polar ecosystems. However, for a long time these areas were believed to be free of chemical contamination, and relatively protected from widespread anthropogenic pressure, due their remoteness and extreme climate conditions. Nowadays, there is a growing amount of data that prove that xenobiotics are transported thousands of kilometers by the air and ocean currents and then they are deposed in colder regions and accumulate in many environments, including the habitats of marine and freshwater cyanobacteria. Cyanobacteria (blue green algae), as a natural part of phytoplankton assemblages, are globally distributed, but in high polar ecosystems they represent the dominant primary producers. These microorganisms are continuously exposed to various concentration levels of the compounds that are present in their habitats and act as nourishment or the factors influencing the growth and development of cyanobacteria in other way. The most common group of contaminants in Arctic and Antarctic are persistent organic pollutants (POPs), characterized by durability and resistance to degradation. It is important to determine their concentrations in all phytoplankton species cells and in their environment to get to know the possibility of contaminants to transfer to higher trophic levels, considering however that some strains of microalgae are capable of metabolizing xenobiotics, make them less toxic or even remove them from the environment.

Microalgae - A promising tool for heavy metal remediation

Biotechnology of microalgae has gained popularity due to the growing need for novel environmental technologies and the development of innovative mass-production. Inexpensive growth requirements (solar light and CO2), and, the advantage of being utilized simultaneously for multiple technologies (e.g. carbon mitigation, biofuel production, and bioremediation) make microalgae suitable candidates for several ecofriendly technologies. Microalgae have developed an extensive spectrum of mechanisms (extracellular and intracellular) to cope with heavy metal toxicity. Their wide-spread occurrence along with their ability to grow and concentrate heavy metals, ascertains their suitability in practical applications of waste-water bioremediation. Heavy metal uptake by microalgae is affirmed to be superior to the prevalent physicochemical processes employed in the removal of toxic heavy metals. In order to evaluate their potential and to fill in the loopholes, it is essential to carry out a critical assessment of the existing microalgal technologies, and realize the need for development of commercially viable technologies involving strategic multidisciplinary approaches. This review summarizes several areas of heavy metal remediation from a microalgal perspective and provides an overview of various practical avenues of this technology. It particularly details heavy metals and microalgae which have been extensively studied, and provides a schematic representation of the mechanisms of heavy metal remediation in microalgae.

Phycoremediation of Tannery Wastewater Using Microalgae Scenedesmus Species

A number of microalgae species are efficient in removing toxicants from wastewater. Many of these potential species are a promising, eco-friendly, and sustainable option for tertiary wastewater treatment with a possible advantage of improving the economics of microalgae cultivation for biofuel production. The present study deals with the phycoremediation of tannery wastewater (TWW) using Scenedesmus sp. isolated from a local habitat. The test species was grown in TWW under laboratory conditions and harvested on the 12th day. The results revealed that the algal biomass during the growth period not only reduced the pollution load of heavy metals (Cr-81.2-96%, Cu-73.2-98%, Pb-75-98% and Zn-65-98%) but also the nutrients (NO3 >44.3% and PO4 >95%). Fourier Transform Infrared (FTIR) spectrums of Scenedesmus sp. biomass revealed the involvement of hydroxyl amino, carboxylic and carbonyl groups. The scanning electron micrograph (SEM) and Energy Dispersive X-ray Spectroscopic analysis (EDS) revealed the surface texture, morphology and element distribution of the biosorbent. Furthermore, the wastewater generated during wet-blue tanning process can support dense population of Scenedesmus sp., making it a potential growth medium for biomass production of the test alga for phycoremediation of toxicants in tannery wastewaters.

A Review of Biosorption of Chromium Ions by Microorganisms

Due to its widespread industrial use, chromium has become a serious pollutant in diverse environmental settings. The main source of chromium pollution including the Republic o Moldova is industry. It is a great need to develop new eco-friendly methods of chromium removal. Biosorption of heavy metals is a most promising technology involved in the removal of toxic metals from industrial waste streams and natural waters. This article is an extended abstract of a communication presented at the Conference Ecological Chemistry 2012.

Arsenic accumulation in native plants of West Bengal, India: prospects for phytoremediation but concerns with the use of medicinal plants

Arsenic (As) is a widespread environmental and food chain contaminant and class I, non-threshold carcinogen. Plants accumulate As due to ionic mimicry that is of importance as a measure of phytoremediation but of concern due to the use of plants in alternative medicine. The present study investigated As accumulation in native plants including some medicinal plants, from three districts [Chinsurah (Hoogly), Porbosthali (Bardhman), and Birnagar (Nadia)] of West Bengal, India, having a history of As pollution. A site-specific response was observed for Specific Arsenic Uptake (SAU; mg kg(-1) dw) in total number of 13 (8 aquatic and 5 terrestrial) collected plants. SAU was higher in aquatic plants (5-60 mg kg(-1) dw) than in terrestrial species (4-19 mg kg(-1) dw). The level of As was lower in medicinal plants (MPs) than in non-medicinal plants, however it was still beyond the WHO permissible limit (1 mg kg(-1) dw). The concentration of other elements (Cu, Zn, Se, and Pb) was found to be within prescribed limits in medicinal plants (MP). Among the aquatic plants, Marsilea showed the highest SAU (avg. 45 mg kg(-1) dw), however, transfer factor (TF) of As was the maximum in Centella asiatica (MP, avg. 1). Among the terrestrial plants, the maximum SAU and TF were demonstrated by Alternanthera ficoidea (avg. 15) and Phyllanthus amarus (MP, avg. 1.27), respectively. In conclusion, the direct use of MP or their by products for humans should not be practiced without proper regulation. In other way, one fern species (Marsilea) and some aquatic plants (Eichhornia crassipes and Cyperus difformis) might be suitable candidates for As phytoremediation of paddy fields.