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Biostrategies for the removal of microplastics: A Review
Abstract
Recent studies on plastic pollution have shown that microscopic plastic particles or microplastics are ubiquitous. Both abiotic and biotic components are affected by microplastics. There are several ways to get rid of microplastics, that include recycling, landfilling, incineration, and biodegradation. Biodegradation is still a widely used remediation technology due to its significant economic and environmental benefits. One or more bio-cultures, such as bacteria, mould, yeast, and algae, can be used for biodegradation. In this review, we look through the contributions of microorganisms in biodegradation and other biotechnological techniques to speed up the process.
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Plastic particles are ubiquitous pollutants in the living environment and food chain but no study to date has reported on the internal exposure of plastic particles in human blood. This study’s goal was to develop a robust and sensitive sampling and analytical method with pyrolysis double shot - gas chromatography/mass spectrometry and apply it to measure plastic particles ≥700 nm in human whole blood from 22 healthy volunteers. Four high production volume polymers applied in plastic were identified and quantified for the first time in blood. Polyethylene terephthalate, polyethylene and polymers of styrene (a sum parameter of polystyrene, expanded polystyrene, acetonitrile butadiene styrene etc.) were the most widely encountered, followed by poly(methyl methylacrylate). Polypropylene was analysed but values were under the limits of quantification. In this study of a small set of donors, the mean of the sum quantifiable concentration of plastic particles in blood was 1.6 µg/ml, showing a first measurement of the mass concentration of the polymeric component of plastic in human blood. This pioneering human biomonitoring study demonstrated that plastic particles are bioavailable for uptake into the human bloodstream. An understanding of the exposure of these substances in humans and the associated hazard of such exposure is needed to determine whether or not plastic particle exposure is a public health risk.
Plastic (polyethylene) pollution is a severe cause of deterioration of a healthy environment. For example, ingestion of plastics in the animal gut, clogging of water canals and retarded solid waste management. Many conventional methods of polyethylene degradation include UV photooxidation, thermal oxidation, incineration, chemical oxidation and landfill are being practiced. However, these methods are not feasible, costlier and not a complete solution for this global issue. Therefore, plausible, alternative solution for this issue is biodegradation. Microbes such as bacteria, fungi and algae are involved in polyethylene degradation in its natural habitat. Among them, algae were given very less importance. In our present study, a potential microalga, morphologically identified as Uronema africanum Borge, isolated from a waste plastic bag collected from a domestic waste dumping site in a freshwater lake. This microalga was further treated with the LDPE sheet in BBM culture medium. Based on the results obtained from light microscopy, dark field microscopy, GC–MS, FT-IR, SEM and AFM, it was concluded that the microalga has initiated degradation of LDPE sheet within 30 days of incubation. Concurrently, the configuration of corrosions, abrasions, grooves and ridges were found similar with the morphological features of the microalga. For example, the configuration of the radial disc-like attachment structure of the microalga was found corresponding to the abrasions on the surface of LDPE sheet at an average size of 20–30 μm in diameter. Whereas, the configuration of ridges and grooves were found similar with the filamentous nature of the microalga (10–15 μm width). This is a hitherto report on the biodegradation of LDPE sheet by the microalga Uronema africanum Borge.
Plastic particles of less than 5 mm size, referred as microplastics, have recently become a major environmental issue. While microplastics are well known in marine and lake systems, there have been less investigations in soils and groundwater. Here we review the origin, shape, impact, and mitigation strategies of soil and groundwater microplastics. We found that littering is the main origin of microplastics in global topsoils, while greenhouses are the main source of microplastics in South Korea. Fibers and pellets are dominant microplastic shapes in soil and groundwater. Microplastic contamination of soil and groundwater is detrimental to human health, plants, nematodes, earthworms, and soil properties. Remediation methods include pyrolysis, replacing plastics by biodegradable plastics, plastic filtration, and subsequent chemical or biological degradation.
Microplastics (plastic particles < 5 mm) are a diverse class of contaminants that are increasingly detected in our biosphere. Their ubiquity in the environment raises increasing concerns about their implications for human health. Recent evidence indicates that humans constantly inhale and ingest microplas-tics, however, whether these contaminants pose a substantial risk to human health is far from understood. We argue that comprehensive understanding of whether these novel contaminants pose a risk to our health is impossible at the moment. The field of microplastics and human health is fraught with uncertainties and lacks crucial data on exposure and hazard. Here we outline major data and knowledge gaps and describe the main steps that are needed to move the field forward. Comprehensive risk assessment is still years away, but, in our opinion, the major research gaps should be addressed now in order to support timely decision making on health policies and mitigation strategies.
It is well known that the inadequate disposal of polymeric materials causes significant environmental problems. Recycling and the use of biodegradable polymers are among the methods used to minimize these problems. However, the low mechanical performance of the majority of biodegradable polymers hinders the direct substitution of synthetic polymers, such as polyethylene (PE), polypropylene (PP) and polystyrene (PS), by biodegradable ones. Blending synthetic and biodegradable polymers is a way to develop recyclable biodegradable products with a good set of mechanical properties. Therefore, in this work we investigate the influence of extrusion cycles on the degradation of a polypropylene/poly (butylene adipate-co-terephthalate)/thermoplastic starch blend before and after inoculation with Aspergillus sp. and Penicillium sp. fungi degradaded for 30 days. The samples were exposed to the fungi and their mass loss, chemical structure, hydrophilicity, and morphology were observed as a function of inoculation time and processing cycles. Our results indicate that thermo-mechanical degradation favors the deposition of fungi in the samples and enables changes in film morphology and hydrophilicity.
Background:
The biological degradation of plastics is a promising method to counter the increasing pollution of our planet with artificial polymers and to develop eco-friendly recycling strategies. Polyethylene terephthalate (PET) is a thermoplast industrially produced from fossil feedstocks since the 1940s, nowadays prevalently used in bottle packaging and textiles. Although established industrial processes for PET recycling exist, large amounts of PET still end up in the environment-a significant portion thereof in the world's oceans. In 2016, Ideonella sakaiensis, a bacterium possessing the ability to degrade PET and use the degradation products as a sole carbon source for growth, was isolated. I. sakaiensis expresses a key enzyme responsible for the breakdown of PET into monomers: PETase. This hydrolase might possess huge potential for the development of biological PET degradation and recycling processes as well as bioremediation approaches of environmental plastic waste.
Results:
Using the photosynthetic microalga Phaeodactylum tricornutum as a chassis we generated a microbial cell factory capable of producing and secreting an engineered version of PETase into the surrounding culture medium. Initial degradation experiments using culture supernatant at 30 °C showed that PETase possessed activity against PET and the copolymer polyethylene terephthalate glycol (PETG) with an approximately 80-fold higher turnover of low crystallinity PETG compared to bottle PET. Moreover, we show that diatom produced PETase was active against industrially shredded PET in a saltwater-based environment even at mesophilic temperatures (21 °C). The products resulting from the degradation of the PET substrate were mainly terephthalic acid (TPA) and mono(2-hydroxyethyl) terephthalic acid (MHET) estimated to be formed in the micromolar range under the selected reaction conditions.
Conclusion:
We provide a promising and eco-friendly solution for biological decomposition of PET waste in a saltwater-based environment by using a eukaryotic microalga instead of a bacterium as a model system. Our results show that via synthetic biology the diatom P. tricornutum indeed could be converted into a valuable chassis for biological PET degradation. Overall, this proof of principle study demonstrates the potential of the diatom system for future biotechnological applications in biological PET degradation especially for bioremediation approaches of PET polluted seawater.
Plastics are widely used in our economy and each year, at least 350-400 million tons are being produced. Due to poor recycling and low circular use, millions of tons accumulate annually in terrestrial or marine environments. Today it has become clear that plastic causes adverse effects in all ecosystems and that microplastics are of particular concern to our health. Therefore, recent microbial research has addressed the question, if and to which extent microorganisms can degrade plastics in the environment. This review summarizes current knowledge on microbial plastic degradation. Enzymes available act mainly on the high molecular weight polymers of polyethylene terephthalate (PET) and ester-based polyurethane (PUR). Unfortunately, the best PUR- and PET-active active enzymes and microorganisms known still have moderate turnover rates. While many reports have been published describing microbial communities degrading chemical additives, no enzymes acting on the high molecular weight polymers polystyrene, polyamides, polyvinylchloride, polypropylene, ether-based polyurethane and polyethylene are known. Altogether these polymers stand for more than 80 % of the annual plastic production. Thus, further research is needed to significantly increase the diversity of enzymes and microorganisms acting on these polymers. This can be achieved by tapping into the global metagenomes of non-cultivated microorganisms and dark matter proteins. Only then, novel biocatalysts and organisms can be delivered that allow rapid degradation, recycling or value-added use of the vast majority of most man-made polymers.
Low-density polyethylene (LDPE) is an environmental problem because it is discarded randomly, and because in dumpsites, it does not readily degrade. This study reports evidence of successful biodegradation by two fungal species (Aspergillus flavus MCP5 and Aspergillus flavus MMP10) and eight bacterial species (Acinetobacter sp. MGP1, Bacillus sp. MGP1, Pseudomonas sp. MMP1, Bacillus sp. MMP5, Staphylococcus sp. MMP10, Bacillus sp. MGP1, Micrococcus sp. MMP5 and Bacillus sp. MMP10). These were demonstrated to have used LDPE as both nitrogen and carbon source. LDPE-users were then characterised and identified using standard microbiological procedures. Biodegradation study was done using selected bacterial and fungal isolates, singly and in consortia, to degrade heat-sterilised ground LDPE in media devoid of carbon source, and carbon and nitrogen source. Biodegradation was monitored using gravimetric methods and Fourier transform infrared spectroscopy. This study revealed some microorganisms can use LDPE as both nitrogen and carbon source in the absence of additives.
Low-density polyethylene (LDPE) waste generates an environmental impact. To achieve the most suitable option for their degradation, it is necessary to implement chemical, physical and biological treatments, as well as combining procedures. Best treatment was prognosticated by Plackett-Burman Experimental Design (PB), evaluating five factors with two levels (0.25 mM or 1.0 gL⁻¹ glucose, 1.0 or 2.0 mM CuSO4, 0.1 or 0.2 mM ABTS [2, 20-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)], pH 4.5 ± 0.2 or 7.0 ± 0.2 and 30 or 90 day incubation), which was reproduced for 150 days. Therefore, PB identified a sequential treatment (plasma followed by fungus) for partial LDPE biodeterioration. Sheets were pretreated with glow discharge plasma (O2, 3.0 x 10⁻² mbar, 600 V, 6 min.), followed by Pleurotus ostreatus biodeterioration. Fungus growth, colonization percentage, and pigment generation followed. Laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP) activities were appraised. Additionally, contact angle (CA), functional group presence and changes and carbonyl and vinyl indices (Fourier transformed infrared spectroscopy) were evaluated. LDPE surface changes were assessed by Young’s modulus, yield strength, scanning electronic microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Plasma discharge increased hydrophilicity, decreasing CA by 76.57% and increasing surface roughness by 99.81%. P. ostreatus colonization was 88.72% in 150 days in comparison with untreated LDPE (45.55%). After this treatment carbonyl groups (C = O), C = C insaturations, high hydrophilicity CA (16 ± 4) °, and low surface roughness (7 ± 2) nm were observed. However, the highest Lac and LiP activities were detected after 30 days (Lac: 2.817 U Lac g⁻¹ and LiP: 70.755 U LiP g⁻¹). In addition, highest MnP activity was observed at day 120 (1.097 U MnP g⁻¹) only for P. ostreatus treated LDPE. Plasma favored P. ostreatus adsorption, adherence, growth and colonization (88.72%), as well as partial LDPE biodeterioration, supported by increased hydrophilicity and presence of specific functional chemical groups. The approximate 27% changes in LDPE physical properties support its biodeterioration.
It is now well established that the oceans contain significant accumulations of plastic debris but only very recently have studies began to look at sources of microplastics (MPs) in river catchments. This work measured MPs up- and downstream of six wastewater treatment plants (WWTPs) in different catchments with varying characteristics and found that all led to an increase in MPs in rivers. Nevertheless, the data collected indicated that there were other important sources of MPs in the catchments studied and that these may include atmospheric deposition, agricultural land to which sewage sludge has been applied, and diffuse release of secondary MPs following the breakdown of larger plastic items. MPs were comprised mainly of fibres, fragments, and flakes with pellets and beads only dominating at one site. Variation in MP pollution occurred over time and this difference was greater at some sites than others. A key research need is the further study of MP sources in river catchments to facilitate management efforts to reduce their presence in freshwater and marine environments.
Wood decay fungi have complex detoxification systems that enable them to cope with secondary metabolites produced by plants. Although the number of genes encoding for glutathione transferases is especially expanded in lignolytic fungi, little is known about their target molecules. In this study, by combining biochemical, enzymatic and structural approaches, interactions between polyphenols and six glutathione transferases from the white-rot fungus Trametes versicolor have been demonstrated. Two isoforms, named TvGSTO3S and TvGSTO6S have been deeply studied at the structural level. Each isoform shows two distinct ligand-binding sites, a narrow L-site at the dimer interface and a peculiar deep hydrophobic H-site. In TvGSTO3S, the latter appears optimized for aromatic ligand binding such as hydroxybenzophenones. Affinity crystallography revealed that this H-site retains the flavonoid dihydrowogonin from a partially purified wild-cherry extract. Besides, TvGSTO6S binds two molecules of the flavonoid naringenin in the L-site. These data suggest that TvGSTO isoforms could interact with plant polyphenols released during wood degradation.
Pharmaceuticals represent an immense business with increased demand due to intensive livestock raising and an aging human population, which guarantee the quality of human life and well-being. However, the development of removal technologies for these compounds is not keeping pace with the swift increase in their use. Pharmaceuticals constitute a potential risk group of multiclass chemicals of increasing concern since they are extremely frequent in all environments and have started to exhibit negative effects on micro- and macro-fauna as well as on human health. In this context, fungi are known to be extremely diverse and poorly studied microorganisms despite being well suited for bioremediation processes, taking into account their metabolic and physiological characteristics for the transformation of even highly toxic xenobiotic compounds. Increasing studies indicate that fungi can transform many structures of pharmaceutical compounds, including anti-inflammatories, β-blockers, and antibiotics. This is possible due to different mechanisms in combination with the extracellular and intracellular enzymes, which have broad of biotechnological applications. Thus, fungi and their enzymes could represent a promising tool to deal with this environmental problem. Here, we review the studies performed on pharmaceutical compounds biodegradation by the great diversity of these eukaryotes. We examine the state of the art of the current application of the Basidiomycota division, best known in this field, as well as the assembly of novel biodegradation pathways within the Ascomycota division and the Mucoromycotina subdivision from the standpoint of shared enzymatic systems, particularly for the cytochrome P450 superfamily of enzymes, which appear to be the key enzymes in these catabolic processes. Finally, we discuss the latest advances in the field of genetic engineering for their further application.
Plastics have outgrown most man-made materials and have long been under environmental scrutiny. However, robust global information, particularly about their end-of-life fate, is lacking. By identifying and synthesizing dispersed data on production, use, and end-of-life management of polymer resins, synthetic fibers, and additives, we present the first global analysis of all mass-produced plastics ever manufactured. We estimate that 8300 million metric tons (Mt) as of virgin plastics have been produced to date. As of 2015, approximately 6300 Mt of plastic waste had been generated, around 9% of which had been recycled, 12% was incinerated, and 79% was accumulated in landfills or the natural environment. If current production and waste management trends continue, roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050.
Research on the uptake and effects of bioplastics by aquatic organisms is still in its infancy. Here, we aim to advance the field by comparing uptake and effects of microplastic particles (MPP) of a biodegradable bioMPP (polyhydroxybutyrate (PHB)) and petroleum-based MPP (polymethylmethacrylate (PMMA)) in the freshwater amphipod Gammarus fossarum. Ingestion of both MPP in different particle sizes (32–250 µm) occurred after 24 h, with highest ingestion of particles in the range 32–63 µm and almost complete egestion after 64 h. A four-week effect-experiment showed a significant decrease of the assimilation efficiency in amphipods exposed to the petroleum-based MPP from week two onwards. The petroleum-based PMMA affected assimilation efficiency significantly in contrast to the biodegradable PHB, but overall differences in direct comparison of MPP types were small. Both MPP types led to a significantly lower wet weight gain relative to the control treatments. After four weeks, differences between both MPP types and silica, used as a natural particle control, were detected. In summary, these results suggest that both MPP types provoke digestive constraints on the amphipods, which go beyond those of natural non-palatable particles. This highlights the need for more detailed research comparing environmental effects of biodegradable and petroleum-based MPP and testing those against naturally occurring particle loads.
Incineration of plastic waste in an open field is a major source of air pollution. Most of the times, the Municipal Solid Waste containing about 12% of plastics is burnt, releasing toxic gases like Dioxins, Furans, Mercury and Polychlorinated Biphenyls into the atmosphere. Further, burning of Poly Vinyl Chloride liberates hazardous halogens and pollutes air, the impact of which is climate change. The toxic substances thus released are posing a threat to vegetation, human and animal health and environment as a whole. Polystyrene is harmful to Central Nervous System. The hazardous brominated compounds act as carcinogens and mutagens. Dioxins settle on the crops and in our waterways where they eventually enter into our food and hence the body system. These Dioxins are the lethal persistent organic pollutants (POPs) and its worst component, 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), commonly known as agentorange is a toxic compound which causes cancer and neurological damage, disrupts reproductive thyroid and respiratory systems. Thus, burning of plastic wastes increase the risk of heart disease, aggravates respiratory ailments such as asthma and emphysema and cause rashes, nausea or headaches, and damages the nervous system. Hence, a sustainable step towards tomorrow's cleaner and healthier environment needs immediate attention of the environmentalists and scientists. This review presents the hazards of incineration; open burning of plastics and effects of plastic in water and also a possibility of working out strategies to develop alternate procedures of plastic waste management.
Importance:
Polyurethane waste disposal has become a serious problem. In this work, fungi strains able to efficiently degrade different types of polyurethanes are reported and their biodegradative activity studied by different experimental approaches. Varnish biodegradation analyses showed that fungi were able to break down the polymer in some of their precursors, offering the possibility that they may be recovered and used for new polyurethane synthesis. Also, the levels of degradation of solid polyether polyurethane foams reported in this work have never been observed previously. Isolation of efficient polyurethane-degrading microorganisms and delving into the mechanisms they used to degrade the polymer provide the basis for the development of biotechnological processes for polyurethane biodegradation and recycling.
Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known, however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the “great Pacific garbage patch.” The concentration of plastic particles in surface seawater within different size classes (2 to 5 mm and >5 mm) ranged from 0.35 to 3.7 particles m⁻³ across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production − community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa, Cyanobacteria, Alphaproteobacteria, and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from the surrounding picoplankton and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes, and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions, and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways, and biogeochemical activities that are distinct from those of free-living planktonic microbial communities.
IMPORTANCE Marine plastic debris is a growing concern that has captured the general public’s attention. While the negative impacts of plastic debris on oceanic macrobiota, including mammals and birds, are well documented, little is known about its influence on smaller marine residents, including microbes that have key roles in ocean biogeochemistry. Our work provides a new perspective on microbial communities inhabiting microplastics that includes its effect on microbial biogeochemical activities and a description of the cross-domain communities inhabiting plastic particles. This study is among the first molecular ecology, plastic debris biota surveys in the North Pacific Subtropical Gyre. It has identified fundamental differences in the functional potential and taxonomic composition of plastic-associated microbes versus planktonic microbes found in the surrounding open-ocean habitat.
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Municipal wastewater treatment plants (WWTPs) are frequently suspected as significant point sources or conduits of microplastics to the environment. To directly investigate these suspicions, effluent discharges from seven tertiary plants and one secondary plant in Southern California were studied. The study also looked at influent loads, particle size/type, conveyance, and removal at these wastewater treatment facilities. Over 0.189 million liters of effluent at each of the seven tertiary plants were filtered using an assembled stack of sieves with mesh sizes between 400 and 45 μm. Additionally, the surface of 28.4 million liters of final effluent at three tertiary plants was skimmed using a 125 μm filtering assembly. The results suggest that tertiary effluent is not a significant source of microplastics and that these plastic pollutants are effectively removed during the skimming and settling treatment processes. However, at a downstream secondary plant, an average of one micro-particle in every 1.14 thousand liters of final effluent was counted. The majority of microplastics identified in this study had a profile (color, shape, and size) similar to the blue polyethylene particles present in toothpaste formulations. Existing treatment processes were determined to be very effective for removal of microplastic contaminants entering typical municipal WWTPs.
Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters that can potentially replace certain plastics derived from petroleum. PHAs can be produced using a combination of renewable feedstocks and biological methods. Native and recombinant microorganisms have been generally used for making PHAs via fermentation processes. As much as 90 % of the microbial dry mass may accumulate as PHAs. A range of PHAs has been produced using fermentation methods, including copolymers and block copolymers. Alternative production schemes based on genetically modified plants are becoming established and may become the preferred route for producing certain PHAs. Production in plants is likely to be inexpensive compared to production by fermentation, but it does not appear to be as versatile as microbial synthesis in terms of the range of products that may be generated. Cell-free enzymatic production of PHAs in vitro is receiving increasing attention and may become the preferred route to some specialty products. This review discusses the recent advances in production of polyhydroxyalkanoates by the various methods. Methods of recovering the polymer from microbial biomass are reviewed. Established and emerging applications of PHAs are discussed.
Filamentous fungi Aspergillus niger, Aspergillus terreus, Aureobasidium pullulans, Paecilomyces varioti, Penicillium funiculosum, Penicillium ochrochloron, Scopulariopsis brevicaulis, Trichoderma viride and their mixture were employed for the biodegradation. Aspergillus niger and Penicillium funiculosum were isolated from dump in Sosnowiec and their identification was carried out by Institute for Ecology of Industrial Areas in Katowice, Poland. The others were purchased from Institute of Fermentation Technology and Microbiology in Łódź, Poland.
After 84-day incubation with filamentous fungi the most intense changes were found on the surface of 40/60 composition. Hyphae and conidiophores of Aspergillus niger (Figure 6a), Aspergillus terreus (Figure 6b), Aureobasidium pullulans (Figure 6c) and Trichoderma viride (Figure 6g) grew out directly from the polymer sample. However, changes induced by the action of these microorganisms deep and distinct. Dense network of fractures was particularly visible after incubation with Aspergillus terreus. Aspergillus niger and Aureobasidium pullulans caused massive exfoliation of the plastic edges. Although Penicillium ochrochloron(Figure 6e) andScopulariopsis brevicaulis (Figure 6f) created mycelium, a considerable part of the film surface was found to be unaffected. Loss of integrity of film resulted into fragile surface entirely covered by dense mycelia of Penicillium funiculosum (Figure 6d) and mixed population of fungi (Figure 6h).
One of the most ubiquitous and long-lasting recent changes to the surface of our planet is the accumulation and fragmentation of plastics. Within just a few decades since mass production of plastic products commenced in the 1950s, plastic debris has accumulated in terrestrial environments, in the open ocean, on shorelines of even the most remote islands and in the deep sea. Annual clean-up operations, costing millions of pounds sterling, are now organized in many countries and on every continent. Here we document global plastics production and the accumulation of plastic waste. While plastics typically constitute approximately 10 per cent of discarded waste, they represent a much greater proportion of the debris accumulating on shorelines. Mega- and macro-plastics have accumulated in the highest densities in the Northern Hemisphere, adjacent to urban centres, in enclosed seas and at water convergences (fronts). We report lower densities on remote island shores, on the continental shelf seabed and the lowest densities (but still a documented presence) in the deep sea and Southern Ocean. The longevity of plastic is estimated to be hundreds to thousands of years, but is likely to be far longer in deep sea and non-surface polar environments. Plastic debris poses considerable threat by choking and starving wildlife, distributing non-native and potentially harmful organisms, absorbing toxic chemicals and degrading to micro-plastics that may subsequently be ingested. Well-established annual surveys on coasts and at sea have shown that trends in mega- and macro-plastic accumulation rates are no longer uniformly increasing: rather stable, increasing and decreasing trends have all been reported. The average size of plastic particles in the environment seems to be decreasing, and the abundance and global distribution of micro-plastic fragments have increased over the last few decades. However, the environmental consequences of such microscopic debris are still poorly understood.
Being the most delicate organ of the body, the brain is protected against potentially toxic substances by the blood-brain barrier (BBB), which restricts the entry of most pharmaceuticals into the brain. The developmental process for new drugs for the treatment of CNS disorders has not kept pace with progress in molecular neurosciences because most of the new drugs discovered are unable to cross the BBB. The clinical failure of CNS drug delivery may be attributed largely to a lack of appropriate drug delivery systems. Localized and controlled delivery of drugs at their desired site of action is preferred because it reduces toxicity and increases treatment efficiency. The present review provides an insight into some of the recent advances made in the field of brain drug delivery.
The various strategies that have been explored to increase drug delivery into the brain include (i) chemical delivery systems, such as lipid-mediated transport, the prodrug approach and the lock-in system; (ii) biological delivery systems, in which pharmaceuticals are re-engineered to cross the BBB via specific endogenous transporters localized within the brain capillary endothelium; (iii) disruption of the BBB, for example by modification of tight junctions, which causes a controlled and transient increase in the permeability of brain capillaries; (iv) the use of molecular Trojan horses, such as peptidomimetic monoclonal antibodies totransport large molecules (e.g. antibodies, recombinant proteins, nonviral gene medicines or RNA interference drugs) across the BBB; and (v) particulate drug carrier systems. Receptor-mediated transport systems exist for certain endogenous peptides, such as insulin and transferrin, enabling these molecules to cross the BBB in vivo.
The use of polymers for local drug delivery has greatly expanded the spectrum of drugs available for the treatment of brain diseases, such as malignant tumours and Alzheimer’s disease. In addition, various drug delivery systems (e.g. liposomes, microspheres, nanoparticles, nanogels and bionanocapsules) have been used to enhance drug delivery to the brain. Recently, microchips and biodegradable polymers have become important in brain tumour therapy.
The intense search for alternative routes of drug delivery (e.g. intranasal drug delivery, convection-enhanced diffusion and intrathecal/intraventricular drug delivery systems) has been driven by the need to overcome the physiological barriers of the brain and to achieve high drug concentrations within the brain. For more than 30 years, considerable efforts have been made to enhance the delivery of therapeutic molecules across the vascular barriers of the CNS. The current challenge is to develop drug delivery strategies that will allow the passage of drug molecules through the BBB in a safe and effective manner.
The culturability of bacteria in the bulk soil of an Australian pasture was investigated by using nutrient broth at 1/100 of its normal concentration (dilute nutrient broth [DNB]) as the growth medium. Three-tube most-probable-number serial dilution culture resulted in a mean viable count that was only 1.4% of the mean microscopically determined total cell count. Plate counts with DNB solidified with agar and with gellan gum resulted in viable counts that were 5.2 and 7.5% of the mean microscopically determined total cell count, respectively. Prior homogenization of the soil sample with an ultrasonic probe increased the viable count obtained by using DNB solidified with gellan gum to 14.1% of the mean microscopically determined cell count. A microscopic examination of the cell aggregates that remained after sonication revealed that the potential CFU count was only 70.4% of the total cell count, due to cells occurring as pairs or in clumps of three or more cells. Staining with SYTO 9 plus propidium iodide indicated that 91.3% of the cells in sonicated soil samples were potentially viable. Together, these findings suggest that the maximum achievable CFU count may be as low as 64.3% of the total cell count. Thirty isolates obtained from plate counting experiments performed with DNB as the growth medium were identified by comparative analysis of partial 16S rRNA gene sequences. A large proportion of these isolates represent the first known isolates of globally distributed groups of soil bacteria belonging to novel lineages within the divisions Actinobacteria, Acidobacteria, Proteobacteria, and Verrucomicrobia.
Airborne microplastics (MPs) have been sampled globally, and their concentration is known to increase in areas of high human population and activity, especially indoors. Respiratory symptoms and disease following exposure to occupational levels of MPs within industry settings have also been reported. It remains to be seen whether MPs from the environment can be inhaled, deposited and accumulated within the human lungs. This study analysed digested human lung tissue samples (n = 13) using μFTIR spectroscopy (size limitation of 3 μm) to detect and characterise any MPs present. In total, 39 MPs were identified within 11 of the 13 lung tissue samples with an average of 1.42 ± 1.50 MP/g of tissue (expressed as 0.69 ± 0.84 MP/g after background subtraction adjustments). The MP levels within tissue samples were significantly higher than those identified within combined procedural/laboratory blanks (n = 9 MPs, with a mean ± SD of 0.53 ± 1.07, p = 0.001). Of the MPs detected, 12 polymer types were identified with polypropylene, PP (23%), polyethylene terephthalate, PET (18%) and resin (15%) the most abundant. MPs (unadjusted) were identified within all regions of the lung categorised as upper (0.80 ± 0.96 MP/g), middle/lingular (0.41 ± 0.37 MP/g), and with significantly higher levels detected in the lower (3.12 ± 1.30 MP/g) region compared with the upper (p = 0.026) and mid (p = 0.038) lung regions. After subtracting blanks, these levels became 0.23 ± 0.28, 0.33 ± 0.37 and 1.65 ± 0.88 MP/g respectively. The study demonstrates the highest level of contamination control and reports unadjusted values alongside different contamination adjustment techniques. These results support inhalation as a route of exposure for environmental MPs, and this characterisation of types and levels can now inform realistic conditions for laboratory exposure experiments, with the aim of determining health impacts.
Microplastic pollution has recently been identified as a major issue for the health of ecosystems. Microplastics have typically sizes of less than 5 mm and occur in various forms, such as pellets, fibres, fragments, films, and granules. Mangroves and coral reefs are sensitive and restricted ecosystems that provide free ecological services such as coastal protection, maintaining natural cycles, hotspots of biodiversity and economically valuable goods. However, urbanization and industrial activities have started contaminating even these preserved ecosystems. Here we review sources, occurrence, and toxicity of microplastics in the trophic levels of mangrove and coral reef ecosystems. We present detection methods, such as microscopic identification and spectroscopy. We discuss mitigating measures that prevent the entry of microplastics into the marine environment.
ccumulation of plastic wastes has been recently recognized as one of the most critical environmental challenges, affecting all life forms, natural ecosystems and economy, worldwide. Under this threat, finding alternative environmentally-friendly solutions, such as biodegradation instead of traditional disposal, is of utmost importance. However, up to date, there is limited knowledge on plastic biodegradation mechanisms and efficiency. From this point of view, the purpose of this review is to highlight the negative effects of the accumulation of the most conventional plastic waste (polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethylene terephthalate and polyurethane) on the environment and to present their degradability potential through abiotic and biotic processes. Furthermore, the ability of different microbial species for degradation of these polymers is thoroughly discussed. The present review also addresses the contribution of invertebrates, such as insects in plastic degradation process, highlighting the vital role that they could play in the future. In total, a schematic pathway of an innovative approach to improve the disposal of plastic wastes is proposed, with view to establishing an effective and sustainable practice for plastic waste management.
Plastics are discarded and accumulated in the environment at an alarming rate. However, their resistance to biodegradation allows them to persist in the environment for prolonged durations. While large plastics are easier to remove, microplastic particles from cosmetics or fragments from larger pieces are extremely difficult to remove from the environment. Furthermore, current techniques such as filters poorly retain microplastics or require harsh chemical treatments in wastewater treatment plants. Hence, microplastics enter the natural environment easily even after effluent treatments, thereby endangering aquatic life and humans who consume seafood. It is imperative to develop sustainable bioaggregation processes to trap microplastics quickly for easier removal from the environment. Here, we showed that microplastics can be trapped and aggregated in the sticky exopolymeric substances (EPS) produced by biofilms. As a proof-of-concept, we engineered a bacterial biofilm with a ‘capture-release mechanism’, whose EPS can first cause bioaggregation of microplastics for easier isolation, followed by an inducible biofilm dispersal mechanism that releases trapped microplastics for downstream resource recovery. We also demonstrated the potential application of the engineered biofilm in mitigating microplastics pollution in seawater samples collected in the vicinity of a sewage outfall. This capture-and-release approach should prove widely applicable to other micropollutants or biofilm-enabled catalysis.
An alarming rise of micro-nano plastics (MNPs) in environment is currently causing the biggest threat to biotic and abiotic components around the globe. These pollutants, apart from being formed through fragmentation of larger plastic pieces and are also manufactured for commercial usage. MNPs enter agro-ecosystem, wildlife, and human body through the food chain, ingestion or through inhalation, causing blockage in the blood-brain barrier, lower fertility, and behavioural abnormalities among other problems. Hence, it becomes essential to develop novel procedures for remediation of MNPs. Among the numerous existing methods, microbial remediation promises to degrade/recover MNPs via a green route. Since microbial remediation processes mostly depend upon biotic and abiotic factors such as (temperature, pH, oxidative stress, etc.), it becomes easy to influence changes in the plastic pollutants. Hence, with the help of recent technologies, a complete degradation/removal of MNPs can be expected by utilizing the respective carbon content as energy sources for growth of microorganisms. In this review, considering the urgent environmental need, the impact of micro-nano plastics on ecosystem along with its corresponding degradation mechanisms has been brought out. Also, importance of the various recent research approaches in MNPs remediation is highlighted. Finally, the role of enzyme and membrane technology, nanoparticle technology, and metagenomics in remediation of MNPs are discussed for the first time in detail to bring out a novel remedy for the environment.
Microplastics (MPs) as emerging persistent pollutants have been a growing global concern. Although MPs are extensively studied in aquatic systems, their presence and fate in agricultural systems are not fully understood. In the agricultural soils, major causes of MPs pollution include application of biosolids and compost, wastewater irrigation, mulching film, polymer-based fertilizers and pesticides, and atmospheric deposition. The fate and dispersion of MPs in the soil environment are mainly associated with the soil characteristics, cultivation practices, and diversity of soil biota. Although there is emerging pollution of MPs in the soil environment, no standardized detection and quantification techniques are available. This study comprehensively reviews the sources, fate, and dispersion of MPs in the soil environment, discusses the interactions and effects of MPs on soil biota, and highlights the recent advancements in detection and quantification methods of MPs. The prospects for future research include biomagnification potency, cytotoxic effects on human/animals, nonlinear behavior in the soil environment, standardized analytical methods, best management practices, and global policies in the agricultural industry for the sake of sustainable development.
Plant biomass is an abundant renewable resource on Earth. Microorganisms harvest energy from plant material by means of complex enzymatic systems that efficiently degrade natural polymers. Intriguingly, microorganisms have evolved to exploit these ancient mechanisms to also decompose synthetic plastic polymers. In this Review, we summarize the mechanisms by which they decompose non-starch plant biomass and the six major types of synthetic plastics. We focus on the structural features of the enzymes that contribute to substrate recognition and then describe the catalytic mechanisms of polymer metabolism. An understanding of these natural biocatalysts is valuable if we are to exploit their potential for the degradation of synthetic polymers. Microorganisms enzymatically degrade natural polymers and synthetic plastics to enable a sustainable environment. This Review describes common features of these enzymes and how they can be harnessed to convert waste into useful precursors.
Phenol is a common water pollutant because of its broad industrial applications. Biological method is a promising alternative to conventional physical and chemical methods for removing this toxic pollutant from the environment. In this study, two metabolic modules were introduced into Escherichia coli, the widely used host for various genetic manipulations, to elucidate the metabolic capacity of E. coli for phenol degradation. The first module catalysed the conversion of phenol to catechol, whereas the second module cleaved catechol into the three carboxylic acid circulating intermediates by the ortho-cleavage pathway. Phenol was completely degraded and imported into the tricarboxylic acid cycle by the engineered bacteria. Proteomics analysis showed that all genes in the phenol degradation pathway were over-expressed and affected cell division and energy metabolism of the host cells. Phenol in coking wastewater was degraded powerfully by BL-phe/cat. The engineered E. coli can improve the removal rate and shorten the processing time for phenol removal and has considerable potential in the treatment of toxic and harmful pollutants.
In this study, we investigated the decomposition of micro-sized polyethylene (PE) by mesophilic mixed bacterial culture isolates obtained from a municipal landfill sediment. Among these, Bacillus sp. and Paenibacillus sp. were more specifically enriched in the non-carbonaceous nutrient medium (i.e., Basal medium) as they were the most dominant species when they were exposed to PE microplastics. They reduced the dry weight of particles (14.7% after 60 d) and the mean particle diameter (22.8% after 60 d; obtained by field-emission scanning electron microscopy analysis). In the gas chromatography-mass spectrometer analysis of biologically aged particles, the amount and types of organic contents eluted from the PE microplastics were far lower in the early decomposition phase; however, they increased in the later phase. Thermal gravimetric analysis showed that the aged particles had higher thermal stability at temperatures greater than 570 °C compared to the control, thereby suggesting that microplastics were degraded by enzymatic chain scission, which could in turn be ascribed to the greater refractory fractions of aged particles remaining at a high combustion temperature. It was further verified that PE particles could be biologically utilized as a sole carbon source and broken down during the test period.
Microplastics are tiny ubiquitous plastic particles present in marine environments. They are not an individual entity, but constitute a cocktail of polymers and additives that can absorb substances from the surrounding environment, including living substances, nutrients and marine pollutants. Given their small size (< 5 μm), microplastics can be ingested by a wide range of marine organisms with the potential to cause harms. Microplastics are a growing threat for marine biota and ecosystem. For organisms, the risks associated with microplastic ingestion are not only due to the material itself, but also to its ability to absorb and concentrate environmental contaminants in seawater and subsequently transfer them through food chains. Moreover, microplastics could influence ecological processes. Recently, plastic debris are recognized as emerging pollutants and represent a great risk for marine biodiversity worldwide. Here, we summarize the main effects of plastics and microplastics on some marine organisms and ecosystem.
Microplastics are a pollutant of environmental concern. Their presence in food destined for human consumption and in air samples has been reported. Thus, microplastic exposure via diet or inhalation could occur, the human health effects of which are unknown. The current review article draws upon cross-disciplinary scientific literature to discuss and evaluate the potential human health impacts of microplastics and outlines urgent areas for future research. Key literature up to September 2016 relating to bioaccumulation, particle toxicity, and chemical and microbial contaminants were critically examined. Whilst this is an emerging field, complimentary existing fields indicate potential particle, chemical and microbial hazards. If inhaled or ingested, microplastics may bioaccumulate and exert localised particle toxicity by inducing or enhancing an immune response. Chemical toxicity could occur due to the localised leaching of component monomers, endogenous additives, and adsorbed environmental pollutants. Chronic exposure is anticipated to be of greater concern due to the accumulative effect which could occur. This is expected to be dose-dependent, and a robust evidence-base of exposure levels is currently lacking. Whilst there is potential for microplastics to impact human health, assessing current exposure levels and burdens is key. This information will guide future research into the potential mechanisms of toxicity and hence therein possible health effects.
Plastic is a broad name given to different polymers with high molecular weight that impact wildlife. Their fragmentation leads to a continuum of debris sizes (meso to microplastics) entrapped in gyres and colonized by microorganisms. In the present work, the structure of eukaryotes, bacteria and Archaea was studied by a metabarcoding approach, and statistical analysis associated with network building was used to define a core microbiome at the plastic surface. Most of the bacteria significantly associated with the plastic waste originated from non-marine ecosystems, and numerous species can be considered as hitchhikers, whereas others act as keystone species (e.g., Rhodobacterales, Rhizobiales, Streptomycetales and Cyanobacteria) in the biofilm. The chemical analysis provides evidence for a specific colonization of the polymers. Alphaproteobacteria and Gammaproteobacteria significantly dominated mesoplastics consisting of poly(ethylene terephthalate) and polystyrene. Polyethylene was also dominated by these bacterial classes and Actinobacteria. Microplastics were made of polyethylene but differed in their crystallinity, and the majorities were colonized by Betaproteobacteria. Our study indicated that the bacteria inhabiting plastics harboured distinct metabolisms from those present in the surrounding water. For instance, the metabolic pathway involved in xenobiotic degradation was overrepresented on the plastic surface.
Plastics have been successfully used as packaging materials, but environmental pollution by plastics is inducing a growing interest for alternative, biocompatible plastics. In this context, bionanocomposites are developed for application in the food packaging sector. This article reviews methods for encapsulation of bioactive compounds into nanostructures, which can be further incorporated into packaging materials to improve food quality and safety. Encapsulation of active compounds in bionanocomposites is done using various methods such as spray drying, spray cooling and chilling, fluidized bed coating, coacervation, liposome entrapment, co-crystallization, nanoemulsion, air suspension, freeze-drying, interfacial polymerization, molecular inclusion and sol–gel. Nonetheless, none of these methods are universally applicable for a bioactive or food component. Alternatively, lipid-based nanostructures such as liposomes and solid lipid nanoparticles have been effectively used for the delivery of bioactive molecules showing antimicrobial and antioxidant activities. Fat-soluble vitamins can be incorporated in nanoemulsions, which in addition to polymeric nanoparticles are suitable vehicles to phytochemicals like quercetin and curcumin. Nanofibers are also promising materials to incorporate bioactive substances in food packaging.
The xenobiotic nature and lack of degradability of polymeric materials has resulted in vast levels of environmental pollution and numerous health hazards. Different strategies have been developed and still more research is being in progress to reduce the impact of these polymeric materials. This work aimed to isolate and characterize polyester polyurethane (PU) degrading fungi from the soil of a general city waste disposal site in Islamabad, Pakistan. A novel PU degrading fungus was isolated from soil and identified as Aspergillus tubingensis on the basis of colony morphology, macro- and micro-morphology, molecular and phylogenetic analyses. The PU degrading ability of the fungus was tested in three different ways in the presence of 2% glucose: (a) on SDA agar plate, (b) in liquid MSM, and (c) after burial in soil. Our results indicated that this strain of A. tubingensis was capable of degrading PU. Using scanning electron microscopy (SEM), we were able to visually confirm that the mycelium of A. tubingensis colonized the PU material, causing surface degradation and scarring. The formation or breakage of chemical bonds during the biodegradation process of PU was confirmed using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. The biodegradation of PU was higher when plate culture method was employed, followed by the liquid culture method and soil burial technique. Notably, after two months in liquid medium, the PU film was totally degraded into smaller pieces. Based on a comprehensive literature search, it can be stated that this is the first report showing A. tubingensis capable of degrading PU. This work provides insight into the role of A. tubingensis towards solving the dilemma of PU wastes through biodegradation.
TfCut2 from Thermobifida fusca KW3 and the metagenome-derived LC-cutinase are bacterial polyester hydrolases capable of efficiently degrading polyethylene terephthalate (PET) films. Since the enzymatic PET hydrolysis is inhibited by the degradation intermediate mono-(2-hydroxyethyl) terephthalate (MHET), a dual enzyme system consisting of a polyester hydrolase and the immobilized carboxylesterase TfCa from Thermobifida fusca KW3 was employed for the hydrolysis of PET films at 60°C. HPLC analysis of the reaction products obtained after 24 h of hydrolysis showed an increased amount of soluble products with a lower proportion of MHET in the presence of the immobilized TfCa. The results indicated a continuous hydrolysis of the inhibitory MHET by the immobilized TfCa and demonstrated its advantage as a second biocatalyst in combination with a polyester hydrolase for an efficient degradation oft PET films. The dual enzyme system with LC-cutinase produced a 2.4-fold higher amount of degradation products compared to TfCut2 after a reaction time of 24 h confirming the superior activity of his polyester hydrolase against PET films.
White-rot fungus Bjerkandera adusta has been tested for its ability to degrade some biocomposites materials based on polypropylene and biomass (Eucalyptus globulus, pine cones, and Brassica rapa). γ-irradiation was applied to initiate the degradation of relatively inert polypropylene matrix. The degradation process has been studied by scanning electron microscopy, atomic force microscopy, infrared spectroscopy, contact angle measurements, rheological and chemiluminescence tests. These analyses showed that the polypropylene/biomass composites properties are worsen under the action of the selected microorganism. The formation of cracks and scrap particles over the entire matrix surface and the decrease of the complex viscosity values, as well as the dynamic moduli of gamma irradiated PP/biomass composite and exposed to Bjerkandera adusta fungus, indicate fungal efficiency in composite degradation.
Zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) comprise a powerful class of tools that are redefining the boundaries of biological research. These chimeric nucleases are composed of programmable, sequence-specific DNA-binding modules linked to a nonspecific DNA cleavage domain. ZFNs and TALENs enable a broad range of genetic modifications by inducing DNA double-strand breaks that stimulate error-prone nonhomologous end joining or homology-directed repair at specific genomic locations. Here, we review achievements made possible by site-specific nuclease technologies and discuss applications of these reagents for genetic analysis and manipulation. In addition, we highlight the therapeutic potential of ZFNs and TALENs and discuss future prospects for the field, including the emergence of clustered regulatory interspaced short palindromic repeat (CRISPR)/Cas-based RNA-guided DNA endonucleases.
Here we use the clustered, regularly interspaced, short palindromic repeats (CRISPR)-associated Cas9 endonuclease complexed with dual-RNAs to introduce precise mutations in the genomes of Streptococcus pneumoniae and Escherichia coli. The approach relies on dual-RNA:Cas9-directed cleavage at the targeted genomic site to kill unmutated cells and circumvents the need for selectable markers or counter-selection systems. We reprogram dual-RNA:Cas9 specificity by changing the sequence of short CRISPR RNA (crRNA) to make single- and multinucleotide changes carried on editing templates. Simultaneous use of two crRNAs enables multiplex mutagenesis. In S. pneumoniae, nearly 100% of cells that were recovered using our approach contained the desired mutation, and in E. coli, 65% that were recovered contained the mutation, when the approach was used in combination with recombineering. We exhaustively analyze dual-RNA:Cas9 target requirements to define the range of targetable sequences and show strategies for editing sites that do not meet these requirements, suggesting the versatility of this technique for bacterial genome engineering.
It has been speculated that marine microplastics may cause negative effects on benthic marine organisms and increase bioaccumulation of persistent organic pollutants (POPs). Here, we provide the first controlled study of plastic effects on benthic organisms including transfer of POPs. The effects of polystyrene (PS) microplastic on survival, activity, and bodyweight as well as the transfer of 19 polychlorinated biphenyls (PCBs), were assessed in bioassays with Arenicola marina (L.). PS was pre-equilibrated in natively contaminated sediment. A positive relation was observed between microplastic concentration in the sediment and both uptake of plastic particles and weight loss by A. marina. Furthermore, a reduction in feeding activity was observed at a PS dose of 7.4% dry weight (DW). A low PS dose of 0.074% increased bioaccumulation of PCBs by a factor 1.1 - 3.6, an effect that was significant for ΣPCBs and several individual congeners. At higher doses, bioaccumulation decreased compared to the low dose, which however, was only significant for PCB105. PS has statistically significant effects on the organisms' fitness and bioaccumulation, but the magnitude of the effects was not high. This may be different for sites with different plastic concentrations, or plastics with a higher affinity for POPs.
Bisphenol A (BPA) is known as an endocrine disruptor and often is found in landfill leachates. Removal of BPA by green alga, Chlorella fusca, was characterized, because we previously found that various phenols were well removed by this strain, including BPA. Chlorella fusca was able to remove almost all BPA in the concentration range from 10 to 80 μM for 168 h under continuous illumination at 18 W/m2. At the low light intensity of 2 W/m2, 82% of 40 μM BPA was removed, and only 27% was removed in the dark. Moreover, C. fusca could remove 90% of 40 μM BPA under the 8:16-h light:dark condition, which was almost as high as that under the continuous-light condition. The amount of BPA contained in the cells was less than the amount of BPA removed from the medium. Monohydroxybisphenol A was detected as an intermediate of BPA degradation. Moreover, estrogenic activity that originated from BPA in the culture medium also completely disappeared. Based on these results, BPA was finally degraded to compounds having nonestrogenic activity. Therefore, C. fusca can be considered a useful organism to remove BPA from landfill leachates.
The toxicity of bisphenol A (BPA) to Stephanodiscus hantzschii, a diatom isolated from tidal water of Futian Mangrove Nature Reserve, China, and the bioaccumulation and removal capability of the marine microalga to BPA were investigated in the present study. Toxicity experiments showed that the 96-h EC50 of BPA was 8.65±0.26 mg/L, and the cell number and chlorophyll a content of S. hantzschii decreased significantly with increases in BPA at concentrations higher than 3.00 mg/L. S. hantzschii had high removal capability at low BPA concentrations as BPA was bioaccumulated and biodegraded by cells. After 16-day treatment, 88%, 99%, 92%, 61%, 48%, 28% and 26% of BPA were removed by the diatom in the media supplemented with 0.01, 0.10, 1.00, 3.00, 5.00, 7.00 and 9.00 mg/L BPA, respectively. The present study demonstrated that S. hantzschii was a tolerant isolate that could be used to remove BPA from contaminated waters.