Toxic response of the freshwater green algae Chlorella pyrenoidosa to combined effect of flotation reagent butyl xanthate and nickel

Insight into the mechanisms of combined toxicity of cadmium and flotation agents in luminescent bacteria: Role of micro/nano particles

Currently, risk assessment and pollution management in mines primarily focus on toxic metals, with the flotation agents being overlooked. However, the combined effects of metals and flotation agents in mines remain largely unknown. Therefore, this study aimed to evaluate the combined effects of Cd and two organic flotation agents (ethyl xanthate (EX) and diethyldithiocarbamate (DDTC)), and the associated mechanisms. The results showed that Cd + EX and Cd + DDTC exhibited synergistic toxicity. The EC50 values for luminescent bacteria were 1.6 mg/L and 1.0 mg/L at toxicity unit ratios of 0.3 and 1, respectively. The synergistic effects were closely related with the formation of Cd(EX)2 and Cd(DDTC)2 micro/nano particles, with nano-particles exhibiting higher toxicity. We observed severe cell membrane damage and cell shrinkage of the luminescent bacteria, which were probably caused by secondary harm to cells through the released CS2 during their decomposition inside cells. In addition, these particles induced toxicity by altering cellular levels of biochemical markers and the transcriptional levels of transport proteins and lipoproteins, leading to cell membrane impairment and DNA damage. This study has demonstrated that particulates formed by Cd and flotation agents contribute to the majority of the toxicity of the binary mixture. This study helps to better understand the complex ecological risk of inorganic metals and organic flotation agents in realistic mining environments.

Mining flotation reagents: Quantitative and robust analysis of metal-xanthate complexes in water

Xanthates, common mining flotation reagents, strongly bind thiophilic metals such as copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) and consequentially change their bioavailability and mobility upon their discharge into the environment. However, accurate quantification of the metal-xanthate complexes has remained elusive. This study develops a novel and robust method that realizes the accurate quantification of the metal-xanthate complexes resulted from single and multiple reactions of three typical xanthates (ethyl, isopropyl, and butyl xanthates) and four thiophilic metals (Cu, Pb, Cd, and Zn) in water samples. This method uses sulfur (S2-) dissociation, followed by tandem solid phase extraction of C18 + PWAX and subsequent LC-MS/MS analysis. It has a wide linearity range (1-1000 μg/L, R2 ≥ 0.995), low method detection limits (0.002-0.036 μg/L), and good recoveries (70.6-107.0 %) at 0.01-10 mg/L of xanthates. Applications of this method showed ubiquitous occurrence of the metal-xanthate complexes as the primary species in flotation wastewaters, which the concentrations were 4.6-28.9-fold higher than those previously determined. It is the first quantitative method established for the analysis of metal-xanthate complexes in water samples, which is of great importance to comprehensively understand the fate and risks of xanthates in the environment.

Effect of suspended particulate matter on physiological, biochemical and photosynthetic characteristics of Chlorella pyrenoidosa in the Jinjiang Estuary (Fujian, China)

Suspended particulate matter (SPM), an important component of the natural water environment, can act as a carrier of many pollutants that affect aquatic organisms. In the present study, the effect of SPM obtained from Jinjiang Estuary on the physiological, biochemical, and photosynthetic properties of typical freshwater algae (Chlorella pyrenoidosa) was investigated. The results showed that under different concentrations of SPM treatment, the superoxide dismutase (SOD), catalase (CAT) activities, and malondialdehyde (MDA) content of C. pyrenoidosa increased, but the soluble protein content decreased. SPM with different particle sizes had less effect on SOD of C. pyrenoidosa, but showed a promoting effect on CAT and MDA as well as soluble protein content. In terms of photosynthetic activity, high concentrations (70, 90 mg/L) and small particle sizes (0-75, 75-120 μm) of SPM had a greater effect on the chlorophyll a content of C. pyrenoidosa. In addition, different concentrations of SPM had no significant effect on the potential photosynthetic activity of PS II (Fv/F0) and the maximum quantum yield of PS II (Fv/Fm), but the inhibition of the initial slope (alpha), the maximum photosynthetic rate (ETRmax) and the semi-light saturation point (Ik) increased with the increase of SPM concentration. Fv/F0, ETRmax, and Ik of C. pyrenoidosa showed some degree of recovery after inhibition in the presence of SPM of different particle sizes.

Chlorella pyrenoidosa as a potential bioremediator: Its tolerance and molecular responses to cadmium and lead

Heavy metal contamination negatively affects plants and animals in water as well as soils. Some microalgae can remove heavy metal contaminants from wastewater. The aim of this study was to screen green microalgae (GM) to identify those that tolerate high concentrations of toxic heavy metals in water as possible candidates for phytoremediation. Analyses of the tolerance, physiological parameters, ultrastructure, and transcriptomes of GM under Cd/Pb treatments were conducted. Compared with the other GM, Chlorella pyrenoidosa showed stronger tolerance to high concentrations of Cd/Pb. The reduced glutathione content and peroxidase activity were higher in C. pyrenoidosa than those in the other GM. Ultrastructural observations showed that, compared with other GM, C. pyrenoidosa had less damage to the cell surface and interior under Cd/Pb toxicity. Transcriptome analyses indicated that the "peroxisome" and "sulfur metabolism" pathways were enriched with differentially expressed genes under Cd/Pb treatments, and that CpSAT, CpSBP, CpKAT2, Cp2HPCL, CpACOX, CpACOX2, and CpACOX4, all of which encode antioxidant enzymes, were up-regulated under Cd/Pb treatments. These results show that C. pyrenoidosa has potential applications in the remediation of polluted water, and indicate that antioxidant enzymes contribute to Cd/Pb detoxification. These findings will be useful for producing algal strains for the purpose of bioremediation in water contamination.

A critical review on the migration and transformation processes of heavy metal contamination in lead-zinc tailings of China

The health risks of lead-zinc (Pb-Zn) tailings from heavy metal (HMs) contamination have been gaining increasing public concern. The dispersal of HMs from tailings poses a substantial threat to ecosystems. Therefore, studying the mechanisms of migration and transformation of HMs in Pb-Zn tailings has significant ecological and environmental significance. Initially, this study encapsulated the distribution and contamination status of Pb-Zn tailings in China. Subsequently, we comprehensively scrutinized the mechanisms governing the migration and transformation of HMs in the Pb-Zn tailings from a geochemical perspective. This examination reveals the intricate interplay between various biotic and abiotic constituents, including environmental factors (EFs), characteristic minerals, organic flotation reagents (OFRs), and microorganisms within Pb-Zn tailings interact through a series of physical, chemical, and biological processes, leading to the formation of complexes, chelates, and aggregates involving HMs and OFRs. These interactions ultimately influence the migration and transformation of HMs. Finally, we provide an overview of contaminant migration prediction and ecological remediation in Pb-Zn tailings. In this systematic review, we identify several forthcoming research imperatives and methodologies. Specifically, understanding the dynamic mechanisms underlying the migration and transformation of HMs is challenging. These challenges encompass an exploration of the weathering processes of characteristic minerals and their interactions with HMs, the complex interplay between HMs and OFRs in Pb-Zn tailings, the effects of microbial community succession during the storage and remediation of Pb-Zn tailings, and the importance of utilizing process-based models in predicting the fate of HMs, and the potential for microbial remediation of tailings.

Living microecological hydrogels for wound healing

Chronic hard-to-heal wounds draw great attention worldwide, as their treatments are limited by infections and hypoxia. Inspired by the natural oxygen production capacity of algae and the competitive advantage of beneficial bacteria over other microbes, we presented a living microecological hydrogel (LMH) with functionalized Chlorella and Bacillus subtilis encapsulation to realize continuous oxygen delivery and anti-infections for promoting chronic wound healing. As the hydrogel consisted of thermosensitive Pluronic F-127 and wet-adhesive polydopamine, the LMH could keep liquid at a low temperature while quickly solidifying and tightly adhering to the wound bed. It was demonstrated that by optimizing the proportion of the encapsulated microorganism, the Chlorella could continuously produce oxygen to relieve hypoxia and support the proliferation of B. subtilis, while B. subtilis could eliminate the colonized pathogenic bacteria. Thus, the LMH substantially promoted the healing of infected diabetic wounds. These features make the LMH valuable for practical clinical applications.

Photo-Fenton self-cleaning carbon fibers membrane supported with Zr-MOF@Fe2O3 for effective phosphate removal from algae-rich water

Adsorbents featuring abundant binding sites and high affinity to phosphate have been used to resolve water eutrophication. However, most of the developed adsorbents were focused on improving the adsorption ability of phosphate but ignored the effect of biofouling on the adsorption process especially used in the eutrophic water body. Herein, a novel MOF-supported carbon fibers (CFs) membrane with high regeneration and antifouling capability, was prepared by in-situ synthesis of well-dispersed MOF on CFs membrane, to remove phosphate from algae-rich water. The hybrid UiO-66-(OH)₂@Fe₂O₃@CFs membrane exhibits a maximum adsorption capacity of 333.3 mg g^-1 (pH 7.0) and excellent selectivity for phosphate sorption over coexisting ions. Moreover, the Fe₂O₃ nanoparticles anchored on the surface of UiO-66-(OH)₂ through 'phenol-Fe(III)' reaction can endow the membrane with the robust photo-Fenton catalytic activity, which improves long-term reusability even under algae-rich condition. After 4 times photo-Fenton regenerations, the regeneration efficiency of the membrane could remain 92.2%, higher than that of hydraulic cleaning (52.6%). Moreover, the growth of C. pyrenoidosa was significantly reduced by 45.8% within 20 days via metabolism inhibition due to membrane-induced P-deficient conditions. Hence, the developed UiO-66-(OH)₂@Fe₂O₃@CFs membrane holds significant prospects for large-scale application in phosphate sequestration of eutrophic water bodies.

Evaluation of acute toxicity response to the algae Chlorella pyrenoidosa of biosynthetic silver nanoparticles catalysts

Biosynthetic of silver nanoparticles (AgNPs) by using fungi has attracted much attention due to its high catalytic efficiency and environmentally friendly characteristic. However, a few studies have focused on the ecological toxicity effects of biogenic AgNPs on algae. Here, we first investigated the catalytic reduction of 4-nitrophenol (4-NP) by WZ07-AgNPs biosynthesized by Letendraea sp. WZ07. WZ07-AgNPs had significant catalytic activity with 97.08% degradation of 4-NP in 3.5 min. Then, the toxic effects of WZ07-AgNPs and commercial-AgNPs were compared by Chlorella pyrenoidosa growth, chlorophyll content, protein content, physiological, and biochemical indexes. The results demonstrated that the algal cell biomass of C. pyrenoidosa was differentially inhibited after exposure to different concentrations of AgNPs, which showed concentration dependence and time dependence. The 96h-EC₅₀ values of WZ07-AgNPs and commercial-AgNPs on C. pyrenoidosa were 15.99 mg/mL and 12.69 mg/mL, respectively. With the increase concentration of AgNPs, the chlorophyll content was gradually decreased, the protein content was first increased and then decreased, the activities of superoxide dismutase (SOD) and catalase (CAT) were decreased, and the level of malondialdehyde (MDA) was increased significantly of C. pyrenoidosa. In general, AgNPs affect the growth of algae to some extent. However, compared with commercial-AgNPs, WZ07-AgNPs is less toxic to C. pyrenoidosa, which could be used as a potential and an eco-friendly catalyst. This study provides a basis for the safe application of biosynthetic AgNPs.

Salinity fluctuation influences the toxicity of 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) to a marine diatom Phaeodactylum tricornutum

In this work, a marine diatom (Phaeodactylum tricornutum) was exposed to 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl) for 96 h at three different salinities (25, 35, and 45 ‰) for investigating their interactive effects. Results showed that values of EC₁₀ and EC₅₀ at 96 h of exposure were 0.29, 1.06, 2.01 μg L^-1 and 7.21, 7.71, 7.25 mg L^-1 when the salinities were 25, 35, and 45 ‰, respectively, meaning that salinity fluctuation affected the toxicity of [C₈mim]Cl to this diatom. Changes in chlorophyll a contents and chlorophyll fluorescence parameters suggested that [C₈mim]Cl and salinity fluctuation had a significant interactive effect on the algal photosynthesis. In addition, soluble protein content and activities of antioxidant enzymes in algal cells changed significantly. Increased malondialdehyde contents indicated that the combined stresses could induce excessive production of reactive oxygen species leading to oxidative damage to the algal cells.

Influence of glyphosate and its metabolite aminomethylphosphonic acid on aquatic plants in different ecological niches

Glyphosate and its metabolite aminomethylphosphonic acid (AMPA) draw great concern due to their potential threat to aquatic ecosystems. The individual and combined effects of glyphosate and AMPA on aquatic plants in different ecological niches need to be explored. This study aimed to investigate the ecotoxicity of glyphosate and AMPA on the emergent macrophyte Acorus calamus, phytoplankton Chlorella vulgaris, and submerged macrophyte Vallisneria natans after their exposure to glyphosate and AMPA alone and to their mixture. Medium and low concentrations of glyphosate (≤ 0.5 mg L^-1) significantly inhibited the growth of V. natans and promoted the growth of C. vulgaris (P < 0.05) but had no significant effect on the growth of A. calamus (P > 0.05). AMPA (≤ 5.0 mg L^-1) did not significantly influence the relative growth rate (except C. vulgaris) or malonaldehyde levels but significantly altered the expression levels of chlorophyll-related genes and superoxide dismutase [Cu-Zn] genes in the aquatic plants examined. AMPA mainly affected the oxidative phosphorylation pathway in V. natans and not those in other two plants, indicating that V. natans was more sensitive to AMPA-induced oxidative damage. Moreover, antagonistic effects on plant growth were observed when plants were exposed to low concentrations of glyphosate + AMPA (≤ 0.1 + 0.1 mg L^-1). When the concentration of glyphosate + AMPA reached 0.5 + 0.5 and 5.0 + 5.0 mg L^-1, the growth of the submerged macrophyte was additively or synergistically inhibited, but the growth of the emergent macrophyte and phytoplankton was antagonistically inhibited. Our results indicated that both the individual and combined effects of glyphosate and AMPA might alter the vertical structure of shallow lakes and accelerate the conversion of shallow lakes from grass-based to algal-based lakes.

Preparation of a novel photocatalytic catalyst PW9@ZnO/Ag and the photocatalytic degradation of butyl xanthate under visible light

Photocatalytic technology is attracting considerable attention for the advantages of low cost and environmentally friendly properties. In this study, a novel photocatalyst PW₉@ZnO/Ag (PZA) was synthesized hydrothermally and characterized by a variety of means. The results indicated that ZnO and Ag NPs were successfully decorated and uniformly dispersed on PW₉ to form the composites. The prepared PZA was applied in the degradation of simulated butyl xanthate (BX) beneficiation wastewater both under the UV light and the xenon lamp, and a maximum degradation of 99.83% was obtained under the visible light with 10% ZnO loading, 1 g/L PZA, initial BX concentration of 20 mg/L, and pH 5.5. The PZA was recovered and reused for 5 times, and the degradation rates remained above 70%. Superoxide radical (·O₂^-) was the main active species for the photocatalytic degradation of BX. The experimental results demonstrate that PZA is a promising photocatalyst, making it a prospective strategy to overcome current challengers in the use of xanthate degradation and beneficiation wastewater treatment under visible light.

A newly-constructed bifunctional bacterial consortium for removing butyl xanthate and cadmium simultaneously from mineral processing wastewater: Experimental evaluation, degradation and biomineralization

Due to the technological limitations associated with beneficiation technology, large amounts of flotation reagents and heavy metals remain in mineral processing wastewater. Unfortunately, however, no treatment methods are available to mitigate the resulting pollution by them. In this study, a bacterial consortium SDMC (simultaneously degrade butyl xanthate and biomineralize cadmium) was constructed in an effort to simultaneously degrade butyl xanthate (BX) and biomineralize cadmium (Cd) by screening and domesticating two different bacterial species including Hypomicrobium and Sporosarcina. SDMC is efficient in removing the combined pollution due to BX and Cd with a 100% degradation rate for BX and 99% biomineralization rate for Cd within 4 h. Besides, SDMC can tolerate high concentrations of Fe(III) (0-40 mg/L). It has an excellent ability to utilize Fe(III) for enhanced removal of the combined pollutants. SDMC can effectively remove pollutants with a pH range of 6-9. Further, we discussed pathways for potential degradation and biomineralization: Cd(BX)₂-Cd²⁺, BX^-; BX^--CS₂, butyl perxanthate (BPX); Cd²⁺-(Ca0.67,Cd0.33)CO₃. The removal of the combined pollutants primarily entails decomposition, degradation, and biomineralization, C-O bond cleavage, and microbially induced carbonate precipitation (MICP). SDMC is a simple, efficient, and eco-friendly bifunctional bacterial consortium for effective treatment of BX-Cd combined pollution in mineral processing wastewater.

An experimental comparison: Horizontal evaluation of valuable metal extraction and arsenic emission characteristics of tailings from different copper smelting slag recovery processes

This study comprehensively investigated arsenic's enrichment, distribution, and characteristics in tailings. XRD and SEM-EDS characterized the phase and morphology of tailings from various smelting processes. At the same time, the embedding characteristics of arsenic in the ore phase were analyzed by EPMA. The differences between arsenic's leading ore phase carriers in different recovery processes were found. It was discussed that this phenomenon would be related to the element-binding ability and the precipitation priority of the ore phase. The occurrence state of arsenic was discussed by sequential chemical extraction experiments. The proportion of leachable arsenic is higher than the low-risk limit, whatever which smelting method is adopted, which leads to high environmental risk. In the experiment of comparing the leaching toxicity of tailings by different leaching methods, the arsenic concentration in the leaching solution of tailings recovered by the flotation method exceeds the specified safety range. Although the tailings after reduction smelting did not show high leaching toxicity, a large number of accumulations also would not represent absolute safety.

Unravelling multiple removal pathways of oseltamivir in wastewater by microalgae through experimentation and computation

Increased worldwide consumption of antiviral drugs (AVDs) amid COVID-19 has induced enormous burdens to the existing wastewater treatment systems. Microalgae-based bioremediation is a competitive alternative technology due to its simultaneous nutrient recovery and sustainable biomass production. However, knowledge about the fate, distribution, and interaction of AVDs with microalgae is yet to be determined. In this study, a concentration-determined influence of AVD oseltamivir (OT) was observed on the biochemical pathway of Chlorella sorkiniana (C.S-N1) in synthetic municipal wastewater. The results showed that high OT concentration inhibited biomass growth through increased oxidative stress and restrained photosynthesis. Nevertheless, complete OT removal was achieved at its optimized concentration of 10 mg/L by various biotic (82%) and abiotic processes (18.0%). The chemical alterations in three subtypes of extracellular polymeric substances (EPS) were primarily investigated by electrostatic (OT +8.22 mV vs. C.S-N1 -18.31 mV) and hydrophobic interactions between EPS-OT complexes supported by secondary structure protein analysis. Besides, six biodegradation-catalyzed transformation products were identified by quadrupole-time-of-flight mass spectrometer and by density functional theory. Moreover, all the TPs exhibited log Kow ≤ 5 and bioconcentration factor values of < 5000 L/kg, meeting the practical demands of environmental sustainability. This study broadens our understanding of microalgal bioadsorption and biodegradation, promoting microalgae bioremediation for nutrient recovery and AVDs removal.

Toxicity mechanism of Nylon microplastics on Microcystis aeruginosa through three pathways: Photosynthesis, oxidative stress and energy metabolism

Nylon has been widely used all over the world, and most of it eventually enters the aquatic environment in the form of microplastics (MPs). However, the impact of Nylon MPs on aquatic ecosystem remains largely unknown. Thus, the long-term biological effects and toxicity mechanism of Nylon MPs on Microcystis aeruginosa (M. aeruginosa) were explored in this study. Results demonstrated that Nylon MPs had a dose-dependent growth inhibition of M. aeruginosa at the initial stage, and the maximum inhibition rate reached to 47.62% at the concentration of 100 mg/L. Meanwhile, Nylon MPs could obstruct photosynthesis electron transfer, reduce phycobiliproteins synthesis, destroy algal cell membrane, enhance the release of extracellular polymeric substances, and induce oxidative stress. Furthermore, transcriptomic analysis indicated that Nylon MPs dysregulated the expression of genes involved in tricarboxylic acid cycle, photosynthesis, photosynthesis-antenna proteins, oxidative phosphorylation, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism. According to the results of transcriptomic and biochemical analysis, the growth inhibition of M. aeruginosa is inferred to be regulated by three pathways: photosynthesis, oxidative stress, and energy metabolism. Our findings provide new insights into the toxicity mechanism of Nylon MPs on freshwater microalgae and valuable data for risk assessment of MPs.

Heavy metal-induced stress in eukaryotic algae-mechanisms of heavy metal toxicity and tolerance with particular emphasis on oxidative stress in exposed cells and the role of antioxidant response

Heavy metals is a collective term describing metals and metalloids with a density higher than 5 g/cm3. Some of them are essential micronutrients; others do not play a positive role in living organisms. Increased anthropogenic emissions of heavy metal ions pose a serious threat to water and land ecosystems. The mechanism of heavy metal toxicity predominantly depends on (1) their high affinity to thiol groups, (2) spatial similarity to biochemical functional groups, (3) competition with essential metal cations, (4) and induction of oxidative stress. The antioxidant response is therefore crucial for providing tolerance to heavy metal-induced stress. This review aims to summarize the knowledge of heavy metal toxicity, oxidative stress and antioxidant response in eukaryotic algae. Types of ROS, their formation sites in photosynthetic cells, and the damage they cause to the cellular components are described at the beginning. Furthermore, heavy metals are characterized in more detail, including their chemical properties, roles they play in living cells, sources of contamination, biochemical mechanisms of toxicity, and stress symptoms. The following subchapters contain the description of low-molecular-weight antioxidants and ROS-detoxifying enzymes, their properties, cellular localization, and the occurrence in algae belonging to different clades, as well as the summary of the results of the experiments concerning antioxidant response in heavy metal-treated eukaryotic algae. Other mechanisms providing tolerance to metal ions are briefly outlined at the end.

Effects of Suspended Particles on Exopolysaccharide Secretion of Two Microalgae in Jinjiang Estuary (Fujian, China)

The effects of suspended particles (SP) of different concentrations and sizes on the secretion of exopolysaccharide (EPS) by Chlorella pyrenoidosa (C. pyrenoidosa) and Microcystis flos-aquae (M. flos-aquae) in Jinjiang Estuary, Fujian Province, China were studied in co-cultures of microalgae and SP. The results show that the SP concentration has an “inhibit–promote–inhibit” effect on the secretion of EPS by C. pyrenoidosa, whereby there is an optimal concentration of SP corresponding to the largest amount of EPS secreted by C. pyrenoidosa. Low concentrations had no significant effect on the secretion of EPS from M. flos-aquae (p > 0.05), whereas higher concentrations had an inhibitory effect. The C. pyrenoidosa EPS content was found to be significantly decreased in response to SP of small particle sizes (0–75 and 75–120 μm) and significantly increased for SP of large particle sizes (120–150 and 150–500 μm). Small particle sizes (0–75 and 75–120 μm) were found to be beneficial to the secretion of EPS from M. flos-aquae, and the promotion of EPS secretion gradually decreased with the increase in SP particle size. However, when the particle size was too large (120–150 and 150–500 μm), SP had no significant effect on EPS secretion. This study is helpful for understanding the microalgae EPS secretion response to SP and provides a scientific basis for studying the mechanism of EPS secretion by algae and the effect of SP on eutrophication of the estuary.