Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) reveals multiple metabolism alterations in microalgae induced by cadmium and mercury

Ionic and nanoparticulate silver alleviate the toxicity of inorganic mercury in marine microalga Chaetoceros muelleri

Toxicological effects of silver nanoparticles (SNPs) in different organisms have been studied; however, interactions of SNPs with other environmental pollutants such as mercury are poorly understood. Herein, bioassay tests were performed according to ΟECD 201 guideline to assess the toxic effects induced by mercury ions (mercury chloride, MCl) on the marine microalga Chaetoceros muelleri in the presence of SNPs or silver ions (silver nitrate, SN). Acute toxicity tests displayed that the presence of SNPs or SN (0.01 mg L-1) significantly reduced the toxicity of MCl (0.001, 0.01, 0.1, 1, 10, and 100 mg L-1) and increased the IC50 of MCl from 0.072 ± 0.014 to 0.381 ± 0.029 and 0.676 ± 0.034 mg L-1, respectively. In the presence of SN or SNPs, the mercury-reducing effect on algal population growth significantly decreased. Considering the increase of IC50, the mercury toxicity decreased approximately 5.44 and 9.66 times in the presence of SNPs or SN, respectively. The chlorophyll a and c contents decreased at all exposures; however, the decrease by MCl-SNPs and MCl-SN was significantly less than MCl except at 1 mg L-1. The lowering effect of MCl-SN on chlorophyll contents was less than MCl and MCl-SNPs. MCl exposure induced significant raises in total protein content (TPC) at concentrations < 0.01mg  L-1, with a maximum of ~ 70.83% attained at 100 mg L-1. The effects of MCl-SNPs and MCl-SN on TPC were significantly less than MCl. Total lipid content (TLC) at all MCl concentrations was higher than the control, while at coexposure to MCl-SN, TLC did not change until 0.01 mg L-1 compared with the control. The effects of MCl-SN and MCL-SNPs on TPC and TLC were in line with toxicity results, and were significantly less than those of MCl individually, confirming their antagonistic effects on MCl. The morphological changes of algal cells and mercury content of the cell wall at MCl-SN and MCl-SNPs were mitigated compared with MCl exposure. These findings highlight the mitigatory impacts of silver species on mercury toxicity, emphasizing the need for better realizing the mixture toxicity effects of pollutants in the water ecosystem.

Assessment of heavy metals and environmental stress conditions on the production potential of polyunsaturated fatty acids (PUFAs) in indigenous microalgae isolated from the Gulf of Mannar coastal waters

The present study evaluated the effects of heavy metals, viz., lead, mercury, and cadmium, on growth, chlorophyll a, b, c, carotenoids, and PUFA content of marine microalgae Chlorella sp. and Cylindrotheca fusiformis. At 96-h exposure, the IC50 values for Hg2+, Pb2+, and Cd2+ were 0.85 mg/L, 2.4 mg/L, and 5.3 mg/L respectively, in Chlorella sp. In C. fusiformis, IC50 values for Hg2+, Pb2+, and Cd2+ were 0.5 mg/L, 1.2 mg/L, and 3 mg/L respectively. The pigment contents of both microalgae were significantly affected upon heavy metal exposure. In Chlorella sp. and C. fusiformis, the exposed concentrations of Hg2+ averagely decreased the PUFA content by 76.34% and 78.68%, respectively. Similarly, Pb2+-exposed concentrations resulted in 54.50% and 82.64% average reductions in PUFA content of Chlorella sp. and C. fusiformis, respectively. Cd2+-exposed concentrations showed 32.58% and 40.54% average reduction in PUFA content of Chlorella sp. and C. fusiformis, respectively. Among the environmental stress conditions, the dark treatment has increased total PUFA content by 6.63% in Chlorella sp. and 3.92% in C. fusiformis. It was observed that the 50% nitrogen starvation (two-stage) significantly improved the PUFA production from 26.47 ± 6.55% to 40.92 ± 10.74% in Chlorella sp. and from 11.23 ± 5.01 to 32.8 ± 14.17% in C. fusiformis. The toxicity for both microalgae was followed in the order Hg2+ > Pb2+ > Cd2+. Among the two species, Chlorella sp. has shown a high tolerance to heavy metals and can be effectively utilized in PUFA production.

Characterization of cellular toxicity induced by sub-lethal inorganic mercury in the marine microalgae Chlorococcum dorsiventrale isolated from a metal-polluted coastal site

Mercury (Hg) is a global pollutant that affects numerous marine aquatic ecosystems. We isolated Chlorococcum dorsiventrale Ch-UB5 microalga from coastal areas of Tunisia suffering from metal pollution and analyzed its tolerance to Hg. This strain accumulated substantial amounts of Hg and was able to remove up to 95% of added metal after 24 and 72 h in axenic cultures. Mercury led to lesser biomass growth, higher cell aggregation, significant inhibition of photochemical activity, and appearance of oxidative stress and altered redox enzymatic activities, with proliferation of starch granules and neutral lipids vesicles. Such changes matched the biomolecular profile observed using Fourier Transformed Infrared spectroscopy, with remarkable spectral changes corresponding to lipids, proteins and carbohydrates. C. dorsiventrale accumulated the chloroplastic heat shock protein HSP70B and the autophagy-related ATG8 protein, probably to counteract the toxic effects of Hg. However, long-term treatments (72 h) usually resulted in poorer physiological and metabolic responses, associated with acute stress. C. dorsiventrale has potential use for Hg phycoremediation in marine ecosystems, with the ability to accumulating energetic reserves that could be used for biofuel production, supporting the notion of using of C. dorsiventrale for sustainable green chemistry in parallel to metal removal.

Rethinking the effects of micro/nanoplastics from the global environmental change and systematic perspective: An aquatic environmental system-based comprehensive assessment approach of micro/nanoplastic impacts

The study on micro/nanoplastic pollution should embrace complexity. Here, we aim to develop an aquatic environmental system-based comprehensive assessment approach of micro/nanoplastic impacts (ACAM) to evaluate the effects of micro/nanoplastics on aquatic ecosystems from the global environmental change (GEC) and systematic perspective. A case study for freshwater systems in Saskatchewan, Canada was conducted to evaluate the comprehensive effects of multiple GEC factors (polystyrene-nanoplastics (PS-NPs), N, P, salinity, dissolved organic matter (DOM), pH, hardness) on Asterococcus superbus based on ten ecologically relevant endpoints. It is found that at the cellular level, PS-NPs and N had an antagonistic interaction on microalgal growth in the Saskatchewan freshwater ecosystem; at the molecular level, the PS-NP-induced changes in lipid composition in microalgae were regulated by P, DOM, and pH. The significance ranking of factor effects suggested that instead of PS-NPs pollution, the fluctuations in pH level, DOM and N concentrations should be paid attention to first in Saskatchewan. Under the combined impact of PS-NPs and other GEC factors, microalgae at station 14 (Qu'Appelle River near highway 56) might have the minimum growth rate with [-0.048, 0.094] d-1 in Saskatchewan. These findings demonstrate the efficacy of the developed ACAM in a more comprehensive and context-specific assessment of MNP risks, providing new insight for the management of MNP pollution.

Toxicological Impacts of TiO2 Nanoparticles on Growth, Photosynthesis Pigments, and Protein and Lipid Content of the Marine Microalga Tetraselmis Suecica

Regarding the widespread use of titanium dioxide nanoparticles (TiO2NPs) in industry, many concerns have been raised about the risks of their potential release into aquatic ecosystems. Among the marine primary producers, Tetraselmis suecica is an ecologically important microalgae species used also as live feed in the shrimp culture industry. In the present study, the impacts of TiO2NPs on growth performance, photosynthetic pigments, lipid and protein content and its interaction with the cells of T. suecica were assessed. Based on the preliminary tests and OECD suggestion, concentrations of 5, 10, 50, 100, 200 and 400 mg/L TiO2NPs were applied to algal cells for 10 days. With increasing concentration, a decrease in T. suecica cell density was observed each day. TiO2NPs induced a half-maximal inhibitory concentration (IC50) of 106.26 mg/L on algal cells on the 3rd day. Chlorophyll a and b contents of the microalga decreased up to 56.08% and 52.74%, respectively following the exposure to TiO2NPs at 400 mg/L. TiO2NPs also decreased the algal contents of protein and lipid up to 7.21% and 50.64%, respectively at the highest concentration. Based on FTIR, FESEM with EDS and mapping analyses, the interaction of TiO2NPs with the T. suecica cells was revealed. The stocks of T. suecica could be damaged by the toxic effects of the released TiO2NPs affecting their application as live feed in mariculture.

Effect of mercury in the influx and efflux of nutrients in the microalga Desmodesmus armatus

Anthropogenic activities such as mining and the metallurgical industry are the main sources of mercury contamination. Mercury is one of the most serious environmental problems in the world. This study aimed to investigate, using experimental kinetic data, the effect of different inorganic mercury (Hg²⁺) concentrations on the response of microalga Desmodesmus armatus stress. Cell growth, nutrients uptake and mercury ions from the extracellular medium, and oxygen production were determined. A Compartment Structured Model allowed elucidating the phenomena of transmembrane transport, including influx and efflux of nutrients, metal ions and bioadsorption of metal ions on the cell wall, which are difficult to determine experimentally. This model was able to explain two tolerance mechanisms against mercury, the first one was the adsorption of Hg²⁺ions onto the cell wall and the second was the efflux of mercury ions. The model predicted a competition between internalization and adsorption with a maximum tolerable concentration of 5.29 mg/L of HgCl₂. The kinetic data and the model showed that mercury causes physiological changes in the cell, which allow the microalga to adapt to these new conditions to counteract the toxic effects. For this reason, D. armatus can be considered as a Hg-tolerant microalga. This tolerance capacity is associated with the activation of the efflux as a detoxification mechanism that facilitates the maintenance of the osmotic balance for all the modeled chemical species. Furthermore, the accumulation of mercury in the cell membrane suggests the presence of thiol groups associated with its internalization, leading to the conclusion that metabolically active tolerance mechanisms are dominant over passive ones.

Investigation of cytotoxic cadmium in aquatic green algae by synchrotron radiation-based Fourier transform infrared spectroscopy: Role of dissolved organic matter

The heavy metal Cd can cause severe toxicity on aquatic algae, but there are few studies on the cytotoxicity of heavy metal on algae based on synchrotron radiation technology. In this study, synchrotron radiation-based Fourier transform infrared spectromicroscopy (SR-FTIR) was used to characterize in vivo the toxic effects of Cd on Cosmarium sp. cells, emphasizing the influence of dissolved organic matter (DOM) on Cd toxicity. Results showed that, in the absence of DOM, obvious growth inhibition, cell volume reduction, and photosynthesis disruption could be observed with increasing Cd concentrations (0-500 μg/L). Based on the SR-FTIR imaging and functional group quantification, it was shown that the biosynthesis of biomolecules such as proteins, lipids, and carbohydrates was inhibited in algal cells. However, the addition of DOM caused significant heterogeneities in biomacromolecule biosynthesis that an increased biosynthesis of carbohydrates and structural lipids but an inhibited biosynthesis of proteins and storage lipids were observed. Furthermore, the correlation analysis and principal component analysis showed a good correlation between v(C-OH)/Amide II and biochemical parameters, indicating that changes of carbohydrates could be used as the biomarker to indicate the cytotoxicity of heavy metals to algal cells. These findings provide insight into the mechanisms of heavy metal cytotoxicity to aquatic algae and systematic cytotoxicity assessment under various aquatic conditions.

Water deficit aggravated the inhibition of photosynthetic performance of maize under mercury stress but is alleviated by brassinosteroids

Mercury (Hg) significantly inhibits maize (Zea mays L.) production, which could be aggravated by water deficit (WD) due to climate change. However, there is no report on the maize in response to combined their stresses. This work was conducted for assessing the response and adaptive mechanism of maize to combined Hg and WD stress using two maize cultivars, Xianyu (XY) 335 and Yudan (YD) 132. The analysis was based on plant growth, physiological function, and transcriptomic data. Compared with the single Hg stress, Hg accumulation in whole plant and translocation factor (TF) under Hg+WD were increased by 64.51 % (1.44 mg kg^-1) and 260.00 %, respectively, for XY 335; and 50.32 % (0.62 mg kg^-1) and 220.02 %, respectively, for YD 132. Combined Hg and WD stress further increased the reactive oxygen species accumulation, aggravated the damage of the thylakoid membrane, and decreased chlorophyll content compared with single stress. For example, Chl a and Chl b contents of XY 335 were significantly decreased by 48.67 % and 28.08 %, respectively at 48 h after Hg+WD treatment compared with Hg stress. Furthermore, transcriptome analysis revealed that most of down-regulated genes were enriched in photosynthetic-antenna proteins, photosynthesis, chlorophyll and porphyrin metabolism pathways (PsbS1, PSBQ1 and FDX1 etc.) under combined stress, reducing light energy capture and electron transport. However, most genes related to the brassinosteroids (BRs) signaling pathway were up-regulated under Hg+WD stress. Correspondingly, exogenous BRs significantly enhanced the maize tolerance to stress by decreasing Hg accumulation and TF, and raising activities of antioxidant enzyme, the content of chlorophyll and photosynthetic performance. The PI, Fv/Fm and Fv/Fo of Hg+WD+BR treatment were increased by 29.88 %, 32.06 %, and 14.56 %, respectively, for XY 335 compared to Hg+WD. Overall, combined Hg and WD stress decreased photosynthetic efficiency by adversely affecting light absorption and electron transport, especially in stress-sensitive variety, but BRs could alleviate the inhibition of photosynthesis, providing a novel strategy for enhancing crop Hg and WD tolerance and food safety.

Investigation of toxic effect of mercury on Microcystis aeruginosa: Correlation between intracellular mercury content at single cells level and algae physiological responses

Single-cell studies can help to understand individual differences and obtain atypical cellular characteristics in view of cellular heterogeneity. Herein, the accumulation of mercury (Hg) in single algae cells was studied by droplet chip-time resolved inductively coupled plasma mass spectrometry analytical system, and the relation of Hg accumulation to the physiological responses of algae cell was explored. When low concentrations of Hg²⁺ (5-20 μg/L) were used in the exposure experiment, the content of Hg in single cells increased in first 2 h, then decreased with further increase of exposure time to 96 h, probably due to the growth dilution effect of the algae. When exposed to 30 μg/L Hg²⁺, the uptake of Hg by individual cells increased over time, which was associated with increased cell membrane permeability. The exposure to Hg²⁺ (5-30 μg/L) inhibited the growth of algae in a concentration-dependent manner and serious growth inhibition occurred under the exposure concentration of 30 μg/L. While the exposure concentration was lower than 20 μg/L, algal cells exhibited a recover tendency due to the self-protection mechanism of algal cells. Bivariate results showed that intracellular Hg accumulation was significantly negatively correlated with cells growth in terms of OD₆₈₀, photosynthetic pigments, F_v/F_m and PI_abs. On the contrast, reactive oxygen species content, superoxide dismutase activity, and cell membrane permeability were significantly positively correlated with the accumulation of intracellular Hg. These results are helpful to further understand the toxic effect of Hg on algae.

Screening of structural and functional alterations in duckweed (Lemna minor) induced by per- and polyfluoroalkyl substances (PFASs) with FTIR spectroscopy

As a class of common emerging pollutants, per- and polyfluoroalkyl substances (PFASs) and their alternatives have been widely detected in various environmental matrices, exhibiting a great threat to the ecological environment and human health. Nevertheless, changes in biomolecular structure and function of duckweed caused by PFASs and their alternatives remain unknown thus far. Herein, the effects of four PFASs, including two common legacy PFASs (perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) and two PFASs alternatives (perfluorobutane sulfonic acid (PFBS) and 1H,1H,2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)) on duckweed (Lemna minor) at biochemical level were investigated with Fourier transform infrared spectroscopy (FTIR). Although no obvious inhibitions were observed in the growth of L. minor with PFASs exposure at three levels of 1 μg L^-1, 100 μg L^-1, and 10 mg L^-1, significant structural and functional alterations were induced at the biochemical level. In response to PFASs exposure, lipid peroxidation, proteins aggregation and α-helix to β-sheet transformation of the protein conformation, as well as changes of DNA conformations were detected. Moreover, alterations in lipid, protein, and DNA were proved to be concentration-related and compound-specific. Compared to the two legacy PFASs (PFOS and PFOA), alternative ones exhibited greater effects on the biological macromolecules of L. minor. The findings of this study firstly reveal structural and functional alterations in L. minor induced by PFASs exposure, providing further understanding of their toxicity effects.

FTIR as a Method for Qualitative Assessment of Solid Samples in Geochemical Research: A Review

This study aims to collect information about soil investigation by FTIR. As we know, the FTIR technique is most often used in organic and bioorganic chemistry, while in geochemistry FTIR spectroscopy is not used very often. Therefore, there is a problem with the identification and interpretation of the IR spectra of minerals contained in sediments and soils. The reason for this is a deficiency of data about characteristic wavenumbers for minerals. Therefore, this study reviews and sums up, in one place, published articles that are connected to an investigation of minerals from 2002 to 2021 (based on the Scopus database). Additionally, the present review highlights various analytical techniques (ATR-FTIR, DRIFT, 2D-IR, and SR-FTIR) and discusses some of them for geochemical study. Additionally, the study describes helpful tools in the data pre-processing of IR spectra (normalization, baseline correction, and spectral derivatives).

The Binding Ability of Mercury (Hg) to Photosystem I and II Explained the Difference in Its Toxicity on the Two Photosystems of Chlorella pyrenoidosa

Mercury (Hg) poses high toxicity to organisms including algae. Studies showed that the growth and photosynthesis of green algae such as Chlorella are vulnerable to Hg stress. However, the differences between the activities and tolerance of photosystem I and II (PSI and PSII) of green microalgae under Hg exposure are still little known. Responses of quantum yields and electron transport rates (ETRs) of PSI and PSII of Chlorella pyrenoidosa to 0.05−1 mg/L Hg2+ were simultaneously measured for the first time by using the Dual-PAM-100 system. The photosystems were isolated to analyze the characteristics of toxicity of Hg during the binding process. The inhibition of Hg2+ on growth and photosystems was found. PSII was more seriously affected by Hg2+ than PSI. After Hg2+ exposure, the photochemical quantum yield of PSII [Y(II)] decreased with the increase in non-photochemical fluorescence quenching [Y(NO) and Y(NPQ)]. The toxic effects of Hg on the photochemical quantum yield and ETR in PSI were lower than those of PSII. The stimulation of cyclic electron yield (CEF) was essential for the stability and protection of PSI under Hg stress and played an important role in the induction of non-photochemical quenching (NPQ). The results showed a strong combination ability of Hg ions and photosystem particles. The number of the binding sites (n) of Hg on PSII was more than that of PSI, which may explain the different toxicity of Hg on PSII and PSI.

Somannavar, Satisha Hegde, Sunil Vernekar, Kusal K. Das, Shivaprasad S. Goudar. Nephroprotective effect of black tea extract on cadmium induced male Wistar rats

Introduction and Aim Cadmium is an environmental pollutant and potential nepho-toxicant to humans. Increase in industrialization interruptions heavy metal pollution in the world. Heavy metal chemicals destruction of organ functions and disrupts physiological homeostasis. Only the chelation therapy that involve the remove the heavy metal. Our study was designed to resolve the nehro-protective possessions of tea beverage on experimentally persuaded cadmium toxicity in the renal of rats. Tea was given orally while cadmium was administered subcutaneously. Method: Adult rats were divided into four groups (n=6/group). One control group (normal saline), two cadmium chloride group (CdCl2, 1.0 mg/kg, b.wt; i.p), Three Black tea extract group (black tea extract, 2.5 gm tea leaf/dl of water that is 2.5% of aqueous BTE) and Cadmium chloride plus black tea extract group (cadmium chloride + BTE). Simultaneously for 21 days. Results: Supplementation of black tea remarkably improves kidney architecture of rats treated with cadmium chloride group. Conclusion: Black tea extract seems to be nephron-protective against cadmium induced oxidative stress.