Exposure to the herbicide 2,4-D produces different toxic effects in two different phytoplankters: A green microalga (Ankistrodesmus falcatus) and a toxigenic cyanobacterium (Microcystis aeruginosa)

Effects of low concentration of gallic acid on the growth and microcystin production of Microcystis aeruginosa

Gallic acid (GA) is an allelochemical that has been utilized in high concentrations for the management of harmful algal blooms (HABs). However, there is limited knowledge regarding its impact on the growth of M. aeruginosa as the GA concentration transitions from high to low during the HABs control process. This study has revealed that as the GA concentration decreases (from 10 mg/L to 0.001 μg/L), a dose-response relationship becomes apparent in the growth of M. aeruginosa and microcystin production, characterized by high-dose inhibition and low-dose stimulation. Notably, at the concentration of 0.1 μg/L GA, the most significant growth-promoting effect on both growth and MCs synthesis was observed. The growth rate and maximum cell density were increased by 1.09 and 1.16 times, respectively, compared to those of the control group. Additionally, the contents of MCs synthesis saw a remarkable increase, up by 1.85 times. Furthermore, lower GA concentrations stimulated the viability of cyanobacterial cells, resulting in substantially higher levels of reactive oxygen species (ROS) and chlorophyll-a (Chl a) compared to other concentrations. Most importantly, the expression of genes governing MCs synthesis was significantly upregulated, which appears to be the primary driver behind the significantly higher MCs levels compared to other conditions. The ecological risk quotient (RQ) value of 0.1 μg/L GA was the highest of all experimental groups, which was approximately 30 times higher than that of the control, indicating moderate risk. Therefore, it is essential to pay attention to the effect of M. aeruginosa growth, metabolism and water ecological risk under the process of reducing GA concentration after dosing during the HABs control process.

Modulation in growth, oxidative stress, photosynthesis, and morphology reveals higher toxicity of alpha-cypermethrin than chlorpyrifos towards a non-target green alga at high doses

Considering the frequent detection of pesticides in the aquatic environment, the ecotoxicological effects of Chlorpyrifos (CHP), an organophosphate, and alpha-cypermethrin (ACM), a pyrethroid, on freshwater microalgae were compared for the first time in this study. High concentrations of both CHP and ACM significantly suppressed the growth of test microalga Graesiella emersonii (p < 0.05). The 96-h EC50 of CHP and ACM were 54.42 mg L-1 and 29.40 mg L-1, respectively. Sub-inhibitory doses of both pesticides increased ROS formation in a concentration-dependent manner, which was accompanied by changes in antioxidant enzymes activities, lipid peroxidation, and variations in photosynthetic pigment concentration. Furthermore, both pesticides influenced photosystem II performance, oxygen-evolving complex efficiency and, intracellular ATP levels. Scanning electron microscopy analysis revealed that high concentrations of both CHP and ACM caused considerable morphological changes in the microalga. In comparison, CHP was more toxic than ACM at low concentrations, whereas ACM was more toxic at high concentrations.

Effect and mechanism of microplastics exposure against microalgae: Photosynthesis and oxidative stress

The occurrence of microplastics (MPs) within aquatic ecosystems attracts a major environmental concern. It was demonstrated MPs could cause various ecotoxicological effects on microalgae. However, existing data on the effects of MPs on microalgae showed great variability among studies. Here, we performed a meta-analysis of the latest studies on the effects of MPs on photosynthesis and oxidative stress in microalgae. A total of 835 biological endpoints were investigated from 55 studies extracted, and 37 % of them were significantly affected by MPs. In this study, the impact of MPs against microalgae was concentration-dependent and size-dependent, and microalgae were more susceptible to MPs stress in freshwater than marine. Additionally, we summarized the biological functions of microalgae that are primarily affected by MPs. Under MPs exposure, the content of chlorophyll a (Chl-a) was reduced and electron transfer in the photosynthetic system was hindered, causing electron accumulation and oxidative stress damage, which may also affect biological processes such as energy production, carbon fixation, lipid metabolism, and nucleic acid metabolism. Finally, our findings provide important insights into the effects of MPs stress on photosynthesis and oxidative stress in microalga and enhance the current understanding of the potential risk of MPs pollution on aquatic organisms.

Pretilachlor-induced physiological, biochemical and morphological changes in Indian paddy field agroecosystem inhabited Anabaena doliolum

Pretilachlor is a systemic, pre-emergence herbicide applied in the paddy fields to kill narrow and broadleaf weeds. The present study evaluates the toxicity of pretilachlor on the non-target diazotrophic free-living cyanobacterium Anabaena doliolum, commonly found in the paddy fields of eastern Uttar Pradesh (India) and used as a biofertilizer. A.doliolum was subjected to several doses (0, 2, 5, 7, 10, 20 and 40 μg/ml) of pretilachlor and its effects were examined in terms of alterations in cellular morphology, ultrastructure, physiology, and biochemical attributes. The treatment of pretilachlor decreased the growth, total pigment content and photosynthetic efficiency of the test organism in a dose-dependent manner. The decline in growth was observed on 20th day at 2, 5, 7, 10, 20 and 40 μg/ml of pretilachlor concentration by 4, 9, 26, 47, 71 and 92%, respectively. Furthermore, Chlorophyll a and phycocyanin levels were noticeably declined. As a result, the photosynthetic performance also registered a similar decline as measured by chlorophyll fluorescence. However, carotenoid content increased by 13%, 41% and 53% at 5, 10 and 20 μg/ml on 5th day reflecting its protective property. A marked increase in fluorescence intensity and malondialdehyde content by 2.65 and 2.45 folds at 10 and 20 μg/ml on 7th day was registered. The enzymatic antioxidants (SOD and CAT) and a concurrent increase in glutathione reductase activity were registered (1.75 and 2.11-fold at 20 and 40 μg/ml on 5th day), indicating pretilachlor mediated ROS generation. Moreover, ultrastructural studies done by SEM and TEM revealed plasma membrane and thylakoid membrane damage and fragmentation. These findings have contributed to the broader comprehension of the stress responses triggered by pretilachlor in cyanobacteria. Moreover, they can aid in the evaluation of the detrimental impact of pretilachlor on A. doliolum, given their crucial function as a nitrogen contributor in paddy fields.

Changes in the morphology and cell ultrastructure of a microalgal community exposed to a commercial glyphosate formulation and a toxigenic cyanobacterium

Human activities significantly influence the health of aquatic ecosystems because many noxious chemical wastes are discharged into freshwater bodies. Intensive agriculture contributes to the deterioration by providing indirectly fertilizers, pesticides, and other agrochemicals that affect the aquatic biota. Glyphosate is one of the most used herbicides worldwide, and microalgae are particularly sensitive to its formulation, inducing displacement of some green microalgae from the phytoplankton that leads to alterations in the floristic composition, which fosters the abundance of cyanobacteria, some of which can be toxigenic. The combination of chemical stressors such as glyphosate and biological ones, like cyanotoxins and other secondary metabolites of cyanobacteria, could induce a combined effect potentially more noxious to microalgae, affecting not only their growth but also their physiology and morphology. In this study, we evaluated the combined effect of glyphosate (Faena^®) and a toxigenic cyanobacterium on the morphology and ultrastructure of microalgae in an experimental phytoplankton community. For this purpose, Microcystis aeruginosa (a cosmopolitan cyanobacterium that forms harmful blooms) and the microalgae Ankistrodesmus falcatus, Chlorella vulgaris, Pseudokirchneriella subcapitata, and Scenedesmus incrassatulus were cultivated, individually and jointly, exposing them to sub-inhibitory concentrations of glyphosate (IC₁₀, IC_20, and IC₄₀). Effects were evaluated through scanning electron (SEM) and transmission electron (TEM) microscopy. Exposure to Faena^® produced alterations in the external morphology and ultrastructure of microalgae both individually and in combined cultures. SEM evidenced the loss of the typical shape and integrity of the cell wall and an increase in the biovolume. TEM revealed reduction and disorganization of the chloroplast, variation in starch and polyphosphate granules, formation of vesicles and vacuoles, cytoplasm degradation, and cell wall continuity loss. The presence of M. aeruginosa was, for microalgae, an additional stress factor adding to the chemical stress produced by Faena^®, increasing the damage in their morphology and ultrastructure. These results alert to the effects that can be caused by glyphosate and the presence of toxigenic bacteria on the algal phytoplankton in contaminated and anthropic and eutrophic freshwater ecosystems.

Toxicity effects of polystyrene nanoplastics and arsenite on Microcystis aeruginosa

Despite the increasing research on the fate of nanoplastics (NPs, <100 nm) in freshwater systems, little is known about the joint toxic effects of metal(loid)s and NPs modified with different functional groups on microalgae. Here, we explored the joint toxic effects of two types of polystyrene NPs [one modified with a sulfonic acid group (PSNPs-SO₃H), and one without this functional group (PSNPs)] and arsenic (As) on the microalgae Microcystis aeruginosa. The results highlighted that PSNPs-SO₃H showed a smaller hydrodynamic diameter and greater potential to adsorb positively charged ions than PSNPs, contributing to the more severe growth inhibition, while both of them produced oxidative stress. Metabolomics further revealed that the fatty acid metabolism of the microalgae was significantly up-regulated under both NPs exposure, while PSNPs-SO₃H down-regulated the tricarboxylic acid cycle (TCA cycle) of the microalgae. As uptake by algae was significantly reduced by 82.58 % and 59.65 % in the presence of 100 mg/L PSNPs and PSNPs-SO₃H, respectively. The independent action model showed that the joint toxicity of both NPs with As was assessed as antagonistic. In addition, PSNPs and PSNPs-SO₃H had dissimilar effects on the composition of the microalgae extracellular polymeric substances (EPS), resulting in different uptake and adsorption of As, thereby affecting the physiology and biochemistry of algae. Overall, our findings propose that the specific properties of NPs should be considered in future environmental risk assessments.

Effect of butachlor on Microcystis aeruginosa: Cellular and molecular mechanisms of toxicity

The rapid development of agriculture increases the release of butachlor into aquatic environments. As a dominant species causing cyanobacterial blooms, Microcystis aeruginosa (M. aeruginosa) can produce microcystin and poses threats to aquatic ecosystems and human health. However, the impact of butachlor on M. aeruginosa remains unclarified. Therefore, the physiochemical responses of M. aeruginosa to butachlor were investigated, and the relevant underlying molecular mechanism was highlighted. There were no significant changes (P > 0.05) in the growth and physiology of M. aeruginosa at the low concentrations of butachlor (0-0.1 mg/L), which evidenced a high level of butachlor tolerance in Microcystis aeruginosa. For the high concentrations of butachlor (4-30 mg/L), the inhibition of photosynthetic activity, disruption of cell ultrastructure, and oxidative stress were dominant toxic effects on M. aeruginosa. Additionally, the impaired cellular integrity and lipid peroxidation may be attributed to the substantial elevations of extracellular microcystin-LR concentration. Downregulation of genes associated with photosynthesis, energy metabolism, and oxidative stress was inferred to be responsible for the growth suppression of M. aeruginosa in 30 mg/L butachlor treatment. The upregulation of gene sets involved in nitrogen metabolism may illustrate the specific effort to sustain the steady concentration of intracellular microcystin-LR. These findings dissect the response mechanism of M. aeruginosa to butachlor toxicity and provide valuable reference for the evaluation of potential risk caused by butachlor in aquatic environments.

Behind the plant-bacteria system: The role of zucchini and its secondary metabolite in shaping functional microbial diversity in MCPA-contaminated soil

MCPA (2-methyl-4-chlorophenoxyacetic acid) contamination is an emerging problem, especially in water reservoirs. The early removal of MCPA residues from soil can prevent its spread to untreated areas. It has been found that the growth of cucurbits and the addition of selected plant secondary metabolites (PSMs) can stimulate MCPA removal from soil. However, the effect of these treatments on soil microbial activity remains poorly studied. Hence, the aim of this research was to evaluate the influence of zucchini (C. pepo cv Atena Polka) and its characteristic PSM: syringic acid (SA) on the functional diversity of soil microorganisms in MCPA-contaminated soil using Biolog® EcoPlates™. It also examines soil physicochemical properties and the growth parameters of zucchini. Microbial activity was enhanced by both zucchini cultivation and SA. All unplanted variants showed significantly lower microbial activity (average well color development, AWCD, ranging from 0.35 to 0.51) than the planted ones (AWCD ranging from 0.77 to 1.16). SA also stimulated microbial activity in the soil: a positive effect was observed from the beginning of the experiment in the unplanted variants, but over a longer time span in the planted variants. SA ameliorated the toxic effect of MCPA on the studied plants, especially in terms of photosynthetic pigment production: the MCPA+SA group demonstrated significantly increased chlorophyll content (401 ± 4.83 μg/g), compared to the MCPA group without SA (338 ± 50.1 μg/g). Our findings demonstrated that zucchini and the amendment of soils with SA, the characteristic PSM of cucurbits, can shape functional diversity in MCPA-contaminated soil. The changes of soil properties caused by the application of both compounds can trigger changes in functional diversity. Hence, both SA and MCPA exert indirect and direct effects on soil microbial activity.

Ecological risk assessment of pesticides in sediments of Pampean streams, Argentina

After their application in agricultural areas, pesticides are dispersed throughout the environment, causing contamination problems. In Argentina, the main promoter of transgenic biotechnology in the region, the total consumption of agrochemicals has increased significantly in recent years. Most chemicals dumped near surface waters eventually end up in bottom sediments and can be toxic to the organisms that live there. However, published data on the mixing of pesticides in this compartment is still scarce. The objective of this work was to detect and quantify pesticide residues in the sediment of rural streams in the Pampas region and to carry out acute and chronic risk assessment in these aquatic ecosystems. The study area comprises the mountainous system of Tandilia, located in one of the most productive agricultural areas in the country. The concentration of atrazine, acetochlor, chlorpyrifos, cypermethrin, and 2,4-D in the sediment of four rural streams was determined in three different seasons, and the toxic units (TU) and the risk ratios (RQ) were calculated. All the compounds analyzed were detected in most of the sampling seasons and study sites, at concentrations higher than those established in the national and international quality guidelines for the protection of aquatic biota in surface waters and for human consumption. Chlorpyrifos, cypermethrin, and acetochlor were the main pesticides contributing to the TU and RQ values, representing a medium or high ecological risk in most of the sites. Therefore, the evaluation of these pesticides in the bottom sediments could be a decisive factor in assessing the risk to the aquatic environment.

Commercial pesticides for urban applications induced population growth and sub-cellular alterations in Raphidocelis subcapitata (Chlorophyceae) at concerning environmental concentrations

Information regarding the safety and environmental risks of pesticides intended for urban use remains limited. This study aimed to assess the effects of four common pesticides on the microalga Raphidocelis subcapitata: DIAZINON® 25% C. E., Roundup®, URBACIN® 20C. E., and VAPODEL® 20% C. E., which are commercial formulations of diazinon, glyphosate, dichlorvos, and cypermethrin, respectively. According to 96-h inhibition of population growth bioassays, the four pesticide toxicities exemplified the following order: DIAZINON® (diazinon) > Roundup® (glyphosate) > VAPODEL® (dichlorvos) > URBACIN® (cypermethrin). Increasing pesticide concentrations elicited alterations in the specific growth rates (µmax). The macromolecule contents and photosynthetic pigments increased in groups exposed to the highest concentrations of DIAZINON® 25%, Roundup®, and URBACIN® 20 compared to the control group, despite these treatments inducing lower population growth rates. VAPODEL® 20% induced higher growth rates and lower macromolecule content compared to the control. Since active ingredients were not quantified, certain comparisons may prove limiting, but it is important to assess the effects of the whole mixtures in the form that they enter the environment, especially for urban-intended applications or generic formulations with higher additive contents. Finally, this study demonstrated that commercial pesticide formulations designed for urban applications might pose a threat to freshwater microalgae due to their underestimated toxic potential, but further studies are required.

Co, Cu, Fe, and Ni Deposited over TiO2 and Their Photocatalytic Activity in the Degradation of 2,4-Dichlorophenol and 2,4-Dichlorophenoxyacetic Acid

Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method were studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model.

Differential Effects of Atrazine on Chlorophyceae Species and Association with Morphology, Photosynthesis, Chlorophyll Content, and Glutathione-S-Transferase Activity

Atrazine is a herbicide widely used in the control of weeds in crops such as corn, sugar cane, and sorghum. It is often found in aquatic environments, where it can potentially endanger nontarget organisms such as microalgae. The present study evaluated atrazine toxicity to seven different species of Chlorophyceae and the tolerance of the species to the herbicide was related to morphological, photosynthetic, chlorophyll-a content and the activity of the glutathione-S-transferase enzyme (GST). The comparison of median effect concentration (EC50) values for growth inhibition indicates higher toxicity of atrazine for Pseudopediastrum boryanum and Desmodesmus communis, intermediate toxicity for Ankistrodesmus densus, Chlamydomonas puliminiorfes, and Raphidocelis subcapitata, and lower toxicity for Kirchneriella lunaris and Ankistrodesmus falcatus (EC50: 38, 42, 66, 103, 248, 1004, and 1585 µg L^-1 atrazine, respectively). Principal component analysis (PCA) with algal characteristics suggested that the atrazine-sensitive algae P. boryanum and D. communis were positively associated with photosynthetic levels and negatively associated with GST activity and chlorophyll-a concentration. The PCA also suggested that the atrazine-tolerant algae A. falcatus and K. lunaris were positively associated with morphological parameters, where the larger the cell size, the more tolerant. Although it is difficult to associate a single characteristic of algae as the key factor determining the tolerance to atrazine, results presented in this work indicate that the cell area, the photosynthetic parameters (mainly saturating irradiance), chlorophyll-a content, and the biotransformation by GST in combination may be potential predictors for the differential tolerance of Chlorophyceae species to the herbicide. Environ Toxicol Chem 2022;41:1675-1685. © 2022 SETAC.

Biomonitoring of Soil Contaminated with Herbicides

The state of environmental pollution is of random character, and it depends on climatic conditions, landforms, development and industrialization. It is estimated that in the last decade as many pollutants have been released into the environment as in the previous 70 years, and the pollution rate still increases. Many scientific reports indicate that, in addition to metals, pesticides are the most commonly detected compounds in the environment. This situation is mainly due to the irrational use of these chemicals by humans. Mostly, soil environment changes caused by the influence of pesticides can be determined by various chemical analyses, which require the use of sophisticated and expensive equipment. However, biological methods, such as those using microbiological activity and an abundance of microorganisms, e.g., organisms responsible for the cycle of organic matter and nutrients, tend to be neglected. For this reason, the aim of the present study is not only to assess the validity of other research studies that were performed based on the available literature but to compile methods and compare them, which allows for an in depth understanding of the complexity of soil processes following herbicide application by conducting comprehensive soil biomonitoring.

Cartap hydrochloride induced stress response in Anabaena variabilis ARM 441

Cartap hydrochloride is a moderately hazardous nereistoxin analogue insecticide that is predominantly applied in paddy fields of India, at a recommended dose of 10 μg ml^-1 to kill chewing and sucking insect pests of rice crop. Toxicity of cartap hydrochloride was studied on non-target free-living nitrogen fixing cyanobacterium Anabaena variabilis ARM 441 commonly used as algal biofertilizer in rice cultivation. Anabaena sp. could tolerate commercial grade insecticide up to 30 μg ml^-1. However, at the recommended dose of 10 μg ml^-1, it caused reduction in algal growth, total nitrogen and heterocyst frequency by 47.28, 24.29 and 17.72% respectively, as well as photosynthetic pigments under pure culture conditions. Scanning electron micrographs revealed cell rupture and breakage in filaments due to cartap exposure with the formation of akinetes. Cartap hydrochloride induced stress, since level of superoxide dismutase, peroxidase and catalase were increased by 108.57, 187.5 and 117% respectively. Generation of superoxide radicals and hydrogen peroxide were also increased by 152.48 and 34% respectively. Lipid peroxidation was increased by 31.03%, whereas there was decline in ascorbate content by 48.45%, however the glutathione content was increased by 128.57%. Increase in osmolytes such as proline from 8.6 to 32.8% and sucrose from 61.22 to 90.13% indicates their possible role in overcoming cartap induced oxidative stress and can be helpful in assessing its detrimental effect on Anabaena variabilis ARM 441, since cyanobacterial biofertilizers are purposely used in paddy fields as nitrogen contributors.

Hormones induce the metabolic growth and cytotoxin production of Microcystis aeruginosa under terpinolene stress

Several organic compounds released into the aquatic environment have a detrimental impact on humans and other organisms. There is a lack of knowledge about natural hormones and herbicides on non-target organisms, including cyanobacteria. In this study, the response of Microcystis aeruginosa to four phytohormones, indole-3-acetic acid (IAA; 10^-5), zeatin (ZT; 10^-5), abscisic acid (ABA; 10^-7), and brassinolide (BRL; 10^-9 mol/L), exposed to terpinolene (TPN; (0.44, 0.88, 1.17, or 1.62 mmol/L) at the cellular and genetic levels were investigated. The results showed that TPN could inhibit the growth and photosynthetic activities and stimulate microcystins (MCs) of M. aeruginosa at various levels through the co-occurrence of oxidative stress, antioxidant defense activities, and an imbalance of the antioxidative system. Hormones played critical roles in the growth promotion and photosynthetic activity by enhancing the antioxidant defense mechanisms and MCs production of M. aeruginosa under TPN stress in both hormone and TPN dose-dependent manner. The growth performance and photosynthetic activities of M. aeruginosa were significant with IAA (p < 0.01) and BSL (p < 0.05) compared to ZT and ABA, as TPN concentrations increased. Hormones stimulated the MCs production significantly BSL (p < 0.05) at various levels and protected the cells against TPN-induced oxidative stress and expression of mcyB and mcyD genes involve in MCs synthesis. Our results indicated that hormone contamination in eutrophic lakes might increase the risk of Microcystis aeruginosa bloom and microcystin production with the TPN association.

Effects of moxifloxacin and gatifloxacin stress on growth, photosynthesis, antioxidant responses, and microcystin release in Microcystis aeruginosa

Moxifloxacin (MOX) and gatifloxacin (GAT) are fourth-generation fluoroquinolone antibiotics that are frequently detected in surface water environments and pose a threat to aquatic organisms. However, research into their toxicity to Microcystis aeruginosa, a cyanobacterium, has thus far been limited. In the present study, we investigated the effects of these antibiotics on M. aeruginosa growth, photosynthesis, oxidative stress, and microcystin (MC) release. The results of the 96 h EC₅₀ values of MOX and GAT were 60.34 and 25.30 μg/L, respectively, and the risk quotients calculated indicated that these antibiotics could pose considerable ecological risks at actual environmental concentrations. Photosynthetic fluorescence intensity was shown to decline markedly, and Fv/Fm significantly decreased without any evidence of recovery, suggesting that the organism's photosystems were irreversibly damaged. Chlorophyll a and carotenoid content decreased, whereas the ratio of carotenoids to chlorophyll a increased, indicating that carotenoids were less susceptible to damage than chlorophyll a. The reactive oxygen species and malondialdehyde content significantly increased, as well as the superoxide dismutase and catalase activities, indicating that exposure caused serious oxidative stress. Additionally, MC release increased. These results demonstrate that the environmental risks posed by MOX and GAT should be given serious consideration, particularly as their use is increasing.

Toxicological parameters of aqueous residue after using Plectranthus neochilus for 2,4-D phytoremediation

Phytoremediation is a technique that reduces the impact and environmental toxicity of toxic agents. Plectranthus neochilus, a species of aromatic plant, has already promoted phytoremediation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). In addition, it was unclear whether the degradation of 2,4-D alone allows for a non-toxic environment (decontamination efficiency). Therefore, the aim of the present study was to verify the changes of the volatile compounds and concentrated essential oil of P. neochilus after phytoremediation of 2,4-D and the subsequent antibacterial activity of this essential oil concentrate. In addition, the toxicity of the plant's tea and the aqueous medium (waste) after the decontamination of 2,4-D was analyzed. The exposure to 2,4-D did not cause many changes in the volatile compounds, nor in the essential oil concentrate from the plant. Therefore, this essential oil concentrate can be used as an antimicrobial after phytoremediation. Regarding the use of this plant in tea form, it was found to be unsafe, even after phytoremediation, as this tea was toxic to the Drosophila melanogaster model (death of up to 100% of flies). The aqueous medium after 2,4-D phytoremediation became less toxic than the initial one (bioassays with Artemia salina and Allium cepa in the waste groups). However, the efficiency of phytoremediation with this plant must be improved. Therefore, we are performing new studies with P. necohilus and 2,4-D in aqueous medium.

Similar toxicity mechanisms between graphene oxide and oxidized multi-walled carbon nanotubes in Microcystis aeruginosa

In photosynthetic microorganisms, the toxicity of carbon nanomaterials (CNMs) is typically characterized by a decrease in growth, viability, photosynthesis, as well as the induction of oxidative stress. However, it is currently unclear how the shape of the carbon structure in CNMs, such as in the 1-dimensional carbon nanotubes (CNTs) compared to the two-dimensional graphene oxide (GO), affects the way they interact with cells. In this study, the effects of GO and oxidized multi-walled CNTs were compared in the cyanobacterium Microcystis aeruginosa to determine the similarities or differences in how the two CNMs interact with and induce toxicity to cyanobacteria. Using change in Chlorophyll a concentrations, the effective concentrations inducing 50% inhibition (EC₅₀) at 96 h are found to be 11.1 μg/mL and 7.38 μg/mL for GO and CNTs, respectively. The EC₅₀ of the two CNMs were not found to be statistically different. Changes in fluorescein diacetate and 2',7'-dichlorodihydrofluorescein diacetate fluorescence, measured at the EC₅₀ concentrations, suggest a decrease in esterase enzyme activity but no oxidative stress. Scanning and transmission electron microscopy imaging did not show extensive membrane damage in cells exposed to GO or CNTs. Altogether, the decrease in metabolic activity and photosynthetic activity without oxidative stress or membrane damage support the hypothesis that both GO and CNTs induced indirect toxicity through physical mechanisms associated with light shading and cell aggregation. This indirect toxicity explains why the intrinsic differences in shape, size, and surface properties between CNTs and GO did not result in differences in how they induce toxicity to cyanobacteria.

Effects of glyphosate on microcystin-LR production and release from Microcystis aeruginosa at different temperatures

Cyanobacterial blooms and their associated toxins are growing issues for many aquatic ecosystems. Microcystin-LR (MC-LR) is a toxic and common cyanobacterial toxin, whereas glyphosate is a commonly used herbicide that is massively applied in agriculture. In this study, the effects of glyphosate on the growth of Microcystis aeruginosa and MC-LR synthesis and release from M. aeruginosa at different temperatures are investigated. In addition, the MC-LR pollution in the Huangpu River in Shanghai urban area is studied. Results indicated that the MC-LR concentration in the Huangpu River is related to water temperature. The laboratory experiments revealed that the growth of M. aeruginosa was slightly promoted at 15 °C and glyphosate concentrations of 1 and 5 mg/L and inhibited in the presence of glyphosate and high temperatures (20 °C, 25 °C, 30 °C, and 35 °C). The intracellular MC-LR contents were remarkably increased by glyphosate at 15 °C, 20 °C, 25 °C, and 30 °C and remarkably decreased at 35 °C. Meanwhile, the extracellular MC-LR contents were remarkably increased at all temperatures and all concentrations except when treated with 1 mg/L glyphosate at 35 °C. The highest extracellular MC-LR content, which was 143.9% higher compared with that of the control, was observed at 30 °C and treatment with 10 mg/L glyphosate. These results were consistent with those of MC-LR investigation in Huangpu River. Furthermore, in accordance with the intracellular MC-LR contents, the ability of a single cell to synthesize MC-LR was enhanced at 15 °C, 20 °C, 25 °C, and 30 °C and decreased at 35 °C. These results provide an understanding on the toxic effects of glyphosate on cyanobacteria and the effects of temperature on MC release. Moreover, these results will be helpful in protecting aquatic ecosystems and human health.

Primary production of freshwater microbial communities is affected by a cocktail of herbicides in an outdoor experiment

Primary production (PP) is a key variable to evaluate the quality of the ecological services provided by freshwater bodies because it gives information on the amount of oxygen and organic matter incorporated into the system. We analysed the impact of a mixture of commercial formulations of glyphosate- and 2,4-D-based herbicides (Roundup Max® and AsiMax 50®, respectively) on freshwater primary production. Primary production was studied through the oxygen exchange method. Four measurements were made during a 23-day experiment in outdoor mesocosms using the light and dark bottle method. High and low concentrations of the active ingredients were assayed to evaluate a concentration-dependent effect. Our results indicated that the mixture of Roundup Max® and AsiMax 50® acted mostly additively on gross and net primary production. Moreover, we found a concentration-dependent effect of each herbicide on PP. Thus, AsiMax 50® at low and Roundup Max® at high concentration induced a significant early decrease in respiration and gross primary production 4 h after application, attributable to physiological responses. Besides, significant increases in primary production were simultaneously recorded with increases in chlorophyll a concentration and micro + nano-phytoplankton abundance 7 days after the application of Roundup Max® at high concentration. This study contributes to the knowledge of the impact of widely used herbicides on freshwater ecosystems.

Influence of eugenol on algal growth, cell physiology of cyanobacteria Microcystis aeruginosa and its interaction with signaling molecules

Essential oils (EOs) are naturally occurring substances that have shown great prospect in the field of antimicrobial, antioxidant and pest control by nontoxic mechanisms. In this regard, EOs are considered the promising and eco-friendly approach for controlling harmful algae. In this study, the anti-cyanobacterial activity of EOs eugenol against Microcystis aeruginosa are evaluated from the perspective of photosynthetic efficiency, the behavior of extracellular organic matter (EOM), endogenous plant hormone synthesis, and nitric oxide signaling pathway. Results showed that the photosynthetic activity of M. aeruginosa decreased significantly after eugenol treatments. Eugenol treatment resulted in cells rupture and the release of EOM. Levels of endogenous plant hormones salicylic acid (SA) and jasmonic acid (JA) were enhanced separately by 2.32 and 2.01 times after 4 d of exposure to eugenol. And the inhibition of SA and JA biosynthesis further promotes the inhibitory effects of eugenol on algae. Additionally, the signaling molecule nitric oxide (NO) increased significantly by 3.78-fold. Furthermore, the influence of NO on microalgae exposed to eugenol was also determined, suggesting that the inhibitory effect of eugenol stress might be associated with NO generation in M. aeruginosa. These findings will be helpful for the understanding of the fate and potential of eugenol in harmful algae control.

Influences of the micropollutant erythromycin on cyanobacteria treatment with potassium permanganate

Cyanobacteria blooms and micropollutants (e.g., antibiotics) in source waters are two increasing environmental issues worldwide. This study hypothesized that the coexisting antibiotics may possibly alter the efficiency of water treatment processes through affecting the physiological and biochemical characteristics of cyanobacterial cells. A toxic strain of Microcystis aeruginosa was exposed to the common antibiotic erythromycin (ERY) at environmentally relevant concentrations; then, samples were collected on days 1, 4 and 6 to assess the efficiency of potassium permanganate (KMnO₄) in cyanobacteria oxidation. The percentage of intact cells remained constant after treatment with 2 mg L^-1 KMnO₄ in M. aeruginosa samples dosed with 0-5.0 μg L^-1 ERY. Although 6 mg L^-1 KMnO₄ could damage cyanobacterial cells, its ability was considerably reduced as the concentrations of ERY increased. KMnO₄ oxidation degraded the intracellular microcystins (MCs) in all of the cyanobacterial samples, even the samples with intact cells, possibly resulting from the stimulation of intracellular reactive oxygen species (ROS). The highest amounts of total MCs remained after oxidation with 2 and 6 mg L^-1 KMnO₄ in 0.2 μg L^-1 ERY-treated cyanobacterial samples, which may be due to large amounts of MC production. The 5.0 μg L^-1 ERY inhibited the growth of cyanobacterial cells and downregulated the expression of the MC synthesis gene (mcyB), which resulted in the lowest amounts of total MCs. However, it led to the highest concentration (4.6 μg L^-1) of extracellular MCs after treatment with 2 mg L^-1 KMnO₄ for 300 min. Generally, this study indicates that the effectiveness of KMnO₄ oxidation in cyanobacteria treatment decreased when the concentration of ERY increased. Hence, the possible risks caused by the coexistence of cyanobacteria and antibiotics, such as reduced efficiency of water treatment processes in cyanobacteria inactivation and degradation of the dissolved MCs, need to be taken into account.

Toxic effects of terpinolene on Microcystis aeruginosa: Physiological, metabolism, gene transcription, and growth effects

Bioherbicide terpinolene is widely employed in the agricultural field because of its unique phytotoxic properties. However, little is known about the toxicity of bioherbicide on harmful algal blooms (HABs) and its mechanisms. Therefore, in this study, the inhibiting effect of bioherbicide terpinolene on the growth and physiological change of Microcystis aeruginosa was determined. Results showed that the cell density and photosynthetic activity of microalgae were significantly inhibited by terpinolene. Activities of nitrate reductase (NR) and glutamine synthetase (GS) were decreased separately by 25.38% and 42.75% after 4 d of exposure to 1.47 mM terpinolene, suggesting the inhibiting effect of terpinolene on algal nitrogen metabolism. However, the transcript abundance of genes related to membrane protein cytochrome c oxidase subunit II (COX II) and ATP-binding cassette transporters (ABC transporter) were enhanced separately by 3.15 and 1.69-fold compared with control, suggesting the resistance response of cells to terpinolene stress. Additionally, terpinolene not only increased the content of endogenous phytohormones including indole-3-acetic acid (IAA), zeatin, and brassinolide, but also inhibited the expression of genes related to calcium-binding protein (CaBPs), one kind of calcium (Ca²⁺) sensors, suggesting its regulation on algal signal molecules. These findings helped to understand the ecotoxicity of terpinolene and guide the rational use of bioherbicide in agriculture.

Resistance of cyanobacteria Microcystis aeruginosa to erythromycin with multiple exposure

Here we report a set of experiments in which water blooming cyanobacteria Microcystis aeruginosa was repeatedly exposed to erythromycin. Growth inhibition increased with increasing erythromycin concentration (1-150 μg/L) upon first exposure. Maximum inhibition rate (76.06%), occurred under 150 μg/L erythromycin. Moreover, 96-h 50% effective concentration (EC₅₀) was 22.97 μg/L, indicating that the growth of M. aeruginosa was affected by erythromycin under common environmental concentrations. Photosynthesis was hindered by chlorophyll and photosystem II limitations. Malondialdehyde, reactive oxygen species, and superoxide dismutase contents increased significantly under certain concentrations of erythromycin, but superoxide dismutase was suppressed by 150 μg/L erythromycin. Synthesis of intracellular and extracellular microcystins was promoted by 10-60 and by 20-60 μg/L erythromycin, respectively, but both were inhibited by 100-150 μg/L. Principal component analysis and Pearson's correlation revealed the accumulation of reactive oxygen species as the dominant mechanism of erythromycin toxicity to cells. M. aeruginosa repeatedly subjected to erythromycin exposure showed obvious resistance against the antibiotic, especially when treated twice with 60 μg/L erythromycin. The 96-h EC₅₀ was 81.29 μg/L. As compared to the first exposure to erythromycin, photosynthetic and antioxidant activities increased, while growth inhibition and oxidation stress decreased upon multiple exposures. Production and release of microcystins were enhanced by repeated exposure to the antibiotic. Thus, erythromycin persistence in water should be examined, as repeated exposure may lead to serious environmental and human health hazards.

Efficient Degradation of Phenoxyalkanoic Acid Herbicides by the Alkali-Tolerant Cupriavidus oxalaticus Strain X32

Phenoxyalkanoic acid (PAA) herbicides are mainly metabolized by microorganisms in soils, but the degraders that perform well under alkaline environments are rarely considered. Herein, we report Cupriavidus oxalaticus strain X32, which showed encouraging PAA-degradation abilities, PAA tolerance, and alkali tolerance. In liquid media, without the addition of exogenous carbon sources, X32 could completely remove 500 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-chloro-2-methylphenoxyacetic acid within 3 days, faster than that with the model degrader Cupriavidus necator JMP134. Particularly, X32 still functioned at pH 10.5. Of note, with X32 inoculation, we observed 2,4-D degradation in soils and diminished phytotoxicity to maize (Zea mays). Furthermore, potential mechanisms underlying PAA biodegradation and alkali tolerance were then analyzed by whole-genome sequencing. Three modules of tfd gene clusters involved in 2,4-D catabolism and genes encoding monovalent cation/proton antiporters involved in alkali tolerance were putatively identified. Thus, X32 could be a promising candidate for the bioremediation of PAA-contaminated sites, especially in alkaline surroundings.

Nanoplastics Promote Microcystin Synthesis and Release from Cyanobacterial Microcystis aeruginosa

Although the fate of nanoplastics (<100 nm) in freshwater systems is increasingly well studied, much less is known about its potential threats to cyanobacterial blooms, the ultimate phenomenon of eutrophication occurrence worldwide. Previous studies have evaluated the consequences of nanoplastics increasing the membrane permeability of microbes, however, there is no direct evidence for interactions between nanoplastics and microcystin; intracellular hepatotoxins are produced by some genera of cyanobacteria. Here, we show that the amino-modified polystyrene nanoplastics (PS-NH₂) promote microcystin synthesis and release from Microcystis aeruginosa, a dominant species causing cyanobacterial blooms, even without the change of coloration. We demonstrate that PS-NH₂ inhibits photosystem II efficiency, reduces organic substance synthesis, and induces oxidative stress, enhancing the synthesis of microcystin. Furthermore, PS-NH₂ promotes the extracellular release of microcystin from M. aeruginosa via transporter protein upregulation and impaired cell membrane integrity. Our findings propose that the presence of nanoplastics in freshwater ecosystems might enhance the threat of eutrophication to aquatic ecology and human health.

Biodegradation Potential and Ecotoxicity Assessment in Soil Extracts Amended with Phenoxy Acid Herbicide (2,4-D) and a Structurally-Similar Plant Secondary Metabolite (Ferulic Acid)

Phenoxy acid 2,4-D (2,4-dichlorophenoxy acid) is one of the most commonly-used herbicide in agriculture. Biodegradation of 2,4-D can be stimulated by structurally-related plant secondary metabolites such as ferulic acid (FA). The aim of this study is to: (1) assess the potential of indigenous soil bacteria to degrade 2,4-D in the presence of FA by PCR analysis of functional tfdA genes, (2) to determine the influence of 2,4-D and FA on samples ecotoxicity using Phytotoxkit^® and Microtox^® biotests. The detection of tfdA genes varied depending on the enrichment of samples with FA. FA suppressed detection of the tfdA genes, 100 µM 2,4-D induced higher detection of studied amplicons, while 500 µM 2,4-D delayed their detection. The ecotoxicity response was specific and differed between plants (PE% Lepidium sativum >  Sinapis alba >  Sorghum saccharatum) and bacteria (PE% up to 99% for Vibrio fischeri). Our findings confirm that 2,4-D and FA had a toxic influence on the used organisms.

Tolerance and sorption of Bromacil and Paraquat by thermophilic cyanobacteria Leptolyngbya 7M from Costa Rican thermal springs

We studied the adsorption ability and tolerance of the thermophilic filamentous cyanobacteria Letolyngbya 7M towards Paraquat and Bromacil. Adsorption isotherms at pH = 7.0 showed an adsorption capacity of 24.4 mg/g and 66.8 mg/g, respectively, and a good fit to the Langmuir model (R² = 0.97 and 0.99, respectively). To evaluate the effect of both herbicides on photosynthetic pigments and viability of cyanobacteria, cell autoflorescence and esterase activity was determined using flow cytometry. Autofluorescence was less sensitive to changes in cell viability, as it was only slightly reduced at high Paraquat and Bromacil concentrations. Herbicide effect on esterase activity is dose-dependent. Bromacil did not cause a significant effect on either chlorophyll a content or cell viability. This study demonstrates the potential of Leptolyngbya 7M to remove Paraquat and Bromacil herbicides from aqueous solution under laboratory conditions.

Effects of pollution on freshwater aquatic organisms

This paper presents the reviews of scientific papers published in 2018 issues on the effects of anthropogenic pollution on the aquatic organisms dwelling in freshwater ecosystem at global scale. The first part of the study provides the summary of relevant literature reviews followed by field and survey based studies. The second part is based on categories of different classes/sources of pollutants which affect freshwater organism. This is composed of several sections including metals and metalloids, wastewater and effluents, sediments, nutrients, pharmaceuticals, polycyclic aromatic hydrocarbons, flame retardants, persistent organic pollutants, pharmaceuticals and illicit drugs, emerging contaminants, pesticides, herbicides, and endocrine disruptors. The final part of the study highlights the reviews of published research work on new pollutants such as microplastics and engineered nanoparticles which affect the freshwater organisms. PRACTITIONER POINTS: Heavy metals concentrations should be assessed at nano-scale in aquatic environment. Air pollutants could have long-term effects on freshwater ecosystem. Future studies should focus on bioremediations of freshwater pollution.

Removal and Ecotoxicity of 2,4-D and MCPA in Microbial Cultures Enriched with Structurally-Similar Plant Secondary Metabolites

The removal of contaminants from the environment can be enhanced by interactions between structurally-related plant secondary metabolites (PSMs), selected xenobiotics and microorganisms. The aim of this study was to investigate the effect of selected PSMs (ferulic acid—FA; syringic acid—SA) on the removal of structurally-similar phenoxy herbicides (PHs): 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA). The study also examines the biodegradation potential of soil bacteria, based on the occurrence of functional tdfA-like genes, and the ecotoxicity of the samples against two test species: Sinapis alba L. and Lepidium sativum L. The microbial cultures spiked with the PSMs demonstrated higher phenoxy acid removal: 97–100% in the case of 2,4-D and 99%–100% for MCPA. These values ranged from 5% to 100% for control samples not amended with FA or SA. The higher herbicide removal associated with PSM spiking can be attributed to acceleration of the microbial degradation processes. Our findings showed that the addition of SA particularly stimulated the occurrence of the total number of tfdA genes, with this presence being higher than that observed in the unamended samples. PSM spiking was also found to have a beneficial effect on ecotoxicity mitigation, reflected in high (102%) stimulation of root growth by the test species.

Evaluation of the use of eucalyptus to control algae bloom and improve water quality

Lakes represent an important source of drinking water resource for human beings. The presence of harmful algae blooms can pose a serious threat to lakes water quality. This study explored the feasibility of using eucalyptus plants and leaves extracts for controlling algae proliferation in an aquatic milieu. After 30 days of treatment, the inhibitory efficiencies were 85.8% and 20.9% for treatments planting eucalyptus and eucalyptus leaves extracts, respectively. The synergistic effects of allelopathy and competitive absorption for macro nutrients were attributed to the effective control of algae proliferation in the mesocosm systems. Moreover, the analysis of microbial community structures indicated that eucalyptus plants or leaves extracts had no adverse effect on species diversity and their relative abundance. The choice of using eucalyptus to control algae bloom will be dictated by environmental and economic considerations within a geographical region.

Integrative Biomarker Assessment of the Influence of Saxitoxin on Marine Bivalves: A Comparative Study of the Two Bivalve Species Oysters, Crassostrea gigas, and Scallops, Chlamys farreri

Harmful algae blooms have expanded greatly in recent decades, and their secreted toxins pose a severe threat to human health and marine ecosystems. Saxitoxin (STX) is a main paralytic shellfish poison naturally produced by marine microalgae of the genus Alexandrium. Despite numerous studies have assessed the impacts of STX on marine bivalves, comparative in vivo study on the toxicity of STX on bivalves with distinct accumulation ability (such as oysters and scallops) has been seldom investigated. The aim of this study was to identify whether distinct sensitivity exists between oysters, Crassostrea gigas, and scallops, Chlamys farreri under the same amount of STX exposure using multiple biomarker responses. The responses of different biochemical markers including oxidative stress markers (catalase, superoxide dismutase, glutathione S-transferase, and lipid peroxidation) and immunotoxicity biomarkers (hemocyte phagocytosis rate, reactive oxidative species production, and DNA damages) were evaluated in bivalves after 12, 48, and 96 h of exposure to STX. The integrated biomarker responses value combined with two-way ANOVA analysis suggested that STX posed slightly severer stress on scallops than oysters for the extended period of time. This study provided preliminary results on the usefulness of a multi-biomarker approach to assess the toxicity associated with STX exposure in marine bivalves.