Sensitivity of the macrophytes Pistia stratiotes and Eichhornia crassipes to hexazinone and dissipation of this pesticide in aquatic ecosystems

Aquatic Macrophytes in the Remediation of Atrazine in Water: A Study on Herbicide Tolerance and Degradation Using Eichhornia crassipes, Pistia stratiotes, and Salvinia minima

Aquatic macrophytes can be used for herbicide remediation provided they exhibit tolerance to the contaminants. This research assessed the remediation potential of Salvinia minima, Echhornia crassipes, and Pistia stratiotes, some common aquatic macrophytes native to Brazil, and their tolerance to atrazine, an herbicide commonly detected in waterbodies. Plants were cultivated under controlled conditions with five atrazine concentrations (0, 2, 20, 200, and 1000 μg L-1) for 15 days. S. minima and E. crassipes tolerated atrazine concentrations equal to or less than 20 μg L-1 and died at 200 and 1000 μg L-1, indicating the herbicide's potential toxicity and its selectivity against sensitive species. P. stratiotes tolerated the herbicide concentration up to 200 μg L-1 and had its growth reduced at 1000 μg L-1. All species demonstrated the ability to reduce atrazine concentrations in water at 20 μg L-1 or lower, E. crassipes being the most efficient, reducing concentrations by 43% and 22% at 2 and 20 μg L-1, respectively. Atrazine levels within Brazilian (2 μg L-1 by CONAMA 2005) and European (0.1 μg L-1 by Directive 2013/33) regulatory limits do not selectively affect these species. Thus, they show potential for use in arazine phytoremediation programs.

Clomazone exposure-driven photosynthetic responses plasticity of Pontederia crassipes

Clomazone is known to contaminate aquatic environments and have a negative impact on macrophytes. However, recent reports suggests that Pontederia crassipes Mart. can withstand clomazone exposure while maintaining growth rates. We hypothesized that this maintenance of growth is supported by photosynthetic plasticity of old leaves (developed before herbicide application), while new leaves (developed after application) exhibit phytotoxic symptoms. To investigate, two experiments were conducted with doses ranging from 0.1 mg L-1 to 0.5 mg L-1 plus untreated controls. Various parameters were measured in old and new leaves over 7, 12, and 15 d post-application, including visual symptoms, chlorophyll index, photosynthetic pigments, chlorophyll fluorescence, gas exchange, glycolate oxidase activity, carbohydrate content, leaf epidermis anatomy, and growth parameters. Clomazone exposure induced chlorosis, particularly in new leaves across all doses. These visual symptoms were accompanied by stomatal closure, restricting gas exchange and CO2 fixation, leading to reduced photosynthetic rates and carbohydrate synthesis. However, clomazone did not affect old leaves, which maintained photosynthetic activity, sustaining essential metabolic processes of the plant, including reproductive functions. By ensuring high reproductive rates and metabolic continuity, old leaves supported the species' persistence despite clomazone presence.

Sensitivity and antioxidant response of forest species seedlings to the atrazine under simulated conditions of subsurface water contamination

Atrazine is an herbicide with a high soil leaching capacity, contaminating subsurface water sources. Once the water table is contaminated, riparian species can be exposed to atrazine. In this way, understanding the impacts of this exposure must be evaluated for planning strategies that minimize the effects of this herbicide on native forest species. We aimed to evaluate forest species' sensitivity and antioxidant response to exposure to subsurface waters contaminated with atrazine, as well the dissipation this herbicide. The experiment was conducted in a greenhouse in a completely randomized design, with three replications and one plant per experimental unit. The treatments were arranged in a 2 × 10 factorial. The first factor corresponded to the presence or absence (control) of the atrazine in the subsurface water. The second factor comprised 10 forest species: Amburana cearensis, Anadenanthera macrocarpa, Bauhinia cheilantha, Enterolobium contortisiliquum, Hymenaea courbaril, Libidibia ferrea, Mimosa caesalpiniifolia, Mimosa tenuiflora, Myracrodruon urundeuva, and Tabebuia aurea. The forest species studied showed different sensitivity levels to atrazine in subsurface water. A. cearensis and B. cheilantha species do not have efficient antioxidant systems to prevent severe oxidative damage. The species A. macrocarpa, E. contortisiliquum, L. ferrea, and M. caesalpiniifolia are moderately affected by atrazine. H. courbaril, M. urundeuva, and T. aurea showed greater tolerance to atrazine due to the action of the antioxidant system of these species, avoiding membrane degradation events linked to the production of reactive oxygen species (ROS). Among the forest species, H. courbaril has the most significant remedial potential due to its greater tolerance and reduced atrazine concentrations in the soil.

Effects of agriculture on river biota differ between crop types and organism groups

While the general effects of agricultural land use on riverine biota are well documented, the differential effects of specific crop types on different riverine organism groups, remain largely unexplored. Here we used recently published land use data distinguishing between specific crop types and a Germany-wide dataset of 7748 sites on the ecological status of macroinvertebrates, macrophytes and diatoms and applied generalized linear mixed models to unravel the associations between land use types, crop types, and the ecological status. For all organism groups, associations of specific crop types with biota were stronger than those of urban land use. For macroinvertebrates and macrophytes, strong negative associations were found for pesticide intensive permanent crops, while intensively fertilized crops (maize, intensive cereals) affected diatoms most. These differential associations highlight the importance of distinguishing between crop types and organism groups and the urgency to buffer rivers against agricultural stressors at the catchment scales and to expand sustainably managed agriculture.

Phytoremediation: A green and low-cost technology to remediate herbicides in the environment

Pesticide dependence is one of the main disadvantages of agriculture. Despite the advances in biological control and integrated management of plant pests and diseases in recent years, herbicides are still essential for weed control and constitute the main class of pesticides worldwide. Herbicide residues in water, soil, air, and non-target organisms are among the biggest agricultural and environmental sustainability obstacles. Therefore, we suggest an environmentally viable alternative to reduce the harmful effects of herbicide residues, a technology called phytoremediation. Remediating plants were grouped into herbaceous, arboreal, and aquatic macrophytes. Phytoremediation can reduce the loss of at least 50% of all herbicide residues to the environment. Among the herbaceous species reported as phytoremediators of herbicides, the Fabaceae family was mentioned in more than 50% of reports. This family is also among the main species of trees reported. Regarding the most reported groups of herbicides, it is observed that most of them, regardless of the group of plants, are triazines. Processes such as extraction or accumulation are the best known and reported for most herbicides. The phytoremediation may be effective against chronic or unknown herbicide toxicity. This tool can be included in proposals for management plans and specific legislation in countries, guaranteeing public policies to maintain environmental quality.

Environmental behaviors of emerging contaminants in freshwater ecosystem dominated by submerged plants: A review

Persistent exposure of emerging contaminants (ECs) in freshwater ecosystem has initiated intense global concerns. Freshwater ecosystem dominated by submerged plants (SP-FES) has been widely constructed to control eutrophic water. However, the environmental behaviors (e.g. migration, transformation, and degradation) of ECs in SP-FES have rarely been concerned and summarized. This review briefly introduced the sources of ECs, the pathways of ECs entering into SP-FES, and the constituent elements of SP-FES. And then the environmental behaviors of dissolved ECs and refractory solid ECs in SP-FES were comprehensively summarized, and the feasibility of removing ECs from SP-FES was critically evaluated. Finally, the challenges and perspectives on the future development for ECs removal from SP-FES were prospected, giving possible research gaps and key directions. This review will provide theoretical and technical support for the effective removal of ECs in freshwater ecosystem, especially in SP-FES.

Sensibility, multiple tolerance and degradation capacity of forest species to sequential contamination of herbicides in groundwaters

Herbicides have already reported environmental contamination in several countries with intense agricultural activity. The transport of these molecules due to leaching and surface runoff has frequently caused contamination of rivers, groundwater and soil in non-agricultural areas. Thereby, we propose to investigate the sensitivity and phytoremediation capacity of 5 native Cerrado species to sequential exposure to 2,4-D, atrazine, diuron and hexazinone. We hypothesized that species have different sensitivity levels to sequential exposure to these herbicides absorbed from contaminated simulated groundwater model. The objectives of this work were: i) to determine the sensitivity of native cerrado species by sequential exposure to 2,4-D, atrazine, diuron and hexazinone via contaminated simulated groundwater model; ii) to evaluate the presence and degradation capacity of these herbicides in the soil and water leached by tolerant species. Some species showed high phytoremediation potential for groundwater already contaminated with 2,4-D, atrazine, diuron and hexazinone. S. macranthera and C. antiphilitica are tolerant and reduce the concentration of herbicides in simulated groundwater model. Among these species, C. antiphilitica reduces the concentration of all herbicides, suggesting greater adaptability to compose decontamination strategies in areas close to agricultural systems that use 2,4-D herbicides, atrazine, diuron and hexazinone. Also, our results show that herbicides can act as a selection factor for Cerrado forest species, however, two species can mitigate the effects of contamination due to their ability to degrade herbicides.

Potential of Egeria densa and Pistia stratiotes for the phytoremediation of water contaminated with saflufenacil

Saflufenacil is an herbicide that is leachable in soil and has the potential to contaminate groundwater, besides having moderate toxicity to aquatic organisms. Some macrophyte species may interfere with the availability of herbicides in water, increasing dissipation in this environment. Thus, the objective of this work was to evaluate the absorption and dissipation of ¹⁴C-saflufenacil in water by Egeria densa and Pistia stratiotes. Dissipation was performed with ¹⁴C-saflufenacil applied directly in water and quantified by liquid scintillation spectrometry (LSS). The evaluation times were 0, 3, 6, 24, 48, 72 and 96 h after application (HAA) for E. densa and 0, 12, 24, 36, 48, 60, 84 and 108 HAA for P. stratiotes. Absorption was analyzed through plant combustion in a biological oxidizer. The presence of the macrophytes increased the dissipation of ¹⁴C-saflufenacil in water. The half-life time (DT₅₀) of the herbicide decreased by 82.6% in the presence of E. densa at 96 HAA. For P. stratiotes, the reduction in DT₅₀ was 94.8% at 108 HAA. The absorption of ¹⁴C-saflufenacil was low for both macrophytes during the evaluated time. However, the macrophytes E. densa and P. stratiotes showed potential for the phytoremediation of water contaminated with saflufenacil.

Transcriptomic profiling of atrazine phytotoxicity and comparative study of atrazine uptake, movement, and metabolism in Potamogeton crispus and Myriophyllum spicatum

The accumulation of atrazine in sediments raises wide concern due to its potential negative effects on aquatic environments. Here we collected sediments and different submerged macrophytes to simulate natural shallow lakes and to measure atrazine levels and submerged macrophyte biomass. We determined gene expressions in submerged macrophytes treated with or without atrazine. We also examined atrazine concentrations and its metabolite structures in submerged macrophytes. When the initial concentration of atrazine in sediments ranged from 0.1 to 2.0 mg kg^-1 dry weight (DW), atrazine levels in the pore water of the sediments ranged from 0.003 to 0.05 mg L^-1 in 90 days. Atrazine did not show obvious long-term effects on the biomass of Potamogeton crispus and Myriophyllum spicatum (P > 0.05). On day 90, gene expressions related to cell wall in P. crispus were changed by atrazine phytotoxicity. Moreover, the decrease in the number genes controlling light-harvesting chlorophyll a/b-binding proteins verified the toxic effects of atrazine on the photosynthesis of M. spicatum. Compared with unexposed plants on day 90, ribosome pathway was significantly enriched with differentially expressed genes after submerged macrophytes were exposed to 2.0 mg kg^-1 DW atrazine (P < 0.05). In addition, shoots and roots of P. crispus and M. spicatum could absorb the equal amount of atrazine (P > 0.05). Once absorbed by submerged macrophytes, atrazine was degraded into 1-hydroxyisopropylatrazine, hydroxyatrazine, deethylatrazine, didealkylatrazine, cyanuric acid, and biuret, and some of its metabolites could conjugate with organic acids, cysteinyl β-alanine, and glucose. This study establishes a foundation for aquatic ecological risk assessments and the phytoremediation of atrazine in sediments.

Water contamination with atrazine: is nitric oxide able to improve Pistia stratiotes phytoremediation capacity?

Atrazine is an herbicide commonly used in several countries. Due to its long half-life, associated with its use in large scales, atrazine residues remain as environmental pollutants in water bodies. Phytoremediation is often pointed out as an interesting approach to remove atrazine from the aquatic environment, but its practical application is limited by the high toxicity of this herbicide. Here, we characterize the damages triggered by atrazine in Pistia stratiotes, evaluating the role of nitric oxide (NO), a cell-signaling molecule, in increasing the tolerance to the pollutant and the phytoremediation potential of this species. Pistia stratiotes plants were exposed to four treatments: Control; Sodium nitroprusside (SNP) (0.05 mg L^-1); Atrazine (ATZ) (150 μg L^-1) and ATZ + SNP. The plants remained under those conditions for 24 h for biochemical and physiological analysis and 3 days for the evaluation of relative growth rate. The presence of atrazine in plant cells triggered a series of biochemical and physiological damages, such as the increase in the generation of reactive oxygen species, damages to cell membranes, photosynthesis impairment, and negative carbon balance. Despite this, the plants maintained greater growth rates than other aquatic macrophytes exposed to atrazine and showed high bioconcentration and translocation factors. The addition of SNP, a NO donor, decreased the herbicide toxicity, with an increase of over 60% in the IC₅₀ value (Inhibitor Concentration). Indeed, the NO signaling action was able to increase the tolerance of plants to atrazine, which resulted in increments in pollutant uptake and translocation, with the maintenance of overall cell (e.g. membranes) and organs (root system) structure, and the functioning of central physiological processes (e.g. photosynthesis). These factors allowed for more quickly and efficient removal of the pollutant from the environment, reducing costs, and increasing the viability of the phytoremediation process.

Plant growth-promoting rhizobacteria isolation from rhizosphere of submerged macrophytes and their growth-promoting effect on Vallisneria natans under high sediment organic matter load

Sediment organic matter is a key stressor for submerged macrophyte growth, which negatively impacts the ecological restoration of lakes. Plant growth-promoting rhizobacteria (PGPR) were screened from the rhizosphere of submerged macrophytes and used due to their promoting effect on Vallisneria natans under a high sediment organic matter load. Root exudates were used as the sole carbon source to obtain the root affinity strains. Eight isolates were selected from the 61 isolated strains, based on the P solubilization, IAA production, cytokinins production and ACC deaminase activity. The analysis of the 16S rDNA indicated that one strain was Staphylococcus sp., while the other seven bacterial strains were Bacillus sp. They were all listed in low-risk groups for safety use in agricultural practices. The plant height significantly increased after inoculation with PGPR strains, with the highest rate of increase reaching 96%. This study provides an innovative technique for recovering submerged macrophytes under sediment organic matter stress.

Phytoextraction of diuron, hexazinone, and sulfometuron-methyl from the soil by green manure species

The herbicides diuron, hexazinone, and sulfometuron-methyl present a potential risk of environmental contamination and are widely used for weed control in sugarcane cultivation. Our objectives were to measure the tolerance of Canavalia ensiformes (L.) DC., Stilizobium aterrimum L., Raphanus sativus L., Crotalaria spectabilis Röth, Lupinus albus L., and Pennisetum glaucum (L.) R. Br. To the herbicides diuron, hexazinone, and sulfometuron-methyl to assess the capacity of these species to extract and accumulate the herbicides in their tissues. Before sowing the green manure species, the soils were individually contaminated with the three ¹⁴C-radiolabeled herbicides. ¹⁴C-diuron and ¹⁴C-sulfometuron-methyl showed higher values remaining in the soil (>90%) for all species of green manure compared to hexazinone (<80%). The green manure species analyzed showed greater potential to remedy soils contaminated with hexazinone than the other herbicides. C. ensiformes showed high phytoextraction of hexazinone when compared to the other species, removing 11.2% of the pollutant from the soil, followed by L. albus (8.6%), S. aterrimum (7.3%), R. sativus (4.8%), C. spectabilis (2.5%), and P. glaucum (1.1%). The results indicate that the phytoextraction of diuron, hexazinone and sulfometuron-methyl is dependent on the species of green manure and can be an important tool for the decontamination of areas polluted by these herbicides.

How does aquatic macrophyte Salvinia auriculata respond to nanoceria upon an increased CO2 source? A Fourier transform-infrared photoacoustic spectroscopy and chlorophyll a fluorescence study

With the continued increase of technological uses of cerium oxide nanoparticles (CeO₂ NPs or nanoceria) and their unregulated disposal, the accumulation of nanoceria in the environment is inevitable. Concomitantly, atmospheric carbon dioxide (CO₂) levels continue to rise, increasing the concentrations of bicarbonate ions in aquatic ecosystems. This study investigates the influence of CeO₂ NPs (from 0 to 100 μgL^-1) in the presence and absence of an elevated bicarbonate (HCO₃^-) ion concentration (1 mM), on vibrational biochemical parameters and photosystem II (PSII) activity in leaf discs of Salvinia auriculata. Fourier transform-infrared photoacoustic spectroscopy (FTIR-PAS) was capable of diagnostic use to understand biochemical and metabolic changes in leaves submitted to the CeO₂ NPs and also detected interactive responses between CeO₂ NPs and HCO₃^- exposure at the tissue level. The results showed that the higher CeO₂ NPs levels in the presence of HCO₃^- increased the non-photochemical quenching (NPQ) and coefficient of photochemical quenching in dark (qP_d) compared to the absence of HCO₃. Moreover, the presence of HCO₃^- significantly decreased the NPQ at all levels of CeO₂ NPs demonstrating that HCO₃^- exposure may change the non-radiative process involved in the operation of the photosynthetic apparatus. Overall, the results of this study are useful for providing baseline information on the interactive effects of CeO₂ NPs and elevated HCO₃^- ion concentration on photosynthetic systems.

Use of Pistia stratiotes for phytoremediation of water resources contaminated by clomazone

The Pistia stratiotes L. was tested for phytoremediation potential of the compound clomazone in water. Clomazone is a post-emergent herbicide marketed as Gamit^®. Five groups with four samples each were evaluated, a low concentration control (LCC: 37.86 mg L^-1), low concentration treatment (LCT: 38.16 mg L^-1), high concentration control (HCC: 54.71 mg L^-1), high concentration treatment (HCT: 54.33 mg L^-1), and a plant control group (PCG). Plant resistance to clomazone at determined concentrations and their ability to remove the herbicide from water by HPLC over 24 days were evaluated. The results demonstrate that P. stratiotes has high resistance to clomazone exposure and was able to eliminate up to 90% of the herbicide residues during the experimental period. Under dissipation by P. stratiotes in water, clomazone had a halflife of 19.6 days for in the control treatments, LCC and HCC, and 8.0 days in the treatment groups, LCT and HCT. This study indicates that Pistia stratiotes is an effective phytoremediation agent for the herbicide clomazone in water.