Aerobic biofilm reactor for treating a commercial formulation of the herbicides 2,4-D and dicamba: Biodegradation kinetics and biofilm bacterial diversity

Acute toxicity of the insecticide Imidacloprid and the herbicide 2,4-D in two species of tropical anurans

The use of pesticides has notably increased in recent years globally. However, sensitive organisms exposed to these environmental pollutants, such as amphibians, may experience adverse effects. The insecticide imidacloprid (IM) and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) are two pesticides commonly used in Colombia, but their toxic impacts on tropical anurans remain poorly understood. In this study, we tested the acute toxic effects of IM and 2,4-D on the survival, total length, and burst swimming speed of tadpoles from two anuran species. Under laboratory conditions, the tadpoles of Boana platanera and Engystomops pustulosus were independently exposed to each pesticide for 96 h. We found that the tadpoles of E. pustulosus were more sensitive to both IM and 2,4-D than those of B. platanera. However, the LC50 values were higher than the reported field concentrations for these pesticides. IM led to a reduction in the total length of B. platanera tadpoles and induced total immobility in surviving individuals of both species. In contrast, the herbicide 2,4-D did not affect the total length or the swimming speed of tadpoles from the two species. In conclusion, based on the results and the reported field concentrations, IM and 2,4-D are not lethal to the studied anurans. Nevertheless, it is important to consider that IM caused strong negative sublethal effects on tadpoles, which could compromise their survival in the future. Finally, we also found that the insecticide IM showed notably greater toxicity to the tested species than did the herbicide 2,4-D.

Complete biodegradation of the oldest organic herbicide 2,4-Dichlorophenoxyacetic acid by engineering Escherichia coli

After nearly 80 years of extensive application, the oldest organic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has caused many problems of environmental pollution and ecological deterioration. Bioremediation is an ideal method for pollutant treatment. However, difficult screening and preparation of efficient degradation bacteria have largely hindered its application in 2,4-D remediation. We have created a novel engineering Escherichia coli with a reconstructed complete degradation pathway of 2,4-D to solve the problem of screening highly efficient degradation bacteria in this study. The results of fluorescence quantitative PCR demonstrated that all nine genes in the degradation pathway were successfully expressed in the engineered strain. The engineered strains can quickly and completely degrade 0.5 mM 2, 4-D within 6 h. Inspiring, the engineered strains grew with 2,4-D as the sole carbon source. By using the isotope tracing method, the metabolites of 2,4-D were found incorporated into the tricarboxylic acid cycle in the engineering strain. Scanning electron microscopy showed that 2,4-D had less damage on the engineered bacteria than the wild-type strain. Engineered strain can also rapidly and completely remedy 2,4-D pollution in natural water and soil. Assembling the metabolic pathways of pollutants through synthetic biology was an effective method to create pollutant-degrading bacteria for bioremediation.

Environmental-friendly hydrochar-montmorillonite composite for efficient catalytic degradation of dicamba and alleviating its damage to crops

In recent years, carbon-based materials catalyzing peroxymonosulfate (PMS) for green degradation of persistent organic pollutants have attracted increasing attention. However, PMS activation by hydrochar composite (e.g. hydrochar-montomorillonite) has rarely been investigated. Herein, a simple preparation, low-cost and eco-friendly catalyst of hydrochar-montmorillonite composite (HC-Mt) was prepared to firstly catalyze PMS for the degradation of dicamba (DIC). The as-prepared HC-Mt showed a remarkably better catalyzing performance for PMS than pure hydrochar (HC) due to its good physicochemical characteristics and abundant oxygen-containing groups. Furthermore, the electron spin resonance (ESR) and quenching tests revealed that active species such as SO₄^-, OH and O₂^- all participated in the degradation process. DIC sites on C6, Cl 10, and O15 exhibited higher reactivity according to the density functional theory (DFT) calculation, which were easily attacked by active species. The DIC degradation mainly occurred via hydroxyl substitution, decarboxylation, oxidation and ring-cleavage and finally most of the intermediates were mineralized into CO₂ and H₂O. Finally, the phytotoxicity assessment was measured by the germination growth situation of tobacco and mung beans in the presence of DIC (with or without treatment by HC-Mt/PMS). The result showed that HC-Mt/PMS could significantly reduce the phytotoxicity of DIC to crops, suggesting that catalyzing PMS using HC-Mt was environmentally friendly. Therefore, this work did not only provide a novel catalyzing PMS strategy using hydrochar composite for wastewater treatment, but also give a new idea for herbicide phytotoxicity management.

Enhancing the eosin-yellowish dye degradation in drinking water by using TiO2 coatings co-doped with Ni and In

This work reports on the structural, morphological, and photocatalytic properties of titanium dioxide (TiO₂) and TiO₂:NiIn (T-NiIn) coatings fabricated by spin coating. The SEM images revealed coatings with average thicknesses of 3.59 and 3.37 μm for the TiO₂ and T-NiIn, respectively. EDS spectra and Raman studies confirmed the presence of TiO₂ co-doped with nickel (Ni) and indium (In) in the coatings. XRD analysis showed the anatase and rutile phases for the TiO₂ coatings, while the T-NiIn coatings presented the rutile and brookite phases. These samples were evaluated in the photocatalytic degradation of the eosin-yellowish (EY) dye. The T-NiIn coatings showed 9.1% higher effectiveness than the undoped TiO₂ coatings after 300 min under UV irradiation. Meanwhile, the T-NiIn coatings exposed to solar light removed 40% more dye than the TiO₂ coatings. Furthermore, T-NiIn coating was the most stable because its effectiveness was reduced by only 1.4% after 4 cycles of reuse. Additionally, the scavenger tests confirmed that the main oxidizing sites were the •OH^- radicals and the superoxides •O₂^-. Thus, the use of coatings based on TiO₂ co-doped with Ni and In is a feasible strategy to increase the degradation of the EY dye in drinking water.

Enhancement of peroxymonosulfate activation for 2,4-dichlorophenoxyacetic acid removal by MoSe2 induced Fe redox cycles

The limited regeneration of Fe2+ in the Fe-catalyzed advanced oxidation processes (AOPs) constrained its application for the removal of organic pollutants. Herein, MoSe2 was introduced to promote the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the Fe2+/PMS system. Compared with Fe2+/PMS processes, the 2,4-D degradation efficiency and PMS decomposition rate respectively increased by 73.8% and 84.2% in the MoSe2/Fe2+/PMS system. DFT simulation results suggested that Se atoms acted smoothly as the bridge supporting the charge transfer from Mo to adjacent Fe atoms, which led to the reduction of Fe3+. The rapid regeneration of Fe2+ boosted the activation of PMS and the degradation of pollutants. Additionally, the electron paramagnetic resonance (EPR) and quenching experiments results indicated that SO4∙-, ∙OH, and 1O2 accounted for 2,4-D degradation, and SO4∙- and 1O2 predominated the reaction. The Mo based co-catalysts showed better co-catalytic effect than the W counterparts, and the moderate adsorption for PMS and lower electron transfer electron transfer resistance accounted for the more excellent co-catalytic performance of MoSe2 than that of WSe2. In addition, the degradation efficiency of 2,4-D was up to 95.5% after five cycles of MoSe2 in the co-catalytic system. The coexistent humic acid (HA) and Cl- showed ignorant negative effect on the degradation, while HCO3- would depress the oxidation reaction. The acidic etching wastewater can be applied as the Fe ions source in this co-catalytic process to remove 2,4-D effectively.

Biofilm-mediated bioremediation is a powerful tool for the removal of environmental pollutants

Biofilm-mediated bioremediation is an attractive approach for the elimination of environmental pollutants, because of its wide adaptability, biomass, and excellent capacity to absorb, immobilize, or degrade contaminants. Biofilms are assemblages of individual or mixed microbial cells adhering to a living or non-living surface in an aqueous environment. Biofilm-forming microorganisms have excellent survival under exposure to harsh environmental stressors, can compete for nutrients, exhibit greater tolerance to pollutants compared to free-floating planktonic cells, and provide a protective environment for cells. Biofilm communities are thus capable of sorption and metabolization of organic pollutants and heavy metals through a well-controlled expression pattern of genes governed by quorum sensing. The involvement of quorum sensing and chemotaxis in biofilms can enhance the bioremediation kinetics with the help of signaling molecules, the transfer of genetic material, and metabolites. This review provides in-depth knowledge of the process of biofilm formation in microorganisms, their regulatory mechanisms of interaction, and their importance and application as powerful bioremediation agents in the biodegradation of environmental pollutants, including hydrocarbons, pesticides, and heavy metals.

Permeable reactive surface-biobarriers. Testing and evaluation of an ecotechnology for the removal of agrotoxic compounds carried by agricultural runoffs

PURPOSE

The objective of the work is to determine the best operating conditions for variants of an ecological engineering tool (permeable reactive surface biobarrier -PRSB-) potentially useful for the protection of water resources, preventing the arrival of sediments and pesticides transported by runoffs and tile drainage from agricultural lands, to water bodies.

METHODS

Four PRB-prototypes were constructed as fixed-bed horizontal channels packed with a porous material supporting an enriched microbial biofilm. Their dynamic and stoichiometric performance was evaluated in the presence or absence of granular activated carbon, with limiting or sufficient O₂ supply. The removal of the pesticides and their leading catabolic derivatives were determined by HPLC. The most abundant cultivable microorganisms were isolated and identified by the sequencing of 16sDNA amplicons.

RESULTS

The pollutant removal efficiencies obtained in the aerobic biobarriers or microaerophilia were similar. In addition, slight differences were observed in the presence of GAC as an adsorbent, meaning that the most economical and straightforward type of biobarrier was adequate to remove the pollutants studied. In addition, among the most abundant microorganisms isolated in the microbial biofilms colonizing the aerobic biobarriers, the microalgae Micractinium sp. showed the capacity to accumulate the insecticides permethrin and cypermethrin.

CONCLUSIONS

The main observed role of Micractinium sp. in the aerobic barriers was the bioaccumulation of pyrethroids, meaning that biosorption is also a valuable removal mechanism operating in the aerobic PRBs. In this aspect, they behave analogously to subsurface constructed wetlands but, instead of superficial plant life, aerobic PRSBs host microalgae.

Performance of a continuous stirred tank bioreactor employing an immobilized actinobacteria mixed culture for the removal of organophosphorus pesticides

In this study, we evaluated polyurethane foam (PF), volcanic rock (VR), and a modified plastic cap (MPC) as supports for the immobilization of organophosphorus (OP) pesticide-degrading actinobacterial strains. The colonization and activity of four streptomycetes were favoured by PF, which was selected as the carrier to use in a continuous stirred tank bioreactor (CSTR) that can be operated at increasing inflows of a pesticide mixture that contains the insecticides chlorpyrifos (CP) and diazinon (DZ). Our results demonstrate that the CSTR can be operated at flow rates of 10 and 40 mL h^-1 with greater than 85% removal of the pesticides in the short term. A significant decrease in the efficiency of CP removal was observed at the highest inflows into the reactor. The CP and DZ loading rates in the bioreactor ranged from 0.44 to 1.68 mg L^-1 h^-1 and from 0.50 to 2.17 mg L^-1 h^-1, respectively. Although the treated wastewater exhibited moderate toxicity for Raphanus sativus, a bioreactor inoculated with a mixed culture formed by Streptomyces spp. strains AC5, AC9, GA11 and ISP13 may provide an effective biotechnological strategy for the reduction of OP pesticide residues produced during agronomic and manufacturing practices and therefore prevent environmental pesticidal pollution.

Combined electrochemical processes for the efficient degradation of non-polar organochlorine pesticides

This study deals with the development of efficient and economic electrochemical treatment processes to confront the treatment of liquid wastes containing non-polar organochlorine pesticides. In previous works, it was demonstrated that it is possible to use electrocoagulation (EC) as a concentration technique for a model organochlorine pesticide (oxyfluorfen). Within this framework, the present work describes a process for the degradation of wastes containing non-polar organochlorines (oxyfluorfen or lindane) in two consecutive stages: 1) a first stage of concentration by electrocoagulation; 2) a second stage of electrochemical degradation by electro-oxidation (EO) or electro-Fenton (EF). The first result reached in the present work is that it is possible to remove close to 50% of both pollutants using EO and more that 94% using EF. Additionally, it was proved that the addition of a pre-concentration stage decreases by a factor of 20 the power consumption needed to deplete by EO the same amount of the initial pollutant. Moreover, when EF process is performed to the concentrated stream, the power consumption is further reduced, getting values (for 1-log removal) as low as 14.51 kWh m^-3 for oxyfluorfen decrease and 49.7 kWh m^-3 for lindane. These results strengthen the fact that the removal efficiency increases with the concentration of the pollutant and demonstrate that the combination of concentration steps and electrochemical degradation technologies is an efficient and promising alternative for the degradation of non-polar organochlorines.

Influence of 2,4-D residues on the soil microbial community and growth of tree species

The 2,4-D (2,4-dichlorophenoxyacetic acid) has low half-life in the soil, but it is capable of altering the soil microbial community. The objective of this study was to evaluate the influence of 2,4-D residues on the structure of the soil microbial community and the growth of tree species. The tolerance and phytoremediation potential of tree species were evaluated. The microbial analysis was performed by T-RFLP. The 2,4-D herbicide reduced the plant height of K. lathrophyton, number of leaves of C. ferrea and K. lathrophyton and root dry matter allocation for C. brasiliense, I. striata, P. heptaphyllum, and T. guianensis. Cucumis sativus intoxication on soil contaminated with 2,4-D was not significant. The structure of Fungi community in the rhizospheric soils of C. ferrea was altered. The herbicide 2,4-D increased the diversity of Fungi in rhizospheric soils of P. heptahyllum and R. grandis. Most tree species were tolerant, and the evaluation time was sufficient to remedy 2,4-D. The structures of the microbial communities Archaea, Bacteria, and Fungi were little influenced by 2,4-D. The diversity of the Archaea domain was not affected, the diversity of the Bacteria in Inga striata decreased while the fungi increased in Protium heptaphyllum and Richeria grandis with 2,4-D.

Parameter optimization and degradation mechanism for electrocatalytic degradation of 2,4-diclorophenoxyacetic acid (2,4-D) herbicide by lead dioxide electrodes

2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most commonly used herbicides in the world. In this work, the electro-catalytic degradation of 2,4-D herbicide from aqueous solutions was evaluated using three anode electrodes, i.e., lead dioxide coated on stainless steel 316 (SS316/β-PbO2), lead dioxide coated on a lead bed (Pb/β-PbO2), and lead dioxide coated on graphite (G/β-PbO2). The structure and morphology of the prepared electrodes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The process of herbicide degradation was monitored during constant current electrolysis using cyclic voltammetry (CV). In this study, the experiments were designed based on the central composite design (CCD) and were analyzed and modeled by response surface methodology (RSM) to demonstrate the operational variables and the interactive effect of three independent variables on 3 responses. The effects of parameters including pH (3-11), current density (j = 1-5 mA cm-2) and electrolysis time (20-80 min) were studied. The results showed that, at j = 5 mA cm-2, by increasing the reaction time from 20 to 80 min and decreasing the pH from 11 to 3, the 2,4-D herbicide degradation efficiency using SS316/β-PbO2, Pb/β-PbO2 and G/β-PbO2 anode electrodes was observed to be 60.4, 75.9 and 89.8%, respectively. Moreover, the results showed that the highest COD and TOC removal efficiencies using the G/β-PbO2 electrode were 83.7 and 78.5%, under the conditions pH = 3, electrolysis time = 80 min and j = 5 mA cm-2, respectively. It was also found that G/β-PbO2 has lower energy consumption (EC) (5.67 kW h m-3) compared to the two other studied electrodes (SS316/β-PbO2 and Pb/β-PbO2). The results showed a good correlation between the experimental values and the predicted values of the quadratic model (P < 0.05). Results revealed that the electrochemical process using the G/β-PbO2 anode electrode has an acceptable efficiency in the degradation of 2,4-D herbicide and can be used as a proper pretreatment technique to treat wastewater containing resistant pollutants, e.g., phenoxy group herbicides (2,4-D).

Simulation and experimental validation of a gradient feeding system for fast assessment of the kinetic behavior of a microbial consortium in a tubular biofilm reactor

This study deals with the mathematical simulation and experimental validation of a gradient system for the gradual change of the imidacloprid loading rate to a tubular biofilm reactor (TBR). The strategy was used for fast studies of the kinetic and stoichiometric impact caused by the increase in the pesticide loading rate in a TBR, running in plug flow regime. Seemingly, this strategy has never been used for biokinetic and stoichiometric studies in biofilm reactors. For this purpose, a mathematical model describing the substrate transient behavior Sg(t) in a concentration gradient generator system using variable volume tanks is proposed. A second model, representing the temporary variation in the loading rate of imidacloprid to an aerated equalizer tank preceding the packed zone of the TBR, is also presented. Both models were experimentally confirmed. After the treatment of the experimental data, the kinetic and stoichiometric changes occurring in the TBR, caused by the gradual increase in the imidacloprid loading rate, were readily evaluated. Although the structure of the microbial community, at the phylum level, showed similar behavior along the tubular reactor, the stress produced by the gradual increase in imidacloprid concentration had functional consequences on the mixed microbial populations which were reflected on the stoichiometric and kinetic parameters. After increasing more than five times the imidacloprid loading rate to the TBR, the imidacloprid removal efficiency decayed about 40%, and the microbial-specific removal rate of the insecticide showed a decrease of about 30%.

Potential impact of the herbicide 2,4-dichlorophenoxyacetic acid on human and ecosystems

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is applied directly to aquatic and conventional farming systems to control weeds, and is among the most widely distributed pollutants in the environment. Non-target organisms are exposed to 2,4-D via several ways, which could produce toxic effects depending on the dose, frequency of exposure, and the host factors that influence susceptibility and sensitivity. An increasing number of experimental evidences have shown concerns about its presence/detection in the environment, because several investigations have pointed out its potential lethal effects on non-target organisms. In this review, we critically evaluated the environmental fate and behavior of 2,4-D along with its eco-toxicological effects on aquatic, plants and human life to provide concise assessment in the light of recently published reports. The findings demonstrate that 2,4-D is present in a low concentration in surface water of regions where its usage is high. The highest concentrations of 2,4-D were detected in soil, air and surface water surrounded by crop fields, which suggest that mitigation strategies must be implanted locally to prevent the entry of 2,4-D into the environment. A general public may have frequent exposure to 2,4-D due to its wide applications at home lawns and public parks, etc. Various in vivo and in vitro investigations suggest that several species (or their organs) at different trophic levels are extremely sensitive to the 2,4-D exposure, which may explain variation in outcomes of reported investigations. However, implications for the prenatal exposure to 2,4-D remain unknown because 2,4-D-induced toxicity thresholds in organism have only been derived from juveniles or adults. In near future, introduction of 2,4-D resistant crops will increase its use in agriculture, which may cause relatively high and potentially unsafe residue levels in the environment. The recent findings indicate the urgent need to further explore fate, accumulation and its continuous low level exposure impacts on the environment to generate reliable database which is key in drafting new regulation and policies to protect the population from further exposure.

Effect of propanil, linuron, and dicamba on the degradation kinetics of 2,4-dichlorophenoxyacetic acid by Burkholderia sp. A study by differential analysis of 2,4-dichlorophenoxyacetic acid degradation data

The successive application of distinct pesticides, or mixtures of them, is a frequent practice that could adversely affect the microbial species inhabiting soil and aquatic ecosystems. The ability of soil or aquatic microbiota to degrade a pesticide could be affected by the presence of another. If the degradation rate of the first compound is inhibited, its dissipation half-life in the environment could be hazardously enlarged. Few studies have been made to quantify the impact on the biodegradation rate of pesticides in soils or water by the presence of other pesticides. In this work, a method for assessing the effect of a pesticide on the biodegradation rate of another, measuring its effect on the biodegradation kinetics of a single bacterial strain is presented. The mathematical analysis is a powerful tool to study the stoichiometry and kinetics of microbial processes, which was used to evaluate independently, in detail, the effect of three pesticides (propanil, linuron, and dicamba) on the biodegradation kinetics of 2,4-dichlorophenoxyacetic acid by a strain of Burkholderia sp. It was evidenced that linuron and dicamba caused a decay of more than 40% in the top instantaneous degradation rate of 2,4-dichlorophenoxyacetic acid, while propanil showed a minimal effect.