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

Analysis of global trends and gaps for studies about 2,4-D herbicide toxicity: A scientometric review

2,4-dichlorophenoxyacetic acid (2,4-D) is a herbicide that is used worldwide in agricultural and urban activities to control pests, reaching natural environments directly or indirectly. The research on 2,4-D toxicology and mutagenicity has advanced rapidly, and for this reason, this review summarizes the available data in Web of Science (WoS) to provide insights into the specific characteristics of 2,4-D toxicity and mutagenicity. Contrary to traditional reviews, this study uses a new method to quantitatively visualize and summarize information about the development of this field. Among all countries, the USA was the most active contributor with the largest publication and centrality, followed by Canada and China. The WoS categories 'Toxicology' and 'Biochemical and Molecular Biology' were the areas of greatest influence. 2,4-D research was strongly related to the keywords glyphosate, atrazine, water and gene expression. The studies trended to be focused on occupational risk, neurotoxicity, resistance or tolerance to herbicides, and to non-target species (especially aquatic ones) and molecular imprinting. In general, the authors have worked collaboratively, with concentrated efforts, allowing important advances in this field. Future research on 2,4-D toxicology and mutagenicity should probably focus on molecular biology, especially gene expression, assessment of exposure in human or other vertebrate bioindicators, and pesticide degradation studies. In summary, this scientometric analysis allowed us to make inferences about global trends in 2,4-D toxicology and mutagenicity, in order to identify tendencies and gaps and thus contribute to future research efforts.

2,4-dichlorophenoxyacetic acid (2,4-D) micropollutant herbicide removing from water using granular and powdered activated carbons: a comparison applied for water treatment and health safety

Activated carbons are well-known porous materials as an effective adsorbent used for the removal of emerging contaminants, such as herbicides, which are increasingly present in water bodies. Most water treatment plants, specially in Brazil, are unable to completely remove such contaminants by the conventional process and advanced treatment using activated carbons is required. The aim of this paper was to verify the influence of the activated carbons granulometry and specific surface area on the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide removal efficiency using distilled-deionized water and filtered water collected from a conventional Water Treatment Plant. Commercial activated carbons samples used in this work were obtained from two different manufacturers. Activated carbons were analyzed by the specific surface area, pore size and volume distribution, nuclear magnetic resonance, infrared and x-ray spectroscopy, moisture, volatile matter and ash contents. Batch adsorption isotherms experiments were used and performed by Langmuir and Freundlich models. Granular and powdered activated carbons removed over 99% of 2,4-D in distilled water and near to 99% using filtered water. The activated carbons evaluated in this work presented high performance and played a key role in water treatment by removing 2,4-D herbicide, ensuring the protection of human health and the ecosystem.

Current-use pesticides in New Zealand streams: Comparing results from grab samples and three types of passive samplers

New Zealand uses more than a ton of pesticides each year; many of these are mobile, relatively persistent, and can make their way into waterways. While considerable effort goes into monitoring nutrients in agricultural streams and programs exist to monitor pesticides in groundwater, very little is known about pesticide detection frequencies, concentrations, or their potential impacts in New Zealand streams. We used the 'Polar Organic Chemical Integrative Sampler' (POCIS) approach and grab water sampling to survey pesticide concentrations in 36 agricultural streams in Waikato, Canterbury, Otago and Southland during a period of stable stream flows in Austral summer 2017/18. We employed a new approach for calculating site-specific POCIS sampling rates. We also tested two novel passive samplers designed to reduce the effects of hydrodynamic conditions on sampling rates: the 'Organic-Diffusive Gradients in Thin Films' (o-DGT) aquatic passive sampler and microporous polyethylene tubes (MPTs) filled with Strata-X sorbent. Multiple pesticides were found at most sites; two or more were detected at 78% of sites, three or more at 69% of sites, and four or more at 39% of sites. Chlorpyrifos concentrations were the highest, with a maximum concentration of 180 ng/L. Concentrations of the other pesticides were generally below 20 ng/L. Mean concentrations of individual pesticides were not correlated with in-stream nutrient concentrations. The majority of pesticides were detected most frequently in POCIS, presumably due to its higher sampling rate and the relatively low concentrations of these pesticides. In contrast, chlorpyrifos was most frequently detected in grab samples. Chlorpyrifos concentrations at two sites were above the 21-day chronic 'No Observable Effect Concentration' (NOEC) values for fish and another two sites had concentrations greater than 50% of the NOEC. Otherwise, concentrations were well-below NOEC values, but close to the New Zealand Environmental Exposure Limits in several cases.

Effects of 2,4-D-based herbicide (DMA® 806) on sensitivity, respiration rates, energy reserves and behavior of tadpoles

Increased use of sugarcane pesticides and their destination to non-target environments in Brazil has generated concerns related to the conservation of more vulnerable groups, such as amphibians. Besides the high skin permeability, tadpoles are constantly restricted to small and ephemeral ponds, where exposure to high concentrations of pesticides in agricultural areas is inevitable. This study evaluated chronic effects caused by sub-lethal concentrations of 2,4-dichlorophenoxyacetic acid herbicide on energy storage, development, respiration rates, swimming performance and avoidance behavior of bullfrog tadpoles (Lithobates catesbeianus). Firstly, we conducted acute toxicity test (96 h) to estipulate sub-lethal concentrations of 2,4-D and evaluate the sensitivity of three tadpoles' species to this herbicide. Results showed that Leptodactylus fuscus presented the lowest LC₅₀ 96 h, 28.81 mg/L, followed by Physalaemus nattereri (143.08 mg/L) and L. catesbeianus (574.52 mg/L). Chronic exposure to 2,4-D (125, 250 and 500 μg/L) delayed metamorphosis and inhibited the growth of tadpoles at concentrations of 125 μg/L. Effects on biochemical reserves showed that 2,4-D increased total hepatic lipids in tadpoles, although some individual lipid classes (e.g. free fatty acids and triglycerides) were reduced. Protein and carbohydrates contents were also impaired by 2,4-D, suggesting a disruption on energy metabolism of amphibians by the herbicide. In addition to biochemical changes, respiration rates and swimming speed were also decreased after chronic exposure to 2,4-D, and these responses appeared to be correlated with the changes detected in the basic energy content. Avoidance test indicated that tadpoles of L. catesbeinus avoided the presence of 2,4-D, however they were unable to detect increasing gradients of the contaminant. Our data showed that chronic exposure to 2,4-D impaired biochemical, physiological and behavioral aspects of tadpoles, which may compromise their health and make them more vulnerable to environmental stressors in natural systems.

2,4-D causes oxidative stress induction and apoptosis in human dental pulp stem cells (hDPSCs)

2,4-Dicholorophenoxy acetic acid (2,4-D) is a worldwide used hormone herbicide. Human dental pulp stem cells (hDPSCs) as a potential source of mesenchymal stem cells provide a confident model system for the assessments of chemicals in vitro. The main objective of this study was to examine the biological effects and damages attributed to 2,4-D on hDPSCs. hDPSCs were isolated from third molar pulp tissues and their mesenchymal identity were evaluated. Then, hDPSCs were treated with increasing concentrations of 2,4-D (0.1 μM-10 mM). Cell viability assay and cumulative cell counting were carried out to address 2,4-D effects on biological parameters of hDPSCs. Cell cycle distribution, ROS level and ALP activity were measured before and after treatment. AO/EB staining and caspase 3/7 activity were investigated to detect the possible mechanisms of cell death. Flow-cytometric immunophenotyping and differentiation data confirmed the mesenchymal identity of cultivated hDPSCs. 2,4-D treatment caused a hormetic response in the viability and growth rate of hDPSCs. G0/G1 cell cycle arrest, enhanced ROS level, and reduced ALP activity were detected in hDPSCs treated with EC50 dose of 2,4-D. AO/EB staining showed a higher percentage of alive cells in lower concentrations of the herbicide. The increment in 2,4-D dose and the number of early and late apoptotic cells were increased. DAPI staining and caspase 3/7 assay validated the induction of apoptosis. 2,4-D concentrations up to 100 μM did not affect hDPSCs viability and proliferation. The intense cellular oxidative stress and apoptosis were observed at higher concentration.

Occurrence, transportation, and distribution difference of typical herbicides from estuary to bay

In several watersheds, agricultural activities are the cause of pollution, mainly due to the discharge of herbicides. Often, these herbicide plumes are transported to the surrounding bays. Samples of water, suspended particulate sediments (SPSs), and sediments from 37 sites in the Jiaozhou Bay in the western Pacific Ocean were collected in April 2018. The total concentrations of atrazine and acetochlor in these samples were analyzed, that showed different patterns in each sampled area. Atrazine had 2-3 times higher concentrations in coastal areas and bays compared to the estuary, indicating that it had a higher residence time in the marine environment. In contrast, acetochlor concentration decreased with an increase in the depth of seawater. Both the spatial distributions and the vertical concentrations in water, SPS, and sediment proved that these two herbicides had different responses during transportation from the estuary to the bay. Despite the significant difference in concentration of the two herbicides in the water and sediment, their spatially averaged value in SPS was very close, indicating that the particles had saturated sorption capability. The organic carbon normalized partition coefficient (LogK_oc) was used to explain the partitioning of the herbicides between water and sediment. The LogK_oc difference between herbicides demonstrated that acetochlor was strongly phase partitioned in the coastal and the bay areas, thereby causing similar distributions of acetochlor in the three matrices. Atrazine had a higher LogK_oc value in the estuary, which explained its higher concentration in the estuary SPS. The correlation and redundancy analyses both demonstrated that the concentrations of the herbicides in water were sensitive to dissolved organic carbon and dissolved oxygen. The current tides and bathymetry were the critical factors in determining the spatial distribution of herbicides in the water and sediment, resulting in a low herbicide load in the river mouth area.

Turbidity matters: differential effect of a 2,4-D formulation on the structure of microbial communities from clear and turbid freshwater systems

We evaluated the effect of AsiMax 50®, a commercial formulation of 2,4-D (2,4-dichlorophenoxyacetic acid), on the structure of both micro + nano phytoplankton (>2 μm; species composition and abundance) and cytometric populations (photosynthetic picoplankton (PPP, 0.2–2 μm), which included prokaryotic phycocyanin-rich picocyanobacteria (PC-Pcy), phycoerythrin-rich picocyanobacteria (PE-Pcy) and eukaryotic phototrophs (PEuk); and bacterioplankton (HB), heterotrophic bacteria), using a microcosms-based approach and a single 7-day exposure. Assays were performed on two different microbial assemblages sampled from freshwater bodies of two contrasting turbidity status: clear (chlorophyll a = 7.6 μgL^-1, turbidity = 1 NTU) and organic turbid systems (chlorophyll a = 25.0 μgL^-1, turbidity = 9 NTU). For each system, the herbicide was applied to 500 mL-Erlenmeyer flasks, at seven concentration levels of the active ingredient (a.i.): 0 (control = no addition), 0.02, 0.2, 2, 20, 200 and 2,000 mg a.i.L⁻¹. The impact of AsiMax 50® seemed to be greater in the turbid system. In this system, total abundance of living (live) micro + nano phytoplankton showed a significant increase at lower concentrations and data were fitted to a humped-shaped curve. For both clear and organic turbid systems, micro + nano phytoplankton decreased in species richness and abundance at higher herbicide concentrations. These results suggest that 2,4-D may mimic hormonal function. Some species, such as Ochromonas sp. and Chlamydomonas sp., showed different responses to herbicide exposure between water systems. In the turbid system, the increase in abundance of the PPP fraction observed at 7-d exposure was probably due to either an increase in PE-Pcy (thus suggesting the existence of auxin pathways) or a reduction in competitive pressure by micro + nano plankton. Our results provide some evidence of the importance of using community-scale approaches in ecotoxicological studies to predict changes in freshwater ecosystems exposed to a 2,4-D-based formulation. However, caution must be taken when extrapolating these effects to real scenarios, as assays were based on a laboratory microcosm experiment.

Enhanced diuron remediation by microorganism-immobilized silkworm excrement composites and their impact on soil microbial communities

In response to the potential threats stemming from the constantly increasing consumption of herbicides, bioremediation offers a beneficial technology for reducing the widespread herbicide contamination. In order to facilitate the in-situ degradation of diuron, Arthrobacter globiformis D47 is captured onto a biocompatible carrier to assemble the microorganism-immobilized silkworm excrement (MSE) composites. By characterization, bacterial cells are intensively entrapped in/onto the carriers, showing high survival and stable catalytic degradation of target pollutants. Meanwhile, MES composites display excellent adaptiveness and feasibility under different conditions, and the average half-life of diuron is shortened to 7.69 d in sugarcane field where diuron is regularly sprayed for weed management. Importantly, we assess that the use of MSE may generally boost the overall xenobiotic-degrading ability, likely due to the slight alternation of the diversity and composition of soil microbial communities. Taking together, the presented MSE provides an attractive in situ approach for the efficient diuron removal as well as for the more feasible utilization of various pollutant-degrading microorganisms.

Determination of Phenoxy Acid Herbicides in Cereals Using High-Performance Liquid Chromatography-Tandem Mass Spectrometry

HIGHLIGHTS

Phenoxy acid herbicide residues were found in cereals. A QuEChERS HPLC-MS/MS method was used for analysis of these herbicide residues. This technique could be used effectively for monitoring the safety of cereals.

Adsorption of herbicide 2,4-D from aqueous solution using organo-modified bentonite clay

This study analyzed the performance of organophilic clays obtained from the chemical modification of sodium bentonite clay when applied to the adsorption of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Kinetic curves and equilibrium isotherms were obtained in order to determine time and adsorption capacity of the material, as well as understand the mechanisms involved in this phenomenon. The results showed that the most predictive kinetic model for experimental data was of pseudo-second order (R² > 0.98), and that external mass transfer is the dominant factor in the time of operation. Isotherms were obtained at temperatures of 298, 308, and 318 K, under which the Dubinin-Radushkevich model was shown to have a good fit to data (R² > 0.96), according to mathematical adjustments. The maximum adsorption capacity obtained experimentally was 50.36 mg g^-1, found at a temperature of 298 K, being higher or compatible with other materials reported in the literature. With help of the thermodynamic studies on the process, it was observed that the adsorption of 2,4-D in organophilic clays refers to a spontaneous (ΔG°_ads < 0), exothermal (ΔH°_ads = - 9.99 kJ mol^-1) process of physical nature. Lastly, it was observed that the adsorbent can be easily regenerated when subjected to eluents such as mixtures containing fractions of ethanol/water (desorption = 95%).

Prenatal exposure to the herbicide 2,4-D is associated with deficits in auditory processing during infancy

INTRODUCTION

Despite widespread use, many herbicides and fungicides are not well studied for neurological effects. Fetal and infant brains are rapidly developing, yet the effects of early-life exposure to these classes of pesticides on visual and auditory function are unknown. Here we examined the effects of prenatal herbicide and fungicide exposure on infant grating visual acuity (VA) and auditory brainstem response (ABR).

METHODS

9 herbicides and 13 fungicides were measured in umbilical cord blood plasma from a cohort of infants in Fuyang County, China (n = 232). Grating VA and ABR latencies for waves I, III, V were measured at 3 time points: 6 weeks, 9 months, and 18 months. Outcomes included VA score, ABR wave V latency and ABR central conduction time (CCT [wave V- wave I]). Pesticides were analyzed as 3-level ordinal (non-detect [ND]/medium/high), or dichotomous (ND/detect), depending on detection rates. Linear mixed models were used to evaluate relations between pesticides and VA and ABR outcomes.

RESULTS

2,4-dichloroacetic acid (2,4-D), prometryn, simazine, and tetrahydrophthalamide (THPI, a metabolite of captan) were detected in 27%, 81%, 17%, and 16% of samples, respectively. Infants prenatally exposed to 2,4-D had slower auditory response times at 6 weeks. Infants with cord levels of 2,4-D > 1.17 ng/mL had wave V latencies that were 0.12 (95% CI: 0.03, 0.22) ms slower (p = 0.01) and overall CCTs that were 0.15 (95% CI:0.05, 0.25) ms slower (p = 0.003) than infants with non-detectable 2,4-D in their cord blood. No other statistically significant findings were observed for the other herbicides and fungicides or for the grating VA outcome.

CONCLUSIONS

Prenatal exposure to the herbicide 2,4-D was associated with slower auditory signal transmission in early infancy. ABR latencies reflect auditory pathway maturation and longer latencies may indicate delayed auditory development.

Effects of drought-stress on seed germination and growth physiology of quinclorac-resistant Echinochloa crusgalli

Echinochloa crusgalli (L.) Beauv. (barnyard grass) is considered a noxious weed worldwide, and is the most pernicious weed decreasing rice yields in China. Recently, E. crusgalli has evolved quinclorac resistance, making it among the most serious herbicide resistant weeds in China. The present study explored differences in germination and growth between quinclorac-resistant and -susceptible E. crusgalli collected in Hunan Province. The order of the seven E. crusgalli biotypes assessed, from high to low quinclorac-resistance, was: quinclorac-resistant, Chunhua, Hanshou, Shimen, Hekou, Dingcheng, and quinclorac-susceptible. With an increased in the level of quinclorac-resistance, the germination rate, length of young shoots and roots, and fresh weight of E. crusgalli were all decreased compared with that in more susceptible biotypes. However, there were no significant differences between quinclorac-resistant and susceptible E. crusgalli biotypes without polyethylene glycol 6000 treatment. Drought had a more obvious effect on glutathione S-transferases (GST) activity, determined by spectrophotometric method, in quinclorac-resistant E. crusgalli. Higher resistance level biotypes showed greater activity, and when treated with polyethylene glycol 6000 for 3 days, all E. crusgalli biotypes showed the highest GST activity. This study demonstrated that as the level of quinclorac-resistance increased, the rate of seed germination decreased, while the growth of young buds, young roots, and fresh weight decreased. Increased quinclorac-resistance may be related to the increased metabolic activity of GST in E. crusgalli.

Influence of electrolysis conditions on the treatment of herbicide bentazon using artificial UVA radiation and sunlight. Identification of oxidation products

The main objective of this work is to demonstrate the viability of solar photoelectro-Fenton (SPEF) process to degrade pesticides in urban wastewater matrix, selecting the herbicide bentazon as a model molecule. In order to provide a correct assessment of the role of the different oxidants and catalysts involved, bentazon was comparatively treated by anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF) and UVA-assisted EF (i.e., PEF) processes as well, either in sulfate or chloride media. Trials were made in a stirred tank reactor with an air-diffusion cathode and a boron-doped diamond (BDD), RuO₂-based or Pt anode. In chlorinated matrices, the herbicide disappeared more rapidly using a RuO₂-based anode because of the generated active chlorine. The best mineralization performance was always obtained using BDD due to its higher oxidation power, which allowed the complete destruction of refractory chloroderivatives. A concentration of 0.50 mM Fe²⁺ was found optimal to catalyze Fenton's reaction, largely enhancing the mineralization process under the action of OH. Among photo-assisted treatments, sunlight was proven superior to a UVA lamp to promote the photolysis of intermediates, owing to its greater UV irradiance and contribution of visible photons, although PEF also allowed achieving a large mineralization. In all cases, bentazon decay obeyed a pseudo-first-order kinetics. SPEF treatment in urban wastewater using BDD at only 16.6 mA cm^-2 yielded 63.2% mineralization. A thorough, original reaction pathway for bentazon degradation is proposed, including seven non-chlorinated aromatics, sixteen chloroaromatics and two chloroaliphatics identified by GC-MS, most of them not previously reported in literature. Ion-exclusion HPLC allowed the detection of seven short-chain linear carboxylic acids.

Combined Toxicity of 2,4-Dichlorophenoxyacetic Acid and Its Metabolites 2,4-Dichlorophenol (2,4-DCP) on Two Nontarget Organisms

2,4-Dichlorophenoxyacetic acid (2,4-D), a phenoxyalkanoic acid herbicide, is among the most widely distributed pollutants in the environment. 2,4-Dichlorophenol (2,4-DCP), as the main metabolite of 2,4-D, always accompanies 2,4-D. In this paper, we did research on the combined toxicities of 2,4-D and 2,4-DCP to Vibrio qinghaiensis sp.-Q67 (Q67) and Caenorhabditis elegans. It was found that the toxicity of 2,4-DCP is more severe than that of its parent 2,4-D at any concentration levels whether to Q67 or to C. elegans. Furthermore, 2,4-DCP to Q67 has the time-dependent toxicity. The toxicity of the mixture of 2,4-D and 2,4-DCP to Q67 is increasing with the exposure time, but that to C. elegans does not change over time. There is a good linear relationship between the pEC₅₀/pLC₅₀ value of binary mixture ray of 2,4-D and 2,4-DCP and the mixture ratio of 2,4-DCP, which implies the predictability of mixture toxicity of 2,4-D and 2,4-DCP. The toxicological interactions of the binary mixtures to Q67 are basically additive actions whether at 0.25 or at 12 h. However, most mixtures have antagonistic interactions against C. elegans.

Dicationic Ionic Liquids of Herbicide 2,4-Dichlorophenoxyacetic Acid with Reduced Negative Effects on Environment

Due to high volatility and water solubility, 2,4-dichlorophenoxyacetic acid (2,4-D) can easily enter into the atmosphere and water bodies by volatilization, drift, leaching, or runoff, which results in potential threats to the environment and human health. The physicochemical properties of pesticides can be regulated by preparing their ionic liquids. In this work, a series of dicationic ionic liquids (DILs) of 2,4-D were prepared to reduce its environmental risk and enhance herbicidal activity. The solubility, octanol-water partition coefficient, surface tension, and volatilization rate results of DILs showed that these properties could be optimized by choosing appropriate countercations. Compared to 2,4-D ammonium salt, DILs have lower volatility, water solubility, and surface tension as well as higher lipophilicity. Benefiting from optimized physicochemical properties, DILs HIL8-12 exhibited better herbicidal activity against three typical broadleaf weeds than 2,4-D ammonium salt, and their fresh weight inhibition rates increased by 2.74-46.84%. The safety assessment experiment indicated that DILs were safer to wheat than commercialized forms of 2,4-D. The DILs could reduce the environmental risk of 2,4-D caused by high volatility and water solubility and would be potential alternatives to its commercialized formulations.

Salinity reduces 2,4-D efficacy in Echinochloa crusgalli by affecting redox balance, nutrient acquisition, and hormonal regulation

Distinct salinity levels have been reported to enhance plants tolerance to different types of stresses. The aim of this research is to assess the interaction of saline stress and the use of 2,4-D as a means of controlling the growth of Echinochloa crusgalli. The resultant effect of such interaction is vital for a sustainable approach of weed management and food production. The results showed that 2,4-D alone treatment reduces the chlorophyll contents, photosynthetic capacity, enhanced MDA, electrolyte leakage, and ROS production (H₂O₂, O₂^·-) and inhibited the activities of ROS scavenging enzymes. Further analysis of the ultrastructure of chloroplasts indicated that 2,4-D induced severe damage to the ultrastructure of chloroplasts and thylakoids. Severe saline stress (8 dS m^-1) followed by mild saline stress treatments (4 dS m^-1) also reduced the E. crusgalli growth, but had the least impact as compared to the 2,4-D alone treatment. Surprisingly, under combined treatments (salinity + 2,4-D), the phytotoxic effect of 2,4-D was reduced on saline-stressed E. crusgalli plants, especially under mild saline + 2,4-D treatment. This stimulated growth of E. crusgalli is related to the higher activities of enzymatic and non-enzymatic antioxidants and dynamic regulation of IAA, ABA under mild saline + 2,4-D treatment. This shows that 2,4-D efficacy was affected by salinity in a stress intensity-dependent manner, which may result in the need for greater herbicide application rates, additional application times, or more weed control operations required for controlling salt-affected weed.