Herbicide formulations

Pesticides impacts on human health and the environment with their mechanisms of action and possible countermeasures

Pesticides are chemical constituents used to prevent or control pests, including insects, rodents, fungi, weeds, and other unwanted organisms. Despite their advantages in crop production and disease management, the use of pesticides poses significant hazards to the environment and public health. Pesticide elements have now perpetually entered our atmosphere and subsequently contaminated water, food, and soil, leading to health threats ranging from acute to chronic toxicities. Pesticides can cause acute toxicity if a high dose is inhaled, ingested, or comes into contact with the skin or eyes, while prolonged or recurrent exposure to pesticides leads to chronic toxicity. Pesticides produce different types of toxicity, for instance, neurotoxicity, mutagenicity, carcinogenicity, teratogenicity, and endocrine disruption. The toxicity of a pesticide formulation may depend on the specific active ingredient and the presence of synergistic or inert compounds that can enhance or modify its toxicity. Safety concerns are the need of the hour to control contemporary pesticide-induced health hazards. The effectiveness and implementation of the current legislature in providing ample protection for human health and the environment are key concerns. This review explored a comprehensive summary of pesticides regarding their updated impacts on human health and advanced safety concerns with legislation. Implementing regulations, proper training, and education can help mitigate the negative impacts of pesticide use and promote safer and more sustainable agricultural practices.

The role of membrane transporters in the absorption of atrazine following nasal exposure

OBJECTIVE

The purpose of these studies was to investigate the uptake of atrazine across the nasal mucosa to determine whether direct transport to the brain through the olfactory epithelium is likely to occur. These studies were undertaken to provide important new information about the potential for the enhanced neurotoxicity of herbicides following nasal inhalation.

MATERIALS AND METHODS

Transport of atrazine from aqueous solution and from commercial atrazine-containing herbicide products was assessed using excised nasal mucosal tissues. The permeation rate and the role of membrane transporters in the uptake of atrazine across the nasal mucosa were also investigated. Histological examination of the nasal tissues was conducted to assess the effects of commercial atrazine-containing products on nasal tissue morphology.

RESULTS

Atrazine showed high flux across both nasal respiratory and olfactory tissues, and efflux transporters were found to play an essential role in limiting its uptake at low exposure concentrations. Commercial atrazine-containing herbicide products showed remarkably high transfer across the nasal tissues, and histological evaluation showed significant changes in the morphology of the nasal epithelium following exposure to the herbicide products.

DISCUSSION

Lipophilic herbicides such as atrazine can freely permeate across the nasal mucosa despite the activity of efflux transporters. The adjuvant compounds in commercial herbicide products disrupt the nasal mucosa's epithelial barrier, resulting in even greater atrazine permeation across the tissues. The properties of the herbicide itself and those of the formulated products play crucial roles in the potential for the enhanced neurotoxicity of herbicides following nasal inhalation.

The acute effects of fipronil and 2,4-D, individually and in mixture: a threat to the freshwater Calanoida copepod Notodiaptomus iheringi

The magnitude of copepods' responses to pesticides, individually and in mixture, is little understood. The aims of this study were to evaluate: (i) the effects of the pesticides fipronil and 2,4-D, individually and in mixture, on the freshwater copepod Notodiaptomus iheringi; and (ii) the survival and the feeding rate of copepods after the exposure. Acute toxicity tests using the commercial formulations of fipronil and 2,4-D, individually and in mixture, were performed. The LC10-48h, LC20-48h, and LC50-48h of fipronil to N. iheringi were 2.38 ± 0.48, 3.08 ± 1.14, and 4.97 ± 3.30 μg L-1, respectively. For 2,4-D the LC10-48h, LC20-48h, and LC50-48h were 371.18 ± 29.20, 406.93 ± 53.77, and 478.24 ± 107.77 mg L-1, respectively. Morphological damages on the copepods exposed to pesticides were observed at all concentrations. Fungal filaments covering dead organisms were presented at the treatment highest concentration (R5:7.43 ± 2.78 μg L-1 fipronil). The mixture of the pesticides presented synergistic effects on the mortality of N. iheringi. Post-exposure tests showed no difference between the treatments and the control on the mortality and on the feeding rate for 4 h. However, since delayed toxicity of pesticides can occur, longer post-exposure tests using N. iheringi should be tested. N. iheringi is a key species in the aquatic Brazilian ecosystem and showed sensitivity to fipronil and 2,4-D; thus, more studies with this species assessing other responses are recommended.

New generation post-emergence herbicides and their impact on arbuscular mycorrhizae fungal association in rice

To prevent weed invasion in direct seeded rice cultivation, several new generation post emergence herbicides viz. bispyribac sodium, flucetosulfuron, ethoxysulfuron, fenoxaprop-p ethyl, penoxsulam, fenoxaprop-p-ethyl plus ethoxysulfuron and cyhalofop‑butyl plus penoxsulam are widely used in sub-tropical rice ecosystems of Eastern India. The main objective of this study was to know whether application of above listed post emergence herbicides at recommended (n1) and double recommended dose (n2) has any negative impact on arbuscular mycorrhizal fungal (AMF) association in rice plants. Further, the effects of herbicides on soil microbial properties viz. microbial biomass carbon (MBC), fluroscein diacetate (FDA), dehydrogenase (DHA), acid phosphatase (AcP) and alkaline phosphatase (AkP) activities were analyzed using unsupervised and supervised learning methods. Results indicated that among different herbicides evaluated only application of penoxsulam significantly (p<0.05) reduced the AMF root colonization (58.0%) at recommended dose (n1) compared to only AMF (70.3%) application. Whereas, application of bispyribac sodium (both n1 and n2 dose) enhanced AMF sporulation (1100 spores/100 g) and root colonization (86.68%) compared to other herbicides application. Unsupervised learning approaches through PCA found that application of bispyribac sodium enhanced both above ground plant growth responses and soil microbial properties, but penoxsulam had negative impact. But, the combined application of penoxsulam and cyhalofop‑butyl did not show any negative impact on AMF association in rice plants. This study concluded that selection of right type of post-emergence herbicides are very important to minimize the harmful effect or enhance AMF association in rice plants.

Systematic, small-scale screening with Arabidopsis reveals herbicides synergies that extend to lettuce

BACKGROUND

Combining herbicides into a mixture is a common approach used to overcome the potential for herbicide resistance in weeds. Many herbicide mixtures can be antagonistic and they are rarely synergistic. Here, 24 commercial herbicides, each representing a different mode of action were used to create a matrix of all 276 unique combinations to search for new synergies in agar using Arabidopsis thaliana.

RESULTS

Herbicides were used at an appropriate sublethal dose such that any synergies gave visible growth inhibition. We found five synergies including three new ones, namely mesotrione-norflurazon, mesotrione-clethodim and clomazone-paraquat. All three were reproducible in soil-grown conditions. Interestingly, the three new combinations all included a bleaching herbicide, suggesting that synergy might be a class-specific phenomenon. We also found that mesotrione-norflurazon and mesotrione-clethodim combinations were also synergistic against lettuce (Lactuca sativa), but not tef (Eragrostis tef).

CONCLUSION

Our study shows that screening herbicide mixtures against A. thaliana is an efficient approach for finding rare herbicide synergies.

Advances in Surfactants in Foliar Application of Agrochemicals on Mango Leaf Surfaces

The surface tension, pH and contact angle of the wetting liquid as well as the complex composition of the leaf surface are important parameters to describe the spreading, wettability and absorption of agrochemicals on the leaf surfaces. The contact angle of aqueous solutions of agrochemicals (multi-micronutrient fertilizers, growth regulator and insecticides) with/without Leaf guard, bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) and Sapindus mukorrossi (Ritha) were measured over the surface of mango leaves. The order of contact angle (mean) values was found to be AOT < Ritha < Leaf guard, which implies that AOT is a better wetting agent, but Ritha has a higher range of adhesion work because of its acidic nature (low pH). The wetting free energy was found to be more negative in the presence of Leaf guard, Ritha and AOT than in water, which indicates that wetting is more spontaneous in the presence of surfactants. The adaxial surface of mango leaves had a higher surface free energy than the abaxial part and hence showed higher wettability than the abaxial part.

Applications of Chemically Modified Clay Minerals and Clays to Water Purification and Slow Release Formulations of Herbicides

This review deals with modification of montmorillonite and other clay-minerals and clays by interacting them with organic cations, for producing slow release formulations of herbicides, and efficient removal of pollutants from water by filtration. Elaboration is on incorporating initially the organic cations in micelles and liposomes, then producing complexes denoted micelle- or liposome-clay nano-particles. The material characteristics (XRD, Freeze-fracture electron microscopy, adsorption) of the micelle– or liposome–clay complexes are different from those of a complex of the same composition (organo-clay), which is formed by interaction of monomers of the surfactant with the clay-mineral, or clay. The resulting complexes have a large surface area per weight; they include large hydrophobic parts and (in many cases) have excess of a positive charge. The organo-clays formed by preadsorbing organic cations with long alkyl chains were also addressed for adsorption and slow release of herbicides. Another examined approach includes “adsorptive” clays modified by small quaternary cations, in which the adsorbed organic cation may open the clay layers, and consequently yield a high exposure of the siloxane surface for adsorption of organic compounds. Small scale and field experiments demonstrated that slow release formulations of herbicides prepared by the new complexes enabled reduced contamination of ground water due to leaching, and exhibited enhanced herbicidal activity. Pollutants removed efficiently from water by the new complexes include (i) hydrophobic and anionic organic molecules, such as herbicides, dissolved organic matter; pharmaceuticals, such as antibiotics and non-steroidal drugs; (ii) inorganic anions, e.g., perchlorate and (iii) microorganisms, such as bacteria, including cyanobacteria (and their toxins). Model calculations of adsorption and kinetics of filtration, and estimation of capacities accompany the survey of results and their discussion.

Urinary Phthalate Metabolites in American Alligators (Alligator mississippiensis) from Selected Florida Wetlands

Phthalates have been shown to cause endocrine disruption in laboratory animals and are associated with altered development of the reproductive system in humans. Further, human have significant exposure to phthalates. However, little is known concerning the exposure of wildlife to phthalates. We report urinary phthalate metabolite concentrations from fifty juvenile alligators from three Florida lakes and a site in the Everglades. Urinary phthalate monoester concentrations varied widely among alligators from the different sites but also among alligators from the same site. Mono-2-ethylhexy phthalate and monobutyl phthalate were found in most samples of alligator urine with maximums of 35,700 ng/mL and 193 ng/mL, respectively. Monobenzyl phthalate was found in 5 alligators with a maximum of 66.7 ng/mL. Other monoesters were found in only one or two alligator urine samples. The wide variation within and among sites, in addition to the high levels of mEHP, mBP and mBzP, is consistent with exposure arising from the intermittent spraying of herbicide formulations to control invasive aquatic plants in Florida freshwater sites. Phthalate diesters are used as adjuvants in many of these formulations.

Assessment of an extended dataset of in vitro human dermal absorption studies on pesticides to determine default values, opportunities for read-across and influence of dilution on absorption

Dermal absorption is a key parameter in non-dietary human safety assessments for agrochemicals. Conservative default values and other criteria in the EFSA guidance have substantially increased generation of product-specific in vitro data and in some cases, in vivo data. Therefore, data from 190 GLP- and OECD guideline-compliant human in vitro dermal absorption studies were published, suggesting EFSA defaults and criteria should be revised (Aggarwal et al., 2014). This follow-up article presents data from an additional 171 studies and also the combined dataset. Collectively, the data provide consistent and compelling evidence for revision of EFSA's guidance. This assessment covers 152 agrochemicals, 19 formulation types and representative ranges of spray concentrations. The analysis used EFSA's worst-case dermal absorption definition (i.e., an entire skin residue, except for surface layers of stratum corneum, is absorbed). It confirmed previously proposed default values of 6% for liquid and 2% for solid concentrates, irrespective of active substance loading, and 30% for all spray dilutions, irrespective of formulation type. For concentrates, absorption from solvent-based formulations provided reliable read-across for other formulation types, as did water-based products for solid concentrates. The combined dataset confirmed that absorption does not increase linearly beyond a 5-fold increase in dilution. Finally, despite using EFSA's worst-case definition for absorption, a rationale for routinely excluding the entire stratum corneum residue, and ideally the entire epidermal residue in in vitro studies, is presented.

Acute and chronic toxicity of Betanal(®)Expert and its active ingredients on nontarget aquatic organisms from different trophic levels

As a way to improve the efficacy to target organisms, new pesticide generation is based on technologically advanced coformulations of two or more active ingredients. One example is Betanal(®)Expert, a postemergence herbicide composed of an Advanced Micro Droplet coformulation of phenmedipham, desmedipham, and ethofumesate. Although its composed formulation brings an increase in the pesticide performance, it can also enhance its toxicity to nontarget species. Therefore, the present study intends to contribute with relevant information on ecotoxicological effects of Betanal(®)Expert and its active ingredients on a battery of bioassays using aquatic species from different trophic levels: bacteria (Vibrio fischeri), microalgae (Pseudokirchneriella subcapitata, Chlorella vulgaris, and Chlamydomonas pseudocostata), macrophyte (Lemna minor), and cladocerans (Daphnia magna and Daphnia longispina) species. Across the organisms tested and endpoints measured, different responses concerning the toxicity of the active ingredients were found: (i) phenmedipham was the most toxic to V. fischeri and L. minor; (ii) desmedipham was the most toxic to P. subcapitata, D. magna, and D. longispina; (iii) and ethofumesate was the most toxic to C. pseudocostata and C. vulgaris. Furthermore, for C. pseudocostata and daphnids, the toxicity observed for some active ingredients was higher than the toxicity of the commercial formulation. In fact, in an attempt to evaluate the contribution of each active ingredient to the overall toxicity of Betanal(®)Expert, it was observed that, in general, the toxicity values obtained for desmedipham and phenmedipham were close or even lower to the values determined for Betanal(®)Expert, indicating that the ethofumesate can act as an antagonist in the three-way coformulation. In spite of the most impaired species being the photosynthetic ones, this study also showed pernicious effects on nonphotosynthetic organisms with distinct target sites. Therefore, our results underline the importance of clarifying the mode of action and metabolic pathways of these compounds on nonphotosynthetic species.

On the role of the three-phase contact line in surface deformation

Viscoelastic braking theories developed by Shanahan and de Gennes and by others predict deformation of a solid surface at the solid-liquid-air contact line. This phenomenon has only been observed for soft smooth surfaces and results in a protrusion of the solid surface at the three-phase contact line, in agreement with the theoretical predictions. Despite the large (enough to break chemical bonds) forces associated with it, this deformation was not confirmed experimentally for hard surfaces, especially for hydrophobic ones. In this study we use superhydrophobic surfaces composed of an array of silicon nanostructures whose Young modulus is 4 orders of magnitude higher than that of surfaces in earlier recorded viscoelastic braking experiments. We distinguish between two cases: when a water drop forms an adhesive contact, albeit small, with the apparent contact angle θ < 180° and when the drop-surface adhesion is such that the conditions for placing a resting drop on the surface cannot be reached (i.e., θ = 180°). In the first case we show that there is a surface deformation at the three-phase contact line which is associated with a reduction in the hydrophobicity of the surface. For the second case, however, there cannot be a three-phase contact line associated with a drop in contact with the surface, and indeed, if we force-place a drop on the surface by holding it with a needle, no deformation is detected, nor is there a reduction in the hydrophobic properties of the surface. Yet, if we create a long horizontal three-phase contact line by partially immersing the superhydrophobic substrate in a water bath, we see a localized reduction in the hydrophobic properties of the surface in the region where the three-phase contact line used to be. The SEM scan of that region shows a narrow horizontal stripe where the nanorods are no longer there, and instead there is only a shallow structure that is lower than the nanorods height and resembles fused or removed nanorods. Away from that region, either on the part of the surface which was exposed to bulk water or the part which was exposed to air, no change in the hydrophobic properties of the surface is observed, and the SEM scan confirms that the nanorods seem intact in both regions.

A prospective observational study of the clinical toxicology of glyphosate-containing herbicides in adults with acute self-poisoning

CONTEXT

The case fatality from acute poisoning with glyphosate-containing herbicides is approximately 7.7% from the available studies but these have major limitations. Large prospective studies of patients with self-poisoning from known formulations who present to primary or secondary hospitals are needed to better describe the outcome from acute poisoning with glyphosate-containing herbicides. Furthermore, the clinical utility of the glyphosate plasma concentration for predicting clinical outcomes and guiding treatment has not been determined.

OBJECTIVE

To describe the clinical outcomes, dose-response, and glyphosate kinetics following self-poisoning with glyphosate-containing herbicides.

METHODS

This prospective observational case series was conducted in two hospitals in Sri Lanka between 2002 and 2007. We included patients with a history of acute poisoning. Clinical observations were recorded until discharge or death. During a specified time period, we collected admission (n = 216, including five deaths) and serial (n = 26) blood samples in patients. Severity of poisoning was graded using simple clinical criteria.

RESULTS

Six hundred one patients were identified; the majority ingested a concentrated formulation (36%, w/v glyphosate). Twenty-seven percent were asymptomatic, 63.7% had minor poisoning, and 5.5% of patients had moderate to severe poisoning. There were 19 deaths (case fatality 3.2%) with a median time to death of 20 h. Gastrointestinal symptoms, respiratory distress, hypotension, altered level of consciousness, and oliguria were observed in fatal cases. Death was strongly associated with greater age, larger ingestions, and high plasma glyphosate concentrations on admission (>734 microg/mL). The apparent elimination half-life of glyphosate was 3.1 h (95% CI = 2.7-3.6 h).

CONCLUSIONS

Despite treatment in rural hospitals with limited resources, the mortality was 3.2%, which is lower than that reported in previous case series. More research is required to define the mechanism of toxicity, better predict the small group at risk of death, and find effective treatments.

Toxicity of three polyethoxylated tallowamine surfactant formulations to laboratory and field collected fairy shrimp, Thamnocephalus platyurus

Polyethoxylated tallowamine (POEA) is a non-ionic surfactant used in herbicide formulations to increase the efficacy of active ingredients. POEA promotes penetration of herbicide active ingredients into plant cuticles, and in animal species is known to cause alterations in respiratory surfaces. POEA use has increased recently with the advent of "Roundup-Ready" crops; however, its potential effects on aquatic invertebrates are relatively unknown. The aquatic macroinvertebrate Thamnocephalus platyurus (Crustacea, Anostraca) was used to assess the acute toxicity of POEA. Three formulations of POEA consisting of a 5:1, 10:1, and 15:1 average oxide:tallowamine were used in this study. All POEA formulations were found to be extremely toxic to T. platyurus with 48-h LC50 concentrations as low as 2.01 microg/L for 15:1. POEA toxicity increased as the tallowamine chain length was reduced, whereas the oxide chain length appeared to only slightly increase toxicity. Based on these results, POEA has the potential to adversely affect aquatic organisms in areas in which it is used.

Effect of two insecticides and two herbicides on the porcine sperm motility patterns using computer-assisted semen analysis (CASA) in vitro

The recent decline in sperm concentration observed in men has developed over a short period of time, suggesting that it could be the result of environmental factors. The present study has evaluated the effects of insecticides Malathion and Diazinon, and herbicides Atrazine and Fenoxaprop-Ethyl on porcine sperm viability and motility patterns in vitro using the eosin-nigrosin staining and a computer-assisted semen analyzer (CASA), respectively. Malathion and Fenoxaprop-Ethyl exerted more deleterious effects than Diazinon and Atrazine. Progressive sperm motility was strongly affected whereas the effect on sperm viability was less pronounced. This suggests that a reduction of sperm motility is not necessarily the result of sperm death. Since sperm motility is dependent on energy metabolism the mechanism of action of these pesticides might be mediated at the level of the mitochondrion, producing a delay in motility and eventual cell death.

Evaluation of toxicity of pesticides and their biodegradation products using human cells

Juvenoids are biologically active compounds, of relatively low toxicity to humans, that efficiently inhibit the fertility of insects. However, little attention has been paid to the stability and toxicity of products that may be generated by their biodegradation in the ecosystem. This study describes a simple comparison of the toxicity of the active compound and its degradation products generated by aerobic soil microbial isolates. Surprisingly we have found that toxicity of a biologically active carbamate juvenoid N-[2-[4-(2,2-ethylenedioxy-1-cyclohexylmethyl)-phenoxylethyl]carbamate (W328) was comparable with that of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT). The toxic effect was evaluated using the determination of the ATP/ADP content and viability of HeLa S3 cells exposed to various concentrations of the chemicals tested for various durations. DDT was used as a reference compound. Its toxicity was compared with two juvenile hormone analogs. The original compound, W328, was found to be the most toxic. The major product (W329) generated both by yeast isolates and the mixture of moulds lost its activity on reproduction of the tested insect. Its toxicity towards human cells was also decreased. Another two W328 degradation HPLC fractions exhibited significantly reduced toxicity compared to W328.