Determination of cutin-bound residues of chlorothalonil by immunoassay

The adsorption-desorption behavior of chlorothalonil in the cuticles of apple and red jujube

The distribution fate of chlorothalonil (CHT) in the environment (soil and water) and fruits is controlled by the capacity of cuticles to adsorb and desorb CHT, which directly affects the safety of both the environment and fruits. Batch experiments were conducted to reveal the adsorption-desorption behaviors of CHT in the cuticles of apple and red jujube. The adsorption kinetics showed that both physisorption and chemisorption occurred during the adsorption process. Furthermore, the isothermal adsorption of CHT in the fruit cuticles followed the Freundlich model. The thermodynamic parameters (ΔG ≤ -26.16 kJ/mol, ΔH ≥ 31.05 kJ/mol, ΔS ≥ 0.20 kJ/(mol K) showed that the whole CHT adsorption process was spontaneous, and the hydrophobic interaction was predominant. The CHT adsorption capacity of the apple cuticle was higher than that of the red jujube cuticle, potentially due to the significantly higher alkanes content of apples than that of red jujubes. An appropriate ionic strength (0.01 moL/L) could induce a higher adsorption capacity. In addition, the desorption kinetics were shown to conform to a Quasi-first-order model, meaning that not all the adsorbed CHT could be easily desorbed. The desorption ratios in apple and red jujube cuticles were 41.38% and 35.64%, respectively. The results of Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy further confirmed that CHT could be adsorbed and retained in the fruit cuticles. Investigating the adsorption-desorption behavior of CHT in the apple and red jujube cuticles allowed to determine the ratio of its final distribution in the fruits and environment, providing a theoretical basis to evaluate the risk of residue pesticide.

Non-target estrogenic screening of 60 pesticides, six plant protection products, and tomato, grape, and wine samples by planar chromatography combined with the planar yeast estrogen screen bioassay

For non-target residue analysis of xenoestrogens in food, sophisticated chromatographic-mass spectrometric techniques lack in biological effect detection. Various in vitro assays providing sum values encounter problems when opposing signals are present in a complex sample. Due to physicochemical signal reduction, cytotoxic or antagonistic effect responses, the resulting sum value is falsified. Instead, the demonstrated non-target estrogenic screening with an integrated planar chromatographic separation differentiated opposing signals, detected and prioritized important estrogenic compounds, and directly assigned tentatively the responsible compounds. Sixty pesticides were investigated, ten of which showed estrogenic effects. Exemplarily, half-maximal effective concentrations and 17β-estradiol equivalents were determined. Estrogenic pesticide responses were confirmed in six tested plant protection products. In food, such as tomato, grape, and wine, several compounds with an estrogenic effect were detected. It showed that rinsing with water was not sufficient to remove selected residues and illustrated that, though not usually performed for tomatoes, peeling would be more appropriate. Though not in the focus, reaction or breakdown products that are estrogenic were detected, underlining the great potential of non-target planar chromatographic bioassay screening for food safety and food control.

Measuring the photostability of agrochemicals on leaves: understanding the balance between loss processes and foliar uptake

BACKGROUND

Photostability is an important property in agrochemicals, impacting their biological efficacy, environmental fate and registrability. As such, it is a property that is routinely measured during the development of new active ingredients and their formulations. To make these measurements, compounds are typically exposed to simulated sunlight after application to a glass substrate. While useful, these measurements neglect key factors that influence photostability under true field conditions. Most importantly, they neglect the fact that compounds are applied to living plant tissue, and that uptake and movement within this tissue provides a mechanism to protect compounds from photodegradation.

RESULTS

In this work, we introduce a new photostability assay incorporating leaf tissue as a substrate, designed to run at medium throughput under standardized laboratory conditions. Using three test cases, we demonstrate that our leaf-disc-based assays provides quantitatively different photochemical loss profiles to an assay employing a glass substrate. And we also demonstrate that these different loss profiles are intimately linked to the physical properties of the compounds, the effect that those properties have on foliar uptake and, thereby, the availability of the active ingredient on the leaf surface.

CONCLUSIONS

The method presented provides a quick and simple measure of the interplay between abiotic loss processes and foliar uptake, supplying additional information to facilitate the interpretation of biological efficacy data. The comparison of loss between glass slides and leaves also provides a better understanding of when intrinsic photodegradation is likely to be a good model for a compound's behaviour under field conditions. © 2023 Society of Chemical Industry.

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

Residue behavior and dietary risk assessment of chlorothalonil and its metabolite SDS-3701 in water spinach to propose maximum residue limit (MRL)

Dietary risk assessment generally combines food consumption data and the concentration of pesticide by using the risk quotient (RQ) method. Chlorothalonil is the second popular fungicide in the world, and its residue and risk assessment in water spinach remain unknown. In this paper, the field trials of chlorothalonil in water spinach were operated under good agricultural practice (GAP) in China to human health protective. The dissipation experiments demonstrated that chlorothalonil was rapidly degraded in water spinach, with the half-lives of 1.8-3.2 days, and the amount of its metabolite SDS-3701 (4-hydroxy-2,5,6-trichloroisophthalonitrile) taken up through the water spinach roots from the soil was minor. The terminal experiments disclosed that the average residues of chlorothalonil and SDS-3701 in water spinach were below 6.59 mg/kg and 0.01 mg/kg, respectively. The results suggested the chronic dietary risk probability of chlorothalonil was 51.95-59.15% in terms of all registered crops, and the acute dietary risk probability of chlorothalonil was 12.30%-63.01% in water spinach, highlighting that the dietary risk of chlorothalonil in water spinach under GAP was acceptable. MRL of chlorothalonil was proposed as 7 mg/kg for water spinach and 5 days was recommended as a safe pre-harvest interval (PHI) for chlorothalonil application in water spinach field.

Antibody-free colorimetric detection of chlorothalonil in cucumberviathe inhibition of an enzyme-triggered reaction

Currently known rapid determination of fungicides usually relies on antibody-based immunoassay. This paper reports a simple antibody-free colorimetric assay for chlorothalonil via the inhibition of an enzyme-triggered reaction. The enzymatic activity of glyceraldehyde-3-phosphate dehydrogenase was significantly inhibited by chlorothalonil, and the color change of NBT-PMS system induced from NADH formation was suppressed, which could be used indirectly to assay chlorothalonil. The limit of detection (LOD) was 0.05 μM with a linear range from 0.5 to 10 μM, and the detection of 1 μM chlorothalonil in solution was achieved with a naked-eye readout. In addition, the colorimetric measurement results of the cucumber samples showed a good recovery rate, although the sensitivity was less effective than the instrumental method. Nevertheless, the results demonstrates that the chlorometric method provides potential opportunities for reliable, cost-effective quantitative detection for chlorothalonil residues in vegetables.

Colorimetric detection of chlorothalonil in cucumber via the inhibition of an enzyme-triggered reaction.

Photoreactivity of the fungicide chlorothalonil in aqueous medium

The photoreactivity of chlorothalonil was studied by means of steady-state irradiation and laser-flash photolysis. Experiments were conducted in water containing acetonitrile as a co-solvent. This fungicide undergoes very slow phototransformation in the first stages of the reaction, but the consumption profile is auto-accelerated. To understand the reaction mechanism, we undertook a detailed study of the rates, products and transient species. The rates and photoproduct distribution vary greatly with the oxygen concentration. Concerning the transient species, we measured the absorption of the triplet, its yield of formation, and its reactivity with oxygen in various water-acetonitrile mixtures and with isopropanol. The reduced radical, CTH˙, could be produced and its transient spectrum was recorded. Combining all the experimental data, it is hypothesized that in the first step of the reaction CT is excited to the triplet state. The triplet has several possible fates including reduction by organic constituents to form the radical which gives photoproducts. Another characteristic of the CT triplet is its capacity to generate singlet oxygen. The production of this species was measured by phosphorescence and compared to the percentage of the triplet trapped by oxygen in air-saturated solutions. The yield varies from 0.88 in pure acetonitrile to 0.48 in water-acetonitrile (95 : 5, v/v). Therefore, in surface waters, chlorothalonil is expected to sensitize the photooxidation of micropollutants, and to be competitively phototransformed through reaction with any H donor or electron donor water constituents.

Photoreduction of chlorothalonil fungicide on plant leaf models

Photodegradation is seldom considered at the surface of vegetation after crop spraying. Chlorothalonil, a broad-spectrum foliar fungicide with a very widespread use worldwide, was considered. To represent the waxy upper layer of leaves, tests were performed within thin paraffin wax films or in n-heptane. Laser flash photolysis together with steady-state irradiation in n-heptane allowed the determination of the photodegradation mechanisms Chlorothalonil ability to produce singlet oxygen was measured; noteworthy its efficiency is close to 100%. Additionally, chlorothalonil photodegradation mainly proceeds through reductive dechlorination. In these hydrophobic media, a radical mechanism was evidenced. Photochemical tests on wax films under simulated solar light show that formulated chlorothalonil is more reactive than pure chlorothalonil. The field-extrapolated half-life of photolysis on vegetation was estimated to 5.3 days. This value was compared to the half-lives of penetration and volatilization available in the literature. It appears that chlorothalonil dissipation from crops is ruled by both photodegradation and penetration. The relative importance of the two paths probably depends on meteorological factors and on physicochemical characteristics of the crop leaf cuticle.

Accumulation and decay of chlorothalonil and selected metabolites in surface soil following foliar application to peanuts

One of the principal uses of the fungicide, chlorothalonil, is control of foliar peanut diseases. Recent assessments indicate its runoff from treated fields in southeastern states presents risks to aquatic life. Two factors that control its runoff are how much reaches soil surfaces and degradation rates. To address these questions and to evaluate accumulation and decay of key metabolites, soil samples (0-2 cm) were collected after seven chlorothalonil applications on experimental peanut plots in south central Georgia during the 1999 growing season. At the start of and during laboratory incubations, samples were analyzed for the parent and degradates by HPLC-PDA-APCI-MS. The maximum observed residue levels were after the second application, after which canopy closure reduced soil deposition from later applications to 5-10% of applied amounts. After the last spray, < 5% of the cumulative chlorothalonil applied was detected in the soil. Foliar interception and dissipation and rapid soil degradation contributed to low residue levels. Soil half-lives were < 1-3.5 days for chlorothalonil and 10-22 days for its principal degradate, 4-hydroxychlorothalonil. Other daughter and granddaughter products were detected, some of which accumulated during the growing season. Results emphasize the plant canopy role in controlling the amount of fungicide sprays that reach soil surfaces and suggest concentration-dependent chlorothalonil degradation with degradation rates increasing as soil loading decreases. The study indicates that the 30-day field half-life often used for risk assessments of this pesticide is too long for one of its most important agronomic uses, i.e., in southeastern peanut production. It also indicates that the principal metabolites are more persistent than the parent, and more study is needed to identify and quantify their fate pathways.