The metabolism of fungicides

Fungicides have transgenerational effects on Rhopalosiphum padi but not their endosymbionts

BACKGROUND

While several agricultural fungicides are known to directly affect invertebrate pests, including aphids, the mechanisms involved are often unknown. One hypothesis is that fungicides with antibacterial activity suppress bacterial endosymbionts present in aphids which are important for aphid survival. Endosymbiont-related effects are expected to be transgenerational, given that these bacteria are maternally inherited. Here, we test for these associations using three fungicides (chlorothalonil, pyraclostrobin and trifloxystrobin) against the bird cherry-oat aphid, Rhopalosiphum padi, using a microinjected strain that carried both the primary endosymbiont Buchnera and the secondary endosymbiont Rickettsiella.

RESULTS

We show that the fungicide chlorothalonil did not cause an immediate effect on aphid survival, whereas both strobilurin fungicides (pyraclostrobin and trifloxystrobin) decreased survival after 48 h exposure. However, chlorothalonil substantially reduced the lifespan and fecundity of the F1 generation. Trifloxystrobin also reduced the lifespan and fecundity of F1 offspring, however, pyraclostrobin did not affect these traits. None of the fungicides consistently altered the density of Buchnera or Rickettsiella in whole aphids.

CONCLUSIONS

Our results suggest fungicides have sublethal impacts on R. padi that are not fully realized until the generation after exposure, and these sublethal impacts are not associated with the density of endosymbionts harbored by R. padi. However, we cannot rule out other effects of fungicides on endosymbionts that might influence fitness, like changes in their tissue distribution. We discuss these results within the context of fungicidal effects on aphid suppression across generations and point to potential field applications. © 2022 Society of Chemical Industry.

Analytical and toxicological aspects of dithiocarbamates: an overview of the last 10 years

Compilation studies related to toxicological aspects and also biological monitoring and analysis methods for specific fungicides and, mainly, those that belong to the class of the dithiocarbamates (DTCs) have not been carried out at least in the last ten years. DTCs - dimethyldithiocarbamates, ethylenebisditiocarbamates, propylenebisditiocarbamates - are organosulfur compounds that form complexes due to the presence of different chemical elements, which bind strongly and inhibit enzymes that are essential to the functioning of the organism, causing a serious proven adverse effect on biological systems, such as alteration of thyroid hormones, teratogenesis and neurotoxicity. It is still evident, as shown by world data, that the growing consumption of fungicides has increasingly exposed the population in general and, in particular, workers who deal with these substances. There is a scarcity of studies in the literature discussing the toxicological and analytical aspects that are important for understanding the real effects of DTCs and monitoring human exposure to them. Therefore, the aim of this work was to expose, in a comprehensive way and through a narrative review, the negligence of research related to the fungicides of the DTCs class, their metabolites, as well as the toxicological and analytical aspects involved. The review is divided into two parts: (1) Toxicological aspects, including toxicokinetics, toxicodynamics and toxidromes; and (2) Analytical Toxicology, which comprises biomarkers, sample preparation and identification/quantification methods.

Identification of pesticides exposure biomarkers for residents living close to vineyards in France

Biomonitoring can be relevant for assessing pesticides exposure of residents living close to vineyards (LCTV). However, because xenobiotics are generally present at low levels in human biological matrices and the sources of pesticide exposure are multiple, several challenges need to be overcome to reliably assess exposure in residents LCTV. This includes particularly identifying the most appropriate exposure biomarkers, the biological matrices in which they should be measured, and analytical methods that are sufficiently sensitive and specific to quantify them. The aim of the present study was to develop a tiered approach to identify relevant biomarkers and matrices for assessing pesticide exposure in residents LCTV. We used samples from a biobank for 121 adults and children included in a national prevalence study conducted between 2014 and 2016 who lived near or far from vineyards. We analyzed five priority pesticides (folpet, mancozeb, tebuconazole, glyphosate, and copper) and their metabolites in urine and hair samples. We identified relevant biomarkers according to three criteria related to: i) the detection frequency of those pesticides and metabolites in urine and hair, ii) the difference in concentrations depending on residence proximity to vineyards and, iii) the influence of other environmental and occupational exposure sources on pesticide levels. This tiered approach helped us to identify three relevant metabolites (two metabolites of folpet and one of tebuconazole) that were quantified in urine, tended to be higher in residents LCTV than in controls, and were not significantly influenced by occupational, dietary, or household sources of pesticide exposure. Our approach also helped us to identify the most appropriate measurement strategies (biological matrices, analytical methods) to assess pesticide exposure in residents LCTV. The approach developed here was a prerequisite step for guiding a large-scale epidemiological study aimed at comprehensively measuring pesticides exposures in French residents LCTV with a view to developing appropriate prevention strategies.

Environmental and biological monitoring for the identification of main exposure determinants in vineyard mancozeb applicators

Grapevine is a vulnerable crop to several fungal diseases often requiring the use of ethylenebisdithiocarbamate (EBDC) fungicides, such as mancozeb. This fungicide has been reported to have goitrogenic, endocrine disrupting, and possibly immunotoxic effects. The aim of this study was to assess workers' exposure in two scenarios of mancozeb application and analyse the main determinants of exposure in order to better understand their mechanism of influence. Environmental monitoring was performed using a modified Organisation for Economic Co-operation and Development (OECD) "patch" methodology and by hand-wash collection, while mancozeb's metabolite, ethylenethiourea (ETU), was measured in 24-h preexposure and postexposure urine samples. Liquid chromatography-mass spectrometry was used for determination of mancozeb and ETU in different kinds of samples. Closed tractor use resulted in 40 times lower potential exposure compared with open tractor. Coveralls reduced skin exposure 4 and 10 times in case of open and closed tractors, respectively. Gloves used during application resulted in 10 times lower hand exposure in open but increased exposure in closed tractors. This study has demonstrated that exposure to mancozeb is low if safe occupational hygiene procedures are adopted. ETU is confirmed as suitable biological marker of occupational exposure to mancozeb, but the absence of biological exposure limits significantly reduces the possibility to interpret biological monitoring results in occupationally exposed workers.

Catalyst-coated cement beads for the degradation and mineralization of fungicide carbendazim using laboratory and pilot-scale reactor: catalyst stability analysis

The fixed-bed photocatalytic degradation of fungicide carbendazim using catalyst-coated spherical cement beads has been investigated. Thirty beads with optimum size 13 mm along with 0.3 gL^-1 H₂O₂ with an initial concentration of carbendazim of 10 mgL^-1 were the optimized conditions for better degradation. The reduction in COD and total organic carbon along with the generation of nitrite and nitrate ions under the optimized conditions confirms the complete mineralization of compound. The suggested degradation pathway for carbendazim has also been proposed as intermediates formed during photodegradation were analyzed through gas chromatography-mass spectrometry. The coated cement beads were found to be durable even after 30 cycles as confirmed by scanning electron microscopy and energy dispersive spectroscopy analysis. Scale-up trails have also been carried out in a solar-baffled fixed-bed reactor for the degradation of pollutant to seek the commercial viability of the technique.

Copper or/and arsenic induce oxidative stress-cascaded, nuclear factor kappa B-dependent inflammation and immune imbalance, trigging heat shock response in the kidney of chicken

Excessive amount of copper (Cu) and inorganic arsenic (iAs) coexists in drinking water in many regions, this is associated with high risk of nephropathy, defined as chronic structural and functional disorders of the kidney. However, the underlying mechanisms are not well understood. In this study, a total of 72 day-old Hy-line chickens were exposed to 300 mg/kg copper sulphate or/and 30 mg/kg arsenic trioxide for 12 weeks. Indicators of oxidative stress, inflammation and heat shock proteins (HSPs) production were analyzed in kidney. The results showed that, when the toxicant was administrated alone, there is an antagonism between redox homeostasis during the first 4 weeks, which follows a collapse of antioxidant system manifested by damaged biomembrane structure. What's worse, oxidative damage-cascaded histopathological lesions were accompanied by increases of proinflammatory mediators and an imbalance of "Th1/Th2 drift" (Th, helper T cell) regulated by nuclear factor kappa B (NF-κB). Simultaneously, intense heat shock response went with the organism. The above-mentioned renal lesions and indicators changes were time-dependent, more complex and deteriorated effects were observed in Cu/iAs combined groups compared with the others. This study supports Cu and iAs have a synergistic type on the nephro-toxicological process additively. In conclusion, oxidative stress and inflammatory induced by Cu or/and iAs are potential mechanisms in their nephrotoxicity, increased heat shock response may play a renoprotection function in tissues damage.

Aldehyde dehydrogenase inhibitors: a comprehensive review of the pharmacology, mechanism of action, substrate specificity, and clinical application

Aldehyde dehydrogenases (ALDHs) belong to a superfamily of enzymes that play a key role in the metabolism of aldehydes of both endogenous and exogenous derivation. The human ALDH superfamily comprises 19 isozymes that possess important physiological and toxicological functions. The ALDH1A subfamily plays a pivotal role in embryogenesis and development by mediating retinoic acid signaling. ALDH2, as a key enzyme that oxidizes acetaldehyde, is crucial for alcohol metabolism. ALDH1A1 and ALDH3A1 are lens and corneal crystallins, which are essential elements of the cellular defense mechanism against ultraviolet radiation-induced damage in ocular tissues. Many ALDH isozymes are important in oxidizing reactive aldehydes derived from lipid peroxidation and thereby help maintain cellular homeostasis. Increased expression and activity of ALDH isozymes have been reported in various human cancers and are associated with cancer relapse. As a direct consequence of their significant physiological and toxicological roles, inhibitors of the ALDH enzymes have been developed to treat human diseases. This review summarizes known ALDH inhibitors, their mechanisms of action, isozyme selectivity, potency, and clinical uses. The purpose of this review is to 1) establish the current status of pharmacological inhibition of the ALDHs, 2) provide a rationale for the continued development of ALDH isozyme-selective inhibitors, and 3) identify the challenges and potential therapeutic rewards associated with the creation of such agents.

Characterization of metabolites of fungicidal cymoxanil in a sensitive strain of Botrytis cinerea

The metabolism of cymoxanil [1-(2-cyano-2-methoxyiminoacetyl)-3-ethyl urea] by a very sensitive strain of Botrytis cinerea toward this fungicide was studied by using [2-(14)C]-cymoxanil. Labeled cymoxanil was added either in a culture of this strain or in its enzymatic extract. The main metabolites, detected in biological samples, were isolated and identified by mass and NMR spectrometry. Their identification allowed us to show that this strain quickly metabolized cymoxanil according to at least three enzymatic pathways: (i) cyclization leading, after hydrolysis, to ethyl parabanic acid, (ii) reduction giving demethoxylated cymoxanil, and (iii) hydrolysis and reduction followed by acetylation leading to N-acetylcyanoglycine. In a cell-free extract of the same strain, only the first and the second enzymatic reactions, quoted above, occurred. Biological tests showed that, among all the metabolites, only N-acetylcyanoglycine is fungitoxic toward this sensitive strain.

Genetic basis of individual differences in the response to small-molecule drugs in yeast

Individual response to small-molecule drugs is variable; a drug that provides a cure for some may confer no therapeutic benefit or trigger an adverse reaction in others. To begin to understand such differences systematically, we treated 104 genotyped segregants from a cross between two yeast strains with a collection of 100 diverse small molecules. We used linkage analysis to identify 124 distinct linkages between genetic markers and response to 83 compounds. The linked markers clustered at eight genomic locations, or quantitative-trait locus 'hotspots', that contain one or more polymorphisms that affect response to multiple small molecules. We also experimentally verified that a deficiency in leucine biosynthesis caused by a deletion of LEU2 underlies sensitivity to niguldipine, which is structurally related to therapeutic calcium channel blockers, and that a natural coding-region polymorphism in the inorganic phosphate transporter PHO84 underlies sensitivity to two polychlorinated phenols that uncouple oxidative phosphorylation. Our results provide a step toward a systematic understanding of small-molecule drug action in genetically distinct individuals.

Agrochemical Poisoning

A general increase in the use of chemicals in agriculture has brought about a concomitant increase in the incidence of agrochemical poisoning. Organophosphates are the most common agrochemical poisons followed closely by herbicides. Many agricultural poisons, such as parathion and paraquat are now mixed with a coloring agent such as indigocarmine to prevent their use criminally. In addition, paraquat is fortified with a “stenching” agent. Organo-chlorines have an entirely different mechanism of action. Whereas organophosphates have an anticholinesterase activity, organochlorines act on nerve cells interfering with the transmission of impulses through them. A kerosene-like smell also emanates from death due to organochlorines. The diagnosis lies in the chemical identification of organochlorines in the stomach contents or viscera. Organochlorines also resist putrefaction and can be detected long after death. Paraquat has been involved in suicidal, accidental, and homicidal poisonings. It is mildly corrosive and ulceration around lips and mouth is common in this poisoning. However, the hallmark of paraquat poisoning, especially when the victim has survived a few days, are the profound changes in lungs. Other agrochemicals such as algicides, aphicides, herbicide safeneres, fertilizers, and so on, are less commonly encountered. Governments in most countries have passed legislations to prevent accidental poisonings with these agents. The US government passed the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) in 1962 and the Indian government passed The Insecticides Act in 1968. Among other things, these acts require manufacturers to use signal words on the labels of insecticides, so the public is warned of their toxicity and accompanying danger.

Male reproductive hormones and thyroid function in pesticide applicators in the Red River Valley of Minnesota

In the present effort, 144 pesticide applicators and 49 urban control subjects who reported no chronic disease were studied. Applicators provided records of the season's pesticides used by product, volumes, dates, and methods of application. Blood specimens for examination of hormone levels were obtained in summer and fall. In the herbicide-only applicator group, significant increases in testosterone levels in fall compared to summer and also elevated levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the fall were noted. With respect to fungicide use, in an earlier cross-sectional epidemiologic study, data demonstrated that historic fungicide use was associated with a significant alteration of the sex ratio of children borne to applicators. As before, among current study subjects it was noted that historic fungicide use was associated with increased numbers of girls being born. Lower mean total testosterone concentrations by quartile were also correlated with increased numbers of live-born female infants. A downward summer to fall seasonal shift in thyroid-stimulating hormone (TSH) concentrations occurred among applicators but not among controls. Farmers who had aerial application of fungicides to their land in the current season showed a significant shift in TSH values (from 1.75 to 1.11 mU/L). Subclinical hypothyroidism was noted in 5/144 applicators (TSH values >4.5 mU/L), but not in urban control subjects. Based on current and past studies, it was concluded that, in addition to pesticide exposure, individual susceptibility and perhaps economic factors may play a supporting role in the reported results.

Ethylenethiourea in urine as an indicator of exposure to mancozeb in vineyard workers

In the present study, the personal exposure to mancozeb and/or ethilenethiourea (ETU) in 13 Italian vineyard workers and in 13 subjects without occupational exposure to pesticides was investigated. With this aim, the level of ETU in urine and the dermal exposure to mancozeb were determined. Baseline urinary ETU results were lower than the analytical limit of detection for all controls (<0.5 microg/g creatinine) and for ten workers (median <0.5, range <0.5-3.4 microg/g creatinine). In workers, urinary ETU was significantly increased at the end of shift (2.5, <0.5-95.2 microg/g creatinine) compared with baseline levels. End-shift urinary ETU was higher in operators using open tractors (n=7) than in those using closed tractors (n=5) (16.2 vs. 2.4 microg/g creatinine), but the difference was not significant (P=0.073). End-shift urinary ETU was positively correlated with dermal exposure to mancozeb determined both over the clothes and on the skin (Spearman's rho=0.770 and 0.702, P=0.009 and 0.024, respectively). Wine consumption positively influenced the excretion of ETU.

Factors affecting R6 fungicide toxicity on sea urchin fertilization and early development: roles of exposure routes and mixture components

A technical fungicide mixture, R6 and its components, cymoxanil (CYM) and cupric oxychloride (Cu-OCl), were tested by sea urchin bioassays (Paracentrotus lividus and Sphaerechinus granularis). A set of toxicity endpoints was evaluated including both lethal and sublethal effects with the following endpoints: (a) acute embryotoxicity, (b) developmental defects, (c) changes in sperm fertilization success, (d) transmissible damage from sperm to the offspring, and (e) cytogenetic abnormalities. Acute effects on developing embryos were observed as early (prehatch) mortality at R6 levels > or =25 microg/ml. The pesticide mixture R6 was tested at realistic concentrations, ranging from 25 ng/ ml to 2.5 microg/ml, and the two components, CYM and Cu-OCl, were tested, either alone or in mixture, at concentrations equal to their levels in the corresponding R6 solutions. R6 was either dissolved in filtered seawater (water only, W-O), or spiked in "pristine" silt-clay sediment or soil samples before bioassays. Developmental toxicity of R6, following W-O dissolution, displayed a significant dose-related increase of larval malformations and differentiation arrest at concentrations of 750 ng/ml to 2.5 microg/ml both in P. lividus and in S. granularis larvae. Developmental toxicity was removed in spiked sediment up to R6 nominal levels (25 microg/ml), 10-fold above the embryotoxic R6 levels in W-O exposure. No significant developmental toxicity was exerted by CYM or Cu-OCl (W-O exposure) up to their concentrations equivalent to 2.5 microg/ml R6. The laboratory-prepared mixture of CYM and Cu-OCl, in the same concentration range, only resulted in minor effects, as larval retardation, suggesting the presence of toxic impurities (or additional components) in the R6 formulation. When sperm from either P. lividus or S. granularis were exposed to R6 before fertilization, a W-O exposure resulted in a dose-related decrease in fertilization of P. lividus sperm (up to 250 microg/ml R6), whereas S. granularis sperm underwent a significant increase of fertilization rate at the highest R6 nominal levels (up to 25 microg/ml). Equivalent CYM or Cu-OCl levels were ineffective on sperm fertilization success in both species. The offspring of S. granularis sperm exposed to 25 microg/ml R6 showed a significant increase in larval malformations, which were not detected in the offspring of R6-exposed P. lividus sperm. Again, CYM or Cu-OCl was unable to exert any transmissible damage from sperm to the offspring in either species. The present study raises the case of possible discrepancies between toxicity of a technical mixture and of its analytical-grade components, also providing evidence for a loss of pesticide toxicity following dispersion in an environmental matrix such as sediment or soil.

Carbendazim and n-butylisocyanate: metabolites responsible for benomyl double action on cytochrome P450 in HepG2 cells

Changes in the cytochrome P450 monooxygenase system were investigated in HepG2 cells treated for 24 h with 1.25, 2.5, 5, 10 and 20 microg/ml of carbendazim (MBC) and n-butylisocyanate (BIC), the principal benomyl metabolites. The results show that n-butylisocyanate leads to a decrease in both ethoxyresorufin deethylase (P4501A1) (EROD) and ethoxycoumarin deethylase (P4502B) (ECOD), whereas MBC has no effect on EROD and increases ECOD. The decrease in ECOD and EROD activities after BIC treatment can be attributed to the detrimental action of this substance. The MBC-induced increase in ethoxycoumarin can be considered an enzyme-specific inductive phenomenon. This hypothesis was confirmed by Western immunoblot analysis and treatment with actinomycin D 8 x 10(-4) microM: the first showed an increase in P4502B isoenzyme content and the second evidence of a partial block of the increase in ECOD activity induced by MBC. Given these results, MBC and BIC seem to be the metabolites responsible for the double opposite action of their parent compound benomyl. Data deriving from an equimolar mixture of the two metabolites suggest that benomyl activity on some cytochrome P450 isoenzymes is the result of a balance between the action of the single metabolites (Radice et al., 1996).