Toxicity characterization and environmental risk assessment of Mancozeb on the South American common toad Rhinella arenarum

The toxicity and health risk of chlorothalonil to non-target animals and humans: A systematic review

Chlorothalonil (CTL), an organochloride fungicide applied for decades worldwide, has been found to be present in various matrixes and even accumulates in humans or other mammals through the food chain. Its high residue and diffusion in the environment have severely affected food security and public health. More and more research has considered CTL as a possible toxin to environmental non-target organisms, via influencing multiple systems such as metabolic, developmental, endocrine, genetic, and reproductive pathways. Aquatic organisms and amphibians are the most vulnerable species to CTL exposure, especially during the early period of development. Under experimental conditions, CTL can also have toxic effects on rodents and other non-target organisms. As for humans, CTL exposure is most often reported to be relevant to allergic reactions to the skin and eyes. We hope that this review will improve our understanding of the hazards and risks that CTL poses to non-target organisms and find a strategy for rational use.

Gonadal morphogenesis in the South American toad Rhinella Arenarum (Anura, Bufonidae) unveils an extremely delayed rate of sex differentiation

Among anurans, Bufonids are recognized for their retarded sex differentiation. However, few studies have addressed gonadal morphogenesis in this family. Here, we analyzed the early gonadogenesis in laboratory-reared Rhinella arenarum. Few germ cells were identified in the genital ridge at Gosner stage 26. At metamorphosis, somatic cells and germ cells were observed in the outer region of the undifferentiated gonad, whereas the central region was occupied by stromal tissue. A cortico-medullary organization was first recognized on Day 7 postmetamorphosis. The cortex was composed of germ cells and encompassing epithelial cells, whereas the medulla contained cells presumptively derived from the coelomic epithelium. Medullary somatic cells formed metameric knots along the length of the undifferentiated gonad. Consequently, a series of 12-14 gonomeres became recognizable externally. The first sign of ovarian differentiation was observed on Day 15 postmetamorphosis, when a cavity was formed within each gonomere. In contrast, testes were recognized by a uniform distribution of germ cells and intermingled somatic cells, as the division into cortex and medulla was lost. By Day 50 postmetamorphosis, the gonadal metameric organization was still apparent both in the ovaries and testes. Follicles containing diplotene oocytes were observed within the ovary. In the testis, an incipient lobular architecture was recognized without initiation of meiosis within the seminiferous cords. These observations reveal an extremely delayed gonadal development in R. arenarum, not reported previously for other anuran species. In addition, the late differentiation of the gonads contrasted with the early appearance of follicles in the Bidder's organ. Lastly, we observed that delayed metamorphs exhibited an undifferentiated gonad, demonstrating that gonadogenesis in this species is more dependent on somatic development than on age.

Mancozeb induces nephrotoxicity by impairing the oxidative phosphorylation pathway: A transcriptome study

This study analyzed the mechanism underlying mancozeb (MCZ)-induced kidney injury by detecting kidney function indicators, combined with transcriptome and metabolome sequencing. Twenty mice were randomly assigned into two groups (control and MCZ groups) to explore the MCZ-induced kidney toxicity. The control group was gavaged with 0.2 mL of deionized water, and the MCZ group with 0.2 mL of 100 mg/kg MCZ for 30 days. The kidney structure of the MCZ group was damaged, with slight hyaline degeneration in the kidney tubular epithelial envelope. The creatinine (CRE) and uric acid (UA) were significantly increased in the MCZ group than in the control group. Moreover, the reactive oxygen species (ROS) significantly accumulated in the MCZ group kidneys. Compared to the control group, superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) were significantly decreased in the MCZ group, while the MDA content was substantially increased. The differentially expressed genes (DEGs) in the MCZ group were mainly enriched in the oxidative phosphorylation pathway. Besides, in the MCZ group, ndufs1 and ndufab1 genes were significantly up-regulated, while cox5b, ndufa5, and ndufa6 genes were significantly down-regulated, consistent with the PCR verification results. The metabolomic analysis identified cGMP-PKG signaling pathway of MCZ-induced nephrotoxicity, with Guanosine monophosphate and Adenosine 5'-monophosphate as the main altered metabolites. These results indicated that MCZ impairs the mice kidneys by obstructing the oxidative phosphorylation pathway, which increases oxidative stress in the kidneys, resulting in kidney injury.

Humane acute testing with tadpoles for risk assessment of chemicals: Avoidance instead of lethality

In spite of the sensitivity of amphibians to contamination, data from fish have been commonly used to predict the effects of chemicals on aquatic life stages. However, recent studies have highlighted that toxicity data derived from fish species may not protect all the aquatic life stages of amphibians. For pesticide toxicity assessment (PTA), EFSA has highlighted that more information on lethal toxicity for the aquatic life stages of amphibians is still needed to reduce uncertainties. The current review aims to propose a test with amphibians based on spatial avoidance, as a more humane alternative method to the lethality tests for chemicals. A review of lethal toxicity tests carried out with amphibians in the period between 2018 and 2021 is presented, then we discuss the suitability of using fish toxicity data as a surrogate to predict the effects on more sensitive amphibian groups. The possible differences in sensitivity to chemicals may justify the need to develop further tests with amphibian embryos and larvae in order to reduce uncertainties. A new test is proposed focused on the avoidance behaviour of organisms fleeing from contamination to replace lethal tests. As avoidance indicates the threshold at which organisms will flee from contamination, a reduction in the population density, or its disappearance, at the local scale due to emigration is expected, with ecological consequences analogous to mortality. Avoidance tests provide an ethical advantage over lethal tests as they respect the concepts of the 3 Rs (mainly Refinement), reducing the suffering of the organisms.

Reproductive toxicity by exposure to low concentrations of pesticides in Caenorhabditis elegans

In view of the recurrent applications of pesticides in agricultural producing countries, the increased presence of these substances in the environment raise a demand for the evaluation of adverse effects on non-target organisms. This study assesses the impact of exposure to five pesticides suspected of being endocrine disruptors (atrazine, 2,4-dichlorophenoxyacetic acid, mancozeb, chlorpyrifos and cypermethrin) on the reproductive development of the nematode Caenorhabditis elegans. To this end, nematodes in the L4 larval stage were exposed to different concentrations of pesticides for 24 h and the consequences on brood size, percentage of gravid nematodes, expression of reproductive-related genes and vitellogenin trafficking and endocytosis were measured. Moreover, 17β-estradiol was used as an estrogenic control for endocrine disrupting compounds throughout the work. The results showed that all the pesticides disturbed to some extent one or more of the evaluated endpoints. Remarkably, we found that atrazine, 2,4-dichlorophenoxyacetic acid and chlorpyrifos produced comparable responses to 17β-estradiol suggesting that these pesticides may have estrogen-like endocrine disrupting activity. Atrazine and 17β-estradiol, as well as 2,4-dichlorophenoxyacetic acid and chlorpyrifos to a lesser extent, decreased the brood size, affected vitellogenin trafficking and endocytosis, and changed the expression of several reproductive-related genes. Conversely, mancozeb and cypermethrin had the least impact on the evaluated endpoint. Cypermethrin affected the brood size at the highest concentration tested and mancozeb altered the distribution of vitellogenin only in approximately 10% of the population. However, both products overexpressed hus-1 and vit-2 genes, indicating that an induction of stress could interfere with the normal development of the nematode. In conclusion, our work proved that C. elegans is a useful biological model to identify the effects of estrogen-like endocrine disruptor compounds, and the sublethal endpoints proposed may serve as an important contribution on evaluating environmental pollutants.

Cardiac developmental toxicity and transcriptome analyses of zebrafish (Danio rerio) embryos exposed to Mancozeb

Mancozeb (MZ), an antibacterial pesticide, has been linked to reproductive toxicity, neurotoxicity, and endocrine disruption. However, whether MZ has cardiactoxicity is unclear. In this study, the cardiotoxic effects of exposure to environment-related MZ concentrations ranging from 1.88 μM to 7.52 μM were evaluated at the larval stage of zebrafish. Transcriptome sequencing predicted the mechanism of MZ-induced cardiac developmental toxicity in zebrafish by enrichment analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). Consistent with morphological changes, the osm, pfkfb3, foxh1, stc1, and nrarpb genes may effect normal development of zebrafish heart by activating NOTCH signaling pathways, resulting in pericardial edema, myocardial fibrosis, and congestion in the heart area. Moreover, differential gene expression analysis indicated that cyp-related genes (cyp1c2 and cyp3c3) were significantly upregulated after MZ treatment, which may be related to apoptosis of myocardial cells. These results were verified by real-time quantitative RT-qPCR and acridine orange staining. Our findings suggest that MZ-mediated cardiotoxic development of zebrafish larvae may be related to the activation of Notch and apoptosis-related signaling pathways.

Effects of mancozeb on heat Shock protein 70 (HSP70) and its relationship with the thermal physiology of Physalaemus henselii (Peters, 1872) tadpoles (Anura: Leptodactylidae)

Negative impacts on amphibians have been reported due to contamination by agrochemicals. However, until now, no study has tested the effect of the fungicide mancozeb (MZ) on thermal tolerance and its relationship with the expression of heat shock proteins (HSPs). MZ is the best-selling broad-spectrum fungicide in the world, which negatively affects non-target organisms. Here, we tested for the first time the effects of MZ on critical thermal maximum (CTmax) and its relationship to the expression of heat shock protein 70 (HSP70) in tadpoles of Physalameus henselii, a colder-adapted species in southernmost of the Neotropical region. A sublethal concentration of 2 mg/L was used. We found that the CTmax of the MZ-treated group was lower than that of the control group. In addition, there was an increase in HSP70 expression in tadpoles exposed to MZ and in tadpoles that underwent heat treatment. However, tadpoles subjected to MZ and heat treatment showed no induced HSP70 protein expression. Our results demonstrated that sublethal doses of the fungicide MZ negatively affected the thermal physiology and heat shock protein expression in tadpoles of P. henselii by inducing an increase in HSP70 concentration and by reducing the critical CTmax supported by tadpoles. It is important to understand the relationship between environmental contamination and physiological thermal limits in our current scenario of high rates of habitat conversion associated with unrestricted use of agrochemicals, as well as the challenging environmental changes induced by global warming.

Toxicological interactions of cadmium and four pesticides on early life stage of rare minnow (Gobiocypris rarus)

Although chemicals have been traditionally regulated on an individual basis in aquatic ecosystems, they often co-exist as different types of complex mixtures. Laboratory assays were conducted for assessing the responses of rare minnow (Gobiocypris rarus) to individual and mixture chemicals [trace element cadmium (Cd), thiamethoxam, deltamethrin, malathion and prochloraz]. Data obtained from 96 h semi-static toxicity assays implied that deltamethrin elicited the highest toxic effect on the various developmental phases (larval, juvenile and adult phases) of G. rarus with LC₅₀ values ranging from 0.00061 to 0.25 mg a.i. L^-1, followed by prochloraz, malathion and Cd with 96-h LC₅₀ values ranging from 0.49 to 1.1, from 7.1 to 26, and from 7.6 to 15 mg a.i. L^-1, respectively. Thiamethoxam elicited the lowest toxic effect on the organisms with 96-h LC₅₀ values ranging from 38 to 202 mg a.i. L^-1. Larval phase was not always the most sensitive period in the three detected phases to most of chemicals. Chemical combinations containing deltamethrin and malathion displayed synergetic responses to the larvae of G. rarus. Besides, the binary mixtures of Cd-deltamethrin and Cd-prochloraz also exhibited synergetic response to rare minnows. Our results indicate that extra information is necessary to develop practical criteria for selecting chemical combinations that require legislative attention according to their likelihood to exert synergetic responses. Thence, more investigations on mixture toxicities of various chemicals should be taken as a priority for producing synergetic interaction to improve the environmental risk assessment of chemicals.