Triazines facilitate neurotransmitter release of synaptic terminals located in hearts of frog (Rana ridibunda) and honeybee (Apis mellifera) and in the ventral nerve cord of a beetle (Tenebrio molitor)

Atrazine exposure can dysregulate the immune system and increase the susceptibility against pathogens in honeybees in a dose-dependent manner

Recently, concerns regarding the impact of agrochemical pesticides on non-target organisms have increased. The effect of atrazine, the second-most widely used herbicide in commercial farming globally, on honeybees remains poorly understood. Here, we evaluated how atrazine impacts the survival of honeybees and pollen and sucrose consumption, investigating the morphology and mRNA expression levels of midgut tissue, along with bacterial composition (relative abundance) and load (absolute abundance) in the whole gut. Atrazine did not affect mortality, but high exposure (37.3 mg/L) reduced pollen and sucrose consumption, resulting in peritrophic membrane dysplasia. Sodium channels and chitin synthesis were considered potential atrazine targets, with the expression of various genes related to lipid metabolism, detoxification, immunity, and chemosensory activity being inhibited after atrazine exposure. Importantly, 37.3 mg/L atrazine exposure substantially altered the composition and size of the gut microbial community, clearly reducing both the absolute and relative abundance of three core gram-positive taxa, Lactobacillus Firm-5, Lactobacillus Firm-4, and Bifidobacterium asteroides. With altered microbiome composition and a weakened immune system following atrazine exposure, honeybees became more susceptible to infection by the opportunistic pathogen Serratia marcescens. Thus, considering its scale of use, atrazine could negatively impact honeybee populations worldwide, which may adversely affect global food security.

Effects of atrazine short-term exposure on jumping ability and intestinal microbiota diversity in male Pelophylax nigromaculatus adults

Atrazine, a common chemical pesticide, has toxicity to adult and juvenile amphibians in natural ecosystems; however, it is more common to study its effects on larvae instead of adults. This study assessed the impacts of atrazine in water through short-term exposure (7 days) on male black spotted frog (Pelophylax nigromaculatus) adults fed every day. The jumping ability, including jumping height, distance, time, and speed, was measured by 3D motion analysis software, and the intestinal content microbiota was determined by 16S rRNA amplicon sequencing with QIIME software. The results showed that male P. nigromaculatus exposure to 200 and 500 μg/L atrazine significantly increased jumping distance and jumping time compared to control groups. Conversely, 500 μg/L atrazine treatments significantly decreased the diversity and changed the composition and structure of intestinal content microflora in male P. nigromaculatus compared to control groups. At the phylum level, Chlamydiae was only detected in the control group, and Actinobacteria, Bacteroidetes, Firmicutes, Fusobacteria, and Proteobacteria were the dominant microflora in the atrazine treatment groups. At the genus level, the abundance of Lactobacillus and Weissella significantly increased in atrazine treatment groups compared to control groups. This study can provide a new framework based on movement behavior and intestinal microbiota to evaluate the response of amphibians to short-term exposure to environmental pollution.

Cardiotoxicity in African clawed frog (Xenopus laevis) sub-chronically exposed to environmentally relevant atrazine concentrations: Implications for species survival

The toxic effects of different atrazine concentrations on tadpoles and adult male African clawed frogs (Xenopus laevis) were assessed in a controlled laboratory environment following 90 days' exposure. The aim was to elucidate the danger of atrazine exposure on the cardiac tissue relative to its critical function of rhythmic contractility, fundamental for optimal blood circulation and homeostasis. Tadpoles and adult frogs were exposed to 0 μg/L (control), 0.01 μg L^-1, 200 μg L^-1 and 500 μg L^-1 concentrations of atrazine for 90 days. Mortality was concenration-dependent and significantly increased in juvenile group (77%, 43%, 23% and 0 respectively for 500 μg L^-1, 200 μg L^-1, 0.01 μg L^-1, and control group). While the mean juvenile heart area decreased concentration-dependently, adult frog mean heart area significantly increased in the 200 μg L^-1 group only and mean heart weight change was variable across all exposure levels. Light microscopy of hematoxylin and eosin (H&E) and Mallory-Heidenhain rapid one-step staining techniques on cardiac tissue sections of the juvenile and adult frogs revealed shrinkage of cardiac muscle cells into thin wavy myocytes. Additionally, disorganized branching of muscle fibres with reduced striations were observed in 0.01 μg L^-1 and 200 μg L^-1 but hypertrophied myocytes, thickened intensely staining myofibrils in the 500 μg L^-1 group in juvenile and adult frogs. Significant increase in the mean percentage area of connective tissue in all the treated groups (p < 0.036) were also recorded. Immunohistochemistry analysis showed decreased eNOS localization in cardiac tissue in 200 μg L^-1 and 500 μg L^-1 of both juvenile and adult group, suggestive of decreased cardiac contractility due to atrazine exposure. The results indicate that environmentally relevant atrazine concentrations cause significant mortality in tadpoles while concentrations ≥200 μg L^-1 adversely affect cardiac muscle morphology and may induce functional perturbations in cardiac tissue contractility and consequent dysfunction which generally may have an adverse impact on their survival and longevity.

Atrazine-induced changes in the myocardial structure of peripubertal rats

The aim of the present study was to investigate the effect of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine) on the left ventricle myocardium in juvenile/peripubertal male Wistar rats. Atrazine was administered orally at 50 or 200 mg/kg of body weight dose for 28 consecutive days. In order to assess possible structural alterations, tissue sections were examined histologically and then subjected to quantification analysis using stereological methods. The tissue specimens were routinely processed and stained with Mallory trichrome method in order to clearly distinguish muscle cells from the connective tissue components. A toluidine blue staining method was additionally used for the demonstration of mast cells. Statistically significant increase in length density and numerical density of capillaries were found at both the investigated doses of atrazine compared with the control. The increase in surface density and volume density of capillaries found at lower dosage of atrazine was significant in comparison with the control. The extensive mast cell degranulation was noted on the histological examination at both doses of the applied chemical. No significant changes were demonstrated for the stereological parameters of cardiomyocytes. Based on the available published data and the present results, it can be concluded that atrazine promoted angiogenesis in the rat myocardium, which might be partially mediated by mast cells.

Alterations in jejunal morphology and serotonin-containing enteroendocrine cells in peripubertal male rats associated with subchronic atrazine exposure

The effect of atrazine on jejunum was investigated by histopathological examination and quantification analysis related to the morphological parameters of the jejunum. The experiment was performed on male Wistar rats from postnatal day 23-51. Atrazine was administered by gavage daily to one group of rats at 50 mg/kg of body weight (bw) dose, to the second at 200 mg/kg bw while the third group was the control. At the end of the experiments after 28 days of treatment, tissue samples were routinely processed and stained with haematoxylin eosin. Additionally, the histochemical staining with periodic acid Schiff-alcian blue was used to demonstrate goblet cells and the immunohistochemistry protocol for serotonin-containing enteroendocrine cells. A significant decrease in the height of epithelial cells covering the intestinal villi, the villus height to total mucosa thickness ratio and the villus height to crypt depth ratio was found at both doses of atrazine. The crypt depth, total mucosa thickness and the thickness of tunica muscularis were significantly increased by the high dose of atrazine only. The number of serotonin-positive endocrine cells significantly decreased in rats treated with the low dose of atrazine. Overall, these results suggest the alterations in intestinal absorption and support the role of atrazine as an endocrine-disrupting compound.

A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians

OBJECTIVE

The biological effects of the herbicide atrazine on freshwater vertebrates are highly controversial. In an effort to resolve the controversy, we conducted a qualitative meta-analysis on the effects of ecologically relevant atrazine concentrations on amphibian and fish survival, behavior, metamorphic traits, infections, and immune, endocrine, and reproductive systems.

DATA SOURCES

We used published, peer-reviewed research and applied strict quality criteria for inclusion of studies in the meta-analysis.

DATA SYNTHESIS

We found little evidence that atrazine consistently caused direct mortality of fish or amphibians, but we found evidence that it can have indirect and sublethal effects. The relationship between atrazine concentration and timing of amphibian metamorphosis was regularly nonmonotonic, indicating that atrazine can both accelerate and delay metamorphosis. Atrazine reduced size at or near metamorphosis in 15 of 17 studies and 14 of 14 species. Atrazine elevated amphibian and fish activity in 12 of 13 studies, reduced antipredator behaviors in 6 of 7 studies, and reduced olfactory abilities for fish but not for amphibians. Atrazine was associated with a reduction in 33 of 43 immune function end points and with an increase in 13 of 16 infection end points. Atrazine altered at least one aspect of gonadal morphology in 7 of 10 studies and consistently affected gonadal function, altering spermatogenesis in 2 of 2 studies and sex hormone concentrations in 6 of 7 studies. Atrazine did not affect vitellogenin in 5 studies and increased aromatase in only 1 of 6 studies. Effects of atrazine on fish and amphibian reproductive success, sex ratios, gene frequencies, populations, and communities remain uncertain.

CONCLUSIONS

Although there is much left to learn about the effects of atrazine, we identified several consistent effects of atrazine that must be weighed against any of its benefits and the costs and benefits of alternatives to atrazine use.