Biomarker analysis of American toad (Anaxyrus americanus) and grey tree frog (Hyla versicolor) tadpoles following exposure to atrazine

Atrazine contaminated sites and bullfrog tadpoles: evasive trends and biochemical consequences

Atrazine (ATZ) is one of the most used active principles in agricultural systems. This pesticide has the ability to easily accumulate in terrestrial and aquatic environments, causing impacts with chronic adverse effects. Avoidance tests are tests that seek to assess the concentration from which a given organism escapes, that is, migrates to another habitat. They are being used as a modality of innovative and minimally invasive ecotoxicological tests. Our objective was to evaluate the sensitivity and possible toxic effects of ATZ in bullfrog tadpoles (Lithobates catesbeianus), through avoidance tests and oxidative stress analyses. We performed the behavioral avoidance test lasting 12 h, with observations every 60 min in a linear multi-compartment system with seven compartments. Each compartment corresponded to a concentration: negative control, 1, 2, 20, 200, 2000, 20,000 µg L^-1. After the selection of habitat, organisms were forcedly maintained in the chosen concentrations for 48 h and then, metabolic effects were measured assessing the blood plasma amino acid profile and liver protein degradation. We also determined the effective concentrations of ATZ tested at 0 h and 48 h. The results showed that there was an effect of the treatment on the distribution of tadpoles, but not on the hours or on the combined effect (interaction). The biochemical analyses also showed a concentration-dependent relationship which caused significant toxic effects even in a short period of time. In conclusion, these frogs were able to avoid places with high concentrations of ATZ in the first hours of exposure, which suggests that in the natural environment these animals can migrate or avoid areas contaminated by this herbicide; however, depending on the selected concentration, serious biochemical consequences can occur.

Combined transcriptome and metabolite profiling analyses provide insights into the chronic toxicity of carbaryl and acetamiprid to Apis mellifera larvae

Despite many studies have revealed that developing honey bee (Apis mellifera) larvae are posting a high risk on exposure to insecticides, the toxicology information on bee larvae remain limited. The present study demonstrated the first assessment of the effects of no observed adverse effect concentration (NOAEC) of carbaryl (CR) and acetamiprid (ACE) on transcriptome and metabolome in honeybee larvae reared in vitro. Chronic exposure to carbaryl caused transcriptional disorders associated with oxidative stress. In addition, a series of metabolic homeostasis were disrupted by carbaryl stress, such amino acid metabolism, purine and pyrimidine metabolism and flavone and flavonol biosynthesis. The activities of enzymic biomarkers including GST, P450, CAT, AChE and SOD were not influenced by ACE stress, while the CR exposure slightly decreased the activity of CAT and SOD. Our results clearly show that ACE and CR display different potential to modulate transcriptome and metabolome associated with their different toxicity against bee larvae.

Differentiating metabolomic responses of amphibians to multiple stressors

One of the biggest challenges in ecological risk assessment is determining the impact of multiple stressors on individual organisms and populations in real world scenarios. Frequently, data derived from laboratory studies of single stressors are used to estimate risk parameters and do not adequately address scenarios where other stressors exist. Emerging 'omic technologies, notably metabolomics, provide an opportunity to address the uncertainties surrounding ecological risk assessment of multiple stressors. The objective of this study was to use metabolomic profiling to investigate the effect of multiple stressors on amphibian metamorphs. We exposed post-metamorphosis (180 days) southern leopard frogs (Lithobates sphenocephala) to the insecticide carbaryl (480 μg/L), predation stress, and a combined pesticide and predation stress treatment. Corticosterone analysis revealed mild support for an induction in response to predation stress alone but strongly suggests that carbaryl exposure, alone or in combination with predation cues, can significantly elevate this known biomarker in amphibians. Metabolomics analysis accurately classed, based on relative nearness, carbaryl and predation induced changes in the hepatic metabolome and biochemical fluxes appear to be associated with a similar biological response. Support vector machine analysis with recursive feature elimination of the acquired metabolomic spectra demonstrated 85-96% classification accuracy among control and all treatment groups when using the top 75 ranked retention time bins. Biochemical fluxes observed in the groups exposed to carbaryl, predation, and the combined treatment include amino acids, sugar derivatives, and purine nucleotides. Ultimately, this methodology could be used to interpret short-term toxicity assays and the presence of environmental stressors to overall metabolomic effects in non-target organisms.

Atrazine exposure and recovery alter the intestinal structure, bacterial composition and intestinal metabolites of male Pelophylax nigromaculatus

The pesticide atrazine poses a potential threat to the health of frogs living in farmland areas. The exposure concentration in traditional pesticide experiments is usually constant, while pesticide pollution in actual water may fluctuate due to periodic or seasonal application. We examined the effects of different concentrations of atrazine (50, 100 and 500 μg/L) over a 14-day exposure and a 7-day recovery on intestinal histology, bacterial composition and intestinal metabolites of male Pelophylax nigromaculatus. HE staining revealed that after a 14-day atrazine exposure, the 100 μg/L and 500 μg/L groups showed obvious cysts and significantly decreased intestinal crypt depth and villus height. After a 7-day recovery, the damaged intestine in the 100 μg/L group was partially recovered, while in the 500 μg/L exposure group there was no improvement. 16S rRNA gene analysis of intestinal bacteria showed that 500 μg/L atrazine exposure significantly caused a persistent decrease in bacterial α diversity. Compared to the control and other atrazine exposure groups, the 500 μg/L group showed significant changes in the relative abundance of predominant bacteria. In addition, most dominant bacteria in the 500 μg/L recovery group showed significant differences with the 50 μg/L and 100 μg/L recovery groups. Nontargeted metabolomics profiling based on UPLC/MS analysis showed that atrazine exposure and recovery induced changes in the intestinal metabolic profile. The changes in metabolites were mainly related to purine/pyrimidine metabolism, glycine, serine and threonine metabolism, and arginine and proline metabolism. In general, these pathways were closely related to energy metabolism and amino acid metabolism. These results suggest that the short-term exposure to 500 μg/L atrazine causes persistent harm to intestinal health. This study is an important step toward a better understanding of the toxic effects of atrazine exposure and recovery in frog intestines.

An NMR-based metabolomics study on sea anemones Exaiptasia diaphana (Rapp, 1829) with atrazine exposure

Sea anemones have been recommended as critical bioindicators for marine environmental stressors; however, the understanding of the biological effects in response to sublethal pollutant exposure is still limited. In this study, NMR-based metabolomics was performed to investigate the effects of atrazine on Exaiptasia diaphana with concentrations ranging from 3 to 90 ppb. As a result, the metabolic profiling of E. diaphana was significantly affected after 70 ppb treatment while a partial perturbation was observed as early as 3 ppb treatment. Glutamate was significantly changed at low atrazine concentrations with increased upregulation in concentrated atrazine experiments which is a potential biomarker for E. diaphana exposed to atrazine stressors. The TCA intermediates succinate and malate as well as the TCA cycle-related metabolites such as alanine, glycine, and taurine downregulated after atrazine treatment which also indicated the lower energy supply of E. diaphana. In summary, our study demonstrated that significant metabolic level perturbation could be detected at low atrazine concentrations before a physical change could be observed, and glutamate or the nitrogen metabolism may be the initial target for sea anemones by atrazine. The study may provide pioneering results for using E. diaphana to predict the impacts of exposure to atrazine toxin in marine systems.

Route of exposure influences pesticide body burden and the hepatic metabolome in post-metamorphic leopard frogs

Pesticides are being applied at a greater extent than in the past. Once pesticides enter the ecosystem, many environmental factors can influence their residence time. These interactions can result in processes such as translocation, environmental degradation, and metabolic activation facilitating exposure to target and non-target species. Most anurans start off their life cycle in aquatic environments and then transition into terrestrial habitats. Their time in the aquatic environment is generally short; however, many important developmental stages occur during this tenure. Post-metamorphosis, most species spend many years on land but migrate back to the aquatic environment for breeding. Due to the importance of both the aquatic and terrestrial environments to the life stages of amphibians, we investigated how the route of exposure (i.e., uptake from contaminated soils vs. uptake from contaminated surface water) influences pesticide bioavailability and body burden for four pesticides (bifenthrin (BIF), chlorpyrifos (CPF), glyphosate (GLY), and trifloxystrobin (TFS)) as well as the impact on the hepatic metabolome of adult leopard frogs (Gosner stage 46 with 60-90 days post-metamorphosis). Body burden concentrations for amphibians exposed in water were significantly higher (ANOVA p < 0.0001) compared to amphibians exposed to contaminated soil across all pesticides studied. Out of 80 metabolites that were putatively identified, the majority expressed a higher abundance in amphibians that were exposed in pesticide contaminated water compared to soil. Ultimately, this research will help fill regulatory data gaps, aid in the creation of more accurate amphibian dermal uptake models and inform continued ecological risk assessment efforts.

Non-targeted metabolomic profiling of atrazine in Caenorhabditis elegans using UHPLC-QE Orbitrap/MS

The widespread use of the herbicides Atrazine (ATR) has been raised attention due to its ubiquitous occurrence in the environment. As an endocrine disruptor, ATR causes reproductive, immune, nervous system toxicity in biota. In this study, we aimed to investigate metabolic profile characteristics and potential metabolic biomarker that reflects specific damage in toxic effect after ATR exposure. Hence, a metabolomics study was performed to determine the significantly affected metabolites and the reproduction and locomotion of C. elegans were investigated. Mediation analysis was used to evaluate the mediating effect of metabolites on association between ATR exposure and toxic effect. ATR (≥0.04 mg/L) caused the significant dose dependent reduction of brood size and locomotion behavior, however, the body length and width were significantly decreased only in 40 mg/L group. These results suggesting that brood size, head thrashes and body bends are more sensitive indictor to assessment ATR toxicity in C. elegans. Meanwhile, metabolomics analysis revealed that ATR exposure can induce metabolic profiles significant alterations in C. elegans. We found that 9 metabolites significantly increased and 18 metabolites significantly decreased, such as phosphatidylcholine, GMP, CDP-choline, neopterin etc. Those alteration of metabolites were mainly involved in the pathways: glycerophospholipid metabolism, glycolysis/gluconeogenesis, folate biosynthesis, glycine, serine and threoninemetabolism, pyrimidine and purine metabolism. Overall, these changes are signs of possible oxidative stress and ATP synthesis disruption modification. Mediation analysis showed a significant indirect effect of ATR exposure on brood size, via 7,8-dihydroneopterin 2',3'-cyclic-p, and phosphatidylcholine might mediate association between ATR exposure and body bends, suggesting that 7,8-dihydroneopterin 2',3'-cyclic-p and phosphatidylcholine might be potentially specificity marker for brood size and body bend respectively. This preliminary analysis investigates metabolic characteristics in C. elegans after ATR exposure, helping to understand the pathways involved in the response to ATR exposure and provide potential biomarkers for the safety evaluation of ATR.

Cross-Taxa Distinctions in Mechanisms of Developmental Effects for Aquatic Species Exposed to Trifluralin

Standard ecological risk assessment practices often rely on larval and juvenile fish toxicity data as representative of the amphibian aquatic phase. Empirical evidence suggests that endpoints measured in fish early life stage tests are often sufficient to protect larval amphibians. However, the process of amphibian metamorphosis relies on endocrine cues that affect development and morphological restructuring and are not represented by these test endpoints. The present study compares developmental endpoints for zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis), 2 standard test species, exposed to the herbicide trifluralin throughout the larval period. Danio rerio were more sensitive and demonstrated a reduction in growth measurements with increasing trifluralin exposure. Size of X. laevis at metamorphosis was not correlated with exposure concentration; however, time to metamorphosis was delayed relative to trifluralin concentration. Gene expression patterns indicate discrepancies in response by D. rerio and X. laevis, and dose-dependent metabolic activity suggests that trifluralin exposure perturbed biological pathways differently within the 2 species. Although many metabolites were correlated with exposure concentration in D. rerio, nontargeted hepatic metabolomics identified a subset of metabolites that exhibited a nonmonotonic response to trifluralin exposure in X. laevis. Linking taxonomic distinctions in cellular-level response with ecologically relevant endpoints will refine assumptions used in interspecies extrapolation of standard test effects and improve assessment of sublethal impacts on amphibian populations. Environ Toxicol Chem 2020;39:1797-1812. Published 2020. This article is a US government work and is in the public domain in the USA.

An overview of the potential impacts of atrazine in aquatic environments: Perspectives for tailored solutions based on nanotechnology

Atrazine is a pre- and post-emergence herbicide used to control weeds in many crops. It was introduced in the late 1950s, but its use has been controversial because of its high potential for environmental contamination. In agriculture, the implementation of sustainable practices can help in reducing the adverse effects atrazine. This review addresses aspects related to the impacts of atrazine in the environment, with focus on its effects on aquatic species, as well as the potential use of nanoencapsulation to decrease the impacts of atrazine. The application of atrazine leads to its dispersal beyond the immediate area, with possible contamination of soils, sediments, plantations, pastures, public supply reservoirs, groundwater, streams, lakes, rivers, seas, and even glaciers. In aquatic ecosystems, atrazine can alter the biota, consequently interfering in the food chains of many species, including benthic organisms. Nanoformulations loaded with atrazine have been developed as a way to reduce the adverse impacts of this herbicide in aquatic and terrestrial ecosystems. Ecotoxicological bioassays have shown that this nanoformulations can improve the targeted delivery of the active ingredient, resulting in decreased dosages to obtain the same effects as conventional formulations. However, more detailed analyses of the ecotoxicological potential of atrazine-based nanoherbicides need to be performed with representative species of different ecosystems.

Biomarkers at different levels of organisation after atrazine formulation (SIPTRAN 500SC®) exposure in Rhinella schineideri (Anura: Bufonidae) Neotropical tadpoles

Brazil is an important consumer of herbicides. In sugarcane cultivation-the country's most extensive agricultural crop-atrazine-based formulations are the principal form of weed control. Several studies have investigated adverse effects of atrazine or their formulations on anurans, but not specifically on Brazilian species. Our aim was therefore to investigate the lethal and sublethal effects of an atrazine-based herbicide in Rhinella schneideri tadpoles and, in particular, effects on the pigmentation system as a new endpoint in ecotoxicological studies. Rhinella schneideri tadpoles at the Gosner-30 stage were exposed to the atrazine-based herbicide formulation, SIPTRAN 500 SC^®, in acute bioassays at concentrations of 1.5-25 mg/L. The lethal and sublethal effects induced were analysed at different ecotoxicological levels: organismal level (alterations in behaviour, growth, development, and body mass; morphologic abnormalities), histological level (liver histopathology), the pigmentation system (melanomacrophages and dermal-melanophores), and cellular level (erythrocyte micronucleus formation and other nuclear-abnormalities). This herbicide induced sublethal effects at the organismal level with alterations in swimming and growth and morphologic abnormalities. These results demonstrated that, in anuran tadpoles, the atrazine-based agrochemical increased the frequency of micronucleus formation and other nuclear-abnormalities in erythrocytes and caused liver damage. In addition, we demonstrated for the first time effects of an atrazine-based formulation on the pigmentation system of anuran tadpoles, specifically an increase in the number of melanomacrophages and dermal melanophores. This study is the first to use several widely differing endpoints at different ecotoxicological levels in a comprehensive manner for assessment of the effects of environmental stressors in order to determine the health status of Neotropical anuran species. In doing so, this study establishes a foundation for future ecological assessments.

Endogenous and exogenous biomarker analysis in terrestrial phase amphibians (Lithobates sphenocephala) following dermal exposure to pesticide mixtures

Pesticide mixtures are frequently co-applied throughout an agricultural growing season to maximize crop yield. Therefore, non-target ecological species (e.g., amphibians) may be exposed to several pesticides at any given time on these agricultural landscapes. The objectives of this study were to quantify body burdens in terrestrial phase amphibians and translate perturbed metabolites to their corresponding biochemical pathways affected by exposure to pesticides as both singlets and in combination. Southern leopard frogs (Lithobates sphenocephala) were exposed either at maximum or 1/10^th maximum application rate to single, double, or triple pesticide mixtures of bifenthrin (insecticide), metolachlor (herbicide), and triadimefon (fungicide). Tissue concentrations demonstrate both facilitated and competitive uptake of pesticides when in mixtures. Metabolomic profiling of amphibian livers identified metabolites of interest for both application rates, however; magnitude of changes varied for the two exposure rates. Exposure to lower concentrations demonstrated down regulation in amino acids, potentially due to their being utilized for glutathione metabolism and/or increased energy demands. Amphibians exposed to the maximum application rate resulted in up regulation of amino acids and other key metabolites likely due to depleted energy resources. Coupling endogenous and exogenous biomarkers of pesticide exposure can be utilized to form vital links in an ecological risk assessment by relating internal dose to pathophysiological outcomes in non-target species.

Effect of hydration status on pesticide uptake in anurans following exposure to contaminated soils

In this study, the impact of hydration status on dermal uptake of pesticides in two species of amphibians is examined. Absorption of pesticides in anurans occurs primarily through a highly vascularized dermal seat patch; however, pesticides can also enter through the superficial dermis following exposure. Despite the growing body of literature on dermal exposure in amphibians, little is known on how hydration status influences uptake. Thus, the objective of this study was to investigate the influence of hydration status on absorption of pesticides (atrazine, triadimefon, metolachlor, chlorothalonil, and imidacloprid) in southern leopard frogs (Lithobates sphenocephala) and Fowler's toads (Anaxyrus fowleri). Amphibian treatments included dehydration periods of 0, 2, 4, 6, 8, or 10 h prior to exposure to pesticide-contaminated soils for 8 h. Following exposure, soil and whole-body homogenates were extracted and analyzed by LC-MS/MS. Dehydration time was then regressed against post-exposure concentrations to infer the impact of dehydration on dermal pesticide uptake. Increased dehydration time resulted in significantly lowered pesticide concentrations in both species (F_{6, 293} = 67.66, p = 0.007) for the five pesticides studied. This phenomenon could be due to an energy and/or dilution effect.

Robust volcano plot: identification of differential metabolites in the presence of outliers

BACKGROUND

The identification of differential metabolites in metabolomics is still a big challenge and plays a prominent role in metabolomics data analyses. Metabolomics datasets often contain outliers because of analytical, experimental, and biological ambiguity, but the currently available differential metabolite identification techniques are sensitive to outliers.

RESULTS

We propose a kernel weight based outlier-robust volcano plot for identifying differential metabolites from noisy metabolomics datasets. Two numerical experiments are used to evaluate the performance of the proposed technique against nine existing techniques, including the t-test and the Kruskal-Wallis test. Artificially generated data with outliers reveal that the proposed method results in a lower misclassification error rate and a greater area under the receiver operating characteristic curve compared with existing methods. An experimentally measured breast cancer dataset to which outliers were artificially added reveals that our proposed method produces only two non-overlapping differential metabolites whereas the other nine methods produced between seven and 57 non-overlapping differential metabolites.

CONCLUSION

Our data analyses show that the performance of the proposed differential metabolite identification technique is better than that of existing methods. Thus, the proposed method can contribute to analysis of metabolomics data with outliers. The R package and user manual of the proposed method are available at https://github.com/nishithkumarpaul/Rvolcano .