Acute toxicity of inorganic nitrogen (ammonium, nitrate and nitrite) to tadpoles of five tropical amphibian species

Lack of glucocorticoid flexibility is indicative of wear-and-tear in Hyla versicolor tadpoles 2 from agricultural environments

In habitats where stressors are frequent or persistent, it can become increasingly difficult for wildlife to appropriately match their endocrine responses to these more challenging environments. The dynamic regulation of glucocorticoid (GC) hormones plays a crucial role in determining how well individuals cope with environmental changes. Amphibians exposed to agricultural stressors can dampen aspects of their GC profile (baseline, agitation, recovery, stress responsiveness, and negative feedback) to cope in these stressful environments, but this dampening can lead to reductions in an individual's reactive scope and a loss of endocrine flexibility. Organic agriculture could potentially limit some of these effects, however, little is known about how amphibians respond physiologically to organic agricultural environments. We compared GC profiles of Hyla versicolor tadpoles from three treatments: natural ponds (<5% agriculture within 500m), ponds near organic farms, and ponds near conventional farms. We hypothesized that tadpoles would cope with agricultural habitats by dampening stress responsiveness and exhibiting more efficient negative feedback and that the magnitude of these changes in response would differ based on agricultural method. We found that tadpoles from conventional and organic ponds were less likely to downregulate GCs via negative feedback after stressor exposure than tadpoles from natural ponds. For agricultural tadpoles that did downregulate GCs after the stressor, we found lower stress responsiveness and faster downregulation to baseline corticosterone than tadpoles from natural ponds. These results point to an accumulation of wear-and-tear, leading to an overall reduction in reactive scope and limited GC flexibility in our agricultural tadpoles. Regardless of agricultural method used, agricultural tadpoles exhibited the same patterns of GC response, indicating that current efforts to incentivize farmers to switch to organic farming methods may not be sufficient to address negative agricultural impacts on amphibians.

Fungicides from rice cultivation (tebuconazole and azoxystrobin) alters biochemical and histological markers of hammertoad tadpoles (Boanafaber)

Tebuconazole (TBZ) and azoxystrobin (AZX) are fungicides frequently used in rice cultivation. Despite protecting crops against fungal diseases, these compounds can contaminate the natural environments close to the crops, exerting negative effects on non-target organisms, the present study aimed to characterize the contamination by fungicides of a river that flows in an area dominated by rice cultivation in the north of the state of Santa Catarina, SC, Brazil. Concentrations of TBZ and AZX found in the field were used to evaluate their negative effects on development, biochemical biomarkers and histopatology of the liver of a native tadpole species, the hammerfrog (Boana faber). Tadpoles were exposed for 16 days to the lowest (1.20 μg/L) and highest (2.60 μg/L) concentration of TBZ, lowest (0.70 μg/L) and highest (1.60 μg/L) concentration of AZX, and the mix of both fungicides at lowest and highest concentration of each found in field analyses. Exposure to the lower TBZ concentration and both concentrations of the Mix accelerated the development of tadpoles. AZX caused an increase in the activities of glutathione S-transferase (GST), carboxylesterase (CbE) and glucose-6-phosphate dehydrogenase (G6PDH) in the liver, an increase in the levels of protein carbonyls (PC) in the liver and an increase in the activity of acetylcholinesterase (AChE) in muscle of tadpoles. TBZ, on the other hand, generated an increase in GST, G6PDH, PC and histopathological severity scores in liver and in muscle AChE activity. The effects were more intense in the groups exposed to the Mix of contaminants. No treatment altered brain AChE. The data showed that the fungicides from in rice cultivation found in natural aquatic environments around the crops pose risks to the health of the animals, compromising their metabolism and development.

Rice Fields as Important Habitats for Three Anuran Species-Significance and Implications for Conservation

Agriculture can have different effects on wildlife depending on land-use type and extensive/intensive practices. The aim of this study was to establish the significance of rice fields in Central Bulgaria as anuran habitats. We used Audiomoth acoustic loggers to record calling activity at three sites near the city of Plovdiv-one shallow pond and two rice fields-from June to September in 2022 and 2023. We registered the three most widespread species in the region-Bufotes viridis, Hyla orientalis and Pelophylax ridibundus-and created pattern-matching models for them using the free web interface Arbimon, which enabled us to perform presence/absence counts and abundance estimates. At the beginning and the end of the rice vegetation period, water samples were collected and analysed for 62 substances. Substance concentrations were compared between ponds and with LC50 data from the available literature. We registered 19 and 21 substances in 2022 and 2023, respectively, with concentrations within the accepted limits, and although some metals were near risk levels, this was not reflected in the presence counts or the abundance estimates. The results indicated that frog activity was not related to any of the registered substances, but that it was positively correlated with daily rainfall and was higher in the rice fields.

Ammonium effects on oxidative stress, telomere length, and locomotion across life stages of an anuran from habitats with contrasting land-use histories

Understanding the mechanistic implications behind wildlife responses to global changes is a central topic in eco-evolutionary research. In particular, anthropic pollution is known to impact wild populations across the globe, which may have even stronger consequences for species with complex life cycles. Among vertebrates, amphibians represent a paradigmatic example of metamorphosis, and their characteristics make them highly vulnerable to pollution. Here, we tested for differences in the redox status, telomere length, and locomotor performance across life stages of green frogs (Pelophylax perezi) from agrosystem and natural habitats, both constitutively and in response to an experimental ammonium exposure (10 mg/L). We found that larvae from the agrosystem constitutively showed an enhanced redox status (better antioxidant balance against H₂O₂, lower lipid peroxidation) but shorter telomeres as compared to larvae from the natural environment. The larval redox response to ammonium was, overall, similar in both habitats. In contrast, after metamorphosis, the redox status of individuals from the natural habitat seemed to cope better with ammonium exposure (denoted by lower lipid peroxidation), and differences between habitats in telomere length were no longer present. Intriguingly, while the swimming performance of larvae did not correlate with individual's physiology, metamorphs with lower glutathione reductase activity and longer telomeres had a better jumping performance. This may suggest that locomotor performance is both traded off with the production of reactive oxygen species and potentiated directly by longer telomeres or indirectly by the mechanisms that buffer their shortening. Overall, our study suggests that contrasting land-use histories can drive divergence in physiological pathways linked to individual health and lifespan. Since this pattern was life-stage dependent, divergent habitat conditions can have contrasting implications across the ontogenetic development of species with complex life cycles.

Combined effects of landscape composition and agrochemicals on frog communities amid sugarcane-dominated agroecosystems

Global demand for crops will continue increasing over the next few decades to cover both food and biofuel needs. This demand will put further pressure to expand arable land and replace natural habitats. However, we are only beginning to understand the combined effects of agrochemicals and land-use change on tropical freshwater biodiversity. In this study, we analyzed how pond-dwelling anuran larvae responded to pond characteristics, landscape composition, and agrochemical contamination in a sugarcane-dominated agroecosystem in Brazil. Then we used an information theoretical approach with generalized linear models to relate species richness and abundance to predictor variables. The variation in tadpole abundance was associated with both agrochemical concentration (e.g., ametryn, diuron, and malathion) and landscape variables (e.g., percentage of forest, percentage of agriculture, and distance to closest forest). The relationship between species abundance and agrochemicals was species-specific. For example, the abundances of Scinax fuscovarius and Physalaemus nattereri were negatively associated with ametryn, and Dendropsophus nanus was negatively associated with tebuthiuron, whereas that of Leptodactylus fuscus was positively associated with malathion. Conversely, species richness was associated with distance to forest fragments and aquatic vegetation heterogeneity, but not agrochemicals. Although we were unable to assign a specific mechanism to the variation in tadpole abundance based on field observations, the lower abundance of three species in ponds with high concentrations of agrochemicals suggest they negatively impact some frog species inhabiting agroecosystems. We recommend conserving ponds near forest fragments, with abundant stratified vegetation, and far from agrochemical runoffs to safeguard more sensitive pond-breeding species.

Enhanced removal of ammonia in Fe(VI)/Br- oxidation system: Kinetics, transformation mechanism and theoretical calculations

This work systematically examined the capability of ferrate (Fe(VI)) for ammonia oxidation, revealing for the first time that bromide ions (Br^-) played an important role in promoting the removal of ammonia in Fe(VI) system. In the presence of 10.0 mM Br^-, the removal efficiency of ammonia was nearly 3.4 times that of the control, and 1.0 mM ammonia was almost completely removed after two rounds addition of 1.0 mM Fe(VI) in 60 min. PMSO probe test, electron paramagnetic resonance spectra and radical quenching experiments were employed to interpret the underlying promotion mechanism of Br^-, and it was proposed that the formation of active bromine (HOBr/OBr^-) played a dominant role in the enhanced oxidative removal of ammonia by Fe(VI). Further kinetic model simulations revealed that HOBr/OBr^- and Fe(VI) were the two major reactive species in Fe(VI)/Br^- system, accounting for 66.7% and 33.0% of ammonia removal, respectively. As the target contaminant, ammonia could quickly consume the generated HOBr/OBr^-, thereby suppressing the formation of brominated disinfection byproducts. Finally, NO₃^- was identified as the dominant transformation product of ammonia, and density functional theory (DFT) calculations revealed that six reaction stages were involved in ammonia oxidation with the first step as the rate-limiting step. This work would enable the full use of coexisting bromides for effective removal of ammonia from natural waters or wastewaters by in situ Fe(VI) oxidation method.

Carryover effects of chronic exposure to ammonium during the larval stage on post-metamorphic frogs

Water contamination poses an important challenge to aquatic fauna, including well-documented effects on amphibian larvae. However, little is known about how contamination during the larval stages may affect post-metamorphic phases, or whether resistance may have evolved in some populations. In this work, we tested the hypothesis that chronic exposure to ammonium (a common contaminant in agroecosystems with confirmed effects on anuran tadpoles) during the larval stage of Pelophylax perezi frogs would affect growth and locomotor performance of metamorph, juvenile, subadult and adult stages. We also predicted that the effects of ammonium would be milder in offspring originated from parental agroecosystem frogs than those originating from forests. We compared tadpoles from both habitats either reared in untreated water or chronically exposed to ammonium. We found that exposure to ammonium during the larval stage inflicted effects on morphology (different measures of body size) and swimming speed after metamorphosis until adulthood. However, these effects were not always consistent through post-metamorphic stages and the effects differed as a function of treatment and habitat. In adults, body size and condition were greater in non-ammonium and ammonium exposed individuals, respectively. These differences were not detectable in metamorphs, for which only ammonium-exposed individuals from agroecosystem showed reduced body size in intermediate post-metamorphic stages. In turn, treatment reduced jumping distance only in agroecosystem adults, subadults and juveniles, which was opposite to the trend observed just after metamorphosis. These changes of patterns throughout the ontogeny of P. perezi could be due to processes such as compensatory growth, delayed energy costs derived from it, or early sexual differences that could be present even before they can be accounted for. In summary, this study suggests that exposure to ammonium during larval stages can result in diverse biological and long-term outcomes in later life stages.

Direct and indirect effects of chronic exposure to ammonium on anuran larvae survivorship, morphology, and swimming speed

Several constituents of the current global change are usually deemed accountable for the worldwide declines of amphibian populations. Among these, water contamination poses a major threat, especially to larval stages, which are unable to escape a polluted water body. This problem is remarkable in agrosystems, one of the main sources of water pollution and whose area is forecasted to increase in the forthcoming decades. However, pollutants represent a selective pressure that may result in tolerance in affected areas. In this work, we tested whether chronic exposure to a sublethal concentration of ammonium (10 mg/L), one of the most frequent agrochemicals, affects differently hatching success, survivorship, morphology and swimming performance of Pelophylax perezi tadpoles from agrosystem and pine grove habitats. Ammonium diminished survivorship at the earliest stages after hatching. Thus, lower density was a by-product of exposure to ammonium. Higher density slowed down development, reduced snout-vent length, and had a sharper negative effect on body mass and tail length and depth of ammonium treated individuals with respect to the control. In turn, ammonium accelerated development and increased body mass, SVL, and tail length and depth. These effects did not depend on provenance habitat. However, only pine grove tadpoles' swimming speed was negatively affected by ammonium, which supports the hypothesis that agrosystem tadpoles are more tolerant to ammonium. Finally, corroborating previous findings, tadpoles with larger bodies and tails were faster swimmers, whereas proportionally more massive individuals were slower, and tail depth was unrelated to swimming speed.

Morphological, behavioral and genotoxic effects of glyphosate and 2,4-D mixture in tadpoles of two native species of South American amphibians

Pesticide contamination is an important factor in the global decline of amphibians. The herbicides glyphosate and 2,4-D are the most applied worldwide. These herbicides are often found in surface waters close to agricultural areas. This study aims at evaluating the chronic effects caused by glyphosate + 2,4-D mixture in Boana faber and Leptodactylus latrans tadpoles. The combined solution of the glyphosate and 2,4-D, in 5 different concentrations, was applied for 168 h. Herbicide mixtures did not affect the survival of the exposed tadpoles but growth and swimming activity were altered; besides causing several damages in the mouth and intestine. The erythrocytes showed micronuclei and other nuclear abnormalities. There is an ecological risk in the exposure of tadpoles of B. faber and L. latrans from the mixture of glyphosate + 2,4-D. Therefore, the approach used in this study provides important information on how commonly used pesticides can affect non-target organisms.

Ammonium nitrate is a risk for environment: A case study of Beirut (Lebanon) chemical explosion and the effects on environment

An attempt has been made in correspondence to explain the consequences of chemical pollution after the explosion of ammonium nitrate (AN) in Beirut (capital of Lebanon). The effects of chemicals in the air, soil, and water have been discussed. In addition, the study emphasizes on the research to restore the environment and enhanced safety measurements.