Developmental and interactive effects of arsenic and chromium to developing Ambystoma maculatum embryos: Toxicity, teratogenicity, and whole-body concentrations

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.

Effects of acute arsenic exposure in two different populations of Hyalella curvispina amphipods from North Patagonia Argentina

Arsenic (As) is a toxic metalloid present in high levels in diverse regions of Argentina. The aim of this study was to determine acute As-mediated toxicity in two different populations of autochthonous Hyalella curvispina amphipods from a reference site (LB) and an agricultural one (FO) within North Patagonia Argentina. Previously, both populations exhibited significant differences in pesticide susceptibility. Lab assays were performed to determine acute lethal concentrations, as well as some biochemical parameters. Lethal concentration (LC₅₀) values obtained after 48 and 96 hr As exposure were not significantly different between these populations, although FO amphipods appeared slightly less susceptible. LC₅₀-48 hr values were 3.33 and 3.92 mg/L As, while LC₅₀-96 hr values were 1.76 and 2.14 mg/L As for LB and FO amphipods. The no observed effect concentration (NOEC) values were 0.5 mg/L As. Cholinesterase (ChE) activity was significantly diminished by As acute exposure (0.5-1.5 mg/L As), indicative of a significant neurotoxic action for this metalloid in both amphipod populations. Activities of catalase (CAT) and glutathione S-transferase (GST) and levels of reduced glutathione (GSH) were differentially altered following As exposure. CAT activity was increased after 96 hr As exposure. GST activity and GSH levels were significantly elevated followed by either a decrease or a return to control values after 96 hr treatment. However, additional studies are necessary to understand the mechanisms underlying the As-mediated oxidative effects in H. curvispina. Our findings suggest that measurement of ChE activity in H. curvispina amphipods might serve as a useful biomarker of As exposure and effect.

Inhibition of Metamorphosis, Thyroid Gland, and Skeletal Ossification Induced by Hexavalent Chromium in Bufo gargarizans Larvae

Hexavalent chromium (Cr [VI]) is one of the major detrimental heavy metal pollutants. In the present study, Bufo gargarizans were exposed to 0, 52, 104, 208, and 416 μg/L Cr (VI) from Gosner stage 2 until metamorphosis; and growth, development, and histological characteristics of the thyroid gland and skeletal ossification were examined. The results demonstrated that the survival rate of larvae exposed to Cr (VI) was not different from that measured in animals from the control group. However, high levels of Cr (VI) (104, 208, and 416 μg/L) were associated with significantly delayed growth and development. The suppression of skeletal ossification was observed at high Cr (VI) levels. Besides, histological alterations of the thyroid gland, such as follicular cell hyperplasia, colloid depletion, and peripheral colloid vacuolation, were found in 52 to 416 μg/L Cr (VI) treatments. The results of the present study highlight reductions in growth and development as well as percent metamorphosis and skeletal ossification due to histological alteration of the thyroid gland during exposure to Cr (VI) in B. gargarizans larvae. The present investigation could provide a basis for understanding the detrimental effects of Cr (VI) in amphibian larvae. Environ Toxicol Chem 2021;40:2474-2483. © 2021 SETAC.

Monitoring of toxicity of As(V) solutions by AMPHITOX test without and with treatment with zerovalent iron nanoparticles

Changes in toxicity of As(V) solutions from acute to chronic exposure have been evaluated by the AMPHITOX test. This test employs Rhinella arenarum, a widely distributed toad in Argentine areas. LOEC values were 6.37 and 1.88 mg L^-1 for embryos and larvae, respectively, and serious sublethal effects have been observed. Toxicity of As(V) solutions has been also evaluated after treatment with zerovalent iron nanoparticles (nZVI). After 60 min of treatment with nZVI, As(V) removal was 77%, and neither lethal nor sublethal effects were observed. However, nZVI had to be eliminated before the bioassay because they caused adverse effects in both embryos and larvae. This work highlights the high sensitivity of R. arenarum to As(V), the relevance to assess toxicity on different periods of the lifecycle, and the need to expand exposure to As(V) to chronic times. The utility of the test for monitoring toxicity changes in As(V) solutions after nZVI treatment has been also shown.

Natural tissue concentrations in adult Ambystoma maculatum and larval DNA damage from exposure to arsenic and chromium

Arsenic (As) and chromium (Cr) are two contaminants that are detected in aquatic and terrestrial habitats. Using the spotted salamander, Ambystoma maculatum, to assess impacts from these contaminants may be advantageous as adults live and breed in such environments. Adult amphibians typically exhibit elevated tissue concentrations of contaminants present in their environment, while larval stages were found to exhibit increased sensitivity to pollutants. From January through March of 2015, during the spring breeding season, 5 adults and approximately 32 egg masses were collected from a local breeding site. Field levels of As and Cr ranged from 5.99 to 8.88 µg/L and 1.45 to 2 µg/L, respectively, while mean adult As tissue concentrations were 56.74 µg/g dry weight for heart, 0.92 µg/g for liver, and 1.21 µg/g for tail tissue. Mean tissue concentrations for Cr were 87.64 µg/g for heart, 1.47 µg/g for liver, and 6.92 µg/g for tail. Developing larvae that were collected from the field and exposed in a lab setting for 12 d to 0.2 or 20 mg/L of either As or Cr displayed little DNA damage attributed to As, but marked damage due to exposure to 20 mg/L Cr when assessed using the comet assay. Exposure to a mixture of either 0.25:0.1 or 25:10 mg/L As and Cr resulted in significant DNA damage at the lower concentration of 0.25:0.1 mg/L. As adult spotted salamanders were found to possess high concentrations of these contaminants in cardiac tissue, and larvae were shown to be susceptible to DNA damage from increased exposures, assessing impacts and potential declines of amphibian populations exposed to As and Cr is needed.

Neuroendocrine disruption of organizational and activational hormone programming in poikilothermic vertebrates

In vertebrates, sexual differentiation of the reproductive system and brain is tightly orchestrated by organizational and activational effects of endogenous hormones. In mammals and birds, the organizational period is typified by a surge of sex hormones during differentiation of specific neural circuits; whereas activational effects are dependent upon later increases in these same hormones at sexual maturation. Depending on the reproductive organ or brain region, initial programming events may be modulated by androgens or require conversion of androgens to estrogens. The prevailing notion based upon findings in mammalian models is that male brain is sculpted to undergo masculinization and defeminization. In absence of these responses, the female brain develops. While timing of organizational and activational events vary across taxa, there are shared features. Further, exposure of different animal models to environmental chemicals such as xenoestrogens such as bisphenol A-BPA and ethinylestradiol-EE2, gestagens, and thyroid hormone disruptors, broadly classified as neuroendocrine disrupting chemicals (NED), during these critical periods may result in similar alterations in brain structure, function, and consequently, behaviors. Organizational effects of neuroendocrine systems in mammals and birds appear to be permanent, whereas teleost fish neuroendocrine systems exhibit plasticity. While there are fewer NED studies in amphibians and reptiles, data suggest that NED disrupt normal organizational-activational effects of endogenous hormones, although it remains to be determined if these disturbances are reversible. The aim of this review is to examine how various environmental chemicals may interrupt normal organizational and activational events in poikilothermic vertebrates. By altering such processes, these chemicals may affect reproductive health of an animal and result in compromised populations and ecosystem-level effects.