Mercury in aquatic ecosystems of two indigenous communities in the Piedmont Ecuadorian Amazon: evidence from fish, water, and sediments.

Mercury is a highly toxic element present in water, soil, air, and biota. Anthropogenic activities, such as burning fossil fuels, mining, and deforestation, contribute to the presence and mobilization of mercury between environmental compartments. Although current research on mercury pathways has advanced our understanding of the risks associated with human exposure, limited information exists for remote areas with high diversity of fauna, flora, and indigenous communities. This study aims to deepen our understanding of the presence of total mercury in water, sediments, and fish, within aquatic ecosystems of two indigenous territories: Gomataon (Waorani Nationality) and Sinangoé (Ai´Cofán Nationality) in the Ecuadorian Amazon. Our findings indicate that, for most fish (91.5%), sediment (100%) and water (95.3%) samples, mercury levels fall under international limits. For fish, no significant differences in mercury levels were detected between the two communities. However, eight species exceeded recommended global limits, and one surpassed the threshold according to Ecuadorian legislation. Piscivore and omnivore fish exhibited the highest concentrations of total mercury among trophic guilds. Only one water sample from each community's territory exceeded these limits. Total mercury in sediments exhibited greater concentrations in Gomataon than Sinangoé. Greater levels of mercury in sediments were associated with the occurrence of total organic carbon. Considering that members of the communities consume the analyzed fish, an interdisciplinary approach, including isotopic analysis, methylmercury sampling in humans, and mercury monitoring over time, is imperative for a detailed risk assessment of mercury exposure in Amazonian communities.

Machine Vision System for Automatic Adjustment of Optical Components in LED Modules for Automotive Lighting.

This paper presents a machine vision system that performs the automatic positioning of optical components in LED modules of automotive headlamps. The automatic adjustment of the module is a process of great interest at the industrial level, as it allows us to reduce reworks, increasing the company profits. We propose a machine vision system with a flexible hardware-software structure that allows it to adapt to a wide range of LED modules. Its hardware is composed of image-capturing devices, which enable us to obtain the LED module light pattern, and mechanisms for manipulating and holding the module to be adjusted. Its software design follows a component-based approach which allows us to increase the reusage of the code, decreasing the time required for configuring any type of LED module. To assess the efficiency and robustness of the industrial system, a series of tests, using three commercial models of LED modules, have been performed. In all cases, the automatically adjusted LED modules followed the ECE R112 regulation for automotive lighting.

Validating the occurrence of the giant mottled eel (Anguilla marmorata) in the Galápagos Islands.

The giant mottled eel (Anguilla marmorata) is distributed mostly in the Indo-West Pacific. However, a few records indicate the presence of this eel in the Tropical Central and East Pacific. In April 2019, an eel specimen was caught in a small stream in San Cristobal Island, Galápagos. Morphological and molecular characters (16S and Cytb mtDNA sequences) confirmed the species as A. marmorata Quoy & Gaimard, 1824. The re-discovery of A. marmorata in Galápagos supports the hypothesis of an eastward range expansion from the west, probably through the North Equatorial Counter-Current.

Relationship of 3 indexes of orthodontic treatment need used by Medicaid and oral health-related quality of life.

INTRODUCTION: This study aimed to assess the relationship between 3 indexes of orthodontic treatment need that are used by Medicaid, namely the Salzmann Index (SI), the handicapping labiolingual deviation (HLD) Index, and the HLD California Modification Index, and oral health-related quality of life (OHRQOL). METHODS: The orthodontic records of 100 participants aged 11-14 years were used to calculate occlusal index scores. The condition-specific oral impacts on daily performances (OIDP) index questionnaire was used to quantify OHRQOL and to identify detriments attributable to malocclusion-related conditions (MRCs). The relationship between occlusal index scores and OHRQOL was analyzed using descriptive statistics, Spearman rank-order and biserial correlations, and logistic regression. RESULTS: The mean index scores were: SI, 15.4; HLD, 13.2; and HLD California Modification, 15.8. Ninety percent of participants did not have normative orthodontic treatment need according to current index criteria. OIDP scores were not normally distributed, and the mean score was 3.1. Of those participants who reported an impact, 83% attributed at least 1 of those impacts to MRCs; however, 90% of these were of mild or moderate intensity. Smiling was the performance most impacted by MRCs. The only statistically significant correlation between an occlusal index and OIDP scores was for the SI, though this association was weak (r = 0.27). None of the variables used in the logistic regression model (age, sex, 3 index scores) were significant predictors of OHRQOL. CONCLUSIONS: No meaningful association exists between the 3 indexes studied and OHRQOL. These findings challenge the validity of current systems for the allocation of Medicaid-funded orthodontic treatment.

Annual Research Review: Youth firearm violence disparities in the United States and implications for prevention.

OBJECTIVE: Research has identified the United States (U.S.) as a global outlier in its firearm ownership rates, with a correspondingly higher risk of youth firearm violence compared to other countries. The relative extent of disparities in youth firearm violence within the U.S. has been less clear. Little is known about factors in the social ecology driving these disparities and whether current firearm violence prevention approaches sufficiently address them. METHOD: Applying a health disparities framework, we synthesized epidemiological, sociological, and prevention science literatures, emphasizing structural inequalities in youth sociocultural positionality in life course developmental context. We also highlighted findings from national injury data and other studies regarding the magnitude and impacts of youth firearm violence disparities. RESULTS: The burden of firearm violence varied markedly at intersections of gender, race, place, developmental stage, and homicidal or suicidal intent. Firearm homicide among Black boys and young men (ages 15-24) was at outlier levels - many times greater than the rates of any other demographic group, developmental stage, or violence intent, particularly in urban settings. Recent research has operationalized structural racism and implicated historically racialized spaces as a root cause of this disparity. In contrast, elevated firearm suicide rates were found among Native and White boys and young men in rural settings; firearm-related cultural attitudes and gender socialization were points of consideration to explain these disparities. We highlighted research-based youth firearm violence preventive interventions, and emphasized gaps in efforts focused on structural and sociocultural factors. CONCLUSIONS: More explicit attention to reducing firearm homicide among Black boys and young men and firearm suicide among Native and rural White boys and young men is urgently needed and has potential to substantially lower overall rates of firearm violence in the U.S.

Improving Life Cycle Economic and Environmental Sustainability of Animal Manure Management in Marginalized Farming Communities Through Resource Recovery.

A growing world population with increasing levels of food consumption will lead to more dairy and swine production and increasing amount of manure that requires treatment. Discharge of excessive nutrients and carbon in untreated animal manure can lead to greenhouse gas emissions and eutrophication concerns, and treatment efforts can be expensive for small scale farmers in marginalized communities. The overall goal of this study was to determine the environmental and economic sustainability of four animal manure management scenarios in Costa Rica: (1) no treatment, (2) biodigesters, (3) biodigesters and struvite precipitation, and (4) biodigesters, struvite precipitation, and lagoons. Life cycle assessment was used to assess the carbon footprint and eutrophication potential, whereas life cycle cost analysis was used to evaluate the equivalent uniform annual worth over the construction and operation and maintenance life stages. Recovery of biogas as a cooking fuel and recovery of nutrients from the struvite reactor reduced the carbon footprint, leading to carbon offsets of up to 2,500 kg CO2 eq/year. Offsets were primarily due to avoiding methane emissions during energy recovery. Eutrophication potential decreased as resource recovery processes were integrated, primarily due to improved removal of phosphorus in effluent waters. Resource recovery efforts led to equivalent uniform annual benefits of $825 to $1,056/year, which could provide a helpful revenue source for lower-income farmers. This research can provide clarity on how small-scale farmers in marginalized settings can utilize resource recovery technologies to better manage animal manure, while improving economic and environmental sustainability outcomes.

Conservation threats and future prospects for the freshwater fishes of Ecuador: A hotspot of Neotropical fish diversity.

Freshwater fish communities in Ecuador exhibit some of the highest levels of diversity and endemism in the Neotropics. Unfortunately, aquatic ecosystems in the country are under serious threat and conditions are deteriorating. In 2018-19, the government of Ecuador sponsored a series of workshops to examine the conservation status of Ecuador's freshwater fishes. Concerns were identified for 35 species, most of which are native to the Amazon region, and overfishing of Amazonian pimelodid catfishes emerged as a major issue. However, much of the information needed to make decisions across fish groups and regions was not available, hindering the process and highlighting the need for a review of the conservation threats to Ecuador's freshwater fishes. Here, we review how the physical alteration of rivers, deforestation, wetland and floodplain degradation, agricultural and urban water pollution, mining, oil extraction, dams, overfishing, introduced species and climate change are affecting freshwater fishes in Ecuador. Although many of these factors affect fishes throughout the Neotropics, the lack of data on Ecuadorian fish communities is staggering and highlights the urgent need for more research. We also make recommendations, including the need for proper enforcement of existing environmental laws, restoration of degraded aquatic ecosystems, establishment of a national monitoring system for freshwater ecosystems, investment in research to fill gaps in knowledge, and encouragement of public engagement in citizen science and conservation efforts. Freshwater fishes are an important component of the cultural and biological legacy of the Ecuadorian people. Conserving them for future generations is critical.

Visual pigment evolution in Characiformes: The dynamic interplay of teleost whole-genome duplication, surviving opsins and spectral tuning.

Vision represents an excellent model for studying adaptation, given the genotype-to-phenotype map that has been characterized in a number of taxa. Fish possess a diverse range of visual sensitivities and adaptations to underwater light, making them an excellent group to study visual system evolution. In particular, some speciose but understudied lineages can provide a unique opportunity to better understand aspects of visual system evolution such as opsin gene duplication and neofunctionalization. In this study, we showcase the visual system evolution of neotropical Characiformes and the spectral tuning mechanisms they exhibit to modulate their visual sensitivities. Such mechanisms include gene duplications and losses, gene conversion, opsin amino acid sequence and expression variation, and A1 /A2 -chromophore shifts. The Characiforms we studied utilize three cone opsin classes (SWS2, RH2, LWS) and a rod opsin (RH1). However, the characiform's entire opsin gene repertoire is a product of dynamic evolution by opsin gene loss (SWS1, RH2) and duplication (LWS, RH1). The LWS- and RH1-duplicates originated from a teleost specific whole-genome duplication as well as characiform-specific duplication events. Both LWS-opsins exhibit gene conversion and, through substitutions in key tuning sites, one of the LWS-paralogues has acquired spectral sensitivity to green light. These sequence changes suggest reversion and parallel evolution of key tuning sites. Furthermore, characiforms' colour vision is based on the expression of both LWS-paralogues and SWS2. Finally, we found interspecific and intraspecific variation in A1 /A2 -chromophores proportions, correlating with the light environment. These multiple mechanisms may be a result of the diverse visual environments where Characiformes have evolved.

Seeing the rainbow: mechanisms underlying spectral sensitivity in teleost fishes.

Among vertebrates, teleost eye diversity exceeds that found in all other groups. Their spectral sensitivities range from ultraviolet to red, and the number of visual pigments varies from 1 to over 40. This variation is correlated with the different ecologies and life histories of fish species, including their variable aquatic habitats: murky lakes, clear oceans, deep seas and turbulent rivers. These ecotopes often change with the season, but fish may also migrate between ecotopes diurnally, seasonally or ontogenetically. To survive in these variable light habitats, fish visual systems have evolved a suite of mechanisms that modulate spectral sensitivities on a range of timescales. These mechanisms include: (1) optical media that filter light, (2) variations in photoreceptor type and size to vary absorbance and sensitivity, and (3) changes in photoreceptor visual pigments to optimize peak sensitivity. The visual pigment changes can result from changes in chromophore or changes to the opsin. Opsin variation results from changes in opsin sequence, opsin expression or co-expression, and opsin gene duplications and losses. Here, we review visual diversity in a number of teleost groups where the structural and molecular mechanisms underlying their spectral sensitivities have been relatively well determined. Although we document considerable variability, this alone does not imply functional difference per se. We therefore highlight the need for more studies that examine species with known sensitivity differences, emphasizing behavioral experiments to test whether such differences actually matter in the execution of visual tasks that are relevant to the fish.

Visual adaptation could aid sympatric speciation in a deep crater lake.

Allopatric speciation was originally suggested to be the primary mechanism of animal speciation (Mayr, 1942; Figure 1). During allopatric speciation, populations diverge when gene flow is reduced across significant biogeographic barriers. Sympatric speciation, where species diverge while inhabiting the same location, was thought to be essentially impossible. However, the advent of theoretical models followed by new experimental evidence made sympatric speciation more plausible (Via, 2001). The cichlid fishes of Barombi Mbo, a small crater lake in western Cameroon, became one of the most widely accepted examples of sympatric speciation (Schliewen, Tautz, & Paabo, 1994). Although the phylogenetic history of this clade is not quite as simple as originally thought, it remains one of the best examples of sympatric speciation (Richards, Poelstra, & Martin, 2018). However, little is known about the molecular mechanisms contributing to the splitting of these species in situ. In a From the Cover article in this issue of Molecular Ecology, Musilova et al. (2019) focus on the diversity of visual systems among these fishes. They identify genetic changes associated with several aspects of visual adaptation that may have contributed to the ecological specialization and sympatric speciation of cichlids in this lake.

Variable vision in variable environments: the visual system of an invasive cichlid (Cichla monoculus) in Lake Gatun, Panama.

An adaptive visual system is essential for organisms inhabiting new or changing light environments. The Panama Canal exhibits such variable environments owing to its anthropogenic origin and current human activities. Within the Panama Canal, Lake Gatun harbors several exotic fish species including the invasive peacock bass (Cichla monoculus), a predatory Amazonian cichlid. In this research, through spectral measurements and molecular and physiological experiments, we studied the visual system of C. monoculus and its adaptive capabilities. Our results suggest that (1) Lake Gatun is a highly variable environment, where light transmission changes throughout the canal waterway, and that (2) C. monoculus has several visual adaptations suited for this red-shifted light environment. Cichla monoculus filters short wavelengths (∼400 nm) from the environment through its ocular media and tunes its visual sensitivities to the available light through opsin gene expression. More importantly, based on shifts in spectral sensitivities of photoreceptors alone, and on transcriptome analysis, C. monoculus exhibits extreme intraspecific variation in the use of vitamin A1/A2 chromophore in their photoreceptors. Fish living in turbid water had higher proportions of vitamin A2, shifting sensitivities to longer wavelengths, than fish living in clear water. Furthermore, we also found variation in retinal transcriptomes, where fish from turbid and clear waters exhibited differentially expressed genes that vary greatly in their function. We suggest that this phenotypic plasticity has been key in the invasion success of C. monoculus.

Color discrimination thresholds in a cichlid fish: Metriaclima benetos.

Color vision is essential for animals as it allows them to detect, recognize and discriminate between colored objects. Studies analyzing color vision require an integrative approach, combining behavioral experiments, physiological models and quantitative analyses of photoreceptor stimulation. Here, we demonstrate, for the first time, the limits of chromatic discrimination in Metriaclima benetos, a rock-dwelling cichlid from Lake Malawi, using behavioral experiments and visual modeling. Fish were trained to discriminate between colored stimuli. Color discrimination thresholds were quantified by testing fish chromatic discrimination between the rewarded stimulus and distracter stimuli that varied in chromatic distance (ΔS). This was done under fluorescent lights alone and with additional violet lights. Our results provide two main outcomes. First, cichlid color discrimination thresholds correspond with predictions from the receptor noise limited (RNL) model but only if we assume a Weber fraction higher than the typical value of 5%. Second, cichlids may exhibit limited color constancy under certain lighting conditions as most individuals failed to discriminate colors when violet light was added. We further used the color discrimination thresholds obtained from these experiments to model color discrimination of actual fish colors and backgrounds under natural lighting for Lake Malawi. We found that, for M. benetos, blue is most chromatically contrasting against yellows and space-light, which might be important for discriminating male nuptial colorations and detecting males against the background. This study highlights the importance of lab-based behavioral experiments in understanding color vision and in parameterizing the assumptions of the RNL vision model for different species.

Antidiarrheal, vasorelaxant, and neuropharmacological actions of the diterpene tilifodiolide.

Salvia tiliifolia is used in folk medicine as a relaxant agent and for the treatment of diarrhea and neurodegenerative diseases. Tilifodiolide (TFD) is a diterpene obtained from this plant. The purpose of this work was to evaluate the antidiarrheal, vasorelaxant, and neuropharmacological actions of TFD. These effects were selected based on the folk medicinal use of S. tiliifolia. The antidiarrheal activity of 1-50 mg/kg p.o. TFD was assessed with the castor oil related tests. The vasorelaxant effect of TFD (0.9-298 µM) was performed with smooth muscle tissues from rats, and its mechanism of action was evaluated using different inhibitors. The sedative, anxiolytic, and antidepressant effects of 1-100 mg/kg TFD were assessed. The possible mechanisms of action of the anxiolytic and antidepressant effects of TFD were evaluated using inhibitors. TFD exhibited antidiarrheal (ED50 = 10.62 mg/kg) and vasorelaxant (EC50 = 48 ± 3.51 µM) effects. The coadministration of TFD with N(ω)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), reverted the vasorelaxant action showed by TFD alone. TFD exerted anxiolytic actions (ED50 = 20 mg/kg) in the cylinder exploratory test, whereas TFD (50 mg/kg) showed antidepressant actions in the tail suspension test by 44%. The pretreatment with 2 mg/kg flumazenil partially reverted the anxiolytic actions of TFD, whereas the pretreatment with 1 mg/kg yohimbine abolished the antidepressant effects of TFD. In summary, TFD exerted antidiarrheal activity by decreasing the intestinal fluid accumulation and vasorelaxant effects mediated by nitric oxide and cyclic guanosine monophosphate. TFD showed anxiolytic and antidepressant effects by the partial involvement of gamma-Aminobutyric acid (GABA) receptors and the possible participation of α2-adrenoreceptors, respectively.

The opsin genes of amazonian cichlids.

Vision is a critical sense for organismal survival with visual sensitivities strongly shaped by the environment. Some freshwater fishes with a Gondwanan origin are distributed in both South American rivers including the Amazon and African rivers and lakes. These different habitats likely required adaptations to murky and clear environments. In this study, we compare the molecular basis of Amazonian and African cichlid fishes' visual systems. We used next-generation sequencing of genomes and retinal transcriptomes to examine three Amazonian cichlid species. Genome assemblies revealed six cone opsin classes (SWS1, SWS2B, SWS2A, RH2B, RH2A and LWS) and rod opsin (RH1). However, the functionality of these genes varies across species with different pseudogenes found in different species. Our results support evidence of an RH2A gene duplication event that is shared across both cichlid groups, but which was probably followed by gene conversion. Transcriptome analyses show that Amazonian species mainly express three opsin classes (SWS2A, RH2A and LWS), which likely are a good match to the long-wavelength-oriented light environment of the Amazon basin. Furthermore, analysis of amino acid sequences suggests that the short-wavelength-sensitive genes (SWS2B, SWS2A) may be under selective pressures to shift their spectral properties to a longer-wavelength visual palette. Our results agree with the 'sensitivity hypothesis' where the light environment causes visual adaptation. Amazonian cichlid visual systems are likely adapting through gene expression, gene loss and possibly spectral tuning of opsin sequences. Such mechanisms may be shared across the Amazonian fish fauna.

Behavioral color vision in a cichlid fish: Metriaclima benetos.

Color vision is the capacity to discriminate color regardless of brightness. It is essential for many fish species as they rely on color discrimination for numerous ecological tasks. The study of color vision is important because it can unveil the mechanisms that shape coloration patterns, visual system sensitivities and, hence, visual signals. In order to better understand the mechanisms underlying color vision, an integrative approach is necessary. This usually requires combining behavioral, physiological and genetic experiments with quantitative modeling, resulting in a distinctive characterization of the visual system. Here, we provide new data on the color vision of a rock-dwelling cichlid from Lake Malawi: Metriaclima benetos. For this study we used a behavioral approach to demonstrate color vision through classical conditioning, complemented with modeling of color vision to estimate color contrast. For our experiments we took into account opsin coexpression and considered whether cichlids exhibit a dichromatic or a trichromatic visual system. Behavioral experiments confirmed color vision in M. benetos; most fish were significantly more likely to choose the trained over the distracter stimuli, irrespective of brightness. Our results are supported by visual modeling that suggests that cichlids are trichromats and achieve color vision through color opponency mechanisms, which are a result of three different photoreceptor channels. Our analyses also suggest that opsin coexpression can negatively affect perceived color contrast. This study is particularly relevant for research on the cichlid lineage because cichlid visual capabilities and coloration patterns are implicated in their adaptive radiation.

Proximate and ultimate causes of variable visual sensitivities: Insights from cichlid fish radiations.

Animals vary in their sensitivities to different wavelengths of light. Sensitivity differences can have fitness implications in terms of animals' ability to forage, find mates, and avoid predators. As a result, visual systems are likely selected to operate in particular lighting environments and for specific visual tasks. This review focuses on cichlid vision, as cichlids have diverse visual sensitivities, and considerable progress has been made in determining the genetic basis for this variation. We describe both the proximate and ultimate mechanisms shaping cichlid visual diversity using the structure of Tinbergen's four questions. We describe (1) the molecular mechanisms that tune visual sensitivities including changes in opsin sequence and expression; (2) the evolutionary history of visual sensitivity across the African cichlid flocks; (3) the ontological changes in visual sensitivity and how modifying this developmental program alters sensitivities among species; and (4) the fitness benefits of spectral tuning mechanisms with respect to survival and mating success. We further discuss progress to unravel the gene regulatory networks controlling opsin expression and suggest that a simple genetic architecture contributes to the lability of opsin gene expression. Finally, we identify unanswered questions including whether visual sensitivities are experiencing selection, and whether similar spectral tuning mechanisms shape visual sensitivities of other fishes. genesis 54:299-325, 2016. © 2016 Wiley Periodicals, Inc.

The Role of Surgery in Local Recurrences after Radical Cystectomy for Bladder Cancer.

INTRODUCTION: Local recurrence (LR) after radical cystectomy (RC) for bladder cancer has a bad prognosis. Treatment options include chemotherapy, radiation therapy and surgical excision, but few data is available on the advantages of surgery for these patients. PATIENTS AND METHODS: We evaluated our series of 8 selected patients who underwent surgery for locally recurrent bladder cancer after RC. RESULTS: The median time to recurrence after cystectomy was 20.8 months. The complications rate and severity were not negligible. Pathology report confirmed urothelial carcinoma with negative margins in all patients. After LR treatment, 4 patients recurred locally for a second time and 3 developed distant metastasis. They all died after a median follow-up of 10.4 months. One patient remained disease free after 14 months. CONCLUSIONS: The prognosis of patients with LR is poor regardless of surgical treatment and reflects the aggressive biological nature of urothelial tumors.

A multi-targeted approach to treating bone metastases.

The treatment of bone-metastatic cancer now takes advantage of the unique biology of this clinical state. The complex interplay between the cancer cells and the bone microenvironment leads to a host of therapeutic targets, with agents in various stages of clinical use or study. Targets include interactions between the cancer cells and osteoclasts, osteoblasts, endothelial cells, stromal cells, hematopoietic progenitor cells, cells of the immune system, and the bone matrix. Efforts at understanding specific mechanisms of drug resistance in the bone are also ongoing. Successful clinical outcomes will be the result of co-targeting and interrupting the various tumor-supportive elements and cooperating pathways at the level of the tumor cell, the primary and metastatic microenvironments, and systemic cancer effects, leading to a "scaled network disruption" to undermine the disease state.

New records of native and introduced fish species in a river basin of Western Ecuador, the Chocó-Darien Ecoregion, using DNA barcoding.

DNA barcoding, based on mitochondrial markers, is widely applied in species identification and biodiversity studies. The aim of this study was to establish a barcoding reference database of fishes inhabiting the Cube River from Western Ecuador in the Chocó-Darien Global Ecoregion (CGE), a threatened ecoregion with high diversity and endemism, and evaluate the applicability of using barcoding for the identification of fish species. Barcode sequences were obtained from seven orders, 17 families, 23 genera and 26 species, which were validated through phylogenetic analysis, morphological measurements, and literature review. Our results showed that 43% of fish species in this region are endemic, confirmed the presence of known species in the area, and included the addition of three new records of native (Hoplias microlepis, Rhamdia guatemalensis and Sicydium salvini) and an introduced species (Xiphophorus maculatus) to Ecuador. In addition, eight species were barcoded for the first time. Species identification based on barcoding and morphology showed discrepancy with species lists from previous studies in the CGE, suggesting that the current baseline of western fishes of Ecuador is still incomplete. Because this study analyzed fishes from a relatively small basin (165 km2), more molecular-based studies focusing on fish are needed to achieve a robust sequence reference library of species inhabiting Western Ecuador. The new sequences of this study will be useful for future comparisons and biodiversity monitoring, supporting the application of barcoding tools for studying fish diversity in genetically unexplored regions and to develop well-informed conservation programs.

Low Concentrations of Gold Nanoparticles as Electric Charge Carriers in Piezoelectric Cement-Based Materials.

Piezoelectric cement-based composites could serve to monitor the strain state of structural elements or act as self-powered materials in structural health monitoring (SHM) applications. The incorporation of piezoelectric materials as an active phase within cement matrices has presented a highly attractive avenue until today. However, their application is challenged by the low electrical conductivity of the hydrated cement matrix. Gold nanoparticles (Au NPs) possess substantial potential for elevating the free electrical charge within the matrix, increasing its electrical conductivity between the Au NPs and the cement matrix, thereby enhancing the piezoelectric response of the composite. In this sense, the objective of this study is to investigate the effects of incorporating low concentrations of gold nanoparticles (Au NPs) (442 and 658 ppm) on the electrical and piezoelectric properties of cement-based composites. Additionally, this study considers the effects of such properties when the material is cured under a constant electric field. Electrical impedance spectroscopy was used to evaluate the polarization resistance and piezoresistive properties of the material. Additionally, open-circuit potential measurements were taken alongside the application of mechanical loads to assess the piezoelectric activity of the composites. The findings revealed a notable decrease in the composite's total electrical resistance, reaching a value of 1.5 ± 0.2 kΩ, almost four times lower than the reference specimens. In the realm of piezoelectricity, the piezoelectric voltage parameter g33 exhibited a remarkable advancement, improving by a factor of 57 when compared to reference specimens. This significant enhancement can be attributed to both the concentration of Au NPs and the electrical curing process. In summary, the outcomes of this study underscore the feasibility of creating a highly electrically conductive cement-based matrix, using low concentrations of gold nanoparticles as electric charge carries, and indicate the possible piezoelectric behavior of the studied compposite.