Bats as bioindicators of heavy metal pollution: history and prospect

Past anthropogenic impacts revealed by trace elements in cave guano

Natural and human-induced toxic elements can accumulate in the environment, posing significant risks to human health and ecosystems. This study explores cave bat guano, an unconventional and relatively under-researched environmental repository, to reveal historical pollution trends and sources. Through trace elements analysis of a 1.5-m-thick guano deposit from Zidită Cave (Romania), we track changes in mining and metallurgy from 1000 CE-2012. We identified substantial pollution primarily from porphyry copper and Au-Ag-Te mines, but also impacts from usage of leaded gasoline and agricultural practices. Our record shows disruptions caused by the Bubonic plague around 1250 CE and a major surge ∼ 1500 CE. After the decline triggered by the European silver market collapse in 1525 CE, our study reveals a brief mining revival. This resurgence was followed by a continuous decline lasting until the early 1800s, driven by socio-economic upheavals and recurrent outbreaks of the bubonic plagues. The Industrial Revolution sparked prolonged growth that lasted until 1989 CE, only briefly interrupted by the Great Depression and World War II. Consequently, cave bat guano proves to be a critical resource for understanding spatial pollution patterns, both locally and regionally, and for identifying specific pollution sources.

A systematic review of trace elements in the tissues of bats (Chiroptera)

Bats constitute about 22% of known mammal species; they have various ecological roles and provide many ecosystem services. Bats suffer from several threats caused by anthropization, including exposure to toxic metals and metalloids. We analyzed 75 papers in a systematic literature review to investigate how species, diet, and tissue-type impact bioaccumulation. Most studies documented element accumulation in fur, liver, and kidney; at least 36 metals and metalloids have been measured in bat tissues, among the most studied were mercury and zinc. Comparisons with known toxicological thresholds for other mammals showed concerning values for mercury and zinc in bat hair, lead and some essential metals in liver, and iron and calcium in kidneys. Moreover, accumulation patterns in tissues differed depending on bat diet: insectivorous bats showed higher metal concentrations in fur than in liver and kidney while frugivorous species showed higher values in liver and kidney than in fur. Finally, among the bat species that have been studied in more than two papers, the big brown bat (Eptesicus fuscus) show values of mercury in hair and copper in liver that exceed the known thresholds; as does copper in the liver of the little brown bat (Myotis lucifugus). Most studies have been conducted in temperate North America and Eurasia, areas with the lowest bat species diversity; there is a paucity of data on tropical bat species. This review points out several information gaps in the understanding of metal contamination in bats, including a lack of measured toxicity thresholds specific for bat tissues. Data on trace element bioaccumulation and its associated health effects on bats is important for conservation of bat species, many of which are threatened.

A paired analysis of mercury among non-invasive tissues to inform bat conservation monitoring

Contaminant exposure can harm wildlife. However, measuring contaminant exposure in wildlife can be challenging due to accessibility of species and/or sampling tissue matrices needed to answer research questions regarding exposure. For example, in bats and other taxa that roost, it may be best to collect pooled feces from colonies for minimal disturbance to species of conservation concern, but fecal contaminant concentrations do not provide contaminant bioaccumulation estimates. Thus, there is a need for quantifying relationships between sample matrices for measuring contaminant exposure to answer research questions pertaining to wildlife health and addressing conservation needs. Our goal was to determine relationships between fecal and fur total mercury (THg). To do so, we collected paired feces and fur from Mexican free-tailed bats (Tadarida brasiliensis) in summer 2023 in western Oklahoma at a maternity roost with no known Hg point source. We analyzed THg in each sample matrix for each individual (n = 48). We found no relationship between individual fecal and fur THg. However, when averaged, fur THg was 6.11 times greater than fecal THg. This factor can be used as a screening-level risk assessment of under-roost feces, which could then be followed by direct assessments of fur THg concentrations and health impacts. We encourage the use of this conversion factor across other insectivorous bat species and sites for estimating initial risks of contaminant exposure with minimal disturbance to species of conservation concern, when timely research for conservation actions are needed, and when a contaminant point source is not yet known.

Ecotoxicology of heavy metal contamination of Neotropical bats

Although bats are responsible for many ecosystem services on which humans depend, they are frequently exposed to multiple anthropogenic stressors. Heavy metal (HM) exposure is an emerging threat of great significance to bats, yet the toxicity threshold for most metallic elements remains unknown. The greatest diversity of bats worldwide is in the Neotropical region, where ecotoxicological studies are scarce. Thus, this review provides a current overview of the knowledge available on HMs contamination of Neotropical bats. Analysis of the results of 17 articles published between 2000 and 2023 documented a trend of increasing interest in the topic, although it is incipient and in few countries. Of the 226 species known for the Neotropics, 95 have been investigated for metal concentrations. Seven different matrices were used to assess concentrations of heavy metals in tissues, with fur being the subject of eight studies, highlighting the search for non-invasive analysis. Twenty-one HMs were detected in bats, with mercury being the most common. The highest concentrations of this HM were detected in insectivorous/omnivorous bats, highlighting its magnification in this trophic guild compared to frugivorous bats. Copper, lead, and cadmium did not differ significantly among the other trophic guilds. This review shows that there is knowledge about concentrations of heavy metals in several Neotropical species, but knowledge about the impact of these concentrations on bat health is limited, which highlights the need for research to determine critical concentrations that cause damage to bat health, and that guide conservation actions for their populations, as well as environmental monitoring actions for these pollutants.

Considering pollinators' ecosystem services in the remediation and restoration of contaminated lands: Overview of research and its gaps

The concept of ecosystem services provides a useful framework for understanding how people are affected by changes to the natural environment, such as when a contaminant is introduced (e.g., oil spills, hazardous substance releases) or, conversely, when contaminated lands are remediated and restored. Pollination is one example of an important ecosystem service; pollinators play a critical role in any functioning terrestrial ecosystem. Other studies have suggested that consideration of pollinators' ecosystem services could lead to better remediation and restoration outcomes. However, the associated relationships can be complex, and evaluation requires synthesis from numerous disciplines. In this article, we discuss the possibilities for considering pollinators and their ecosystem services when planning remediation and restoration of contaminated lands. To inform the discussion, we introduce a general conceptual model of how pollinators and the ecosystem services associated with them could be affected by contamination in the environment. We review the literature on the conceptual model components, including contaminant effects on pollinators and the direct and indirect ecosystem services provided by pollinators, and identify information gaps. Though increased public interest in pollinators likely reflects increasing recognition of their role in providing many important ecosystem services, our review indicates that many gaps in understanding-about relevant natural and social systems-currently impede the rigorous quantification and evaluation of pollinators' ecosystem services required for many applications, such as in the context of natural resource damage assessment. Notable gaps include information on non-honeybee pollinators and on ecosystem services beyond those benefitting the agricultural sector. We then discuss potential research priorities and implications for practitioners. Focused research attention on the areas highlighted in this review holds promise for increasing the possibilities for considering pollinators' ecosystem services in the remediation and restoration of contaminated lands. Integr Environ Assess Manag 2024;20:322-336. © 2023 SETAC.

Mercury bioaccumulation in bats in Madre de Dios, Peru: implications for Hg bioindicators for tropical ecosystems impacted by artisanal and small-scale gold mining

Mercury (Hg) endangers human and wildlife health globally, primarily due to its release from artisanal small-scale gold mining (ASGM). During gold extraction, Hg is emitted into the environment and converted to highly toxic methylmercury by microorganisms. In Madre de Dios (MDD), Peru, ASGM dominates the economy and has transformed rainforests into expansive deforested areas punctuated by abandoned mining ponds. The aim of this study was to evaluate the use of bats as bioindicators for mercury pollution intensity in tropical terrestrial ecosystems impacted by ASGM. We collected 290 bat fur samples from three post-ASGM sites and one control site in Madre de Dios. Our results showed a wide Hg distribution in bats (0.001 to 117.71 mg/kg) strongly influenced by feeding habits. Insectivorous and piscivorous bats from ASGM sites presented elevated levels of Hg surpassing the mercury small mammal threshold for small mammals (10 mg/kg). We observed the highest reported fur mercury concentrations for insectivorous Neotropical bats reported to date (Rhynchonycteris naso, 117 mg/kg). Our findings further confirm that Hg emissions from ASGM are entering local food webs and exposing wildlife species at several trophic levels to higher levels of Hg than in areas not impacted by mining. We also found that three bat genera consistently showed increased Hg levels in ASGM sites relative to controls indicating potential usefulness as bioindicators of mercury loading in terrestrial ecosystems impacted by artisanal and small-scale gold mining.

Microplastic abundance in urban vs. peri-urban mangroves: The feasibility of using invertebrates as biomonitors of microplastic pollution in two mangrove dominated estuaries of southern Africa

Microplastic (MP) prevalence has been well documented, however, knowledge gaps exist for African mangrove forests. This research is the first to compare MP pollution (using FT-IR analysis) in an urban (Durban Bay) and peri-urban (Mngazana Estuary) mangrove forest in South Africa, across different compartments. MP pollution (typology, abundance, and distribution) was quantified in estuarine surface water, sediment and the soft tissue of three keystone species (Austruca occidentalis, Chiromantes eulimene and Cerithidea decollata) in relation to disturbances acting on these systems. MP averages ranged from 99 to 82 MPs/kg sediment, 177 to 76 MPs/L water and 82 to 59 MP/g-1 DW in biota. Overall fibres were the dominant MP type across all compartments. The three invertebrate species exhibited MP bioaccumulation, however, significant differences were observed between MP concentrations in the soft body tissue of invertebrates and abiotic compartments, providing evidence that they are not effective biomonitors of MP pollution.

Species and reproductive status influence element concentrations in bat fur

To assess the impact of increasing pollutant levels on wildlife, we measured chemical contaminant loads in bats with different habitat and dietary preferences. Samples were taken from the fur of bats (Eptesicus nilssonii, Myotis brandtii, Myotis mystacinus and Plecotus auritus) to measure concentrations of 55 elements by inductively coupled plasma mass spectrometry (ICP-MS). Variations in element concentrations between different bat groups (species, sex, reproductive status) were analysed with a focus on arsenic (As), mercury (Hg) and lead (Pb) as these are known to cause specific health concerns in wildlife. For M. brandtii we found the highest As concentrations, especially in lactating bats, with a maximum exceeding those from other studies where bats had compromised health. Whereas for M. mystacinus there was a negative correlation between body condition index (BCI) and As concentration, indicating a potential danger for bats in the study area. In M. mystacinus and M. brandtii Hg concentrations were higher for sixteen individuals than in other studies where bats suffered genotoxic effects, although median levels were still below this threshold. Lactating bats from P. auritus and M. brandtii had higher Hg concentrations than bats of other reproductive status, which could endanger offspring as Hg can be transferred through lactation. In females from M. mystacinus Pb concentrations were more than three times higher compared to males. There was also a negative correlation between Pb concentration and BCI, which could mean that Pb has an adverse effect on health. Although many other biotic and abiotic factors should be considered, some of the variations in element concentrations could be due to different behaviours (foraging, roosting, etc.) in the studied species. The high levels of chemical contamination in some of the bats in our study, particularly reproductive individuals, is of conservation concern as bats are important agents for insect control.

Variation in habitat use and its consequences for mercury exposure in two Eastern Ontario bat species, Myotis lucifugus and Eptesicus fuscus

The St. Lawrence River in Eastern Ontario, Canada, has been a designated an area of concern due to past industrial contamination of sediment in some areas and transport of mercury from tributaries. Previous research using bats as sentinel species identified elevated concentrations of total mercury (THg) in fur of local bats and species-specific variation between little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus). Here, we investigated the mercury exposure pathways for these two species by testing the hypothesis that diet variation, particularly the reliance on aquatic over terrestrial insects, is a determinant of local bat mercury concentrations. We analyzed THg concentration and stable isotope ratios of δ15N and δ13C in fur of little and big brown bats, and in aquatic and terrestrial insects. Big brown bats, especially males, accumulated significantly higher THg concentrations in their fur compared to little brown bats. However, this difference was not related to diet because big brown bats consumed terrestrial insects, which were lower in mercury than aquatic insects, the primary prey for little brown bats. We also evaluated whether fur THg concentrations translate into molecular changes in tissues linked to (methyl)mercury toxicity by quantifying tissue changes in global DNA methylation and mitochondrial DNA abundance. No significant changes in DNA molecular markers were observed in relation to fur THg concentration, suggesting mercury exposure to local bats did not impact molecular level changes at the DNA level. Higher mercury in bats was not associated with local aquatic contamination or genotoxicity in this study area.

Genotoxic, mutagenic, and cytotoxic analysis in bats in mining area

Pollution generated by the mining industry can cause harm to wildlife. This study aimed to evaluate the cytotoxicity, genotoxicity and mutagenicity in bats environmentally exposed to open pit mining. Thus, 62 bats of the following species, Carollia perspicillata, Glossophaga soricina, Phyllostomus hastatus, and Desmodus rotundus exposed to mining activities (ferronickel) were used in the analysis. The animals were obtained in samplings in July and November of 2021, totaling 8 days of sampling in the field. The results indicated that species differ in the frequency of genotoxic damage between sampling points within the mining landscape. Cytotoxicity was observed by scoring of karyorrhexis, pyknosis and karyolysis. The most captured species, C. perspicillata, showed differences in DNA damage between exposed and unexposed populations, but no differences were observed between males (n = 14) and females (n = 20). G. soricina was also a sensitive species for indicating a high frequency of DNA damages compared to the omnivore P. hastatus. Elements such as Mn, Cr, Pb, and Zn observed in water samples were at high levels in the mining area. We conclude that bats in mining areas are susceptible to increased DNA damage as already identified for other species.

Damage on DNA and hematological parameters of two bat species due to heavy metal exposure in a nickel-mining area in central Brazil

Exposure to heavy metals in mining zones is a significant threat, which can affect ecosystem services and contribute to the decline of wild bat populations. The present study investigated the impacts caused by mining on two bat species in central Brazil, the nectarivorous Glossophaga soricina and the frugivorous Carollia perspicillata. The bats were collected from a nickel-mining zone (treatment) and a protected area (control). The leukocyte profile of each species was compiled and genotoxicity (comet assay) and mutagenicity (micronucleus test) were determined using the appropriate procedures. Glossophaga soricina presented significantly higher frequencies of eosinophils and monocytes in the mining zone in comparison with the protected area, whereas C. perspicillata presented higher frequencies of lymphocytes in the mining zone, but significantly lower frequencies of monocytes. Concomitantly, G. soricina also presented a higher frequency of DNA damage, although no variation was found in this parameter in C. perspicillata when comparing environments. We also found no significant differences between populations in terms of the frequency of micronuclei and other nuclear abnormalities. Overall, the results of the study indicate that bats are susceptible to immunological disorders and DNA damage in mining zones, with the nectarivorous G. soricina appearing to be relatively more susceptible and thus a potentially effective bioindicator of the impact of contamination in these environments.

Histopathological and health risk assessment of heavy metals in the straw-colored fruit bat, Eidolon helvum, in Nigeria

There is heightening concern regarding heavy metals environmental pollution requiring renewed global attention because of their bioaccumulation and toxicity at varying levels. The concern is most important in the highly migratory Eidolon helvum (E. helvum) that is very common and traverses wide geographical areas within the sub-Saharan Africa. The present study aimed to evaluate levels of cadmium (Cd), lead (Pb), and zinc (Zn) bioaccumulation in 24 E. helvum of both sexes from Nigeria to assess their indirect health risks to the human consumers of the bats in addition to their direct bioaccumulation and toxic damages in the bats themselves based on standard procedures. Lead, Zn, and Cd bioaccumulation concentrations were 2.83 ± 0.35, 0.42 ± 0.03, and 0.05 ± 0.01 mg/kg, respectively, with significant (p < 0.05) Pb bioaccumulation compared to either Cd or Zn in the affected bats. However, only Pb (markedly) and Cd (marginally) bioaccumulated above small mammals' critical threshold levels as there are no existing established threshold levels for bats. Sex played no major role in their bioaccumulation levels. The bioaccumulation levels posed no life-long non-carcinogenic nor carcinogenic risks to the human consumers of the bats at detected concentrations. The observed lungs, liver, and kidney histopathological changes suggested the possible direct effects of the metals in the bats. Nevertheless, other anthropogenic factors might be responsible as no significant (p > 0.05) correlation existed between cellular changes and the bioaccumulation levels. The presence of the heavy metals and their bioaccumulations above critical threshold levels suggested some levels of environmental contamination and pollution, which might have direct and indirect health implications to the bats and their human consumers.

Could a city-dwelling bat (Pipistrellus kuhlii) serve as a bioindicator species for trace metals pollution?

Bats are an endangered group of mammals that are very sensitive to environmental stresses. One of such stress factor is trace metals pollution which threatens populations of insectivorous bats due to their top position in the food webs and exceptionally long life span. In our research Pipistrellus kuhlii was tested as a promising indicator species (urban-dwelling, sedentary, with limited daily home-range) for trace metal exposure of bats. We measured concentrations of Pb, Cu, Zn and Cd in internal and external tissues of bats from the industrial city Mariupol and the village Karlovka, Ukraine, to answer the following questions: (1) Do metal concentrations in soil samples differ between urban and rural areas, and between populations of P. kuhlii from those areas? (2) Does metal contamination differ between individuals of different sexes and ages? (3) Whether fur and/or wing membrane, the two tissues that can be collected from live bats, can be used as proxies of metal contamination in internal tissues (liver, kidney, lung, forearm bones) of P. kuhlii? Metal concentrations in soil samples were significantly higher in the city. Bats from the city accumulated significantly more Cd, Pb and Zn in external tissues than those from the rural area. Females accumulated more Cd than males, and this-year-born did not differ significantly from adult individuals. We did not find, however, significant positive correlations between metal concentrations in external and internal tissues, indicating that external tissues cannot serve as an indicator of the metal contamination of internal tissues in P. kuhlii.

Influence of landscape ecology and physiological implications in bats from different trophic guilds

Bats may serve as bioindicators of human impact on landscape ecology. This study aimed to evaluate the health condition of bats from different food guilds captured in two areas with different land use profiles in Brazil and to compare data on the oxidant-antioxidant balance and histopathological changes due to different anthropogenic pressures. Bats were collected from a protected area in Serra do Cipó National Park (SCNP), MG, Brazil, and an area with intense agricultural activity in the municipality of Uberaba (UB), MG, Brazil. Despite the differences in land use and occupation between the studied areas, bats showed similar responses. However, the trophic guilds were affected differently. Frugivorous bats in both areas showed lower activities of the enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) and concentrations of malondialdehyde (MDA) than other guilds, which can be explained by the greater intake of antioxidants from the diet in addition to the lower production of reactive oxygen species (ROS). Histopathological analysis of the livers revealed that the animals had a similar prevalence in the two areas, with some differences related to guilds. Compared with other bats, hematophagous bats from SCNP had a higher prevalence of steatosis and, together with frugivorous bats from Uberaba, had higher frequencies of ballooning degeneration, suggesting that these animals are subjected to anthropogenic factors capable of inducing disturbances in hepatic metabolism. Hematophagous bats from Uberaba had a higher prevalence of portal inflammation, while insectivorous bats from Uberaba had a higher prevalence of lobular and portal inflammation. The profiles of use and occupation of the areas are different; Uberaba bats seem to face worse conditions because they show more liver damage owing to lipoperoxidation.

Assessment of Seasonal Variability of the Spectrum of Free Amino Acids in the Blood Plasma of the Boreal Bat Species (Myotis dasycneme Boie, 1825) of the Ural Fauna

A comparative analysis of the content of free amino acids in the blood plasma of a representative of the bat fauna of the Urals, Myotis dasycneme (Boie, 1825), in seasonal periods of their annual life cycle is presented for the first time. The blood plasma of the pond bats contains a full spectrum of essential amino acids: threonine, valine, lysine, leucine, isoleucine, methionine, phenylalanine, arginine, histidine, and tryptophan. A significant accumulation of metabolically active glucoplastic alanine in the blood of M. dasycneme in the autumn (2.5 times) and winter (2.2 times) periods indicates its role as a low-temperature adaptogen.

Bats and pollution: Genetic approaches in ecotoxicology

Environmental pollution drives the decline of species and, as flying mammals, bats can be considered to be excellent indicators of environmental quality, and the analysis of genetic biomarkers in these animals can provide important parameters for the assessment of environmental health. This review verifies the trends in pollution research, in particular, the use of genetic markers in the study of bats, based on a literature search of the Web of Science and Scopus platforms. Sixteen publications were identified during the search, which focused on the timeframe between 1996 and March 2022, including investigations of the effects of heavy metals, agricultural pesticides, and radiation. The studies were based primarily on the application of biomarkers for genotoxic analysis, including the comet assay, micronucleus test, and the Polymerase Chain Reaction (PCR). Only 55 bat species have been investigated up to now, that is, 4% of the 1447 currently recognized. In general, bats exposed to polluted environments presented a higher frequency of genotoxic and mutagenic damage than those sampled in clean environments. Given the importance of the diverse ecological functions provided by bats, including pest control, pollination, and seed dispersal, it is increasingly necessary to investigate the damage caused to the health of these animals exposed to areas with high concentrations of contaminants. Although genetic biomarkers have been used to investigate physiological parameters in bats for more than two decades, then, many knowledge gaps remain, worldwide, in terms of the number of species and localities investigated.

Testis and brown adipose tissue xenografts from yellowish myotis (Myotis levis)

Yellowish myotis present a seasonal reproduction, influenced by rainfall distribution, in which the testis mass, germ cell composition, and brown adipose tissue mass change along the reproductive stages. In the present study, tissue xenografts were performed in immunodeficient mice to investigate spermatogenesis development in a stable endocrine milieu and the possible androgenic role of brown adipose tissue. Forty-one adult male bats were captured in the Santuário do Caraça, Minas Gerais, Brazil. The gonads and brown adipose tissue were collected, weighed, and grafted under the mice's back skin. Mice biometric and hormonal data were evaluated after grafting, and the testis grafts and mice gonads were fixed for histological and immunohistochemical analyses. As a result, testis grafts from adult bats presented a continuous germ cell development in all reproductive phases, showing round spermatids in all testis tissues. Furthermore, testis fragments in the Rest stage presented elongating spermatids as the most advanced germ cell type in the seminiferous epithelium after seven months of grafting. These data indicated that yellowish myotis spermatogenesis could be continued (presenting a constant spermatogonial differentiation) in a stable endocrine milieu, as found in mice. In addition, the best spermatogenic development was achieved when testis fragments were transplanted at their lowest activity (Rest stage). Regarding the brown adipose tissue grafts, the adipose tissue consumption by mice increased seminal vesicle mass and testosterone serum levels. This data proved that the brown adipose tissue is related to testosterone synthesis, which may be critical in stimulating the differentiation of spermatogonia in yellowish myotis.

Land use, season, and parasitism predict metal concentrations in Australian flying fox fur

Urban-living wildlife can be exposed to metal contaminants dispersed into the environment through industrial, residential, and agricultural applications. Metal exposure carries lethal and sublethal consequences for animals; in particular, heavy metals (e.g. arsenic, lead, mercury) can damage organs and act as carcinogens. Many bat species reside and forage in human-modified habitats and could be exposed to contaminants in air, water, and food. We quantified metal concentrations in fur samples from three flying fox species (Pteropus fruit bats) captured at eight sites in eastern Australia. For subsets of bats, we assessed ectoparasite burden, haemoparasite infection, and viral infection, and performed white blood cell differential counts. We examined relationships among metal concentrations, environmental predictors (season, land use surrounding capture site), and individual predictors (species, sex, age, body condition, parasitism, neutrophil:lymphocyte ratio). As expected, bats captured at sites with greater human impact had higher metal loads. At one site with seasonal sampling, bats had higher metal concentrations in winter than in summer, possibly owing to changes in food availability and foraging. Relationships between ectoparasites and metal concentrations were mixed, suggesting multiple causal mechanisms. There was no association between overall metal load and neutrophil:lymphocyte ratio, but mercury concentrations were positively correlated with this ratio, which is associated with stress in other vertebrate taxa. Comparison of our findings to those of previous flying fox studies revealed potentially harmful levels of several metals; in particular, endangered spectacled flying foxes (P. conspicillatus) exhibited high concentrations of cadmium and lead. Because some bats harbor pathogens transmissible to humans and animals, future research should explore interactions between metal exposure, immunity, and infection to assess consequences for bat and human health.

Machine Learning for Evaluating the Cytotoxicity of Mixtures of Nano-TiO2 and Heavy Metals: QSAR Model Apply Random Forest Algorithm after Clustering Analysis

With the development and application of nanomaterials, their impact on the environment and organisms has attracted attention. As a common nanomaterial, nano-titanium dioxide (nano-TiO₂) has adsorption properties to heavy metals in the environment. Quantitative structure-activity relationship (QSAR) is often used to predict the cytotoxicity of a single substance. However, there is little research on the toxicity of interaction between nanomaterials and other substances. In this study, we exposed human renal cortex proximal tubule epithelial (HK-2) cells to mixtures of eight heavy metals with nano-TiO₂, measured absorbance values by CCK-8, and calculated cell viability. PLS and two ensemble learning algorithms are used to build multiple QSAR models for data sets, and the test set R² is increased from 0.38 to 0.78 and 0.85, and RMSE is decreased from 0.18 to 0.12 and 0.10. After selecting the better random forest algorithm, the K-means clustering algorithm is used to continue to optimize the model, increasing the test set R² to 0.95 and decreasing the RMSE to 0.08 and 0.06. As a reliable machine algorithm, random forest can be used to predict the toxicity of the mixture of nano-metal oxides and heavy metals. The cluster analysis can effectively improve the stability and predictability of the model, and provide a new idea for the prediction of cytotoxicity model in the future.

Bioremediation of organic/heavy metal contaminants by mixed cultures of microorganisms: A review

Although microbial remediation has been widely used in the bioremediation of various contaminants, in practical applications of biological remediation, pure cultures of microorganisms are seriously limited by their adaptability, efficiency, and capacity to handle multiple contaminants. Mixed cultures of microorganisms involve the symbiosis of two or more microorganisms. Such cultures exhibit a collection of the characteristics of each microorganism species or strain, showing enormous potential in the bioremediation of organic or heavy metal pollutants. The present review focuses on the mixed cultures of microorganisms, demonstrating its importance and summarizing the advantages of mixed cultures of microorganisms in bioremediation. Furthermore, the internal and external relations of mixed culture microorganisms were analyzed with respect to their involvement in the removal process to elucidate the underlying mechanisms.

Torpor/hibernation cycle may enhance the risk of insecticides for bats: an in vitro study

Exposure to pollutants is considered one of the potential reasons of population declines in bats. In the context of previous studies, we managed to create and keep a wide collection of cell lines from European bat species. Liver cells were chosen for testing, as they represent the preferred model for toxicological studies. Bats are protected, cell lines replacing experimental animals thus represent a unique opportunity to examine effects of pollutants which animals are exposed to in their environments. Moreover, cell incubation temperature variation may simulate physiological states of heterothermic bats. Liver cell lines were cultivated to the required cell number. Exposure to five different concentrations of permethrin (PM) and imidacloprid (IMI) were used to determine cytotoxic effects of these pesticides on Nyctalus noctula-derived liver cells cultivated at 37 °C and 8 °C for 24 h. An assay based on the measurement of activity of lactate dehydrogenase released from damaged cells was used for quantitating cytotoxicity. Cytotoxicity of IMI ranged from 0% to 47% and from 56% to 67% at 37 °C and 8 °C, respectively. Cytotoxicity of PM ranged from 36% to 56% and from 43% to 88% at 37 °C and 8 °C, respectively. Permethrin was tested on the cells at an order of magnitude lower concentrations; even so, higher degree of cytotoxicity was recorded. Imidacloprid was more toxic to bat liver cells at a hibernation temperature than at body temperature of 37 °C.

Non-invasive sampling of bats reflects their potential as ecological indicators of elemental exposure in a diamond mining area, northern Limpopo Province, South Africa

Bats have been proposed as reliable bioindicators for monitoring bioaccumulation of elements and chemicals in natural and transformed ecosystems. Non-invasive methods are becoming more popular as research moves away from destructive methodologies. We present the first concentrations of 23 elements in Mops condylurus and Tadarida aegyptiaca (Molossidae) fur and blood from an opencast diamond mine and reference area using inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of B, K, Rb and Cd in the bats' fur were significantly higher in the mining footprint compared to the reference area (P < 0.05). Other elements such as Zn and Hg were significantly higher in the blood of bats from the mining footprint than the reference area (P < 0.05), whereas Mn was significantly higher in the blood of bats from the reference area than from the mining footprint (P < 0.05). Sixteen of the 22 elements above the limit of detection, with the exception of Ba, were significantly higher in the fur samples than in the blood due to elements being incorporated over time into the fur as it grows, whereas blood reveals short-term exposure to elements. Concentrations of most of the elements were reasonably low except Al, Fe and Zn. In general, the element concentrations particularly in the fur samples were comparable with other international studies reporting elemental fur concentrations from anthropogenically impacted and natural areas. Fur and blood have the potential to be viable indicators of environmental toxicity, but research is required on toxic thresholds and physiological and ecological unknowns around element concentrations in bat tissues and organs.

Contaminant exposure as an additional stressor to bats affected by white-nose syndrome: current evidence and knowledge gaps

Bats are exposed to numerous threats including pollution and emerging diseases. In North America, the fungal disease white-nose syndrome (WNS) has caused declines in many bat species. While the mechanisms of WNS have received considerable research attention, possible influences of contaminants have not. Herein, we review what is known about contaminant exposure and toxicity for four species whose populations have been severely affected by WNS (Myotis sodalis, M. septentrionalis, M. lucifugus, and Perimyotis subflavus) and identify temporal and spatial data gaps. We determine that there is limited information about the effects of contaminants on bats, and many compounds that have been detected in these bat species have yet to be evaluated for toxicity. The four species examined were exposed to a wide variety of contaminants; however, large spatial and knowledge gaps limit our ability to evaluate if contaminants contribute to species-level declines and if contaminant exposure exacerbates infection by WNS.

Bats are an excellent sentinel model for the detection of genotoxic agents. Study in a Colombian Caribbean region

Wildlife animals have been affected by human activities and the diminution of the areas needed to develop wildlife. In Colombia, artisanal and industrial mining focuses on gold extraction, which uses mercury and causes contamination in water sources. Bats may be susceptible to chemical contamination and primarily to bioaccumulated heavy metal contaminants in the food chain. The primary source of exposure is contaminated food and water ingest, followed by dermic exposition and inhalation. The objective was to evaluategenotoxic damage and mercury concentration in bats. Forty-five samples of blood and organs of bats captured in Ayapel and Majagual were collected. Erythrocytes were searched for micronuclei by peripheral blood smear. Mercury concentration in 45 liver and spleen samples was determined by atomic absorption spectroscopy (DMA80 TRICELL, Milestone Inc, Italy). Bats from four families were studied: Phyllostomidae (6 species), Molossidae (3 species), Vespertilionidae (1 species), and Emballonuridae (1 species). Mercury was found in all bat species from the different dietary guilds. Insectivores had the highest concentration of mercury in the liver (0,23 µg/g) and spleen (0,25 µg/g) and the highest number of micronuclei (260 micronuclei/10,000). The specimens captured in Majagual had the highest frequency of micronuclei (677 micronuclei/10,000), and those captured in Ayapel had the highest mercury concentration (0,833 µg/g). This is the first study in Colombia to report that bats could act as sentinels to the environment's genotoxic chemical agents. Mercury and a high frequency of micronuclei were found in the tissues of captured bats. In addition to mercury contamination, there could also be other contaminants affecting Chiroptera.

Microplastic distribution in urban vs pristine mangroves: Using marine sponges as bioindicators of environmental pollution

Sessile benthic organisms are considered good bioindicators for monitoring environmental quality of coastal ecosystems. However, these environments are impacted by new pollutants such as microplastics (MPs), where there is limited information about organisms that can be used as reliable bioindicators of these emerging contaminants. We evaluated MP concentrations in three compartments: surface sediment, water and in three marine sponge species (Haliclona implexiformis, Halichondria melanadocia and Amorphinopsis atlantica), to determine whether these organisms accumulate MPs and reflect their possible sources. Results showed MPs in all three compartments. Average concentrations ranged from 1861 to 3456 items kg^-1 of dry weight in marine sponges, 130 to 287 items L^-1 in water and 6 to 11 items kg^-1 in sediment. The maximum MP concentration was in the sponge A. atlantica, which registered 5000 items kg^-1 of dry weight, in water was 670 items L^-1 and in sediment was 28 items kg^-1, these values were found in the disturbed study area. The three sponge species exhibited MP bioaccumulation and showed significant differences between disturbed and pristine sites (F = 11.2, p < 0.05), suggesting their use as bioindicators of MP.

Do We Need to Use Bats as Bioindicators?

Simple Summary

Bioindicators are organisms that react to the quality or characteristics of the environment and their changes. They are vitally important to track environmental alterations and take action to mitigate them. As choosing the right bioindicators has important policy implications, it is crucial to select them to tackle clear goals rather than selling specific organisms as bioindicators for other reasons, such as for improving their public profile and encourage species conservation. Bats are a species-rich mammal group that provide key services such as pest suppression, pollination of plants of economic importance or seed dispersal. Bats show clear reactions to environmental alterations and as such have been proposed as potentially useful bioindicators. Based on the relatively limited number of studies available, bats are likely excellent indicators in habitats such as rivers, forests, and urban sites. However, more testing across broad geographic areas is needed, and establishing research networks is fundamental to reach this goal. Some limitations to using bats as bioindicators exist, such as difficulties in separating cryptic species and identifying bats in flight from their calls. It is often also problematic to establish the environmental factors that influence the distribution and behaviour of bats.

Abstract

Bats show responses to anthropogenic stressors linked to changes in other ecosystem components such as insects, and as K-selected mammals, exhibit fast population declines. This speciose, widespread mammal group shows an impressive trophic diversity and provides key ecosystem services. For these and other reasons, bats might act as suitable bioindicators in many environmental contexts. However, few studies have explicitly tested this potential, and in some cases, stating that bats are useful bioindicators more closely resembles a slogan to support conservation than a well-grounded piece of scientific evidence. Here, we review the available information and highlight the limitations that arise in using bats as bioindicators. Based on the limited number of studies available, the use of bats as bioindicators is highly promising and warrants further investigation in specific contexts such as river quality, urbanisation, farming practices, forestry, bioaccumulation, and climate change. Whether bats may also serve as surrogate taxa remains a controversial yet highly interesting matter. Some limitations to using bats as bioindicators include taxonomical issues, sampling problems, difficulties in associating responses with specific stressors, and geographically biased or delayed responses. Overall, we urge the scientific community to test bat responses to specific stressors in selected ecosystem types and develop research networks to explore the geographic consistency of such responses. The high cost of sampling equipment (ultrasound detectors) is being greatly reduced by technological advances, and the legal obligation to monitor bat populations already existing in many countries such as those in the EU offers an important opportunity to accomplish two objectives (conservation and bioindication) with one action.

Mercury Concentrations in Big Brown Bats (Eptesicus fuscus) of the Finger Lakes Region, New York

The northeastern United States receives elevated mercury (Hg) deposition from United States and global emissions, making it critical to understand the fate of Hg in watersheds with a variety of aquatic habitats and land use types, such as the Finger Lakes region of New York State. Bats are valuable and important organisms to study chronic Hg exposure, because they are at risk of sublethal effects from elevated Hg exposure. The objectives of this study were to: (1) determine total Hg (THg) and methylmercury (MeHg) concentrations in big brown bats (Eptesicus fuscus) of the Finger Lakes region; (2) assess whether morphometric, temporal, or spatial factors predict bat Hg concentrations; and (3) investigate the role of trophic position and diet represented by stable isotopes of carbon and nitrogen in explaining variations in bat Hg concentrations. We found comparable THg and MeHg concentrations to previous studies (THg range 1-45 ppm, MeHg range 0.5-38 ppm) in big brown bat fur collected throughout the Finger Lakes region. On average, MeHg made up 81% of THg in bat fur. Fifteen percent of our samples showed higher THg than a proposed toxicity threshold of 10 ppm. Together, dominant land cover and % wetland cover explained bat THg in the Finger Lakes. Trophic position (i.e., δ¹⁵N) was strongest in predicting bat THg in forests but was a weaker predictor of Hg bioaccumulation in bats from agricultural and urban areas. The range of Hg concentrations found in this study warrants further examination into the potential toxicological impacts of Hg to wildlife and the role of land use in Hg exposure to terrestrial organisms of the Finger Lakes.

A comparison of nutritional value of native and alien food plants for a critically endangered island flying-fox

Habitat loss and alteration are two of the biggest threats facing insular flying-foxes. Altered habitats are often re-vegetated with introduced or domestic plant species on which flying-foxes may forage. However, these alien food plants may not meet the nutritional requirements of flying-foxes. The critically endangered Christmas Island flying-fox (CIFF; Pteropus natalis) is subject to habitat alteration and the introduction of alien food plants, and therefore is a good model species to evaluate the potential impact of alien plant species on insular flying-foxes. In this study, we evaluated nutritional content of native food plants to determine how flying-foxes historically met their nutritional requirements. Furthermore, we compared the nutritional content of native and alien fruits to predict possible impacts of alien plants on insular flying-foxes. Native and alien fruits and flowers, and native foliage (leaves, petals, and petioles) commonly consumed by the CIFF were collected and evaluated for soluble sugars, crude protein, non-fiber carbohydrates, and nine minerals. Evaluation of native food plants suggests that flying-foxes meet energy requirements by consuming fruit and nectar. However, fruit and nectar are low in protein and essential minerals required for demanding life periods; therefore, flying-foxes likely supplement their diets with pollen and foliage. Thus, flying-foxes require a diverse array of plants to meet their nutritional requirements. Compared to native fruits, alien fruits contained significantly higher non-fiber carbohydrates, and this may provide an important energy source, particularly from species that bear fruit year-round. Median mineral concentrations in alien fruit species, however, were deficient compared to native fruits, suggesting major (or even seasonal) shifts in the proportion of alien species in the CIFF diet could lead to nutritional imbalances. This study confirms the need to quantify nutritional parameters in addition to feeding ecology when evaluating habitat quality to inform conservation actions that can be applied both locally and globally.

Wing membrane and Fur as indicators of metal exposure and contamination of internal tissues in bats

All European bats are protected by the EU and Associated Members legal regulations. Being insectivorous and top predators, they can be particularly exposed to persistent organic and inorganic pollutants. It is surprising how little is known about the impact of environmental pollutants on bats from physiological to populational levels. In this study we focused on contamination with trace metals of first-year bats from Kharkiv city, NE Ukraine. Tissues from the carcasses of two species, Nyctalus noctula (n = 20) and Eptesicus serotinus (n = 20), were used for metal analysis. The samples of external (wing membrane, fur) and internal (liver, lung, kidney, bones) tissues were analysed for contents of Pb, Cu, Zn, and Cd to see whether fur or wing membrane can be used as proxies for metal contamination of the vital internal tissues. In E. serotinus, significant positive correlations in Pb concentrations were found between all external and internal tissues. For Cd only, correlation between the fur and lung was found, for Cu between the fur and liver, and for Zn between the fur and kidney. In contrast, for N. noctula, only one such correlation was found - between Zn concentrations in the fur and kidney. The tissues differed significantly in concentrations of all studied metals, with no difference between the species. The results showed that the fur and wing membrane can be used as good proxies for Pb concentrations in internal organs of E. serotinus, but not necessarily for other metals or for N. noctula. The results for Pb are, however, encouraging enough to conclude that the topic is worth further studies, covering more species, a wider age range and more diverse environments.

Wastewater treatment works change the intestinal microbiomes of insectivorous bats

Mammals, born with a near-sterile intestinal tract, are inoculated with their mothers’ microbiome during birth. Thereafter, extrinsic and intrinsic factors shape their intestinal microbe assemblage. Wastewater treatment works (WWTW), sites synonymous with pollutants and pathogens, receive influent from domestic, agricultural and industrial sources. The high nutrient content of wastewater supports abundant populations of chironomid midges (Diptera), which transfer these toxicants and potential pathogens to their predators, such as the banana bat Neoromicia nana (Vespertilionidae), thereby influencing their intestinal microbial assemblages. We used next generation sequencing and 16S rRNA gene profiling to identify and compare intestinal bacteria of N. nana at two reference sites and two WWTW sites. We describe the shared intestinal microbiome of the insectivorous bat, N. nana, consisting of seven phyla and eleven classes. Further, multivariate analyses revealed that location was the most significant driver (sex, body size and condition were not significant) of intestinal microbiome diversity. Bats at WWTW sites exhibited greater intestinal microbiota diversity than those at reference sites, likely due to wastewater exposure, stress and/or altered diet. Changes in their intestinal microbiota assemblages may allow these bats to cope with concomitant stressors.

Exposure to pesticides in bats

Bats provide a variety of ecological services that are essential to the integrity of ecosystems. Indiscriminate use of pesticides has been a threat to biodiversity, and the exposure of bats to these xenobiotics is a threat to their populations. This study presents a review of articles regarding the exposure of bats to pesticides published in the period from January 1951 to July 2020, addressing the temporal and geographical distribution of research, the studied species, and the most studied classes of pesticides. The research was concentrated in the 1970s and 1980s, mostly in the Northern Hemisphere, mainly in the USA. Of the total species in the world, only 5% of them have been studied, evaluating predominantly insectivorous species of the Family Vespertilionidae. Insecticides, mainly organochlorines, were the most studied pesticides. Most research was observational, with little information available on the effects of pesticides on natural bat populations. Despite the advances in analytical techniques for detecting contaminants, the number of studies is still insufficient compared to the number of active ingredients used. The effects of pesticides on other guilds and tropical species remain poorly studied. Future research should investigate the effects of pesticides, especially in sublethal doses causing chronic exposure. It is crucial to assess the impact of these substances on other food guilds and investigate how natural populations respond to the exposure to mixtures of pesticides found in the environment.

Landscape-level toxicant exposure mediates infection impacts on wildlife populations

Anthropogenic landscape modification such as urbanization can expose wildlife to toxicants, with profound behavioural and health effects. Toxicant exposure can alter the local transmission of wildlife diseases by reducing survival or altering immune defence. However, predicting the impacts of pathogens on wildlife across their ranges is complicated by heterogeneity in toxicant exposure across the landscape, especially if toxicants alter wildlife movement from toxicant-contaminated to uncontaminated habitats. We developed a mechanistic model to explore how toxicant effects on host health and movement propensity influence range-wide pathogen transmission, and zoonotic exposure risk, as an increasing fraction of the landscape is toxicant-contaminated. When toxicant-contaminated habitat is scarce on the landscape, costs to movement and survival from toxicant exposure can trap infected animals in contaminated habitat and reduce landscape-level transmission. Increasing the proportion of contaminated habitat causes host population declines from combined effects of toxicants and infection. The onset of host declines precedes an increase in the density of infected hosts in contaminated habitat and thus may serve as an early warning of increasing potential for zoonotic spillover in urbanizing landscapes. These results highlight how sublethal effects of toxicants can determine pathogen impacts on wildlife populations that may not manifest until landscape contamination is widespread.

Investigation into the utility of flying foxes as bioindicators for environmental metal pollution reveals evidence of diminished lead but significant cadmium exposure

Due to their large range across diverse habitats, flying-foxes are potential bioindicator species for environmental metal exposure. To test this hypothesis, blood spots, urine, fur, liver and kidney samples were collected from grey-headed flying-foxes (Pteropus poliocephalus) and black flying-foxes (P. alecto) from the Sydney basin, Australia. Concentrations of arsenic, cadmium, copper, lead, mercury and zinc and 11 other trace metals were determined using inductively coupled plasma mass spectrometry. As predicted, kidney and fur lead concentrations were lower compared to concentrations found in flying-foxes in the early 1990's, due to reduced environmental lead emissions. Tissue cadmium concentrations in flying-foxes were higher compared to previous studies of flying-foxes and other bat species, suggesting that flying-foxes were exposed to unrecognized cadmium sources. Identification of these sources should be a focus of future research. Urine concentrations of arsenic, cadmium, mercury, and lead were proportional to kidney concentrations. Given that urine can be collected from flying-foxes without handling, this demonstrates that many flying-foxes can be assessed for metal exposure with relative ease. The analysis of blood spots was not viable because of variable metal concentrations in the filter paper used. Fur concentrations of metals correlated poorly with tissue concentrations at the low levels of metals found in this study, but fur could still be a useful sample if flying-foxes are exposed to high levels of metals. Lastly, heat inactivation had minimal impact on metal concentrations in kidney and liver samples and should be considered as a tool to protect personnel working with biohazardous samples.

Mercury bioaccumulation in tropical bats from a region of active artisanal and small-scale gold mining

Mercury negatively affects human and animal health. Artisanal and small-scale gold mining can be a major local source of mercury contamination, especially into aquatic systems in tropical areas. Animals associated with mercury-contaminated aquatic systems are at high risk of experiencing effects of this heavy metal, but it is not clear how far the effects may extend into nearby terrestrial systems. We report mercury contamination levels in bats in agricultural areas at increasing distances from gold mining (~3-89 km of distance). We hypothesized that bat mercury concentrations would differ between feeding guilds, land use types, and be higher at sites closer to gold mining areas. We collected 112 fur samples from 30 bat species and eight guilds, and provide the first reports of concentrations in 12 species. All mercury concentrations were below the level at which health is likely to be affected (10 ppm). We found guild-influenced differences among mercury concentration levels, with the highest concentrations in aerial insectivores and carnivores, and the lowest in canopy frugivores. Our results suggest insectivorous and carnivorous bats may still be at some risk even at sites distant from aquatic mercury contamination. We did not find an effect of agricultural land-use type on mercury concentrations within species or guilds, suggesting mercury contamination did not extend to agricultural sites from areas of gold mining activities, and that these agricultural activities themselves were not an important source of mercury. We conclude bats did not demonstrate a signature of mercury risk either as a result of proximity of gold mining, or as a result of agricultural activities.

Insectivorous bats as biomonitor of metal exposure in the megalopolis of Mexico and rural environments in Central Mexico

The Megalopolis of Mexico is one of the largest cities in the world and presents substantial problems of metal pollution. Insectivorous bats that inhabit this city are potentially exposed to metals and could therefore serve as a good biomonitor. We collected 70 adult male individuals of Tadarida brasiliensis (Chiroptera: Molossidae) from two areas inside the Megalopolis (Cuautitlán and Xochimilco) and two rural environments in Central Mexico (Tequixquiac and Tlalcozotitlán). We analyzed livers to determine the total concentrations of ten metals by the ICP-MS technique, compared concentrations among study sites to provide evidence of metal exposure, and explored the associations between metals and their accumulation patterns in bats. The hepatic metal concentrations we recorded were generally consistent with those of similar studies in insectivorous bats. Higher concentrations of Cu and Zn in Cuautitlán and Xochimilco bats were associated with vehicular traffic. Higher concentrations of V, Cr, and Co in Tequixquiac bats and Cd in Tlalcozotitlán bats were linked with industrial, agricultural, or sewage sources. Variations in Fe and Mn concentrations were related to geogenic sources or local conditions. Similar Ni and Pb concentrations were linked with strong homeostatic controls or historical pollution. Accumulation patterns showed that all urban bats belonged to a single population with similar degrees of metal exposure, while rural bats belonged to two different populations exposed to different metals. Our results highlight the need to monitor the emissions generated by particular sources in each study site.

Sentinel species for biomonitoring and biosurveillance of environmental heavy metals in Nigeria

Nigeria receives copious annual precipitation to nourish its forests and agriculture, it has an extensive river drainage system, and it possesses valuable mineral deposits that stimulate both commercial and artisan mining activities. The combination of these features complicates Nigeria's efforts to produce adequate amounts of healthy foods to support its population. Toxic heavy metals like lead, cadmium, and mercury, and toxic metalloids such as arsenic, are also present in its mineral deposits and they migrate gradually into the soil and water of Nigeria by natural means. However, mining activities can liberate higher levels of toxic metals, which adversely affect Nigerian ecosystems and its food chains. Thus, environmental pollution due to anthropogenic activities is a major public health concern in Nigeria. This review covers the importance of native Nigerian and African wild and cultivated plants along with livestock and wild animals as sentinel species to evaluate heavy metals as environmental stressors and the use of sentinel species for food safety monitoring and for predicting potential risks to human health.

Current Status of Ecotoxicological Studies of Bats in Brazil

Bats are sensitive to contaminants generated by agricultural activities, mining, and urbanization. In this review, we update the status of bat toxicology in Brazil. Agriculture, for example, in addition to habitat fragmentation and loss, undoubtedly affects non-target organisms through the use of pesticides. Other factors such as trace metals are a neglected problem in the country, as they can deposit on insects and plants reaching bats through the ingestion of these foods. Of the 184 species of bats in the country, only 4.9% have been investigated. The frugivorous species, Artibeus lituratus, has frequently been studied for the effects of pesticide exposure, and impacts at the cellular level on metabolism and reproduction have been observed. Given the scarcity of studies on bat ecotoxicology, we encourage national researchers and scientists elsewhere to increase knowledge of the effects of chemical contaminants on bats in Brazil.

Energy Balance as a Moderator of Neurologic Disease Risk and Progression

Amyotrophic lateral sclerosis (ALS) is a devastating disease that like multiple other neurologic diseases has no curative treatment currently available. Environmental exposures to known neurotoxic compounds (e.g., pesticides, heavy metals, cyanobacterial toxins, etc.) are identified as risk factors associated with ALS. Assuming these environmental factors have causative roles in disease risk and given the ubiquity of these types of exposures for the modern human, why are not more people afflicted with ALS? Herein is proposed an energy balance moderation framework (EBMF)-a framework that postulates energy balance as a key moderator of neurologic disease risk. The EBMF proposes that the ability of the body to handle toxic compound exposures through excretion, metabolism, and/or storage impacts the acute and chronic tissue-specific toxicity which is moderated by energy balance. In this model, positive energy balance (weight gain or excess body weight/mass) would be protective against acute neurotoxic exposure permitting the assimilation and sequestration of toxic compounds within body stores separate from the nervous system. However, this protective buffering could be lost during sustained negative energy balance (weight loss) with the release of sequestered compounds redistributing to the nervous system. The EBMF may have relevance beyond ALS for other neurologic diseases with demonstrated environmental risks (such as Alzheimer's and Parkinson's disease) and offers new insights into potential strategies to reduce disease risk and develop novel treatments.

Micronucleus test in tadpole erythrocytes: Trends in studies and new paths

The micronucleus test has been applied for more than three decades in tadpoles, generating an early warning of environmental quality. In this study, we reviewed 48 articles on the micronucleus test in tadpoles, published between 1987 and 2018. The findings reveal that pesticides have been the main topic discussed in the induction of micronucleus and other nuclear abnormalities in anuran larvae to the detriment of the widespread use of compounds used in agriculture. In addition to pesticides, a number of other xenobiotic agents have been targeted for genotoxic damage, such as heavy metals, radiation and wastewater. An appeal is reported to environmental contaminants, which when released naturally into the environment or because of human activities may contaminate aquatic habitats, threatening populations of tadpoles that depend on these environments for their survival. Larvae can bioaccumulate these contaminants that cause progressive impacts, ranging from DNA damage to metamorphosis delays, as well as malformations. We found that Argentina is the main driving force for the application of this test in anuran larvae along with Brazil. Different erythrocyte malformations have been reported for the erythrocyte nuclear abnormalities test, binucleated cells, nuclear buds, notched, lobed, reniform, nuclear bebbled, anucleated, picnotic and apoptotic cells are the most cited. In summary, the presence of chemical or physical agents, along with other disturbances of the habitat, can have a significant impact on the life history of the species, contributing to the decline of anuran populations.

Environmental exposure to non-essential trace elements in two bat species from urbanised (Tadarida teniotis) and open land (Miniopterus schreibersii) areas in Italy

Bats are particularly suited as bioindicators of trace element pollution due to their longevity and their position in the trophic chain. In this study, the concentrations of ten non-essential trace elements (Al, As, Ba, Cd, Hg, Pb, Sb, Sr, Th, Tl) were determined in the tissues (whole body, skin-fur, skinned body, liver, kidney and bone) of lactant Tadarida teniotis from a nursery colony in Rome. A large number of bats from this nursery died before fledging and had bone deformities and fractures. The concentrations of non-essential trace elements in bone and whole body were also analysed in adult specimens of Miniopterus schreibersii from a colony located in a natural park in Northern Italy. In lactant T. teniotis, the Pb concentration decreased in the following order: bone>liver>skinned body>whole body>skin-fur>kidney, and exceeded the toxic threshold associated with negative effects reported for different mammalian species. The levels of the other non-essential trace elements were within a range indicative of low environmental contamination in both species. Significant interspecies differences (P < 0.05) were observed for concentrations of Pb and Ba, higher in the bones of T. teniotis, and of Cd, Hg and Sr, higher in the bones of M. schreibersii. In lactant T. teniotis, the different sources of Pb exposure, through inhalation and/or food, may represent a potential threat to the colony of this synanthropic European bat.

Wing membrane and fur samples as reliable biological matrices to measure bioaccumulation of metals and metalloids in bats

There is a growing conservation concern about the possible consequences of environmental contamination in the health of bat communities. Most studies on the effects of contaminants in bats have been focused on organic contaminants, and the consequences of bat exposure to metals and metalloids remain largely unknown. The aim of this study was to evaluate the suitability of external biological matrices (fur and wing membrane) for the assessment of exposure and bioaccumulation of metals in bats. The concentration of arsenic, cadmium, cobalt, chromium, copper, manganese, nickel, lead, selenium and zinc was measured in internal organs (liver, heart, brain), internal (bone) and external tissues (wing membrane, fur) collected from bat carcasses of four species (Hypsugo savii, Nyctalus leisleri, Pipistrellus pipistrellus, Pipistrellus pygmaeus) obtained in windfarm mortality searches. With the exception of zinc (P = 0.223), the results showed significant differences between the concentrations of metals in the analyzed tissues for all metals (P < 0.05). Significant differences were also found between organs/tissues (P < 0.001), metals (P < 0.001) and a significant interaction between organs/tissues and metals was found (P < 0.001). Despite these results, the patterns in terms of metal accumulation were similar for all samples. Depending on the metal, the organ/tissue that showed the highest concentrations varied, but fur and wing had the highest concentrations for most metals. The variability obtained in terms of metal concentrations in different tissues highlights the need to define standardized methods capable of being applied in monitoring bat populations worldwide. The results indicate that wing membrane and fur, biological matrices that may be collected from living bats, yield reliable results and may be useful for studies on bats ecotoxicology, coupled to a standardized protocol for large-scale investigation of metal accumulation.

Mercury Concentrations in the Two-Toed Amphiuma (Amphiuma means) and the Lesser Siren (Siren intermedia): Validating Non-lethal Sampling Methods in Southeastern Aquatic Salamanders

The global decline of amphibians is a major conservation issue. Many stressors are recognized for this decline including exposure to environmental contaminants. Mercury (Hg) is an environmental contaminant that bioaccumulates in wildlife and can cause a variety of negative impacts across taxa, including amphibians. Amphiuma and Siren spp. can comprise a large portion of biomass within their respective ecosystems, and thus, likely serve as important predators or prey in wetland communities. However, due to their cryptic nature, little is known about their ecology, diet, and accumulation potential. We sought to validate a nonlethal sampling method to quantify total mercury (THg) in two enigmatic species of aquatic salamanders: the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia). We examined relationships between THg content in lethal (whole-body) and nonlethal (tail clip) samples. Tail clips were statistically significant predictors of whole-body THg (all p < 0.001), explaining 84-89% of variation in whole-body THg. Average whole-body THg (mg/kg) did not significantly differ between the two species (p = 0.97), and overall, they had similar whole-body THg content (S. intermedia = 0.330 ± 0.04, n = 18; A. means = 0.333 ± 0.07, n = 11). To our knowledge, these data represent the first reported Hg burdens in A. means and S. intermedia.

Research trends on bats in China: A twenty-first century review

In this century, China has sustained unparalleled economic development, leading to exponentially growing investments in scientific research. Yet, the demand for research-funding is large and tracing the current knowledge is a key step to define priority research topics. In this same span, studies on bats in China have uncovered an overlooked diversity and revealed novelties in bats’ evolutionary history and life-history aspects. All this 21st-century knowledge, however, is scattered and a large part is concealed from most of the international scientific community in Mandarin-language articles. Here, we summarize the post-millennium (2000–2017) research on bats in China and point out trends and future directions based on neglected topics, groups, and regions. In addition, we provide an up-to-date list of bat species in China. We retrieved 594 publications related to bats in China, nearly half were written in Mandarin. At least 147 bat species are present in China, which places it among the most bat-rich countries in the world. There was a significant positive trend on the number of publications, from 12.5 annual average in 2000–2005 to 46.5 in recent years, reflecting the Chinese economic-scientific development in this century. We found marked taxonomic and spatial biases. Half of the studies in this century focused on Rhinolophus, Myotis, and Hipposideros, and the southern and eastern provinces were the most studied. Systematic/taxonomy and Ecology were the predominant topics post-millennium, whereas only 10 articles have clear conservation-driven goals. Our review shows that the majority of studies were focused on the least concern, cave-dweller species, and on bat-rich provinces. Future projects should address the effects of human-modified landscapes on bat community to define proper conservation actions. We discuss some priority actions and projects that will help to enhance bat protection in China.

Micronucleus and other nuclear abnormalities in exfoliated cells of buccal mucosa of bats at different trophic levels

The micronucleus (MN) test in exfoliated cells of the buccal mucosa is a relatively non-invasive method for the monitoring of populations exposed to genotoxic risks. In this study, the MN test was used as bats conservation strategy. The highest frequencies of micronuclei were recorded in the frugivorous bats sampled in both urban and agricultural environments, as well as in insectivorous bats from the urban zone. Female of this group (insectivorous) presented higher frequency of MN when compared to males. Other guilds showed no difference in gender assessments in each environment, as well as in the correlation between weight and MN. In addition to micronuclei, a number of other types of nuclear abnormality were recorded, including binucleated cells and karyolysis in the frugivores from the agricultural environment. Binucleated cells were also relatively common in urban frugivores and insectivores, and karyolysis was common in insectivores. Nectarivorous bats did not exhibit a significant increase in any type of nuclear abnormality in either environment. In summary, study results indicate that buccal mucosa of bats is a sensitive site for detecting micronuclei and other nuclear abnormalities. However, more research is needed to indicate whether xenobiotic agents are affecting this cellular integrity.