Contents lists available at ScienceDirect

Environmental Research

journal homepage: www.elsevier.com/locate/envres

Insectivorous bats as biomonitor of metal exposure in the megalopolis ofMexico and rural environments in Central MexicoDaniel Ramos-Ha,b,∗, Rodrigo A. Medellínb, Ofelia Morton-Bermeac

a Posgrado en Ciencias Biológicas, Universidad Nacional Autónoma de México, Av. Ciudad Universitaria 3000, Ciudad Universitaria, C.P. 04510, Coyoacán, Ciudad deMéxico, Mexicob Laboratorio de Ecología y Conservación de Vertebrados Terrestres, Instituto de Ecología, Universidad Nacional Autónoma de México, Circuito Exterior s/n, CiudadUniversitaria, C.P. 04510, Coyoacán, Ciudad de México, Mexicoc Laboratorio de ICP-MS, Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica s/n, Ciudad Universitaria, C.P. 04510,Ciudad de México, Mexico

A R T I C L E I N F O

Keywords:Urban batsHepatic metal concentrationsMetal associationsAccumulation patternsAnthropogenic sources

A B S T R A C T

The Megalopolis of Mexico is one of the largest cities in the world and presents substantial problems of metalpollution. Insectivorous bats that inhabit this city are potentially exposed to metals and could therefore serve asa good biomonitor. We collected 70 adult male individuals of Tadarida brasiliensis (Chiroptera: Molossidae) fromtwo 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 theICP-MS technique, compared concentrations among study sites to provide evidence of metal exposure, andexplored the associations between metals and their accumulation patterns in bats. The hepatic metal con-centrations we recorded were generally consistent with those of similar studies in insectivorous bats. Higherconcentrations of Cu and Zn in Cuautitlán and Xochimilco bats were associated with vehicular traffic. Higherconcentrations 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 localconditions. Similar Ni and Pb concentrations were linked with strong homeostatic controls or historical pollu-tion. Accumulation patterns showed that all urban bats belonged to a single population with similar degrees ofmetal exposure, while rural bats belonged to two different populations exposed to different metals. Our resultshighlight the need to monitor the emissions generated by particular sources in each study site.

1. Introduction

Large cities centralize several human activities that generate pol-lution problems, impacting biotic and abiotic metal accumulation(Davydova, 2005). The Metropolitan Area of Mexico City (hereafterreferred to as the Megalopolis), which comprises Mexico City and itssurrounding conurbation in the Estado de México, is one of the largesturban areas in the world and presents significant levels of metal pol-lution (Morton-Bermea et al., 2009, 2018). The Secretary of the En-vironment of Mexico City (SEDEMA, 2016) reported emissions of 5.3million motor vehicles and 70 thousand factories as principal sources ofmetal pollution in the Megalopolis, which has more than 21 millioninhabitants.

Previous studies inside the Megalopolis analyzed samples of topsoil(Morton-Bermea et al., 2009; Rodríguez-Salazar et al., 2011) and

particulate matter (Morton-Bermea et al., 2018; Querol et al., 2008),and they found that chromium (Cr), cobalt (Co), manganese (Mn), andiron (Fe) were linked with geogenic sources, whereas copper (Cu), zinc(Zn), lead (Pb) and cadmium (Cd) were associated with anthropogenicsources. The presence of vanadium (V) and nickel (Ni) were linked withboth source types. Metals in wastewater and aerial emissions generatedby the Megalopolis can impact its surrounding areas, and metalsemitted from the Tula Industrial Complex can influence metal contentsin the Megalopolis (Flores et al., 1997; Lucho-Constantino et al., 2005;Querol et al., 2008).

Studies of metal pollution on living organisms provide evidence ofharm and exposure (Nordberg et al., 2015; O'Shea and Johnston, 2009).Previous works investigating metals in plants, fishes and birds in theMegalopolis (Aldana et al., 2018; Delgado et al., 1994; García-Sánchezet al., 2019; Guzmán-Morales et al., 2011) have shown evidence of

https://doi.org/10.1016/j.envres.2020.109293Received 23 June 2019; Received in revised form 21 February 2020; Accepted 22 February 2020

∗ Corresponding author. Laboratorio de Ecología y Conservación de Vertebrados Terrestres, Instituto de Ecología, Universidad Nacional Autónoma de México,Circuito Exterior s/n, Ciudad Universitaria, C.P. 04510, Coyoacán, Ciudad de México, Mexico.

E-mail address: danielramosh7@iecologia.unam.mx (D. Ramos-H).

Environmental Research 185 (2020) 109293

Available online 22 February 20200013-9351/ © 2020 Elsevier Inc. All rights reserved.

T

exposure. However, cautious interpretation is needed because theirmetal concentrations could be strongly influenced by very local or ex-ternal sources. According to Clark and Shore (2001), O'Shea andJohnston (2009), and Zukal et al. (2015), bats can serve as biomonitorsfor metal exposure at a regional scale since they show several ecologicaland methodological advantages over other animals. In contrast to othersmall mammals or birds, bats have high rates of metabolism and foodintake, so they can be more susceptible to metal accumulation throughdiet. Bats can also be used to indicate metal exposure in large areas dueto their high mobility. Capture techniques are accessible and allowobtaining a representative sample size of the bat populations. Since batsinhabit different human-dominated ecosystems, they can be useful tocompare the metal exposure among habitats or across pollution gra-dients. It has been reported that bats have been exposed to metals frommining activities (O'Shea et al., 2001; Zocche et al., 2010), untreatedwastewater (Naidoo et al., 2013), and atmospheric pollution (Harionoet al., 1993).

Insectivorous bats like Tadarida brasiliensis (Chiroptera: Molossidae)that inhabit the Megalopolis are potentially exposed to metals andcould constitute a good biomonitor of metal exposure in CentralMexico. This bat species feeds on a great number of insects per night(Lee and McCracken, 2005; López, 2009) and therefore will bioaccu-mulate metals from its diet (Thies and Gregory, 1994; Zocche et al.,2010). Insectivorous bats also need to drink water (Wilkins, 1989) socan ingest metals from polluted water. Since this species is highlymobile and can disperse easily in its habitats (Ávila-Flores and Fenton,2005; McCracken et al., 2016), it can inhale or ingest a large amount ofmetal particles present in the atmosphere during flight. Metals de-posited in its fur can be absorbed by the skin or ingested whengrooming (Hariono et al., 1993; Rendón-Lugo et al., 2017). It is possibleto perform comparisons among sites with different levels of humandisturbance because T. brasiliensis is a resident and a common bat in theMegalopolis and its surrounding rural environments (García, 2018;Pérez, 2015; Sánchez et al., 1989).

Livers of mammalian species play an important role in the meta-bolism and accumulation of metals (Nordberg et al., 2015; Sidhu et al.,2004; Stamoulis et al., 2007), and this tissue is commonly used formetal analysis (Hernout et al., 2016; López-Alonso et al., 2004; Zukalet al., 2015). Essential metals such as Cr, Co, Mn, Ni, Fe, Cu, and Znparticipate in different physiological processes, thus they must be ab-sorbed and excreted constantly by the organism to remain at homeo-static levels. In excess, essential metals can be toxic, and if they arescarce, deficiencies can occur. In contrast, V, Pb, and Cd have no knownimportance in the metabolism of mammals and are considered non-essentials metals. However, they can cause toxicity even in low con-centrations since they may induce mutagenesis and carcinogenesis, aswell as disturb the metabolism of the essential metals (Nordberg et al.,2015; Sidhu et al., 2004; Soetan et al., 2010). Although interactionsbetween metals have been investigated in laboratory animals, little isknown in wild mammals. The knowledge of metal interactions inwildlife could be useful to suggest co-exposure of metals (Hernout et al.,2016) or mechanisms in the metabolism of metals (as suggested incattle by López-Alonso et al., 2004).

In this study, we evaluated the total concentrations of V, Cr, Co, Ni,Mn, Fe, Cu, Zn, Pb, and Cd in livers of Tadarida brasiliensis (Chiroptera:Molossidae) individuals inhabiting two sites inside the Megalopolis andtwo rural environments in Central Mexico. Our aims were: a) to de-termine the metal concentrations in Tadarida brasiliensis in CentralMexico; b) to compare the metal concentrations among bats from ourstudy sites to provide evidence of exposure; c) to explore the associationbetween pairs of metals; and d) to explore the accumulation patterns ofmetals in bats. We hypothesized that variations of metal concentrationsamong bats from our sites would be mainly associated with differenttypes and intensities of anthropogenic sources.

2. Materials and methods

2.1. Study area

Bats were collected in roosts located in four sites in Central Mexicothat displayed different types and intensities of human intervention.Two of our study sites were located within the Megalopolis, in thenorthern and southern part, hereafter Cuautitlán and Xochimilco, re-spectively (Fig. 1). Urban bats were collected in the Cuautitlán

Fig. 1. Location of the study sites in Central Mexico. The Tula IndustrialComplex (TIC) is located north of our study sites, inside the Mezquital Valley inthe State of Hidalgo.

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

2

municipality (19°39′42″N, 99°10′33″W) in the Estado de México and inthe Xochimilco municipality (19°14′55″N, 99°06′21″W) in the Ciudadde México. Urban habitats like large parks and illuminated areas are themost preferred by Tadarida brasiliensis for foraging (Ávila-Flores andFenton, 2005). The rainy season in the Megalopolis and surroundingareas in Central Mexico usually occurs from May to October, with thedry season extending over the rest of the year. Particulate matter in theMegalopolis can show high levels during periods with dry conditions(Morton-Bermea et al., 2018; Mugica et al., 2002). The prevailing winddirection in the Megalopolis is from north and northeast to south(Jáuregui, 2000). The northern part of the Megalopolis has higherconcentration of industrial activities and vehicular movement as well asgreater population density than the southern part, where residentialand commercial activities dominate, and large extensions of green andconservation areas are present (Guzmán-Morales et al., 2011;Rodríguez-Salazar et al., 2011). The predominant parent material in theMegalopolis is extrusive igneous (Morton-Bermea et al., 2018). Ap-proximately 3 km from Xochimilco is located Xochimilco Lake, in theCiudad de México, which receives both treated and untreated domesticand agricultural wastewater (Aldana et al., 2018).

Rural bats were collected at two study sites from rural environmentslocated 30 km north and 145 km south from the Megalopolis, hereafterTequixquiac and Tlalcozotitlán, respectively (Fig. 1). In rural environ-ments where farming occurs, Tadarida brasiliensis use agricultural andrelated areas as foraging habitats, feeding on substantial amounts ofinsect pests (Lee and McCracken, 2005; López, 2009). Bats from the firstrural site were collected in an agricultural area in the Tequixquiacmunicipality (19°56′49″N, 99°06′48″W) in the Estado de México.Farming activities are conducted in 42.3% of the municipal territory,whereas grassland, urban areas, and xerophytic scrubland occupy 25.5,17.8 and 14.4%, respectively. The predominant rocks at the Te-quixquiac municipality are extrusive igneous (INEGI, 2010). Two un-treated sewage canals emerge 6 km from Tequixquiac, taking waste-water from the Megalopolis toward the Mezquital Valley in the State ofHidalgo. The sewage is used in farming both in the Tequixquiac mu-nicipality and Mezquital Valley (Lucho-Constantino et al., 2005; Pérez,2015). The Tula Industrial Complex is located 20 km northwest fromTequixquiac in the southern part of Mezquital Valley, and it comprisesseveral factories including a petroleum refinery, an electricity powerplant, and various cement plants (Zambrano et al., 2009). Bats from thesecond rural site were collected in a cave located in the town of Tlal-cozotitlán (17°53′00″N, 99°07′32″W) in the Copalillo municipality,State of Guerrero. Dry deciduous tropical forest and agriculture occupy68.1 and 13.5% of the municipal territory, respectively, while the urbanareas do not exceed 0.5%. Sedimentary rock is the predominant parentmaterial in the Copalillo municipality (INEGI, 2010). There are no largecities or industrial areas at a distance of at least 100 km from Tlalco-zotitlán. A summary of the main characteristics of each sampling site isavailable as supplementary material (Supplemental Table 1).

2.2. Bat sampling

Bats were captured using mist nests placed in front of roost entriesat the time bats exited or returned. We sampled bats from April to June2017 and collected 20 bats from each of our study sites, except fromTlalcozotitlán where only ten bats were collected. We only sacrificedadult male specimens to avoid variations caused by age and sex(Scientific Community License SGPA/DGVS/14509/16). Bats were eu-thanized according to the IACUC protocol of the ASM (Sikes, 2016).Liver from each bat was removed and deposited into plastic cryotubeswith a 96% ethanol solution, following Williams et al. (2010). Tissuesamples and bat carcasses were kept at the Institute of Ecology, Na-tional Autonomous University of Mexico (UNAM).

2.3. Chemical analysis and quality control

Liver samples were prepared at the Laboratory of EnvironmentalAnalysis of the School of Science, UNAM. Liver tissues were dried in anoven at 40 °C for 48 h and then weighed with an analytical scale.Around 0.16 g of dried samples were digested in a microwave oven(Mars x, CEM Corporation) with 7 ml of 50% concentrated nitric acid(HNO3) in Teflon vessels. Total hepatic concentrations of V, Cr, Co, Ni,Mn, Fe, Cu, Zn, Pb and Cd were determined by Inductively CoupledPlasma-Mass Spectrometry (ICP-MS; model iCAP Q, Thermo Scientific)at the Institute of Geophysics, UNAM. These metals were selected be-cause they are recognized as of greatest concern for wildlife (Nordberget al., 2015; Zukal et al., 2015) and for environmental conditions in theMegalopolis and its surrounding areas (Lucho-Constantino et al., 2005;Morton-Bermea et al., 2009, 2018; Zambrano et al., 2009). The ICP-MStechnique has a high capacity to quantify metals even at very lowconcentrations and allows the analysis of several metals simultaneously(O'Shea and Johnston, 2009). For the analytical procedure, a calibra-tion curve was generated using a 15-point curve (between 0.1 and500 ng/L) with standard solutions, which were prepared by diluting10 μg/g multi-element standard solutions (High Purity Standard) with2% HNO3. Instrumental drift was corrected using indium as the internalstandard prepared from a certified stock solution of 10 ng/g (HighPurity Standard). Detection limits for ten metals were estimated asthree times the standard deviation values of ten replicates of the blanksamples. These were 9.1 ng/g for Fe and less than 0.6 ng/g for the restof metals (Supplemental Table 2). All reagents used were of analyticalgrade.

The quality of the analytical procedure was assessed using DOLT-4dogfish liver as standard reference material (National Research CouncilCanada). Five replicates of DOLT-4 samples were analyzed togetherwith the bat liver samples, and they were performed to the same pro-cedure of preparation and analysis (Supplemental Table 2). All metalrecoveries ranged from 63.5 to 123.5%, except for Mn. Reference ma-terial was not certified for Mn. However, Mn concentrations among thefive replicates were consistent with a 5.6% coefficient of variation. Thecoefficients of variation of all metals varied between 3.8 and 17.6%.Liver samples were measured randomly in duplicates and triplicates,which had consistent concentrations for the ten metals analyzed. Wedid not find greater interference in the blank samples. Concentrationswere expressed in μg/g on a dry weight (dw) basis.

2.4. Statistical analysis

All data generated in our work were used for statistical purposes,including those non-detected concentrations, which were replaced by avalue of one-half the corresponding detection limit. Since most of theresiduals for the hepatic metal concentrations did not show normaldistribution nor variance homogeneity, we used non-parametricmethods to analyze our data. We used Kruskal-Wallis test to comparehepatic metal concentrations among study sites, followed by a Dunnpost hoc test for each pair of study sites considering Bonferroni adjust-ment of α/2. Spearman rank correlations were used to assess the as-sociations between pairs of metal concentrations. Factor analysis wasperformed on the normalized data for the concentrations of the tenmetals to evaluate the accumulation patterns of metals in bats. Theextraction method of this statistical technique was the correlationsmatrix of the principal component analysis. The level of statisticalsignificance considered was below α = 0.05. We used the software R-studio (version 3.4.2) (R Core Team, 2017) and Past (version 1.7)(Hammer et al., 2001).

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

3

3. Results

3.1. Hepatic metal concentrations in Tadarida brasiliensis from CentralMexico

Total concentrations of V, Cr, Co, Ni, Mn, Fe, Cu, Zn, Pb and Cd inliver of all 70 adult male bats Tadarida brasiliensis collected were ana-lyzed (Table 1). The hierarchy of metal concentrations in liver tissueswas Fe > Zn > Cu ≈ Mn > Ni ≈ Cd ≈ Pb ≈ V ≈ Co ≈ Cr. Withthe exception of one individual that showed V and Cr concentrationsbelow the detection limits, all samples analyzed had quantifiable con-centrations for all metals evaluated. Records of Ni in one bat (9.3 μg/g)and Pb in three bats (4.1, 8.2 and 13.5 μg/g) were double or more thanin the rest of bats, so we considered them as highly elevated con-centrations.

3.2. Variations of metal concentrations among sites

We found significant differences in the hepatic concentration ofsome metals among our study sites: V (Kruskal-Wallis test: F = 20.5,P < 0.001), Cr (F = 20, P < 0.001), Co (F = 38.2, P < 0.001), Mn(F = 13.9, P = 0.003), Fe (F = 13.5, P = 0.004), Cu (F = 26.4,P < 0.001), and Cd (F = 16.8, P < 0.001). Comparisons betweenpairs of study sites showed significant differences in metal concentra-tions. Recalling that the two urban sites are Cuautitlán and Xochimilco,and the rural sites are Tequixquiac and Tlalcozotitlán, bats fromTequixquiac (Dunn test: D = 4.3, P < 0.001) and Cuautitlán (D = 3.6,P = 0.001) had higher concentrations of V than Tlalcozotitlán bats(Fig. 2A). Tequixquiac bats had higher concentrations of Cr and Co thanbats from Cuautitlán (Cr: D = 4.16, P < 0.001; Co: D = 4.41,P < 0.001), Xochimilco (Cr: D = 2.7, P = 0.024; Co: D = 5.39,P < 0.001) and Tlalcozotitlán (Cr: D = 3.16, P = 0.005; Co: D = 4.68,P < 0.001) (Fig. 2B and C). Xochimilco bats had higher Mn levels thanTlalcozotitlán bats (D = 3.53, P = 0.001) (Fig. 2D). Tlalcozotitlán batshad lower Fe concentrations than bats from Tequixquiac (D = 2.98,P = 0.009), Cuautitlán (D = 3.37, P = 0.002), and Xochimilco(D = 3.27, P = 0.003) (Fig. 2F). Tequixquiac bats had lower levels ofCu than bats from Cuautitlán (D = 4.42, P < 0.001) and Xochimilco(D = 4.48, P < 0.001) (Fig. 2G). Tlalcozotitlán bats had higher Cdlevels than bats from Tequixquiac (D = 3.22, P = 0.004), Cuautitlán(D = 4.03, P < 0.001), and Xochimilco (D = 2.78, P = 0.016)

(Fig. 2J). Concentrations of Ni (F = 1.2, P = 0.76), Zn (F = 7.6,P = 0.055), and Pb (F = 0.21, P = 0.97) did not vary among sites(Fig. 2E, H, I).

We found no differences in the concentrations of any of the analyzedmetals between bats from Cuautitlán and Xochimilco, both urban sites.Tlalcozotitlán bats showed lower variations in their V, Fe, Cu and Znlevels compared to bats from the other sites. Tequixquiac bats only hadlower variations of Cu and Zn. Zinc and Cu concentrations of bats fromthe rural sites Tequixquiac and Tlalcozotitlán were slightly lower thanbats from the urban Cuautitlán and Xochimilco sites (Fig. 2).

3.3. Associations between metal concentrations

Almost two-thirds of the 45 associations between pairs of metals ofthe 70 bats analyzed were significant (Table 2). Nine of these associa-tions had correlations coefficients of rho ≥ 0.4, so we considered themas associations with a high correlation. The association between Cu andZn was the highest (rho = 0.76, P < 0.001) and was the only re-lationship that was direct and consistent (Fig. 3A). This pattern waspresent in both urban and rural bats as well as in the bats of each studysite. Likewise, Zn was the metal with more associations with rho ≥ 0.4,being also related to Mn, Pb and Cd (Table 2). The association betweenCo and Cr (rho = 0.55, P < 0.001) was high and displayed a differentpattern with respect to the previous one (Fig. 3B). Individuals with Coconcentrations above 0.2 μg/g showed higher dispersion in their Crconcentrations than those below this threshold. There were not im-portant negative associations between concentrations of any metals.

3.4. Accumulation patterns of metals in bats

We performed the factor analysis with data from all bats. Thisanalysis showed three factors with eigenvalues greater than 1, whichtogether explained 60.8% of the variance (Supplemental Table 3).Factor 1 explained 29.5% of the variance and was positively associatedwith the concentrations of Zn, Mn, Cu, V, and Fe. Factor 2 explained19.1% of the variance and was positively associated with the con-centrations of Cu and Zn, and negatively associated with Co, V, and Cr.Finally Factor 3 explained 12.2% of the variance and was associatedwith the concentrations of the remaining metals, positively with Pb andCd, and negatively with Fe and Ni (Supplemental Table 3).

We projected the bats onto the first two-factor axes according to the

Table 1Metal concentrations (μg/g dw) in livers of insectivorous bats reported in our study and similar studies.

Metal This study Allinson et al. (2006) Naidoo et al. (2013) Hernout et al. (2016)

Mexico, n = 70 Australia, n = 20 South Africa, n = 26 United Kingdom, n = 191

(median, range) (mean) (range) (median, range)

V 0.124 (0.025–0.731)a 0.0155Cr 0.038 (0.006–0.382)a 0.33 ≤0.007Co 0.146 (0.065–0.473) 0.0805Mn 16.13 (7.73–37.63) 25.2Ni 0.378 (0.126–2.446)b ≤0.015Fe 967.2 (398.8–1923.4) 706–2118.8Cu 19.24 (10.78–41.54) 29.2 8.054–25.39 10.7 (0.033–30)c

Zn 72.76 (41.64–168.5) 152 191.1–376.2 18.8 (0.8–274)c

Pb 0.164 (0.022–2.004)b 0.18 < 0.042 0.33 (0.0024–10)c

Cd 0.375 (0.08–1.631) 0.45 ≤2.867 0.03 (0.0015–2.5)c

Analytical method ICP-MS ICP-MS ICP-OES ICP-MSReference material DOLT-4 DORM-2 SRM1566b BCR-185R

(dogfish liver) (dogfish muscle) (dried oyster tissue) (bovine liver)Recovery rate 64–123% 85–134% 67–150% 85–100%

a Range without a concentration below the detection limit.b Range without concentrations highly elevated (μg/g): Ni (9.28); Pb (4.07, 8.22, 13.5).c Range that contains most of the samples. Maximum concentrations (μg/g): Cu (71); Zn (5205); Pb (5040); Cd (13).

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

4

Fig. 2. Metal concentrations (μg/g) in livers of Tadarida brasiliensis from our four study sites in Central Mexico. Study sites are ordered from north (left) to south(right). Different letters indicate significant differences among sites (P < 0.025; Dunn test considering a Bonferroni adjustment of α/2). Sample size for Tequixquiac,Cuautitlán and Xochimilco was n = 20, and for Tlalcozotitlán was n = 10. One record of Ni and three of Pb are off-scale.

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

5

accumulation patterns of the ten metals analyzed, and the scatterplotdisplayed three groups (Fig. 4). Factor 1 axis showed Tlalcozotitlán batsas a more homogeneous group since almost all of them had negativevalues. Factor 2 axis showed a clear separation of Tequixquiac bats, asthey were in the negative side of the axis. Cuautitlán and Xochimilcobats were the most dispersed along the Factor 1 axis, and almost all batswere on the positive side of Factor 2 axis.

4. Discussion

4.1. Hepatic metal concentrations in Tadarida brasiliensis from CentralMexico

The hierarchy of metal concentrations presented here could providean insight into their degree of importance in the physiological processesthat take place in the liver of insectivorous bats. This hierarchy supportsthose previously reported by similar studies (Allinson et al., 2006;Hernout et al., 2016; Naidoo et al., 2013). Thus, among the essentialmetals, Fe is the mineral with the highest physiological requirement,followed by Zn, Cu and Mn. Finally Ni, Co, and Cr are required in loweramounts. Unlike the previous metals, V, Pb and Cd are considered asnon-essential metals (Nordberg et al., 2015; Soetan et al., 2010), whichmight explain their relatively lower concentrations in our liver samples.

We recorded very high concentrations of Ni and Pb in some in-dividuals. Isolated cases of excessive levels of metals in soft tissues ofbats have been attributed to their individual characteristics, such asexposure to extreme conditions of metal pollution or problems in metalmetabolism and excretion (Hariono et al., 1993; Hoenerhoff andWilliams, 2004; Williams et al., 2010). Considering that our study sitespresented a wide array of human activities, we cannot discard thepossibility that the high metal concentration values we recorded con-tributed to toxicity. However, according to Thies and Gregory (1994),capturing bats during their periods of activity could suggest they dis-play normal foraging behavior and would be healthy individuals.Therefore, we could expect that the high metal concentrations recordedhere do not represent lethal levels of toxicity, but rather tolerable

levels, or that bats are not conditioned by natural and anthropogenicstressors, such as other pollutants, infectious agents, and food con-straints (Soetan et al., 2010; Zukal et al., 2015). On the other hand,hepatic Fe, Cu and Pb concentrations of 4603, 4540 and 21.3 μg/g dwrespectively in frugivorous bats have been associated with toxic effects(Farina et al., 2005; Hariono et al., 1993; Hoenerhoff and Williams,2004). In spite of differences in the methods of analysis, none of ourconcentrations were close to those reported by previous studies.

We compared our results to hepatic metal concentrations (μg/g dw)of insectivorous bats reported by Allinson et al. (2006) in breedingcaves in Australia, by Naidoo et al. (2013) in natural and sewage-pol-luted sites in South Africa, and by Hernout et al. (2016) in sites alongthe pollution gradient on a national scale in the United Kingdom(Table 1). These studies used an ICP technique and standard referencematerial as we did in our study, and they showed recovery rates similarto the one reported here, in spite of differences in the way we collected,stored and digested our samples. In general, we found that our hepaticconcentrations of Cr, Mn, Fe, Cu, Zn, Pb, and Cd of Tadarida brasiliensiswere consistent with those recorded by previous studies. In contrast,our concentrations of V, Co and Ni were above reported levels in theliterature. It is important to consider that we evaluated only adult malebats of a Molossid species, while the other studies analyzed Vesperti-lionid bats of variable sex. Consequently, these differences could berelated to inherent physiological characteristics of distinct bat families,their feeding habits and the degree of exposure associated with the dateand locality of collection (Walker et al., 2007; Zocche et al., 2010).

4.2. Variations of metal concentrations among sites

Higher concentrations and variation of V in Tequixquiac bats couldbe associated with the fossil fuel combustion generated by the TulaIndustrial Complex (TIC) located 20 km northwest (Querol et al., 2008;Zambrano et al., 2009). Although the half-life of V in mammalian softtissues is estimated in weeks (Nordberg et al., 2015), it could be pos-sible that V concentrations in Tequixquiac bats were related to chronicexposure due strong and constant V emissions from the TIC. Urban bats

Table 2Spearman rank correlations between metal concentrations in livers of Tadarida brasiliensis (n = 70). Rho values are in the left and P-values are in the right. Rho ≥ 0.4are in bold. Significant P-values are in italic (P < 0.05).

Metal V Cr Co Mn Ni Fe Cu Zn Pb Cd

V – 0.026 < 0.001 0.11 0.16 0.003 0.48 0.029 0.034 0.097Cr 0.27 – < 0.001 0.036 0.04 0.16 0.86 0.13 0.052 0.24Co 0.61 0.55 – 0.03 0.021 0.009 0.37 0.09 < 0.001 0.14Mn 0.19 0.25 0.26 – 0.014 0.004 < 0.001 < 0.001 < 0.001 0.17Ni 0.17 0.25 0.28 0.290 - 0.16 0.024 0.002 0.019 0.037Fe 0.35 0.17 0.31 0.34 0.17 – 0.012 0.011 0.13 0.68Cu 0.09 −0.02 −0.11 0.46 0.27 0.30 – < 0.001 0.006 0.004Zn 0.26 0.18 0.20 0.45 0.36 0.30 0.76 – < 0.001 < 0.001Pb 0.25 0.23 0.40 0.39 0.28 0.18 0.32 0.57 – < 0.001Cd 0.20 0.14 0.18 0.16 0.25 −0.05 0.34 0.46 0.43 –

Fig. 3. Relationship between metal concentrations (μg/g) in livers of Tadarida brasiliensis (n = 70) from Tequixquiac (circles), Cuautitlán (squares), Xochimilco(c͉rosses) and Tlalcozotitlán (triangles).

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

6

were collected 45 and 85 km south from the TIC, so their intermediateV concentrations could reflect a lower influence of TIC emissions(Querol et al., 2008) as well as the influence of local fossil fuel com-bustion and igneous rock dusts (Guzmán-Morales et al., 2011; Morton-Bermea et al., 2009, 2018). Lower V concentrations and variation inTlalcozotitlán bats, which were collected more than 200 and 145 kmsouth from the TIC and the Megalopolis respectively, indicate that thesebats were not exposed to important sources of V.

Tequixquiac bats had higher concentrations and variations of Cr andCo, which suggest the influence of local sources. However, importantsources of both metals in the Tequixquiac municipality and its sur-rounding are unknown. The farming areas cover 42% of the municipalterritory (INEGI, 2010) and the wastewater used for irrigation can beenriched with metals released by domestic and industrial waste fromthe Megalopolis (Flores et al., 1997; Lucho-Constantino et al., 2005).Therefore, this water could be a route of exposure of Cr and Co to in-sectivorous bats when they drink it and feed on emergent aquatic in-sects (Naidoo et al., 2013; O'Shea et al., 2001). On the other hand, theessential metals display an unclear biological half-life because they arerequired by the organisms and have effective homeostatic controls(Nordberg et al., 2015; Pokorny and Ribarič-Lasnik, 2002), making itcomplex to explain their exposure times.

Similar to the above, local exposure to a water source could be in-volved in the Mn concentrations of Xochimilco bats, which seemed beslightly higher than those of the other bats. These bats were collected3 km from Xochimilco Lake, where Aldana et al. (2018) found that Mnis very abundant in the water and is significantly bioaccumulated in fishgills.

Although the Ni contents in the Megalopolis and the northern sur-rounding areas have been linked with different sources, including TIC(Morton-Bermea et al., 2018; Querol et al., 2008; Zambrano et al.,2009), similar Ni concentrations among our bats may be related tostrong homeostatic controls. Nickel concentrations in mammal liverscan be regulated by Zn action (Sidhu et al., 2004).

Differences in Fe concentrations between wild and captive mam-mals, as well as among livestock raised in different ways, have beenattributed to the unintentional intake of dust and soil enriched withvariable levels of Fe particles (Clauss and Paglia, 2012). Following fromthis, it would be possible that the variations in Fe concentrations werecorded were associated with differences in the amount of Fe releasedfrom the weathering of parent material from our study sites. According

to Lozano and Bernal (2005), igneous rocks in Mexico present greateramounts of Fe than sedimentary rocks, with approximate Fe2O3 andFeO rates of 1100:1 and 300:1 respectively. Igneous parent material hasbeen recognized as the most important source of Fe in the Megalopolisand the northern surrounding areas (Morton-Bermea et al., 2018;Querol et al., 2008; Zambrano et al., 2009). Iron particles can becomevery abundant in the particulate matter PM2.5, even reaching 67.7% ofthe total mass as reported in the Megalopolis (Morton-Bermea et al.,2018). In contrast, lower Fe concentrations in Tlalcozotitlán bats couldbe related to low levels of Fe particles generated by sedimentary parentmaterial, which is predominant in the Copalillo municipality and itssurroundings (INEGI, 2010).

Although the liver of mammals exerts strong homeostatic processeson hepatic Cu and Zn concentrations (Nordberg et al., 2015; Stamouliset al., 2007), our urban bats seemed to show slightly higher con-centrations and variations of both metals than rural bats. In addition,the high correlation between Cu and Zn we found emphasizes that bothmetals could be associated with a common source (Hernout et al.,2016). Copper and Zn contents in the Megalopolis have been mainlyrelated to vehicular traffic (Guzmán-Morales et al., 2011; Querol et al.,2008; Rodríguez-Salazar et al., 2011) because these metals can be re-leased from the wear of brake pads and tires (Apeagyei et al., 2011).

Lead concentrations in our bats did not vary among sites. Similarhepatic Pb concentrations among mammals throughout urbanizationgradients have been reported (Bilandẑić et al., 2010; Dip et al., 2001),which may be related to the wide distribution of Pb in the environment(López-Alonso et al., 2007). Although the use of Pb as gasoline additivewas banned in Mexico in 1997, Morton-Bermea et al. (2011) andRodríguez-Salazar et al. (2011) recognized that Pb pollution along theMegalopolis originating from this source during the past decades wasstill significant 11 years later (2008). Thus, historical pollution of Pbmay have impacted the bats we analyzed, as was suggested by Walkeret al. (2007) in bats from Britain. Likewise, Pb accumulates significantlyin the skeleton where it has a half-life over 10 years, so its turnoverfrom bones to soft tissues may result in endogenous Pb exposure for along time (Nordberg et al., 2015).

Variations in hepatic Cd concentrations in mammals can be morerelated to differences in foraging habits than to exposure due to thedegree of urbanization (Bilandẑić et al., 2010; Dip et al., 2001). Thus,higher Cd concentrations in Tlalcozotitlán bats indicate that their preywas exposed to important sources of Cd in comparison to those eaten by

Fig. 4. Scatterplot for factor analysis scores of livers of Tadarida brasiliensis (n = 70) from Tequixquiac (circles), Cuautitlán (squares), Xochimilco (c͉rosses) andTlalcozotitlán (triangles).

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

7

bats in other sites. Tadarida brasiliensis in rural environments feedmainly on insect families belonging to Lepidoptera and Coleoptera (Leeand McCracken, 2005; López, 2009), which are usually crop pests andcan act as an exposure route of metals from agriculture activities toinsectivorous bats (Thies and Gregory, 1994). Given that some agro-chemicals can have a high amount of Cd (Oruc, 2010; Soetan et al.,2010), it is necessary to explore the agrochemicals employed in theCopalillo municipality. Likewise, Cd concentrations in Tlalcozotitlánbats may reflect long-term exposure due to the fact that this metal has ahalf-life on the order of 10–30 years (Nordberg et al., 2015), andtherefore, its content in soft tissues increases with age (Pokorny andRibarič-Lasnik, 2002; Walker et al., 2007).

4.3. Associations between metal concentrations

Although a high percentage of significant correlations performedhere were not strong (rho < 0.4), they were numerous, reflecting thepossible importance of the liver for metabolizing metals (López-Alonsoet al., 2004). We recorded a high and consistent positive correlationbetween Cu and Zn, which could represent a synergic accumulationassociated with proportional requirements (Nordberg et al., 2015) orwith co-exposure to a common anthropogenic source (Hernout et al.,2016). Zinc showed considerable correlations (rho ≥ 0.4) with otherthree metals (Mn, Pb, and Cd), which could reflect the importance of Znfor metal homeostasis in mammalian livers (Sidhu et al., 2004;Stamoulis et al., 2007). In addition, correlations between Zn and bothCu and Cd in the liver could be related to the capacity of these metals toinduce the synthesis of metallothioneins (López-Alonso et al., 2004;Streit and Nagel, 1993).

It seems that when Co exceeds 0.2 μg/g, it can cause a large var-iation in Cr concentrations. However, we did not find other research onthis interaction, and we suggest further attention. The rest of the cor-relations between pairs of metals showed unclear two-way relationshipsregardless of high or intermediate correlation coefficients. Interactionsbetween metals during bioaccumulation in mammal tissues are com-plex since more than two metals can be involved as well as differentbiomolecules and physiological processes (Jarzyńska and Falandysz,2011; López-Alonso et al., 2004; Soetan et al., 2010). Curiously, we didnot observe important negative correlations, although antagonistic in-teractions have been reported between metals in soft tissues of la-boratory mammals and livestock under extreme conditions of exposureor deficiency (Nordberg et al., 2015; Sidhu et al., 2004; Soetan et al.,2010).

4.4. Accumulation patterns of metals in bats

We found three groups and the individuals of each group showedsimilar accumulation patterns as a reflection of similar exposure fromparticular geographic conditions where they inhabit, so each group canbe considered as representative of one population (Fig. 4) (Sánchez-Chardi and López-Fuster, 2009; Yang et al., 2002). Although temporalvariations of metal exposure on bat populations can be possible, theseneed to be explored. Available information of particulate matter in theMegalopolis indicates that even though it can reach high levels duringperiods with dry conditions, several metals show concentrations withunclear seasonal patterns (Morton-Bermea et al., 2018; Mugica et al.,2002).

Tlalcozotitlán bats showed lower values and/or low variability intheir hepatic concentrations of those essential and non-essential metalsassociated with Factor 1. Since essential metals are required and re-mained in homeostatic levels (Nordberg et al., 2015; Soetan et al.,2010), low variability in hepatic Fe, Cu, and Zn concentrations could berelated to an adequate accumulation or little interference from antag-onistic metals. Likewise, low V variation could be associated with thelack of V pollution. Considering that Tlalcozotitlán bats were collectedin a rural environment far from large cities and industrial areas, we can

assume that these bats represent a reference population for metal ex-posure (except for Cd).

Tequixquiac bats had higher concentrations of V, Cr, Co as well aswider variations of these metals associated with Factor 2. This resultmay reflect pollution conditions from local sources (Nordberg et al.,2015; Zambrano et al., 2009), which were different to those observed inthe Megalopolis. As with Tlalcozotitlán bats, Tequixquiac bats had lowconcentrations of Cu and Zn, which were also associated with Factor 2.This suggests that differences in hepatic Cu and Zn concentrations inbats were related to the degree of vehicular traffic, which was moreimportant in the Megalopolis (Apeagyei et al., 2011; Rodríguez-Salazaret al., 2011).

A higher contribution of metals from industrial activities has beenidentified in the northern part of the Megalopolis (Guzmán-Moraleset al., 2011; Rodríguez-Salazar et al., 2011). Metal concentrations inFicus leaf samples from the northern part were two to three times higherthan in the southern (Guzmán-Morales et al., 2011). However, Cuau-titlán and Xochimilco bats did not show significant differences in theirmetal concentrations, having similar accumulation patterns. This resultsuggests that all urban bats were exposed to metals in a similar wayalong the Megalopolis and belonged to the same population. Thisfinding may be associated with the great flight capacity of Tadaridabrasiliensis (Ávila-Flores and Fenton, 2005; McCracken et al., 2016;Wilkins, 1989) or a homogeneous distribution of metals throughout theMegalopolis (Morton-Bermea et al., 2018). On the other hand, Factor 3recognized slight differences in the ranges of Pb and Cd concentrationsbetween Cuautitlán and Xochimilco bats. Higher metals variations inXochimilco bats can be associated with additional very local sources inthe southern part of the Megalopolis.

5. Conclusions

All urban bats were exposed to metals in a similar way throughoutthe Megalopolis, and they showed higher levels of exposure to only twometals associated with anthropogenic sources related to this city. Ruralbats from each site were exposed to different metals, which weremainly associated with anthropogenic sources unrelated to theMegalopolis. Thus, our data highlight the need to monitor the emissionsgenerated by particular sources in each study site, such as vehiculartraffic in the Megalopolis, industrial activities and sewage around theTequixquiac municipality, and agricultural activities in the Copalillomunicipality. Given that metal concentrations in livers proved to besensitive to the spatial heterogeneity of metal sources in our study area,like other insectivorous bats evaluated elsewhere, Tadarida brasiliensiscan act as a biomonitor of metal exposure on wildlife in human-dominated ecosystems. Additional studies of metal concentrations inkidneys, the main tissue of detoxification, would be advisable to com-plement our interpretations, while the analysis in hair samples could beuseful to explore them as a less-invasive proxy of metal exposure. Theevaluation of feeding habits of T. brasiliensis, the metal concentrationsin its main preys, and particles adhered in its fur are required to de-termine the routes of exposure in the study area.

CRediT authorship contribution statement

Daniel Ramos-H: Conceptualization, Methodology, Software,Formal analysis, Investigation, Data curation, Writing - original draft,Visualization. Rodrigo A. Medellín: Methodology, Resources, Writing -review & editing, Supervision. Ofelia Morton-Bermea: Validation,Resources, Writing - review & editing, Supervision.

Acknowledgements

This article is a requirement to obtain the Master's degree inBiological Sciences, in the field of Ecology, of the Posgrado en CienciasBiológicas at Universidad Nacional Autónoma de México (UNAM).

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

8

Authors thank the Posgrado en Ciencias Biológicas (UNAM) as well asCONACYT for scholarship number 612519 to Daniel Ramos-H. We aregrateful to Elizabeth Hernández and Sarah Ordoñez of the Laboratoriode ICP-MS (Instituto de Geofísica-UNAM), and Claudia Ponce de Leónand Manuel Hernandez of the Laboratorio de Análisis Ambiental(Facultad de Ciencias-UNAM), for the analytical assistance. We thankBegoña Iñarritu, Abigail Martínez, Daniela Cafaggi and members of theLaboratorio de Ecología y Conservación de Vertebrados Terrestres(Instituto de Ecología-UNAM), as well as Alberto Almazán, ÁngelOsorio and Alejandro Taboada of the Instituto para el Manejo yConservación de la Biodiversidad (INMACOB AC.), and Yezenia García,Ernesto Pérez, Gema Sánchez, Patricia Ramírez, Kevin Meza, FalcoGarcía, Tania Castrejón, Rafael Ávila-Flores and Claudia Muñoz fortheir field support. We also thank Jorge E. Schondube, Joaquín Arroyo-Cabrales, Livia León and Fernando Cervantes for their many usefulsuggestions to our previous versions, as well as Ernesto Vega for thesupport in the statistical analysis. Finally we acknowledge FarahCarrasco, Maripaula Valdés, Fernanda de Alba and Anjali Kumar fortheir assistance in the English translation.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.envres.2020.109293.

Funding

This research did not receive any specific grant from fundingagencies in the public, commercial, or not-for-profit sectors.

References

Aldana, G., Hernández, M., Cram, S., Arellano, O., Morton, O., Ponce de León, C., 2018.Trace metal speciation in a wastewater wetland and its bioaccumulation in tilapiaOreochromis niloticus. Chem. Speciat. Bioavailab. 30 (1), 23–32. https://doi.org/10.1080/09542299.2018.1452635.

Allinson, G., Mispagel, C., Kajiwara, N., Anan, Y., Hashimoto, J., Laurenson, L., Allinson,M., Tanabe, S., 2006. Organochlorine and trace metal residues in adult southern bent-wing bat (Miniopterus schreibersii bassanii) in southeastern Australia. Chenosphere 64,1464–1471. https://doi.org/10.1016/j.chemosphere.2005.12.067.

Apeagyei, E., Bank, M.S., Spengler, J.D., 2011. Distribution of heavy metals in road dustalong an urban-rural gradient in Massachusetts. Atmos. Environ. 45, 2310–2323.https://doi.org/10.1016/j.atmosenv.2010.11.015.

Ávila-Flores, R., Fenton, M.B., 2005. Use of spatial features by foraging insectivorous batsin a large urban landscape. J. Mammal. 86 (6), 1193–1204. https://doi.org/10.1644/04-MAMM-A-085R1.1.

Bilandẑić, N., Dežđek, D., Sedak, M., Đokić, M., Solomun, B., Varenina, I., Knežević, Z.,Slavica, A., 2010. Concentrations of trace elements in tissues of red fox (Vulpes vulpes)and stone marten (Martes foina) from suburban and rural areas in Croatia. Bull.Environ. Contam. Toxicol. 85, 486–491. https://doi.org/10.1007/s00128-010-0146-2.

Clark, D.R., Shore, R.F., 2001. Chiroptera. In: Shore, R.F., Rattner, B.A. (Eds.),Ecotoxicology of Wild Mammals. John Wiley & Sons, United States, pp. 159–214.

Clauss, M., Paglia, D.E., 2012. Iron storage disorders in captive wild mammals: thecomparative evidence. J. Zoo Wildl. Med. 43 (3), 6–18. https://doi.org/10.1638/2011-0152.1.

Davydova, S., 2005. Heavy metals as toxicants in big cities. Microchem. J. 79, 133–136.https://doi.org/10.1016/j.microc.2004.06.010.

Delgado, R.A., Fortoul, T.I., Rosiles, R., 1994. Concentraciones de plomo, cadmio y cromoy su relación con algunas modificaciones morfológicas en tejidos de palomas Columbalivia de la Ciudad de México e Ixtlahuaca, Estado de México. Veterinaria México. 25(2), 109–115. https://www.medigraphic.com/cgi-bin/new/resumen.cgi?IDARTICULO=23430, Accessed date: 17 May 2019.

Dip, R., Stieger, C., Deplazes, P., Hegglin, D., Müller, U., Dafflon, O., Koch, H., Naegeli,H., 2001. Comparison of heavy metal concentrations in tissues of red foxes fromadjacent urban, suburban, and rural areas. Arch. Environ. Contam. Toxicol. 40,551–556. https://doi.org/10.1007/s002440010209.

Farina, L.L., Heard, D.J., LeBlanc, D.M., Hall, J.O., Stevens, G., Wellehan, J.F.X., Detrisac,C.J., 2005. Iron storage disease in captive Egyptian fruit bats (Rousettus aegyptiacus):relationship of blood iron parameters to hepatic iron concentrations and hepatichistopathology. J. Zoo Wildl. Med. 36 (2), 212–221. https://doi.org/10.1638/03-115.1.

Flores, L., Blas, G., Hernández, G., Alcalá, R., 1997. Distribution and sequential extractionof some heavy metals from soils irrigated with wastewater from Mexico City. Water,Air Soil Pollut. 98, 105–117. https://doi.org/10.1023/A:1026472611589.

García, Y., 2018. Localización y descripción de los refugios urbanos utilizados por

murciélagos residentes y su relación con las áreas verdes, en la zona centro-sur de laCiudad de México, México. Tesis para obtener el título de Bióloga. UniversidadNacional Autónoma de México, Mexico, pp. 82. http://oreon.dgbiblio.unam.mx/F/L1UKLM26LLCFPSHKTNSM963UHYBBSLTCU49C6KCC1L7M4U5M69-05537?func=find-b&request=yezenia+garc%C3%ADa&find_code=WRD&adjacent=N&local_base=TES01&x=0&y=0&filter_code_2=WYR&filter_request_2=&filter_code_3=WYR&filter_request_3=, Accessed date: 17 May 2019.

García-Sánchez, I.E., Barradas, V.L., Ponce de León, C.A., Esperón-Rodríguez, M., Rosas,I., Ballinas, M., 2019. Effect of heavy metals and environmental variables on theassimilation of CO2 and stomatal conductance of Ligustrum lucidum, an urban treefrom Mexico City. Urban Forestry & Urban Greening 42, 72–81. https://doi.org/10.1016/j.ufug.2019.05.002.

Guzmán-Morales, J., Morton-Bermea, O., Hernández-Álvarez, E., Rodríguez-Salazar,M.T., García-Arreola, M.E., Tapia-Cruz, V., 2011. Assessment of atmospheric metalpollution in the urban área of Mexico City, using Ficus benjamina as biomonitor. Bull.Environ. Contam. Toxicol. 86, 495–500. https://doi.org/10.1007/s00128-011-0252-9.

Hammer, Ø., Harper, D.A.T., Ryan, P.D., 2001. PAST: Palaeontological Statistics softwarepackage for education and data analysis. Palaeontologia Electronica, 4, pp. 9. https://folk.uio.no/ohammer/past/, Accessed date: 17 October 2019.

Hariono, B., Ng, J., Sutton, R.H., 1993. Lead concentrations in tissues of fruit bats(Pteropus sp.) in urban and non-urban locations. Wildl. Res. 20 (3), 315–320. https://doi.org/10.1071/WR9930315.

Hernout, B.V., Arnold, K.E., McClean, C.L., Walls, M., Baxter, M., Boxall, A.B.A., 2016. Anational level assessment of metal contamination in bats. Environ. Pollut. 214,847–858. https://doi.org/10.1016/j.envpol.2016.04.079.

Hoenerhoff, M., Williams, K., 2004. Copper-associated hepatopathy in a Mexican fruit bat(Artibeus jamaicensis) and establishment of a reference range for hepatic copper inbats. J. Vet. Diagn. Invest. 16, 590–593. https://doi.org/10.1177/104063870401600619.

INEGI, 2010. Compendio de información geográfica municipal de los Estados UnidosMexicanos. Instituto Nacional de Estadística y Geografía, Mexico. http://www.inegi.org.mx/geo/contenidos/topografia/compendio.aspx, Accessed date: 17 May 2019.

Jarzyńska, G., Falandysz, J., 2011. Selenium and 17 other largely essential and toxicmetals in muscle and organ meats of red deer (Cervus elaphus) - consequences tohuman health. Environ. Int. 37, 882–888. https://doi.org/10.1016/j.envint.2011.02.017.

Jáuregui, E., 2000. El clima de la Ciudad de México. Universidad Nacional Autónoma deMéxico. Plaza y Valdés, Mexico, pp. 131.

Lee, Y.F., McCracken, G.F., 2005. Dietary variation of Brazilian free-tailed bats links tomigratory populations of pest insects. J. Mammal. 86 (1), 67–76. https://doi.org/10.1644/1545-1542(2005)086<0067:DVOBFB>2.0.CO;2.

López, L.J., 2009. Dieta de Tadarida brasiliensis mexicana en el noreste y sur de México enel contexto de la fenología del maíz (Zea mays). In: Tesis para obtener el gradoacadémico de Maestro en Ciencias Biológicas (Biología Ambiental). UniversidadNacional Autónoma de México, Mexico, pp. 136. http://oreon.dgbiblio.unam.mx/F/L1UKLM26LLCFPSHKTNSM963UHYBBSLTCU49C6KCC1L7M4U5M69-11048?func=full-set-set&set_number=004073&set_entry=000001&format=999, Accesseddate: 17 May 2019.

López-Alonso, M., Prieto, F., Miranda, M., Castillo, C., Hernández, J., Benedito, L., 2004.Interactions between toxic (As, Cd, Hg and Pb) and nutritional essential (Ca, Co, Cr,Cu, Fe, Mn, Mo, Ni, Se, Zn) elements in the tissues of cattle from NW Spain. Biometals17, 389–397. https://doi.org/10.1023/B:BIOM.0000029434.89679.a2.

López-Alonso, M., Miranda, M., García-Partida, P., Cantero, F., Hernández, J., Benedito,J.L., 2007. Use of dogs as indicators of metal exposure in rural and urban habitats inNW Spain. Sci. Total Environ. 372, 668–675. https://doi.org/10.1016/j.scitotenv.2006.10.003.

Lozano, R., Bernal, J.P., 2005. Characterization of a new set of eight geological referencematerials for XRF major and trace element analysis. Rev. Mex. Ciencias Geol. 22 (3),329–344. http://www.scielo.org.mx/scielo.php?script=sci_abstract&pid=S1026-87742005000300329&lng=es&nrm=iso&tlng=en, Accessed date: 17 May 2019.

Lucho-Constantino, C.A., Prieto-García, F., Del Razo, L.M., Rodríguez-Vázquez, R., Poggi-Varaldo, H.M., 2005. Chemical fractionation of boron and heavy metals in soils ir-rigated with wastewater in Central Mexico. Agric. Ecosyst. Environ. 108, 57–71.https://doi.org/10.1016/j.agee.2004.12.013.

McCracken, G.F., Safi, K., Kunz, T.H., Dechmann, D.K.N., Swartz, S.M., Wikelski, M.,2016. Airplane Tracking Documents the Fastest Flight Speeds Recorded for Bats.Royal Society Open Science, pp. 10. https://doi.org/10.1098/rsos.160398.

Morton-Bermea, O., Hernández-Álvarez, E., González-Hernández, G., Romero, F., Lozano,R., Beramendi-Orosco, L.E., 2009. Assessment of heavy metal pollution in urbantopsoil from the metropolitan area of Mexico City. J. Geochem. Explor. 101,218–224. https://doi.org/10.1016/j.gexplo.2008.07.002.

Morton-Bermea, O., Rodríguez-Salazar, M.T., Hernández-Álvarez, E., García-Arreola,M.E., Lozano-Santacruz, R., 2011. Lead isotopes as tracers of anthropogenic pollutionin urban topsoils of Mexico City. Chem. Erde 71, 189–195. https://doi.org/10.1016/j.chemer.2011.03.003.

Morton-Bermea, O., Garza-Galindo, R., Hernández-Álvarez, E., Amador-Muñoz, O.,García-Arreola, M.E., Ordoñez-Godínez, S.L., Beramendi-Orosco, L., Santos-Medina,G.L., Miranda, J., Rosas-Pérez, I., 2018. Recognition of the importance of geogenicsources in the content of metals in PM2.5 collected in the Mexico City MetropolitanArea. Environ. Monit. Assess. 190, 83–100. https://doi.org/10.1007/s10661-017-6443-z.

Mugica, V., Maubert, M., Torresm, M., Muñoz, J., Rico, E., 2002. Temporal and spatialvariations of metal content in TSP and PM10 in Mexico City during 1996-1998. J.Aerosol Sci. 33, 91–102. https://doi.org/10.1016/S0021-8502(01)00151-3.

Naidoo, S., Vosloo, D., Schoeman, M.C., 2013. Foraging at wastewater treatment works

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

9

increases the potential for metal accumulation in an urban adapter, the banana bat(Neoromicia nana). Afr. Zool. 48 (1), 39–55. https://doi.org/10.3377/004.048.0111.

Nordberg, G.F., Fowler, B.A., Nordberg, M., 2015. Handbook on the Toxicology of Metals,fourth ed. Academic Press, United Kingdom, pp. 1542.

O'Shea, T.J., Clark, D.R., Boyle, T.P., 2001. Impacts of mine-related contaminant on bats.In: Vories, K.C., Throgmorton, D. (Eds.), Proceeding of Bat Conservation and Mining:A Technical Interactive Forum. Southern Illinois University Press and U. S. Office ofSurface Mining, United States, pp. 17.

O'Shea, T.J., Johnston, J.J., 2009. Environmental contaminants and bats: investigatingexposure and effects. In: Kunz, T.H., Parsons, S. (Eds.), Ecological and BehavioralMethods for the Study of Bats, second ed. The Johns Hopkins University Press, UnitedStates, pp. 500–528.

Oruc, H.H., 2010. Fungicides and their effects on animals. In: Carisse, O. (Ed.),Fungicides. InTech, United Kingdom, pp. 349–362.

Pérez, L.E., 2015. Registro de murciélagos (Chiroptera) en cinco sitios del municipio deTequixquiac, estado de México. Tesis para obtener el título de Biólogo. UniversidadNacional Autónoma de México, Mexico, pp. 70. http://oreon.dgbiblio.unam.mx/F/L1UKLM26LLCFPSHKTNSM963UHYBBSLTCU49C6KCC1L7M4U5M69-20620?func=find-b&REQUEST=ernesto+p%C3%A9rez+tequixquiac&find_code=WRD&ADJACENT=N&local_base=TES01&x=0&y=0&filter_code_2=WYR&filter_request_2=&filter_code_3=WYR&filter_request_3=, Accessed date: 17 May 2019.

Pokorny, B., Ribarič-Lasnik, C., 2002. Seasonal variability of mercury and heavy metals inroe deer (Capreolus capreolus) kidney. Environ. Pollut. 117, 35–46. https://doi.org/10.1016/S0269-7491(01)00161-0.

Querol, X., Pey, J., Minguillón, M.C., Pérez, N., Alastuey, A., Viana, M., Moreno, T.,Bernabé, R.M., Blanco, S., Cárdenas, B., Vega, E., Sosa, G., Escalona, S., Ruiz, H.,Artiñano, B., 2008. PM speciation and sources in Mexico during the MILAGRO-2006campaign. Atmos. Chem. Phys. 8, 111–128. https://doi.org/10.5194/acp-8-111-2008.

R Core Team, 2017. R: A language and environment for statistical computing. RFoundation for Statistical Computing, Vienna, Austria. https://www.r-project.org/,Accessed date: 17 October 2019.

Rendón-Lugo, A.N., Santiago, P., Puente-Lee, I., León-Paniagua, L., 2017. Permeability ofhair to cadmium, copper and lead in five species of terrestrial mammals and im-plications in biomonitoring. Environ. Monit. Assess. 189, 640–650. https://doi.org/10.1007/s10661-017-6338-z.

Rodríguez-Salazar, M.T., Morton-Bermea, O., Hernández-Álvarez, E., Lozano, R., Tapia-Cruz, V., 2011. The study of metal contamination in urban topsoils of Mexico Cityusing GIS. Environ. Earth Sci. 62, 899–905. https://doi.org/10.1007/s12665-010-0584-5.

Sánchez, O., López-Ortega, G., López-Wilchis, R., 1989. Murciélagos de la Ciudad deMéxico y sus alrededores. In: Gio-Argaéz, R., Hernández, R.I., Saínz-Hernández, E.(Eds.), Ecología Urbana. Sociedad Mexicana de Historia Natural, Mexico, pp.141–165.

Sánchez-Chardi, A., López-Fuster, M.J., 2009. Metal and metalloid accumulation inshrews (Soricomorpha, Mammalia) from two protected Mediterranean coastal sites.

Environ. Pollut. 157, 1243–1248. https://doi.org/10.1016/j.envpol.2008.11.047.SEDEMA, 2016. Inventario de Emisiones de la CDMX 2014. Secretaría del Medio

Ambiente del Gobierno de la Ciudad de México, Mexico, pp. 134.Sidhu, P., Garg, M.L., Morgenstern, P., Vogt, J., Butz, T., Dhawan, D.K., 2004. Role of zinc

in regulating the levels of hepatic elements following nickel toxicity in rats. Biol.Trace Elem. Res. 102, 161–172. https://doi.org/10.1385/BTER:102:1-3:161.

Sikes, R.S., the Animal Care and Use Committee of the American Society ofMammalogists, 2016. Guidelines of the American Society of Mammalogists for theuse of wild mammals in research and education. J. Mammal. 97 (3), 663–688.https://doi.org/10.1093/jmammal/gyw078.

Soetan, K.O., Olaiya, C.O., Oyewole, O.E., 2010. The importance of mineral elements forhumans, domestic animals and plants: a review. Afr. J. Food Sci. 4 (5), 200–222.https://academicjournals.org/journal/AJFS/article-abstract/045441523024,Accessed date: 17 May 2019.

Stamoulis, I., Kouraklis, G., Theocharis, S., 2007. Zinc and the liver: an active interaction.Dig. Dis. Sci. 52, 1595–1612. https://doi.org/10.1007/s10620-006-9462-0.

Streit, B., Nagel, A., 1993. Element assessment in tissue samples from European bats(Microchiroptera). Fresenius Environ. Bull. 2, 162–167.

Thies, M., Gregory, D., 1994. Residues of lead, cadmium, and arsenic in livers of Mexicanfree-tailed bats. Bull. Environ. Contam. Toxicol. 52, 641–648. https://doi.org/10.1007/BF00195481.

Walker, L.A., Simpson, V.R., Rockett, L., Wienburg, C.L., Shore, R.F., 2007. Heavy metalcontamination in bats in Britain. Environ. Pollut. 148, 483–490. https://doi.org/10.1016/j.envpol.2006.12.006.

Wilkins, K.T., 1989. Tadarida brasiliensis. Mamm. Species 331, 1–10. https://doi.org/10.2307/3504148.

Williams, M., Ramos, D., Butrón, A., Gonzales-Zúñiga, S., Ortiz, N., La Torre, B., 2010.Concentraciones de metales pesados en murciélagos del lodge “Cock of the Rocks” yalrededores, Kosñipata, Cuzco, Perú. Ecol. Apl. 9 (2), 133–139. http://www.lamolina.edu.pe/ecolapl/Articulo_14_Vol_9_No_2.htm, Accessed date: 17 May 2019.

Yang, J., Kunito, T., Tanabe, S., Amano, M., Miyazaki, N., 2002. Trace elements in skin ofDall's porpoises (Phocoenoides dalli) from the northern waters of Japan: an evaluationfor utilization as non-lethal tracers. Mar. Pollut. Bull. 45, 230–236. https://doi.org/10.1016/S0025-326X(01)00328-9.

Zambrano, A., Medina, C., Rojas, A., López, D., Chang, L., Sosa, G., 2009. Distribution andsources if bioaccumulative air pollutants at Mezquital Valley, Mexico, as reflected bythe atmospheric plant Tillandsia recurvata L. Atmos. Chem. Phys. 9, 6479–6494.https://doi.org/10.5194/acp-9-6479-2009.

Zocche, J.J., Leffa, D.D., Damiani, A.P., Carvalho, F., Mendonça, R.A., dos Santos, C.E.I.,Boufleur, L.A., Dias, J.F., Andrade, V.M., 2010. Heavy metals and DNA damage inblood cells of insectivore bats in coal mining areas of Catarinense coal basin. Brazil.Environ. Res. 110, 684–691. https://doi.org/10.1016/j.envres.2010.06.003.

Zukal, J., Pikula, J., Bandouchova, H., 2015. Bats as bioindicators of heavy metal pol-lution: history and prospect. Mamm. Biol. 80, 220–227. https://doi.org/10.1016/j.mambio.2015.01.001.

D. Ramos-H, et al. Environmental Research 185 (2020) 109293

10