Mercury and metallothioneins in blood fractions and tissues of captive Morelet's crocodiles in Quintana Roo, Mexico

Body Condition of Reproductive and Non-Reproductive Broad-Snouted Caiman Females

In this work, we calculated the body condition indices, K-Fulton and scaled mass index (SMI), of reproductive and non-reproductive Caiman latirostris adult females as an indication of stored energy. We considered 87 adult females captured from 2001 to 2018, both reproductive and non-reproductive. The body condition was calculated considering two scenarios: (a) only the weight of the female, and (b) the sum of the weight of the female and the average dry weight of her nest. We tested the difference in body condition between reproductive and non-reproductive females. We also evaluated the minimal body condition required to guarantee that females above it are reproductive by drawing a line that separated the body condition of strictly reproductive individuals from those that may or may not be reproductive. Reproductive females had better body condition than non-reproductive ones. Our SMI.S line separated almost 70% of the reproductive females. Based on our results, we can guarantee that a female whose body condition is above the line will reproduce, although not all those females below the line are non-reproductive, as a few of those under the line will nest. With this information, we have one more biological indicator to take into account when making management and conservation decisions.

Using Crocodylians for monitoring mercury in the tropics

Mercury contamination is a widespread phenomenon that impacts ecosystems worldwide. Artisanal Small Scale Gold Mining (ASGM) activities are responsible for more than a third of atmospheric Hg emission. Due to Hg toxicity and its broad and elevated prevalence in the environment resulting from ASGM activities in the tropics, its biomonitoring is essential to better understand the availability of its methylmercury (MeHg) form in the environment. The Minamata Convention was ratified with the objective to "protect human health and the environment from anthropogenic emissions and releases of mercury compounds". Biomagnification of MeHg occurs through the trophic food web, where it biomagnifies and bioaccumulates in top predators. To monitor environmental MeHg contamination, studies have evaluated the use of living organisms; however, reptiles are among the least documented vertebrates regarding MeHg exposure. In this review we evaluate the use of crocodylians for Hg biomonitoring in tropical ecosystems. We found that out of the 28 crocodiles species, only 10 have been evaluated regarding Hg contamination. The remaining challenges when using this taxon for Hg biomonitoring are inconsistencies in the applied methodology (e.g., wet versus dry weight, tissues used, quantification method). However, due to their life history traits, crocodylians are particularly relevant for monitoring MeHg contamination in regions where ASGM activities occur. In conclusion and given their ecological and socio-economic importance, crocodylians are at great risk of MeHg contamination and are excellent bioindicators for tropical ecosystems.

Stress responses in captive Crocodylus moreletii associated with metal exposure

Environmental pollution by metals has repercussions on wildlife health. It is known that some metals can have an influence on the neuroendocrine stress response, and at the same time, metals have pro-oxidant effects that can overwhelm the antioxidant system and cause oxidative stress. This study evaluates the association of metals with neuroendocrine stress activity and biomarkers of oxidative stress in 42 captive female Morelet's crocodiles (Crocodylus moreletii). We measured five metals of ecotoxicological importance (Hg, Cd, Pb, Cu and Zn), and three biomarkers of the oxidative stress response in the liver: glutathione (GSH) and glutathione disulfide (GSSG) as markers for antioxidant system and thiobarbituric acid reactive substances (TBARS) for oxidative damage. We also measured one biomarker of the neuroendocrine response to stress: corticosterone (B) in blood plasma. The mean ± SD concentrations of metals in the liver expressed in μg/g (dw) were: Cd: 0.004 ± 0.003, Hg: 0.014 ± 0.019, Cu: 0.017 ± 0.013, Zn: 0.043 ± 0.035, Pb: 0.16 ± 0.256. The mean ± SD of GSH was 0.42 ± 0.35 nmol/mg protein, the mean ± SD of GSSG was 0.24 ± 0.20 nmol/mg protein, the mean ± SD concentrations of TBARS were 0.36 ± 0.21 nmol/mg protein, and the mean ± SD of B was 393.57 ± 405.14 pg/mL. Hg presented a significant negative relationship with corticosterone. Cd had a negative relationship with both GSH and GSSG; meanwhile, Zn showed a negative relationship with TBARS levels, could be a protective element against hepatic oxidative damage. Finally, B had negative relationship with oxidative damage. The connection found between Hg and the neuroendocrine stress response, as well as the correlations of Cd and Zn with oxidative damage and antioxidant activity should be studied further, given their toxicological importance and implications for the conservation of C. moreletii and other crocodilians.

Heavy Metals in the Blood Serum and Feces of Mugger Crocodile (Crocodylus palustris) in Sistan and Baluchistan Province, Iran

This study was conducted to measure concentrations of cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), copper (Cu), chromium (Cr), and iron (Fe) in blood serum and feces of mugger crocodile (Crocodylus palustris) and in water and sediment of their habitat (Negour site, Chabahar County in Sistan and Baluchistan Province, Iran). Heavy metal contents in crocodile serum and feces, water, and sediments were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES spectrometer-Spectro Genesis). The highest levels of heavy metals in the mugger crocodile's serum were Fe > Hg > Pb > Cr > Cu > Cd > As, respectively. The total metal concentrations in the feces exhibited the following decreasing order from Fe > As > Pb = Cr > Hg > Cd > Cu. The highest average levels of heavy metals in water were Hg > Fe > As > Pb > Cu > Cr > Cd respectively and As > Fe > Pb > Cu > Hg > Cd > Cr in the sediment of lagoons. A significant difference was observed in the concentration of Fe and Pb between male and female crocodiles. Moreover, correlation analysis indicated significant negative correlations between sex and bioconcentrations of Cd, Fe, Pb, As, and Hg in the serum. In conclusion, this study showed that the environmental conditions of Negour lagoons are not suitable for crocodiles regarding habitat health and water quality. Furthermore, since these lagoons and fish are the most important sources of drinking water and seafood for the residents of the area, contamination of these pools with heavy metals can also threaten people's health.

Freshwater aquatic reptiles (Testudines and Crocodylia) as biomonitor models in assessing environmental contamination by inorganic elements and the main analytical techniques used: a review

Despite the general lack of studies that use reptiles as bioindicators, the value of freshwater turtles and crocodilians in ecotoxicology has been proven, due to their importance as sentinel species. The aim of this study was to compile information on the use of freshwater turtles and crocodilians as environmental biomonitors of inorganic element contamination. We searched for articles in databases using specific keywords. A total of 104 studies published between the years 1970 and 2020 were collected. We noted a general increase in the number of studies involving turtles and crocodilians during the study time period. The Order Testudines were the subjects of 46% of the analysed publications, and the Order Crocodylia accounted for 54%. Within these studies, we counted 39 species (turtles n = 29 and crocodilians n = 10). Forty chemical elements were evaluated in the analysed articles, of which the majority represented non-essential elements (Hg, Cd, Pb). Although internal organs constituted the main biological matrix chosen for each group (37%), we observed an increase in the use of non-destructive matrices in both groups (scale, blood, tail muscle, carapace). The majority of analysed studies used HNO₃ for the sample decomposition, with the majority of analyses being performed using atomic absorption spectroscopy (53%). Mainly blank controls (19%), analyte recovery (18%) and replicates (18%) were used as methods of validating analytical procedures. Furthermore, the studies used certified reference materials, which measure the accuracy of the methods used. We conclude that the increase in the use of aquatic reptiles in environmental monitoring research is mainly due to their ability to reveal integrated changes in ecosystems, aiding in environmental public policy decision-making and effective management plans.

Variation of Total Mercury Concentrations in Different Tissues of Three Neotropical Caimans: Implications for Minimally Invasive Biomonitoring

Mercury (Hg) is a global environmental contaminant that affects ecosystems. It is known to biomagnify through food webs and to bioaccumulate especially in the tissues of top predators. Large-scale comparisons between taxa and geographic areas are needed to reveal critical trends related to Hg contamination and its deleterious effects on wildlife. Yet, the large variety of tissues (keratinized tissues, internal organs, blood) as well as the variability in the units used to express Hg concentrations (either in wet- or dry-tissue weight) limits straightforward comparisons between studies. In the present study, we assessed the moisture content that could influence the total Hg (THg) concentrations measured in several tissues (claws, scutes, total blood, and red blood cells) of three caiman species. We evaluated the moisture content from the different tissues to provide information on THg concentrations in various matrices. Our results show a difference of THg concentrations between the tissues and intra- and interspecific variations of moisture content, with the highest THg values found in keratinized tissues (scute keratinized layers and claws). For the three species, we found positive relationships between body size and THg concentration in keratinized tissues. In the blood, the relationship between body size and THg concentration was species-dependent. Our results emphasize the need for a standardized evaluation of THg concentration and trace elements quantification based on dry weight analytical procedures. In addition, the use of both blood and keratinized tissues offers the possibility to quantify different time scales of THg exposure by non-lethal sampling.

Preferential Liver Accumulation of Mercury Explains Low Concentrations in Muscle of Caiman yacare (Alligatoridae) in Upper Amazon

Caiman yacare is considered one of the top predators in the Amazon basin, and understanding pollutant distribution within its tissues may help its sustainable management. As a top predator, C. yacare should have the highest mercury concentrations, but has lower Hg concentrations than carnivorous fish (Rivera et al. 2016), which are part of their diet. We compared total Hg among liver, kidney, fat, and muscle of C. yacare, and whether trends in the distribution of Hg among tissues were like other crocodilians, aquatic birds, omnivorous, and carnivorous fish. Fat had the lowest concentrations (0.025 ± 0.03 mg kg^-1) followed by muscle (0.15 ± 0.06 mg kg^-1), kidney (0.57 ± 0.30 mg kg^-1) and liver (1.81 ± 0.80 mg kg^-1). Such preferential accumulation makes C. yacare meat a safer alternative for human consumption than carnivorous fish. The relation between Hg accumulation in liver and muscle is highest in crocodilians, which has evolutive and environmental implications.

Toxicity assessment of two-dimensional nanomaterials molybdenum disulfide in Gallus gallus domesticus

Recently two-dimensional nanomaterials, such as graphene and molybdenum disulfide (MoS₂), have received much attention as adsorbent materials for the effective removal of organic contaminants. MoS₂ is attracting attention, not only for its chemical-physical properties, but also for its wide availability in nature as a constituent of molybdenite. The aim of this investigation was to assess the effects of different MoS₂ concentrations (5 × 10^-1, 5 × 10^-2 and 5 × 10^-3 mg/ml) on the embryonated eggs of Gallus gallus domesticus, according to Beck method. We evaluated the toxic effect of the MoS₂ powder purchased at Sigma-Aldrich indicated as "received" and MoS₂ powder treated via mechanical milling indicated as "ball mille". Subsequently, the embryos were sacrificed at different times of embryonic development (11th, 15^th and 19^th day after incubation) in order to evaluate their embryotoxic and teratogenic effects. The alterations of the embryonic development were studied by morphological and immunohistochemical analysis of the tissues. The results obtained have shown the toxicity of both powders of MoS₂ with a high percentage of deaths and growth delays. Moreover, the immunohistochemical analysis performed on several tissue sections showed a strong positivity to the anti-metallothionein1 antibody only for the erythrocytes.

Distribution of metals in tissues of captive and wild Morelet's crocodiles and the potential of metallothioneins in blood fractions as a biomarker of metal exposure

The distribution of Hg, Cd, Cu, and Zn in keratinized tissues, blood fractions, and excretory organs, and MTs in blood fractions and excretory organs was determined in captive, semicaptive, and wild Morelet's crocodiles and they were compared to select the most useful non-destructive tissues for the monitoring of metal exposure and to assess the potential of MTs as a biomarker. Our results indicate blood plasma, claws, and caudal scutes altogether are suitable tissues for xenobiotic metals exposure, with concentrations in blood plasma being an indicator of recent exposure, whereas concentrations in claws and caudal scutes are indicators of chronic exposure. Results in keratinized tissues suggest they are an important detoxification strategy in crocodiles, and claws presented the highest concentrations of metals in both captive (Hg = 0.44 ± 0.23 μg g^-1, Cd = 11.10 ± 5.89 μg g^-1, Cu = 45.98 ± 23.18 μg g^-1, Zn = 124.75 ± 75.84 μg g^-1) and wild populations (Hg = 1.31 ± 0.32 μg g^-1, Cd = 26.47 ± 21.15 μg g^-1, Cu = 191.75 ± 165.91 μg g^-1, Zn = 265.81 ± 90.62 μg g^-1). Thus, they are an appropriate tool for assessing metal exposure in populations where scutes clipping as a marking technique is not allowed, and their collection is less complicated than with other tissues. MTs are a suitable biomarker in blood plasma, whereas in erythrocytes detoxification processes might depend on hemoglobin, rather than MTs. Future studies should consider the implementation of these tools for the monitoring of wild populations.

Mercury levels and genotoxic effect in caimans from tropical ecosystems impacted by gold mining

One of the most representative predator species in tropical ecosystems is caiman that can provide relevant information about the impact of mercury (Hg) associated with artisanal and small-scale gold mining. To evaluate the degree to which adverse effects are likely to occur in Caiman crocodilus, total Hg (THg) concentrations in different tissues and DNA damage in erythrocytes were determined. Samples of claws, scutes, and blood were taken from 65 specimens in sites impacted by upstream gold mining, and in a crocodile breeding center as control site, located in a floodplain in northern Colombia. In all the sites, the highest THg among tissues was in the following order: claws >> scutes > blood. High concentrations of THg were found in the different tissues of the specimens captured in areas impacted by mining activities, with mean values in claws (1100 ng/g ww), caudal scutes (490 ng/g ww), and blood (65 ng/g ww), and statistically significant differences compared to those of the control site (p < 0.05). THg in scutes from impacted sites are 15-fold higher than in control, whereas for claws and blood are 8 times higher, and a high significant correlation with THg was found in all the tissues. The comet assay reveals significant differences in the DNA damage in the exposed reptiles compared to the controls (p < 0.01). In sum, C. crocodilus from La Mojana floodplain presents a high ecological risk given its genotypic susceptibility to Hg levels present in its habitat, which could possibly influence vital functions such as reproduction of the species and the ecological niche that it represents within the ecosystem.

Myclobutanil accumulation, transcriptional alteration, and tissue injury in lizards (Eremias argus) treated with myclobutanil enantiomers

Enantioselective toxicokinetics, accumulation, and toxicity of myclobutanil were investigated by oral exposure of myclobutanil enantiomers to lizards. After a single oral administration, the absorption half-lives ( [Formula: see text] ) and elimination half-lives (t_1/2k) were in the range of 0.133-14.828 and 3.641-17.682 h, respectively. The absorption and elimination half-lives of (+)-myclobutanil showed no significant differences from those of (-)-myclobutanil in lizard blood, whereas preferential enrichment of (-)-enantiomer was observed in the liver, fat, skin, intestine, lung and kidney. In the bioaccumulation experiments, the residue of (-)-myclobutanil was detected in most tissues at 7, 14, and 28 days, while (+)-myclobutanil was found only in lizard skin, at a concentration lower than that of (-)-myclobutanil. Thus, (-)-myclobutanil was preferentially accumulated in lizards. The transcriptional responses of metabolic enzyme genes indicated that cytochrome P450 1a1 (cyp1a1), cyp2d3, cyp2d6, cyp3a4 and cyp3a7 played a crucial role in the metabolism of (+)-myclobutanil, whereas cyp1a1, cyp2d3, cyp2d6, cyp2c8, and cyp3a4 contributed to the metabolism of (-)-myclobutanil. The difference in metabolism pathways may be a reason for the enantioselectivity of myclobutanil in lizard. Myclobutanil also affected the expression of antioxidant enzyme genes, and the (+)-myclobutanil treatment might produce higher oxidative stress in lizard liver when compared with its antipode. Hepatic histopathological changes such as hepatocellular hypertrophy, nuclear pyknosis, vacuolation, and non-zonal macrovesicular lipid accumulation were observed in the liver of lizards for both (+)-myclobutanil and (-)-myclobutanil treatments. Thus, myclobutanil could affect lizard liver upon multiple exposure. The findings of this study provide specific insights into the enantioselective metabolism and toxicity of chiral triazole fungicides in lizards.